Nutrition and Aerobic Exercise 9780841209497, 9780841211261, 0-8412-0949-9

Table of contents :
Title Page......Page 1
Half Title Page......Page 3
Copyright......Page 4
ACS Symposium Series......Page 5
FOREWORD......Page 6
PdftkEmptyString......Page 0
PREFACE......Page 7
1 Nutrition and Exercise: An Overview......Page 8
Influence of Aerobic Exercise on Nutritional Needs......Page 9
Literature Cited......Page 12
Muscle Adaptations......Page 15
Muscle Fiber Types......Page 16
Important Training Parameters......Page 18
Functional Significance of Training Adaptations in Muscle......Page 23
Summary......Page 27
Literature Cited......Page 28
3 Influence of Aerobic Exercise on Fuel Utilization by Skeletal Muscle......Page 34
Fuel reserves of the body......Page 35
Factors Regulating Fuel Utilization during Aerobic Performance......Page 37
Biochemical Regulation of Fuel Utilization during Exercise......Page 45
Summary......Page 47
Literature Cited......Page 48
4 Protein and Amino Acid Metabolism During Exercise......Page 51
Amino Acid Metabolism Associated with Anaerobic Exercise......Page 52
Amino Acid Metabolism Associated with Aerobic Training......Page 54
Protein Requirements for Endurance Exercise......Page 59
Literature Cited......Page 61
5 The Effect of Exercise on Lipid and Lipoprotein Metabolism......Page 65
Cross-Sectional and Longitudinal Studies on Healthy Subjects, Persons with Hyperlipidemia and Survivors of a Myocardial Infarct......Page 66
Factors Affecting Plasma Lipids and Lipoproteins with Exercise......Page 69
Mechanisms of Exercise-Induced Changes in Plasma Lipids: Lipoprotein Lipase, Hepatic Triglyceride Lipase and Lecithin Cholesterol Acyl Transferase......Page 71
Hepatic Lipid and Lipoprotein Production......Page 76
Effect of Exercise on the Development and Progression of Atherosclerosis......Page 80
Summary......Page 81
Literature Cited......Page 82
6 Riboflavin Requirements and Exercise......Page 86
Is There Experimental Evidence That Riboflavin Requirements Are Influenced by the Level of Physical Activity?......Page 87
Can the Riboflavin Requirements of Athletes be Met by Food Sources of Riboflavin?......Page 89
Summary......Page 90
Literature Cited......Page 91
7 Trace Elements and Calcium Status in Athletic Activity......Page 93
Iron......Page 94
Calcium......Page 97
Copper and Zinc......Page 104
Summary......Page 107
Literature Cited......Page 108
Anatomy of Body Fluid Compartments......Page 113
Exercise and Body Water......Page 115
Thirst and Drinking During Exercise......Page 122
Literature Cited......Page 125
9 Aerobic Exercise and Body Composition......Page 131
Effect of Aerobic Exercise on the Body Composition of Humans......Page 132
Measurements of Body Composition......Page 135
Effect of Aerobic Exercise on the Body Composition of Experimental Animals......Page 137
Body Composition Changes Due to Diet and Exercise......Page 140
Summary......Page 141
Literature Cited......Page 142
Glossary......Page 148
Author Index......Page 151
B......Page 152
E......Page 153
L......Page 154
P......Page 155
W......Page 156

Citation preview

Nutrition and Aerobic Exercise

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

ACS SYMPOSIUM SERIES 294

Nutrition and Aerobi Exercis Donald K. Layman, EDITOR University of Illinois at Urbana-Champaign

American Chemical Society, Washington, D.C. 1986 In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Library of Congress Cataloging in Publication Data Nutrition and aerobic exercise. (ACS symposium series, ISSN 0097-6156; 294) Developed from a symposium held Apr. 10, 1984, in St. Louis, entitled "The Influence of Aerobic Exercise on Energy Metabolism and Nutrient Requirements", sponsored by the Division of Agricultural and Food Chemistry of the American Chemical Society, the Quaker Oats Company, and the Dart-Kraft Company. Includes bibliographies and index Contents: Nutrition and exercise Layman—Biochemical adaptations in skeletal muscle induced by exercise training/ Ronald L. Terjung and David A . Hood—Influence of aerobic exercise on fuel utilization/ Michael N. Goodman—[etc.] 1. Nutrition—Congresses. 2. Exercise—Physiological aspects—Congresses. I. Layman, Donald K., 1950- . II. American Chemical Society. Division of Agricultural and Food Chemistry. III. Quaker Oats Company. IV. Dart & Kraft. V. Series. QP141.A1N86I55 1986 ISBN 0-8412-0949-9

612'.3

85-26872

Copyright © 1986 American Chemical Society All Rights Reserved. The appearance of the code at the bottom of the first page of each chapter in this volume indicates the copyright owner's consent that reprographic copies of the chapter may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc., 27 Congress Street, Salem, M A 01970, for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating a new collective work, for resale, or for information storage and retrieval systems. The copying fee for each chapter is indicated in the code at the bottom of the first page of the chapter. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. Registered names, trademarks, etc., used in this publication, even without specific indication thereof, are not to be considered unprotected by law. P R I N T E D IN T H E U N I T E D STATES O F A M E R I C A

American Chemical Society Library 1155 16th St., N.W.

In Nutrition and Aerobic Exercise; Layman, D.; Washington, D.C. 20036 ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

ACS Symposium Series M . Joan Comstock, Series Editor Advisory Board Harvey W. Blanch University of California—Berkeley

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In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

FOREWORD SYMPOSIUM SERIES

The ACS was founded in 1974 to provide a medium for publishing symposia quickly in book form. The format of the Series parallels that of the continuing except that, in order to save time, the papers are not typese by the authors in camera-read the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however, verbatim reproductions of previously published papers are not accepted. Both reviews and reports of research are acceptable, because symposia may embrace both types of presentation.

IN CHEMISTRY SERIES

ADVANCES

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

PREFACE

THE POTENTIAL HEALTH BENEFITS

of a combined program of nutrition and exercise have increasingly been recognized during the past decade. World-class athletes have long known the importance of controlling caloric intake to maintain desired body weight and that a poor diet will diminish performance. However, as the general public becomes more conscious of health and fitness, routine health maintenance for larg questions about the impact of exercise on nutritional requirements. This book addresses the principal questions concerning the interaction of nutrition and aerobic exercise training. Each chapter reviews the basic topics and examines new findings and important questions remaining to be solved. The book is written for an audience that has a basic understanding of physiology and intermediary metabolism. However, it assumes little or no background in nutrition or exercise physiology. It is intended to provide an easily read insight into the current knowledge about nutrition and exercise, and it should appeal to both the specialist and nonspecialist. This book originated from a symposium entitled "The Influence of Aerobic Exercise on Energy Metabolism and Nutrient Requirements" and was sponsored by the Division of Agricultural and Food Chemistry of the American Chemical Society, the Quaker Oats Company, and the Dart-Kraft Company. I would like to especially thank John Whitaker, David Hurt, and Robert Bursey as the representatives of the respective sponsors.

DONALD K. LAYMAN University of Illinois Urbana, IL 61801 September 19, 1985

IX

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

1 Nutrition and Exercise: An Overview Donald K. Layman Department of Foods and Nutrition, Division of Nutritional Sciences, University of Illinois, Urbana, IL 61801

Across the United States, interest has increased in physical fitness, exercise, and nutrition. Almost one-half of adult Americans state that they exercise regularly (1). Activities include walking, running, swimming, biking, racketball, tennis, aerobic dancing, and many others. The renewed interest in exercise appears to be due, in large part, to the association of exercise with health. Most health organizations, including the American Heart Association, the American Diabetes Association, the American Dietetic Association, and theAmericanMedical Association, advocate exercise for maintenance of health and to reduce the risk of the onset of the adult diseases of obesity, hypertension, heart disease, and diabetes (2-4). Likewise, health-related changes have occurred in the American diet. The Dietary Goals for the United States developed in 1977 by the Senate Select Committee on Nutrition (5) recommended that adults reduce their calorie intake, reduce total fat, saturated fat, and cholesterol, avoid excessive salt intake, and increase consumption of complex carbohydrates and fiber. These recommendations have r e s u l t e d i n t r e n d s toward lower consumption o f a n i m a l p r o d u c t s p l u s use o f low f a t p r o d u c t s and i n c r e a s e d consumption o f f r u i t s and vegetables. Consumers a r e s e l e c t i n g l e s s sugar and s a t u r a t e d f a t (6). D u r i n g the p a s t 3 y e a r s , use o f p o u l t r y and f i s h has i n c r e a s e d about 16%, w h i l e use o f b e e f and eggs has decreased 16% (7). T h i s i n c r e a s e d c o n s c i o u s n e s s o f the g e n e r a l p u b l i c t o n u t r i t i o n has a l s o l e d to a p r o l i f e r a t i o n o f m i r a c l e d i e t s , q u i c k weight l o s s schemes, and v i t a m i n s u p p l e m e n t s . Surveys i n d i c a t e t h a t the m a j o r i t y o f Americans t a k e v i t a m i n supplements (6) and many have t r i e d a f a d weight l o s s d i e t ( 8 ) . The response o f t h e American p u b l i c t o u t i l i z e d i e t and e x e r c i s e f o r maintenance o f h e a l t h has i n c r e a s e d the need f o r more d e f i n i t i v e s c i e n t i f i c i n f o r m a t i o n about t h e i n t e r a c t i o n s o f e x e r c i s e w i t h d i e t a r y needs. T h i s book r e v i e w s some o f the p h y s i o l o g i c a l and m e t a b o l i c changes t h a t o c c u r d u r i n g e x e r c i s e t r a i n i n g and examines the impact o f r o u t i n e e x e r c i s e on n u t r i t i o n a l r e q u i r e m e n t s . 0097-6156/86/0294-O001$06.00/0 © 1986 American Chemical Society

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

2

NUTRITION A N D AEROBIC EXERCISE

P h y s i o l o g i c a l and M e t a b o l i c Responses to

Exercise

The i n f l u e n c e o f p h y s i c a l a c t i v i t y on n u t r i t i o n a l r e q u i r e m e n t s and h e a l t h i s not the same f o r a l l a c t i v i t i e s . For the purposes o f t h i s book, e x e r c i s e w i l l be c l a s s i f i e d as e i t h e r a n a e r o b i c or a e r o b i c activities. These terms p r o v i d e d e s c r i p t i v e i n f o r m a t i o n about both the l e v e l o f e x e r t i o n and the d u r a t i o n o f the a c t i v i t y and a r e u s e f u l i n r e l a t i n g a c t i v i t i e s to n u t r i t i o n a l n e e d s . Anaerobic e x e r c i s e i n c l u d e s a c t i v i t i e s such as w e i g h t l i f t i n g and s p r i n t i n g , and i n v o l v e s maximum e x e r t i o n f o r p e r i o d s o f time l e s s than 1 or 2 minutes. A e r o b i c a c t i v i t i e s are performed f o r p e r i o d s u s u a l l y i n e x c e s s o f 15 minutes a t l e s s than maximum speed o r s t r e n g t h . A e r o b i c e x e r c i s e r e q u i r e s g r e a t e r endurance and i n c l u d e s a c t i v i t i e s such as d i s t a n c e r u n n i n g , swimming, b i k i n g , and w a l k i n g . Some o f t h e r e s p o n s e s by t h e body t o a n a e r o b i c e x e r c i s e are v i s u a l l y obvious. G r e a t e r s t r e n g t h , s p e e d , and muscle development are reasons t h a t a t h l e t e r e s e a r c h has shown t h a t even the e f f e c t s on the amount o f muscle mass a r e n o t e n t i r e l y c l e a r (9). The e f f e c t s o f t h e s e s h o r t - d u r a t i o n e x e r c i s e s on cardiopulmonary f u n c t i o n and on n u t r i t i o n a l r e q u i r e m e n t s are m i n i m a l . A e r o b i c e x e r c i s e i n v o l v e s endurance t r a i n i n g . As the body performs a c t i v i t i e s f o r extended p e r i o d s , p h y s i o l o g i c a l and c e l l u l a r a d a p t a t i o n s occur ( 1 0 - 1 2 ) . These a d a p t a t i o n s focus on the a b i l i t y o f the body t o s u p p l y oxygen to the muscle c e l l s , the c a p a c i t y o f the c e l l s to u t i l i z e oxygen, and a s h i f t i n the f u e l s o u r c e to g r e a t e r use o f f a t t y a c i d s . The magnitude o f these changes d e f i n e s a e r o b i c c a p a c i t y and e n d u r a n c e . A e r o b i c t r a i n i n g produces numerous p h y s i o l o g i c a l changes, i n c l u d i n g changes i n h e a r t r a t e and oxygen u p t a k e . There i s a decrease i n the r e s t i n g h e a r t r a t e and the h e a r t r a t e a t any s p e c i f i c work l o a d . However, c a r d i a c o u t p u t i s m a i n t a i n e d because s t r o k e volume i s i n c r e a s e d . Changes a l s o occur w i t h i n the muscle c e l l s t h a t a l l o w f o r i n c r e a s e d oxygen uptake from the c i r c u l a t i n g blood. Thus, a e r o b i c e x e r c i s e t r a i n i n g i n c r e a s e s s t r o k e volume, t h e e f f i c i e n c y o f oxygen u p t a k e by muscles (A-V 0 2 ) , V02 max and r e d u c e s t h e h e a r t r a t e d u r i n g submaximal e x e r c i s e ( 1 0 , 1 3 - 1 4 ) . At the c e l l u l a r l e v e l , a e r o b i c e x e r c i s e t r a i n i n g i n c r e a s e s the o x i d a t i v e c a p a c i t y o f t h e t i s s u e s ( 1 1 ) , and produces numerous changes i n the f u n c t i o n o f the muscle c e l l s . Changes i n s p e c i f i c s k e l e t a l muscle c e l l s and the e f f e c t s o f e x e r c i s e i n t e n s i t y , d u r a t i o n , and frequency are d i s c u s s e d i n C h a p t e r 2 . M i t o c h o n d r i a i n c r e a s e i n s i z e and number which a l l o w s f o r i n c r e a s e d oxygen use i n f u e l c o n v e r s i o n t o energy f o r muscular c o n t r a c t i o n . T r a i n i n g a l s o produces a s h i f t i n the primary s o u r c e o f f u e l f o r e x e r c i s e from c a r b o h y d r a t e s to f a t t y a c i d s . S i n c e f a t t y a c i d s are the p r i n c i p a l form o f f u e l s t o r a g e i n the body, t h i s s h i f t i s c r i t i c a l i n a l l o w i n g for prolonged a c t i v i t y . Use o f c a r b o h y d r a t e s and l i p i d s d u r i n g a e r o b i c e x e r c i s e i s examined i n Chapter 3 . I n f l u e n c e o f A e r o b i c E x e r c i s e on N u t r i t i o n a l Needs I n t e r e s t i n the r e l a t i o n s h i p o f n u t r i t i o n and e x e r c i s e a r i s e s from many s o u r c e s . A t h l e t e s and coaches o f t e n seek an e x t r a edge from s p e c i f i c foods or s u p p l e m e n t s . W r e s t l e r s , d a n c e r s , and gymnasts

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

1.

LAYMAN

Overview

3

f r e q u e n t l y attempt t o c o n t r o l food i n t a k e to modify body w e i g h t ; and, as s t a t e d above, l a r g e numbers o f p e o p l e a r e now l o o k i n g t o the c o m b i n a t i o n o f improved n u t r i t i o n and e x e r c i s e f o r maintenance o f health. Thus, the t o p i c s o f " N u t r i t i o n and E x e r c i s e " produce a wide v a r i e t y o f q u e s t i o n s from a d i v e r s e audience w i t h d i f f e r e n t needs and g o a l s . Q u e s t i o n s most f r e q u e n t l y asked i n c l u d e : I s e x e r c i s e i m p o r t a n t f o r weight c o n t r o l ? I s i n c r e a s e d p r o t e i n e s s e n t i a l f o r muscle b u i l d i n g o r strength? Does e x e r c i s e reduce t h e r i s k o f h e a r t d i s e a s e ? Should a t h l e t e s t a k e v i t a m i n supplements? Are s a l t t a b l e t s or e l e c t r o l y t e d r i n k s e s s e n t i a l f o r e x e r c i s e d u r i n g h o t weather? Is e x e r c i s e important for a d i a b e t i c ? Does a e r o b i c e x e r c i s e c r e a t e an i n c r e a s e d need f o r i r o n ? Does e x e r c i s e p r e v e n T h i s book a d d r e s s e s these i s s u e s and examines the c u r r e n t r e s e a r c h i n these a r e a s . To e v a l u a t e n u t r i t i o n r e q u i r e m e n t s , t h e r e a d e r needs a b a s i c u n d e r s t a n d i n g o f n u t r i e n t s and the parameters t h a t a f f e c t t h e i r n e e d s . N u t r i e n t s a r e c h e m i c a l s u b s t a n c e s needed to m a i n t a i n l i f e which are s u p p l i e d to the body i n food or d r i n k s . The n u t r i e n t s i n c l u d e v i t a m i n s , m i n e r a l s , c a r b o h y d r a t e s , f a t s , p r o t e i n s , and w a t e r . These c l a s s i f i c a t i o n s o f n u t r i e n t s encompass a p p r o x i m a t e l y 45 d i f f e r e n t c h e m i c a l s t h a t a r e i n v o l v e d i n every f u n c t i o n or s t r u c t u r e o f the body. While some o f these f u n c t i o n s t h a t a r e d i r e c t l y i n f l u e n c e d by e x e r c i s e w i l l be d i s c u s s e d i n the subsequent c h a p t e r s , a complete l i s t i n g o f these f u n c t i o n s i s beyond the scope o f t h i s book. For a more thorough r e v i e w o f n u t r i e n t f u n c t i o n s , t h e r e a d e r i s r e f e r r e d t o any one o f a number o f e x c e l l e n t n u t r i t i o n references (5-6,15-16). To a s s e s s the impact o f e x e r c i s e on the needs f o r s p e c i f i c n u t r i e n t s , n u t r i e n t f u n c t i o n s must be e v a l u a t e d . At a g e n e r a l i z e d l e v e l , t h e f u n c t i o n s o f n u t r i e n t s a r e (a) growth or maintenance o f the s t r u c t u r e s o f the body (one can c o n s i d e r e i t h e r m a c r o - s t r u c t u r e s l i k e muscles and b o n e s , o r m i c r o - s t r u c t u r e s l i k e c e l l membranes and enzymes), (b) f u e l s f o r the energy t o run the body p r o c e s s e s , (c) f l u i d s and r e g u l a t i o n o f body f l u i d s , and (d) p r o t e c t i o n from t o x i c s u b s t a n c e s i n c l u d i n g t o x i c c h e m i c a l s , c a r c i n o g e n s , and a n t i g e n s . The e f f e c t s o f e x e r c i s e on n u t r i t i o n a l r e q u i r e m e n t s can be a s s e s s e d a g a i n s t the l i k e l i h o o d o f s u b s t a n t i a l changes i n one or more o f these f u n c t i o n s . As the e f f e c t s o f e x e r c i s e on the body a r e examined, c l e a r l y the primary e f f e c t s a r e on body f l u i d s and f u e l s . Movement o f the body r e q u i r e s a d d i t i o n a l f u e l s and the p r o c e s s o f c o n v e r s i o n o f these f u e l s i n t o energy produces h e a t which must be d i s s i p a t e d , i n l a r g e p a r t , by e v a p o r a t i o n o f sweat from the s k i n . Water i s the most c r i t i c a l o f the e f f e c t s o f e x e r c i s e on n u t r i t i o n a l requirements. As d i s c u s s e d i n Chapter 8 , e x e r c i s e produces i n c r e a s e d body h e a t and i n c r e a s e d water l o s s e s . I f t h i s r e s u l t s i n d e h y d r a t i o n , i t w i l l decrease performance and can produce n a u s e a , i r r e g u l a r i t i e s i n h e a r t b e a t , h e a t s t r o k e , and d e a t h . A s s o c i a t e d w i t h water l o s s e s , t h e r e a r e l o s s e s o f s a l t s or

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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NUTRITION A N D AEROBIC EXERCISE

electrolytes. However, water l o s s i s c l e a r l y t h e most l i m i t i n g f a c t o r f o r work c a p a c i t y as d e f i n e d i n a p o s i t i o n paper by the American C o l l e g e o f S p o r t s M e d i c i n e ( 1 7 ) . A f t e r s u p p l y i n g an adequate amounT o f w a t e r , t h e n e x t most i m p o r t a n t d i e t a r y i s s u e i s adequate e n e r g y . P h y s i c a l a c t i v i t y i s the major v a r i a b l e o f energy e x p e n d i t u r e and the o n l y component under v o l u n t a r y c o n t r o l . The o t h e r components a r e b a s a l metabolism (the energy expended to m a i n t a i n the v i t a l body p r o c e s s e s w h i l e a t r e s t ) and S p e c i f i c Dynamic A c t i o n (the energy u t i l i z e d d u r i n g t h e d i g e s t i o n , a b s o r p t i o n , and a s s i m i l a t i o n o f n u t r i e n t s a f t e r a m e a l ) . These two components expend about 1000-2000 k i l o c a l o r i e s o f energy per day, depending on the s i z e o f the body and c o m p o s i t i o n o f m e a l s . However, food i n t a k e s range from 2000 to 6000 k c a l s per d a y , depending on the l e v e l o f a c t i v i t y . Sedentary a d u l t s need about 2000-2500 k c a l / d a y , w h i l e a t h l e t e s consume a p p r o x i m a t e l y 3000-4000 k c a l / d a y ( 1 8 ) . The primary f a c t o r s d e t e r m i n i n g the energy expenditure o f e x e r c i s e traveled. While i t i s t r u w a l k i n g speeds v e r s u s r u n n i n g due to g r e a t e r e f f i c i e n c i e s i n movement, over a f a i r l y wide range o f r u n n i n g speeds energy e x p e n d i t u r e i s e s s e n t i a l l y independent o f speed f o r a g i v e n d i s t a n c e (19-20). F u e l s f o r the body a r e l i m i t e d to c a r b o h y d r a t e s , f a t s , and proteins. In the American d i e t , these f u e l s are consumed i n a r a t i o o f a p p r o x i m a t e l y 4 6 : 4 2 : 1 2 w i t h t h e recommended r a t i o b e i n g c l o s e r to 53:35:12 (5). Thus i n a nongrowing a d u l t , t h e s e r a t i o s p r o v i d e e s t i m a t e s o f t h e f u e l use f o r d a i l y a c t i v i t i e s . The primary f u e l s f o r e x e r c i s e are c a r b o h y d r a t e s and f a t s . C h a p t e r 3 examines u t i l i z a t i o n of s p e c i f i c fuels during aerobic e x e r c i s e . As the amount o f d a i l y e x e r c i s e i n c r e a s e s , t h e r e i s an i n c r e a s e d energy e x p e n d i t u r e and hence i n c r e a s e d need f o r energy n u t r i e n t s u s u a l l y r e f l e c t e d i n i n c r e a s e d food c o n s u m p t i o n , decreased body f a t , or b o t h (see Chapter 9 ) . P r o t e i n has l o n g been a dominant f e a t u r e a t the t r a i n i n g t a b l e f o r a t h l e t e s who b e l i e v e t h a t h i g h i n t a k e s o f p r o t e i n are e s s e n t i a l f o r muscle development and s t r e n g t h . However, r e s e a r c h i n d i c a t e s t h a t l i t t l e or no a d d i t i o n a l p r o t e i n i s r e q u i r e d f o r maximum muscle growth. I n t e r e s t i n g l y , recent s t u d i e s suggest t h a t a e r o b i c e x e r c i s e may have l a r g e r e f f e c t s on p r o t e i n metabolism than a n a e r o b i c t r a i n i n g (21). The e f f e c t s o f both a n a e r o b i c and a e r o b i c e x e r c i s e on the n u t r i t i o n a l needs f o r p r o t e i n a r e r e v i e w e d i n C h a p t e r 4 . As d i s c u s s e d above, a e r o b i c e x e r c i s e produces numerous p h y s i o l o g i c and m e t a b o l i c changes i n the body. Many o f t h e s e changes a r e b e l i e v e d to be b e n e f i c i a l f o r p r e v e n t i o n o f h e a r t d i s e a s e . The e f f e c t s on cardiopulmonary f u n c t i o n were mentioned e a r l i e r and a r e c l e a r l y b e n e f i c i a l , as a r e t h e changes i n body composition described i n Chapter 9. Further, a e r o b i c e x e r c i s e a p p e a r s to have p o s i t i v e e f f e c t s on b l o o d c h o l e s t e r o l and o t h e r lipids. These e f f e c t s o f e x e r c i s e on the metabolism o f l i p i d s and the important t r a n s p o r t p a r t i c l e s c a l l e d l i p o p r o t e i n s are discussed i n Chapter 5 . A t h l e t e s have l o n g sought to maximize performance by use o f special nutrients. "Ergogenic A i d s " have been promoted to i n c r e a s e endurance, s t r e n g t h , o r performance. Ergogenic a i d s i n c l u d i n g v i t a m i n s , m i n e r a l s , and o t h e r substances are suggested to "supply"

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

1.

LAYMAN

Overview

o r "produce" more e n e r g y . B e s i d e s pure v i t a m i n and m i n e r a l s u p p l e m e n t s , o t h e r a i d s i n c l u d e honey, wheat germ o i l , g e l a t i n , g l u c o s e , and v i t a m i n E. With t h e e x c e p t i o n o f p o s s i b l e p s y c h o l o g i c a l b e n e f i t s , any o t h e r suggested b e n e f i t s a r e w i t h o u t sound s c i e n t i f i c documentation ( 2 2 ) . As w i t h most m i s l e a d i n g a d v e r t i s i n g , the premise b e g i n s w i t h a b a s i c f a c t and then p l a y s t o t h e d e s i r e s o f t h e consumer. For example, c o n v e n t i o n a l wisdom h o l d s t h a t the r e q u i r e m e n t s o f many o f the B - v i t a m i n s are dependent on the amount o f energy o r number o f c a l o r i e s used by t h e body. For t h i a m i n , r i b o f l a v i n , n i a c i n , p a n t o t h e n i c a c i d , and b i o t i n , the needs c o u l d i n c r e a s e p r o p o r t i o n a l to energy e x p e n d i t u r e . Thus the a t h l e t e b u r n i n g t w i c e the energy o f the n o n - a t h l e t e was assumed t o have a p p r o x i m a t e l y t w i c e the B - v i t a m i n needs. W h i l e the " l o g i c " t h a t e x e r c i s e i n c r e a s e s B - v i t a m i n needs i s r e a s o n a b l e , o n l y r i b o f l a v i n has been s p e c i f i c a l l y s t u d i e d . Chapter 6 summarizes t h e s e f i n d i n g s and i n d i c a t e s t h a t w h i l e r i b o f l a v i n needs a r e i n c r e a s e d , the i n c r e a s e i s s m a l l and th s h o u l d be adequate to mee The e f f e c t s o f e x e r c i s e on the d i e t a r y needs f o r m i n e r a l s have n o t been e x t e n s i v e l y s t u d i e d . Of p a r t i c u l a r i n t e r e s t i s the impact o f e x e r c i s e on the m i n e r a l s i r o n and c a l c i u m which a r e examined i n C h a p t e r 7 . I r o n i s an e s s e n t i a l component o f hemoglobin which i s r e s p o n s i b l e f o r t r a n s p o r t o f oxygen w i t h i n r e d b l o o d c e l l s i n the b l o o d . Thus, i r o n d e f i c i e n c y (anemia) w i l l decrease oxygen c a r r y i n g c a p a c i t y o f t h e b l o o d and hence lower a e r o b i c c a p a c i t y . This problem appears t o be most i m p o r t a n t f o r women who f r e q u e n t l y have m a r g i n a l i r o n i n t a k e s (_5). C a l c i u m needs and m e t a b o l i s m have become an i m p o r t a n t n u t r i t i o n i s s u e due to the i n c r e a s e d p r e v a l e n c e o f o s t e o p o r o s i s . Osteoporosis i s a d i s e a s e o f f r a g i l i t y o f major bones such as the p e l v i s , femur, and s p i n e caused by an a g e - r e l a t e d l o s s o f bone m i n e r a l s . As d i s c u s s e d i n C h a p t e r 7 , c a l c i u m i n t a k e and p h y s i c a l a c t i v i t y may f a v o r a b l y a f f e c t the c a l c i u m c o n t e n t o f bones and d e l a y the onset o f osteoporosis. These i s s u e s and a s s o c i a t e d t o p i c s a r e d i s c u s s e d i n more d e t a i l i n the f o l l o w i n g c h a p t e r s . Each o f the i n d i v i d u a l a u t h o r s has p r o v i d e d background i n f o r m a t i o n and r e s e a r c h d a t a i n an e f f o r t t o r e v i e w and e v a l u a t e the i m p o r t a n t i s s u e s . F i n a l l y , each a u t h o r has p r o v i d e d a summary s t a t e m e n t d e f i n i n g t h e n u t r i e n t needs d u r i n g an a e r o b i c e x e r c i s e program.

Literature Cited 1. U.S. Department of Health, Education, and Welfare. (1979) Healthy people. The Surgeon General's report on health promotion and disease prevention. DHEW (PHS) Publ. No. 79-55071. 2. American Heart Association. (December, 1981) Statement on Exercise. Springfield, IL. 3. American Dietetic Association. (1980) Nutrition and physical fitness. J. Am. Diet. Assoc. 76, 437.

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6 4.

NUTRITION AND AEROBIC EXERCISE

Castelli, W. P. (1979) Exercise and high-density lipoproteins (editorial). J. Am. Med. Assoc. 242, 2217.

5. Guthrie, H. A. (1983) Introductory Nutrition. 5th edition. C. V. Mosby Co., St. Louis. 6. Hamilton, Ε. M., Whitney, Ε. N. & Sizer, F. S. (1985) In: Nutrition: Concepts and Controversies. West Publishing Co., St. Paul. 7. American Institute for Cancer Research. (Summer, 1985) Trends in Food Consumption. In: AICR Newsletter. Falls Church, VA. 8. Stern, J. S. (1983) Diet and Exercise. In: Obesity (Greenwood, M.R.C., ed.), pp. 65-84, Churchill Livingstone, New York. 9. Clark, D. H. (1973 endurance resulting from exercise. Exer. Sport Sci. Rev. 1, 73-102. 10. McArdle, W. D., Katch, F. I. & Katch, V. L. (1981) Exercise Physiology: Energy, Nutrition, and Performance. Lea & Febiger, Philadelphia. 11. Holloszy, J. O. & Booth, F. W. (1976) Biochemical adaptations to endurance exercise in muscle. Ann. Rev. Physiol. 38, 273-291. 12. Pollock, M. L. (1973) The quantification of endurance training programs. Exer. Sport Sci. Rev. 1, 155-188. 13. Saltin, B. (1973) Metabolic fundamentals in exercise. Med. Sci. Sports 5, 137-146. 14.

Keul, J. (1973) The relationship between circulation and metabolism during exercise. Med. Sci. Sports 5, 209-219.

15. Briggs, G. M. & Calloway, D. H. (1979) Nutrition and Physical Fitness. 10th edition. W. B. Saunders Co., Philadelphia. 16. Pike, R. L. & Brown, M. L. (1984) Nutrition: An integrated approach. 3rd edition. John Wiley & Sons, New York. 17. American College of Sports Medicine. (1975) Position Paper. Med. Sci. Sports 7:7. 18. Buskirk, E. R. (1981) Some nutritional considerations in the conditioning of athletes. Ann. Rev. Nutr. 1, 319-350. 19. Fellingham, G. W., Roundy, E. S., Fisher, A. G. & Bryce, G. R. (1978) Caloric cost of walking and running. Med. Sci. Sports 10, 132-136.

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

1. LAYMAN 20.

Overview

Howley, Ε. T. & Glover, M. E. (1974) The caloric cost of running and walking one mile for men and women. Med. Sci. Sports 6, 235-237.

21. Lemon, P.W.R. & Nagle, F. J. (1981) Effects of exercise on protein and amino acid metabolism. Med. Sci. Sports 13, 141-149. 22. Williams, M. H. (1985) Ergogenic foods. In: Nutritional Aspects of Human Physical and Athletic Performance. 2nd edition, pp. 296-321, Charles C. Thomas, Springfield, IL. RECEIVED September

6, 1985

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2 Biochemical Adaptations in Skeletal Muscle Induced by Exercise Training Ronald L. Terjung and David A. Hood Department of Physiology, Upstate Medical Center, State University of New York, Syracuse, NY 13210

Exercise performance seems to be greatly affected by the chronic level of physical activit For example, difference capacity prolonge obvious between wild and domesticated animals. This is probably due, in part, to inherent biochemical differences between the muscles of active and less active species (1). Muscles of wild animals appear darker than those of their domesticated counterparts (2). Further, variations in activity patterns due to seasonal change (3) or hibernation (4), are associated with differences in the enzymes related to oxidative metabolism. Thus, in a general sense physical activity seems to be associated with biochemical changes that enhance the muscle's capacity for aerobic metabolism. Muscle Adaptations The specific biochemical changes induced by increased physical activity are well characterized from laboratory studies and have been the subject of a number of excellent reviews (5-9). The fundamental change found in skeletal muscle after exercise training is an enhanced capacity for energy provision via aerobic metabolism. There i s an i n c r e a s e i n m i t o c h o n d r i a l p r o t e i n content and c r i s t a e component enzymes a s s o c i a t e d w i t h t h e e l e c t r o n t r a n s p o r t . In a thorough s t u d y , H o l l o s z y (10) found t h a t an e x e r c i s e program o f p r o l o n g e d t r e a d m i l l r u n n i n g i n c r e a s e d the m i t o c h o n d r i a l content o f l a b o r a t o r y r a t s by a p p r o x i m a t e l y 100%. S i m i l a r t r a i n i n g responses are found i n a wide v a r i e t y o f o t h e r animals i n c l u d i n g man (9,11). Subsequent m o r p h o l o g i c a l s t u d i e s have shown t h a t the m i t o c h o n d r i a o f t r a i n e d muscles appear t o be more abundant (12) and l a r g e r (13). Thus, t h e c r o s s - s e c t i o n o f the t r a i n e d muscle appears more d e n s e l y packed w i t h m i t o c h o n d r i a . M i t o c h o n d r i a i s o l a t e d from muscles o f t r a i n e d animals e x h i b i t the same dependence on ADP t o s t i m u l a t e and i n c r e a s e r e s p i r a t i o n , and a r e as e f f i c i e n t i n t h e c o u p l i n g o f ATP p r o d u c t i o n t o oxygen consumption as muscle o b t a i n e d from s e d e n t a r y animals (10). Thus, the i n c r e a s e d m i t o c h o n d r i a l content r e p r e s e n t s a t r u e i n c r e a s e i n the p o t e n t i a l f o r a e r o b i c ATP g e n e r a t i o n w i t h i n the muscle. I n a d d i t i o n t o the g r e a t e r e l e c t r o n t r a n s p o r t c a p a c i t y , t h e r e i s a l s o a c o o r d i n a t e d i n c r e a s e i n t h e enzymes o f support 0097-6156/ 86/ 0294-0008$06.00/ 0 © 1986 American Chemical Society

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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TERJUNG AND HOOD

Biochemical

Adaptations

in Skeletal

Muscle

9

systems necessary t o s u p p l y the r e d u c i n g e q u i v a l e n t s f o r the e l e c t r o n t r a n s p o r t and ATP s y n t h e s i s . Thus, the c a p a c i t i e s f o r carboh y d r a t e o x i d a t i o n ( 1 4 ) , f a t t y a c i d o x i d a t i o n (15,16), k e t o n e body o x i d a t i o n ( 1 7 ) , t r i c a r b o x y l i c a c i d c y c l e enzymes ( 1 8 ) , and m i t o c h o n d r i a l s h u t t l e pathways (19) are i n c r e a s e d by endurance t r a i n i n g . I n a d d i t i o n , the content of m y o g l o b i n , w h i c h i s thought t o f a c i l i t a t e oxygen t r a n s f e r w i t h i n the c e l l (20,21), i n c r e a s e s i n the t r a i n e d muscle ( 2 , 2 2 ) . Thus, t h e r e i s a c o o r d i n a t e d i n c r e a s e i n the c a p a c i t y of the t r a i n e d muscle f o r ATP p r o v i s i o n v i a o x i d a t i v e metabolism. These changes c o n t r i b u t e to the d a r k e r appearing muscles of the t r a i n e d a n i m a l s . The p r i m a r y m e t a b o l i c s i g n i f i c a n c e of the enhanced a e r o b i c c a p a c i t y i s p r o b a b l y r e l a t e d t o the c o n t r o l of energy metabolism and a s h i f t i n s u b s t r a t e source from carboh y d r a t e to f a t i n the muscles d u r i n g submaximal e x e r c i s e (6,8,23). S p e c i f i c i t y of

Adaptations

The b i o c h e m i c a l a d a p t a t i o n to the w o r k i n g m u s c l e s . F o r example, an i n c r e a s e i s found i n the h i n d l i m b muscle of t r e a d m i l l run r a t s , but not i n l i v e r (24) o r the l e s s a c t i v e abdominal muscles of the same animals ( 2 2 ) . Further, when a unique t r a i n i n g program t h a t e x e r c i s e s o n l y one l i m b on a c y c l e ergometer i s employed, the a d a p t a t i o n i s induced i n the e x e r c i s e d l e g , but not the u n t r a i n e d c o n t r a l a t e r a l l e g ( 1 3 , 2 5 ) . Thus, the t r a i n i n g a d a p t a t i o n i s not a g e n e r a l i z e d response w i t h i n the i n d i v i d u a l . T h i s i n d i c a t e s t h a t the s t i m u l u s r e s p o n s i b l e f o r b r i n g i n g about the b i o c h e m i c a l change i s s p e c i f i c t o the w o r k i n g muscle and r e l a t e d t o the demands p l a c e d upon the muscle by the exercise effort. F a c t o r s t h a t determine the magnitude of the t r a i n i n g e f f e c t are f a i r l y complex, due i n p a r t t o the o r d e r e d p a t t e r n of motor u n i t r e c r u i t m e n t found d u r i n g normal l o c o m o t i o n and/or a s p e c i f i c work t a s k . The type and i n t e n s i t y of the e x e r c i s e e f f o r t l a r g e l y d e t e r mine w h i c h motor u n i t s w i l l be u t i l i z e d t o p e r f o r m the work ( 2 6 ) . Each motor u n i t w i t h i n a muscle i s composed of a s i n g l e nerve axon and the muscle f i b e r s t h a t i t i n n e r v a t e s . W h i l e a l l f i b e r s w i t h i n a g i v e n motor u n i t have the same p r o p e r t i e s , i t i s now r e c o g n i z e d t h a t at l e a s t t h r e e d i f f e r e n t s k e l e t a l muscle f i b e r types (and thus motor u n i t s ) e x i s t i n mammals. They d i f f e r c o n s i d e r a b l y i n t h e i r c o n t r a c t i l e c h a r a c t e r i s t i c s , i n t h e i r inherent biochemical c a p a b i l i t i e s , and p r o b a b l y i n t h e i r response to t r a i n i n g . Thus, i t i s i m p o r t a n t to c o n s i d e r the impact of the d i f f e r e n t types of s k e l e t a l muscle motor u n i t s . M u s c l e F i b e r Types Mammalian s k e l e t a l muscle can be s e p a r a t e d i n t o two d i s t i n c t f i b e r p o p u l a t i o n s , based on r e l a t i v e c o n t r a c t i o n c h a r a c t e r i s t i c s , and are r e f e r r e d t o as s l o w - t w i t c h (Type I ) o r f a s t - t w i t c h (Type I I ) f i b e r s . The s l o w - t w i t c h f i b e r type e x h i b i t s a r e l a t i v e l y low s h o r t e n i n g v e l o c i t y ( 2 7 ) , a low r a t e of t e n s i o n development ( 2 7 ) , a low myosin ATPase a c t i v i t y (28) and a low r a t e of c a l c i u m s e q u e s t r a t i o n by the sarcoplasmic reticulum (29). The c o n v e r s e i s t r u e f o r the f a s t twitch fibers. Since c o n t r a c t i o n v e l o c i t y h i g h l y c o r r e l a t e s w i t h myosin ATPase a c t i v i t y ( 3 0 ) , i t i s p o s s i b l e t o e a s i l y i d e n t i f y ,

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w i t h i n a muscle c r o s s - s e c t i o n , f a s t and s l o w - t w i t c h f i b e r s by the i n t e n s i t y of s t a i n i n g of the myosin ATPase u s i n g h i s t o c h e m i c a l p r o c e d u r e s ( 3 1 ) . The s l o w - t w i t c h f i b e r s are c h a r a c t e r i s t i c a l l y r e d i n appearance, i n d i c a t i v e of a r e l a t i v e l y h i g h m i t o c h o n d r i a l content (14), e x h i b i t a h i g h b l o o d f l o w (32,33), and have a low g l y c o g e n o l y t i c c a p a c i t y (e.g., phosphorylase a c t i v i t y ) (7,34). The fastt w i t c h f i b e r s u n i f o r m l y possess a r e l a t i v e l y h i g h g l y c o g e n o l y t i c c a p a c i t y ( 7 , 3 4 ) , but can be s u b d i v i d e d by t h e i r c o n t r a s t i n g c a p a c i t i e s f o r o x i d a t i v e m e t a b o l i s m . I n f a c t , the g r e a t e s t d i f f e r e n c e i n m i t o c h o n d r i a l content f o r most non-primate mammalian muscle i s found between the f a s t - t w i t c h red and the f a s t - t w i t c h w h i t e f i b e r types (14,35). I n humans, the m i t o c h o n d r i a l content of s l o w - t w i t c h r e d f i b e r s i s t y p i c a l l y g r e a t e r than t h a t of the f a s t - t w i t c h r e d f i b e r s (7,35). S i m i l a r l y , measurements of b l o o d f l o w s t o s e c t i o n s of m u s c l e , which are p r i m a r i l y composed of a s i n g l e f i b e r t y p e , e x h i b i t l a r g e d i f f e r e n c e s c o n s i s t e n t w i t h the expected demands of oxygen s u p p l y based on m i t o c h o n d r i a s k e l e t a l muscle i s t y p i c a l l f u n c t i o n a l l y d i s t i n c t f i b e r types: s l o w - t w i t c h r e d , f a s t - t w i t c h r e d and f a s t - t w i t c h w h i t e . These f i b e r types are a l s o commonly r e f e r r e d to as Type I , Type l i a , and Type l i b , r e s p e c t i v e l y (7). C o n t r a c t i o n p e r f o r m a n c e of t h e s e d i f f e r e n t f i b e r t y p e s i s p r e d i c t a b l e from a knowledge of t h e i r b i o c h e m i c a l and b l o o d f l o w differences. F o r example, the s l o w - t w i t c h r e d f i b e r type can cont r a c t f o r l o n g p e r i o d s of time w i t h o u t a l o s s i n t e n s i o n development (36). A l t h o u g h the r e l a t i v e l y h i g h f u n c t i o n a l a e r o b i c c a p a c i t y must be important f o r s u s t a i n e d performance ( 3 7 ) , i t i s a l s o known t h a t the s l o w - t w i t c h f i b e r type r e q u i r e s l e s s energy t o m a i n t a i n t e n s i o n (38). T h e r e f o r e , t h i s f i b e r type seems w e l l - s u i t e d f o r p r o l o n g e d s u s t a i n e d a c t i v i t y such as t h a t r e q u i r e d f o r p o s t u r a l s u p p o r t . The f a s t - t w i t c h red muscle f i b e r i s f a i r l y f a t i g u e r e s i s t a n t and capable of repeated powerful contractions before tension development declines s i g n i f i c a n t l y (36). A l t h o u g h t h i s f i b e r type has a h i g h c a p a c i t y f o r l a c t a t e p r o d u c t i o n ( 3 9 , 4 0 ) , i t s performance d u r i n g p r o l o n g e d c o n t r a c t i o n p e r i o d s i s made p o s s i b l e by i t s r e l a t i v e l y h i g h f u n c t i o n a l a e r o b i c c a p a c i t y ( 4 0 ) . I n c o n t r a s t , the f a s t - t w i t c h w h i t e muscle f i b e r e x h i b i t s a r a p i d l o s s of t e n s i o n development and i s capable of p o w e r f u l c o n t r a c t i o n s f o r o n l y a b r i e f p e r i o d of time (36). A h i g h r a t e of g l y c o g e n o l y s i s , r e s u l t i n g i n a h i g h l a c t a t e content and c e l l u l a r a c i d o s i s , would be found d u r i n g i n t e n s e cont r a c t i o n c o n d i t i o n s i n t h i s f i b e r type ( 4 1 ) . The s l o w - t w i t c h muscle f i b e r s are r e l a t i v e l y s m a l l i n d i a m e t e r and belong to motor u n i t s t h a t are t y p i c a l l y the f i r s t t o be r e c r u i t e d d u r i n g any motor t a s k . Thus, d u r i n g s i m p l e muscle a c t i v i t y r e q u i r e d f o r p o s t u r a l support of s t a n d i n g , the s l o w - t w i t c h motor u n i t s are v e r y a c t i v e and, i n some c a s e s , f u n c t i o n near t h e i r maxi m a l f o r c e output ( 4 2 ) . The f a s t - t w i t c h red f i b e r s belong t o l a r g e r motor u n i t s (26) and are r e c r u i t e d f o r muscle a c t i o n s t h a t are more f o r c e f u l (42). T h e i r r e c r u i t m e n t i n c r e a s e s , f o r example, when r u n n i n g at i n c r e a s i n g speeds on a t r e a d m i l l ( 4 2 ) . F i n a l l y , the f a s t - t w i t c h w h i t e f i b e r s belong t o l a r g e p o w e r f u l motor u n i t s and a r e r e c r u i t e d d u r i n g v e r y i n t e n s e e x e r c i s e (43,44) o r d u r i n g ext r e m e l y f o r c e f u l movements such as jumping ( 4 2 ) . The r e l a t i v e l y i n f r e q u e n t and s p e c i a l i z e d u t i l i z a t i o n of the f a s t - t w i t c h w h i t e motor u n i t s i s e s p e c i a l l y p u r p o s e f u l , s i n c e these i n t e n s e e x e r c i s e

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e f f o r t s and e x p l o s i v e body movements are u s u a l l y s h o r t l i v e d . Thus, the r a p i d f a t i g u e and r e l a t i v e l y poor endurance performance of t h i s f i b e r type (36) do not g e n e r a l l y i n f l u e n c e muscle f u n c t i o n d u r i n g moderate e x e r c i s e of submaximal i n t e n s i t y (43,44)« Athough t h e r e can be a s i g n i f i c a n t o v e r l a p i n the p r o g r e s s i v e r e c r u i t m e n t of motor u n i t p o p u l a t i o n s as the i n t e n s i t y of e x e r c i s e becomes g r e a t e r , the g e n e r a l p a t t e r n of o r d e r e d r e c r u i t m e n t from s l o w - t w i t c h red t o f a s t - t w i t c h red and then to f a s t - t w i t c h w h i t e motor u n i t s o c c u r s d u r i n g most p h y s i c a l a c t i v i t y ( 4 5 ) . The s k e l e t a l musculature of those non-primate mammals t h a t have been examined i s comprised p r i m a r i l y of ( i . e . , 80-95%) f a s t - t w i t c h f i b e r s (46,47). The f a s t t w i t c h f i b e r s a r e , i n t u r n , comprised of a p p r o x i m a t e l y equal p o r t i o n s of f a s t - t w i t c h red and f a s t - t w i t c h w h i t e f i b e r s . In contrast the s k e l e t a l muscle of man i s comprised of a p p r o x i m a t e l y 50% f a s t t w i t c h and 50% s l o w - t w i t c h muscle ( 7 , 4 8 ) . A l t h o u g h the l o w - o x i d a t i v e f a s t - t w i t c h w h i t e muscle f i b e r s are found i n humans ( 7 , 4 9 ) , they t y p i c a l l y r e p r e s e n as compared t o most lowe I n summary, a l l mammals possess a l a r g e f r a c t i o n of h i g h - o x i d a t i v e muscle. The ordered p a t t e r n of motor u n i t r e c r u i t m e n t i n v o l v e s these h i g h o x i d a t i v e muscle f i b e r s b e f o r e the l o w - o x i d a t i v e f i b e r s , as e x e r c i s e i n t e n s i t y p r o g r e s s e s from m i l d , t o moderate, t o s e v e r e . T h i s p r o g r e s s i o n f a v o r s an enhanced e x e r c i s e performance a t submaximal e x e r c i s e i n t e n s i t i e s , s i n c e the slow and f a s t - t w i t c h r e d f i b e r s are capable of repeated c o n t r a c t i o n s f o r l o n g p e r i o d s of time. Important

T r a i n i n g Parameters

S e v e r a l i m p o r t a n t t r a i n i n g v a r i a b l e s are known t o i n f l u e n c e the magnitude of the b i o c h e m i c a l response. These i n c l u d e the d u r a t i o n of the t r a i n i n g program, the i n t e n s i t y of the e x e r c i s e e f f o r t , the d u r a t i o n of each e x e r c i s e bout ( m i n u t e s / d a y ) , and the f r e q u e n c y of e x e r c i s e ( i . e . , days/week). Training Duration. I t i s i n t u i t i v e l y obvious t h a t the d u r a t i o n of t r a i n i n g must be s u f f i c i e n t l y l o n g f o r the maximal response t o be developed. T h i s i s due, i n p a r t , to the n a t u r e of most t r a i n i n g programs t h a t t y p i c a l l y p r o g r e s s from r e l a t i v e l y m i l d or moderate e x e r c i s e e f f o r t s t o the more i n t e n s e e x e r c i s e bouts t h a t w i l l be m a i n t a i n e d t h e r e a f t e r . Thus, the c e l l u l a r s t i m u l u s f o r a d a p t a t i o n i s p r o b a b l y c o n t i n u a l l y changing u n t i l the peak e x e r c i s e e f f o r t , t h a t w i l l be r o u t i n e l y s u s t a i n e d f o r the steady s t a t e t r a i n i n g program, i s a c h i e v e d . A f t e r t h i s time the f u l l t r a i n i n g response might be e x p e c t e d . However, t h e r e i s an a d d i t i o n a l time d e l a y b e f o r e r e a l i z i n g the f u l l a d a p t i v e change. T h i s a d d i t i o n a l time i s due t o the c e l l u l a r events a s s o c i a t e d w i t h the a d a p t i v e response w i t h i n the c e l l . I n the case of a b i o c h e m i c a l change of an i n c r e a s e i n m i t o c h o n d r i a l p r o t e i n , the f u l l y developed response, r e p r e s e n t i n g the steady s t a t e change w i t h i n the muscle f i b e r , i s dependent upon the c e l l u l a r dynamics of p r o t e i n t u r n o v e r . S p e c i f i c a l l y , the r a t e at w h i c h a new steady s t a t e c o n c e n t r a t i o n of m i t o c h o n d r i a o c c u r s w i t h i n the muscle i s dependent upon the d e g r a d a t i o n r a t e c o n s t a n t of the m i t o c h o n d r i a l components ( 5 0 ) . Since p r o t e i n degradation i s a f i r s t - o r d e r p r o c e s s , the time course of m i t o c h o n d r i a l c o n t e n t change

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i s n o n - l i n e a r and i s c o n v e n i e n t l y c o n s i d e r e d i n terms of h a l f - l i f e . I n t h i s c o n t e x t , the h a l f - l i f e can be c o n s i d e r e d as the time r e q u i r e d f o r the m i t o c h o n d r i a l content t o proceed through o n e - h a l f the change, from the e x i s t i n g v a l u e , toward the new steady s t a t e v a l u e determined by the t r a i n i n g s t i m u l u s . A l t h o u g h i t i s p r o b a b l e t h a t the t u r n o v e r of m i t o c h o n d r i a does not o c c u r at the same r a t e i n a l l muscle f i b e r types ( 5 1 ) , an average h a l f - l i f e of a p p r o x i m a t e l y 1 week i s a r e a s o n a b l e v a l u e f o r mixed muscle of animals (52,53) and man ( 5 4 ^ . Thus, even i f the c e l l u l a r s t i m u l u s , s u f f i c i e n t to i n c r e a s e cytochrome c t o double t h a t n o r m a l l y found, were t o o c c u r i n s t a n t a n e o u s l y and remain c o n s t a n t t h e r e a f t e r , o n l y o n e - h a l f of the response would be measured when t r a i n i n g proceeded f o r the next week. T r a i n i n g the subsequent week would then produce a n o t h e r o n e - h a l f of the e f f e c t , t o b r i n g the response t o 75% c o m p l e t i o n . Each subsequent h a l f - l i f e d u r a t i o n would b r i n g about o n e - h a l f of the remaining e f f e c t . I t would then take a p p r o x i m a t e l y 5 h a l f - l i v e ( a p p r o x i m a t e l y 5 weeks s t a t e response. Thus l e a s t 5-6 weeks, a f t e r a c h i e v i n g a f u l l t r a i n i n g program, w i l l always tend t o u n d e r e s t i m a t e the t r u e magnitude of the b i o c h e m i c a l change w i t h i n the w o r k i n g muscles. T h i s i l l u s t r a t e s the need f o r the t r a i n i n g d u r a t i o n to be s u f f i c i e n t l y p r o l o n g e d f o r the a d a p t i v e change t o f u l l y d e v e l o p . The f i r s t - o r d e r n a t u r e of t h i s p r o c e s s r a i s e s an i m p o r t a n t a s p e c t w i t h r e g a r d t o d e t r a i n i n g . I f t r a i n i n g i s stopped, f o r even a b r i e f p e r i o d of t i m e , a s i g n i f i c a n t r e g r e s s i o n of the i n c r e a s e i n m i t o c h o n d r i a l c o n t e n t can o c c u r ( 5 1 - 5 4 ) . A g a i n , the change i n m i t o c h o n d r i a l c o n t e n t w i l l be n o n - l i n e a r over time. F o r example, i n the f i r s t week ( i . e . , f i r s t h a l f - l i f e ) of d e t r a i n i n g , the e l e v a t e d m i t o c h o n d r i a l c o n t e n t w i l l d e c l i n e a p p r o x i m a t e l y 50% of the way toward the lower n o n - t r a i n e d v a l u e ( F i g u r e 1 ) . F u r t h e r , the second and subsequent weeks of d e t r a i n i n g w i l l p e r m i t a d d i t i o n a l d e c l i n e s i n m i t o c h o n d r i a l c o n t e n t , each r e p r e s e n t i n g o n e - h a l f of the remaini n g f a l l toward the normal p r e t r a i n i n g v a l u e . Thus, because of the f i r s t - o r d e r n a t u r e of p r o t e i n t u r n o v e r , the g r e a t e s t a b s o l u t e change i n the d e t r a i n i n g p r o c e s s o c c u r s i n i t i a l l y . T h i s i n d i c a t e s t h a t the e x e r c i s e program s h o u l d be r o u t i n e l y performed, i f the peak a d a p t i v e response i s t o be m a i n t a i n e d . H i c k s o n (55) has shown t h a t t r a i n i n g induced b i o c h e m i c a l changes i n muscle can be o p t i m i z e d by r u n n i n g almost d a i l y ( i . e . , 6 days/week). T h i s i s c o n s i s t e n t w i t h the need to m a i n t a i n the t r a i n i n g s t i m u l u s operant w i t h i n the muscle cont i n u o u s l y over t i m e . As d i s c u s s e d by Booth ( 5 6 ) , i f a one week p e r i o d of d e t r a i n i n g has o c c u r r e d , a d i s p r o p o r t i o n a l d u r a t i o n of t r a i n i n g would be n e c e s s a r y f o r the m i t o c h o n d r i a l content t o r e c o v e r f u l l y , even i f the f u l l t r a i n i n g s c h e d u l e i s q u i c k l y r e e s t a b l i s h e d (Figure 1). R e c a l l t h a t d u r i n g the a d a p t i v e p r o c e s s each week of t r a i n i n g p e r m i t s o n l y o n e - h a l f of the change p o s s i b l e . Thus, app r o x i m a t e l y 4 weeks would be r e q u i r e d t o permit f u l l r e c o v e r y of the m i t o c h o n d r i a l c o n t e n t . A l t h o u g h t h i s extended p e r i o d of time would be needed t o r e c o v e r from the i n i t i a l d e c l i n e i n m i t o c h o n d r i a l c o n t e n t , the r e c o v e r y of o t h e r t r a i n i n g responses, such as a l t e r e d b l o o d t r i g l y c e r i d e content ( 5 7 ) , may f o l l o w a v e r y d i f f e r e n t time course. T h e r e f o r e , as d i s c u s s e d below, the e x i s t e n c e of r e l a t i v e l y s m a l l d i f f e r e n c e s i n m i t o c h o n d r i a l c o n t e n t may have l i t t l e impact on the r e c o v e r y of e x e r c i s e performance f o l l o w i n g a b r i e f p e r i o d of inactivity.

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E x e r c i s e I n t e n s i t y . The importance of e x e r c i s e i n t e n s i t y was f i r s t apparent when comparing the response induced by swimming v e r s u s t r e a d m i l l r u n n i n g t r a i n i n g programs. Swim t r a i n i n g does not produce as g r e a t an i n c r e a s e i n m i t o c h o n d r i a l c o n t e n t i n animals as found w i t h r u n n i n g ( 1 0 , 5 8 ) . I n f a c t , e a r l y s t u d i e s e v a l u a t i n g an e x e r c i s e response w i t h swim t r a i n i n g f a i l e d t o f i n d a s i g n i f i c a n t b i o c h e m i c a l change i n the h i n d l i r a b muscles ( 5 9 ) . I t i s l i k e l y t h a t the w e i g h t b e a r i n g a c t i v i t y a s s o c i a t e d w i t h t r e a d m i l l r u n n i n g exaggerates the c e l l u a r s t i m u l u s r e q u i r e d t o induce a l a r g e b i o c h e m i c a l response. I n g e n e r a l , the g r e a t e r the e x e r c i s e i n t e n s i t y the g r e a t e r w i l l be the induced response w i t h i n the w o r k i n g muscles (44,60,61). This g e n e r a l i z a t i o n , however, must be tempered by the known o r d e r e d p a t t e r n of muscle f i b e r type r e c r u i t m e n t mentioned above ( 4 4 ) . T h i s becomes e v i d e n t from the d a t a p r e s e n t e d i n F i g u r e 2, showing the i n c r e a s e i n cytochrome c content (an i n d e x of m i t o c h o n d r i a l c o n t e n t ) i n the t h r e e f i b e r types as a f u n c t i o n of i n t e n s i t y of t r e a d m i l l running. This figure i n f l u e n c e of i n c r e a s i n programs at each r u n n i n g i n t e n s i t y (10, 20, 30, 40, 50, and 60 meters/minute) ( 4 4 ) . The peak response o b t a i n e d f o r each r u n n i n g i n t e n s i t y , w h i c h u s u a l l y corresponded t o an a s y m p t o t i c v a l u e , was then p l o t t e d a g a i n s t e x e r c i s e i n t e n s i t y . This provides a charact e r i z a t i o n of the i n t e n s i t y i n f l u e n c e t h a t i s e s s e n t i a l l y independent of the d u r a t i o n of d a i l y e x e r c i s e ( 4 4 ) . I t i s apparent t h a t the f a s t - t w i t c h red f i b e r s e c t i o n of the v a s t u s l a t e r a l i s and the s l o w - t w i t c h r e d s o l e u s muscles adapt w i t h a n e a r l y l i n e a r i n c r e a s e i n m i t o c h o n d r i a l c o n t e n t over the e a s y - t o moderate range of e x e r c i s e c o n d i t i o n s (10, 20, and 30 m/min). T h i s response emphasizes the importance of e x e r c i s e i n t e n s i t y i n i n d u c i n g the b i o c h e m i c a l change. Indeed, t h e r e i s a r e l a t i v e l y l a r g e adapt i v e change w i t h o n l y s m a l l changes i n e x e r c i s e i n t e n s i t y as r e f l e c t e d i n t r e a d m i l l speed. However, i t i s o b v i o u s t h a t the increase i n m i t o c h o n d r i a l content, that occurs w i t h i n c r e a s i n g t r e a d m i l l speed, i s not l i n e a r . I n the case of the f a s t - t w i t c h r e d muscle s e c t i o n , a maximal response was found w i t h t r a i n i n g a f t e r speeds of a p p r o x i m a t e l y 30 m/min ( F i g u r e 2 ) . T h i s corresponds t o an e s t i m a t e d e x e r c i s e i n t e n s i t y f o r the r a t of a p p r o x i m a t e l y 80 - 85% of i t s maximal oxygen consumption ( 6 2 ) . The b r i e f p r o p o r t i o n a l response phase up t o 30 m/min, t o g e t h e r w i t h the p l a t e a u , c o u l d account f o r the apparent l a c k of an i n t e n s i t y e f f e c t observed i n some s t u d i e s (61 ). A l t h o u g h t h i s p l a t e a u suggests t h a t e x e r c i s e i n t e n s i t y i s no l o n g e r i m p o r t a n t , a more p h y s i o l o g i c a l i n t e r p r e t a t i o n seems a p p r o p r i a t e . I t may be t h a t t h i s f i b e r t y p e was r e c r u i t e d i n an i n c r e a s i n g manner over the lower speeds, but t h a t a s a t u r a t i o n of t h i s motor u n i t p o o l o c c u r r e d at a p p r o x i m a t e l y 30 - 40 m/min. I f t h i s were the case, then t r e a d m i l l r u n n i n g at speeds of 50 and 60 m/min c o u l d not be accomplished w i t h o u t the involvement of a d d i t i o n a l motor u n i t s . These a d d i t i o n a l motor u n i t s may be the f a s t - t w i t c h white f i b e r s . There was no change i n cytochrome c c o n t e n t i n the f a s t - t w i t c h w h i t e s e c t i o n throughout the m i l d t o moderate e x e r c i s e i n t e n s i t y . However, an a d a p t i v e change became apparent i n the f a s t - t w i t c h w h i t e s e c t i o n w i t h i n c r e a s i n g e x e r c i s e i n t e n s i t y above 30 - 40 m/min ( F i g u r e 2 ) . T h i s corresponds t o the

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

14

NUTRITION A N D AEROBIC EXERCISE Φ

3 £

Training 2hr/day

T r a |

F i g u r e 1, The p r e d i c t e d consequences o f one week o f d e t r a i n i n g and t h e time o f r e t r a i n i n g r e q u i r e d t o r e c o v e r the f u l l i n c r e a s e i n cytochrome c content ( a n i n d e x o f m i t o c h o n d r i a l c o n t e n t ) i n the w o r k i n g muscle. Note t h a t i n one week of i n a c t i v i t y (approx. 1 h a l f - l i f e ) , n e a r l y 50% o f t h e t r a i n i n g e f f e c t i s l o s t . Simi­ l a r l y , each week o f r e t r a i n i n g r e c o v e r s approx, 50% o f t h e way toward t h e f u l l t r a i n i n g e f f e c t . Since the process e x h i b i t s f i r s t - o r d e r k i n e t i c s , i t takes longer t o recover f u l l y . "Repro­ duced w i t h p e r m i s s i o n from R e f . 56. C o p y r i g h t 1977, New Y o r k Academy of S c i e n c e s . " f

1

30 f 28 26 24 22 20 18 16 14 12 10 8 6 4 2

red vastus

5 — 7

soleus

Q

\

/

white vastus

62% 73% 83% 94% 105% H6%maxV0 —I 1 1 1 1 1— 10 20 30 40 50 60 meter/min EXERCISE

2

INTENSITY

F i g u r e 2. The i n f l u e n c e o f e x e r c i s e i n t e n s i t y ( t r e a d m i l l r u n ­ n i n g ) on muscle cytochrome c content i n the r a t . Red v a s t u s = f a s t - t w i t c h r e d f i b e r s e c t i o n ; Soleus - s l o w - t w i t c h r e d f i b e r s e c t i o n ; White v a s t u s = f a s t - t w i t c h w h i t e f i b e r s e c t i o n . "Re­ produced w i t h p e r m i s s i o n from R e f . 44. C o p y r i g h t 1982, A m e r i c a n Physiological Society ." 1

1

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

2.

TERJUNG AND HOOD

Biochemical

Adaptations

in Skeletal

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15

t r e a d m i l l speeds where the response i n the f a s t - t w i t c h red s e c t i o n reached a p l a t e a u . Thus, the g e n e r a l response t o t r a i n i n g i n t e n s i t y , i l l u s t r a t e d i n F i g u r e 2, i s c o n s i s t e n t w i t h the e x p e c t e d o r d e r e d p a t t e r n of motor u n i t r e c r u i t m e n t . These d a t a a l s o i l l u s t r a t e t h a t care must be e x e r c i s e d when i n t e r p r e t i n g the t r a i n i n g response o b t a i n e d from mixed muscle s e c t i o n s , where each component f i b e r type may be a d a p t i n g i n a q u a n t i t a t i v e l y d i f f e r e n t manner. N o n e t h e l e s s , i t i s c l e a r t h a t the i n t e n s i t y of e x e r c i s e e x e r t s a p r o f o u n d i n f l u e n c e on the magnitude of the b i o c h e m i c a l change. F u r t h e r , t h i s response need not be s i m i l a r f o r a l l f i b e r t y p e s . For example, at the most i n t e n s e t r a i n i n g program of 60 m/min, the cytochrome c content i n the f a s t - t w i t c h w h i t e f i b e r s e c t i o n was 3 . 0 - f o l d normal, but o n l y 1 . 5 - f o l d normal i n the f a s t - t w i t c h r e d muscle s e c t i o n . T h i s q u a n t i t a t i v e d i f f e r e n c e may be e x p e c t e d , i f the s t i m u l u s i n d u c i n g the i n c r e a s e i n o x i d a t i v e c a p a c i t y i s at a l l i n f l u e n c e d by the p r e e x i s t i n g m i t o c h o n d r i a l content w i t h i n the muscle f i b e r . Note t h a red s e c t i o n i s approximatel s e c t i o n (see y - a x i s of F i g u r e 2 ) . Thus, i t i s p r o b a b l e t h a t a g r e a t e r t r a i n i n g s t i m u l u s i s needed to b r i n g about an a d a p t a t i o n i n the well-endowed h i g h - o x i d a t i v e f i b e r s as compared w i t h the lowoxidative fibers. T h i s i s c o n s i s t e n t w i t h the g e n e r a l i m p r e s s i o n concerning t r a i n i n g adaptations. I n d i v i d u a l s who p o s s e s s a r e l a t i v e l y h i g h a e r o b i c work c a p a c i t y must t r a i n " h a r d e r " i n o r d e r t o a c h i e v e a s i g n i f i c a n t a d a p t i v e change ( 6 3 ) . E x e r c i s e Bout D u r a t i o n . The g e n e r a l e x p e c t a t i o n t h a t t r a i n i n g programs which r e q u i r e l o n g e r d a i l y e x e r c i s e bouts produce g r e a t e r a d a p t a t i o n s has been found f o r the b i o c h e m i c a l changes i n muscle (44,60,64). A l t h o u g h l e n g t h e n i n g e x e r c i s e bout d u r a t i o n appears to induce a f a i r l y l i n e a r i n c r e a s e i n m i t o c h o n d r i a l content (44,60,64), t h e r e i s p r o b a b l y a f i n i t e range f o r t h i s r e l a t i o n s h i p . When e x e r c i s e d u r a t i o n was v e r y p r o l o n g e d ( i . e . , 4 h r / d a y ) , the a d a p t i v e change was not d i f f e r e n t from t h a t found when d a i l y e x e r c i s e i n v o l v e d r u n n i n g 2 hr/day ( 6 0 ) . Thus, t h e r e i s an e x e r c i s e bout d u r a t i o n w h i c h , when exceeded, does not produce any added i n c r e a s e i n mitochondrial content. F u r t h e r , i t i s p r o b a b l e t h a t the r e l a t i o n s h i p between the b i o c h e m i c a l a d a p t a t i o n i n muscle and e x e r c i s e bout d u r a t i o n can be d e s c r i b e d as a f i r s t o r d e r p r o c e s s where the i n f l u e n c e of time i s not c o n s t a n t ( 4 4 ) . This i s i l l u s t r a t e d i n F i g u r e 3 f o r the i n c r e a s e i n cytochrome c content i n the f a s t - t w i t c h w h i t e muscle s e c t i o n of t r a i n e d r a t s . This r e l a t i o n s h i p indicates t h a t , d u r i n g steady s t a t e t r a i n i n g , the i n i t i a l minutes of the e x e r c i s e bout are the most important i n c r e a t i n g the c e l l u l a r s t i m u l u s t h a t induces the b i o c h e m i c a l change. The f u r t h e r i n c r e a s e i n t h i s c e l l u l a r s t i m u l u s d i m i n i s h e s as the d u r a t i o n of each e x e r c i s e bout i n c r e a s e s , u n t i l an e x e r c i s e bout d u r a t i o n i s reached where added time has l i t t l e i f any impact. A l t h o u g h l i t t l e i s known about the exact s i g n a l w i t h i n the c e l l t h a t produces the i n c r e a s e i n m i t o c h o n d r i a l c o n t e n t , i t may be i n some way i n f l u e n c e d by the e x i s t i n g o x i d a t i v e c a p a c i t y of the muscle f i b e r . F o r example, the d e c r e a s i n g importance of e x e r c i s e bout d u r a t i o n c o u l d be e x p l a i n e d i f the magnitude of the c e l l u l a r s t i m u l u s were m o d i f i e d by the a d a p t i v e response i t s e l f . Thus, the t h i r d 15 minute p e r i o d of e x e r c i s e would be e x p e c t e d t o induce a s m a l l e r e f f e c t than the f i r s t

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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15 minute p e r i o d of e x e r c i s e , s i n c e t h e r e a l r e a d y e x i s t s a s i g n i f i cant a d a p t i v e response caused by the i n i t i a l e x e r c i s e time p e r i o d . A n o t h e r example may be the exaggerated i n c r e a s e i n m i t o c h o n d r i a l content i n the low o x i d a t i v e f a s t - t w i t c h w h i t e s e c t i o n , as compared to the h i g h o x i d a t i v e f a s t - t w i t c h r e d s e c t i o n , d u r i n g i n t e n s e e x e r c i s e t r a i n i n g . However, u n l i k e a s i m p l e change i n e x e r c i s e bout d u r a t i o n , i t i s not known whether the u t i l i z a t i o n of each muscle type was the same d u r i n g the i n t e n s e e x e r c i s e bouts. I n t e r a c t i o n Between E x e r c i s e D u r a t i o n and I n t e n s i t y . Although e x e r c i s e bout d u r a t i o n and i n t e n s i t y a r e d i s t i n c t t r a i n i n g p a r a m e t e r s , they a l s o i n t e r a c t t o f u r t h e r a l t e r the a d a p t i v e r e s p o n s e . T h i s becomes apparent when n o t i n g the time n e c e s s a r y t o a c h i e v e the maximal a d a p t i v e change f o r each of the r u n n i n g i n t e n s i t i e s . This i s b e s t i l l u s t r a t e d by the response i n the f a s t - t w i t c h w h i t e muscle ( F i g u r e 3 ) . The g r e a t e r the i n t e n s i t y of e x e r c i s e the more r a p i d y the change i n cytochrom r e s p o n s e . Thus, i t i s w i t h i n muscle r u n n i n g f o r a s h o r t e r time/day, i f the i n t e n s i t y of exercise i s increased accordingly. The f a c t o r ( s ) t h a t change(s) w i t h i n the muscle c e l l e n a b l i n g the i n i t i a l minutes of e x e r c i s e t o produce a g r e a t e r t r a i n i n g s t i m u l u s i s not known. However, the e x a g g e r a t e d m e t a b o l i c response t h a t o c c u r s w i t h i n muscle as e x e r c i s e i n t e n s i t y i s i n c r e a s e d may be i m p l i c a t e d . Thus, e x e r c i s e i n t e n s i t y a f f e c t s b o t h the magnitude of the a d a p t i v e response, as w e l l as the e x e r c i s e bout time n e c e s s a r y t o a c h i e v e the peak response. F u n c t i o n a l S i g n i f i c a n c e of T r a i n i n g A d a p t a t i o n s

i n Muscle

The i n c r e a s e i n m i t o c h o n d r i a l content w i t h i n t r a i n e d muscle c o u l d have s e v e r a l s i g n i f i c a n t f u n c t i o n a l i n f l u e n c e s d u r i n g e x e r c i s e . F i r s t , t h e g r e a t e r b i o c h e m i c a l c a p a c i t y f o r ATP p r o v i s i o n v i a a e r o b i c metabolism c o u l d g r e a t l y i n c r e a s e the maximal oxygen consumption of muscle. T h i s would be t r u e i f a) muscle c o u l d u t i l i z e a g r e a t e r ATP t u r n o v e r than e v i d e n t at maximal a e r o b i c work c a p a c i t y p r i o r t o t r a i n i n g , and b) the g r e a t e r m i t o c h o n d r i a l content was s u p p l i e d w i t h s u f f i c i e n t oxygen to support the g r e a t e r ATP t u r n o v e r . S i n c e muscle e x h i b i t s a d e p l e t i o n of p h o s p h o c r e a t i n e (PCr) and, a t t i m e s , a r e d u c t i o n i n ATP content d u r i n g severe c o n t r a c t i o n c o n d i t i o n s (37,39,65,66), i t i s p r o b a b l e t h a t a h i g h e r energy u t i l i z a t i o n c o u l d h a v e o c c u r r e d i f more e n e r g y were a v a i l a b l e t o meet t h e demand. Thus, the p o t e n t i a l t h a t an i n c r e a s e d m i t o c h o n d r i a l c o n t e n t might i n c r e a s e the maximal oxygen consumption of muscle p r o b a b l y r e s t s on the a v a i l a b i l i t y of oxygen. An i n c r e a s e d s u p p l y of oxygen to m i t o c h o n d r i a of c o n t r a c t i n g muscle would occur i f a) t h e r e was an i n c r e a s e d e x t r a c t i o n of oxygen from the a r t e r i a l b l o o d f l o w i n g t h r o u g h the muscle, and/or b) t h e r e was a g r e a t e r b l o o d f l o w t h r o u g h the muscle ( a r t e r i a l b l o o d oxygen content remains remarkably cons t a n t d u r i n g a l l i n t e n s i t i e s of e x e r c i s e ( 6 7 ) . Oxygen e x t r a c t i o n a c r o s s w o r k i n g muscle d u r i n g maximal e x e r c i s e i s g e n e r a l l y v e r y l a r g e ( a p p r o x i m a t e l y 80% or more), even i n u n t r a i n e d i n d i v i d u a l s (67 ). A s m a l l i n c r e a s e i n oxygen e x t r a c t i o n ( a p p r o x i m a t e l y 10-15%) a c r o s s w o r k i n g muscle a f t e r t r a i n i n g has been observed (63,68), but not c o n s i s t e n t l y ( 2 5 , 6 9 ) . Thus, an i n c r e a s e i n oxygen s u p p l y due t o a g r e a t e r e x t r a c t i o n c o u l d not p o s s i b l y support a l l of the l a r g e

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

TERJUNG AND HOOD

Biochemical

30 RUN

TIME

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60

in Skeletal

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90

(MINUTES/DAY)

F i g u r e 3· The i n f l u e n c e o f e x e r c i s e d u r a t i o n , d u r i n g d i f f e r e n t i n t e n s i t i e s of t r e a d m i l l r u n n i n g , on cytochrome c content i n t h e w h i t e s e c t i o n of t h e v a s t u s l a t e r a l i s muscle ( f a s t - t w i t c h w h i t e f i b e r s ) of r a t s . Running speed: ( Ο ) 10 m/min, ( • ) 20 m/min, ( Δ ) 30 m/min, ( · ) 40 m/min, ( • ) 50 m/min, ( • ) 60 m/min. "Reproduced w i t h p e r m i s s i o n from R e f . 44. C o p y r i g h t 1982, American Physiological Society'."

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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i n c r e a s e i n m i t o c h o n d r i a l content ( e . g . , 100%) t y p i c a l l y found w i t h endurance t r a i n i n g . T h i s i n d i c a t e s t h a t b l o o d f l o w must be i n c r e a s e d i f the g r e a t e r c a p a c i t y f o r o x i d a t i v e metabolism w i t h i n the t r a i n e d muscle i s to be u t i l i z e d m a x i m a l l y . Measurements e v a l u a t i n g the p o t e n t i a l f o r changes i n peak b l o o d f l o w d u r i n g maximal e x e r c i s e h a v e p r o v i d e d e q u i v o c a l r e s u l t s ( 7_0 ) . Thus, t h e r e i s l i t t l e a s s u r a n c e t h a t t r a i n i n g g r e a t l y a l t e r s maximal b l o o d f l o w . Recent evidence, obtained i n t r a i n e d r a t s using r a d i o l a b e l e d microspheres, has demonstrated a s i g n i f i c a n t i n c r e a s e i n peak muscle b l o o d f l o w i n muscle of t r a i n e d r a t s (71 ). However, the i n c r e a s e of a p p r o x i m a t e l y 40 - 50% was found o n l y i n the low o x i d a t i v e f a s t - t w i t c h w h i t e muscle f i b e r s e c t i o n . A l t h o u g h t h i s appears t o be a s i g n i f i c a n t change, i t s o v e r a l l c o n t r i b u t i o n to an i n c r e a s e i n t o t a l body oxygen consumption of the animal would be r a t h e r s m a l l . T h i s low mitochond r i a l f i b e r s e c t i o n r e c e i v e s o n l y a p p r o x i m a t e l y 20 - 25% of the b l o o d f l o w d e l i v e r e d t o the h i g h o x i d a t i v e f a s t - t w i t c h r e d s e c t i o n (32,33). T h e r e f o r e , th at l e a s t 80% of the maxima T h i s r e l i g a t e s any change i n peak b l o o d f l o w t o the f a s t - t w i t c h w h i t e s e c t i o n due t o t r a i n i n g as e x e r t i n g a r e l a t i v e l y m i n o r i n f l u e n c e on t o t a l body maximal oxygen consumption. Similarly, in humans, t r a i n i n g induces a change i n maximal oxygen consumption t h a t i s r e l a t i v e l y s m a l l ( e . g . , t y p i c a l l y 15 - 2 5 % ) , compared t o the i n c r e a s e i n m i t o c h o n d r i a l content induced i n the w o r k i n g muscle (e.g., 54). Thus, i t i s g e n e r a l l y r e c o g n i z e d t h a t the f u l l potent i a l of the enhanced o x i d a t i v e c a p a c i t y i s not f u l l y r e a l i z e d . D a v i e s , et a l (72) r e c e n t l y r e p o r t e d i n t e r e s t i n g d a t a w h i c h i l l u s t r a t e the r e l a t i o n s h i p between oxygen t r a n s p o r t c a p a c i t y and maximal oxygen consumption d u r i n g e x e r c i s e . They found, as exp e c t e d , t h a t r e d u c i n g the oxygen t r a n s p o r t c a p a c i t y by d e c r e a s i n g hemoglobin c o n c e n t r a t i o n w i t h an i r o n d e f i c i e n t d i e t , g r e a t l y d e c r e a s e d the maximal oxygen consumption d u r i n g e x e r c i s e i n r a t s . D u r i n g the subsequent i r o n r e f e e d i n g p e r i o d , the time course of the r e t u r n of maximal oxygen consumption n i c e l y corresponded t o the time course of the r e c o v e r y of oxygen t r a n s p o r t c a p a c i t y ( i . e . , hemoglobin content). F u r t h e r , when the oxygen t r a n s p o r t c a p a c i t y of i r o n d e f i c i e n t r a t s was r e t u r n e d t o normal by i n f u s i o n of packed red b l o o d c e l l s , the maximal oxygen consumption d u r i n g e x e r c i s e essent i a l l y recovered to normal ( 7 3 ) . These r e s u l t s i l l u s t r a t e the g e n e r a l f i n d i n g t h a t maximal a e r o b i c work c a p a c i t y i s c l o s e l y r e l a t e d t o maximal c a r d i o v a s c u l a r t r a n s p o r t of o x y g e n . ( 7 4 ) . Theref o r e , the f u n c t i o n a l s i g n i f i c a n c e of the a d a p t i v e i n c r e a s e i n m i t o c h o n d r i a l content may be r e l a t e d to c e l l u l a r responses w i t h i n the w o r k i n g muscle d u r i n g submaximal e x e r c i s e . Oxygen t r a n s p o r t i s d i s c u s s e d i n more d e t a i l i n the T r a c e Element c h a p t e r by McDonald and Saltman. C e l l u l a r Responses i n T r a i n e d M u s c l e . Recent e v i d e n c e , obtained from a p p r o p r i a t e measurements of m e t a b o l i t e s w i t h i n the c e l l d u r i n g c o n t r a c t i o n s , suggests t h a t s k e l e t a l muscle of t r a i n e d i n d i v i d u a l s i s b e t t e r a b l e t o a d j u s t , as compared t o s k e l e t a l muscle of unt r a i n e d i n d i v i d u a l s , t o the energy demands of a submaximal c o n t r a c t i o n e f f o r t . T h i s i s apparent s i n c e m e t a b o l i c c o n d i t i o n s a l t e r e d by c o n t r a c t i o n s w i t h i n t r a i n e d muscle change l e s s than i n u n t r a i n e d muscle from t h a t found at r e s t . F o r example, the PCr content of

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muscle decreases I n p r o p o r t i o n t o e x e r c i s e i n t e n s i t y throughout the submaximal range of e x e r c i s e (66,75). D u r i n g moderately i n t e n s e c o n t r a c t i o n c o n d i t i o n s , the decrease i n PCr content t o t r a i n e d muscle of r a t s i s l e s s than t h a t of u n t r a i n e d muscle ( 4 0 ) . Simil a r l y , the decrease i n PCr content d u r i n g submaximal c y c l e e x e r c i s e (150 w a t t s ) i n humans was l e s s a f t e r p h y s i c a l t r a i n i n g ( 7 6 ) . Thus, a g r e a t e r work output ( i . e . , energy t u r n o v e r ) can be a c h i e v e d a f t e r t r a i n i n g f o r the same decrease i n PCr c o n c e n t r a t i o n . The decrease i n PCr, t h r o u g h the c e l l ' s c o r r e s p o n d i n g i n c r e a s e i n i n o r g a n i c phosphate c o n c e n t r a t i o n ( 7 7 ) , i s thought t o c o n t r i b u t e to the c e l l u l a r s i g n a l t h a t s t i m u l a t e s the m i t o c h o n d r i a t o i n c r e a s e r e s p i r a t i o n (78,79). T h i s c o u l d be p a r t o f t h e r e s p o n s e t h a t accounts f o r the t i g h t c o u p l i n g between m i t o c h o n d r i a l ATP p r o d u c t i o n (and, t h e r e f o r e , oxygen consumption) and the g r e a t e r energy demands as e x e r c i s e i n t e n s i t y i n c r e a s e s . I f the decrease i n PCr c o n t r i b u t e s to the c e l l u l a r s i g n a l t o a c c e l e r a t e m i t o c h o n d r i a l respiration (78,79), then a h i g h e r r a t a r e l a t i v e l y smaller i n t r a c e l l u l a respiration. T h i s i s r e a s o n a b l e s i n c e t h e r e are more m i t o c h o n d r i a w i t h i n the t r a i n e d muscle f i b e r t o respond and r e p h o s p h o r y l a t e ADP to ATP ( 5 , 2 3 ) . Thus, t r a i n e d muscle seems t o be a b l e t o f u n c t i o n a t a g i v e n oxygen consumption (work r a t e ) w i t h a s m a l l e r m e t a b o l i c signal driving mitochondrial respiration; alternatively, trained muscle can f u n c t i o n at a h i g h e r oxygen consumption ( i . e . , work r a t e ) a t the same apparent c e l l u l a r s t i m u l u s as found i n u n t r a i n e d muscle w o r k i n g at a lower oxygen consumption. Thus, i t i s p r o b a b l e t h a t the t r a i n i n g induced change i n m i t o c h o n d r i a l content a l t e r s metab o l i c c o n t r o l parameters. Another i n f l u e n c e of the t r a i n i n g a d a p t a t i o n may be d u r i n g the t r a n s i t i o n from r e s t i n g metabolism t o the a c c e l e r a t e d r a t e of r e s p i r a t i o n r e q u i r e d by c o n t r a c t i o n s . F o r example, a h i g h e r mitochond r i a l d e n s i t y w i t h i n t r a i n e d muscle might e f f e c t a more r a p i d t r a n s i t i o n toward a steady s t a t e a e r o b i c energy p r o v i s i o n at the onset of c o n t r a c t i o n s . I f the energy demands were being b e t t e r met by m i t o c h o n d r i a l r e s p i r a t i o n , then the r a t e of a n a e r o b i c energy p r o d u c t i o n c o u l d be l e s s . That t h i s o c c u r s i s suggested by the c e l l u l a r content of l a c t i c a c i d t h a t d e v e l o p s at the onset of cont r a c t i o n s (40). L a c t a t e content i n c r e a s e d t o 13.2+1.31 pmole/g i n f a s t - t w i t c h red muscle of s e d e n t a r y animals compared t o o n l y 7.1+0.84 i n t r a i n e d muscle d u r i n g the f i r s t minute of c o n t r a c t i o n s (40). These r e s u l t s are t y p i c a l (25,76,80) and c o u l d r e p r e s e n t the f a v o r e d m e t a b o l i c s i t u a t i o n i n t r a i n e d muscle t h a t c o n t r i b u t e s t o a more r a p i d achievement of steady s t a t e oxygen consumption (81,82,83) and a reduced c i r c u l a t i n g l a c t a t e content (76,80) observed a f t e r exercise training. A l t e r e d S u b s t r a t e U t i l i z a t i o n by T r a i n e d M u s c l e . I t i s l i k e l y t h a t the g r e a t e r m i t o c h o n d r i a l content a l s o s e r v e s t o a l t e r the energy s u b s t r a t e u t i l i z e d d u r i n g prolonged submaximal e x e r c i s e . This probably c o n t r i b u t e s to the much enhanced endurance performance t y p i c a l of the endurance t r a i n e d i n d i v i d u a l . I t has l o n g been r e c o g n i z e d t h a t t r a i n e d i n d i v i d u a l s o b t a i n a g r e a t e r f r a c t i o n of t h e i r energy needs from the o x i d a t i o n of f a t t y a c i d s than u n t r a i n e d i n d i v i d u a l s e x e r c i s i n g at the same work i n t e n s i t y ( c f . 6 ) . The g r e a t e r e x t e n t of l i p i d o x i d a t i o n , e v i d e n t by a lower r e s p i r a t o r y

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q u o t i e n t o f t r a i n e d i n d i v i d u a l s , h a s b e e n c o n f i r m e d by d i r e c t measurements of enhanced C02 p r o d u c t i o n from i n f u s e d l a b e l e d p a l m i t a t e (84)« A l t h o u g h an enhanced c o n c e n t r a t i o n o f c i r c u l a t i n g f a t t y a c i d s can i n c r e a s e f a t o x i d a t i o n and extend e x e r c i s e time ( 8 5 , 8 6 ) , the i n c r e a s e d l i p i d o x i d a t i o n i n t r a i n e d i n d i v i d u a l s i s apparent even when c i r c u l a t i n g f a t t y a c i d l e v e l s a r e not d i f f e r e n t from t h a t o f the n o n - t r a i n e d ( 8 7 ) . Thus, t h e r e i s p r o b a b l y some fundamental a l t e r a t i o n w i t h i n t h e w o r k i n g muscle t o p e r m i t t h e g r e a t e r r a t e of b e t a o x i d a t i o n . R e c a l l t h a t an i n c r e a s e i n t h e capacity f o r f a t t y acid oxidation i s included i n the adaptive response of a g r e a t e r m i t o c h o n d r i a l c o n t e n t ( 1 5 ) . A g r e a t e r enzyme c o n t e n t w i t h i n t h e muscle c o u l d r e s u l t i n a g r e a t e r r a t e o f f a t t y a c i d o x i d a t i o n , even when t h e same f a t t y a c i d c o n c e n t r a t i o n i s a v a i l a b l e f o r b e t a o x i d a t i o n (15). One d i r e c t c o n s e q u e n c e o f o b t a i n i n g a g r e a t e r f r a c t i o n of the energy from f a t t y a c i d d e r i v e d a c e t y l C o A i s t o l e s s e n the demand f o r o t h e r carbon s o u r c e s f o r o x i d a t i o n . T h i s would b and p o t e n t i a l l y t h e r a t muscle. Recent e v i d e n c e i n d i c a t e s t h a t enhancing f a t t y acid o x i d a t i o n does, i n d e e d , spare muscle g l y c o g e n (85,86,88). These metabolic changes a r e d i s c u s s e d i n more d e t a i l i n t h e f o l l o w i n g c h a p t e r by Goodman. S i n c e t h e d e p l e t i o n of muscle g l y c o g e n s t o r e s d u r i n g p r o l o n g e d submaximal e x e r c i s e c o r r e s p o n d s w i t h exhaustion, t h e r e i s now r e a s o n t o c o u p l e t h e t r a i n i n g a d a p t a t i o n o f an i n c r e a s e d m i t o c h o n d r i a l c o n t e n t w i t h i n t h e w o r k i n g muscle t o t h e marked i n c r e a s e i n endurance performance. S p e c i f i c a l l y , t h e g r e a t e r m i t o c h o n d r i a l content p e r m i t s an enhanced energy s u p p l y from l i p i d o x i d a t i o n ; t h i s , i n t u r n , r e t a r d s t h e r a t e o f u t i l i z a t i o n o f muscle g l y c o g e n , thereby p e r m i t t i n g muscle g l y c o g e n t o be used over an extended exercise time. A l t h o u g h many o t h e r p h y s i o l o g i c a l , m e t a b o l i c and e n d o c r i n e changes must be i m p o r t a n t i n the t r a i n i n g p r o c e s s , b i o c h e m i c a l a d a p t a t i o n s w i t h i n t h e w o r k i n g muscles appear t o e x e r t a s i g n i f i c a n t i n f l u e n c e on energy metabolism and muscle performance. 1I+

Summary R o u t i n e l y performed p h y s i c a l a c t i v i t y , such as c y c l i n g o r r u n n i n g , i n c r e a s e s one's endurance c a p a c i t y f o r p r o l o n g e d submaximal work. A s s o c i a t e d w i t h t h i s response a r e b i o c h e m i c a l changes w i t h i n t h e w o r k i n g m u s c l e s . T h i s i n c l u d e s an i n c r e a s e i n the c o n t e n t of m i t o c h o n d r i a , the c e l l u l a r o r g a n e l l e where energy (ATP) i s produced by the o x i d a t i o n of f u e l s ( g l u c o s e and f a t ) i n the presence o f oxygen. The magnitude o f t h i s i n c r e a s e i n m i t o c h o n d r i a l c o n t e n t i s i n f l u enced, i n a complex manner, by t h e i n t e n s i t y and d u r a t i o n of e x e r c i s e , s i n c e not a l l s k e l e t a l muscle f i b e r s may be r e c r u i t e d and t h e r e a r e marked d i f f e r e n c e s between muscle f i b e r t y p e s . Most mammalian muscle i s composed of t h r e e d i f f e r e n t f i b e r t y p e s : 1) s l o w - t w i t c h r e d (Type I ) w h i c h i s r e l a t i v e l y slow c o n t r a c t i n g and has a h i g h m i t o c h o n d r i a l c o n t e n t and endurance c a p a c i t y , 2) f a s t t w i t c h r e d (Type l i a ) w h i c h i s r e l a t i v e l y f a s t c o n t r a c t i n g and has a high mitochondrial c o n t e n t and endurance c a p a c i t y , and 3) f a s t t w i t c h w h i t e (Type l i b ) which i s r e l a t i v e l y f a s t c o n t r a c t i n g and has a low m i t o c h o n d r i a l content and endurance c a p a c i t y . These f i b e r types a r e r e c r u i t e d p r o g r e s s i v e l y b e g i n n i n g w i t h Type I , then Type

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l i a and f i n a l l y Type l i b as t h e I n t e n s i t y o f e x e r c i s e i n c r e a s e s . Thus, r e g u l a r p h y s i c a l a c t i v i t y o f moderate i n t e n s i t y w i l l i n c r e a s e the m i t o c h o n d r i a l content o f p r i m a r i l y Type I and Type l i a f i b e r s , w h i l e p r o p o r t i o n a l l y l a r g e r i n c r e a s e s are induced i n Type l i b f i b e r s d u r i n g more i n t e n s e p h y s i c a l t r a i n i n g when these f i b e r s a r e r e cruited. One major b e n e f i t o f enhancing the m i t o c h o n d r i a l content i n the w o r k i n g muscles i s r e l a t e d t o the much g r e a t e r c a p a c i t y o f the muscle t o o x i d i z e f a t f o r energy. A g r e a t e r s u p p l y o f energy from f a t s e r v e s t o preserve the intramuscular glucose store ( g l y c o g e n ) w h i c h i s i n l i m i t e d s u p p l y . D e p l e t i o n o f muscle g l y c o g e n has been i m p l i c a t e d as a f a c t o r c a u s i n g f a t i g u e d u r i n g p r o l o n g e d m o d e r a t e l y i n t e n s e e x e r c i s e ( e . g . , r u n n i n g f o r more than 1 h r ) . Thus, the enhanced m i t o c h o n d r i a l content and i t s r e l a t e d i n c r e a s e i n f a t o x i d a t i o n p r o b a b l y c o n t r i b u t e t o the g r e a t l y improved endurance performance f o l l o w i n g e x e r c i s e t r a i n i n g . Acknowledgments C i t e d work by t h e a u t h o r s was supported by N a t i o n a l I n s t i t u t e s o f H e a l t h Grant AM-21617 and R e s e a r c h C a r e e r Development Award AM-00681 ( t o R.L.T.).

Literature Cited 1. Lawrie, R. A. (1953) The activity of the cytochrome system in muscle and its relation to myoglobin. Biochem. J. 55: 298-305. 2. Lawrie, R. A. (1953) Effect of enforced exercise on myoglobin concentration in muscle. Nature London. 171: 1069-71. 3. John-Alder, H. (1984) Seasonal variations in activity, aerobic energetic capacities, and plasma thyroid hormones (T3 and T4) in an iguanid lizard. J. Comp. Physiol. B. 154: 409-419. 4. Armstrong, R. B., Ianuzzo, C. D., Kunz, T. H. (1977) Histochemical and biochemical properties of flight muscle fibers in the little brown, bat, Myotis lucifugus. J. Comp. Physiol. 119: 141-54. 5. Holloszy, J. O. (1973) Biochemical adaptations to exercise: aerobic metabolism. Ex. Sport. Sci. Rev. 1: 45-71. 6. Holloszy, J. O. and Booth, F. W. (1976) Biochemical adaptations to endurance exercise in muscle. Ann. Rev. Physiol. 38: 273-291, 1976. 7. Saltin, B. and Gollnick, P.D. (1983) Skeletal muscle adaptability: significance for metabolism and performance. In Handbook of Physiology, Section 10: Skeletal Muscle (Peachey, L. D., ed.), pp. 555-631, Am. Physiol. Soc., Bethesda, MD. 8. Holloszy, J. O. and Coyle, E. F. (1984) Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 56: 831-8. 9. Salmons, S. and Henriksson, J. (1981) The adaptive response of skeletal muscle to increased use. Muscle Nerve 4: 94-105. 10. Holloszy, J. O. (1967) Biochemical adaptations in muscle. Effects of exercise on mitochondrial oxygen uptake and respiratory enzyme activity in skeletal muscle. J. Biol. Chem. 242: 2278-82.

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11. Saltin, B., Henriksson, J., Nygaard, E., Andersen, P. and Jansson, E. (1977) Fiber types and metabolic potentials of skeletal muscles in sedentary man and endurance runners. In The Marathon: Physiological, Medical, Epidemiological and Psychological Studies (Milvy, P., ed), pp. 3-29, Annals of the New York Academy of Sciences, Vol. 301, New York, NY. 12. Gollnick, P.D., Ianuzzo, C. D. and King, D.W. (1971) Ultrastructural and enzyme changes in muscles with exercise. In Muscle Metabolism During Exercise (Pernow, B. and Saltin, B., eds), pp. 69-85, Advances in Experimental Medicine and Biology, Vol. 11, Plenum Press, New York, NY. 13. Morgan, T. E., Cobb, L. Α., Short, F. Α., Ross, R. and Gunn, D. R. (1971) Effects of long term exercise on human muscle mitochndria. In Muscle Metabolism During Exercise (Pernow, B. and Saltin, B., eds), pp. 87-95, Advances in Experimental Medicine and Biology Vol 11, Plenum Press New York NY 14. Baldwin, Κ. M., Klinkerfuss and Holloszy, J. O. and intermediate muscle: adaptive response to exercise. Am. J. Physiol. 222: 373-8. 15. Molé, P. Α., Oscai, L. B. and Holloszy, J. O. (1971) Adaptation of muscle to exercise. Increase in levels of palmityl CoA synthetase, carnitine palmityl-transferase and palmityl CoA dehydrogenase and in the capacity to oxidize fatty acids. J . Clin. Invest. 50: 2323-30. 16. Costill, D. L., Fink, W. J., Getchell, L. H., Ivy, J. L. and Witzmann, F. A. (1979) Lipid metabolism in skeletal muscle of endurance trained males and females. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 47: 787-91. 17. Winder, W. W., Baldwin, Κ. M. and Holloszy, J. O. (1975) Exercise-induced increase in the capacity of rat skeletal muscle to oxidize ketones. Can. J. Physiol. Pharmacol. 53: 86-91. 18. Holloszy, J. O., Oscai, L. B., Don, I. J. and Molé, P.A. (1970) Mitochondrial citric acid cycle and related enzymes: adaptive response to exercise. Biochem. Biophys. Res. Commun. 40: 1368-73. 19. Holloszy, J. O., Booth, F. W., Winder, W. W. and Fitts, R. H. (1975) Biochemical adaptation of skeletal muscle to prolonged physical exercise. In Metabolic Adaptation to Prolonged Physical Exercise (Howald, H. and Poortmans, J. R., eds.), pp. 438-47, Birkhauser Verlag, Basel. 20. Wittenberg, Β. Α., Wittenberg, J. B. and Caldwell, P.R.B. (1975) Role of myoglobin in the oxygen supply to red skeletal muscle. J. Biol. Chem. 250: 9038-43. 21. Cole, R. P. (1982) Myoglobin function in exercising skeletal muscle. Science 216: 523-525. 22. Pattengale, P. K. and Holloszy, J. O. (1967) Augmentation of skeletal muscle myoglobin by a program of treadmill running. Am. J. Physiol. 213: 783-5. 23. Gollnick, P. D. and Saltin, B. (1982) Significance of skeletal muscle oxidative enzyme enhancement with endurance training. Clin. Physiol. 2: 1-12.

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24. 25.

26.

27. 28. 29.

30. 31. 32. 33. 34. 35. 36.

37. 38. 39.

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Winder, W. W., Baldwin, Κ. M. and Holloszy, J. O. (1974) Enzymes involved in ketone utilization in different types of muscle: adaptation to exercise. Eur. J. Biochem. 47: 461-7. Saltin, B., Nazar, K., Costill, D. L . , Stein, E . , Jansson, E . , Essen, B. and Gollnick, P.D. (1976) The nature of the training response; peripheral and central adaptations to one-legged exercise. Acta Physiol. Scand. 96: 289-305. Burke, R. E. (1981) Motor units: anatomy, physiology, and functional organization. In Handbook of Physiology: The Nervous System 2 (Brookhart, J . M. and Mountcastle, V. B., eds.), pp. 345-422, Am. Physiol. Soc., Bethesda, MD. Close, R. I. (1972) Dynamic properties of mammalian skeletal muscles. Physiol. Rev. 52: 129-197. Baldwin, Κ. Μ., Winder, W. W. and Holloszy, J . O. (1975) Adaptation of actomyosin ATPase in different types of muscle to endurance exercise Am J. Physiol 229: 422-6 Martonosi, A. N. an transport by sarcoplasmi Physiology: Skeletal Muscle (Peachey, L. D., ed.), pp. 417-485, Am. Physiol. Soc., Bethesda, MD. Barany, M. (1967) ATPase activity of myosin correlated with speed of muscle shortening. J . Gen. Physiol. 50, Suppl. pt. 2: 197-218. Brooke, M. H. and Kaiser, Κ. K. (1970) Three myosin adenosine triphosphatase systems: the nature of their pH lability and sulfhydryl dependence. J . Histochem. Cytochem. 18: 670-2. Laughlin, M. H. and Armstrong, R. B. (1982) Muscular blood flow distribution patterns as a function of running speed in rats. Am. J . Physiol. 243: H296-H306. Mackie, B. G. and Terjung, R. L. (1983) Blood flow to different skeletal muscle fiber types during contraction. Am. J . Physiol. 245: H265-H275. Baldwin, Κ. Μ., Winder, W. W., Terjung, R. L. and Holloszy, J . O. (1973) Glycolytic enzymes in different types of skeletal muscles: adaptation to exercise. Am. J. Physiol. 225: 962-6. Hintz, C. S., Lowry, C. V., Kaiser, K. K., McKee, D. and Lowry, O. H. (1980) Enzyme levels in individual rat muscle fibers. Am. J . Physiol. 239: C58-C65. Burke, R. E . , Levine, D. Ν., Zajac, F. E . , Tsairis, P. and Engel, W. K. (1971) Mammalian motor units: physiological-histochemical correlation in three types of cat gastrocnemius. Science 174: 709-12. Meyer, R. A. and Terjung, R. L. (1979) Differences in ammonia and adenylate metabolism in contracting fast and slow muscle. Am. J . Physiol. 237: C111-C118. Rall, J . (1985) Energetic aspects of skeletal muscle contraction: implications of fiber types. Ex. Sport. Sci. Rev. Vol. 13. Meyer, R. Α., Dudley, G. A. and Terjung, R. L. (1980) Ammonia and IMP in different skeletal muscle fibers after exercise in rats. J . Appl. Physiol.: Respirat. Environ. Exercise Physiol. 49: 1037-41. Dudley, G. A. and Terjung, R. L. (1985) Influence of aerobic metabolism on IMP accumulation in fast-twitch muscle. Am. J . Physiol. 248: C37-C42.

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58. Baldwin, K. M., Fitts, R. H., Booth, F. W., Winder, W. W. and Holloszy, J. O. (1975) Depletion of muscle and liver glycogen during exercise. Pflugers Arch. 354: 203-12. 59. Hearn, G. R. and Wainio, W. W. (1956) Succinic dehydrogenase activity of the heart and skeletal muscle of exercise rats. Am. J. Physiol. 185: 348-50. 60. Terjung, R. L. (1976) Muscle fiber involvement during training of different intensities and durations. Am. J. Physiol. 230: 946-50. 61. Harms, S. J. and Hickson, R. C. (1983) Skeletal muscle mitochondria and myoglobin, endurance, and intensity of training. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 54: 798-802. 62. Shepherd, R. E. and Gollnick, P. D. (1976) Oxygen uptake of rats at different work intensities. Pflugers Arch. 362: 219-22. 63. Saltin, B., Blomqvist Wildenthal, K. an after bed rest and after training. Circulation 38, Suppl. 7: 1-78. 64. Fitts, R. H., Booth, F. W., Winder, W. W. and Holloszy, J. O. (1975) Skeletal muscle respiratory capacity, endurance, and glycogen utilization. Am. J. Physiol. 228: 1029-33. 65. Sahlin, K., Palmskog, G. and Hultman, E. (1978) Adenine nucleotide and IMP contents of the quadriceps muscle in man after exercise. Pflugers Arch. 374: 193-8. 66. Karlsson, J. (1971) Lactate and phosphagen concentrations in working muscle of man. Acta Physiol. Scand. Suppl. 358: 1-72. 67. Astrand, P.-O. and Rodahl, K. (1977) Textbook of Work Physiology, pp. 182-4, McGraw-Hill, Inc., New York, NY. 68. Ekblom, B., Astrand, P.-O., Saltin, B., Stenberg, J. and Wallstrom, B. (1968) Effect of training on the circulatory response to exercise. J . Appl. Physiol. 24: 518-28. 69. Kilborn, A. and Astrand, I. (1971) Physical training with submaximal intensities in women. II. Effect on cardiac output. Scand. J. Clin. Lab. Invest. 28: 163-75. 70. Hudlicka, O. (1977) Effect of training on macro- and microcirculatory changes in exercise. Ex. Sport. Sci. Rev. 5: 181-230. 71. Mackie, B. G. and Terjung, R. L. (1983) Influence of training on blood flow to different skeletal muscle fiber types. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 55: 1072-8. 72. Davies, K. J. Α., Maguire, J. J., Brooks, G. Α., Dallman, P. R. and Packer, L. (1982) Muscle mitochondrial bioenergetics, oxygen supply, and work capacity during dietary iron deficiency and repletion. Am. J. Physiol. 242: E418-E427. 73. Davies, K. J. Α., Donovan, C. M., Refino, C. J., Brooks, G. Α., Packer, L. and Dallman, P. R. (1984) Distinguishing effects of anemia and muscle iron deficiency on exercise bioenergetics in the rat. Am. J. Physiol. 246: E535-E543. 74. Gledhill, N. (1985) The influence of altered blood volume and oxygen transport capacity on aerobic performance. Ex. Sport. Sci. Rev. Vol. 13.

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Dudley, G. A. and Terjung, R. L. (1985) Influence of acidosis on AMP deaminase activity in contracting fast-twitch muscle. Am. J . Physiol. 248: C43-C50. 42. Walmsley, B., Hodgson, J . A. and Burke, R. E. (1978) Forces produced by medial gastrocnemius and soleus muscles during locomotion in freely moving cats. J . Neurophysiol. 41: 1203-15. 43. Sullivan, T. E. and Armstrong, R. B. (1978) Rat locomotory muscle fiber activity during trotting and galloping. J . Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44: 358-63. 44. Dudley, G. Α., Abraham, W. M. and Terjung, R. L. (1982) Influence of exercise intensity and duration on biochemical adaptations in skeletal muscle. J . Appl. Physiol.: Respirat. Environ. Exercise Physiol. 53: 844-50. 45. Burke, R. E. and Edgerton, V. R. (1975) Motor unit properties and selective involvement in movement Ex Sport Sci Rev 3: 31-81. 46. Ariano, Μ. Α., Armstrong Hindlimb muscle fiber populations of five mammals. J . Histochem. Cytochem. 21: 51-55. 47. Armstrong, R. B. and Phelps, R. O. (1984) Muscle fiber type composition of the rat hindlimb. Am. J. Anatomy 171: 259-72. 48. Costill, D. L., Daniels, J., Evans, W., Fink, W., Krahenbuhl, G. and Saltin, Β. (1976) Skeletal muscle enzymes and fiber composition in male and female track athletes. J . Appl. Physiol. 40: 149-54. 49. Lowry, C. V., Kimmey, J. S., Felder, S., Chi, M.-Y., Kaiser, K. K., Passonneau, P. Ν., Kirk, K. A. and Lowry, O. H. (1978) Enzyme patterns in single human muscle fibers. J . Biol. Chem. 253: 8269-77. 50. Schimke, R. T. and Doyle, D. (1970) Control of enzyme levels in animals tissues. Ann. Rev. Biochem. 39: 929-76. 51. Terjung, R. L. (1979) The turnover of cytochrome c in different skeletal muscle fiber types of the rat. Biochem. J . 178: 569-74. 52. Terjung, R. L. (1975) Cytochrome c turnover in skeletal muscle. Biochem. Biophys. Res. Commun. 66: 173-8. 53. Booth, F. W. and Holloszy, J . O. (1977) Cytochrome c turnover in rat skeletal muscles. J . Biol. Chem. 252: 416-19. 54. Henriksson, J . and Reitman, J . S. (1977) Time course of changes in human skeletal muscle succinate dehydrogenase and cytochrome oxidase activities and maximal oxygen uptake with physical activity and inactivity. Acta Physiol. Scand. 99: 91-7. 55. Hickson, R. C. (1981) Skeletal muscle cytochrome c and myoglobin, endurance, and frequency of training. J . Appl. Physiol.: Respirat. Environ. Exercise Physiol. 51: 746-9, 1981. 56. Booth, F. W. (1977) Effects of endurance exercise on cytochrome c turnover in skeletal muscle. In The Marathon: Physiological, Medical, Epidemiological, and Psychological Studies (Milvy, P., ed.), pp. 431-439, Annals of the New York Academy of Sciences, Vol. 301, New York, NY. 57. Oscai, L. B., Patterson, J . Α., Bogard, E. L., Beck, R. J. and Rothermel, B. L. (1972) Normalization of serum triglycerides and lipoprotein electrophoretic patterns by exercise. Am. J . Cardiol. 30: 775-80.

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75. Bergstrom, J., Harris, R. C., Hultman, E. and Nordesjö, L. O. (1971) Energy rich phosphagens in dynamic and static work. In Muscle Metabolism During Exercise (Pernow, B. and Saltin, B., eds.), pp. 341-55, Advances in Experimental Medicine and Biology, Vol. 11, Plenum Press, New York, NY. 76. Karlsson, J., Nordesjö, L.-O., Jorfeldt; L. and Saltin, B. (1972) Muscle lactate, ATP, and CP levels during exercise after physical training in man. J. Appl. Physiol. 33: 199-203. 77. Meyer, R. Α., Sweeney, H. L. and Kushmerick, M. J. (1984) A simple analysis of the "phosphocreatine shuttle". Am. J. Physiol. 246: C365-77, 1984. 78. Erecinska, Μ., Wilson, D. F. and Nishiki, K. (1978) Homeostatic regulation of cellular energy metabolism: experimental characterization in vivo and fit to a model. Am. J . Physiol. 234: C82-C89, 1978. 79. Erecinska, M. and Wilson, D. F. (1982) Regulation of cellular energy metabolism 80. Henriksson, J. (1977 muscle and metabolism during submaximal exercise. J. Physiol. 270: 661-75. 81. Hickson, R. C., Bomze, H. A. and Holloszy, J. O. (1978) Faster adjustment of O uptake to the energy requirement of exercise in the trained state. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44: 877-81. 82. Cerretelli, P., Pendergast, D., Paganelli, W. C. and Rennie, O. W. (1979) Effects of specific muscle training on VO on-response and early blood lactate. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 47: 761-9. 83. Hagberg, J. M., Hickson, R. C., Ehsani, A. A. and Holloszy, J. O. (1980) Faster adjustment to and recovery from submaximal exercise in the trained state. J . Appl. Physiol.: Respirat. Environ. Exercise Physiol. 48: 218-24. 84. Paul, P. (1971) Uptake and oxidation of substrates in the intact animal during exercise. In Muscle Metabolism During Exercise (Pernow, B. and Saltin, B., eds.), pp. 225-248, Advances in Experimental Medicine and Biology, Vol. 11, Plenum Press, New York, NY. 85. Hickson, R. C., Rennie, M. J., Conlee, R. K., Winder, W. W. and Holloszy, J. O. (1977) Effects of increased plasma free fatty acids on glycogen utilization and endurance. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 43: 829-33. 86. Costill, D. L., Coyle, E., Dalsky, G., Evans, W., Fink, W. and Hooper, D. (1977) Effects of elevated plasma FFA and insulin on muscle glycogen usage during exercise. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 43: 695-9. 87. Holloszy, J. O., Winder, W. W., Fitts, R. H., Rennie, M. J., Hickson, R. C. and Conlee, R. K. (1978) Energy production during exercise. In: 3rd International Symposium on Biochemistry of Exercise (Landry, F. and Orban, W. A. R., eds.), pp. 61-74, Symposia Specialists, Inc., Miami, FL. 88. Rennie, M. J., Winder, W. W. and Holloszy, J. O. (1976) A sparing effect of increased plasma free fatty acids on muscle and liver glycogen content in the exercising rat. Biochem. J. 156: 647-55. 2

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RECEIVED May 14, 1985

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

3 Influence of Aerobic Exercise on Fuel Utilization by Skeletal Muscle Michael N. Goodman Department of Medicine and Physiology, Boston University School of Medicine, Boston, M A 02118

During the past decade interest in muscular potentia y have on the health of the individual. Evidence is available that exercise can prevent or at least delay cardiovascular disease, lower risk factors for atherosclerosis, help in weight reduction and may help prevent complications of certain diseases such as diabetes (1,2). The impact physical exertion has had on our society is quite evident by the numbers or aerobic-related advertisements in non-scientific publications as well as the numbers of individuals running, walking or cycling. Years ago these activities were usually confined to the athlete, and at that time athletes may have been more concerned with what was the best foodstuff for maximum performance or endurance rather than on how physical exertion may prevent complications or delay debilitating diseases. Nevertheless, the impact of nutrition on physical performance capacity has been a subject of considerable interest for numerous years. Even today, individuals who exercise for health benefits may manipulate their diet so as to gain better performance capacity. The present r e v i e w w i l l focus on a p a r t i c u l a r a s p e c t o f t h i s s u b j e c t , s p e c i f i c a l l y how the use of v a r i o u s m e t a b o l i c fuels are regulated during muscular e x e r c i s e . F o r t h e m o s t p a r t s t u d i e s i n man w i l l be c i t e d , b u t some s e c t i o n s w i l l i n c l u d e r e f e r e n c e t o a n i m a l s t u d i e s f o r a p a r t i c u l a r emphasis. The q u e s t i o n o f what f u e l s are used by the w o r k i n g muscles d u r i n g p h y s i c a l performance and the r e l a t i v e i m p o r t a n c e o f each i s n o t new and has b e e n d e b a t e d f o r a l o n g t i m e . E a r l y s t u d i e s as f a r b a c k as 1896 s u g g e s t e d t h a t c a r b o h y d r a t e s w e r e t h e o n l y f u e l t h a t c o u l d be o x i d i z e d by the w o r k i n g muscles Ci,4). I t was only l a t e r that s t u d i e s e s t a b l i s h e d that both carbohydrates ( i . e . , p l a s m a g l u c o s e and m u s c l e g l y c o g e n ) and l i p i d s ( i . e . , p l a s m a f r e e f a t t y a c i d s and m u s c l e t r i g l y c e r i d e s ) c o u l d be u t i l i z e d by t h e w o r k i n g m u s c l e s . The use o i p r o t e i n a s a f u e l a l s o r e c e i v e d a t t e n t i o n i n e a r l y s t u d i e s , but more r e c e n t s t u d i e s s u g g e s t t h a t i t s u s a g e by m u s c l e i s s m a l l i n r e l a t i o n t o c a r b o h y d r a t e s and l i p i d s (4). 0097-6156/86/0294-0027$06.00/0 © 1986 American Chemical Society

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

28

NUTRT IO IN AND AEROBC I EXERCS IE Some i n s i g h t s i n t o now c a r b o h y d r a t e and l i p i d u t i l i z a t i o n may be r e g u l a t e d d u r i n g e x e r c i s e may be g a i n e d by c o m p a r i n g e x e r c i s e t o t h e m e t a b o l i s m o f s t a r v a t i o n . As c a n be s e e n i n F i g u r e 1, e x e r c i s e and s t a r v a t i o n have s e v e r a l f e a t u r e s i n common. D u r i n g s t a r v a t i o n , b l o o d g l u c o s e f a l l s e a r l y i n the f a s t and then r e m a i n s r e m a r k a b l y s t a b l e . C o n c o m i t t a n t l y , c i r c u l a t i n g l i p i d f u e l s (i.e., f r e e f a t t y a c i a s and ketone b o d i e s ) r i s e . The f a l l i n i n s u l i n d u r i n g the f a s t p r o b a b l y o r c h e s t r a t e s the i n c r e a s e i n l i p o i y s i s by s t i m u l a t i n g t h e b r e a k d o w n o f t r i g l y c e r i d e s stored i n adipose t i s s u e . Although v a r i a b l e g l u c a g o n may r i s e e a r l y i n t h e f a s t and t h e n f a i l as the f a s t i s lengthened. A somewhat s i m i l a r m e t a b o l i c p r o f i l e o c c u r s d u r i n g e x e r c i s e , e s p e c i a l l y i f i t i s of the t y p e t h a t i s o f l i g h t t o moderate i n t e n s i t y w i t h a d u r a t i o n o f one hour o r l o n g e r . T e l e o l o g i c a l l y , the g o a l of these m e t a b o l i c changes i s to m a i n t a i n a c o n s t a n t f u e l s u p p l y t o the b r a i n w h i l e p r o v i d i n g the p e r i p h e r a l t i s s u e s suc form of l i p i d ( e i t h e r e p l a c e g l u c o s e (5,6). As shown i n F i g u r e 2, as fasting p r o g r e s s e s , l i p i d becomes the most i m p o r t a n t source of f u e l f o r m u s c l e , w h i l e the use o f c a r b o h y d r a t e d i m i n i s h e s . This i s r e f l e c t e d i n a f a l l of the r e s p i r a t o r y q u o t i e n t a c r o s s muscle. D u r i n g e x e r c i s e , c a r b o h y d r a t e i s o f p r i m e i m p o r t a n c e as a f u e l d u r i n g the e a r l y minutes. As e x e r c i s e p r o g r e s s e s , l i p i d becomes a more i m p o r t a n t f u e l . H o w e v e r , c a r b o h y d r a t e o x i d a t i o n i s n o t n e g l i g i b l e and seems i m p o r t a n t i n p r e v e n t i n g e x h a u s t i o n . In e l i t e u l t r a d i s t a n c e runners who can r e m a i n a c t i v e f o r 24 h o u r s , l i p i d becomes t h e s o l e f u e l as g l y c o g e n s t o r e s i n t h e m u s c l e become exhausted (7). The r e s p i r a t o r y q u o t i e n t at t h i s t i m e i s a b o u t 0.7. These e l i t e r u n n e r s a l s o e x p e r i e n c e a marked r e d u c t i o n i n power output i n d i c a t i n g t h a t somehow muscle glycogen may be i m p o r t a n t i n m a i n t a i n i n g maximum e f f i c i e n c y d u r i n g exercise. Thus, i t i s e v i d e n t t h a t the m o b i l i z a t i o n and p r o v i s i o n o f l i p i d to muscle d u r i n g e x e r c i s e , l i k e during starvation, r e s t r i c t s the usage of c a r b o h y d r a t e . I f t h i s d i d not o c c u r d u r i n g e x e r c i s e , g l y c o g e n s t o r e s w i t h i n muscle (as w e l l as i n the l i v e r ) w o u l d be d e p l e t e d more r a p i d l y t h a n n o r m a l and may s i g n i f i c a n t l y l i m i t the d u r a t i o n o f e x e r c i s e . Hypoglycemia c o u l d a l s o r e s u l t and l i m i t performance. F u e l r e s e r v e s of the body The i m p o r t a n c e o f r e g u l a t i n g c a r b o h y d r a t e s t o r e s w i t h i n muscle (and l i v e r ) d u r i n g a e r o b i c work can be r e a d i l y a p p r e c i a t e d when one c o n s i d e r s t h a t t h e d i s t a n c e o f a m a r a t h o n (20.2 m i l e s ) i s c o m p l e t e d by top r u n n e r s i n about 130 minutes w i t h a t o t a l energy expenditure of a b o u t 2,600 k i i o c a l o r i e s , roughly 20 k i l o c a l o r i e s / m i n u t e (8,9). One of the problems i n c o m p l e t i n g the d i s t a n c e i n s u c h t i m e i s the p r o v i s i o n o f s u f f i c i e n t f u e l t o s a t i s f y the r a t e o f energy e x p e n d i t u r e . As shown i n Table I , the l a r g e s t f u e l r e s e r v e i n t h e body i s t r i g l y c e r i d e l o c a t e d p r i m a r i l y i n a d i p o s e t i s s u e w i t h a s m a l l e r amount i n s k e l e t a l muscle. Compared t o the t r i g l y c e r i d e s t o r e s , a much s m a l l e r amount o f f u e l i s a v a i l a b l e as g l y c o g e n s t o r e d w i t h i n l i v e r and

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

3.

Fuel

GOODMAN

Utilization

Glucose (mM)

29

5.0 2.5 J

Lipid fuels (mM)

I

I

L

6

3 Insulin

8

(μυ/ml)

Glucagon i(pg/ml) 10 n r % / " n 5

0

24

Days of starvation

0

2

4

Hours of exercise

F i g u r e 1 - E f f e c t o f s t a r v a t i o n and e x e r c i s e o f m o d e r a t e i n t e n s i t y on t h e c o n c e n t r a t i o n s o f b l o o d g l u c o s e , l i p i d s ( f r e e f a t t y a c i d s and ketone b o d i e s ) , i n s u l i n and glucagon. Data from C a h i l l (5) and F e l i g and Wahren (11).

100

Ζ» ο Ο φ

»

carbohydrate

Si ο *

a oc

0

3

24

Days of starvation

0

2

4

24

Hours of exercise

F i g u r e 2 - U t i l i z a t i o n o f c a r b o h y d r a t e and l i p i d by s k e l e t a l muscle d u r i n g s t a r v a t i o n and e x e r c i s e . R e s p i r a t o r y q u o t i e n t (RQ) i s the r a t i o of p r o d u c e a / 0 2 consumed. D a t a f r o m Owen and R e i c h a r d ( 6 ) , F e l i g and Wahren (11) and Wahren (12).

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

30

NUTRITION AND AEROBIC EXERCISE

muscle. A l t h o u g n p r o t e i n nas been o m i t t e d , the c a l o r i c v a l u e of p r o t e i n i n t h e body may a c c o u n t f o r 15% o f t h e body f u e l r e s e r v e s ; however, i t s u s e f u l l n e s s as a f u e l i s l i m i t e d because i t s c o n s u m p t i o n would n e c e s s i t a t e the d i s s o l u t i o n of s k e l e t a l muscle. I t can be seen i n l a b l e I, t h a t i f a normal 70kg man were to undergo t o t a l s t a r v a t i o n and r e m a i n i n the b a s a l s t a t e he c o u l d , i n t h e o r y , s u r v i v e f o r about 60 days w i t n h i s f u e l r e q u i r e m e n t s b e i n g met by t r i g l y c e r i d e breakdown. On the o t h e r hand, a t t h i s b a s a l r a t e of m e t a b o l i s m , c a r b o h y d r a t e s t o r e s would be d i m i n i s h e d w i t h i n a day. I f t h i s i n d i v i d u a l w e r e t o r u n a m a r a t h o n (20 k c a l / m i n ) , t r i g l y c e r i d e s t o r e s c o u l d p r o v i d e energy f o r about 5 d a y s , w h e r e a s , c a r b o h y d r a t e s t o r e s f o r o n l y 90 m i n u t e s . The l a t t e r i s p r o b a b l y an o v e r e s t i m a t i o n , i f one c o n s i d e r s t h a t not a l l m u s c l e s w o u l d be u s e d d u r i n g t h e r u n and t h a t the c o n v e r s i o n o f c a r b o h y d r a t e o x i d a t i o n to ATP g e n e r a t i o n i s not a t 100% e f f i c i e n c y . W i t h provide energy f o r perhap needed f o r c o m p l e t i o n o f a marathon. Factors Regulating Fuel U t i l i z a t i o n during Aerobic

Performance

From t h e a b o v e d i s c u s s i o n , i t i s e v i d e n t t h a t t h e p r o v i s i o n of f u e l f o r the m u s c l e i s a major l i m i t i n g f a c t o r d u r i n g e x e r c i s e and s e l e c t i o n o f f u e l s f o r o x i d a t i o n by t h e m u s c l e i s o f c o n s i d e r a b l e i m p o r t a n c e i n d e l a y i n g tne o n s e t of f a t i g u e , e s p e c i a l l y i n t h e t y p e o f e x e r t i o n t h a t may go b e y o n d 10 o r 20 minutes. A number of f a c t o r s can r e g u l a t e f u e l u t i l i z a t i o n d u r i n g e x e r c i s e i n c l u d i n g 1) muscle f i b e r type, 2) d u r a t i o n and i n t e n s i t y of e x e r c i s e , 3; p h y s i c a l t r a i n i n g and 4) d i e t . Musc l e F i b e r T y p e s . S k e l e t a l m u s c l e i s u s u a l l y c l a s s i f i e d a c c o r d i n g t o i t s f i b e r type. T h i s c l a s s i f i c a t i o n i s based upon s t a i n i n g p r o p e r t i e s of some muscle enzymes as w e l l as measurement of b i o c h e m i c a l markers (10). I n man, muscle f i b e r s are c l a s s i f i e d as b e i n g o f e i t h e r t y p e I o r t y p e I I (A o r B) ( T a b l e II). Type I f i b e r s are s l o w - t w i t c n h i g h l y o x i d a t i v e f i b e r s w i t h a h i g h c a p i l l a r y d e n s i t y . These c h a r a c t e r i s t i c s u s u a l l y c o n f e r a h i g h c a p a b i l i t y f o r l i p i d o x i d a t i o n . Type I I f i o e r s on the o t h e r hand a r e f a s t - t w i t c h f i b e r s . Type I1A f i b e r s a r e somewhat s i m i l a r t o t h o s e o f t y p e I i n t h a t t h e y a l s o nave a m o d e r a t e l y h i g h o x i d a t i v e c a p a c i t y ; i n a d d i t i o n , they have a m o d e r a t e l y h i g h g l y c o l y t i c c a p a c i t y . Type 11B f i b e r s a l s o have a n i g h g l y c o l y t i c but low o x i d a t i v e c a p a c i t y . One can u s u a l l y p r e d i c t from these v a r i o u s c h a r a c t e r i s t i c s w h e t h e r o r n o t a p a r t i c u l a r m u s c l e w o u l d be more i n v o l v e d i n e n d u r a n c e v e r s u s s p r i n t a c t i v i t y as w e l l as t h e f u e l o r f u e l m i x t u r e used. F o r e x a m p l e , as d i s c u s s e d i n t h e preceding c h a p t e r by T e r j u n g type I and I I A f i b e r s are more i n v o l v e d w i t h e n d u r a n c e p e r f o r m a n c e r e l y i n g on a f u e l m i x t u r e o f b o t h l i p i d s and c a r b o h y d r a t e . On t h e o t h e r n a n d , t y p e l i b f i b e r s a r e more involved w i t h short s p r i n t - t y p e of a c t i v i t y w i t h a f u e l d e p e n d e n c e a l m o s t e x c l u s i v e l y on c a r b o h y d r a t e . The fiber c o m p o s i t i o n o f m u s c l e f r o m a few a n i m a l s and man i s shown i n T a b l e I I I . A n i m a l s r a i s e d f o r q u i c k " s t o p and go" a c t i v i t y

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Data from Newsholme ( 3 7 ) .

Blood g l u c o s e

71

4

0.60

0.03

1,500

8U

350

20

Muscle g l y c o g e n

18

0.15

375

90

L i v e r glycogen

7143

Minutes o f a marathon

86

60

Days o f starvation

E s t i m a t e d p e r i o d f o r which f u e l s t o r ^ would p r o v i d e energy

0.72

1,800

Muscle t r i g l y c e r i d e

200

(kcal)

15ϋ,0ϋϋ

(g)

Approximate t o t a l fuel reserve

16,000

Adipose t i s s u e t r i g l y c e r ide

Tissue of source

Table I. Fuel Reserves and Rates of U t i l i z a t i o n under Different Conditions i n Humans

32

NUTRT IO IN AND AEROBC I EXERCS IE

Table II

Characteristics of Different Fiber Types Muscle f i b e r type

Characteristics

1. 2. 3. 4. 5. 6.

M y o f i b r i l l a r ATPase M i t o c h o n d r i a l eyzymes G l y c o l y t i c enzymes Lipids Glycogen Capillary density

liB

IIA

I slow-•twitch high low

lasc-twitch intermediate intermediate

fast-twitch low high

high

intermediate

low

Data from S a l t i n e t a l . ( 1 0 ) .

Table I I I . Fiber Composition of Muscle from Horses, Dogs and Man Percentage f i b e r c o m p o s i t i o n Type I

Type I I

Horse Quarterhorse

7

93

Dog Greyhound

3

97

53 24 79

47 76 21

Man untrained Sprinters E l i t e runners

Data from Newshoime and Leech ( 7 ) .

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

3.

GOODMAN

Fuel

utilization

( q u a r t e r h o r s e ) o r v e r y s h o r e d i s t a n c e speed r u n n i n g (greyhound) have a h i g h p r o p o r t i o n o f t y p e I I m u s c l e f i b e r s . I n man, i n d i v i d u a l s c o n s i d e r e d n o n - a t h l e t e s o r u n t r a i n e d have an equal number o f t y p e I and I I f i b e r s , w h e r e a s , s p r i n t e r s h a v e a preponderance o f type 11 f i b e r s and e l i t e d i s t a n c e runners more type I f i b e r s . I t i s i n t r i g u i n g t h a t some i n d i v i d u a l s h a v e a h i g h p r o p o r t i o n (70-80%) o f e i t h e r type I or I I f i b e r s . It r e m a i n s t o be d e t e r m i n e d whether o r not t h i s i s due t o a g e n e t i c predisposition.

D u r a t i o n and i n t e n s i t y o f E x e r c i s e . A k e y f a c t o r r e g u l a t i n g c a r b o h y d r a t e as w e l l as l i p i d u t i l i z a t i o n d u r i n g aerobic performance i s both the i n t e n s i t y of the e x e r c i s e as w e l l as i t s d u r a t i o n . As shown i n F i g u r e 3, t h e i n c r e a s e i n g l u c o s e u p t a k e by the w o r k i n g l e g muscles i s an e a r l y event and the uptake i s p r o p o r t i o n a l t o t h e wor e x e r c i s e , l e g glucose of a f a l l i n blood g l u c o s e i n d i c a t i n g t h a t l i v e r g l y c o g e n s t o r e s are nearing exhaustion. i t i s noteworthy that the increase i n m u s c l e g l u c o s e u p t a k e o c c u r s as i n s u l i n l e v e l s i n p l a s m a f a l l ( F i g u r e 1) i n d i c a t i n g t h i s response i s not mediated by i n c r e a s e d s e c r e t i o n o f i n s u l i n (12). Whether i n s u l i n i s p e r m i s s i v e f o r t h i s r e s p o n s e r e m a i n s t o be d e t e r m i n e d ( 1 4 ) . £arly i n t h e e x e r c i s e , l e g g l u c o s e uptake i s matched by s p l a n c h n i c ( i . e . l i v e r ) g l u c o s e o u t p u t but as l i v e r g l y c o g e n becomes d e p l e t e d s p l a n c h n i c g l u c o s e o u t p u t f a l l s (11,12). Glycogen breakdown w i t h i n w o r k i n g muscles a l s o o c c u r s d u r i n g the e a r l y s t a g e s o f e x e r c i s e and i t s breakdown i s p r o p o r t i o n a l t o t h e w o r k l o a d (15) ( F i g u r e 4 ) . A t h i g h w o r k l o a d s (80% o f VO2 max), g l y c o g e n d e p l e t i o n o c c u r s r a p i d l y and l i m i t s d u r a t i o n o f the e x e r c i s e . I t s d e p l e t i o n i s more g r a d u a l w i t h l i g h t to moderate e x e r c i s e and may not be a l i m i t i n g f a c t o r u n t i l l a t e i n the e x e r c i s e . L i k e g l y c o g e n , muscle t r i g l y c e r i d e breakdown can a l s o occur d u r i n g e x e r c i s e (15) however, t h i s has not been as w e l l s t u d i e d as muscle g l y c o g e n breakdown t o i n d i c a t e w h e t n e r o r n o t i t s d e g r a d a t i o n i s a l s o i n f l u e n c e d by i n t e n s i t y and d u r a t i o n o f e x e r c i s e . On t h e o t h e r h a n d , i t h a s b e e n shown t h a t u p t a k e o f f r e e f a t t y a c i d s f r o m p l a s m a by w o r k i n g m u s c l e i n c r e a s e s s t e a d i l y d u r i n g e x e r c i s e (11,12). From m e a s u r e m e n t s o f t h e u p t a k e o f g l u c o s e and f r e e f a t t y a c i d s and g l y c o g e n b r e a k d o w n by t h e w o r k i n g m u s c l e s , one c a n estimate t h e c o n t r i b u t i o n made oy e a c h f u e l t o t h e t o t a l o x i d a t i v e m e t a b o l i s m . As shown i n T a b l e I V , d u r i n g t h e f i r s t s e v e r a l hours of l i g h t t o moderate e x e r c i s e the m a j o r i t y o f the f u e l f o r t h e m u s c l e i s d e r i v e d f r o m p l a s m a g l u c o s e and m u s c l e glycogen. Between 3-4 hours, plasma f r e e f a t t y a c i d s become the more i m p o r t a n t f u e l , as p l a s m a g l u c o s e l e v e l s f a l l and m u s c l e g l y c o g e n becomes d e p l e t e d . A l t h o u g h m u s c l e and p l a s m a t r i g l y c e r i d e s are also u t i l i z e d during exercise, their c o n t r i b u t i o n to t o t a l o x i d a t i v e metabolism during prolonged e x e r c i s e i s n o t p r e c i s e l y known s i n c e t h e i r p a t t e r n o f u s a g e t h r o u g h o u t e x e r c i s e has not been w e l l d e t e r m i n e d . One may s p e c u l a t e , however, t h a t l i k e f a t t y a c i d s t h e i r c o n t r i b u t i o n t o the f u e l m e t a b o l i s m of muscle may r i s e as e x e r c i s e i s prolonged.

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

33

34

NUTRITION AND AEROBIC EXERCISE

F i g u r e 4 - Glycogen d e p l e t i o n from the quadraceps f e m o r i s e x e r c i s e . Data from Essen ( 1 5 ) .

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

during

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986. Muscle

36 22 14 8

glycogen

27 41 36 30

Plasma

glucose Plasma

37 37 j>0 62

fatty

Percentage c o n t r i b u t i o n t o oxygen uptake acids

D a t a f r o m F e l i g and Wahren (11) and N e w s h o l m e and L e e c h ( 7 ) . G l u c o s e , f r e e f a t t y a c i d s and oxygen uptake and g l y c o g e n breakdown by the w o r k i n g muscles were d e t e r m i n e d . C a l c u l a t i o n s d e r i v e d f r o m t h e s e d a t a assume t h a t a l l s u b s t r a t e s are c o m p l e t e l y o x i d i z e d by the w o r k i n g muscles. The c a l c u l a t i o n s a l s o assume t h a t the complete m e t a b o l i s m o f one mole o f g l u c o s e (or g l y c o g e n ) r e q u i r e s 6 moles o f oxygen w h i l e one mole of f a t t y a c i d r e q u i r e s 25 moles o f oxygen.

40 90 IdO 240

P e r i o d of exercise (minutes)

Table IV. Contribution of Glucose, Glycogen and Fatty Acids to Oxygen Consumption of Leg Muscles of Man during Mild Prolonged Exercise

36

NUTRT IO IN AND AEROBC I EXERCS IE Physical Training. Programs o f l i g h t to moderate endurance e x e r c i s e (i.e. t r a i n i n g ) have been found t o i n c r e a s e t h e r e s p i r a t o r y c a p a c i t y o f s k e l e t a l m u s c l e (16,17). T h i s response i s a s s o c i a t e d w i t h both an i n c r e a s e i n the number o f m i t o c h o n d r i a as w e l l as a m o u n t s o f o x i d a t i v e e n z y m e s . As shown i n T a b l e V, the a d a p t i v e response t o t r a i n i n g i n v o l v e s i n c r e a s e s i n o x i d a t i v e enzyme a c t i v i t i e s i n a l l muscle f i b e r types. T h i s i n d i c a t e s t h a t the m a j o r f a c t o r t h a t d e t e r m i n e s t h e r e s p i r a t o r y c a p a c i t y o f a m u s c l e f i b e r a p p e a r s t o be i t s c o n t r a c t i l e a c t i v i t y ; t h e more f r e q u e n t l y a muscle f i b e r c o n t r a c t s t h e g r e a t e r i t s m i t o c h o n d r i a l c o n t e n t and o x i d a t i v e c a p a c i t y . I n c o n t r a s t t o changes i n m i t o c h o n d r i a l o x i d a t i v e enzymes, many o f t h e e n z y m e s o f g l y c o l y s i s e i t h e r do n o t c h a n g e o r may e v e n d e c r e a s e f o l l o w i n g t r a i n i n g (17,18). This a d a p t a t i o n i s s p e c i f i c to endurance e x e r c i s e s i n c e s t r e n g t h e x e r c i s e ( i . e . w e i g h t l i f t i n g ) which can r e s u l t i n muscle hypertrophy does n o t i n d u c e an i n c r e a s e i n muscle m i t o c h o n d r i a (8) Due t o the a d a p t i v muscle p h y s i c a l l y t r a i n e d i n d i v i d u a l s d e r i v e a g r e a t e r p r o p o r t i o n o f t h e i r energy from o x i d a t i o n o f f a t and l e s s from c a r b o h y d r a t e d u r i n g submaximal e x e r c i s e (17,19). Ample e v i d e n c e suggests t h a t d e p l e t i o n o f body c a r b o h y d r a t e s t o r e s can p l a y an i m p o r t a n t r o l e i n the development of p h y s i c a l exhaustion during prolonged e x e r c i s e (16,17,£0). One m e c h a n i s m by w h i c h t r a i n i n g may i n c r e a s e endurance appears t o i n v o l v e a g l y c o g e n - s p a r i n g e f f e c t . D i r e c t m e a s u r e m e n t s o f m u s c l e g l y c o g e n i n man and a n i m a l s f o l l o w i n g s u b m a x i m a l e x e r c i s e have shown t h a t i t s c o n t e n t d e c r e a s e s more s l o w l y f o l l o w i n g t r a i n i n g (17,20). I t i s a l s o o f i n t e r e s t that p h y s i c a l t r a i n i n g can lead to l e s s hepatic glycogen d e p l e t i o n f o l l o w i n g s u b m a x i m a l e x e r c i s e ( 2 0 ) . The b e n e f i c i a l e f f e c t o f t h i s a d a p t a t i o n i s t o p r o t e c t the t r a i n e d i n d i v i d u a l o r a n i m a i a g a i n s t h e p a t i c g l y c o g e n d e p l e t i o n and the development o f hypoglycemia during prolonged e x e r c i s e . D i e t . There i s a w i d e l y h e l d n o t i o n t h a t a h i g h muscle g l y c o g e n c o n t e n t p r i o r t o a d i s t a n c e r u n c a n e n h a n c e p e r f o r m a n c e and delay exhaustion. Indeed t h i s has l e d t o the p o p u l a r b e l i e f t h a t " g l y c o g e n l o a d i n g " d i e t s s e v e r a l days p r i o r t o a d i s t a n c e r u n may p r o l o n g e n d u r a n c e and p e r f o r m a n c e ( s e e r e f 7 ) . Too e l e v a t e m u s c l e g l y c o g e n , i t s l e v e l i s f i r s t d e p l e t e d by r u n n i n g a t a moderate t o h i g h i n t e n s i t y f o r a p r o l o n g e d time. F o r t h e next 24 days p r i o r t o a d i s t a n c e r u n , a d i e t h i g h i n c a r b o h y d r a t e ( p a s t a and breads) i s consumed. D u r i n g t h i s t i m e d a i l y t r a i n i n g bouts can continue. This regimen s u c c e s s f u l l y leads t o muscle g l y o c g e n c o n t e n t s h i g h e r t h a n n o r m a l a phenomenon t e r m e d "supercompensation". As can be seen i n T a b l e VI (Group 1), human subjects undergoing a "glycogen loading" regimen p r i o r to a d i s t a n c e r u n o f moderate i n t e n s i t y had a h i g h g l y c o g e n c o n t e n t and c o u l d r u n s i g n i f i c a n t l y l o n g e r t h a n s u b j e c t s c o n s u m i n g a mixed o r a low c a r b o h y d r a t e d i e t . On t h e o t h e r hand, s e v e r a l s t u d i e s have s u g g e s t e d t h a t d i e t s low i n c a r b o h y d r a t e s t h a t r e d u c e m u s c l e g l y c o g e n may n o t be a t a l l d e l e t e r i o u s o r r e d u c e d u r a t i o n o f e x e r c i s e . I n one study by Phinney e t a l . (21), obese i n d i v i d u a l s were p l a c e d on a w e i g h t r e d u c i n g d i e t c o n s i s t i n g o f a h i g h q u a l i t y p r o t e i n ( " p r o t e i n s p a r i n g m o d i f i e d f a s t " ) . As shown

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

3.

Fuel

GOODMAN

Table V.

utilization

37

Effects of Training on Mitochondrial Enzyme A c t i v i t y of Rat Skeletal Muscle

F i b e r types Enzyme

Group

C i t r a t e synthase

Sedentary Trained

Carnitine palmityltransferase

Sedentary Trained

3-hydroxybutyrate dehydrogenase

Sedentar Traine

Cytochrome o x i d a s e

Sedentary Trained

IIB

IIA

I

10.3 18.5

36 70

23 41

0.11 0.20

0.72 1.20

0.63 1.20

167 339

830 2041

621 1347

Enzyme activités i n umole/g.rain, except cytochrome o x i d a s e which i s i n u l C^/g x min. Data from B a l d w i n e t a l . ( 1 6 ) .

Table VI. E f f e c t of Diet on Muscle Glycogen Content and Duration of Exercise Subjects

Diet

Muscle g l y c o g e n content before exercise (umol/g)

Duration of exercise (minutes)

Humans

Normal mixed d i e t Low c a r b o h y d r a t e d i e t f o r 3 days High c a r b o h y d r a t e d i e t f o r 3 days (glycogen loading)

97 36 103

116 57 166

Humans

Normal mixed d i e t Low c a r b o h y d r a t e d i e t f o r 6 weeks

85 58

168 249

54 40

30 47

Rats

Normal chow d i e t Low c a r b o h y d r a t e d i e t f o r 5 weeks

Data i n group 1 from Bergstrom e t a l . ( 3 8 ) , Group 2 from Phinney e t a l . ( 2 1 ) , and Group 3 from M i l l e r e t a l . ( 2 2 ) .

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NUTRT IO IN AND AEROBC I EXERCS IE i n T a b l e VI (Group 2 ) , a f t e r ό weeks on t h i s d i e t muscle g l y c o g e n was r e d u c e d b u t t h e a b i l i t y o f t h e s e i n d i v i d u a l s t o r e m a i n a c t i v e at a low i n t e n s i t y e x e r c i s e i n c r e a s e d by 50%. In another s t u d y (22), r a t s fed a low c a r b o h y d r a t e ( h i g h f a t ) d i e t f o r 5 weeks were a b l e t o t o l e r a t e an i n t e n s e t r e a d m i l l run l o n g e r t h a n r a t s on a n o r m a l d i e t ( T a b l e V I , Group 3 ) . T h u s , d i e t s t h a t may a c t u a l l y l o w e r muscle g l y c o g e n c o n t e n t are not a l w a y s a s s o c i a t e d w i t h reduced performance. I t i s conceivable that i n g r o u p s 2 and 3 t h e p r i m a r y f u e l f o r t h e w o r k i n g m u s c l e s w e r e p r o v i d e d by f r e e f a t t y a c i d s and t r i g l y c e r i d e s r e s u l t i n g i n s p a r i n g o f g l y c o g e n , i f s u c h was t h e c a s e , i t may h e l p e x p l a i n why e x e r c i s e d u r a t i o n was prolonged. I t would a l s o re-emphasize t h a t p r o t e c t i o n of g l y c o g e n s t o r e s are i m p r o t a n t i n d e l a y i n g the onset of e x h a u s t i o n d u r i n g e x e r c i s e . More a c u t e d i e t a r y m a n i p u l a t i o n s h a v e a l s o b e e n shown t o m o d i f y e x e r c i s e performance When f r e e f a t t y a c i d l e v e l s were a r t i f i c i a l l y raised i were a b l e t o r u n abou b e c o m i n g e x h a u s t e d (9,23,24). T h i s was a s s o c i a t e d w i t h a g l y c o g e n - s p a r i n g e f f e c t d u r i n g the run i n t h a t both b l o o d g l u c o s e and m u s c l e g l y c o g e n d e c l i n e d more s l o w l y . In t h i s a s s o c i a t i o n the g l y c o g e n - s p a r i n g e f f e c t was p o s t u l a t e d t o be due t o an e n h a n c e d o x i d a t i o n o r f a t t y a c i d s . On t h e o t h e r h a n d , g l u c o s e i n g e s t i o n during prolonged l i g h t - i n t e n s i t y e x e r c i s e r e s u l t e d i n augmented uptake and o x i d a t i o n of g l u c o s e by w o r k i n g muscles i n a s s o c i a t i o n w i t h d i m i n i s h e d l i p o l y s i s (25,26). It i s also t h o u g h t t h a t e x o g e n o u s g l u c o s e may r e d u c e e n d o g e n o u s g l y c o g e n breakdown ( 2 6 ) . B i o c h e m i c a l R e g u l a t i o n of F u e l U t i l i z a t i o n d u r i n g E x e r c i s e The p r e v i o u s s e c t i o n s have i n d i c a t e d t h a t both c a r b o h y d r a t e s and l i p i d s can be u t i l i z e d by muscle d u r i n g a e r o b i c performance. Due to the s m a l l r e s e r v e of c a r b o h y d r a t e i n the body ( T a b l e I ) , i t s use as a f u e l i s l i m i t e d . To o b t a i n maximal performance d u r i n g e n d u r a n c e r u n n i n g ( i . e . , m a r a t h o n ) , b o t h c a r b o h y d r a t e and l i p i d f u e l s must be u s e d s i m u l t a n e o u s l y ( 7 ) . As much f a t t y a c i d as p o s s i b l e m u s t be o x i d i z e d t o a l l o w t h e l i m i t e d c a r b o h y d r a t e r e s e r v e s t o l a s t f o r the d u r a t i o n of e x e r c i s e . Hypoglycemia m u s t be p r e v e n t e d and g l u c o s e must be s u p p l i e d t o t h e b r a i n a t a l l t i m e s . T h i s c a r b o h y d r a t e s p a r i n g a t the expense of f a t t y a c i d o x i d a t i o n has been proposed t o be f a c i l i t a t e d by a s p e c i f i c i n t r a c e l l u l a r c o n t r o l mechanism. I t i s w e l l documented t h a t g l u c o s e u p t a k e , g l y c o l y s i s , g l y c o g e n b r e a k d o w n and p y r u v a t e o x i d a t i o n are i n h i b i t e d i n the h e a r t by o x i d a t i o n o£ l a t t y a c i d s (27). R a n d l e and c o w o r k e r s (27) p r o p o s e d t h a t t h i s i n h i b i t i o n of c a r b o h y d r a t e u t i l i z a t i o n by f a t t y a c i d s was a g e n e r a l phenomenon. T h i s i n h i b i t i o n i s m e d i a t e d by t h e r i s e i n m u s c l e a c e t y l - C o A , c i t r a t e and g l u c o s e - 6 - p h o s p h a t e d u r i n g f a t t y a c i d o x i d a t i o n ( F i g u r e 5). An i n c r e a s e i n the a c e t y l - C o A r a t i o w i l l i n h i b i t pyruvaue dehydrogenase and reduce c a r b o h y d r a t e o x i d a t i o n ; c i t r a t e produced w i t h i n the m i t o c h o n d r i a w i l l be t r a n s p o r t e d i n t o t h e c y t o p l a s m and w i l l i n h i b i t p h o s p h o f r u e t o k i n a s e t h e r e b y r e s t r i c t i n g g l y c o l y s i s ; and t h e r e s u l t a n t r i s e i n g l u c o s e - 6 p h o s p h a t e c a n i n h i b i t h e x o k i n a s e r e s t r i c t i n g g l u c o s e uptake by

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

GOODMAN

Fuel

Utilization

F i g u r e 5 - I n t e r a c t i o n of c a r b o h y d r a t e snd l i p i d metabolism d u r i n g e x e r c i s e . G6P, glucose--6-phosphate;F6P, fructose-6phosphate; FDP, f r u c t o s e - 1 , 6 - d i p h o s p h a t e ; P y r , P y r u v a t e ; FFA, f r e e f a t t y a c i d TG, t r i g l y c e r i d e - , HK, h e x o k i n a s e ; PL, p h o s p h o r y l a s e ; PFK, p h o s p h o f r u c t o k i n a s e and PDH, p y r u v a t e dehydrogenase.

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

40

NUTRT IO IN AND AEROBC I EXERCS IE muscle. There i s a l s o e v i d e n c e t h a t a r i s e i n g l u c o s e - 6 p h o s p h a t e may i n h i b i t g l y c o g e n b r e a k d o w n ( 7 ) . A l t h o u g h t h i s mechanism i s o p e r a t i v e i n c a r d i a c muscle, s t u d i e s u s i n g s k e l e t a l muscle ( i n c u b a t e d in_ v i t r o o r p e r f u s e d j j i s i t u ) have not a l w a y s demonstrated an i n h i b i t o r y e f f e c t o f f a t t y a c i d s ( o r o t h e r l i p i d f u e l s ) on g l u c o s e m e t a b o l i s m (28-30). When demonstrated, i t has been c o n f i n e d t o t h o s e m u s c l e s t h a t have a h i g h c a p a c i t y t o o x i d i z e l i p i d f u e l s such as type I and I I A f i b e r s (29,30). As n o t e d p r e v i o u s l y , l i k e s k e l e t a l m u s c l e , g l y c o g e n d e p l e t i o n i n l i v e r d u r i n g e n d u r a n c e e x e r c i s e i s much l e s s i n t r a i n e d a n i m a l s and i n a n i m a l s who have h a d f r e e f a t t y a c i d s a r t i f i c i a l l y e l e v a t e d . No e v i d e n c e e x i s t s t h a t t h e m e c h a n i s m proposed by Randle t o account f o r the i n h i b i t i o n o f c a r b o h y d r a t e m e t a b o l i s m i n muscle by o x i d a t i o n o f f a t t y a c i d s i s o p e r a t i v e i n the l i v e r . Thus o t h e r f a c t o r s must be r e s p o n s i b l e f o r the s l o w e r rate o f l i v e r glycogen d e p l e t i o n i n these s i t u a t i o n s Such f a c t o r s may i n c l u d e a smaller reduction i n b l o o d f l o w t o the l i v e r d u r i n g e x e r c i s e (19,20). Carbohydrate M e t a b o l i s m F o l l o w i n g

Exercise

Following e x e r c i s e , g l u c o s e u p t a k e by t h e p r e v i o u s l y w o r k i n g muscles does not f a l l t o p r e - e x e r c i s e l e v e l s but remains e l e v a t e d (31). T e l e o l o g i c a l l y , t h i s would ensure t h a t muscle g l y c o g e n s t o r e s d e p l e t e d d u r i n g e x e r c i s e a r e r a p i d l y r e p l e n i s h e d upon c e s s a t i o n o f e x e r c i s e . Recent s t u d i e s i n the r a t have shown t h a t f o l l o w i n g e x e r c i s e , g l u c o s e t r a n s p o r t and g l y c o g e n s y n t h e s i s i n s k e l e t a l m u s c l e a r e e n h a n c e d due a t l e a s t , i n p a r t , t o an i n c r e a s e i n i n s u l i n s e n s i t i v i t y (32-36). I t was a l s o shown t h a t the i n c r e a s e i n i n s u l i n s e n s i t i v i t y o c c u r s p r e d o m i n a n t l y i n muscle f i b e r s t h a t a r e d e g l y c o g e n a t e d d u r i n g e x e r c i s e , i n o t h e r words, i n the a c t i v e muscles (33). The p r e c i s e mechanism f o r the i n c r e a s e i n i n s u l i n s e n s i t i v i t y f o l l o w i n g e x e r c i s e i s not known nor i s i t a s s o c i a t e d w i t h an i n c r e a s e i n i n s u l i n b i n d i n g t o i t s r e c e p t o r on the muscle c e l l (34-36). Summary During the e a r l y minutes o f e x e r c i s e , carbohydrate (plasma g l u c o s e and m u s c l e g l y c o g e n ) i s t h e p r e d o m i n a n t f u e l f o r t h e w o r k i n g muscles. When the e x e r c i s e i s p r o l o n g e d and i n t e n s i v e , c a r b o h y d r a t e remains a predominant f u e l w i t h l i p i d s (plasma f r e e f a t t y a c i d s and muscle t r i g l y c e r i d e s ) b e i n g o f l e s s e r importance. When t h e e x e r c i s e i s o f m o d e r a t e i n t e n s i t y , l i p i d s e v e n t u a l l y become the p r i m a r y f u e l as c a r b o h y d r a t e s t o r e s a r e reduced. A f t e r t r a i n i n g , which increases the o x i d a t i v e c a p a c i t y of t h e m u s c l e s , l i p i d f u e l s become t h e m a j o r e n e r g y s o u r c e o f t h e w o r k i n g muscles d u r i n g p r o l o n g e d e x e r t i o n s p a r i n g c a r b o h y d r a t e utilization. Both low and h i g h c a r b o n y d r a t e d i e t s can i n c r e a s e e x e r c i s e d u r a t i o n ; however, low c a r b o h y d r a t e d i e t s may d i m i n i s h the power output or max d u r i n g e x e r t i o n . Althouth d i e t s high i n c a r b o h y d r a t e o r f a t ( l o w c a r b o h y d r a t e ) may e n h a n c e e x e r c i s e performance, i t i s recommended t h a t a mixed d i e t be consumed by

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

3.

GOODMAN

Fuel

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41

those undertaking exercise f o r h e a l t h b e n e f i t s or weight reduction. During recovery from e x e r c i s e , glucose u p t a k e by t h e p r e v i o u s l y working muscles remains elevated. T h i s i s due, i n p a r t , t o an i n c r e a s e i n the s e n s i t i v i t y o f m u s c l e t o i n s u l i n , f a c i l i t a t i n g glycogen repletion.

Literature Cited 1. 2. 3. 4.

5.

7. 8.

10.

11. 12. 13. 14. 15. lo.

Ruderman, N.B. α Haudenschild, C. (1984) Diabetes as an atherogenic factor. Progress in Cardiovascular Diseases 26:373-412. Richter, E.A., Ruderman, N.B. and Schneider, S.H. (1984) Diabetes and Exercise. Am. J. Med. 70:201-209. Gollnick, P.D. (1977) Free fatty acid turnover and the quantability of substrate exercise. Ann. N.Y Goodman, M.N. and Ruderman, N.B. (1982) Influence of muscle use on amino acid metabolism. In, Exercise and Sport Science Reviews, ed. by R.L. Terjung, The Franklin Institute, Philadelphia, PA, 1-26. Cahill, G.F. (1970) Starvation in man. New Eng. J. Med. 282:668-675, 6. Owen, O.E. and Reichard, G.A. (1971) Human forearm metabolism during progressive starvation. J. Clin, Invest. 50:1536-1545. Newsholme, E.A., and Leech, A.R. (1983) Metabolism in Exercise. In, Biochemistry for the Medical Sciences John Wiley and sons, New York, Chapter 9. Newsholme, E.A. (1977) The regulation of intracellular and extracellular fuel supply during sustained exercise. Ann. N.Y. Acad. Sci. 301:81-91, 9. Holloszy, J.O., Rennie, M.J., Hickson, R.C., Conlee, R.K. and Hagberg, J.M. (1977) Consequences of the biochemical adaptations to endurance exercise. Ann. N.Y. Acad. Sci. 301:440-450. Saltin, B., Henriksson, J., Nygaard, E. and Andersen, P. (1977) Fiber types and metabolic potentials of skeletal muscles in sedentary man and endurance runners. Ann. N.Y. Acad. Sci. 301:3-29. Felig, P. and Wahren, J. (1975) Fuel homeostasis in exercise. N. Engl. J. Med. 293:1078-1084. Wahren, J.: Glucose turnover during exercise in man (1977) Ann. N.Y. Acad. Sci. 301:45-53. Wahren, J., Felig, P. and Hagenfeldt, L. (1978) Physical exercise and fuel homeostasis in diabetes mellitus. Diabetologia, 14:213-222. Berger, M., riagg, S. and Kuderman, N.B. (1975) Glucose metabolism in perfused skeletal muscle. Biochem. J. 146:231238. Essen, B. (1977) Intramuscular substrate utilization during prolonged exercise. Ann. N.Y. Acad. Sci. 301:30-44. Baldwin, K.M., Klinkerfuss, G.H., Terjung, R.L., Mole, P.A. and Holloszy, J.O. (1972) Respiratory capacity of white, red, and intermediate muscle: adaptive response to exercise. Am. J. Physiol. 222:373-378.

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NUTRITION AND AEROBIC EXERCISE

17. Holloszy, J.O. and Coyle, E.F. (1984) Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J. Appl. Physiol. 56:831-838. 18. Baldwin, K.M., Winder, W.W., Terjung, R.L., and Holloszy, J.O. (1973) Glycolytic enzymes in different types of skeletal muscle: adaptation to exercise. Am. J. Physiol. 225:962-906. 19. Koivisto, V., R. Hendler, R., Nadel, E. & Felig, P. (1982) Influence of physical training on the fuel-hormone response to prolonged low intensity exercise. Metabolism 31;192—197. 20. Baldwin, K.M. Fitts, R.H., Booth, F.W., Winder, W.W. & holloszy, J.O. (1975) Depletion of muscle and liver glycogen during exercise. Pflugers Arch.354;203-212 1975. 21. Phinney, S.D., Harton, E.S., Sims, E.A., Hanson, J.S., Danforth, E. & La Grange, B.M. (1984) Capacity for moderate exercise in obes subject afte adaptatio t hpyocaloric, ketogeni 66;1152-1161. 22. Miller, W.C., Bryce, R.K. & Conlee, R.K. (1984) Adaptations to a night-fat diet that increases exercise endurance in male rats. J. Appl. Pnysiol. 58; 78-83. 23. Hickson, R.C., Rennie, M.J., Conlee, R.K., Winder, W.W. & Holloszy, J.O. (1977) Effects of increased plasma fatty acids on glycogen utilization and endurance. J. Appl. Physiol. 43, 829-633. 24. Rennie, M.J., Winder, W.W. & Holloszy, J.O. (1976) A sparing effect of increased plasma fatty acids on muscle and liver glycogen content in exercising rat. Biochem. J. 156: 647-655. 25. Ahlborg, G. & Felig, P. (1976) Influence of glucose ingestion on fuel-hormone response during prolonged exercise. J. App;. Physiol. 41: 683-688. 26. Krezentowski, G., Freddy, P., Luyckx, A.S., Lacroix, M. Mosora, F. & Letebvre, P.J. (1984) Effects of physical training on utilization of a glucose load given orally during exercise. Am, J. Physiol. 246, E412-E417. 27. Randle, P.J., Garland, P.B., Hales, C.N., Newsholme, E.A., Denton, R.M. & Pogson, C.I. (1966) Interactions of metabolism and physiological role of insulin.Rec. Prog. Horm. Res. 22, 1-44. 28. Goodman, M.N., Berger, M. & Ruderman, N.B. (1974) Glucose metabolism in rat skeletal muscle at rest. Diabetes 23; 881-888. 29. Maizels, E.Z., Ruderman, N.B., Goodman, M.N. & Lau, D. (1977) Effects of acetoacetate on glucose metabolism in soleus and extensor digitorum longus muscles of the rat. Biochem, J. 162; 557-568. 30. Rennie, M.J. & Holloszy, J.O. (1977) Inhibition of glucose uptake and glycogenolysis by availability of oleate in well-oxygenated perfused skeletal muscle. Biochem. J. 168; 161-170. 31. Wahren, J., Felig, P., Hendler, R. & Ahlborg, G. (1973) Glucose and amino acid metabolism during recovery after exercise. J. Appl. Physiol. 34; 838-845.

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

3. GOODMAN 32. 33. 34.

35. 36. 37.

38.

Fuel Utilization

Ivy, J. & Holloszy, J.O. (1981) Persistent increase in glucose uptake by rat skeletal muscle following exercise. Am. J. Physiol. 241, C200-C203. Richter, E.A., Garetto, L.P., Goodman, M.N. & Ruderman, N.B. (1982) Muscle glucose metabolism following exercise in the rat. J. Clin. Investigation. 69, 765-793. Garetto, L.P., Richter, E.A., Goodman, M.N. & Ruderman, N.B. (1983) Enhanced insullin sensitivity of skeletal muscle following exercise. In: Biochemistry of Exercise, ed. by H. Knuttgen, J. Vogel and J. Poortman. Champaign, IL., p. 681687. Horton, E.G. (1983) Increased insulin sensitivity without altered insulin binding in rat soleus muscle. Excerpta Med. Int. Cong. Ser. 577, 182. Ian, M. & Bonen, Α. (1983) Exercise enhances glycogenesis in muscle without affectin thei insuli bindin d2 deoxyglucose uptake Newsholme, E.A (1983) integration of fuel supply for the marathon runner. In: Biochemistry of Exercise, ed. by H. Knuttgen, J. Vogel and J. Poortman. Champaign, IL., p.144-150. Bergstrom, J., Hermansen, L. & Hultman, E. (1967) Diet, muscle glycogen and physical performance. Acta. Physiol. Scand. 71, 140-150.

RECEIVED May 14, 1985

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4 Protein and Amino Acid Metabolism During Exercise Donald K. Layman and Melissa K. Hendrix Department of Foods and Nutrition, Division of Nutritional Sciences, University of Illinois, Urbana, IL 61801

Athletes associate performance with diet Meat became a staple of ancient Greek and Roma strength and enduranc kingdom. As knowledge of nutrition and muscle physiology increased, athletes became convinced that to increase muscle mass and strength required increased dietary protein. However, nutrition textbooks (1,2) and the Recommended Dietary Allowances (RDA's) established by the National Academy of Sciences (3) state that there is little or no need for extra protein for exercise. Review of the nutrition and exercise literature indicates that physical activity produces changes in protein metabolism. A few of these changes are increased urinary nitrogen, increased nitrogen in sweat, and increased protein mass of muscles. These physiological changes, which suggest an increased need for dietary protein, together with the renewed popular interest in exercise have led to a reevaluation of protein utilization during exercise. Aspects of this topic have been addressed in other recent reviews (4,5,6). To examine the i n f l u e n c e o f e x e r c i s e on p r o t e i n m e t a b o l i s m , i t i s i m p o r t a n t t o c o n s i d e r the d i f f e r e n c e s between t y p e s o f exercise. The p r e v i o u s c h a p t e r s by T e r j u n g and Goodman have examined the e f f e c t s o f e x e r c i s e i n t e n s i t y and d u r a t i o n on d i f f e r e n t muscles and the p r i m a r y f u e l s r e q u i r e d f o r s p e c i f i c activities. F o r the purpose o f t h i s c h a p t e r , e x e r c i s e w i l l be c l a s s i f i e d as a n a e r o b i c o r a e r o b i c . These terms i n d i c a t e m e t a b o l i c d i f f e r e n c e s and i m p l y d i f f e r e n c e s i n i n t e n s i t y and d u r a t i o n . A n a e r o b i c a c t i v i t i e s a r e o f b r i e f d u r a t i o n and a t , o r a p p r o a c h i n g , maximum e x e r t i o n . A n a e r o b i c t r a i n i n g emphasizes s t r e n g t h and f r e q u e n t l y r e s u l t s i n muscle h y p e r t r o p h y . Aerobic e x e r c i s e f e a t u r e s p r o l o n g e d a c t i v i t i e s a t l e s s than maximum exertion. T r a i n i n g emphasizes endurance work and r e s u l t s i n i n c r e a s e d o x i d a t i v e c a p a c i t y o f the muscles w i t h l i t t l e o r no change i n muscle mass. Thus, the t y p e o f e x e r c i s e can i n f l u e n c e muscle mass and the amount o f muscle p r o t e i n s and presumably the needs f o r d i e t a r y p r o t e i n . To c o n c e p t u a l i z e amino a c i d m e t a b o l i s m , i t i s u s e f u l t o c o n s i d e r a model which d e s c r i b e s the f l u x o f amino a c i d s through 0097-6156/ 86/ 0294-0045S06.00/ 0 © 1986 American Chemical Society

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f r e e amino a c i d p o o l s . The most commonly used model i s one t h a t f e a t u r e s a s i n g l e amino a c i d p o o l which a c c o u n t s f o r t h e f l u x o f amino a c i d s t o p r o t e i n s y n t h e s i s o r o x i d a t i o n from a s i n g l e homogeneous p o o l ( 7 , 8 ) . FREE INTAKE

> AMINO ACID «

> PROTEIN

POOL

OXIDATION

As the model s u g g e s t s , t h e d i e t a r y need f o r amino a c i d s i s determined by the r a t e s o f d e p l e t i o n o f the f r e e amino a c i d p o o l by o x i d a t i o n o r s y n t h e s i s o f p r o t e i n . During steady s t a t e c o n d i t i o n s , the c o n t r i b u t i o n t o the f r e e p o o l from d i e t a r y i n t a k e and p r o t e i n breakdown s h o u l d be e x a c t l y balanced by t h e f l u x out o f the p o o l t o s y n t h e s i s and o x i d a t i o n . Any c o n d i t i o n t h a t i n c r e a s e s d e p o s i t i o n o f p r o t e i n i n t h e body o r the r a t e o f amino a c i d o x i d a t i o n s h o u l d produce an i n c r e a s e d need f o r p r o t e i n . For example, muscle h y p e r t r o p h y i s dependent on a p o s i t i v e b a l a n c e o f the p r o t e i n t u r n o v e r p r o c e s s . I f s y n t h e s i s o f p r o t e i n exceeds the c a t a b o l i s m o f p r o t e i n , then muscle mass w i l l i n c r e a s e and the f r e e amino a c i d p o o l would be d e p l e t e d . Thus, a net i n c r e a s e i n p r o t e i n r e q u i r e s an i n c r e a s e i n i n t a k e o r a decrease i n o x i d a t i o n . L i k e w i s e , t h e same arguments h o l d f o r an i n c r e a s e i n o x i d a t i o n o f amino a c i d s . Amino A c i d M e t a b o l i s m A s s o c i a t e d w i t h A n a e r o b i c

Exercise

S p e c i f i c e x e r c i s e such as w e i g h t l i f t i n g can i n c r e a s e muscle mass ( 9 , 1 0 ) . While the p o t e n t i a l t o develop muscle mass i s e s t a b l i s h e d , t h e m e t a b o l i c changes t h a t l e a d t o t h e s e changes remain u n c l e a r . R e l a t i v e l y few s t u d i e s have examined amino a c i d metabolism d u r i n g e x e r c i s e - i n d u c e d h y p e r t r o p h y . The primary reason f o r t h e l a c k o f i n f o r m a t i o n i s t h e absence o f a c o n v e n i e n t animal model f o r w e i g h t l i f t i n g s t u d i e s . Human s t u d i e s u t i l i z i n g n o n r a d i o a c t i v e , s t a b l e i s o t o p e s have not yet been done. While few s t u d i e s e x i s t t h a t a r e designed t o e v a l u a t e amino a c i d metabolism d u r i n g and a f t e r a n a e r o b i c e x e r c i s e , some i n s i g h t i n t o changes i n p r o t e i n s y n t h e s i s can be g a i n e d from s t u d i e s t h a t produce muscle h y p e r t r o p h y u s i n g n o v e l s u r g i c a l p r o c e d u r e s o r m e c h a n i c a l s t i m u l a t i o n s . One s e r i e s o f s t u d i e s from the l a b o r a t o r y o f A . L . Goldberg examined h y p e r t r o p h y o f s p e c i f i c muscles a f t e r s u r g i c a l removal o f a s y n e r g i s t i c muscle ( 1 1 , 1 2 ) . These i n v e s t i g a t o r s u t i l i z e d the t r i a d o f muscles e x t e n d i n g from the knee t o the a n k l e on the back o f the h i n d l i m b o f r a t s . These t h r e e m u s c l e s , t h e s o l e u s , p l a n t a r i s , and g a s t r o c n e m i u s , s e r v e t o extend the a n k l e j o i n t . S p e c i f i c a l l y , Goldberg and h i s c o l l e a g u e s

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

4. LAYMAN AND HENDRIX

Protein and Amino

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47

severed t h e a c h i l l e s tendon o f t h e g a s t r o c n e m i u s and observed t h e changes i n p r o t e i n s y n t h e s i s i n t h e s o l e u s and p l a n t a r i s muscles as t h e s e muscles h y p e r t r o p h i e d under t h e f u n c t i o n a l o v e r l o a d i n an attempt t o m a i n t a i n t h e a b i l i t y o f t h e a n i m a l t o extend t h e f o o t . T h i s t r e a t m e n t produced a 40% i n c r e a s e i n t h e weight o f t h e s o l e u s and a 25% i n c r e a s e i n t h e weight o f t h e p l a n t a r i s by 5 days a f t e r they were s u r g i c a l l y o v e r l o a d e d . These i n v e s t i g a t o r s demonstrated t h a t t h e r e was a c o r r e s p o n d i n g i n c r e a s e i n p r o t e i n c o n t e n t and r e l a t e d i n c r e a s e s i n RNA c o n t e n t , ribosome a c t i v i t y , and i n c o r p o r a t i o n o f amino a c i d s i n t o p r o t e i n . They c o n c l u d e d t h a t muscle h y p e r t r o p h y was produced by a d r a m a t i c i n c r e a s e i n p r o t e i n synthesis. A second e x p e r i m e n t a l model t h a t may approximate w e i g h t l i f t i n g e x e r c i s e i s "stretch-induced hypertrophy" ( 1 3 , 1 4 ) . As t h e term i m p l i e s , s t r e t c h - i n d u c e d h y p e r t r o p h y c o n s i s t s o f p r o d u c i n g muscle h y p e r t r o p h y by f o r c i n g a muscle i n t o f u l l e x t e n s i o n t h r o u g h t h e us m e t a b o l i c changes a r e s i m i l a produce a r a p i d i n c r e a s e i n muscle weight and p r o t e i n c o n t e n t and i n t h e r a t e o f p r o t e i n s y n t h e s i s (Table 1 ) . These i n v e s t i g a t o r s e s t i m a t e d t h e r a t e o f p r o t e i n d e g r a d a t i o n and c o n c l u d e d t h a t p r o t e i n d e g r a d a t i o n was a l s o e l e v a t e d b u t h y p e r t r o p h y o c c u r r e d because t h e i n c r e a s e i n s y n t h e s i s exceeded t h e i n c r e a s e i n degradation (14).

Table 1.

Time

Changes i n P r o t e i n Turnover i n A n t e r i o r L a t i s s i m u s D o r s i M u s c l e s o f C h i c k e n s D u r i n g S t r e t c h - I n d u c e d Hypertrophy

(days) 0 1 3 7

Degradation

Synthesis

(X/day) 16.5 21.6 23.0 27.5

16.5 33.0 32.5 31.3

S y n t h e s i s measured u s i n g t h e c o n s t a n t i n f u s i o n o f l ^ C - p r o l i n e and d e g r a d a t i o n c a l c u l a t e d a s t h e d i f f e r e n c e between t h e r a t e o f s y n t h e s i s and t h e r a t e o f p r o t e i n a c c r e t i o n . From L a u r e n t e t a l . (14). These e x p e r i m e n t a l models i n d i c a t e t h a t muscle h y p e r t r o p h y o c c u r s t h r o u g h i n c r e a s e s i n p r o t e i n s y n t h e s i s and suggest t h a t w e i g h t l i f t i n g s h o u l d r e q u i r e i n c r e a s e d d i e t a r y p r o t e i n . The c o n f u s i o n i s d e r i v e d from t h e i n t e r p r e t a t i o n o f t h e q u a n t i t y o f p r o t e i n needed t o meet t h i s i n c r e a s e d need. The R D A s s t a t e t h a t "there i s l i t t l e e v i d e n c e t h a t muscular a c t i v i t y i n c r e a s e s t h e need f o r p r o t e i n , except by t h e s m a l l amount r e q u i r e d f o r t h e development o f muscles d u r i n g c o n d i t ^ o n i n a . " The amount has been f

American Chemical Society Library In Nutrition and Aerobic Exercise; Layman, D.; 1155 16th St., N.W. ACS Symposium Series; American Chemical Society: Washington, DC, 1986. Washington, D.C. 20036

48

NUTRT IO IN AND AEROBC I EXERCS IE

r e p o r t e d to be a maximum o f 7 grams o f a d d i t i o n a l p r o t e i n per day (15). The impact o f 7 grams o f p r o t e i n per day on t h e American d i e t i s v i r t u a l l y n e g l i g i b l e . The d a i l y p r o t e i n needs range from a p p r o x i m a t e l y 40 t o 90 grams per day ( 0 . 8 grams per k i l o g r a m body w e i g h t ) , w h i l e the average American consumes n e a r l y t w i c e the need o r about 110 grams per d a y . Thus, t h e i n c r e a s e d need f o r muscle h y p e r t r o p h y s h o u l d be a d e q u a t e l y met by normal i n t a k e s w i t h o u t supplementation. Though t h e amount o f muscle p r o t e i n gained per day d u r i n g weight t r a i n i n g does not j u s t i f y an i n c r e a s e d p r o t e i n i n t a k e , many a t h l e t e s b e l i e v e t h a t high l e v e l s o f p r o t e i n are e s s e n t i a l to s t i m u l a t e maximum muscle development. However, as shown i n F i g . 1, i n t a k e s o f p r o t e i n above the requirement produce no stimulation of protein synthesis. By f e e d i n g d i f f e r e n t l e v e l s o f p r o t e i n t o r o d e n t s , we found t h a t maximum muscle mass and the maximum r a t e o f p r o t e i levels of dietary protei l e v e l produced no a d d i t i o n a l s t i m u l a t i o n ( 1 6 ) . G o l d b e r g and h i s c o l l e a g u e s p r o v i d e d f u r t h e r e v i d e n c e t h a t d i e t a r y p r o t e i n i s not a l i m i t i n g f a c t o r f o r muscle h y p e r t r o p h y ( 1 2 ) . U s i n g t h e i r s u r g i c a l model f o r compensatory h y p e r t r o p h y , they found t h a t the i n c r e a s e i n p r o t e i n s y n t h e s i s and muscle mass could occur during periods of t o t a l s t a r v a t i o n . Thus, h y p e r t r o p h y o f s p e c i f i c muscles was produced by the s e l e c t i v e t r a i n i n g , w o r k l o a d , o r s t r e t c h put on t h a t muscle and was not dependent on diet. O b v i o u s l y , the t o t a l muscle mass o f the body cannot be i n c r e a s e d d u r i n g t o t a l s t a r v a t i o n , but G o l d b e r g ' s work s u g g e s t s t h a t the body i s c a p a b l e o f r e d i s t r i b u t i n g p r o t e i n t o a c h i e v e a f u n c t i o n a l need o f s p e c i f i c m u s c l e s . In summary, a n a e r o b i c e x e r c i s e can i n d u c e muscle h y p e r t r o p h y which r e q u i r e s some a d d i t i o n a l p r o t e i n beyond maintenance n e e d s . However, the r a t e o f p r o t e i n a c c r e t i o n s u g g e s t s t h a t the i n c r e a s e d need i s not more than 7 grams o f p r o t e i n per d a y . R e l a t i v e l y few s t u d i e s have determined changes i n p r o t e i n t u r n o v e r d u r i n g and a f t e r anaerobic e x e r c i s e . I t has not been e s t a b l i s h e d i f any changes o c c u r i n the e f f i c i e n c y o f p r o t e i n g a i n d u r i n g a n a e r o b i c e x e r c i s e o r i f t h e t i m i n g o f p r o t e i n i n t a k e r e l a t i v e t o the exercise i s important. Amino A c i d M e t a b o l i s m A s s o c i a t e d w i t h A e r o b i c

Training

The r o l e o f p r o t e i n and amino a c i d s as a s o u r c e o f energy d u r i n g e x e r c i s e i s u n c l e a r . A s t r a n d (17) suggested t h a t " f u e l s f o r working muscles a r e l i m i t e d t o c a r b o h y d r a t e and f a t . " Statements such as t h i s one suggest t h a t p r o t e i n i s not used as a f u e l . However, i f we examine the c o m p o s i t i o n o f the American d i e t f o r nongrowing a d u l t s t h i s statement appears t o be an oversimplification. P r o t e i n a c c o u n t s f o r a p p r o x i m a t e l y 12% o f the d a i l y c a l o r i c i n t a k e w i t h 46% d e r i v e d from c a r b o h y d r a t e s and 42% from l i p i d s ( 2 ) . The p o t e n t i a l f o r use o f amino a c i d s f o r energy was f u r t h e r s u p p o r t e d by C a h i l l ( 1 8 ) . In h i s p u b l i c a t i o n " S t a r v a t i o n i n M a n , " he r e p o r t e d amino a c i d s t o be an i m p o r t a n t energy s o u r c e d u r i n g s t a r v a t i o n . S p e c i f i c a l l y , p r o t e i n breakdown i n s k e l e t a l muscle served as an i m p o r t a n t s o u r c e o f s u b s t r a t e f o r the process of gluconeogenesis.

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Protein and Amino

LAYMAN AND HENDRX I

Acid

Metabolism

0.3

10 PROTEIN

15 20 IN DIET (%)

F i g u r e 1. The r a t e o f p r o t e i n s y n t h e s i s i n s o l e u s muscles from r a t s f e d d i f f e r e n t l e v e l s o f d i e t a r y p r o t e i n . S y n t h e s i s was measured as the i n c o r p o r a t i o n o f a r a d i o a c t i v e amino a c i d ( t y r o s i n e ) i n t o muscle p r o t e i n s . Data from Ref. 16.

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Reviews by Ruderman (19) and A d i b i (20,21) i n d i c a t e t h a t the b r a n c h e d - c h a i n amino a c i d s , p a r t i c u l a r l y l e u c i n e , have an important r o l e along with a l a n i n e i n gluconeogenesis. L e u c i n e and the o t h e r two b r a n c h e d - c h a i n amino a c i d s a r e c a t a b o l i z e d i n s k e l e t a l m u s c l e . The n i t r o g e n t h a t i s removed from the b r a n c h e d c h a i n amino a c i d s i n s k e l e t a l muscle i s combined w i t h p y r u v a t e and r e t u r n e d t o the l i v e r as a l a n i n e . In the l i v e r t h e n i t r o g e n i s removed f o r u r e a p r o d u c t i o n and the carbon c h a i n i s u t i l i z e d as s u b s t r a t e f o r s y n t h e s i s o f g l u c o s e . A d i b i e t a l . (22) r e p o r t e d t h a t d u r i n g the c a t a b o l i c c o n d i t i o n s o f s t a r v a t i o n , o x i d a t i o n o f l e u c i n e and f a t t y a c i d s i n c r e a s e s i n s k e l e t a l m u s c l e s . While g l u c o s e o x i d a t i o n i s r e d u c e d , the c a p a c i t y f o r o x i d a t i o n o f the f a t t y a c i d p a l m i t a t e more than d o u b l e d , and l e u c i n e o x i d a t i o n i n c r e a s e d by a f a c t o r o f s i x . A h l b o r g e t a l . (23) extended these f i n d i n g s u s i n g s i x u n t r a i n e d a d u l t males e x e r c i s e d a t 30% V0o ax o bicycle ergometer. They examine b e f o r e and a f t e r 40 minute measured a r t e r i a l / v e n o u s d i f f e r e n c e s a c r o s s the l e g muscles v e r s u s the s p l a n c h n i c bed and found s i g n i f i c a n t d i f f e r e n c e s i n b l o o d l e v e l s o f a l a n i n e and the b r a n c h e d - c h a i n amino a c i d s . A l a n i n e i s removed from the b l o o d by the l i v e r f o r g l u c o n e o g e n e s i s and the uptake was i n c r e a s e d by e x e r c i s e . On the o t h e r hand, l e u c i n e and i s o l e u c i n e a r e r e l e a s e d by the l i v e r and t a k e n up by s k e l e t a l m u s c l e s . Both the r e l e a s e by l i v e r and the uptake by muscles a r e increased during exercise. These d a t a demonstrate a change i n amino a c i d f l u x d u r i n g e x e r c i s e which i s an i n c r e a s e i n the r e l e a s e o f b r a n c h e d - c h a i n amino a c i d s from v i s e r a i t i s s u e s t o s k e l e t a l muscles and the r e t u r n o f a l a n i n e as a p r e c u r s o r f o r glucose s y n t h e s i s . n

Table 2.

Amino A c i d

Arterial-Venous Exercise

D i f f e r e n c e i n Amino A c i d Uptake D u r i n g

S p l a n c h n i c Exchange (umol/min) Rest

Alanine

a

58

Leg Exchange (umol/min)

40 m i n .

Rest

90

-30

40 m i n . -45

Leucine

- 2.2

- 8.8

- 0.8

13.2

Isoleucine

- 1.0

- 2.9

- 0.4

8.2

S i x u n t r a i n e d males were e x e r c i s e d f o r 4 hours a t 30% V 0 2 on a b i c y c l e ergometer. P o s i t i v e numbers i n d i c a t e uptake and n e g a t i v e numbers i n d i c a t e r e l e a s e . From A h l b o r g et a l . (24). m a x

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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Metabolism

51

S u b s e q u e n t l y , Dohm e t a l . (24) demonstrated an i n c r e a s e d p r o d u c t i o n o f carbon d i o x i d e from l e u c i n e d u r i n g e x e r c i s e . They found a 50% i n c r e a s e i n CO2 p r o d u c t i o n i n muscle t i s s u e from trained rats. The study by Dohm e t a l . (24) u t i l i z e d a m o t o r - d r i v e n t r e a d m i l l w i t h an e i g h t degree i n c l i n e and r a n t h e a n i m a l s a t 35 meters p e r minute f o r 60 minutes p e r d a y , 6 days p e r week. These e x p e r i m e n t a l c o n d i t i o n s produce an e x e r c i s e i n t e n s i t y o f 75-80% o f V 0 . T h i s program was used f o r 6 t o 8 weeks. The e f f e c t s o f e x e r c i s e on b r a n c h e d - c h a i n amino a c i d s may be u n i q u e . The b r a n c h e d - c h a i n amino a c i d s a r e e s s e n t i a l i n t h e d i e t and a r e u n i q u e l y c a t a b o l i z e d i n s k e l e t a l m u s c l e s . These amino a c i d s may p r o v i d e an energy s o u r c e f o r muscles o r may s e r v e an intermediate r o l e i n m a i n t a i n i n g blood glucose through production o f a l a n i n e v i a t r a n s a m i n a t i o n w i t h p y r u v a t e i n muscles ( 1 9 ) . The uniqueness o f l e u c i n e can be f u r t h e r demonstrated by examining muscle p r o t e i n s y n t h e s i s . We have shown t h a t l e u c i n e has t h e a b i l i t y t o s t i m u l a t c a t a b o l i c c o n d i t i o n s suc o f l e u c i n e , p r o t e i n s y n t h e s i s can be s t i m u l a t e d 50% i n muscles from s t a r v e d r a t s . The s i g n i f i c a n c e o f t h i s e f f e c t remains c o n t r o v e r s i a l ; however, t h e i n v i t r o a c t i v i t y i s c l e a r and emphasizes t h e unique m e t a b o l i c p o t e n t i a l o f l e u c i n e . These s t u d i e s have demonstrated t h a t e x e r c i s e a f f e c t s amino a c i d metabolism w i t h s p e c i f i c e f f e c t s on l e u c i n e . Dohm e t a l . (26) extended t h e s e f i n d i n g s by s t u d y i n g t h e i n f l u e n c e o f e x e r c i s e on p r o t e i n s y n t h e s i s i n p e r f u s e d r a t m u s c l e s . They demonstrated t h a t e x e r c i s e decreased t h e r a t e o f p r o t e i n s y n t h e s i s and t h a t t h e l e v e l o f e x e r t i o n was i m p o r t a n t t o t h e magnitude o f t h e e f f e c t . M i l d e x e r c i s e produced by swimming r a t s f o r one hour d e c r e a s e d p r o t e i n s y n t h e s i s by 17%. While more i n t e n s e t r e a d m i l l r u n n i n g reduced s y n t h e s i s by 30% and an e x h a u s t i v e r u n o f t h r e e hours i n h i b i t e d s y n t h e s i s by 70%. These d a t a suggest t h a t e x e r c i s e may produce a c a t a b o l i c c o n d i t i o n i n muscles which would make amino a c i d s a v a i l a b l e f o r o x i d a t i o n and t h a t t h i s e f f e c t i s dependent on the i n t e n s i t y and d u r a t i o n o f t h e e x e r c i s e . U s i n g e x h a u s t i v e r u n n i n g , Dohm e t a l . (27) examined t h e magnitude o f t h e c a t a b o l i c e f f e c t . They r a n r a t s a t 28 meters p e r minute f o r 4 hours and measured t h e e x c r e t i o n o f u r i n a r y u r e a and 3 - m e t h y l h i s t i d i n e (Table 3 ) . Urea e x c r e t i o n i n c r e a s e d by 31% d u r i n g t h e f i r s t 12 hours a f t e r t h e e x h a u s t i v e bout o f e x e r c i s e , but r e t u r n e d t o normal d u r i n g t h e next 12 h o u r s . It i s interesting t o note t h e d e l a y e d e f f e c t . D u r i n g e x e r c i s e t h e r e i s decreased r e n a l c l e a r a n c e and t h e b l o o d u r e a i n c r e a s e s . P o s t - e x e r c i s e u r e a increases i n the u r i n e . U r i n a r y 3 - m e t h y l h i s t i d i n e , which i s an i n d i c a t o r o f t h e r a t e o f muscle p r o t e i n breakdown, a l s o i n c r e a s e d a f t e r the e x e r c i s e . However, t h e i n c r e a s e i n t h e 3 - m e t h y l h i s t i d i n e d i d not o c c u r u n t i l 12 t o 36 hours a f t e r t h e e x e r c i s e . Based on t h e s e f i n d i n g s , t h e s e i n v e s t i g a t o r s e s t i m a t e d t h a t 15 t o 20% o f the energy f o r endurance e x e r c i s e may come from p r o t e i n . I f t h i s i s t r u e a e r o b i c e x e r c i s e c o u l d double the d i e t a r y need f o r p r o t e i n . The s u g g e s t i o n t h a t e x e r c i s e produces a c a t a b o l i c c o n d i t i o n was f u r t h e r s u p p o r t e d by Rennie e t a l . (28) s t u d y i n g a e r o b i c e x e r c i s e i n humans. They e x e r c i s e d s i x male s u b j e c t s on a t r e a d m i l l f o r 3 3/4 hours a t 50% V 0 x measured t h e r a t e s 2 m a x

2 m a

a

n

d

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

NUTRT IO IN AND AEROBC I EXERCS IE

52 Table 3 .

E f f e c t o f E x h a u s t i v e Running on P r o t e i n M e t a b o l i s m i n Rats Urea E x c r e t i o n (mmol/kg) Control Exercised

Time A f t e r Exercise

F i r s t 12 h r s . Second 12 h r s . Second 24 h r s . From Dohm e t a l .

10.0 15.8 24.6

13.1* 17.7 28.4

3-Methylhistidine Excretion (mmol/kg) Exercised Control 10.4 11.4* 21.4*

9.4 7.8 17.8

(27).

o f p r o t e i n s y n t h e s i s an e x e r c i s e , the r a t e o f s y n t h e s i d e g r a d a t i o n i n c r e a s e d by 54%. T h i s study i s a l s o i m p o r t a n t because i t i s one o f the few s t u d i e s t o make measurements both d u r i n g and a f t e r t h e e x e r c i s e b o u t . P o s t - e x e r c i s e t h e r a t e o f s y n t h e s i s i n c r e a s e d above the i n i t i a l l e v e l s s u g g e s t i n g the recovery p a t t e r n a f t e r the e x e r c i s e . These p o s t - e x e r c i s e r e s u l t s a r e i m p o r t a n t i n a s s e s s i n g the impact o f e x e r c i s e on the n u t r i t i o n a l requirement. Table 4 .

P r o t e i n Turnover a t R e s t , D u r i n g , and A f t e r

Synthesis

Degradation

(mg o f n i t r o g e n / k g χ Rest Exercised Post-exercise

33.0 + 2.0 2 8 . 4 +_ 1.6 40.3+1.9

Exercise

hr) 26.5 + 2.1 4 0 . 9 +_ 2 . 6 35.4+1.2

S i x male s u b j e c t s were e x e r c i s e d on a t r e a d m i l l f o r 3 . 7 5 hours at 50% V 0 . From Rennie e t a l . ( 2 8 ) . 2 m a x

The mechanism t h a t produces i n c r e a s e d amino a c i d o x i d a t i o n d u r i n g e x e r c i s e i s unknown. White and Brooks (29) demonstrated a r e l a t i o n s h i p o f amino a c i d o x i d a t i o n t o use o f b l o o d g l u c o s e . Concomitant w i t h i n c r e a s e s i n t h e i n t e n s i t y o f e x e r c i s e and l e u c i n e o x i d a t i o n , t h e o x i d a t i o n o f g l u c o s e and a l a n i n e i n c r e a s e d . These d a t a i n c o m b i n a t i o n w i t h the e a r l i e r r e p o r t s o f i n c r e a s e d f l u x o f l e u c i n e t o s k e l e t a l muscles and a l a n i n e from muscles t o the l i v e r suggest t h a t the o x i d a t i o n o f amino a c i d s may be l i n k e d t o the need f o r g l u c o s e and t o g e n e r a t i o n o f s u b s t r a t e s f o r gluconeogenesis.

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

4.

LAYMAN AND HENDRX I

53 Protein and Amino

Acid

Metabolism

The r e l a t i o n s h i p o f amino a c i d o x i d a t i o n t o c a r b o h y d r a t e s t a t u s was examined by Lemon and M u l l i n ( 3 0 ) . Employing s i x p h y s i c a l l y a c t i v e men, t h e s e i n v e s t i g a t o r s m a n i p u l a t e d t h e d i e t a r y i n t a k e o f c a r b o h y d r a t e t o determine the e f f e c t s o f a e r o b i c e x e r c i s e on p r o t e i n c a t a b o l i s m . T h e i r d i e t s c o n s i s t e d o f a s i n g l e c a r b o h y d r a t e - f r e e meal f o l l o w e d by an o v e r n i g h t f a s t o r t h r e e days o f h i g h c a r b o h y d r a t e f e e d i n g . Based on p r e v i o u s l y p u b l i s h e d r e p o r t s , t h e s e d i e t s were assumed t o p r o d u c e , r e s p e c t i v e l y , d e p l e t i o n o r e l e v a t i o n o f muscle g l y c o g e n s t o r e s . They e s t i m a t e d p r o t e i n c a t a b o l i s m from serum u r e a c o n c e n t r a t i o n and the n i t r o g e n c o n t e n t o f sweat b e f o r e and a f t e r 1 hour o f moderate i n t e n s i t y bicycle exercise. The e x e r c i s e bout produced no change i n serum u r e a i n the group f e d the h i g h c a r b o h y d r a t e d i e t , b u t d i d produce some l o s s o f u r e a by sweat (Table 5 ) . However, under the same e x e r c i s e c o n d i t i o n s f o l l o w i n g the carbohydrate-free meal, these men e x p e r i e n c e d s i g n i f i c a n t e l e v a t i o n s i n both b l o o d u r e a and sweat n i t r o g e n . These d a t amino a c i d s d u r i n g e x e r c i s availability.

Table 5 .

Loss o f N i t r o g e n V i a Sweat a f t e r A e r o b i c E x e r c i s e

Sweat Urea (mg n i t r o g e n / h r ) Rest CHO-Loaded CHO-Depleted

10 600 1450

S i x males were e x e r c i s e d on a b i c y c l e ergometer a t 61% V0 f o r 1 hour. From Lemon & M u l l i n ( 3 0 ) . 2 m a x

P r o t e i n Requirements f o r Endurance E x e r c i s e The i m p a c t o f a e r o b i c e x e r c i s e on p r o t e i n r e q u i r e m e n t s remains uncertain. E x e r c i s e c l e a r l y can d i s r u p t p r o t e i n m e t a b o l i s m , both p r o t e i n t u r n o v e r and amino a c i d o x i d a t i o n . However, i t remains t o be determined i f t h e s e e f f e c t s a r e a c u t e e f f e c t s o f e x h a u s t i v e e x e r c i s e o r i f moderate e x e r c i s e i n t r a i n e d i n d i v i d u a l s s t i l l produces i n c r e a s e d o x i d a t i o n o f amino a c i d s . The work by Wolfe e t a l . ( 3 1 , 3 2 ) s e r v e s t o emphasize some o f t h e s e p r o b l e m s . They u t i l i z e d a m i l d b i c y c l e e x e r c i s e and examined t h e e f f e c t s on l e u c i n e o x i d a t i o n and u r e a p r o d u c t i o n . Four u n t r a i n e d men were e x e r c i s e d f o r 105 minutes on a b i c y c l e ergometer a t an i n t e n s i t y d e s i g n e d t o m a i n t a i n a h e a r t r a t e o f 110 beats/minute ( a p p r o x i m a t e l y 30% V 0 ). Comparing a p r e - e x e r c i s e r e s t p e r i o d t o i m m e d i a t e l y p o s t - e x e r c i s e , they found a 2 - to 3 - f o l d i n c r e a s e i n t h e p r o d u c t i o n o f C 0 from l e u c i n e , b u t they found no i n c r e a s e i n u r e a p r o d u c t i o n . They a l s o determined t h a t w h i l e m i l d e x e r c i s e i n c r e a s e d o x i d a t i o n o f l e u c i n e , t h e r e was no e f f e c t on the c a t a b o l i s m o f a n o t h e r e s s e n t i a l amino 2 m a x

2

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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NUTRT IO IN AND AEROBC I EXERCS IE

a c i d , l y s i n e ( 3 2 ) . These s t u d i e s demonstrate t h a t the e f f e c t o f e x e r c i s e on l e u c i n e o x i d a t i o n can o c c u r a t very low e x e r c i s e i n t e n s i t y , but they a l s o suggest t h a t e x e r c i s e may have a unique e f f e c t on l e u c i n e m e t a b o l i s m , a t l e a s t under m i l d e x e r c i s e conditions. A r e c e n t paper f u r t h e r q u e s t i o n s the p o t e n t i a l impact o f e x e r c i s e on p r o t e i n r e q u i r e m e n t ( 3 3 ) . These i n v e s t i g a t o r s s t a t e t h a t w h i l e p e r t r u b a t i o n s i n p r o t e T n and amino a c i d metabolism may e x i s t d u r i n g the i n i t i a l a d a p t a t i o n t o e x e r c i s e , no one has demonstrated a l o n g - t e r m c a t a b o l i c e f f e c t o f e x e r c i s e on l e a n body mass. F u r t h e r , they suggest t h a t the r e s u l t s from many o f the e x e r c i s e s t u d i e s a r e confounded by a f a i l u r e t o d e f i n e o r c o n t r o l energy i n t a k e . In t h e i r experiments u s i n g low i n t e n s i t y e x e r c i s e , they found a n e g a t i v e n i t r o g e n b a l a n c e i n young men r e c e i v i n g a m a r g i n a l p r o t e i n i n t a k e ( 0 . 5 7 g/kg). U s i n g the same p r o t e i n i n t a k e and e x e r c i s e l e v e l s , n i t r o g e n b a l a n c e became p o s i t i v e when the energy i n t a k e was i n c r e a s e by a d d i t i o n a l e x e r c i s e major e f f e c t o f e x e r c i s e on n i t r o g e n b a l a n c e i s a t r a n s i e n t change d u r i n g t h e i n i t i a l a d a p t a t i o n t o a new e x e r c i s e program but t h a t w i t h adequate energy i n t a k e the e f f i c i e n c y o f p r o t e i n u t i l i z a t i o n a c t u a l l y improves d u r i n g e x e r c i s e . P r e l i m i n a r y work i n our l a b o r a t o r y s u g g e s t s t h a t the e f f e c t o f e x e r c i s e on l e u c i n e o x i d a t i o n i s not j u s t a t r a n s i e n t e f f e c t o f b e g i n n i n g an e x e r c i s e program, and t h a t the magnitude o f the e f f e c t i s dependent on the d u r a t i o n o f the e x e r c i s e ( F i g . 2 ) . Male r a t s were t r a i n e d t o run on a t r e a d m i l l a t 28 meters/minute ( a p p r o x i m a t e l y 80% V 0 ) f o r 50 o r 120 minutes/day. After 6 weeks o f t r a i n i n g t h e r a t e o f l e u c i n e o x i d a t i o n was d e t e r m i n e d . The c u r v e s i n F i g u r e 2 i n d i c a t e t h a t e x e r c i s e i n c r e a s e s l e u c i n e o x i d a t i o n and t h a t the s t i m u l a t i o n may be d i r e c t l y r e l a t e d t o duration of exercise. 2 m a x

0

30 60 90 120 TIME A F T E R L E U C I N E I N J E C T I O N (MIN)

F i g u r e 2 . The e f f e c t s o f t h e d u r a t i o n o f e x e r c i s e on the p r o d u c t i o n o f r a d i o a c t i v e C 0 from l ^ C - l a b e l e d l e u c i n e (see t e x t ) . 2

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

4. LAYMAN AND HENDRX I

Protein and Amino

Acid

Metabolism

Summary E a r l y r e s e a r c h on p r o t e i n r e q u i r e m e n t s e s t a b l i s h e d t h a t p r o t e i n was not a major f u e l f o r e x e r c i s e , and t h a t f a t and c a r b o h y d r a t e s were q u a n t i t a t i v e l y more i m p o r t a n t . The Recommended D i e t a r y A l l o w a n c e (RDA) f o r p r o t e i n i s 0 . 8 grams per k i l o g r a m o f body weight ( 0 . 3 6 grams/pound). These g u i d e l i n e s suggest t h a t p r o t e i n needs range from a p p r o x i m a t e l y 40 t o 90 grams p e r day depending on body w e i g h t . C u r r e n t l y , the average d a i l y i n t a k e o f p r o t e i n i n t h e U n i t e d S t a t e s i s 100-110 grams p e r d a y , which s u g g e s t s t h a t s u p p l e m e n t a l p r o t e i n i s u n l i k e l y t o be n e c e s s a r y f o r r o u t i n e exercise. However, r e c e n t experiments w i t h e x h a u s t i v e e x e r c i s e have r a i s e d a d d i t i o n a l q u e s t i o n s about the needs f o r p r o t e i n during aerobic exercise. E x e r c i s e i s known t o have a c u t e c a t a b o l i c e f f e c t s on muscle protein turnover. During e x e r c i s e p r o t e i n s n y t h e s i s i s depressed which l e a d s t o p r o t e i n c a t a b o l i s m r e l a t i v e l y s h o r t e x e r c i s e bout on 24-hour p r o t e i n needs i s u n c l e a r . A n a e r o b i c e x e r c i s e can produce h y p e r t r o p h y o f s p e c i f i c muscles depending on the type o f t r a i n i n g u t i l i z e d . The h y p e r t r o p h y i s due t o a p o s i t i v e b a l a n c e i n p r o t e i n t u r n o v e r which appears t o be produced by an i n c r e a s e i n the r a t e o f p r o t e i n s y n t h e s i s a f t e r exercise. The i n c r e a s e d need f o r p r o t e i n d u r i n g a n a e r o b i c e x e r c i s e i s u n l i k e l y t o be more than 7 grams p e r d a y . A e r o b i c e x e r c i s e u s u a l l y i n c r e a s e s the p e r c e n t a g e o f muscle mass due to a d e c r e a s e i n body f a t , but produces no a b s o l u t e change i n t h e amount o f m u s c l e . A e r o b i c e x e r c i s e has been shown t o a l t e r p r o t e i n metabolism i n c l u d i n g i n c r e a s e s i n amino a c i d o x i d a t i o n w i t h s p e c i f i c e f f e c t s on the b r a n c h e d - c h a i n amino a c i d l e u c i n e , i n c r e a s e d u r i n a r y u r e a , and i n c r e a s e d sweat n i t r o g e n . The magnitude o f each o f t h e s e e f f e c t s appears t o depend on t h e i n t e n s i t y and d u r a t i o n o f the a c t i v i t y w i t h l a r g e r e f f e c t s o c c u r r i n g a t more e x h a u s t i v e l e v e l s . The a b s o l u t e e f f e c t s o f a e r o b i c e x e r c i s e on the r e q u i r e m e n t s f o r p r o t e i n o r a s p e c i f i c e s s e n t i a l amino a c i d remain t o be d e t e r m i n e d . However, because a e r o b i c e x e r c i s e produces changes i n amino a c i d m e t a b o l i s m , i t i s i m p o r t a n t f o r i n d i v i d u a l s w i t h the h i g h e s t p r o t e i n n e e d s , such as growing c h i l d r e n and a d o l e s c e n t s , women d u r i n g pregnancy and l a c t a t i o n , and i n d i v i d u a l s on low c a l o r i c d i e t s , t o m a i n t a i n adequate p r o t e i n i n t a k e s when p a r t i c i p a t i n g i n a e r o b i c e x e r c i s e .

Literature Cited 1. Guthrie, H. (1983) In: Introductory Nutrition. Fifth Edition. C.V. Mosby Co., St. Louis, MO. 2. Whitney, E.N. (1982) In: Nutrition Concepts and Controversies. Second Edition. West Publishing Co., St. Paul, MN. 3. Recommended Dietary Allowances. (1980) Protein and amino acids. Ninth Edition. National Academy of Sciences, Washington, D.C., pp. 39-54.

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4. Lemon, P.W.R. & Nagle, F.J. (1981) Effects of exercise on protein and amino acid metabolism. Med. Sci. Sports & Exercise 13, 141-149. 5. Goodman, M.N. & Ruderman, N.B. (1982) Influence of muscle use on amino acid metabolism. In: Exercise and Sport Sciences Reviews. R.L. Terjung, ed., pp. 1-26. The Franklin Institute, Philadelphia, PA. 6. Evans, W.J., Fisher, E.C., Hoerr, R.A. & Young, V.R. (1983) Protein metabolism and endurance exercise. Physician & Sportmedicine 11, 63-72. 7. Waterlow, J.C., Garlick, P.J. & Millward, D.J. (1978) In: Protein Turnover in Mammalian Tissues and in the Whole Body. Elsevier/North Holland NY 8. Wolfe, R.R. (1984) Radioisotope and Stable Isotope/Mass Spectrometry Methods. Alan R. Liss, Inc., NY. 9. Misner, J.E., Boileau, R.A., Massey, B.H. & Mayhew, J.L. (1974) Alterations in the body composition of adult men during selected physical training programs. J. Amer. Geriatric Soc. 22, 33-38. 10. Goldspink, G. (1964) The combined effects of exercise and reduced food intake on skeletal muscle fibers. J. Cell. Comp. Physiol. 63, 209-216. 11. Goldberg, A.L. (1967) Work-induced growth of skeletal muscle in normal and hypophysectomized rats. Am. J. Physiol. 213, 1193-1198. 12. Goldberg, A.L. (1971) Biochemical events during hypertrophy of skeletal muscle. In: Cardiac Hypertrophy. N.R. Alpert, ed., pp. 301-314. Academic Press, NY. 13. Goldspink, D.F. (1978) The influence of passive stretch on the growth and protein turnover of the denervated extensor digitorium longus muscle. Biochem. J. 174, 595-602. 14. Laurent, G.J., Sparrow, M.P. & Millward, D.J. (1978) Muscle protein turnover in the adult fowl II. Changes in rates of protein synthesis and breakdown during hypertrophy of the anterior and posterior latissimus dorsi muscle. Biochem. J. 176, 407-417. 15. Durmin, J.V.G.A. (1978) Protein requirements and physical activity. In: Nutrition, Physical Fitness, and Health. J. Parizkova & V.A. Rogozkin, eds., pp. 53-60. University Park Press, Baltimore, MD.

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

4. LAYMAN AND HENDRIX

Protein and Amino Acid Metabolism

16. Smith, C.K., Durschlag, R.P. & Layman, D.K. (1982) Response of skeletal muscle protein synthesis and breakdown to levels of dietary protein and fat during growth in weanling rats. J. Nutr. 112, 255-262. 17. Astrand, P.O. (1979) Nutrition and physical performance. In: Nutrition and the World Food Problem, p. 63. Basel:Karger Press. 18. Cahill, G.F. (1970) Starvation in man. The New England Journal Medicine, March 19, 668-675. 19. Ruderman, N.B. (1975) Muscle amino acid metabolism and gluconeogenesis. Ann. Rev. Med. 26, 245-258. 20. Adibi, S.A. (1976) Metabolis in altered nutrition

f branched-chai amin acid

21. Hogg, S.A., Morse, E.L. & Adibi, S.A. (1982) Effect of exercise on rates of oxidation, turnover, and plasma clearance of leucine in human subjects. Amer. J. Physiol. 242, E407-E410. 22. Adibi, S.A., Krzysik, B.A. & Morse, E.L. (1974) Oxidative energy metabolism in the skeletal muscle: biochemical and ultrastructural evidence for adaptive changes. J. Lab. Clin. Invest. 83, 548-562. 23. Ahlborg, G., Felig, P., Hagenfeldt, L., Hendler, R. & Wahren, J. (1974) Substrate turnover during prolonged exercise in man. J. Clin. Invest. 53, 1080-1090. 24. Dohm, G.L., Hecker, A.L., Brown, W.E., Klain, G.J., Puente, F.R., Askew, E.W. & Beecher, G.R. (1977) Adaptation of protein metabolism to endurance training. Biochem. J. 164, 705-708. 25. Hong, S.C. & Layman, D.K. (1984) Effects of leucine on in vitro protein synthesis and degradation in rat skeletal muscles. J. Nutr. 114, 1204-1212. 26. Dohm, G.L., Tapscott, E.B., Barakat, H.A. & Kasperek, G.J. (1982) Measurement of in vivo protein synthesis in rats during an exercise bout. Biochem. Med. 27, 367-373. 27. Dohm, G.L., Williams, R.T., Kasperek, G.J. & van Rij, A.M. (1982) Increased excretion of urea and N -methylhistidine by rats and humans after a bout of exercise. J. Appl. Physiol. 52, 27-33. T

28. Rennie, M.J., Edwards, R.N.T., Krywawych, S., Davies, C.T.M., Halliday, D., Waterlow, J.C. & Millward, D.J. (1981) Effect of exercise on protein turnover in man. Clin. Sci. 61, 627-639.

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29. White, T.P. & Brooks, G.A. (1981) U -C glucose, -alanine, and -leucine oxidation in rats at rest and two intensities of running. Am. J. Physiol. 240, E155-E165. 30. Lemon, P.W.R. & Mullin, J.P. (1980) Effect of initial muscle glycogen levels on protein catabolism during exercise. J. Appl. Physiol. 48, 624-629. 31. Wolfe, R.R., Goodenough, R.D., Wolfe, M.H., Royle, G.T. & Nadel, E.R. (1982) Isotopic analysis of leucine and urea metabolism in exercising humans. J. Appl. Physiol. 52, 458-466. 32. Wolfe, R.R., Wolfe, M.H., Nadel, E.R. & Shaw, J.H.F. (1984) Isotopic determination of amino acid-urea interactions in exercise in humans J Appl Physiol 56 221-229 33. Butterfield, G.E. improves protein utilization in young men. Brit. J. Nutr. 51, 171-184. RECEIVED

June 21, 1985

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

5 The Effect of Exercise on Lipid and Lipoprotein Metabolism P. M . Kris-Etherton Nutrition Program, The Pennsylvania State University, University Park, PA 16802

Associations Between Physica Since the late 1960s, the incidence of coronary heart disease (CHD) has decreased in the United States (1). The Surgeon General has attributed this decline to major changes in lifestyle made by Americans (2). Specifically, fewer people smoke, more people monitor their blood pressure and daily stress, many have adopted leaner diets that are lower in cholesterol and saturated fat, and more Americans are participating in daily exercise. According to the results of a Gallup Poll, twice as many Americans reported exercising daily in 1977 as in 1960 (3). Currently, it is estimated that 27-30 million Americans jog a minimum of 1-3 miles weekly, and approximately one-half of American adults report participating in some form of exercise daily. The association between occupational and leisure time physical activity and the incidence of CHD has been recognized since the early 1950s. The incidence of fatal ischemic heart disease (IHD) was two times greater in the professional and business classes than in unskilled workers in Great Britian (4). Bus drivers (who have a low l e v e l of occupational physical a c t i v i t y ) had a higher incidence of mortality from IHD than conductors (who had a higher l e v e l of occupational physical a c t i v i t y ) (5). Ten years l a t e r i t was reported that postal clerks had higher death rates from IHD than mail c a r r i e r s (6,7). Other studies published throughout the 1960s, however, f a i l e d to show a relationship between occupational physical a c t i v i t y and IHD (8-10). Studies published during the 1950s and 1960s that examined the relationship between occupational physical a c t i v i t y and CHD were generally not designed to assess l e i s u r e time physical a c t i v i t y . The f a i l u r e to account for a c t i v i t y during l e i s u r e time probably explains the disparate findings of these epidemiological studies. However, i n three recent studies, where occupational and l e i s u r e time physical a c t i v i t y were both assessed, exercise was associated with a lower incidence of CHD (11-13). In the Framingham study, a prospective investigation was done examining the relationship between l e v e l of physical a c t i v i t y and mortality due to cardiovascular disease (CVD) and IHD. 0097-6156/86/0294-0059$06.25/0 © 1986 American Chemical Society

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Approximately 2,000 men and 2,000 women completed a questionnaire designed to assess t h e i r l e v e l of physical a c t i v i t y . They were studied for fourteen years and were observed for the manifestations of CVD. Death due to CVD, IHD, and a l l other causes decreased i n men as t h e i r physical a c t i v i t y increased. After age and associated cardiovascular r i s k factors were taken into account, however, the relationship of physical a c t i v i t y to o v e r a l l mortality persisted but was diminished. Kannel and Sorlie (11) reported a similar relationship between physical a c t i v i t y and mortality due to CVD and IHD i n men when other r i s k factors were considered. In women, however, while there was a s t a t i s t i c a l l y s i g n i f i c a n t relationship between physical a c t i v i t y and mortality due to CVD, t h i s association disappeared when an adjustment was made for age and other r i s k factors. The authors concluded that exercise i s indeed a protective factor against death from coronary disease, but i t s impact i s not as strong as other r i s k factors. Cross-Sectional and Longitudinal Studies on Healthy Subjects, Persons with Hyperlipidemia and Survivors of a Myocardial Infarct Recognition of a b e n e f i c i a l effect of exercise on the incidence of CHD has led to numerous cross-sectional and longitudinal studies designed to examine the influence of physical a c t i v i t y on major coronary r i s k factors, with p a r t i c u l a r emphasis on plasma l i p i d s and lipoproteins. A number of comprehensive reviews have summarized these studies (14-18). In general, i n cross-sectional studies, high density lipoprotein (HDL) cholesterol i s elevated (14) and t o t a l plasma and very low density lipoprotein (VLDL) t r i g l y c e r i d e s are lower i n endurance trained subjects than in sedentary control subjects (14). In a study of 23 top-level male athletes, Lehtonen and V i i k a r i (19) found a s t a t i s t i c a l l y s i g n i f i c a n t relationship between the number of kilometers that the athletes ran or skied weekly and t h e i r plasma HDL cholesterol concentration (P

H 0 +02 2

2

Formation of collagen cross-links

Tyrosinase

Copper and Zinc i n Aerobic Metabolism. Cytochrome oxidase, the termi n a l oxidase i n the electron transport chain contains an atom of copper. On this enzyme the protons and electrons generated during oxidative metabolism combine with elemental oxygen to form water. During copper deficiency the tissue concentration of cytochrome o x i dase i s reduced. While the effects of lower cytochrome oxidase act i v i t y on exercise has not been described, i t i s l i k e l y that aerobic energy metabolism w i l l be diminished. This effect of copper d e f i ciency was f i r s t described i n animals with myelin aplasis — the degeneration myelin (86). The oxidative process of phospholipid synthesis, a primary component of myelin, was depressed. L i v e r mitochondria had impaired respiratory a c t i v i t y (87). Cytochrome oxidase a c t i v i t y was also depressed i n brain, heart and l i v e r . Superoxide dismutase, a copper- and zinc-containing mitochond r i a l enzyme, may play a s i g n i f i c a n t role i n exercise performance (88). Superoxide dismutase catalyzes the d e t o x i f i c a t i o n of oxygenfree radicals to oxygen and hydrogen peroxide. During exercise, i t i s proposed that the energy-yielding reactions of the mitochondria also produce p o t e n t i a l l y damaging superoxide. The rate of production of this compound i s d i r e c t l y proportional to the rate of oxygen consumption. Since endurance training increases the t o t a l amount of mitochondria, the trained i n d i v i d u a l would have more dismutase and thus should be able to detoxify more superoxide. I t would therefore appear that endurance training may decrease c e l l u l a r damage caused by l i p i d membrane peroxidation. Since superoxide dismutase a c t i v i t y can be impaired by copper or zinc deficiency, the mechanism of t h i s act i o n should be experimentally explored. Bone Disorders. Copper deficiency causes gross s k e l e t a l abnormalit i e s i n both humans and animal systems. Recently, our laboratory was able to induce experimental osteopenia i n rats moderately d e f i cient i n copper and manganese (89). After one year on a low copper, low manganese d i e t , these animals showed reduced mineralization of calcium i n femurs (Figure 8). The primary biochemical l e s i o n i n the

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

NUTRITION AND AEROBIC EXERCISE

F i g u r e 8. Radiographs o f humeri from r a t s r a i s e d on e i t h e r a cont r o l - n o r m a l ( M n C u ) , o r a moderate-manganese, moderate-copper (Mn C u ) , o r a manganese-free (Mn^ C u ) d i e t f o r 12 months. n

m

m

n

n

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Trace Elements

7. MCDONALD AND SALTMAN

and Calcium

Status

101

bones of copper-deficient animals i s a reduction i n the a c t i v i t y of the copper enzyme l y s y l oxidase, which plays a central role i n the formation of cross-links i n collagen and e l a s t i n (90). In a reaction that has not been f u l l y elucidated, l y s y l oxidase catalyzes the o x i ­ dative deamination of l y s y l and hydroxylysyl residues. The r e s u l t i n g a l l y s y l and hydroxyallysyl residues c r o s s - l i n k by spontaneously form­ ing S c h i f f s bases. C a l c i f i c a t i o n i s reduced i n the altered organic matrix. f

Cardiovascular Disorders and Copper. Sudden cardiac f a i l u r e has been associated with copper deficiency (9Γ). There are two a t t r a c ­ t i v e mechanisms. F i r s t , the coronary arteries and aorta may become weakened from an i n a b i l i t y to synthesize e l a s t i n due to a decrease i n l y s y l oxidase a c t i v i t y . Rupture of these major blood vessels has been shown to cause sudden death i n animals suffering from copper de­ f i c i e n c y . Second, a decrease i n cytochrome oxidase a c t i v i t during copper deficiency impair creases the r i s k of hypertrophy output congestive heart f a i l u r e , i s exacerbated by hypochromic anemia also caused by copper deficiency. Zinc and Immunity. Zinc i s required for immunocompetence. Recently published reviews have detailed the role of zinc (92-95). Early c l i n i c a l descriptions of zinc deficiency and impaired immune function were f i r s t reported by Brummerstedt et al.(96) who reported that calves with a genetically acquired i n a b i l i t y to absorb zinc suffered from stunted growth, several skin disorders, v i r a l and fungal i n f e c ­ tions, and atrophied thymus glands. These symptoms could be r e ­ versed by the administration of large amounts of dietary zinc. The mechanism by which zinc mediates immune function i s not clear; the depression of DNA synthesis during zinc deficiency i s im­ p l i c a t e d (93). McDaffrey et a l . (97) demonstrated that a zinc-con­ taining DNA polymerase i s present i n the thymus but does not appear i n the mature Τ c e l l . A reduction i n thymus tissue caused by zinc deficiency would adversely a f f e c t the immunocompetence of thymocytes. This hypothesis has been confirmed i n experiments where a sharp drop i n the thymic hormone i s induced by zinc deficiency. While many a jogger has suggested that exercise can improve h i s / her resistance to i n f e c t i o u s diseases, conclusive s c i e n t i f i c evidence that exercise enhances immune response has yet to be presented. Ex­ perimental zinc deficiency i n animals may provide a workable model for such investigations. It i s well known that exercise induces hy­ pertrophy of adrenal glands with a concomitant increase i n the serum concentration of glucocorticoids. Zinc deficiency decreases Τ c e l l helper a c t i v i t y and thymic involution followed by a r i s e i n gluco­ corticoids (98). The observations cited above suggest that i t i s possible to delineate experimentally the roles of zinc and exercise i n immune response. Summary The e s s e n t i a l i t y of the trace elements and calcium for optimal phys­ i c a l performance i s clear. The amount of dietary intake of these elements to achieve these levels i s less clear. Our best estimates

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NUTRITION AND AEROBIC EXERCISE

are those given by the U.S. RDA's (Table IV). I t i s rather simple to read and understand the dosage i n those tables. But i t i s d i f f i c u l t to be certain that the food intake does indeed supply the necessary amounts. Most athletes who a v a i l themselves of a wide v a r i e t y of foods including adequate meats and dairy products and who consume calories s u f f i c i e n t to meet energy requirements, should be optimally nourished. The need for supplemental trace elements i s more i n the nature of "insurance" of a t h l e t i c potency both p h y s i o l o g i c a l l y and psychologically. Certainly any regimen that suggests "mega-dosing" of trace elements should be avoided. Every important trace element and calcium i s toxic at high concentrations. The body i s not able to adequately control uptake and storage of those v i t a l nutrients at excessive concentrations. Further, there i s no reason to believe that exercise increases the demand of the body f o r trace elements much above that for the normal healthy non-competitive adult. In the f i n a l analysis, the best friend of the athlete remains "good genes mental stamina, and d i s c i p l i n e Table IV. Food and N u t r i t i o n Board, National Academy of SciencesRecommended Daily Dietary Allowances for Adults Iron ( g)

Calcium* (mg)

Males

10

800

2

15

Females

18

800

2

15

m

Copper** (mg)

Zinc (mg)

*The National Academy i s expected to increase t h i s requirement to 1000-1200 mg. - " T h i s i s a suggested f o r copper.

amount.

No o f f i c i a l RDA has been e s t a b l i s h e d

Acknowledgment s We wish to thank Dr. Linda Strause for advice and counsel. This work was supported i n part by grants from the Weingart Foundation and USPHS NIH Research Grant AM 12386.

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67. Chavapil, M.; Bartos, D.; Bartos, F. Gerontologia 1973, 19, 263-77. 68. Kiishinen, Α.; Heikkinen, J. Appl. Physiol. 1978, 44, 50-4. 69. Cuthberton, D. P. Biochem. J. 1929, 23, 1328-45. 70. Issekutz, B.; Blizzard, J. J.; Birkhead, N. C.; Rodahl, K. J. Appl. Physiol. 1966, 21, 1013-20. 71. Nordin, Β. E. C.; Hodgkinson, Α.; Peacock, M. Clin. Orthop. 1967, 52, 293-322. 72. Howard, J. E.; Parson, W.; Binghan, R. S. Bull. Johns Hopkins Hosp. 1945, 291-313. 73. Whedon, G. D.; Shorr, E. J. Clin. Invest. 1957, 36, 966-81. 74. McDonald, R. Unpublished data, 1984. 75. Bogert, L. J.; Kirkpatrick, Ε. E. J. Biol. Chem. 1922, 54, 375-86. 76. Shohl, A. T.; Sato, A. J. Biol. Chem. 1923, 58, 257-66. 77. Lemann, J.; Litzou J R.; Lennon Ε J J Clin Invest 1967, 46, 1318-28 78. Greenberg, A. J.; , ; McCrory, , 69, 610-18. 79. Walser, M. In "Renal Pharmacology"; Appleton-Century-Crofts: New York, 1971; p. 21. 80. Underwood, E. J. In "Trace Elements in Human and Animal Nutri­ tion"; Academic Press: New York, 1977; p. 56. 81. O'Dell, B. L. In "Present Knowledge in Nutrition, 5th Ed."; Nutrition Foundation: Washington, D. C. 1984; p. 506. 82. Li, T-K.; Vallee, B. C. In "Modern Nutrition in Health and Disease, 6th Ed."; Goodhard, R. S.; Shils, M. E. Eds., Lea and Febiger: Philadelphia, 1980; p. 408. 83. Prasad, A. S. Nutrition Reviews 1983, 41, 197-208. 84. Underwood, E. J. In "Trace Elements in Human and Animal Nutri­ tion"; Academic Press: New York, 1977; p. 196. 85. Sandstead, H. H.; Evans, G. W. In "Present Knowledge in Nutri­ tion, 5th Ed."; Nutrition Foundation: Washington, D. C., 1984, p. 479. 86. Fell, B. F.; Mills, R. B.; Boyne, R. Res. Vet. Sci. 1965, 6, 10-14. 87. Gallagher, C. H.; Reeve, V. E. Aust. J. Exp. Biol. Med. Sci. 1971, 49, 21-31. 88. Davies, K. J.; Packer, L.; Brooks, G. A. Arch. Biochem. Biophys. 1982, 215, 260-265. 89. Strause, L.; Hegenauer, J.; Saltman, P.; Cone, R.; Resnick, D. Am. J. Clin. Nutr. Submitted, 1984. 90. Siegal, R. C.; Pinnell, S. R.; Markin, G. R. Biochemistry 1970, 9, 4486-90. 91. Gubler, C. J.; Cartwright, G. E.; Wintrobe, M. M. J. Biol. Chem. 1957, 224, 533-46. 92. Schloen, L. H.; Fernades, G.; Garofalo, J. Α.; Good, R. A. Clinical Bulletin 1979, 9, 63-75. 93. Good, R. Α.; Fernades, G.; Garofalo, J. Α.; Cunningham-Rundles, C.; Iwata, J.; West, A. In "Clinical Biochemical and Nutri­ tional Aspects of Trace Elements"; Prasad, A. S. Eds.; Alan R. Liss, Inc.: New York, 1982, p. 189. 94. Chandra, R. K.; Dayton, B. Nutrition Research 1982, 2, 721-33. 95. Prasad, A. S. Nutrition Reviews 1983, 41, 197-208.

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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96. Brummerstedt, E.; Flagstad, T.; Basse, Α.; Andersen, E. Acta Pathol. Microbiol. Scand. 1971, 79, 686-88. 97. McCaffrey, R.; Smoler, D. F.; Baltimore, D. L. Proc. Nat. Acad. Sci. 1973, 70, 521-25. 98. De Pasquale-Jardiew, R.; Fraker, P. J. J. Nutr. 1979, 109, 1847-55. RECEIVED April 19, 1985

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

8 Water and Electrolytes John E. Greenleaf and Michael H . Harrison Laboratory for Human Environmental Physiology, Biomedical Research Division, NASA Ames Research Center

Under optimal conditions humans have been able to survive about 10 minutes without oxygen, up to 18 days without water, but nearly 60 days without food. Despite the fact that oxidation of nutrients produces water, there is a longer lasting supply of foodstuffs within the body than water. Part of the fatigue mechanism occurring during physical exercise can be attributed to fluid loss (dehydration) from the body and possibly to fluid-electrolyte shifts within the body. There is no adaptation to successive periods of dehydration and the performance of the strongest and fittest people will deteriorate rapidly with dehydration. When compared with the daily variability of many physico-chemical parameters, the least variability is found in body temperature, and plasma sodium, chloride, calcium, and osmolality (1). There is a close association between thermoregulation and the sodium, calcium, and osmotic concentration of the extracellular fluid; increases in plasma sodium concentration (hypernatremia) and plasma osmotic concentration (hyperosmotemia) tend to increase body temperature while hypercalcemia tends to decrease body temperature (2-4). The precise control of the concentration of these ions suggests that their functions are of major importance for optimal physiological homeostasis and s u r v i v a l of the organism. In t h i s paper we w i l l discuss the anatomy of the f l u i d spaces i n the body, the f l u i d s h i f t s and losses during exercise and their effects on performance, and t h i r s t and drinking during exercise with comments on carbohydrate ingestion. Anatomy of Body F l u i d Compartments Total body water i s a r b i t r a r i l y divided into that contained within c e l l s ( c e l l u l a r ) and that located outside the c e l l s ( e x t r a c e l l u l a r ) . The e x t r a c e l l u l a r water i s further divided into that contained within the vascular system excluding the erythrocytes (plasma), and that located outside the vascular system and outside the c e l l s ( i n t e r s t i t i a l f l u i d ) (Figure 1 ) . This chapter not subject to U.S. copyright. Published 1986, American Chemical Society

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NUTRT IO IN AND AEROBC I EXERCS IE

Approximate volumes and p e r c e n t o f body weight o f t h e v a r i o u s f l u i d compartments, and a d a i l y water b a l a n c e o f a r e s t i n g 80-kg man ( 5 ) , a r e g i v e n i n T a b l e s I and I I . W i t h e x e r c i s e , t h e sweat l o s s and beverage ( f l u i d ) i n t a k e would be g r e a t e r . O x i d a t i o n o f 1 gram o f v a r i o u s f o o d s t u f f s would y i e l d t h e f o l l o w i n g approximate water p r o d u c t i o n ( 5 ) : monosaccharides ( g l u c o s e ) = 0.6 g, d i s a c c h a r i d e s ( s u c r o s e ) = 0.6 g, s t a r c h = 0.6 g, f a t ( l a r d ) = 1.1 g, and p r o t e i n = 0.4 g. The preformed volume o f water would v a r y w i t h t h e q u a n t i t y and t y p e o f f o o d s t u f f m e t a b o l i z e d ( 5_). I t s sources are the p o l y m e r i z a t i o n o f g l u c o s e , c o n d e n s a t i o n o f amino a c i d s , e s t e r i f i c a t i o n o f f a t s ( g l y c e r o l ) , h y d r a t i o n o f p r o t e i n , and bound water (water of a s s o c i a t i o n ) ; t h e l a t t e r s o u r c e i s 1 g o f p r o t e i n a s s o c i a t e d w i t h 3 g H 0 , 1 g n e u t r a l f a t w i t h 0.1 g H 0 , and 1 g g l y c o g e n w i t h 2.7 g 2

2

H2O.

Table I .

F l u i d Compartmen

Compartment Extracellular : Plasma Interstitial Cellular Total

Volume, l i t e r s

Body w e i g h t , %

4 19 30

5 24 37

53

66

^ M o d i f i e d from ( 5) . Table I I . D a i l y Water Balance o f a R e s t i n g 80 kg Man* Weight, grams

Percent

Input , Beverage Food water ( l i q u i d ) O x i d a t i o n water ( m e t a b o l i c ) Preformed water ( m e t a b o l i c )

1200 1000 250 50

48 40 10 2

Total

2500

100

Output U r i n e water I n s e n s i b l e water (vapor) F e c a l water Sweat

1400 900 200 0

56 36 8 0

Total

2500

100

Water b a l a n c e ( i n p u t - o u t p u t )

0

* M o d i f i e d from ( 5 ) . Depending upon t h e q u a n t i t y o f f a t i n t h e body, body water i n normal h e a l t h y p e o p l e comprises 50$ t o 70% o f t h e body w e i g h t . The h i g h e r t h e p e r c e n t a g e o f l e a n body mass, t h e h i g h e r t h e p e r c e n t a g e o f

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Water and

8. GREENLEAF AND HARRS ION

Electrolytes

109

water because l e a n mass (muscle) c o n t a i n s more water than f a t t i s s u e (Table I I I ) . I n the g e n e r a l p o p u l a t i o n , t h e body water c o n t e n t a v e r ­ ages about βΐ % (_6_). The h a l f - l i f e o f body water m o l e c u l e s i s about 12 days (1); t h e t o t a l water volume i s r e g u l a t e d d a i l y t o w i t h i n ±0.22% (±150 g) o f the body weight (8), and plasma volume t o w i t h i n ±0.7% (±25 g) (9_). Table I I I .

Weight and Water Content o f Body T i s s u e From a 70.6 kg Man*

Tissue S t r i a t e d muscle Skeleton Adipose t i s s u e Skin Lungs Liver B r a i n and s p i n a l c o r d Alimentary t r a c t Alimentary t r a c t contents Heart Kidneys Spleen Pancreas Bile Teeth Hair Remaining t i s s u e s Liquid Solid T o t a l Body

Percent water content 79.5 31.8 50.1

Percent of body weight 31.6 14.8 13.6

3.4 2.5 2.1 0.8 0.7 0.5 0.2 0.2 0.2 0.1 0.1

71.5 73.3 79.1

3.7 13.5

93.3 70.4

100.0

67.2

73.7 79.5 78.7 73.1 5.0

* M o d i f i e d from ( 6 ) . Except f o r r e s p i r a t o r y and dermal i n s e n s i b l e water-vapor l o s s e s , a l l r e m a i n i n g water l o s t by the body c o n t a i n s e l e c t r o l y t e s , m a i n l y sodium and c h l o r i d e . The normal c a t i o n and a n i o n c o n s t i t u e n t compo­ s i t i o n of the f l u i d spaces i s g i v e n i n T a b l e IV. I n the e x t r a c e l l u ­ l a r f l u i d space, sodium i s the major c a t i o n and c h l o r i d e the major a n i o n . Those two i o n s c o n s t i t u t e 95% o f the e x t r a c e l l u l a r f l u i d o s m o l a l i t y . Changes i n plasma sodium c o n c e n t r a t i o n r e f l e c t changes i n e x t r a c e l l u l a r f l u i d volume. Potassium i s t h e major c e l l u l a r c a t i o n and phosphates and p r o t e i n s comprise the major a n i o n s . The t o t a l c e l l u l a r o s m o l a l i t y (175 + 135 = 310 mosmol/kg H 0) i s e q u a l t o the t o t a l e x t r a c e l l u l a r o s m o l a l i t y (155 + 155 = 310 mosmol/kg H 0 ) ; t h e r e f o r e , e q u a l t o t a l o s m o t i c c o n c e n t r a t i o n s a r e m a i n t a i n e d between two f l u i d compartments o f w i d e l y d i f f e r e n t i o n i c c o n t e n t s ( T a b l e I V ) . 2

2

E x e r c i s e and Body Water E x e r c i s e has two s p e c i f i c e f f e c t s on body w a t e r . F i r s t , i t a l t e r s the d i s t r i b u t i o n of w a t e r , c o l l o i d s ( p r o t e i n ) , and c r y s t a l l o i d s

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110

NUTRT IO IN AND AEROBC I EXERCS IE T a b l e IV.

Normal C o m p o s i t i o n o f F l u i d Spaces i n Man

Other F l u i d space

Extracellular Cellular Total

Na

+

K

+

Ca

+ 2

Other"

+

• Mg

+ 2

0smols

+

Cl"

HC0~

3

P0jj

3

+ PRO"

Osmols"

mEq/1

mEq/1

mEq/1

mosmol/kg

mEq/1

mEq/1

mEq/1

mosmol/kg

142 10 152

5 145 150

8 20 28

155 175 330

103 2 105

27 8 35

25 190 215

155 135 290

(ions) within the body f l u i l o s t that i s not replaced by f l u i d intake, the r e s u l t i s a decrease in t o t a l body water content which, i n hot environments, may be of s u f f i c i e n t magnitude to reduce markedly the capacity for prolonged exercise (10,11, Figure 2). F l u i d S h i f t s with Exercise. During exercise some plasma water i s l o s t (shifted) from the vascular compartment to the i n t e r s t i t i a l compartment and to the c e l l u l a r compartment of the active muscle (12,13); at the same time f l u i d i s s h i f t e d at a lower rate from the i n t e r s t i t i a l compartment of inactive muscle to the vascular space (14). The r e s u l t i s an absolute loss of plasma water (and e l e c t r o lytes) that i s d i r e c t l y proportional to the i n t e n s i t y of the exercise (Figure 2). These transcompartmental f l u i d s h i f t s occur as a r e s u l t of alterations i n the balance of osmotic and hydrostatic forces acting along and across the c a p i l l a r y networks of a l l tissues whose blood flow i s altered by exercise; e.g., muscle, skin, kidney, gut, and l i v e r . For exercise (cycling) performed i n a seated position, the f l u i d balance favors net c a p i l l a r y f i l t r a t i o n which r e s u l t s i n a reduction of plasma volume or hemoconcentration (15). For exercise performed i n an upright position such as running, the hemoconcentration i s often minimal (16) because the act of standing causes a subs t a n t i a l hemoconcentration; edema-preventing mechanisms, such as increased i n t e r s t i t i a l f l u i d pressure, act to reduce the potential for further hemoconcentration (17,18). Exercise at an i n t e n s i t y above 50% of peak working capacity i s usually accompanied by increased concentrations of plasma e l e c t r o l y t e s ; sodium, chloride, and especially potassium, with an accompanying increase i n osmolality. There i s , however, l i t t l e change i n plasma e l e c t r o l y t e and osmotic concentrations at exercise l e v e l s below 50? of the peak working capacity because the plasma f i l t r a t e i s isotonic with respect to e x i s t i n g plasma t o n i c i t y (19-21). At exercise levels above 50? of peak capacity, there i s an exponential increase i n plasma sodium and osmolality that i s associated with the linear decrease i n plasma volume (Figure 3) (20). Apart from an increase i n plasma-potassium concentration induced by the moderate muscular contraction, which may be augmented by the breakdown of glycogen to glucose (glycogenolytic a c t i v i t y ) i n active muscle, the

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Water and

GREENLEAF AND HARRS ION

Electrolytes

11

CELLULAR FLUID

INTERSTITIAL FLUID

ONCOTIC-OSMOTIC PRESSURE HYDROSTATIC PRESSURE

F i g u r e 1. C e l l u l a r and e x t r a c e l l u l a r (plasma and f l u i d compartments.

PLASMA FLUID

interstitial)

F i g u r e 2. E f f e c t o f d r i n k i n g water on r e c t a l temperature l e v e l s d u r i n g t r e a d m i l l e x e r c i s e (37.7°C d r y - b u l b temperature and 35-45? r e l a t i v e h u m i d i t y ) i n one s u b j e c t . From r e f . 49 w i t h permission.

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NUTRT IO IN AND AEROBC I EXERCS IE

e l e v a t i o n s i n plasma e l e c t r o l y t e and o s m o t i c c o n c e n t r a t i o n s appear t o be a r e s u l t of the t r a n s c o m p a r t m e n t a l f l u i d s h i f t s . I f moderate d e h y d r a t i o n i s added t o the s t r e s s of moderate e x e r c i s e , e s p e c i a l l y when performed i n a hot environment, the e l e v a t i o n i n plasma sodium and o s m o t i c c o n c e n t r a t i o n s can be s u f f i c i e n t t o i m p a i r t e m p e r a t u r e r e g u l a t i o n (2,4). F l u i d s h i f t s d u r i n g e x e r c i s e o c c u r m a i n l y as a r e s u l t of i n c r e a s e d c a p i l l a r y f i l t r a t i o n from the v a s c u l a r compartment t o the i n t e r s t i t i a l space caused by the i n c r e a s e s i n h y d r o s t a t i c and s y s t e m i c b l o o d p r e s s u r e s (13,21,22), w i t h a s s i s t a n c e from the i n c r e a s e d t i s s u e o s m o l a l i t y (14,23) r e s u l t i n g from e l e v a t e d muscle metabol i s m . The l a t t e r would t e n d t o draw i n t e r s t i t i a l f l u i d i n t o the muscle c e l l s (13) and, i n c o n j u n c t i o n w i t h the s h i f t of water from i n a c t i v e muscle, would i n c r e a s e t i s s u e t o t a l p r e s s u r e ( F i g u r e 1 ) . The r e v e r s e f l u x of f l u i d from the i n t e r s t i t i a l t o the v a s c u l a r space (14) i s caused by i n c r e a s e d i n t e r s t i t i a l f l u i d p r e s s u r e (12) and i n c r e a s e d plasma p r o t e i hyperosmotemia, or b o t h 50?-peak c a p a c i t y ) and d u r a t i o n o f the e x e r c i s e . I n c r e a s e d i n t e r s t i t i a l h y d r o s t a t i c p r e s s u r e and i n c r e a s e d plasma o s m o t i c p r e s s u r e s r e t a r d the f l u i d s h i f t from plasma t o the i n t e r s t i t i u m . Equilibrium i s r e a c h e d when i n t e r s t i t i a l p r e s s u r e b a l a n c e s c a p i l l a r y f i l t r a t i o n p r e s s u r e ( 2 4 ) . A f t e r c e s s a t i o n o f e x e r c i s e , r e s t i t u t i o n of plasma volume t a k e s 40-60 minutes (21,22) u n l e s s s i g n i f i c a n t d e h y d r a t i o n i s present. The immediate p o s t - e x e r c i s e hyperosmotemia, the r e l a t i v e h y p e r p r o t e i n e m i a , and the r e d u c t i o n i n s y s t e m i c b l o o d p r e s s u r e cont r i b u t e t o the r e s t o r a t i o n o f plasma volume. The r e d u c t i o n i n b l o o d p r e s s u r e , which produces a f a l l i n l o c a l h y d r o s t a t i c p r e s s u r e w i t h i n the c a p i l l a r i e s of the p r e v i o u s l y a c t i v e muscle, i s p r o b a b l y the s i n g l e most i m p o r t a n t f a c t o r . Consequences of Sweating. Sweating o c c u r s d u r i n g moderate e x e r c i s e l e v e l s i n the c o l d as w e l l as a t h i g h e r e n v i r o n m e n t a l t e m p e r a t u r e s . At low ambient t e m p e r a t u r e s a g r e a t e r p o r t i o n of the m e t a b o l i c heat p r o d u c t i o n (depending upon e x e r c i s e i n t e n s i t y and c l o t h i n g ) i s d i s s i pated by c o n v e c t i o n and r a d i a t i o n and a minor p o r t i o n by e v a p o r a t i o n of sweat and r e s p i r a t o r y w a t e r . As ambient temperature r i s e s , the p o r t i o n o f heat d i s s i p a t e d by c o n v e c t i o n and r a d i a t i o n d e c r e a s e s p r o g r e s s i v e l y i n c o n c e r t w i t h a p r o p o r t i o n a l i n c r e a s e i n the r a t e of s w e a t i n g and e v a p o r a t i v e heat l o s s . The c o o r d i n a t i o n o f the r a t e of heat l o s s between c o n d u c t i o n , r a d i a t i o n , and e v a p o r a t i o n i s so p r e c i s e t h a t , f o r ambient d r y - b u l b t e m p e r a t u r e s between 5°C and 29°C, the e q u i l i b r i u m l e v e l of c o r e ( r e c t a l ) temperature i s r e l a t e d d i r e c t l y t o the i n t e n s i t y of the e x e r c i s e l o a d and i s independent of e n v i r o n m e n t a l temperature ( 2 5 ) . I n c o o l environments the i n c r e a s e i n m e t a b o l i c heat p r o d u c t i o n and c o r e temperature d u r i n g e x e r c i s e can be c o n s i d e r e d as an i n t e r n a l t h e r m a l s t r e s s . The f l u i d s h i f t s t h a t o c c u r d u r i n g e x e r c i s e i n warm and hot environments are m o d i f i e d by what can be c o n s i d e r e d as an a d d i t i o n a l e x t e r n a l t h e r m a l s t r e s s . Even under i d e a l ( c o o l ) c l i m a t i c c o n d i t i o n s e x e r c i s e i s a n t i h o m e o s t a t i c , h a v i n g the c a p a b i l i t y of imposing s i m u l t a n e o u s s t r e s s e s upon n e a r l y a l l the body's r e g u l a t o r y systems. P r o l o n g e d e x e r c i s e performed i n hot c o n d i t i o n s imposes a p a r t i c u l a r l y s e v e r e s t r a i n on the c a r d i o v a s c u l a r system which must p r o v i d e not o n l y f o r t h e m e t a b o l i c r e q u i r e m e n t s of the w o r k i n g

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

8.

GREENLEAF AND HARRS ION

113 Water and

Electrolytes

m u s c l e s , but a l s o f o r t h e d i s s i p a t i o n o f m e t a b o l i c and e n v i r o n m e n t a l heat v i a r e g u l a t i o n o f t h e cutaneous c i r c u l a t i o n . Under t h e c i r c u m ­ s t a n c e o f g r e a t i n t e r n a l and e x t e r n a l t h e r m a l s t r e s s , t h e dominant t h e r m o r e g u l a t o r y mechanism i s t h e p r o d u c t i o n and e v a p o r a t i o n o f sweat. For each m i l l i l i t e r o f sweat e v a p o r a t e d , 2.4 k i l o j o u l e s (0.58 k c a l ) o f heat a r e l o s t from t h e body. D u r i n g marathon runs i n the h e a t , sweat r a t e s may approach 2 l i t e r s per hour ( 2 6 ) ; i f t h e body water l o s t i s n o t r e p l a c e d , d e h y d r a t i o n o c c u r s . Even i n c o o l environments, where c o n v e c t i o n and r a d i a t i o n a r e t h e main avenues o f heat d i s s i p a t i o n , s w e a t i n g may s t i l l r e s u l t i n s i g n i f i c a n t dehydra­ t i o n because o f t h e i n c r e a s e i n c o r e t e m p e r a t u r e . T h e r e f o r e , appro­ p r i a t e f l u i d i n t a k e i s an i m p o r t a n t r e q u i r e m e n t d u r i n g p r o l o n g e d e x e r c i s e performed i n c o o l environments as w e l l as i n t h e h e a t . Q u a n t i f y i n g " p r o l o n g e d " and " h e a t " i s d i f f i c u l t , s i n c e t h e two a r e i n t e r a c t i v e . The heat produced by metabolism d u r i n g i n t e n s e e x e r c i s e can exceed t h e a b s o r p t i o of seven ( 2 7 ) , but t h i s s h o r t p e r i o d s o f t i m e . Rates o f m e t a b o l i c heat p r o d u c t i o n e x c e e d i n g 600 W a t t s , which i s t h r e e times a s e v e r e e n v i r o n m e n t a l heat l o a d , can be s u s t a i n e d f o r s e v e r a l hours by endurance a t h l e t e s . A wet-bulb g l o b e - t e m p e r a t u r e (WBGT) i n d e x [ ( 0 . 7 χ wet-bulb temp.) + (0.2 χ b l a c k g l o b e temp.) + (0.1 χ d r y - b u l b temp.)] g r e a t e r than 18°C (65°F) p r o ­ v i d e s a c o n d i t i o n f o r a p o t e n t i a l r i s k o f heat i n j u r y d u r i n g e x e r ­ c i s e . Thus, t h e more i n t e n s e and p r o l o n g e d t h e e x e r c i s e , t h e lower the s a f e WBGT i n d e x . Sweat i s composed o f water and many s o l i d s u b s t a n c e s , m a i n l y t h e e l e c t r o l y t e s sodium, p o t a s s i u m , and c h l o r i d e ( 2 8 ) . W h i l e l o s s o f water and t h e e n s u i n g i n c r e a s e i n t o t a l body d e h y d r a t i o n may become a m e d i c a l problem, c o n t r a r y t o p o p u l a r b e l i e f , t h e accompanying l o s s o f e l e c t r o l y t e s does not c o n s t i t u t e a problem under most e x e r c i s e and e n v i r o n m e n t a l s i t u a t i o n s as l o n g as f o o d consumption i s normal. Sweat i s much more d i l u t e ( h y p o t o n i c ) than plasma (sweat = 0 . 4 ? s o l u t e , plasma = 0.9? s o l u t e ) . T h i s h y p o t o n i c i t y i n c r e a s e s i n sub­ j e c t s who have undergone e x e r c i s e t r a i n i n g i n t h e heat ( a c c l i m a t i z a ­ t i o n ) (29). Consequently, sweating d u r i n g e x e r c i s e r e s u l t s i n i n c r e a s e s i n plasma e l e c t r o l y t e and o s m o t i c c o n c e n t r a t i o n s s i n c e p r o p o r t i o n a l l y more water t h a n s a l t ( e l e c t r o l y t e ) i s b e i n g l o s t i n the sweat. But i n t r a v a s c u l a r e l e c t r o l y t e c o n t e n t i s a l s o b e i n g decreased by l o s s e s i n sweat. Once s w e a t i n g c e a s e s , and any body water d e f i c i t i n c u r r e d i s r e p l a c e d by d r i n k i n g pure w a t e r , t h e r e s u l t i n g i n t r a v a s c u l a r e l e c t r o l y t e c o n c e n t r a t i o n w i l l be decreased from t h e p r e s w e a t i n g l e v e l u n l e s s a d d i t i o n a l e l e c t r o l y t e s a r e con­ sumed. The b e s t time t o r e p l a c e e l e c t r o l y t e s l o s t d u r i n g e x e r c i s e i s a f t e r e x e r c i s e ceases because i n g e s t i o n o f e l e c t r o l y t e s d u r i n g e x e r ­ c i s e w i l l add t o t h e e x i s t i n g e x e r c i s e - i n d u c e d h y p e r o s m o l a l i t y . D r i n k i n g c o l d o r warm water d u r i n g e x e r c i s e i s more e f f e c t i v e i n a t t e n u a t i n g t h e r i s e i n c o r e temperature than d r i n k i n g an e q u a l volume b e f o r e e x e r c i s e o r p r o v i d i n g a r t i f i c i a l sweat by sponging t h e body w i t h water d u r i n g e x e r c i s e ( 3 0 ) . I n a d d i t i o n , h y p e r n a t r e m i a and h y p e r o s m o l a l i t y tend t o i n h i b i t s w e a t i n g and e v a p o r a t i v e heat l o s s (as does wet s k i n ) and a c c e n t u a t e t h e a l r e a d y e l e v a t e d core tempera­ t u r e (2,4,31). There a r e c i r c u m s t a n c e s when some e l e c t r o l y t e replacement i s n e c e s s a r y , f o r example d u r i n g r e p e a t e d bouts o f s t r e n u o u s e x e r c i s e

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performed d a i l y for many consecutive days, or when physical work or exercise i s performed continuously over a 12- to 24-hour period and adequate rest periods and meals are not a v a i l a b l e . Muscle cramping i s a common response to s a l t (NaCl) depletion which usually can be prevented by increasing s a l t intake. Heat cramp and the syndrome of s a l t and/or water depletion heat exhaustion are commonly the result of inappropriate l e v e l s of heat acclimatization and physical f i t n e s s (32). The enhanced a b i l i t y to conserve body sodium i n sweat and urine are major adaptive responses to heat acclimatization, and excessive e l e c t r o l y t e depletion i s usually a problem only during the f i r s t few days of work i n the heat. Further, i t should be noted that s i g n i f i c a n t l y increased s a l t intake during the f i r s t few days of heat stress can i n h i b i t the secretion of aldosterone (29), a hormone that aids s a l t conservation by f a c i l i t a t i n g reabsorption of sodium i n the sweat glands and kidney tubules. Provided that the diet i s adequate there i s no substantial evidence to suggest tha n u t r i t i o n a l status or exercis ble exception i s iron; the low l e v e l of bone marrow iron content observed i n some endurance-trained athletes (33) may be due to excessive losses of as much as 40 micrograms of iron per 100 m i l l i l i t e r s of sweat (34). Iron metabolism i s discussed i n more d e t a i l i n the chapter by McDonald and Saltman. Dehydration and Exercise. Water loss corresponding to as l i t t l e as 1? of the body weight leads to accentuated increases i n body temperature and heart rate during exercise (Figure 4) (35). If water loss approaches 4 to 5% of the body weight, the capacity for prolonged work may be reduced by 20 to 30? (36). The adverse cardiovascular and thermoregulatory e f f e c t s of dehydration are p a r t l y a r e s u l t of reduction i n plasma volume (hypovolemia) and an increase i n plasma osmolality. Hypovolemia also reduces stroke volume and cardiac output, and reduces the rate of heat loss by r a i s i n g temperature thresholds for cutaneous vasodilatation and sweating (18). Thermal dehydration also elevates blood e l e c t r o l y t e s and osmolality, and t h i s too reduces the s e n s i t i v i t y of heat-dissipation mechanisms independently of any dehydration-induced reduction i n plasma volume (3)· Therefore, any factor which reduces plasma osmolality can only be advantageous to the endurance athlete or worker performing i n the h e a t — another strong argument for not adding e l e c t r o l y t e s to l i q u i d s consumed during exercise. Dehydration also a f f e c t s the plasma volume response to exerc i s e . For example, during cycling i n the heat, the magnitude of the exercise hemoconcentration i s greater when the c y c l i s t i s dehydrated than when dehydration i s prevented by drinking water (3). During walking, the prevention of dehydration by water consumption increases the tendency for hemodilution rather than for hemoconcentration (37). Thus, preventing or minimizing dehydration improves performance during exercise through s p e c i f i c b e n e f i c i a l e f f e c t s on both the cardiovascular and thermoregulatory systems. Heat Acclimatization and Endurance Training. Primary adaptive responses to repeated intermittent exposure to exercise i n the heat are (1) chronic expansion of the plasma volume, (2) increased retent i o n of body sodium, (3) increased capacity for sweating and, hence,

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115 Water and

Electrolytes

THIRST THRESHOLD, AND THRESHOLD FOR IMPAIRED EXERCISE THERMOREGULATION LEADING TO DECREMENT IN PHYSICAL WORK CAPACITY STRONGER THIRST, VAGUE DISCOMFORT AND SENSE OF OPPRESSION, LOSS OF APPETITE DRY MOUTH, INCREASING HEMOCONCENTRATION, REDUCTION IN URINARY OUTPUT DECREMENT OF 20-30% IN PHYSICAL WORK CAPACITY DIFFICULTY IN CONCENTRATING, HEADACHE, IMPATIENCE, SLEEPINESS SEVERE IMPAIRMENT IN EXERCISE TEMPERATURE REGULATION, INCREASED RESPIRATORY RATE LEADING TO TINGLING AND NUMBNESS OF EXTREMITIES LIKELY COLLAPSE IF COMBINED WITH HEAT AND EXERCISE

F i g u r e 4.

Adverse e f f e c t s of d e h y d r a t i o n .

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f o r e v a p o r a t i v e heat l o s s , and (4) some r e s i d u a l i n c r e a s e i n cutaneous b l o o d f l o w ( 3 8 , 3 9 ) . These r e s p o n s e s p r o v i d e f o r i n c r e a s e d heat d i s s i p a t i o n d u r i n g e x e r c i s e , which a l l o w s c o r e temperature t o be r e g u l a t e d a t a l o w e r l e v e l , and f o r reduced s t r e s s on t h e c a r d i o v a s c u l a r system a f t e r a c c l i m a t i z a t i o n . The p r a c t i c a l importance o f e x p a n s i o n o f t h e plasma volume w h i c h o c c u r s w i t h heat a c c l i m a t i z a t i o n and endurance t r a i n i n g remains c o n t r o v e r s i a l . C e r t a i n l y i t i n c r e a s e s t h e c a p a c i t y o f t h e c a r d i o v a s c u l a r system t o m a i n t a i n an adequate b l o o d f l o w t o muscle and s k i n d u r i n g e x e r c i s e i n t h e heat w i t h o u t compromising e i t h e r t h e r m o r e g u l a t i o n o r r e g u l a t i o n o f b l o o d p r e s s u r e . On t h e o t h e r hand, t h e magnitude o f t h e h e m o c o n c e n t r a t i o n (hypovolemia) i n d u c e d d u r i n g c y c l i n g i s g r e a t e r a f t e r heat a c c l i m a t i z a t i o n . Corresponding data f o r running e x e r c i s e are not a v a i l a b l e . Even though t h e r e i s no a d a p t a t i o n t o s u c c e s s i v e bouts o f d e h y d r a t i o n , heat a c c l i m a t i z a t i o n seems t o a t t e n u a t e t h e a d v e r s e e f f e c t s o f d e h y d r a t i o n on t h e c a r d i o v a s c u l a r r e s p o n s e s t o heat and exercise (40). Nothin performing prolonged e x e r c i s acclimatized individuals. I t s h o u l d be emphasized t h a t t h e p h y s i c a l l y c o n d i t i o n e d endurance a t h l e t e needs as much and p r o b a b l y more water t h a n u n t r a i n e d p e o p l e because o f t h e i n c r e a s e d s w e a t i n g o f t h e athlete. Endurance e x e r c i s e t r a i n i n g , when c a r r i e d o u t i n c o o l e n v i r o n ments, i n d u c e s a d a p t i v e responses which a r e q u a l i t a t i v e l y s i m i l a r t o those i n d u c e d d u r i n g heat a c c l i m a t i z a t i o n ; i . e . , i n c r e a s e d sweat r a t e , reduced h e a r t r a t e , and i n c r e a s e d plasma volume ( 4 1 , 4 2 ) . When heat a c c l i m a t i z a t i o n i s induced by r a i s i n g c o r e temperature w i t h s u b j e c t s a t r e s t i n a h o t environment, t h e s e same a d a p t i v e r e s p o n s e s are enhanced t o some degree (41,43). I t has been observed t h a t physi c a l l y f i t s u b j e c t s do not e x h i b i t t h e s e c h a r a c t e r i s t i c r e s p o n s e s when exposed t o a s t a n d a r d a c c l i m a t i z a t i o n regimen i n v o l v i n g i n t e r m i t t e n t w a l k i n g e x e r c i s e i n a hot environment ( 4 4 ) , s u g g e s t i n g t h a t they had a l r e a d y adapted i n t h e same manner as a c c l i m a t i z e d subj e c t s . There appears t o be some a d d i t i v e e f f e c t on t h e magnitude o f the a d a p t i v e responses between t h o s e i n d u c e d by r e s t i n g i n t h e h e a t , and e x e r c i s i n g i n c o o l and h o t environments ( 4 5 ) . The l a r g e s t adapt i v e r e s p o n s e s o c c u r d u r i n g t h e performance o f moderate t o heavy e x e r c i s e i n t h e heat (18,41,42,46-48). T h i r s t and D r i n k i n g D u r i n g E x e r c i s e A l t h o u g h i t has been known f o r many y e a r s t h a t d e h y d r a t i o n and hypoh y d r a t i o n i m p a i r p h y s i c a l performance, many people who engage i n e x e r c i s e and e x e r c i s e t r a i n i n g may not know how s e r i o u s t h a t i m p a i r ment can be o r what t o do about i t , e s p e c i a l l y d u r i n g c o m p e t i t i o n when t h e y a r e c o n f r o n t e d by r u l e s t h a t may p r o h i b i t o r r e s t r i c t l i q u i d consumption. A b e w i l d e r i n g a r r a y o f h y d r a t i o n d r i n k s a r e a v a i l a b l e c o m m e r c i a l l y t h a t bombard t h e i n d i v i d u a l w i t h a v a r i e t y o f c l a i m s , some o f which b o r d e r on t h e l u d i c r o u s . The t r u t h i s s i m p l e ; d u r i n g e x e r c i s e pure water i s b e s t . A l t h o u g h p r e v e n t i o n o f dehydrat i o n by replacement o f a l l f l u i d l o s s e s would be t h e i d e a l p r o c e d u r e f o r m a x i m i z i n g e x e r c i s e performance i n c o o l o r h o t environments ( 4 9 ) , i n p r a c t i c e u n f o r t u n a t e l y , t h i s f u l l replacement i s v i r t u a l l y imposs i b l e t o achieve.

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Stimuli f o r Drinking. T h i r s t s t i m u l a t i o n and t h e a c t o f d r i n k i n g a r e b a s i c p h y s i o l o g i c a l r e s p o n s e s . The t h r e e major c i r c u m s t a n c e s known t o s t i m u l a t e t h i r s t and d r i n k i n g a r e (1) a d e f i c i t o f body water ( h y p o h y d r a t i o n and h y p o v o l e m i a ) , (2) an i n c r e a s e i n t h e o s m o l a l i t y o f the e x t r a c e l l u l a r f l u i d volume ( h y p e r o s m o l a l i t y and hyperosmotemia), and (3) consumption o f d r y food ( p r a n d i a l t h i r s t ) ( 5 0 ) . These t h r e e f a c t o r s can f u n c t i o n i n d e p e n d e n t l y , but they a r e o f t e n i n t e r a c t i v e ; e.g., a hypovolemic s u b j e c t i s o f t e n h y p e r o s m o t i c . I n a d d i t i o n , t h e hormone a n g i o t e n s i n I I a c t s as a s t i m u l a n t f o r d r i n k i n g (dipsogen) i n a n i m a l s , and p o s s i b l y i n man ( 5 1 ) . I n humans e x p e r i e n c i n g t h e r m a l l y s t r e s s f u l c o n d i t i o n s , t h e r a t e of v o l u n t a r y f l u i d i n t a k e under o p t i m a l c o n d i t i o n s f o r d r i n k i n g , i . e . , where c o o l p a l a t a b l e water o r f r u i t j u i c e (52) a r e r e a d i l y a c c e s s i b l e i s , u n f o r t u n a t e l y , o n l y about h a l f t h e r a t e o f water l o s s (51). Unless there i s f o r c e d d r i n k i n g , these s t r e s s e d people a r e almost always i n n e g a t i v e water b a l a n c e This c o n d i t i o n i s r e f e r r e d t o as i n v o l u n t a r y d e h y d r a t i o e l e c t r o l y t e system o c c u r environment. When t h e f a c t o r s h y d r a t i o n - d e h y d r a t i o n , e x e r c i s e - r e s t , and h o t - c o o l environments a r e s e p a r a t e d , i t i s found t h a t dehyd r a t i o n , e x e r c i s e , and t h e h o t environment a l l have g r e a t e r i n h i b i t o r y e f f e c t s on d r i n k i n g t h a n t h e i r h y d r a t i o n , r e s t , and c o o l e n v i ronment c o n t r o l c o n d i t i o n s . Of t h e s e t h r e e s t r e s s e s , heat exposure has t h e l e a s t i n h i b i t o r y e f f e c t , p r i o r d e h y d r a t i o n has an i n t e r mediate e f f e c t , and moderate e x e r c i s e per se has t h e g r e a t e s t i n h i b i t o r y e f f e c t on v o l u n t a r y r e h y d r a t i o n a f t e r s t r e s s - i n d u c e d f l u i d l o s s ( 5 4 ) . I n s p i t e o f the d i f f e r i n g n a t u r e o f t h e s e v a r i o u s s t i m u l i used t o reduce body w a t e r , t h e r a t e o f r e h y d r a t i o n i s t h e same when f o o d and f l u i d s a r e a v a i l a b l e ad l i b i t u m d u r i n g a c o m f o r t a b l e r e c o v e r y p e r i o d . The more s t r e s s f u l t h e t o t a l c o n d i t i o n , t h e g r e a t e r i s t h e l e v e l o f d e h y d r a t i o n and t h e l o n g e r i t t a k e s t o r e s t o r e t h e l o s t water ( 5 4 ) . I n p r e v i o u s l y d e h y d r a t e d men, f o r c e d f l u i d r e p l a c e m e n t over a 3 h o u r p e r i o d o f t h e f l u i d d e f i c i t f a i l e d t o r e s t o r e plasma volume and plasma o s m o l a l i t y t o p r e d e h y d r a t i o n l e v e l s ( 5 5 ) . The threshold f o r involuntary dehydration i n hydrated subjects occurs w i t h a water (sweat) l o s s o f o n l y 75 g/hr; w i t h heat exposure t h e t h r e s h o l d i s about 275 g/hr (54,56). T h i s means t h a t water l o s s e s below 75 g/hr and 275 g/hr a r e f u l l y r e p l a c e d by d r i n k i n g v o l u n t a r i l y ; above t h e s e t h r e s h o l d s they a r e n o t r e p l a c e d f u l l y . T h i s i s why d r i n k i n g s h o u l d be i n i t i a t e d b e f o r e o r i m m e d i a t e l y upon exposure t o a s t r e s s f u l f l u i d - d e p l e t i n g s i t u a t i o n before f e e l i n g s of t h i r s t a r i s e (30); otherwise, s i g n i f i c a n t l e v e l s of dehydration w i l l occur that cannot be r e s t o r e d e a s i l y by d r i n k i n g . R e s u l t s from a r e c e n t s t u d y (51) i n d i c a t e t h a t heat a c c l i m a t i z a t i o n a c t s t o reduce t h e l e v e l o f i n v o l u n t a r y d e h y d r a t i o n d u r i n g e x e r c i s e i n t h e heat by a p r o g r e s s i v e l y s h o r t e n e d time t o t h e f i r s t d r i n k , a t h r e e f o l d i n c r e a s e i n t h e number o f d r i n k s per exposure, and a s i g n i f i c a n t i n c r e a s e i n t h e mean volume per d r i n k . The r e s u l t i s t h a t v o l u n t a r y d r i n k i n g can be i n c r e a s e d c o m f o r t a b l y from 450 ml/hr t o 1000-1200 ml/hr ( 5 1 ) . Thus, t h e r e appears t o be an a d a p t i v e p h y s i o l o g i c a l r e s p o n s e t h a t a l l o w s one t o i n c r e a s e f l u i d i n t a k e . _

Water, E l e c t r o l y t e , and C a r b o h y d r a t e Replacement D u r i n g E x e r c i s e . To h e l p m i n i m i z e t h e r e q u i r e m e n t f o r water replacement d u r i n g e x e r c i s e , adequate h y d r a t i o n s h o u l d be a t t a i n e d b e f o r e e x e r c i s e commences.

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Some forced drinking may be appropriate, but i t must be planned caref u l l y because the s t a r t of a competitive race i s no time to have a f u l l bladder! Another method of storing water i s by making use of the 2.7 g of water of association with each gram of glycogen. Increasing glycogen stores by consuming additional carbohydrates a few days before exercise has the double advantage of providing addit i o n a l reserves of both energy and water (36,57,58). Enough has been said on the subject of e l e c t r o l y t e intake to strongly suggest that the r u l e i s to avoid s a l t (sodium and potassium). But there w i l l be occasions when s t r i c t adherence to t h i s rule i s inappropriate. Sometimes diet alone may not provide adequate e l e c t r o l y t e s or trace elements, for example when athletes perform where customary foods are unavailable and l o c a l foods are unpalatable. If e l e c t r o l y t e supplements are necessary, they should be taken with meals i n conjunction with f l u i d s . Under no circumstance should s a l t be taken immediately before or during exercise espe c i a l l y i n hot environment are greatest and the rat e l e c t r o l y t e consumption i s necessary, f o r example when the exercise must be performed over many hours i n the heat (as i n ultramarathon events), then a very d i l u t e s a l t solution (less than 0.5 grams per 100 m i l l i l i t e r s of H 0) i s much better than s a l t tablets, which can cause gastric i r r i t a t i o n . Calcium should not be used i n rehydration drinks because i t i n h i b i t s the normal hypervolemic response to f l u i d ingestion (59). The ideal time for e l e c t r o l y t e supplementation i s after exercise when a s u f f i c i e n t amount of water can be taken to d i l u t e the s a l t to i s o t o n i c i t y (0.9 grams of NaCl per 100 m i l l i l i t e r s of H 2 O ) , i . e . , the normal concentration of plasma. Normally these e l e c t r o l y t e supplements w i l l be unnecessary as a balanced diet w i l l provide s u f f i c i e n t e l e c t r o l y t e s and trace elements to restore any temporary d e f i c i t . 2

Gastric emptying time (the normal maximal rate being about 600-800 ml/hr (60)) imposes a physiological l i m i t a t i o n upon the rate of f l u i d uptake into the c i r c u l a t o r y system. Acute g a s t r i c discomf o r t usually arises when an attempt i s made to drink large volumes of l i q u i d too quickly during exercise. A modest volume taken at f r e quent intervals (100-125 ml or 4 ounces per 10 min) i s usually a l l that i s comfortably possible, but the b e n e f i c i a l effect can be considerable. Water i s absorbed from the stomach at a rate of about 2.6% of the ingested volume per minute, but at 20% of the ingested amount per minute from the small i n t e s t i n e . Therefore, i t i s cert a i n l y the retention of f l u i d within the stomach that produces the discomfort. The stomach can be envisioned e s s e n t i a l l y as a pump that passes material into the duodenum (61). The rate of g a s t r i c emptying increases i n proportion to the volume ingested (60-62), and the addition of even small amounts of carbohydrates (monosaccharides and disaccharides) has been reported to retard g a s t r i c emptying ( 6 0 , 6 3 - 6 5 ) . The addition of potassium chloride to a test meal slows g a s t r i c emptying s i m i l a r l y to that induced by glucose, but the KC1 i s more nauseating than glucose (65)« Optimal g a s t r i c emptying occurs when s a l i n e , of a concentration that i s nearly isosmotic with the plasma, i s introduced into the stomach (61); hypertonic solutions empty more slowly (61,66). With prolonged exercise i t may be necessary to provide addit i o n a l carbohydrate energy sources since glycogen appears to be the

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p r e f e r r e d s u b s t r a t e f o r energy p r o d u c t i o n (67)» Compared w i t h t h e consumption o f a normal mixed d i e t , consumption o f a c a r b o h y d r a t e e n r i c h e d d i e t p r i o r t o e x e r c i s e can r e s u l t i n s i g n i f i c a n t l y b e t t e r r u n n i n g performance (60). D e p l e t i o n o f muscle g l y c o g e n by e x e r c i s e and subsequent r e p l e n i s h m e n t w i t h enhanced c a r b o h y d r a t e f e e d i n g has a l s o been r e p o r t e d t o i n c r e a s e subsequent p h y s i c a l performance (69). I n g e s t i o n o f a g l u c o s e polymer supplement d u r i n g e x e r c i s e i n c r e a s e s endurance time a t a work r a t e o f 45? o f t h e maximal capa­ c i t y ( 7 0 ) . Thus, c a r b o h y d r a t e f e e d i n g appears t o enhance e x e r c i s e performance, b u t , as w i t h water and e l e c t r o l y t e s , m o d e r a t i o n i s i m p o r t a n t t o m i n i m i z e the r e t a r d a t i o n e f f e c t on g a s t r i c emptying. Summary D e t e r i o r a t i o n o f p h y s i c a l e x e r c i s e performance due t o d e h y d r a t i o n b e g i n s when body weight d e c r e a s e b about 1? U n a c c l i m a t i z e d human under t h e r m a l and e x e r c i s about h a l f o f the r a t e f l u i d l o s s (275 m l / h r ) ; the maximal r a t e o f f l u i d i n t a k e i s about 600-800 m l / h r , t h e normal maximal r a t e o f g a s t r i c emptying. D u r i n g the e x e r c i s e - h e a t a c c l i m a t i z a t i o n p r o c e d u r e , the v o l u n t a r y f l u i d i n t a k e can be i n c r e a s e d from 450 ml/hr t o 1000-1200 ml/hr w i t h no adverse e f f e c t s . E l e c t r o l y t e s u p p l e m e n t a t i o n i n d r i n k i n g f l u i d i s not recommended d u r i n g e x e r c i s e bouts l a s t i n g l e s s t h a n 3 t o 5 hours because the i n c r e a s e d c o n c e n t r a t i o n o f sodium i n t h e plasma a c c e n ­ t u a t e s the h y p e r t h e r m i a . E l e c t r o l y t e and c a r b o h y d r a t e supplementa­ t i o n i s recommended d u r i n g l o n g e r work o r e x e r c i s e p e r i o d s , espe­ c i a l l y i n hot e n v i r o n m e n t s , and when r e g u l a r meals a r e n o t a v a i l a b l e . Thus, t h e r e has been no s i g n i f i c a n t e v i d e n c e t h a t would change t h e c o n c l u s i o n o f P i t t s e t a l . i n 1944 ( 4 9 ) : " . . . i n t h e case of w e l l a c c l i m a t i z e d young men whose d a i l y d i e t i s adequate, t h e b e s t performance o f i n t e r m i t t e n t work i n the heat i s t o be a c h i e v e d by r e p l a c i n g water l o s s hour by hour and s a l t l o s s meal by meal."

Literature Cited 1. Sargent, F., II; Weinman, K. (1963) Physiological variability in young men. In: Physiological Measurements of Metabolic Functions in Man (Consolazio, C.F., Johnson, R.E., and Pecora, L.J., eds.), p. 453, McGraw-Hill, New York, NY. 2. Greenleaf, J.E. (1979) Hyperthermia and exercise. In: Int. Rev. Physiol., Environ. Physiol. III, Vol. 20 (Robertshaw, D., ed.), p. 157, University Park Press, Baltimore, MD. 3. Harrison, M.H., Edwards, R.J. & Fennessy, P.A. (1978) Intravascular volume and tonicity as factors in the regulation of body temperature. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44, 69-75. 4. Kozlowski, S., Greenleaf, J.E., Turlejska, E. & Nazar, Κ. (1980) Extracellular hyperosmolality and body temperature during physical exercise in dogs. Am. J. Physiol. 239 (Regulatory Integrative Comp. Physiol. 8), R180-R183. 5. Johnson, R.E. (1964) Human nutritional requirements for water in long space flights. In: Nutrition in Space and Related Waste Problems (Helvey, T.C., ed.), p. 159, National Aeronautics and Space Administration, Washington, DC.

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39. Sciaraffa, D., Fox, S.C., Stockmann, R. & Greenleaf, J.E. (1980) Human acclimation and acclimatization to heat: a compendium of research (1968-1978). NASA Tech. Memo. 81181, 1-102. 40. Sawka, M.N., Toner, M.M., Francesconi, R.P. & Pandolf, K.B. (1983) Hypohydration and exercise: effects of heat acclimation, gender, and environment. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 55, 1147-1153. 41. Convertino, V.A., Greenleaf, J.E. & Bernauer, E.M. (1980) Role of thermal and exercise factors in the mechanism of hypervolemia. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 48, 657-664. 42. Shvartz, E., Bhattacharya, Α., Sperinde, S.J., Brock, P.J., Sciaraffa, D., Haines, R.F. & Greenleaf, J.E. (1979) Deconditioning-induced exercise responses as influenced by heat acclimation. Aviat Space Environ Med 50 893-897 43. Fox, R.H., Goldsmith Acclimatization to temperature. J. Physiol. (London) 166, 530-547. 44. Greenleaf, J.E. (1964) Lack of artificial acclimatization to heat in physically fit subjects. Nature 203, 1072. 45. Gisolfi, C. & Robinson, S. (1969) Relations between physical training, acclimatization, and heat tolerance. J. Appl. Physiol. 26, 530-534. 46. Convertino, V.A., Shvartz, Ε., Haines R.F., Bhattacharya, Α., Sperinde, S.J., Keil, L.C. & Greenleaf, J.E. (1977) Heat acclimation and water-immersion deconditioning: fluid and electrolyte shifts with tilting. Aerospace Med. Asso. Preprints, 13-14. 47. Senay, L.C., Mitchell, D. & Wyndham, C.H. (1976) Acclimatiza­ tion in a hot humid environment: body fluid adjustments. J. Appl. Physiol. 40, 786-796. 48. Harrison, M.H., Edwards, R.J., Graveney, M.J., Cochrane, L.A., & Davies, J.A. (1981) Blood volume and plasma protein responses to heat acclimatization in humans. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 50, 597-604. 49. Pitts, G.C., Johnson, R.E. & Consolazio, F.C. (1944) Work in the heat as affected by intake of water, salt and glucose. Am. J. Physiol. 142, 253-259. 50. Adolph, E.F. (1967) Regulation of water intake in relation to body water content. In: Handbook of Physiology, Section 6: Alimentary Canal, Vol. 1, Control of food and water intake (Code, C.F., ed.), p. 163, American Physiological Society, Washington, DC. 51. Greenleaf, J.E., Brock, P.J., Keil, L.C. & Morse, J.T. (1983) Drinking and water balance during exercise and heat acclima­ tion. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 54, 414-419. 52. Sohar, E., Gilat, A.T., Tennenbaum, J. & Nir, M. (1961) Reduction of voluntary dehydration during effort in hot envi­ ronments. J. Med. Asso. Israel 60, 319-323. 53. Greenleaf, J.E. (1966) Involuntary hypohydration in man and animals: a review. NASA Special Publication 110, 1-34. 54. Greenleaf, J.E. & Sargent, F., II (1965) Voluntary dehydration in man. J. Appl. Physiol. 20, 719-724.

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70.

Ivy, J.L., Miller, W., Dover, V., Goodyear, L.G., Sherman, W.M., Farrell, S. & Williams, H. (1983) Endurance improvement by ingestion of a glucose polymer supplement. Med. Sci. Sports Exerc. 15, 466-471. 71. Greenleaf, J.E. (1982) The body's need for fluids. In: Nutrition and Athletic Performance (Haskell, W., Scala, J. & Whittam, J., eds.), p. 34, Bull Publishing Co., Palo Alto, CA. RECEIVED March 15, 1985

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9 Aerobic Exercise and Body Composition 1

2

Donald K. Layman and Richard A. Boileau 1

Department of Foods and Nutrition, Division of Nutritional Sciences, University of Illinois, Urbana, IL 61801 Department of Physical Education, Division of Nutritional Sciences, University of Illinois, Urbana, IL 61801

2

Body composition is a ter constituents of the body body composition partitions the organism into fat and fat-free body components. These components are of particular importance because of their relationship to obesity which is one of the most compelling problems in nutrition and health in western societies. Obesity is the accumulation of excess fat and, thus, is characterized by overfatness as opposed to simply overweight. To demonstrate the magnitude of obesity as a health problem, it has been estimated that adult Americans carry 2.3 billion pounds of excess fat (1). While little agreement on a precise definition of obesity can be found, useful but arbitrary standards are fat contents in excess of 20-25% of body weight for males and 25-30% for females. Using these figures, the prevalence of obesity has been estimated as 25-50% of the adult American population (2,3). F u r t h e r , the p r e v a l e n c e o f c h i l d h o o d o b e s i t y has been e s t i m a t e d t o range from 5 t o 30% i n developed c o u n t r i e s ( 4 , 5 ) . In f a c t , t h e i d e n t i f i c a t i o n o f o b e s i t y i n c h i l d h o o d has become an i m p o r t a n t a s p e c t o f t h e r e v i s e d H e a l t h - R e l a t e d F i t n e s s T e s t (6) g i v e n n a t i o n a l l y t o s c h o o l c h i l d r e n . The r e c e n t 1985 N a t i o n a l C h i l d r e n and Youth F i t n e s s Study (7) shows a c o n t i n u i n g p a t t e r n o f i n c r e a s i n g f a t n e s s based on s k i n f o l d t h i c k ness measures i n s c h o o l c h i l d r e n r e l a t i v e t o d a t a c o l l e c t e d t h r o u g h out t h e I 9 6 0 s as p a r t o f t h e N a t i o n a l H e a l t h E x a m i n a t i o n Survey (8,9). While the d i r e c t e f f e c t o f b e i n g obese on i n c r e a s e d m o r b i d i t y and m o r t a l i t y i s d i f f i c u l t t o a s s e s s , o b e s i t y has been d e s i g n a t e d as a s i g n i f i c a n t h e a l t h problem based on i t s s t a t i s t i c a l a s s o c i a t i o n w i t h the i n c r e a s e d r i s k s o f d e v e l o p i n g h e a r t d i s e a s e , h y p e r c h o l e s terolemia, hypertriglyceridemia, cancer, a r t h r i t i s , hypertension, d i a b e t e s m e l l i t u s , and gout ( 1 0 ) . There i s a l s o an i n c r e a s e d r i s k r e l a t e d t o the a d m i n i s t r a t i o n o f a n e s t h e t i c s d u r i n g s u r g e r y (11) and o b e s i t y i s known t o c o n t r i b u t e t o pulmonary s t r e s s ( 1 2 ) . I t i s g e n e r a l l y accepted t h a t the primary e t i o l o g y o f o b e s i t y c o n c e r n s problems o f energy b a l a n c e as a consequence o f n u t r i t i o n a l e x c e s s and p h y s i c a l i n a c t i v i t y w i t h l e s s than 1% o f c a s e s a s s o c i a t e d w i t h e n d o c r i n e d y s f u n c t i o n ( 1 3 ) . Changes i n body weight o r body c o m p o s i t i o n depend on the r e l a t i o n s h i p o f energy i n t a k e t o energy 1

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expenditure. T h i s r e l a t i o n s h i p , which i s u s u a l l y r e f e r r e d t o as energy b a l a n c e , i s p o s i t i v e when i n t a k e exceeds e x p e n d i t u r e . P o s i t i v e energy b a l a n c e produces i n c r e a s e s i n body w e i g h t , body f a t , o r b o t h . Weight l o s s o c c u r s when e x p e n d i t u r e exceeds i n t a k e . While t h e energy b a l a n c e r e l a t i o n s h i p i s c l e a r , a p p l i c a t i o n o f the concept has not proven t o be s t r a i g h t f o r w a r d o r e a s y . The components o f energy b a l a n c e a r e i n t a k e , which i s the consumption o f f o o d , and e x p e n d i t u r e , which i s a c o m b i n a t i o n o f b a s a l m e t a b o l i s m ( t h e energy expended a t r e s t ) , s p e c i f i c dynamic a c t i o n (the energy expended i n d i g e s t i o n , a b s o r p t i o n , and a s s i m i l a t i o n o f n u t r i e n t s a f t e r a m e a l ) , and e x e r c i s e . Of t h e components o f t h i s e q u a t i o n o n l y i n t a k e and e x e r c i s e can be v o l u n t a r i l y a l t e r e d . Thus f o r an i n d i v i d u a l t o a l t e r body weight o r c o m p o s i t i o n r e q u i r e s changes i n i n t a k e and/or e x e r c i s e . Most a t t e m p t s t o a l t e r body weight i n v o l v e c a l o r i c r e s t r i c t i o n o r dieting. While i t i s c l e a r t h a t c a l o r i c r e s t r i c t i o n w i l l cause weight l o s s , t h e d a t a sho weight w i l l r e g a i n some w i l l be d i s c u s s e d l a t e r , l i t t l e or no improvements may have o c c u r r e d i n body c o m p o s i t i o n . On the e x p e n d i t u r e s i d e o f energy b a l a n c e , e x e r c i s e i s viewed by many as a c r i t i c a l f a c t o r i n d e t e r m i n i n g body weight. While o t h e r s b e l i e v e t h a t moderate, a e r o b i c e x e r c i s e produces an i n s i g n i f i c a n t e x p e n d i t u r e o f c a l o r i e s . T h i s c h a p t e r w i l l r e v i e w the r e l a t i v e c o n t r i b u t i o n s o f e x e r c i s e and food i n t a k e t o changes i n body weight and more s p e c i f i c a l l y body c o m p o s i t i o n . The emphasis o f t h i s c h a p t e r i s on e x e r c i s e as a m o d a l i t y f o r f a t r e d u c t i o n and f a t - f r e e weight maintenance w i t h t h e f o c u s on a e r o b i c e x e r c i s e which has g r e a t e r p o t e n t i a l t o modify body c o m p o s i t i o n due t o l a r g e r e f f e c t s on energy b a l a n c e . The f i r s t s e c t i o n r e v i e w s the e f f e c t s o f a e r o b i c e x e r c i s e on body c o m p o s i t i o n i n humans. The second s e c t i o n a d d r e s s e s t e c h n i q u e s f o r measurement o f body c o m p o s i t i o n and l i m i t a t i o n s o f t h e s e measurements i n humans. The t h i r d s e c t i o n examines the use o f e x p e r i m e n t a l a n i m a l s f o r s t u d i e s o f e x e r c i s e and body c o m p o s i t i o n , and the f o u r t h s e c t i o n examines t h e i n t e r a c t i o n s o f d i e t and e x e r c i s e . E f f e c t o f A e r o b i c E x e r c i s e on t h e Body C o m p o s i t i o n o f Humans E x e r c i s e r e p r e s e n t s the most v a r i a b l e f a c t o r on the e x p e n d i t u r e s i d e o f the energy b a l a n c e e q u a t i o n . I t i s p o s s i b l e t o i n c r e a s e the energy e x p e n d i t u r e 10-20 f o l d a t peak e x e r c i s e l e v e l s . Not o n l y i s the m e t a b o l i c r a t e i n c r e a s e d d u r i n g e x e r c i s e , but the c a l o r i g e n i c e f f e c t o f e x e r c i s e may remain s i g n i f i c a n t l y e l e v a t e d f o r s e v e r a l hours a f t e r e x e r c i s e both i n terms o f r e c o v e r y energy e x p e n d i t u r e (15) and a p p e t i t e s u p r e s s i o n ( 1 6 ) . On the o t h e r hand, the use o f e x e r c i s e as t r e a t m e n t f o r body weight m o d i f i c a t i o n and f a t l o s s has been c r i t i c i z e d on a t l e a s t two c o u n t s . F i r s t , t h e r e i s the b e l i e f t h a t c a l o r i c consumption a s s o c i a t e d w i t h moderate a e r o b i c e x e r c i s e i s i n s i g n i f i c a n t when compared t o the much p u b l i c i z e d s e m i s t a r v a t i o n diets. There i s a l s o the b e l i e f t h a t e x e r c i s e s t i m u l a t e s the a p p e t i t e so t h a t any c a l o r i c d e f i c i t e f f e c t e d by e x e r c i s e i s o f f s e t by i n c r e a s e d food i n t a k e . Research t o answer t h e s e and o t h e r q u e s t i o n s has not been c o n v i n c i n g and c e r t a i n l y not d e f i n i t i v e . While one can g e n e r a l l y c o n c l u d e t h a t e x e r c i s e a l o n e evokes a modest m o d i f i c a t i o n i n body c o m p o s i t i o n , e x i s t i n g human r e s e a r c h has been

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p l a g u e d by t h e l a c k o f c o n t r o l l e d s t u d i e s w i t h r e s p e c t t o r e s e a r c h d e s i g n , q u a n t i f i c a t i o n o f energy i n t a k e and o u t p u t , and methodol o g i c a l c o n s i d e r a t i o n s i n body c o m p o s i t i o n a s s e s s m e n t . In a d d i t i o n , most human r e s e a r c h has been l i m i t e d t o r e l a t i v e l y s h o r t - t e r m s t u d i e s due t o problems a s s o c i a t e d w i t h a d h e r e n c e , whereas t h e e n e r g e t i c s o f e x e r c i s e would suggest t h a t p h y s i o l o g i c a l l y s i g n i f i c a n t changes i n body c o m p o s i t i o n can o n l y be a c c o m p l i s h e d through l o n g - t e r m programs. For example, a t y p i c a l e x e r c i s e program c o n s i s t i n g o f 30 minutes o f e x e r c i s e per s e s s i o n , 3 days p e r week may o n l y i n c r e a s e c a l o r i c e x p e n d i t u r e by 600-900 K c a l per week, a r a t e e q u i v a l e n t t o a one pound f a t l o s s every 4 - 5 weeks a t t r i b u t a b l e solely to exercise. The e v i d e n c e s u g g e s t i n g t h a t e x e r c i s e i s a s i g n i f i c a n t f a c t o r i n c o n t r o l l i n g and m o d i f y i n g human body c o m p o s i t i o n has come from both c o m p a r a t i v e and e x p e r i m e n t a l r e s e a r c h d e s i g n s . When p h y s i c a l l y a c t i v e i n d i v i d u a l s , such as a t h l e t e s o r t h o s e i n v o l v e d i n heavy p h y s i c a l l a b o r , a r e compare f a t n e s s r a t i o i s i n v a r i a b l y h i g h e r i n a c t i v e i n d i v i d u a l s . The normal range o f r e l a t i v e f a t n e s s i s 15-20% body weight f o r males and 20-25% f o r f e m a l e s . On the o t h e r hand, the range f o r a t h l e t i c groups i s n o r m a l l y 5-15% f a t f o r males and 10-20% f o r f e m a l e s . D e s c r i p t i o n s o f the body c o m p o s i t i o n c h a r a c t e r i s t i c s o f v a r i o u s male and female a t h l e t i c groups have been p r o v i d e d i n o t h e r r e v i e w s (17,18). I t must be n o t e d , however, t h a t w h i l e c r o s s - s e c t i o n a l comparisons o f p h y s i c a l l y a c t i v e t o i n a c t i v e groups s u g g e s t t h a t e x e r c i s e i n f l u e n c e s an i n c r e a s e i n the l e a n n e s s t o f a t n e s s r a t i o , t h i s i n t e r p r e t a t i o n must be tempered by c o n s i d e r a t i o n t h a t l e a n i n d i v i d u a l s more f r e q u e n t l y s e l e c t o r a r e s e l e c t e d t o p a r t i c i p a t e i n p h y s i c a l l y demanding a c t i v i t i e s . I n t e r p r e t a t i o n o f t h e e x p e r i m e n t a l e v i d e n c e c o n c e r n i n g the e f f e c t o f e x e r c i s e on human body c o m p o s i t i o n must a l s o be viewed c o n s e r v a t i v e l y s i n c e o n l y i n f r e q u e n t l y a r e c o n t r o l groups employed, ad l i b i t u m d i e t a r y p r a c t i c e s a r e assumed t o remain c o n s t a n t but a r e r a r e l y monitored over t h e d u r a t i o n o f the experiment and o f t e n a mismatch e x i s t s between e x e r c i s e energy e x p e n d i t u r e and body c o m p o s i t i o n changes. The l a t t e r c o n c e r n has been p r e v i o u s l y r e p o r t e d by Grande ( 1 9 ) , Moody e t a l . ( 2 0 ) , Wilmore e t a l . ( 2 1 ) , and B o i l e a u e t a l . ( 2 2 ) . In t h e s e s t u d i e s , t h e energy e q u i v a l e n t o f f a t r e d u c t i o n and FFB g a i n f a r exceeded the energy expended i n e x e r c i s e . T h i s problem i s l i k e l y m u l t i f a c e t e d and may be r e l a t e d t o inadvertent dietary c a l o r i c reduction, inaccurate estimation of e x e r c i s e c a l o r i c e x p e n d i t u r e , change i n normal p h y s i c a l a c t i v i t y h a b i t s , o r body c o m p o s i t i o n m e t h o d o l o g i c a l c o n s i d e r a t i o n s . In s p i t e o f the a f o r e m e n t i o n e d problems i n c o n d u c t i n g body c o m p o s i t i o n r e s e a r c h on humans, t h e r e i s c o n v i n c i n g e v i d e n c e t o suggest t h a t e x e r c i s e i s a s i g n i f i c a n t f a c t o r i n body weight c o n t r o l and f a t r e d u c t i o n i n nonobese and m i l d l y obese i n d i v i d u a l s . However, when compared t o a n i m a l d a t a , t h e r e l a t i v e e f f e c t s i n humans appear a t b e s t t o be modest. F u r t h e r , t h e r e i s g e n e r a l consensus t h a t i n s e v e r e o b e s i t y e x e r c i s e a l o n e i s an i n s u f f i c i e n t treatment ( 2 3 , 2 4 ) . S e v e r a l r e v i e w s have addressed the e f f e c t o f a e r o b i c e x e r c i s e on body weight and c o m p o s i t i o n m o d i f i c a t i o n ( 1 8 , 2 5 , 2 6 , 2 7 ) . A summary o f 32 s t u d i e s i n v o l v i n g a d u l t m a l e s , a d u l t f e m a l e s , and c h i l d r e n i s p r e s e n t e d i n T a b l e I. The s t u d i e s ranged from 8 t o 20

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NUTRT IO IN AND AEROBC I EXERCS IE Table I.

Summary o f the E f f e c t o f 8 - 2 0 Weeks o f A e r o b i c E x e r c i s e on Changes i n Body Composition-'-

X SD

Body Wt. (kq) -1.2 1.1

%Fat -1.7 1.2

Fat (kq) -1.7 1.3

FFB (kq) 0.4 1.1

Females (7 sample groups)

X SD

-1.9 2.3

-3.3 3.3

-2.9 2.6

1.0 1.7

Children (10 sample groups)

X SD

-1.6 3.7

-2.6 3.3

-2.1 2.9

0.5 1.1

Group Males (24 sample groups)

T h i s t a b l e was c o n s t r u c t e d from a summary o f d a t a p r e s e n t e d by Wilmore (18) which i n c l u d e d 25 s t u d i e s o f 8 - 2 0 weeks' d u r a t i o n . The d a t a f o r c h i l d r e n i n c l u d e seven s t u d i e s and were summarized from Boileau et a l . (27). weeks d u r a t i o n a n d , i n g e n e r a l , t r a i n i n g exceeded 30 minutes p e r s e s s i o n w i t h an average frequency o f 3 days per week. The mode o f a e r o b i c e x e r c i s e c o n s i s t e d m o s t l y o f w a l k i n g , j o g g i n g , r u n n i n g , and bicycling. W h i l e r e l a t i v e l y l a r g e v a r i a t i o n s can be seen among t h e s t u d i e s , a mean body weight r e d u c t i o n o f 1 . 2 , 1 . 9 , and 1.6 kg was observed f o r a d u l t m a l e s , a d u l t f e m a l e s , and c h i l d r e n , r e s p e c t i v e l y . As expected i n a e r o b i c e x e r c i s e , f a t l o s s exceeded body weight l o s s s u g g e s t i n g t h a t the FFB was a t l e a s t m a i n t a i n e d . T h i s i s s i g n i f i c a n t s i n c e d i e t a r y r e s t r i c t i o n a l o n e o f t e n l e a d s t o l o s s o f body p r o t e i n and FFB ( 2 8 ) . I t i s i n t e r e s t i n g t h a t the 1.7 kg f a t l o s s and 0 . 4 kg FFB g a i n observed a c r o s s t h e a d u l t male s t u d i e s r e p r e s e n t s an e x p e n d i t u r e o f 15000 K c a l which i s r o u g h l y e q u i v a l e n t t o a moderate a e r o b i c e x e r c i s e program o f 1 0 - 1 5 weeks d u r a t i o n . W h i l e t h e s e s t u d i e s l e a d t o the c o n c l u s i o n t h a t e x e r c i s e evokes a modest body weight and f a t l o s s w h i l e m a i n t a i n i n g t h e FFB, t h e c o m b i n a t i o n o f moderate d i e t a r y c a l o r i c r e d u c t i o n and moderate e x e r c i s e energy e x p e n d i t u r e may p r o v i d e the o p t i m a l r e s p o n s e . Zuti and G o l d i n g (29) s t u d i e d t h r e e body c o m p o s i t i o n m o d i f i c a t i o n programs i n c l u d i n g d i e t a r y c a l o r i c r e d u c t i o n (500 K c a l / d a y ) , e x e r c i s e (500 K c a l / d a y ) , and a c o m b i n a t i o n o f d i e t (250 K c a l / d a y ) and e x e r c i s e (250 K c a l / d a y ) i n a d u l t women judged t o be 9 - 1 8 kg o v e r w e i g h t . The body weight decrease was s i m i l a r among the groups r a n g i n g from 4 . 5 t o 5 . 5 kg d u r i n g t h e program. Most o f t h e weight l o s s was accounted f o r by f a t l o s s which was 4 . 2 , 5 . 7 , and 6 . 0 kg f o r t h e d i e t , e x e r c i s e , and c o m b i n a t i o n g r o u p s , r e s p e c t i v e l y . Fat l o s s i n the e x e r c i s e and c o m b i n a t i o n groups was s i m i l a r but s i g n i f i c a n t l y more than the d i e t group. A l s o , t h e e x e r c i s e and c o m b i n a t i o n groups m a i n t a i n e d t h e i r FFB g a i n i n g 0 . 5 and 0 . 9 k g , r e s p e c t i v e l y , whereas the d i e t group l o s t 1.1 kg o f F F B . C l e a r l y , the maintenance o f FFB appears t o be an advantage p r o v i d e d by e x e r c i s e and needs t o be c o n s i d e r e d an i m p o r t a n t a s p e c t among t h e various o b e s i t y treatment m o d a l i t i e s . 1

1

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Measurements o f Body C o m p o s i t i o n Measurements o f body c o m p o s i t i o n c o n s i s t o f d i r e c t and i n d i r e c t methods. D i r e c t methods i n c l u d e measures o f body p r o t e i n , w a t e r , f a t , and ash ( m i n e r a l s ) . An a l t e r n a t i v e d i r e c t approach i s measurement o f i n d i v i d u a l t i s s u e w e i g h t s . While t h e s e methods a r e unambiguous and p r e f e r r e d , they are g e n e r a l l y l i m i t e d t o s t u d i e s w i t h a n i m a l s . In n o n - s a c r i f i c i a l b e i n g s , d i r e c t d e t e r m i n a t i o n s o f t i s s u e w e i g h t s a r e i m p o s s i b l e , and d e t e r m i n a t i o n s o f body c o m p o s i t i o n a r e r e s t r i c t e d t o use o f i n d i r e c t , n o n i n v a s i v e methods. Human body c o m p o s i t i o n assessment r e l i e s on i n d i r e c t measurement t e c h n i q u e s . V a l i d a t i o n o f t h e s e t e c h n i q u e s i s l i m i t e d t o d i r e c t a n a l y s i s o f 4 o r 5 a d u l t c a d a v e r s , depending on the measurement method ( 3 0 , 3 1 ) . The measurement t e c h n i q u e s most o f t e n employed i n c l u d e d e n s i t o m e t r y , hydrometry, by gamma-ray s p e c t r o m e t r y , and anthropometry. The methodology o f t h e s e t e c h n i q u e s has been reviewe several reports (17,26,32,33) have p r o v i d e d s e v e r a l a d d i t i o n a l t e c h n i q u e s such as n e u t r o n a c t i v a t i o n a n a l y s i s (34) and o t h e r p r o m i s i n g but as y e t u n v a l i d a t e d a p p r o a c h e s , i n c l u d i n g t o t a l body impedance ( 3 5 ) , e l e c t r i c a l c o n d u c t i v i t y ( 3 6 ) , and n u c l e a r magnetic resonance imagery ( 3 7 ) . A primary m e t h o d o l o g i c a l c o n s i d e r a t i o n i n the use o f the i n d i r e c t t e c h n i q u e s i s the c o m p o s i t i o n a l model o f the body. Several models have been proposed i n c l u d i n g : a four-compartment system (28) c o n s i s t i n g o f bone m i n e r a l , c e l l s , and e x t r a c e l l u l a r water as the energy u t i l i z i n g component p l u s f a t as the energy s t o r a g e component; a three-component model (38) i n c l u d i n g f a t , m u s c l e , and a remainder mass (muscle f r e e l e a n ) ; and two-component models c o n s i s t i n g o f e i t h e r f a t - f r e e body (32) o r l e a n body mass (LBM) (39) and f a t . The c o n c e p t u a l d i f f e r e n c e between the f a t - f r e e body weight and l e a n body mass models i s t h a t LBM i n c l u d e s e s s e n t i a l f a t . The two-component model i s used a l m o s t e x c l u s i v e l y and d a t a a r e d e r i v e d from t h e measurement methods mentioned above. S i n c e d e n s i t o m e t r y i s c o n s i d e r e d the s t a n d a r d a g a i n s t which o t h e r t e c h n i q u e s a r e compared and v a l i d a t e d , d i s c u s s i o n here i s l i m i t e d t o a p p l i c a t i o n o f the t w o component model u s i n g the d e n s i t o m e t r i c method f o r e s t i m a t i o n o f body c o m p o s i t i o n . Body d e n s i t y (D ) i s t h e r a t i o o f body weight ( B W ) t o body volume. Body volume can be measured by water d i s p l a c e m e n t o r h e l i u m d i l u t i o n , but t h e method o f c h o i c e i s underwater w e i g h i n g (BWL^Q) w i t h c o r r e c t i o n s f o r the d e n s i t y o f water (DH^QO and r e s i d u a l l u n g volume (RV) ( 4 0 ) . D e n s i t y i s then e s t i m a t e d as f o l l o w s : B

A I R

B W

B W

air

air » J

B W

H20

- RV

H20

When the two-component system i s a p p l i e d t o the d e n s i t o m e t r i c e s t i m a t i o n o f f a t and f a t - f r e e body, c e r t a i n c r i t i c a l assumptions must be made: (1) the d e n s i t i e s o f f a t and FFB a r e known and a d d i t i v e ; (2) the d e n s i t i e s o f the FFB components ( e . g . , w a t e r ,

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m i n e r a l , and p r o t e i n ) a r e r e l a t i v e l y c o n s t a n t w i t h i n and among i n d i v i d u a l s ; (3) t h e p r o p o r t i o n o f each FFB component i s r e l a t i v e l y c o n s t a n t w i t h i n and among i n d i v i d u a l s w i t h r e s p e c t t o t h e t o t a l F F B ; and (4) t h e i n d i v i d u a l b e i n g a s s e s s e d d i f f e r s o n l y from a s t a n d a r d " r e f e r e n c e man" i n t h e amount o f depot f a t p o s s e s s e d . U s i n g t h e s e a s s u m p t i o n s , M o r a l e s e t a l . (41) d e s c r i b e d t h e f o l l o w i n g m a t h e m a t i c a l model f o r t h e r e l a t i o n s h i p o f ϋ β t o t h e f a t and t h e components o f f a t - f r e e body:

1

- f

Dp Β

+w

D~

D

r

+m D

w

+p

m m

D^

ρ

where f , w, m, and ρ a r e t h e f r a c t i o n s o f f a t , w a t e r , m i n e r a l , and p r o t e i n , r e s p e c t i v e l y , and D f , D , D , and D t h e d e n s i t i e s o f each component. The r e l a t i o n s h i p between body f a t c o n t e n t ( F f ) and body d e n s i t y has been d e s c r i b e f a t and FFB t o be 0.900 gm/cc and 1.100 gm/cc, r e s p e c t i v e l y : w

F

f

m

p

= 4.95 - 4.50 D

B

The assumption o f FFB constancy both w i t h i n an i n d i v i d u a l and among i n d i v i d u a l s i s , a t b e s t , o n l y t e n a b l e w i t h i n s e l e c t e d phases o f t h e l i f e c y c l e and v a l i d w i t h i n sex and r a c i a l groups (43,44). Evidence d u r i n g growth and m a t u r a t i o n suggests t h a t t h e FFB i s c h e m i c a l l y "immature" w i t h t h e water c o n t e n t h i g h e r (45,46,47) and t h e m i n e r a l c o n t e n t lower (48,49) than a d u l t l e v e l s . S i n c e water c o n s t i t u t e s a h i g h p e r c e n t a g e o f t h e FFB b u t a r e l a t i v e l y low d e n s i t y (0.9934 gm/cc a t 37°c) and m i n e r a l a low p e r c e n t a g e o f t h e FFB b u t a h i g h d e n s i t y (3.0 gm/cc) w i t h r e s p e c t t o o v e r a l l FFB d e n s i t y , t h e a c c e p t e d v a l u e o f 1.10 gm/cc generated f o r t h e a d u l t model i s l i k e l y not a p p l i c a b l e t o t h e growing i n d i v i d u a l . T h i s s u g g e s t s t h a t t h e FFB d e n s i t y i s lower and may range from 1.070 t o 1.100 gm/cc d u r i n g growth and development (49,50). There i s a l s o e v i d e n c e t h a t t h e FFB d e n s i t y may be a l t e r e d i n the l a t e r s t a g e s o f t h e a g i n g c o n t i n u u m . T a b l e I I p r e s e n t s e s t i m a t e s o f change i n t h e FFB d e n s i t y throughout t h e l i f e c y c l e . W h i l e t h e s e d a t a a r e i n c o m p l e t e , t h e t r e n d s u g g e s t s t h a t a primary assumption i n t h e use o f d e n s i t o m e t r i c a n a l y s i s f o r assessment o f body c o m p o s i t i o n may n o t be t e n a b l e . I t i s w e l l known t h a t t h e r e i s bone m i n e r a l l o s s w i t h a g i n g (52) which i s p a r t i c u l a r l y e v i d e n t i n the postmenopausal f e m a l e . T h i s l o s s i s a t l e a s t one f a c t o r a f f e c t i n g a l t e r a t i o n s i n t h e r e l a t i v e p r o p o r t i o n s o f t h e FFB c o n s t i t u e n t s . The e x t e n t t o which water and p r o t e i n change w i t h a g i n g both i n r e l a t i v e and a b s o l u t e amounts i s a l s o an i m p o r t a n t c o n s i d e r a t i o n . The magnitude o f t h e s e changes a n d , t h u s , t h e change i n FFB d e n s i t y needs t o be more d e f i n i t i v e l y d e s c r i b e d i n f u t u r e r e s e a r c h so t h a t a c c u r a t e e s t i m a t e s o f body f a t and f a t - f r e e body can be made. Not o n l y i s t h e d e n s i t o m e t r i c e s t i m a t i o n o f body c o m p o s i t i o n a f f e c t e d by l i f e c y c l e changes i n t h e c o m p o s i t i o n o f t h e FFB s o , t o o , a r e o t h e r methods which a r e based on s i m i l a r a s s u m p t i o n s . F o r

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

9.

LAYMAN AND BOL IEAU Table I I .

131 Aerobic

Exercise and Body

Composition

E s t i m a t e d Changes i n D e n s i t y o f t h e F a t - F r e e Body Throughout the L i f e C y c l e f o r M a l e s 3

Age 5 10 12 15 20-29 40-49 50-59 60-69 70-79

Ν

— 39 21 52 45 34 30 25 21

%FFB 85.4 83.5 83.6 85.1 83.1 69.7 68.7 68.4 70.4

D e n s i t y FFB gm/cc 1.078 1.082 1.091 1.096 1.106 1.092 1.089 1.085 1.085

'Estimates o f the f a t - f r e e body d e n s i t y were made from d e n s i t y and body water d a t a [ S i r i ( 4 2 ) ] a l . (49) f o r the 5 - y e a r - o l d m a l e , B o i l e a u e t a l . (50) f o r t h e 1 0 t o 2 9 - y e a r - o l d m a l e s , and N o r r i s e t a l . (51) f o r t h e 4 0 - t o 79-year-old males. example, changes i n the h y d r a t i o n o f the FFB and p o t a s s i u m c o n t e n t o f the FFB r e q u i r e fundamental adjustments i n the "assumed" c o n s t a n t s f o r e s t i m a t i o n o f body c o m p o s i t i o n by hydrometry and K spectrometry. Perhaps t h e most p o p u l a r c l i n i c a l method u t i l i z e d t o e s t i m a t e body f a t employs the s k i n f o l d c a l i p e r t o measure subcutaneous f a t . The method i s based on the f a c t t h a t a r e l a t i v e l y l a r g e p r o p o r t i o n o f t o t a l body f a t l i e s j u s t below the s k i n . Skinfold thickness i s i n v e r s e l y r e l a t e d t o body d e n s i t y . Based on the r e l a t i o n s h i p between subcutaneous f a t and body d e n s i t y , s k i n f o l d t h i c k n e s s measures a r e used t o e s t i m a t e body d e n s i t y v i a r e g r e s s i o n e q u a t i o n s . While t h i s r e l a t i o n s h i p can p r o v i d e a c c u r a t e e s t i m a t e s o f body c o m p o s i t i o n , t h e r e l i a b i l i t y depends on the a c c u r a c y o f t h e s k i n f o l d measurements, the q u a l i t y o f the r e g r e s s i o n e q u a t i o n s , and t h e v a l i d i t y o f the d e n s i t y v a l u e s . Because o f t h e s e f a c t o r s the r e l a t i o n s h i p o f s k i n f o l d t h i c k n e s s t o body d e n s i t y appears t o change throughout the l i f e c y c l e ( 5 3 ) ; t h e r e f o r e , the r e g r e s s i o n e q u a t i o n employed must be v a l i d f o r the sample group b e i n g a s s e s s e d . 4 0

E f f e c t o f A e r o b i c E x e r c i s e on the Body C o m p o s i t i o n o f Experimental Animals While i t i s c r i t i c a l t o study the e f f e c t s o f a e r o b i c e x e r c i s e on humans, the l i m i t a t i o n s o f body c o m p o s i t i o n methodology p l u s the even more d i f f i c u l t problems o f c o n t r o l l i n g and d e f i n i n g d i e t a r y i n t a k e and t o t a l p h y s i c a l a c t i v i t y make use o f a n i m a l models essential. Use o f e x p e r i m e n t a l a n i m a l s a l l o w s f o r c o n t r o l o f d i e t and e x e r c i s e p l u s p r e c i s e c h a r a c t e r i z a t i o n o f e x p e r i m e n t a l groups ( i . e . , a g e , s e x , w e i g h t , and g e n e t i c b a c k g r o u n d ) . Further, experimental conditions i n c l u d i n g c a l o r i c i n t a k e , length of study, and e x e r c i s e i n t e n s i t y and d u r a t i o n can be m o d i f i e d o v e r a l a r g e r range. These f a c t o r s make experiments w i t h a n i m a l s i m p o r t a n t f o r t h e e v a l u a t i o n and u n d e r s t a n d i n g o f d a t a from s t u d i e s w i t h humans.

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132

NUTRITION AND AEROBIC EXERCISE

Under c o n t r o l l e d c o n d i t i o n s o f d i e t a r y i n t a k e and d a i l y e x e r c i s e , i t i s c l e a r t h a t a e r o b i c e x e r c i s e reduces body weight i n e x p e r i m e n t a l a n i m a l s ( 5 4 , 5 5 , 5 6 ) . To i l l u s t r a t e t h i s p o i n t , we have p r e s e n t e d d a t a from our l a b o r a t o r y u s i n g a moderate a e r o b i c e x e r c i s e program [ a p p r o x i m a t e l y 75% V Û 2 x ( 5 7 ) ] i n Table I I I . Male r a t s m a

Table I I I .

Tissues Body weight

Body and T i s s u e Weights A f t e r 12 Weeks of Exercise Training Units

Sedentary

Trained

(g)

578 + 1 0 . 3

493 + 7.9

*

Organs Heart Liver Adrenals

(mg)

24 +

S k e l e t a l Muscles Soleus Plantaris Gastrocnemius Psoas

(mg) (mg) (g) (g)

163 + 492 + 2.35 1.45

6 24 0.05 0.04

164 + 5 449 + 8 2.24 + 0.04 0.04 1.42

Adipose T i s s u e s Perirenal Epididymal Inguinal

(g) (g) (g)

3.63 + 2.88 + 5.19 +

0.16 0.10 0.24

1.86 + 0 . 1 6 * 0.09* 1.91 3.18 + 0 . 1 3 *

1.23

0.26 1

1.20

0.04

27 + 1

*

V a l u e s a r e Means + SEM, η = 2 1 , * ρ < 0 . 0 5 . (Quig and Layman, u n p u b l i s h e d . ) 8 weeks o l d and w e i g h i n g 200 g were t r a i n e d 5 days/week f o r 12 weeks on a m o t o r - d r i v e n t r e a d m i l l w i t h an 8 ° i n c l i n e a t a speed o f 28 meters/minute f o r 60 minutes each d a y . These a n i m a l s were young and s t i l l growing. The f i n a l body w e i g h t s a r e p r e s e n t e d i n Table III. T h i s r e l a t i v e l y m i l d e x e r c i s e program produced a 15% d i f f e r e n c e i n w e i g h t s between the t r a i n e d and sedentary g r o u p s . The d i f f e r e n c e i n body w e i g h t s between the t r a i n e d and s e d e n t a r y a n i m a l s was a l m o s t e x c l u s i v e l y due t o a lower amount o f body f a t i n the t r a i n e d g r o u p . The w e i g h t s o f i n d i v i d u a l t i s s u e s a r e p r e s e n t e d i n Table I I I . The t r a i n e d a n i m a l s have v i r t u a l l y no d i f f e r e n c e i n muscle o r organ w e i g h t s but have a p p r o x i m a t e l y 40% l e s s body f a t . I n d i v i d u a l a d i p o s e t i s s u e s range from 34 t o 49% l e s s than i n t h e sedentary a n i m a l s . Other s t u d i e s have examined t h e changes i n t h e c o m p o s i t i o n o f the t o t a l body w i t h r e s p e c t t o w a t e r , p r o t e i n , f a t and ash and the r e s u l t s a r e s i m i l a r t o t h o s e found w i t h t i s s u e analysis. These s t u d i e s found d e c r e a s e s i n both t h e r e l a t i v e and a b s o l u t e amounts o f body f a t , p l u s an i n c r e a s e i n t h e p e r c e n t a g e o f FFB i n growing ( 5 5 , 5 8 , 5 9 ) o r a d u l t (60) a n i m a l s . Thus the d i f f e r ­ ence i n w e i g h t s between sedentary and t r a i n e d a n i m a l s was a l m o s t e n t i r e l y due t o l o w e r body f a t i n the endurance t r a i n e d a n i m a l s .

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

9.

LAYMAN AND BOL IEAU

Aerobic

Exercise and Body

133

Composition

As s t a t e d above, moderate a e r o b i c e x e r c i s e has l i t t l e e f f e c t on w e i g h t s o f o t h e r t i s s u e s (Table I I I ) . There a r e some r e p o r t s o f i n c r e a s e d h e a r t weights due t o a e r o b i c e x e r c i s e ( 5 4 , 6 1 ) ; however, most s t u d i e s found o n l y changes i n f u n c t i o n a l parameters such as h e a r t r a t e and s t r o k e volume ( 5 4 , 6 2 ) . S k e l e t a l muscles d i r e c t l y a s s o c i a t e d w i t h p e r f o r m i n g a e r o b i c e x e r c i s e g e n e r a l l y do not increase in s i z e (63). I n s t e a d , changes i n s k e l e t a l muscles o c c u r a t the c e l l u l a r l e v e l through i n c r e a s e s i n m i t o c h o n d r i a l number and s i z e and i n c r e a s e s i n o x i d a t i v e c a p a c i t y ( 6 4 ) . The i n c r e a s e i n t h e weight o f the a d r e n a l g l a n d i s a c o n s i s t e n t f i n d i n g d u r i n g a e r o b i c t r a i n i n g and r e f l e c t s t h a t e x e r c i s e i s a s t r e s s t o the body which g e n e r a t e s an e n d o c r i n e response ( 5 4 ) . The study p r e s e n t e d i n T a b l e I I I demonstrates t h a t a e r o b i c e x e r c i s e a l t e r s energy b a l a n c e and reduces body f a t . The mechanism f o r t h i s response was addressed by Mayer ( 6 5 , 6 6 ) . He r e p o r t e d t h a t e x e r c i s e i n f l u e n c e d energy b a l a n c e by i n c r e a s i n g c a l o r i c e x p e n d i t u r e and by r e d u c i n g a p p e t i t e a e r o b i c e x e r c i s e produce r a t s ( 5 9 , 6 0 ) . These i n v e s t i g a t o r s suggested t h a t t h e e f f e c t was r e l a t e d t o the i n t e n s i t y and d u r a t i o n o f the e x e r c i s e program. The food i n t a k e d a t a f o r the s t u d y d e s c r i b e d i n T a b l e I I I a r e p r e s e n t e d i n Table IV and appear t o s u p p o r t t h i s c o n c l u s i o n . A f t e r o n l y

T a b l e IV.

Average D a i l y Food I n t a k e Weeks o f

Training

-

Group

7

(Kcal/day)

Sedentary

70.3 + 3.7

72.0 + 2.5

Trained

5 9 . 5 + 2^5*

73.3 + 4.6

V a l u e s a r e Means + SEM, η = 7, * ρ < 0 . 0 5 . (Quig and Layman, u n p u b l i s h e d . ) 4 weeks o f t r a i n i n g , a n i m a l s consumed 15% l e s s energy each d a y . However, a f t e r 7 weeks o f t r a i n i n g , the f o o d i n t a k e o f the t r a i n e d a n i m a l s had r e t u r n e d t o n o r m a l . T h i s f i n d i n g i s s i m i l a r t o t h e r e p o r t o f A p p l e g a t e e t a l . (67) u s i n g a lower i n t e n s i t y e x e r c i s e w i t h obese r a t s . Thus n e g a t i v e energy b a l a n c e can be produced d u r i n g e x e r c i s e due t o i n c r e a s e d energy e x p e n d i t u r e , o r d e c r e a s e d c a l o r i c i n t a k e , or both. In c o n t r a s t t o male r a t s , female r a t s s u b j e c t e d t o endurance t r a i n i n g m a i n t a i n body weight comparable t o s e d e n t a r y age c o n t r o l s by i n c r e a s i n g food i n t a k e ( 6 5 ) . However, w h i l e females m a i n t a i n t o t a l body w e i g h t , e x e r c i s e s t i l l produces the same e f f e c t s on body c o m p o s i t i o n . Thus i n e v a l u a t i n g a n i m a l s t u d i e s , i t i s i m p o r t a n t t o remember t h a t , d u r i n g moderate t o heavy e x e r c i s e t r a i n i n g , male r a t s e x p e r i e n c e a p p e t i t e s u p p r e s s i o n and l o s e body weight and body f a t . W h i l e under s i m i l a r c o n d i t i o n s , female r a t s w i l l m a i n t a i n body

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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w e i g h t by i n c r e a s i n g food i n t a k e . Female r a t s s t i l l e x p e r i e n c e t h e decrease i n b o t h the a b s o l u t e and r e l a t i v e amounts o f body f a t but may have a s m a l l i n c r e a s e i n LBM. Body C o m p o s i t i o n Changes Due t o D i e t and E x e r c i s e Lay p u b l i c a t i o n s a r e i n u n d a t e d w i t h f a d d i e t s d e s i g n e d t o reduce body weight " q u i c k l y and e a s i l y " u s i n g a v a r i e t y o f c a l o r i c r e s t r i c t i o n s ( 6 8 ) . Most i n d i v i d u a l s attempt t o produce a n e g a t i v e energy b a l a n c e and reduce body weight by d e c r e a s i n g food i n t a k e . The advantage o f u s i n g food r e s t r i c t i o n i s t h a t i t a c c e l e r a t e s the r a t e o f weight l o s s . However, the enthusiasm f o r these d i e t s d i s s i p a t e s a f t e r two o r t h r e e weeks and the weight i s r e g a i n e d . In a d d i t i o n , i t i s u n c l e a r i f the weight l o s s g e n e r a t e d by t h e s e d i e t s produces any improvement i n body c o m p o s i t i o n . There a r e numerous s t u d i e s i n v o l v i n g humans o r a n i m a l s t h a t have examined t h e e f f e c t o f weight l o s s ( 6 9 , 7 0 , 7 1 , 7 2 ) r e s t r i c t i o n causes d e c r e a s e s i n body weight and body f a t , and t h a t the magnitude o f t h e s e l o s s e s i s p r o p o r t i o n a l t o the l e n g t h and the s e v e r i t y o f t h e food d e p r i v a t i o n . There a r e a l s o s u b s t a n t i a l l o s s e s o f s k e l e t a l muscle and organ t i s s u e s ( 7 1 , 7 2 ) . Assuming the g o a l i s t o o p t i m i z e h e a l t h , then the o b j e c t i v e i s t o decrease body f a t c o n t e n t , and m a i n t a i n FFB weight which w i l l maximize t h e b e n e f i t s o f weight l o s s . T h e r e f o r e , i t i s i m p o r t a n t t o examine t h e s p e c i f i c e f f e c t s o f d i e t i n g on body c o m p o s i t i o n . D u r i n g t h e e a r l y phase o f d i e t i n g , water a c c o u n t s f o r a l a r g e p e r c e n t a g e o f the weight l o s t ( 6 9 ) . Hence, the r a t e o f weight l o s s i s much h i g h e r d u r i n g t h e f i r s t few days o f d i e t m o d i f i c a t i o n , because the c a l o r i c d e n s i t y o f t h e weight l o s s i s l o w . A f t e r the i n i t i a l a d a p t a t i o n t o a lower c a l o r i c i n t a k e , t h e weight l o s s i s d e r i v e d p r e d o m i n a n t l y from s t o r e s o f body f a t p l u s l o s s e s o f FFB t o p r o v i d e s u f f i c i e n t amino a c i d s f o r e s s e n t i a l p r o t e i n s y n t h e s i s and g l u c o n e o g e n e s i s ( 7 3 ) . These l o s s e s o c c u r a t a r e l a t i v e l y c o n s t a n t r a t i o w i t h FFB e s t i m a t e d t o c o n t r i b u t e 35-50% o f the weight l o s s ( 1 4 ) . T h i s r a t i o d i f f e r s depending on the percentage o f body f a t and age o f the a n i m a l , but the r a t i o remains a p p r o x i m a t e l y c o n s t a n t f o r an a n i m a l throughout a p e r i o d o f f o o d r e s t r i c t i o n ( 7 2 ) . Thus weight l o s s by d i e t a l o n e w i l l decrease body w e i g h t , but produces l i t t l e improvement i n body c o m p o s i t i o n . Weight l o s s produced by d i e t a r y r e s t r i c t i o n i n c o m b i n a t i o n w i t h a e r o b i c e x e r c i s e appears t o p r o v i d e a more o p t i m a l weight l o s s based on improvements i n body c o m p o s i t i o n . The amount o f body f a t l o s t i s p r o p o r t i o n a l t o the c a l o r i c d e f i c i t ( i . e . , the d e c r e a s e i n i n t a k e p l u s t h e i n c r e a s e i n e x p e n d i t u r e ) , but the c o m p o s i t i o n o f the weight l o s s i s a l s o dependent on the amount o f FFB l o s t . The l o s s o f FFB i s reduced by e x e r c i s e which s e l e c t i v e l y m a i n t a i n s muscle mass. Thus, weight l o s s a s s o c i a t e d w i t h e x e r c i s e becomes more s p e c i f i c a l l y l o s s o f body f a t ( 6 0 ) . These d a t a s u g g e s t t h a t the o p t i m a l regimen f o r r e d u c i n g body f a t i s a c o m b i n a t i o n o f d i e t r e s t r i c t i o n and a e r o b i c e x e r c i s e . The components o f an e x e r c i s e program a r e d e f i n e d by t h e parameters i n t e n s i t y , d u r a t i o n , and f r e q u e n c y . I n t e n s i t y r e f e r s t o the v i g o r o f the a c t i v i t y and can be d e f i n e d by h e a r t r a t e . Duration d e s c r i b e s the l e n g t h o f the workout, and frequency i n d i c a t e s the

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number o f s e s s i o n s each week. The primary o b j e c t i v e o f an e x e r c i s e program designed t o improve body c o m p o s i t i o n i s t o maximize the amount o f energy expended and t o do so under c o n d i t i o n s t h a t w i l l o p t i m i z e m o b i l i z a t i o n and u t i l i z a t i o n o f f a t as the energy s o u r c e . To most e f f e c t i v e l y a c c o m p l i s h these o b j e c t i v e s , i t i s i m p e r a t i v e t h a t the e x e r c i s e i n t e n s i t y be moderate. A moderate e x e r c i s e program c o n s i s t s o f m a i n t a i n i n g an e x e r c i s e h e a r t r a t e o f 130-150 b e a t s per minute (b/min) i n t h e 2 0 - t o 5 0 - y e a r age range (110-130 b/min i n the 5 0 - t o 8 0 - y e a r range) f o r 30 t o 45 minutes per s e s s i o n w i t h a frequency o f 3 t o 4 days per week ( 7 4 ) . T h i s program w i l l u t i l i z e a p p r o x i m a t e l y 1000 K c a l per week and l e a d t o f a t l o s s . The type o f e x e r c i s e s h o u l d r e q u i r e use o f a major p o r t i o n o f the muscle mass. W a l k i n g , j o g g i n g , b i c y c l i n g , and swimming are n o r m a l l y a c t i v i t i e s o f c h o i c e . In the s e v e r e l y o b e s e , b i c y c l i n g and swimming a r e p a r t i c u l a r l y u s e f u l a c t i v i t i e s s i n c e they a r e non-weight b e a r i n g and t h u s produce l e s s o r t h o p e d i c s t r e s s . Summary O b e s i t y i s a major h e a l t h problem i n the U n i t e d S t a t e s . I t i s e s t i m a t e d t h a t the body c o m p o s i t i o n o f one i n every t h r e e Americans c o n t a i n s an e x c e s s i v e amount o f body f a t which may p r e d i s p o s e t h e s e i n d i v i d u a l s to increased r i s k of high blood pressure, heart d i s e a s e , d i a b e t e s , g o u t , and o t h e r a d u l t d i s e a s e s . M o d i f i c a t i o n o f body c o m p o s i t i o n , and s p e c i f i c a l l y r e d u c t i o n o f body f a t , r e q u i r e s a decrease i n food i n t a k e and/or an i n c r e a s e i n e x e r c i s e . These changes i n the b a l a n c e o f energy i n t a k e and e x p e n d i t u r e w i l l reduce body w e i g h t . The a c t u a l c o m p o s i t i o n o f t h e weight l o s s i s dependent on the l e v e l o f d i e t a r y r e s t r i c t i o n and the amount o f p h y s i c a l activity. Weight l o s s due t o " d i e t i n g " a l o n e has a r e l a t i v e l y s m a l l e f f e c t on body c o m p o s i t i o n because body f a t and muscle a r e l o s t i n a p p r o x i m a t e l y e q u a l amounts. D i e t i n g p l u s a e r o b i c e x e r c i s e decreases body weight by i n c r e a s i n g the use o f energy s t o r e d i n body f a t , but a l s o s e r v e s t o m a i n t a i n t h e muscle mass through i n c r e a s e d usage. A p r e s c r i p t i o n f o r m o d i f i c a t i o n o f body c o m p o s i t i o n must c o n s i d e r the i n t e n s i t y , d u r a t i o n , and frequency o f e x e r c i s e as w e l l as the n u t r i t i o n a l i n t a k e . The g e n e r a l g u i d e l i n e s f o r such a p r e s c r i p t i o n i n c l u d e r e d u c t i o n o f d i e t a r y i n t a k e by 500-1000 C a l o r i e s each day w i t h a minimum o f t h r e e s e s s i o n s o f a e r o b i c e x e r c i s e each week. T h i s program s h o u l d produce a slow weight l o s s o f a p p r o x i m a t e l y one pound per week and s h o u l d m a i n t a i n the d a i l y food i n t a k e above 1200 C a l o r i e s , which i s c o n s i d e r e d the minimum f o r a n u t r i t i o n a l l y adequate d i e t . The e x e r c i s e program s h o u l d e n t a i l t h r e e o r f o u r s e s s i o n s o f a e r o b i c e x e r c i s e per week w i t h each s e s s i o n l a s t i n g 3 0 - 4 0 m i n u t e s . The d e s i r e d i n t e n s i t y o f t h e s e a c t i v i t i e s can be b e s t gauged by h e a r t r a t e , which s h o u l d be i n a range o f 130-150 b e a t s p e r m i n u t e . T h i s program i s d e s i g n e d t o reduce body f a t and m a i n t a i n muscle mass. Use o f the e x e r c i s e a l o n e w i l l s e r v e t o m a i n t a i n body c o m p o s i t i o n and p r e v e n t the a g e - r e l a t e d i n c r e a s e s i n body f a t f r e q u e n t l y observed i n a d u l t s .

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Glossary Anthropometry: s t u d y o f comparative measurements o f t h e body, i n c l u d i n g h e i g h t o r l e n g t h , c i r c u m f e r e n c e s , and s k i n f o l d s . Apoliproteins: the surface p r o t e i n s of l i p o p r o t e i n s ; a p o l i p r o t e i n s A I and A l l a r e t h e major a p o l i p r o t e i n s o f HDL; apo C I I i s a l i p o p r o t e i n p r e s e n t on c h y l o m i c r o n s and VLDL which a c t i v a t e s t h e enzyme l i p o p r o t e i n l i p a s e . Black-Globe temperature: t h e temperature i n s i d e a h o l l o w copper sphere 15.2 cm (6 i n . ) i n diameter p a i n t e d m a t t - b l a c k on the o u t s i d e and c o n t a i n i n g a thermometer i n s e r t e d so t h a t i t s sensing u n i t i s a t the c e n t e r o f the sphere. This temperature i s a measure o f t h e i n t e n s i t y o f r a d i a n t heat from t h e s u r r o u n d i n g s o r the sun. Calories: a unit of r a i s e t h e temperature o f 1 Kg o f water 1 C. C a l o r i e w i t h a c a p i t a l C " i s e q u i v a l e n t t o k i l o c a l o r i e ( K c a l ) and i s used i n n u t r i t i o n t o d e s c r i b e energy i n t a k e and e x p e n d i t u r e . M

Chylomicron: t r i g l y c e r i d e r i c h l i p o p r o t e i n that transports l i p i d s of dietary o r i g i n to peripheral tissues. Coronary Heart D i s e a s e (CHD): a t h e r o s c l e r o s i s ; a p a r t i c u l a r type o f h a r d e n i n g o f t h e a r t e r i e s i n v o l v i n g i n f i l t r a t i o n of f a t t y m a t e r i a l s i n t o the a r t e r i a l w a l l . Dehydration: t h e p r o c e s s o f d e p l e t i o n o f body water from deprivation or loss. Dipsogen:

a substance that s t i m u l a t e s

thirst.

Dry-bulb temperature: t h e temperature i n d i c a t e d by a d r y - b u l b thermometer, s h i e l d e d from the sun, w i t h a d i a m e t e r l a r g e enough t o a l l o w f r e e passage o f a i r around t h e b u l b ; t h e a c t u a l temperature o f t h e a i r . D o u b l e - b l i n d experiment: e x p e r i m e n t a l d e s i g n where t h e s u b j e c t s do n o t know whether t h e y a r e r e c e v i n g the e x p e r i m e n t a l treatment o r a p l a c e b o . F a t f r e e body: or f a t s . Glycogenolysis:

t h e remainder o f t h e body e x c l u d i n g a l l l i p i d s

t h e breakdown o f g l y c o g e n t o g l u c o s e .

Gluconeogenesis: s y n t h e s i s o f g l u c o s e from n o n - c a r b o h y d r a t e p r e c u r s o r s such as amino a c i d s . High d e n s i t y l i p o p r o t e i n (HDL): an a n t i a t h e r o g e n i c l i p o p r o t e i n t h a t f a c i l i t a t e s t h e removal o f c h o l e s t e r o l from t i s s u e s f o r subsequent c a t a b o l i s m .

142

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143

GLOSSARY Hypernatremia: i n c r e a s e i n t h e plasma sodium above t h e normal l e v e l .

concentration

Hyperosmotemia: i n c r e a s e i n the plasma osmolar ( s a l t ) t i o n above normal l e v e l .

concentra-

Hyperproteinemia: i n c r e a s e i n the plasma ( t o t a l ) p r o t e i n c o n c e n t r a t i o n above normal l e v e l . Hypervolemia: level.

i n c r e a s e i n t h e plasma volume above t h e normal

Hypohydration: an e q u i l i b r i u m l e v e l o f t o t a l body water below the normal volume. Hypovolemia: level.

r e d u c t i o n i n t h e plasma volume below t h e normal

In v i t r o : i n t h e t e s t tube; u s u a l l y r e f e r s t o c h e m i c a l o c c u r r i n g i n a t e s t tube.

reactions

In v i v o : i n the l i v i n g being; u s u a l l y r e f e r s t o chemical p r o c e s s e s o c c u r i n g w i t h i n the body. Ischemic Heart d i s e a s e : the h e a r t m u s c l e .

inadequate c i r c u l a t i o n o f b l o o d t o

Lean body mass (LBM): t h e mass o f t h e body e x c l u d i n g t h e a d i p o s e t i s s u e s ; LBM i s t h e same as FFB p l u s a p p r o x i m a t e l y 3% e s s e n t i a l f a t c o n t a i n e d i n c e l l membranes. Low d e n s i t y L i p o p r o t e i n ( L P L ) : a l i p o p r o t e i n that transports c h o l e s t e r o l to t i s s u e s ; associated with increased r i s k of coronary heart disease. M y o c a r d i a l i n f a r c t i o n ( M I ) : h e a r t a t t a c k ; death o f t h e h e a r t muscle due t o a b l o o d c l o t i n a c o r o n a r y a r t e r y . Splanchnic: v i s e r a i ; organs o f the d i g e s t i v e , c i r c u l a t o r y , r e s p i r a t o r y , and e n d o c r i n e systems. Turnover: t h e c o n t i n u o u s p r o c e s s e s o f s y n t h e s i s and breakdown; o f t e n used t o d e s c r i b e the s t e a d y - s t a t e o f p r o t e i n . Very low d e n s i t y l i p o p r o t e i n (VLDL): a t r i g l y c e r i d e r i c h l i p o p r o t e i n t h a t t r a n s p o r t s l i p i d t o t i s s u e s and s e r v e s as a p r e c u r s o r o f LDL. max:

maximum oxygen consumption.

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NUTRT IO IN AND AEROBC I EXERCS IE Wet-bulb globe temperature index: a mathematical expression comprised of the dry-bulb, wet bulb, and black-globe temperatures, which indicates the combined effects of temperature, humidity, a i r movement, and thermal radiation as an environmental stress. Wet-bulb temperature: the temperature indicated by a wet-bulb thermometer where the bulb i s covered by a thin cotton or muslin sleeve, wetted with d i s t i l l e d water, and a i r i s drawn over the bulb i n a v e l o c i t y of at least 107 meters/ minute (350 feet/min).

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Author Index Belko, Amy Z., 80 Boileau, Richard Α . , 125 Greenleaf, John Ε . , 107 Goodman, Michael Ν . , 27 Harrison, Michael H., 107 Hendrix, Melissa Κ . , 45 Hood, David Α . , 8 Kris-Etherton, P.M., 59 Layman, Donald Κ . , 1, 45, 125 Saltman, Paul, 87 Terjung, Ronald L., 8

Subject Index A

Amino acids, source of energy during exercise, 48-50 Anaerobic exercise affecting dietary protein requirements, 47-48 amino acid metabolism, 46-48 c h a r a c t e r i s t i c s , 45 description, 2 Anemia, effect on aerobic capacity, 5

Adipose tissue t r i g l y c e r i d e , fuel reserve, 31t Aerobic exercise amino acid levels in blood, 50 characteristics, 45 effect on maximal oxygen consumption, 2 nitrogen loss, 53t description, 2 Aerobic training, amino acid metabolism, 48 Aerobic work capacity, cardiovascular oxygen transport, 18 Alanine, role in gluconeogenesis, 50 Amino acid arterial-venous difference uptake, 50t levels in blood during aerobic exercise, 50 metabolism during exercise, 45-55 role in gluconeogenesis 50 Amino acid metabolism aerobic training, 48-53 during anaerobic exercise, 46-68 model, 45-46 Amino acid oxidation relationship to carbohydrate status, 53 need for glucose, 52

Β Biochemical adaptation, effect of bout duration, 15 Biochemical adaptations, skeletal muscle, 8-21 Biochemical response, training parameters, 11-13 Blood flow, effect of aerobic exercise training, 18 Blood glucose, fuel reserve, 31t Blood l i p i d s , effect on exercised women, 61 Body weight, decrease related to HDL cholesterol, 63 Bone mineral content, effect of exer­ cise on e l d e r l y , 97f Bout duration effect on mitochondrial content, 15

145

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Author Index Belko, Amy Z., 80 Boileau, Richard Α . , 125 Greenleaf, John Ε . , 107 Goodman, Michael Ν . , 27 Harrison, Michael H., 107 Hendrix, Melissa Κ . , 45 Hood, David Α . , 8 Kris-Etherton, P.M., 59 Layman, Donald Κ . , 1, 45, 125 Saltman, Paul, 87 Terjung, Ronald L., 8

Subject Index A

Amino acids, source of energy during exercise, 48-50 Anaerobic exercise affecting dietary protein requirements, 47-48 amino acid metabolism, 46-48 c h a r a c t e r i s t i c s , 45 description, 2 Anemia, effect on aerobic capacity, 5

Adipose tissue t r i g l y c e r i d e , fuel reserve, 31t Aerobic exercise amino acid levels in blood, 50 characteristics, 45 effect on maximal oxygen consumption, 2 nitrogen loss, 53t description, 2 Aerobic training, amino acid metabolism, 48 Aerobic work capacity, cardiovascular oxygen transport, 18 Alanine, role in gluconeogenesis, 50 Amino acid arterial-venous difference uptake, 50t levels in blood during aerobic exercise, 50 metabolism during exercise, 45-55 role in gluconeogenesis 50 Amino acid metabolism aerobic training, 48-53 during anaerobic exercise, 46-68 model, 45-46 Amino acid oxidation relationship to carbohydrate status, 53 need for glucose, 52

Β Biochemical adaptation, effect of bout duration, 15 Biochemical adaptations, skeletal muscle, 8-21 Biochemical response, training parameters, 11-13 Blood flow, effect of aerobic exercise training, 18 Blood glucose, fuel reserve, 31t Blood l i p i d s , effect on exercised women, 61 Body weight, decrease related to HDL cholesterol, 63 Bone mineral content, effect of exer­ cise on e l d e r l y , 97f Bout duration effect on mitochondrial content, 15

145

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NUTRITION AND AEROBIC EXERCISE

Bout duration—Continued exercise, 15-16 interaction with exercise intensity, 16

C Calcium, role in muscle contraction, 94f Calcium excretion, endurance athletes vs. control group, 97f Carbohydrate fuel during exercise, 28 fuel during fasting, 28 u t i l i z a t i o n during exercise and starvation, 29f Carbohydrate metabolism following exercise, 40 interaction with l i p i d metabolism, 39f Carbohydrate sparing mechanism, 38-40 Carbohydrate stores, during aerobic work, 28-30 Cardiovascular disease mortality, l e v e l of physical a c t i v i t y , 59-60 Cellular f l u i d , compartments, 111f C e l l u l a r response to exercise, 2 C e l l u l a r responses, trained muscle, 18 Contraction, fiber types, 10 Coronary heart disease leisure time relationship, 59 occupational relationship, 59 relationship to physical a c t i v i t y , 59-60 Cytochrome c during changing exercise intensity, 15 during detraining, retraining, I4f effect of exercise duration, 17f effect of exercise intensity, I4f

D

Dehydration, adverse effects, 115f Diet effect on muscle glycogen, 37t glycogen loading, 36 influencing fuel u t i l i z a t i o n , 36-38 influencing plasma l i p i d relationships, 63 low carbohydrate, 36 Dietary factors, influence on HDL cholesterol, 63

Dietary goals for the United States, 1 Dietary protein, effect on muscle hypertrophy, 48

Ε Endurance exercise energy from protein, 51 protein requirements, 53-54 Energy expenditure components, 4 factors determining, 4 Ergogenic aids, 4 Exercise carbon dioxide increase, 51 cellular level, 2 comparison with starvation metabolism, 28 correlation with cholesterol, 61 duration and intensity, 33 duration on carbon dioxin production, 54f effect of water, 3 effect on protein and amino acid metabolism, 45-55 effect on leucine, 51,53-54 intensity, 13-15 interaction of carbohydrate and l i p i d metabolism, 39f physiological and metabolic responses, 2 primary effects on body, 3 primary fuels, 4 producing catabolic condition, 51-52 protein requirements questioned, 54 protein turnover before and after, 52t training duration, 11-12 treadmill times of anemic vs. normal r a t s , 92f, 94f Exercise among Americans, 1 Exercise intensity effect on cytochrome c, 13 effect on HDL cholesterol in females, 62t interaction with bout duration, 16 relationship to motor unit recruitment, 13 response in muscles, 13 Exercise training, effect of blood flow, 18 Extracellular f l u i d , compartments, 111f

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147

INDEX Glycogen-sparing effect, 38 Glycogen stores, during aerobic work, 28-30

F

Fast-twitch muscle f i b e r , characteristics, 9 Fast-twitch red muscle f i b e r , motor units, 10 Fast-twitch white muscle fiber contraction, 10 motor units, 10 Fatty acid oxidation effect on glycogen, 20 i n t r a c e l l u l a r mechanism, 38-40 Fatty acids, contribution to oxygen consumption, 35t Fiber composition, man, horses and dogs, 32t Fiber types, c h a r a c t e r i s t i c s , 32t Food intakes, kcal per day Free fatty acids, fuel for oxidativ metabolism, 33 Fuel during exercise, 28 during fasting, 28 Fuel reserves, rates of u t i l i z a t i o n , 31t Fuel u t i l i z a t i o n biochemical regulation, 38-40 regulating factors, 30 skeletal muscle, 27-41 Fuels reserves of the body, 28-30 used by muscles, 27 Fuels for the body, 4

Gluconeogenesis, 50 Glucose amino acid oxidation necessity, 52 contribution to oxygen consumption, 35t fuel for oxidative metabolism, 33 Glucose uptake, 33 during bicycle exeercise, 34f Glycogen contribution to oxygen consumption, 35t effect on fatty acid oxidation, 20 fuel during exercise, 28 Glycogen breakdown during exercise, 33 oxidative metabolism, 33 Glycogen depletion, during bicycle exercise 34f Glycogen-loading diets, 36 r

H

Hemoglobin concentration vs. work time, 92f description, 5 percent vs. iron depletion, 92f High-density lipoprotein (HDL) cholesterol, endurance vs. sedentary subjects, 60 High-density lipoprotein (HDL)

women, 60-61 effect on sex, 65 females, 62t increase via hepatic l i p a s e , 69f increase via LCAT a c t i v i t y , 69f increase via LPL a c t i v i t y , 69f

I Iron depletion, vs. percent hemoglobin, oxygen consumption, and PK, 92f

Lactate content, trained and untrained muscle, 19 Leucine effect of exercise, 51 role in gluconeogenesis, 50 role in protein synthesis, 51 Leucine oxidation, effect on exercise, 54 Lipid fuel during exercise, 28 fuel during fasting, 28 L i p i d metabolism effect of exercise, 59-76 interaction with carbohydrate metabolism, 39f L i p i d oxidation, trained vs. untrained individuals, 20 Lipid u t i l i z a t i o n , 29f

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In Nutrition and Aerobic Exercise; Layman, D.; Washington, 20036 ACS Symposium Series; American ChemicalD.C. Society: Washington, DC, 1986.

NUTRITION AND AEROBIC EXERCISE

148 Lipoprotein lipase a c t i v i t y , effect on plasma l i p i d s , 65 Lipoprotein metabolism, effect of exercise, 59-76 Lipoproteins changes after exercise program, 62t factors affecting with exercise, 63-65 64t Liver glycogen depletion, 40 fuel reserve, 31t Low-density lipoprotein (LDL) cholesterol, decreased by exercise, 61

Ν

Nitrogen, loss after aerobic exercise, 53t Nutrients definition, 3 function, 3 Nutrition awareness among Americans, 1 Nutritional requirements, assessment of effective exercise, 3

0 M Maximal oxygen consumption effect of aerobic exercise, 2 effect of aerobic metabolism, 16 influence of exercise training, 18 Metabolic responses to exercise, 2 Metabolism, protein and amino acid, 45-55 Mitochondrial content discontinued training, 12 during submaximal exercise, 18 during training, 11-12 effect on maximal oxygen consumption, 16 h a l f - l i f e , 12 influence on muscle fiber oxidative capacity, 15-16 Mitochondrial enzyme a c t i v i t y , t r a i n ­ ing effect, 37t Motor units composition, 9 fast-twitch red muscle f i b e r , 10 fast-twitch white muscle f i b e r , 10 recruitment pattern, 11 Muscle fiber types during physical a c t i v i t y , 33 fast twitch, 9-10 fast-twitch, 30-33 slow-twitch, 9-10 30-33 type IIA, 30-33 type IIB, 30-33 Muscle hypertrophy, protein synthesis increase, 46-47 Muscle t r i g l y c e r i d e , fuel reserve, 31t Muscles exercised-produced catabolic condition, 51-52 fuels used, 27

Ρ PCr content, submaximal exercise effect, 18-19 Physical a c t i v i t y , relationship to heart disease, 59 Physical t r a i n i n g , influencing fuel u t i l i z a t i o n , 36 Physiological, responses to exercise, 2 Plasma, volume s h i f t with exercise intensity, 115f Plasma cholesterol, effect on exer­ cised women, 61 Plasma l i p i d relationships, effect of d i e t , 63 Plasma l i p i d s changes after exercise program, 62t effect on exercised women, 61 factors affecting with exercise, 63-65 64t influence of diet and exercise, 65 mechanisms of exercised-induced changes, 65-70 Plasma t r i g l y c e r i d e , effect of exercise, 61 Protein energy for endurance, 51 metabolism during exercise, 45-55 source of energy during exercise, 48-50 usefulness as a f u e l , 30 Protein catabolism, effects of aerobic exercise, 53

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INDEX

Protein metabolism changes through exercise, 45 e f f e c t of exhaustive running, 52t Protein requirements e f f e c t of anaerobic exercise, 47-48 endurance exercise, 53-54 Protein synthesis effect on muscle hypertrophy, 46-47 rate vs. dietary protein l e v e l , 49f role of leucine, 51 Protein turnover before and a f t e r exercise, 52t muscles i n chickens, 47t

S

Skeletal muscle biochemical adaptation specificity, 9 biochemical adaptations, 8-21 changes a f t e r exercise t r a i n i n g , 8 c o n t r a c t i l e a c t i v i t y , 36 contractual energy demands, 18 mitochondrial content, 8 oxidative capacity, 18 respiratory capacity, 36 Slow-twitch muscle fiber characteristics, 9 motor units, 10 Slow-twitch red muscle fiber, contraction, 10 Starvation, metabolism, 28 Stretch-induced hypertrophy, protein synthesis, 47 Submaximal exercise e f f e c t on PCr content, 18-19

Submaximal exercise—Continued measurements of glycogen, 36 sources of energy, 36

Τ Trained muscle altered substrate u t i l i z a t i o n , 19-20 lactate content, 19 rate of respiration, 19 Training duration length, 12 maximal response, 11-12 Triglyceride breakdown, during exercise 33

Triglycerides decreased by exercise, 61 e f f e c t on exercised women, 61

V

Very low-density lipoprotein (VLDL) t r i g l y c e r i d e s , endurance vs. sedentary subjects, 60 W

Water, e f f e c t on r e c t a l temperature during exercise, 111f

In Nutrition and Aerobic Exercise; Layman, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.