An investigation of the relation between man’s fitness for strenuous work and his ability to withstand high headward acceleration
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AN INVESTIGATION OF THE RELATION BETWEEN MAN’S FITNESS FOR STRENUOUS WORK AND HIS ABILITY TO WITHSTAND HIGH HEADWARD ACCELERATION
A Dissertation Presented to the Faculty of the Department of Physical Education The University of Southern California
In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy
by Janet A. Wessel June
1950
UMI Number: DP29687
All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion.
UMI Dissertation Publishing
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T h is dissertation, w ritten by O z U c t t r f ' (a ) x
m
J
.........
under m e guidance of hks,.... F a c u lty Com m ittee on Studies, and app ro ved by a l l its members, has been presented to and accepted by the C o u n c il on G ra duate Study and Research, in p a r t ia l f u l fillm e n t of requirements f o r the degree of DOCTOR
OF
P H IL O S O P H Y
i
C om m ittee on Studies
lan
JU
ii TABLE OF CONTENTS
CHAPTER I
II
PAGE
INTRODUCTION........................
1
Statement of the problem............................
1
Definition of t e r m s ...............................
2
Importance of the p r o b l e m ..........................
3
Limitations of the study............................
5
HISTORICAL DISCUSSION................................. Cardiovascular responses of man to hisforceenvironment .
6 6
The effect of g r a v i t y .............................
6
Effects on man of forces greater than g r a v i t y .......
11
The effect of training on blood pressure andpulse rate. .
19
Blood pressure measurements........................
19
Pulse r a t e .........................................
23
Tests based on recuperation of pulse after exercise for predicting cardiovascular fitness
..................
26
Schneider t e s t .....................................
26
Pulse ratio t e s t s .................................
26
Harvard step t e s t .................................
27
iii CHAPTER
PAGE Army Air Force physical fitness t e s t ..................
III
30
Development of the Army Air Force t e s t ...............
30
Effects of gaining on the physical fitness rating
...
30
Chapter S u m m a r y .....................................
31
M E T H O D S ..............................................
32
Outline of the problem...............................
32
Personnel and time s c h e d u l e ..........................
32
Subjects...........................................
32
Examiners.........................................
33
Time s c h e d u l e .....................................
33
Measurement of G-tolerance and physical fitness for strenuous w o r k .....................................
34
Fitness for strenuous w o r k ......................
34
G-tolerance
34
.........................
Procedures used in the three test p e r i o d s ............. Determination of physical fitness for strenuous work . .
37 37
The hand dynamometer strength test .
...............
38
Determination of G-tolerance . . . . .
...............
39
The training program............
42
Non-training program.................................
43
Chapter s u m m a r y .....................................
43
IV R E S U L T S ..............................................
44
Statistical analysis of the d a t a ............
45
Consideration of results..............................
46
iv CHAPTER
V
PAGE Summary of results...................................
55
DISCUSSION............................................
59
Effects of the training program on subjects' G-tolerance .
59
Influence of the cessation of systematic training on
VI
G-tolerance.......................................
60
Inter-relation of subjects' fitness scores to G-tolerance.
6l
SUMMARY AND CONCLUSIONS...............................
63
S u m m a r y ............................. .
63
Conclusions.........................................
65
BIBLIOGRAPHY............................................
66
A P P E N D I X ................................................
76
Appendix A , Fitness Tables for the Three TestPeriods
76
. .
Appendix A, G-tolerance Tables for theThree Test Periods.
87
Appendix B, Figures 1 - 1 2 ........................
9^
Appendix C, Raw data s h e e t s ....................
102
V
LIST OF TABLES TABLE
PAGE I
WEIGHT LIFTING EXERCISES, SET I ...................
76
II
WEIGHT LIFTING EXERCISES, SET I I .................
77
III
HARVARD STEP TEST S C O R E S ........................
78
IY
CHANGES RECORDED IN THE ARMY AIR FORCE PHYSICAL FITNESS TEST SCORES FROM TEST PERIOD I TO TEST PERIOD II
V
...
...
VTII
.
8l
CHANGES RECORDED FOR THE HAND DYNAMOMETER STRENGTH TEST .
82
CHANGES IN THE HARVARD STEP TEST GROUPS FROM TEST PERIOD I TO TEST PERIOD II.........................
IX
8^
CHANGES IN THE ARMY AIR FORCE PHYSICAL FITNESS TEST GROUPS FROM TEST PERIOD II TO TEST PERIOD I I I ............
XIII
83
CHANGES IN THE ARMY AIR FORCE PHYSICAL FITNESS TEST GROUPS FROM TEST PERIOD I TO TEST PERIOD I I ........
XII
83
CHANGES IN THE HARVARD STEP TEST GROUPS FROM TEST PERIOD I TO TEST PERIOD I I I .......................
XI
83
CHANGES IN THE HARVARD STEP TEST GROUPS FROM TEST PERIOD II TO TEST PERIOD I I I .....................
X
80
CHANGES RECORDED IN THE ARMY AIR FORCE PHYSICAL FITNESS TEST SCORES FROM TEST PERIOD I TO TEST PERIOD III . . .
VII
79
CHANGES RECORDED IN THE ARMY AIR FORCE PHYSICAL FITNESS TEST SCORES FROM TEST PERIOD II TO TEST PERIOD III
VI
.
8^
CHANGES IN THE ARMY AIR FORCE PHYSICAL FITNESS TEST GROUPS FROM TEST PERIOD I TO TEST PERIOD I I I ......
8^
LIST OF TABLES TABLE XIV
PAGE CHANGES RECORDED IN PULSE BATES FOR HARVARD STEP
TEST
FROM TEST PERIOD I TO TEST PERIOD I I ................... XV
CHANGES RECORDEDIN BLOOD PRESSURE MEASUREMENTS FOLLOWING THE HARVARD STEP TEST FROM TEST PERIOD I TO TEST PERIOD II
XVT
85
CHANGES RECORDEDIN PULSE RATES FOR HARVARD STEP TEST FROM TEST PERIOD II TO TEST PERIOD I I I .............
XVII
85
CHANGES RECORDED
86
IN BLOOD PRESSURE MEASUREMENTS
FOLLOWING THE HARVARD STEP TEST FROM TEST PERIOD II TO TEST PERIOD I I I ................................... XVIII
CHANGES RECORDED IN PULSE BATES FOR HARVARD STEPTEST FROM TEST PERIOD I TO TEST PERIOD I I I .................
XIX
86
87
CHANGES RECORDED IN BLOOD PRESSURE MEASUREMENTS FOLLOWING THE HARVARD STEP TEST FROM TEST PERIOD I TO TEST PERIOD I I I ...................................
XX
87
AGE, HEIGHT, WEIGHT, FLYING AND CENTRIFUGE EXPERIENCE, AND PERFORMANCE ON THE POSITIVE 5G TEST RUNS FOR EACH
XXI XXII
S U B J E C T ............................................
88
GROUP PERFORMANCE ON POSITIVE 5G TEST R U N S .............
89
CHANGES RECORDED IN EAROPACITY AND PULSE RATES FOR SUBJECTS WHO ENDURED POSITIVE 5G FOR 30 SECONDS FROM TEST PERIOD I TO TEST PERIOD I I ......................
90
vii LIST OF TABLES TABLE XXIII
PAGE CHANGES EECOEDED IN EABOPACITY AND PULSE BATES
FOB
SUBJECTS WHO ENDURED POSITIVE 50 FOB 30 SECONDS FROM TEST PERIOD II TO TEST PERIOD I I I .................... XXIV
CHANGES EECOEDED IN EABOPACITY AND PULSE RATES
91
FOR
SUBJECTS WHO ENDUBED POSITIVE 5G FOR 30 SECONDS FROM TEST PERIOD I TO TEST PERIOD I I I .................... XXV
92
RANK ORDER CORRELATION BETWEEN G-TOLERANCE ANDFITNESS FOR THOSE SUBJECTS WHO ENDURED POSITIVE 5G FOR 30 SECONDS
93
LIST OF FIGURES FIGURE 1
PAGE Mean value and standard deviations for earopacity for the 9 subjects who endured +5 G for 30” in all 3 test periods.........
2
9^-
Mean values and range of the pulse rates for the 9 subjects who endured +5 G for 30" in all 3 test p e r i o d s .........................................
3
95
Earopacity changes related to Harvard Step Test scores for all subjects who endured +5 G for 30" in Test Period I .........................................
4
96
Pulse rates after exposure to +5 G for 30" as related to Harvard Step Test scores for all subjects in Test Period I
5
...................................
96
Earopacity changes related to Harvard Step Test scores for all subjects who endured +5 G for 30" in Test Period I I .......................................
6
97
Pulse rates after exposure to +5 G for 30" as related to Harvard Step Test scores for all subjects in Test Period I I ...................................
7
97
Earopacity changes related to Harvard Step Test scores for all subjects who endured +5 G for 30" in Test Period I I I ............................................
98
FIGURE
8
PAGE
Pulse rates after exposure to +5 G for 30" as related to Harvard Step Test scores for all subjects in
Test Period I I I ................................. 9
98
Earopacity changes as related to Harvard Step Test scores for all subjects who endured +5 G for 30" in the 3 test periods.........
10
99
Pulse rates for 30" as related to HST scores for all
subjects who endured +5 G for 30" in 3 test periods. . 11
99
Earopacity changes for all subjects who greyed out at +5 G runs as related to the Harvard Step Test
scores........................................... 12
100
Pulse rates as related to Harvard Step Test scores for all subjects who greyed out at +5 G
................
101
CHAPTER I INTRODUCTION Force and force changes are considered important components of man's environment today.
Through the development of modem aircraft, a
variety of new stresses has been brought to bear upon man.
Acceleration
in high-speed, maneuverable aircraft has produced stresses many times greater than the normal gravitational force of the earth.
The sudden
change in direction of flight which occurs in sharp turns and in pulling out of dives at high speed produces a centrifugal force of such magni tude that the pilot is often rendered temporarily blind or unconscious (Armstrong and Heim, 1938).
Man's susceptibility to the force changes
of high acceleration is often the limiting factor in the performance of military maneuvers in aircraft (Wood, Lambert, Baldes and Code, 1926). The devising of methods to counteract or avoid the effects of high acceleration upon man was one of the most urgent problems confront ing aviation in the last war.
Rapid advances in aeronautical engineer
ing have produced aircraft capable of even greater speed and maneuver ability, thereby accentuating the effects of high acceleration; thus, this problem continues to loom large in the immediate future of military aviation. Statement of the problem. The purpose of this study was to in vestigate the relation between man's fitness for strenuous work and his ability to withstand the gravitational force of high headward accelera tion.
This study was designed to investigate three separate problems:
2 first, to determine ma n ’s tolerance to high headward acceleration in relation to his fitness for strenuous work; second, to study the effects of a training program upon the G-tolerance of man; and, third, to in vestigate the possibility of a parallelism in the decline in fitness for strenuous work and m a n ’s G-tolerance.
Definitions of terms.
Man could travel at any imaginable velocity
if he were moving at constant speed in a straight line and were not ex posed directly to the dynamic effects of motion (McFarland, 19^-6).
If
motion involves a change of velocity or if it departs from a straight line, an element of force appears.
The rate of change of velocity is,
by definition, termed acceleration.
As velocity has both direction and rate of motion, a change in either may produce a type of acceleration. of acceleration may occur:
In aviation three major forms
(l) linear, in which the change is in rate
alone, e.g., catapult take-offs, crash landings and seat ejections; (2) angular, in which the change is one of direction, a rotation around a center within the pilot, e.g., sudden turns of the head, tumbling, either in the aircraft cockpit or freely falling in space, and other movements stimulating the vestibular apparatus; and (3) radial, in which the change is primarily one of direction, but the change of curvature is beyond the pilot, usually at some distance, e.g., tunas, loops, pushovers and pullouts from dives (Wood, Lambert, Baldes and Code, 19^-6). Force changes most often encountered in aviation are the result of acceleration acting on a body moving in a curved path, e.g., the
3 centrifugal force of radial acceleration.
When the direction of this
force is through the long axis of the body (head to seat), it is termed positive acceleration.
Positive acceleration is encountered by the pilot
when at high speed the flight of the plane is altered from a straight line, as in a pull-up from a dive, a tight turn or in a diving spiral. The lift of the wings of the plane produces a centrifugal force at a tangent to the long axis of the plane, the force equalling the product of the mass of the body times the acceleration.
The magnitude of this
2 acceleration can be determined mathematically by the equation F = V E (F = acceleration, V = speed per second, and E = radius of the turn in feet).
This acceleration would then be expressed in feet per second per
second.
These dimensions are the same as for the earth's gravitational,
pull, which is 32 feet per second per second.
This value, represented
by the symbol G, is taken as the unit of measurement of accelerational forces in aviation (Ham and Armstrong, 19^-3) • The effect of centrifugal force on the human body is apparent as weight.
The force of gravity, 1 G, gives man the weight to which he is
accustomed.
If then, by positive acceleration, man’s force environment
were suddenly increased to 5 G, his body weight and every constituted part of the body, including the circulating fluids, would weigh five times the ordinary weight; that is, acceleration of 5 G would produce a force five times that which the earth's gravity exerts on man’s body. Importance of the problem. Through investigations of man's abil ity to withstand high positive acceleration, it has been found that re peated exposures to headward acceleration are fatiguing (Ham, 19^+3)•
k
Even when using an anti-G suit, the pilot must make muscular adjustments to protect himself (Clark and Christy, 19^6).
It is possible that mus
cular strength and cardiovascular endurance for strenuous work may increase the pilot’s tolerance to the forces of positive acceleration. On the other hand, it has been suggested that the increase in the muscular capillary bed during conditioning for strenuous muscular work may reduce a pilot's resistance to headward acceleration by providing in the lower extremities a larger reservoir in which blood can pool (Arm strong, 1939)• The major effect of positive acceleration on man is hydrostatic in nature; for as the body is restrained in its curved flight path, the relatively unrestrained fluids in the body, especially in the cardio vascular system, will tend to move along the vessels toward that part of the body away from the center of curvature.
The main dynamic effect of
centrifugal acceleration appears to be the redistribution of blood, to gether with a diminished effective circulation (Voyneck, 19^3).
Many
investigators in the field of man's cardiovascular responses to normal postural changes have reported better responses to prolonged standing in subjects in good condition and after a physical training program (Turner, 1930; Crampton, 1920; Schneider and Truesdell, 1922; Graybiel and McFarland, 19^1; Allen, Taylor and Hall, 19^5).
It is possible, then,
that in changes resulting from positive accelerations, as in postural changes, many of the effects may be decreased by increasing the effect iveness of certain anti-pooling mechanisms.
Knowledge of the relation of man's exercise tolerance to his
5 adaptation energy for withstanding acceleration will he useful in estab lishing optimum physical training programs for flyers. Limitations of the study. Although in military maneuvers the pilot encounters numerous stresses, including low oxygen, decreased at mospheric pressure, vibration, prolonged concentration, crouched position and acceleration, only acceleration was considered in this investigation. The maximum positive acceleration was 5 G for 30 seconds or until greyout. Twenty-three healthy male university students were used as sub jects.
It was not possible to regulate their dietary intake, sleep or
living habits. The training program lasted for six weeks and was controlled to the extent that each subject was required to perform a prescribed amount of work and exercise each week.
Some subjects performed only the requir
ed exercises, while others participated in additional physical activities, thus attaining a higher degree of physical conditioning. The non-training program was eight weeks in duration.
During this
period the subjects were requested to limit their physical activities. Some subjects complied, while others, being varsity athletes, were un able to do so. As far as possible, such measurements as blood pressure, pulse rate and G-tolerance were taken at approximately the same time of day in the initial period, the training period and the non-training period.
6 CHAPTER II HISTORICAL DISCUSSION The human body is constantly acted upon by the earth's gravity. Man's postural reflex mechanisms are geared to respond to a force of this magnitude because man has to maintain his upright posture during most of his waking hours (MacLean, Horton, Berry, 19^0).
The handicap
imposed by gravity upon man's circulatory mechanisms has been attri buted largely to the effect of pressure of the increased venous hydro static column in opposing venous return (Hellebrandt and Franseen, 19^3).
Physiological- research on man's cardiovascular responses and
compensatory reactions to the effects of acceleration may be convenient ly divided into an old, extensive study of the effects of gravity, as seen in postural changes, and a new, incomplete, but intensive attack upon the effect of high forces of acceleration.
CARDIOVASCULAR RESPONSES OF MAN TO HIS FORCE ENVIRONMENT The effect of gravity. Physiologists have long been concerned with the effects of gravity imposed directly upon the cardiovascular system by vertical posture.
Normal postural changes and the compensa
tory reactions to the vertical position have been widely studied under a variety of conditions.
Subjects have been passively tilted to study
conditions of graded gravitational stress while eliminating the compli cations introduced by muscular work of active change of position (Turner
7 et al., 1930* Ghrist, 1930)-
Observations have been made within 10
seconds after the change in posture (Wald, Guernsey and Scott, 1937) and. have been continued without interruption for periods of more than an hour (Barach and Marks, 1911* Turner, 1929).
The subjects have been required
to stand completely at ease, as quietly as possible, or have been re strained from movement by extrinsic supports (Wald, Guernsey and Scott, 1937; Hellebrandt and Brogden, 193^; Turner et al., 1929* 1930)• Fair agreement of the experimental results for normal responses to alterations in posture has been reported.
Turner (1927), Schneider
and Crampton (193^) and. Asmussen et al. (1939) reported a diminution of cardiac output in the normal vertical stance.
Changes in blood volume
in the leg as a result of postural alterations were reported.
Turner
(1930) and Asmussen et al.. (1939) showed progressively increasing blood volume in the legs during the erect position.
There exists general
agreement that during the erect posture a retardation of blood flow occurred (Hellebrandt and Franseen, 19^-3) • On change from horizontal to upright position, normal subjects exhibited an increase or no change in diastolic blood pressure, an increase in pulse rq,te and a slight increase or fall in systolic blood pressure.
Rough averages for these changes
were an increase in pulse rate of about 12 beats per minute, an increase in diastolic blood pressure of about 12 mm. of mercury, and a change in systolic blood pressure between an increase or a decrease of 10 mm. of mercury (Barach and Marks, 1913* Ellis, 1921; Schneider and Truesdell, 1922; Turner, 1927* Ghrist, 1921; Wald, Guernsey and Scott, 1937)* It has been reported that immediately after standing, subjects
8 showed a sharp decrease in systolic blood pressure amounting to from 5 to 50 mm*
mercury within the first 10 seconds.
In about 75 per cent
of the normal persons, the diastolic blood pressure increased in the first 10 seconds.
When the blood pressure was taken 30 seconds after
the subjects had been standing, the systolic value was usually higher than that taken when they were supine, demonstrating that the adaptive mechanisms had overcompensated.
At 60 seconds the systolic and diastolic
pressures and the pulse rate were stabilized (Wall, Guernsey and Scott, 1937)*
Prolonged standing exerts a severe strain on the circulatory system.
This was demonstrated by requiring subjects to stand motionless
for long periods of time.
Many of the normal subjects fainted (Barach
and Marks, 1913* Turner, 1927* Wald, Guernsey and Scott, 1937)*
Studies
have shown that support of subjects at increasing angles from the verti cal will alter arterial, pressures and pulse rates directly as a result of the increased gravitational stress exerted on the circulation (Turner, 1930* Ghrist, 1930)•
It was noted also that circulatory adjustment is
effected by each person according to his own pattern, some patterns show ing better adaptation than others (Turner, 1929)•
This fact led to the
investigation of compensatory mechanisms which existed to offset the hydrostatic effects of gravity. Despite extensive investigation, knowledge of postural adaptation mechanisms is incomplete.
The attention of investigators has been direct
ed toward vasoconstriction, acceleration of heart rate and general tonus of muscles as subjects of inquiry in this regard.
9 Piorry (1826), one of the early investigators, suggested, the im portance of blood volume and general condition as factors to be consider ed in man’s resistance to gravity.
The first systematic study dealing
with the problem of compensatory mechanisms for gravity collapse was done in the laboratory by Leonard Hill in 1895*
From his classical ex
periments on rabbits, dogs, cats and monkeys, he concluded that splanchnic vasoconstriction and cardiac acceleration were important compensatory reactions in combating gravity. Later research has shown that cardiac acceleration in the erect position is a universal finding (Asmussen et al., 1930» Berry, Horton and MacLean, 19^0; Ellis, 1921; Ghrist- 1921; Hellebrandt and Franseen, 19^3; Turner, 1930; Schneider and Truesdell, 1922).
When the body is in
the erect position, the elevation of heart rate may be considered in inverse relation to the adequacy of other compensatory mechanisms and, as such, has been incorporated into postural tests of circulatory fit ness proposed by Crampton (1913)* Schneider (1930) and Turner (1927, 1929)* Research investigations of the problem of peripheral vasocon striction as a factor of compensation in the erect or tilted body posture have been at variance (Hellebrandt and Franseen, 19^-3)-
Observations on
the general tone of the skeletal muscles with regard to venous return have emphasized the importance of muscle tone in preventing dilatation of capillaries and advancing blood toward the heart (Mayerson and Burch, 1939)•
Henderson (1931) strongly supported the view that muscular tonus,
especially that of the diaphragm, abdominal muscles and intestines, is important in maintaining blood pressure while the individual is standing.
10 The degree of change in the normal response to alterations of posture (blood pressure and pulse rate) with regard to physical fitness has been investigated.
Crampton (1920) found that the pulse rate did
not rise as much in vigorous subjects as in wearied subjects, the pulse rate increasing as much as
beats per minute in the latter.
Turner
(1930) found that physical, education students responded better to pro longed standing than did other unselected female subjects.
The McCurdy
condition test (1939) emphasized pulse rate changes as a test of fitness. Graybiel and McFarland (19^-1), attempted to determine the physical fitness of pilots and their physiological aptitude for flying by means of a cardiovascular response to the tilt test.
Results of this study
showed that there is great individual variability in cardiovascular re sponse to alterations in posture.
Among the most important factors
affecting the response were (l) infection, (2) lack of food, (3) warm environment, and (4) lack of physical fitness.
These investigators
considered the tiltboard test as of possible utility in determining circulatory efficiency.
It was believed that a correlation existed
between susceptibility to fainting and "blacking out" in flying.
The
authors found also that the response to the tilt table was improved with a physical training program. Allen, Taylor and Hall (19^ ) investigated the possibility of de veloping a tiltboard test for measurement of physical fitness, as well as aptitude for flying.
The fluctuations of heart rate, systolic and dia
stolic pressures of fainters and nonfainters on the tiltboard were fol lowed.
A reliable factor to identify fainters was not found except by
11 carrying the tiltboard test through to completion.
The predictive value
of the tiltboard response as a measure of fitness to withstand centrifu gal forces was considered doubtful; this would require actual comparisons of rating of the subjects in both experimental procedures.
Nonfainters
had higher treadmill scores, lower resting and post-exercise heart rates, longer breath-holding times and, in changes from reclining to tilted positions, showed lesser acceleration of heart rate and a smaller drop in systolic blood pressure.
Further analysis showed the relationship
between orthostatic inadequacy and exercise tolerance to be very slight; nevertheless, the tendency, though slight, was consistent.
In a special
study, a subject who was extremely susceptible to fainting was trans formed into a nonfainter by means of a three-week physical training pro gram consisting of leg and abdominal exercise. Effects on man of forces greater than gravity. of*the human centrifuge.
(a) Development
The effects of centrifugal force on man depend
upon its magnitude, its rate of application, its duration and the con dition of the pilot (Ham, 19^3} Armstrong, 19^3)*
One of the first
pioneers in Aviation Medicine recognized that centrifugal forces develop ed in turns of high speed aircraft might be of sufficient magnitude to draw blood away from the head and cause unconsciousness (Bauer, 1926). Early attempts by physiologists to study the conditions in planes showed this approach to be impractical.
Solution of the problem required
exacting physiological techniques, which meant bringing the program into the laboratory.
This lead to the development of the human centrifuge.
12 The earliest human centrifuge was developed in Berlin (Diringshofen, 19333 193^)«
The first centrifuge which satisfactorily duplicated the
conditions of flight was put into operation by the Royal Canadian Air Force in 19^1.
In the United States, the first centrifuge appeared in
19^2 at The Mayo Clinic; the second in 19^3 at Wright Field, used by the Army Air Force; the third in 1 9 ^ at the University of Southern Califor nia; the fourth in 19^5 at the Naval Air Station at Pensacola; and the fifth in 1950 at the Naval Air Development Center, Johnsville, Pennsyl vania. Modem human centrifuges have been designed to reproduce centri fugal forces similar to those encountered in aircraft, e.g., similar in rate of development, intensity and duration of acceleration (Baldes and Porter, 19^5j Baldes, Code, Lambert and Wood, 19^-6; Franks, Kerr and Rose, 19^5).
The human centrifuge has been demonstrated to be a valid
means of studying the physiologic effects of acceleration as encountered in aircraft (Lambert, 19^6; Drury, 19^7 J Lambert, 19^9)*
Physiological
studies which have been carried out during the past ten years on the human centrifuge have yielded valuable data concerning the physiological reaction of man to high positive acceleration. (b) acceleration.
Instruments used to measure man’s reactions to high positive Electrical, recording devices for registering changes in
the cardiovascular responses of man to G have been developed by those working with the human centrifuge.
During a centrifuge run, it is usual
to record heart rate, electrocardiograms, earopacity and ear pulse, forces of G applied, and reaction time of the subject to visual and
13 auditory stimuli (Baldes, Code, Lambert, Wood, 19^6; Frank, Kerr, Ross, 19^5; Ham and Landis, 19^-2, 19^3)The earopacity unit is used as an accurate measure of the changes in the amount of blood in the ear.
This device determines the blood
content of the ear by photoelectric measurement of variations in the amount of light transmitted through the ear by a constant source of light.
A downward deflection of the galvanometer in the record indicates
loss of blood from the ear.
The magnitude of the decrease in the blood
content of the ear is proportional to the severity of the subject’s symptoms (Code, Wood, Sturm, Lambert and Baldes, 19^-5) • Changes in vision are determined by testing the subject’s ability to respond to light signals placed in the peripheral and central fields of vision. lights.
The subject taps keps as long as he is able to see signal
Visual changes range from clear vision, dimming of the visual
field, loss of peripheral vision to complete blackout (Ham and Landis, 19^3; Lambert, Hallenbeck, Baldes and Wood, 19^5)* The magnitude of positive acceleration is determined by calcu lations from records of revolutions per minute of the human centrifuge (Lombard, 19^9)•
The recordings of all of these variables are contin
uous and simultaneous. (c)
Physiological reactions of man to high positive acceleration.
The effects of acceleration on man are due to the increased weight of the different parts of the body.
Movement becomes increasingly difficult
as the force increases; at 2.5 G it is impossible for a man to rise from a sitting position; at 4 G, the leg generally cannot be lifted and the
Ik
arm can be moved only with great effort (Lambert and Wood, 19^+6). The most dramatic physiological effects on man due to high posi tive acceleration are attributed to the action of the cardiovascular system, for the blood is the most mobile tissue in the body.
Because
the force involved under positive G is greater than gravity, the results are manifested much more rapidly, and before the body's normal compensa tory mechanisms have a chance to come into play (Baldes, Code, Lambert, Wood, 19^6). The height of the column of blood between the heart and the brain, measured in the direction of the force, determines the amount of accele ration which can be tolerated for relatively long periods of time (3 seconds or more), (Armstrong, 19^-3) • If normally the heart forces a column of fluid 12 inches upward into the head, during acceleration of 5 G the heart would have to develop five times as much pressure to force the fluid to the head, e.g., the heart would have to be able to raise a 60 inch column of blood to the head.
Hence, there tends to be pooling
of blood in the abdominal regions and lower extremities.
The increase
in volume of the pooled blood varies directly with the magnitude of G (Slaughter and Lambert, 19^6)„ Because the eyes are located a considerable distance above the heart and the circulation through them is subjected to an added intra ocular pressure of approximately 28 mm. of mercury, these organs are the first to show the effects of positive acceleration.
Diminished circula
tion to the retina of the eye is manifested in greyout or in narrowing of the visual fields and in blackout when vision is lost (Ham, 19^-3) •
15 Greyout and "blackout are colloquial terms referring respectively to the narrowing of the visual fields and to the temporary blindness occurring during high positive acceleration.
Greyout occurs when the
circulation through the eye becomes so weak that an inadequate supply of oxygen reaches the less resistant light sensitive cells of peripheral vision.
Central vision is the last to fail.
Circulation through the
brain is still possible at this point since the pressure of the cere brospinal fluid, or the pressure inside the head, is negative when one is sitting.
Thus, with the brain, but not the retina, supplied with
oxygen by circulating blood, a person remains conscious but can see nothing (Lombard, 19^9)• It was found that the increased weight of the blood during high positive acceleration initiated a definite sequence of physiologic events in man:
(l) a period of progressive failure characterized by blood
draining from the head, increased blood pressure below the heart, in creased pulse rate, progressive loss of blood content of the ear, reduc tion of vision to and including blackout and unconsciousness; (2) a period of compensation, which terminated the above period and became effective in about 6 to 12 seconds, the average time being 7 seconds after onset of acceleration.
This period tended toward reversal of the
events during failure and was attributed primarily to the carotid sinus and similar reflexes (Code, Wood, Sturm, Lambert and Baldes, 19^-5) • In general, the degree of compensation was inversely proportional to the magnitude of the force of G (Ham, 19^\3j Armstrong, 19^-3)* It was believed by some investigators that the changes in blood
16
pressure are the key to the orderly pattern of changes in other variables. Earopacity, heart rate, ear pulse and visual symptoms only reflect the alterations in blood pressure (Lambert, Hallenbeck, Baldes, Wood and Code, 19^5)•
A convenient summary has been suggested (Wood, Lombard, Baldes
and Code, 19^-6): (1) (2) (3) (4)
acceleration increases the weight of the blood and tissues. the increased weight of blood reduces the blood disturbance in vision and consciousness may occur. the decrease in blood pressure at head level initiates pressor reflexes, which become effective in about 7 seconds. the resulting increase in arterial pressure at heart level is usually sufficient to produce some degree of recovery at head level, even though the force is maintained.
On the basis of these physiologic changes, routine methods for observing the cardiovascular effects of positive acceleration on man have been developed.
The bioassy procedure is based on the recognition and
determination of the G level at which various subjective symptoms occur (dimming, loss of peripheral vision, complete loss of vision), and on measures of certain objective changes in the subject (loss of blood from the ear, reduction of blood pulsations in the ear, the degree of change in pulse rate, increase and magnitude of blood pressure changes) during exposure to various units of acceleration (Hallenbeck, Lambert, Wood and Allen, 191*6). Some of the results of the bioassy procedure for determining Gtolerance indicated definitely that earopacity began to decrease with the onset of increased G, reaching a minimum in 4 to 6 seconds after G became constant.
The decrease in earopacity was directly, but not quan
titatively, related to the magnitude of G applied.
The heart rate
17 increased rapidly at the onset, the maximum rate reaching 120 to 190 heats per minute, depending upon the magnitude of G and its duration. When the maximum G was maintained for more than 10 to 20 seconds, the maximum heart rate became relatively constant or decreased until G was reduced.
In the relaxed subject, the average positive acceleration at
which vision dimmed, peripheral lights were lost and vision completely failed was, on the average, 4.3 G, 4.8 G and 5*3 G, respectively.
In
the alert subject who attempted to resist the effects of the applied forces by straining both legs and abdominal muscles, collapse usually did not result until 7 G (Lombard, 1949) • Prolongation of a given force level beyond 10 seconds, if it did not cause unconsciousness, usually resulted in recovery of the sensorium to a greater or lesser degree (Lombard, 19^9> Lambert, Hallenbeck, Baldes, Wood and Code, 1945). (d) G-tolerance and protection of pilots.
Many methods have been
described for raising G-tolerance of pilots exposed to high positive acceleration.
From these studies, two general approaches evolved for
increasing man’s ability to withstand G:
either by limiting the dura
tion of the force or by employing anti-pooling mechanisms. By limiting the duration of the force to a period of less than that usually required for development of symptoms, pilots could avoid the physiologic consequences of exposure to centrifugal force; however, the drawback here was the need for accurate timing and definite plot of maneuvers (Wood, Lambert, Baldes and Code, 1946). Anti-pooling mechanisms for alleviation of the effects of high positive acceleration have included positions which reduce vertical
18 hydrostatic distances and procedures ■which increase the blood pressure. Postural changes, such as crouching, involving a marked decrease in the height of the hydrostatic column, have provided the circulating mechanisms with greater anti-G reserve (Wood, Lambert, Baldes and Code, 19^-6).
The
practical difficulties of flying a plane in various postures are numerous. Procedures which increase the blood pressure have been widely used and investigated.
Water immersion to counteract the distention of
the lower body (Wood, Lambert, Baldes and Code, 19^-6), straining to shunt arterial, flow toward the head instead Of the lower abdomen (Wood, 19^-7) y and the increased abdominal pressure present after meads (Clark and Jorgenson, 19^6) have raised the blackout threshold of pilots.
The per
formance of straining to prevent blackout was effective, but had a distinct disadvantage--it decreased the pilot’s efficiency and increased his fatigue (Ham, 19^+3) - German observers found a definite increase in tolerance through contraction of the abdominal muscles, and advocated special training of these muscles (Lambert and Wood, 19^6).
Many forms
of restrictive clothing, such as leggings, body taping, abdominal belts and anti-blackout suits, which increase the blood pressure at heart level, have been used in maintaining circulation at head level during exposure to positive G.
The respective values of each in maintaining cerebral
blood flow is well summarized by Wood, Lambert, Baldes and Code, (19^6). Research in the field of the physical status of the pilot and its effects upon G-tolerance is limited.
It is known that the capacity to
withstand acceleration varies in individuals and in the same individual at different times (Fulton, 19^-2).
The belief has been expressed that
19 subjects of short stature withstand positive acceleration better than tall subjects.
This observation was based on the fact that the column
of blood from head to heart is of necessity longer in the tall person, and therefore, a given blood pressure will maintain cerebral circulation against a given hydrostatic force more adequately in a short person (Diringshofen, 193^0 • Lower G-tolerance to high positive acceleration has been noted in cases of infections of the respiratory tract, loss of sleep, fatigue, emotional upsets and fear (Armstrong, 1939)*
THE EFFECT OF TRAINING ON BLOOD PRESSURE AND PULSE RATE Blood pressure measurements. Many studies and experiments have been conducted concerning blood pressure.
The majority of these have
been centered around blood pressure responses to differences in work loads and are, therefore, not directly related to this study.
A review
of the literature since 1900 in regard to the effect of training and the present physical condition of the subject on arterial blood pressure in dicates disagreement. (a)
Resting blood pressure.
The normal arterial blood pressure
ranges from 90 to 120 mm. of mercury systolic and 60 to 80 mm. diastolic. Slight diurnal variations in blood pressure from 5 to 10 mm. of mercury systolic occur, the peak being in the afternoon and the lowest level in the early morning hours (Robinson and Brucer, 1939) • Variations within these ranges mean very little according to some investigators (Dawson, 1920).
A low systolic pressure is commonly found in weak and debilitated
20 subjects (Berry, Horton and MacLean, 1940). One study compared resting systolic, diastolic and pulse pressures of 202 Olympic athletes, and indicated all measurements to be within the ranges common to persons of similar ages (Bramwell and Ellis, 1929)• Some evidence showed that the average resting systolic blood pressure was slightly higher among 44 better competitive swimmers (McCurdy and Larson, 1939)•
McCloy (1942) has classified high diastolic pressure as
good from the fitness point of view.
An experiment comparing the resting
cardiovascular state with aspects of physical fitness reported findings indicating that the greater resting systolic blood pressure was directly related to speed of movement, strength and time of moderate effort to fatigue (Cullimbine, 1949)J however, most investigators agree that ath letes cannot be distinguished from nonathletes by blood pressures alone (Cureton, 19^7)• (b)
Effect of exercise.
One of the early studies on blood
pressure changes during exercise utilized continuous records of systolic pressure during work on a bicycle ergometer.
Observations showed a
rapid rise in pressure at the beginning of exercise, followed by a more gradual secondary rise to a maximum, which was reached in 5 to 10 minutes.
The pressure then remained fairly constant.
An abrupt fall,
almost to the resting level, took place on cessation of exercise (Bowen, 1904).
Experiments on subjects at the close of a long run showed that
the systolic blood pressure temporarily increased due to the exercise and returned to normal more or less slowly, usually becoming subnormal. The time of return to normal for systolic, diastolic and pulse pressures
21 was proportional to the severity of the exercise.
In subjects in poor
cardiovascular condition, the return to normal required a longer period of time (Lowsley, 19H) • An abrupt fall in systolic pressure in the first few seconds after exercise, with a subsequent rise, reaching a maximum 20 to 30 seconds later was reported (Cotton and Rapport, 1917)* Changes in diastolic pressure in response to exercise have not been studied as extensively as changes in systolic pressure.
A rise in
diastolic pressure during exercise, with a subsequent fall below normal following cessation of work has been reported (Morehouse and Miller, 19^8). Salit and Tuttle (19^-) concluded that blood pressure measures fail to distinguish differing degrees of physical fitness in healthy young adults. (c)
Effect of training.
One of the most recent studies on the
effect of training on blood pressure responses employed the Harvard Step Test (stepping on and off a 20 inch bench at the rate of thirty steps per minute) as the control exercise.
The subject maintained a prescribed
dietary intake, sleep and living habits during the training period.
Re
sults of this study indicated that the resting and post-exercise systolic blood pressures tended to decrease with training, as did the resting and one minute post-exercise diastolic pressures.
Trends in the two or three
minute post-exercise diastolic blood pressures were not observed (Cogswell, i-9^-6) • Reductions in blood pressures due to six weeks of physical train ing and artificial ultraviolet irradiation were observed in experiments on students at the University of Illinois (Cureton and Allen, 19^-5) • In his review of the literature on blood pressure, Steinhaus (1933) stated
22 that Herxheimer (192^), Ewig (1925) and Ackerman (1927) observed that the resting systolic blood pressure was reduced considerably with training.
Ackerman (1927) reported that 88 per cent of the subjects
showed a decrease in diastolic pressure.
Without experimental evidence,
Gunewardene (1937) of India has called attention to the part that physi cal inactivity plays in hypertension.
This assumption was based on his
observation that hypertension occurred rarely among rickshaw runners who took violent exercise with long, exhausting hours; whereas, hypotension was common among groups who led sedentary lives and indulged in over eating. Some investigators have reported results which indicate no obser vable change in blood pressure during training.
The classical study in
this area experimented with different training procedures over a three year period in an effort to determine the effect of physical training on blood pressure.
The results of this study showed that the effect of
training on resting blood pressure was neither striking nor constant. Pulse pressure tended to increase about 6 mm. of mercury due to training (Dawson, 1920).
Another study on the physiologic effect of muscular
training showed no significant changes occurring in blood pressures as a result of training (Gimmill, 1930)* Studies of blood pressure changes during exercise before and after training are few.
One reported that during exercise a trained man main
tained a systolic plateau, while an untrained man had a fall of systolic blood pressure below normal during the exercise period (Cruchet, 1920). Bock and his coworkers (1928) experimented on men working on a stationary
23 bicycle.
They observed that training causes a lesser rise in systolic
blood pressure during exercise, and consequently, a lower post-exercise blood pressure.
Most investigators reported that the systolic blood
pressure in trained subjects showed a rapid return to normal after exer cise; in untrained subjects, however, the systolic blood pressure might fall below normal after exercise, then gradually return to normal as fatigue was eliminated (Cureton, 1947). It would appear from this review of the literature that blood pressure measures fail to distinguish degrees of fitness in healthy young adults.
Training may lower the arterial blood pressure.
In recovery
from exercise, a trained person might show a quicker recovery to the rest' ing level of systolic, diastolic and pulse pressures. Pulse Bate. individuals.
(a) Besting pulse rate.
The normal pulse varies in
A range of 50 to 100 has been accepted as normal by the
American Heart Association.
In a recent study one author found that the
basal heart rates average 6l to 64 beats per minute in healthy young aviators (Graybiel et al., 1944).
The time of day did not seem to affect
the pulse rate if the subjects were supine; whereas, when they were standing, the pulse rate was higher by about 6 beats per minute in the late afternoon (Schneider and Truesdell, 1923). Some investigators have reported a tendency for the heart rate to be slower in subjects in good physical condition.
Cook and Pembrey
(1913) found slower rates in men trained for muscular work then in un trained men.
One investigator demonstrated that training slowed the
2k
resting pulse rate by 9 beats per minute on an average and that the con tinued practice of some form of exercise, such as rowing, extended over a period of years might progressively lower the rate of the heart beat (Dawson, 1917)-
A comparison of the influence of various types of
training was reported in a study of 202 Olympic athletes.
The main con
clusion of the comparison was that those athletes with relatively greater athletic history had lower pulse rates (Bramwell and Ellis, 1929)• Cotton (1932) made a comparison of pulse rates of athletes and nonathletes and reported that low pulse rates were noted among athletes. Other workers have reported slightly contradictory results.
One
extensive study made on 129 students and 18 varsity oarsmen in training showed no relation between basal pulse rates, differences between stand ing and recumbent pulse rates and capacity to perform hard muscular work (Brouha and Heath, 19^-3) • 0ne study testing the validity of heart rate as a determinant of physical fitness concluded that the quiet resting heart rate did provide a good means for selecting individuals of superior condition (Salit and Tuttle, 19^-).
An investigation of the relation
between basal, function and exercise tolerance failed to demonstrate a significant relationship (Taylor, 19^-) • (b)
Effect of exercise.
Fair agreement is evident among the
investigators studying the behavior of the pulse rate during and after the exercise period.
A comparison of the heart's reaction of ten trained
men and ten untrained men in the performance of the same task on a bicycle ergometer showed the average increase in pulse frequency 103 per cent for nonathletes and 10^ per cent for athletes.
The average pulse
25 rate during rest for nonathletes was 8l and for athletes, 66 (Henderson, Haggard and Dolley, 1927). (Bock et al., 1928).
A similar study corroborated these results
A later study on a cycle ergometer compared the
behavior of pulse rate of trained and untrained subjects.
The resting
pulse rate for the untrained subject was 82, working pulse, 155; the trained subject showed a resting pulse rate of 6l, working pulse rate of 129.
The rise in the trained person was proportionately greater than in
the untrained, 111 per cent and 89 per cent, respectively (Schneider and Crampton, 19^+0). Another difference reported in the behavior of the pulse rate in the trained and untrained man was the more speedy return to the resting rate after exercise for the trained man.
The early workers who helped
to settle this question included Pembrey and Todd (1908) and Cook and Pembrey (1913)•
One study on the relation between heart rate during ex
ercise and that immediately after exercise stated that the time to recuperate was related to the work load and the condition of the subject. Faster recovery in the fit subject and greater increase in pulse rate proportional to the severity of the work load were noted (Cotton and Dill, 1933). In summary of the above studies, it seems apparent that the trained man has the advantage of a lower pulse rate, a greater proportional rise during exercise and a more speedy return to the pre-exercise level after exercise ceased.
The widespread recognition of the more speedy return
of the pulse rate to normal in the trained man led to the development of various tests of circulatory efficiency.
26 TESTS BASED ON RECUPERATION OE PULSE AFTER EXERCISE FOR PREDICTING CARDIOVASCULAR FITNESS Schneider test. One of the first attempts at this problem was based on the recuperation of pulse from mild exercise (Schneider, 1920). The Schneider Index was computed from the effect of postural changes on pulse rate and blood pressure and the effects of muscular exercise (l8 inch stool with five steps in 15 seconds) on pulse rate and blood pressure.
This test has been widely used, but it has failed to determine
man's capacity for strenuous work and has classified cardiovascular conditions into gross categories only (Cureton, 19^-7)*
Also because of
the mildness of the exercise, the validity of the pulse rate response has been questioned (Cotton and Dill, 193*0 • There still exists much doubt as to the value of postural changes in pulse rate and blood pres sure responses as an indication of physical condition (Brouha and Heath, 19^3)• Pulse ratio tests. Another approach to the problem of a test for circulatory efficiency is based on the theory of pulse ratio, the latter representing the ratio of pulse rate during the first minute after exer cise to the resting pulse rate.
One of the first studies of pulse ratio
utilized stepping up and down on a 13 inch stool.
The measure used was
the number of steps per minute required to produce a pulse ratio of 2.5 (Collis, Pembrey and Hunt, 1911)•
Campbell (1917) later pointed out that
while for average subjects a high pulse rate is a reliable sign of unfit ness, the test as formulated gives those with high initial pulse rate an
27 advantage over those with low pulse rate.
He recommended stepping for 3
minutes and counting the pulse for 2 minutes after exercise as a better test. A two point pulse ratio test was later developed, with a chart for quick interpolation of a 2.5 pulse ratio in terms of the number of steps per minute required to obtain it (Tuttle, 1931) •
In later research,
however, Tuttle returned to the pulse ratio used by Collis and Pembrey in 1911.
The simplified pulse ratio was arrived at by counting the pulse
for 2 minutes after walking 30 steps per minute on a 13 inch stool and dividing this figure by the sitting pulse rate before exercise (Tuttle and Dickinson, 1938)• One of the criticisms of the pulse ratio tests was that one minute of exertion failed to push any normal subject to the limit of his endurance.
Recent observers have shown that more reliable results are
obtained when the stool stepping is at 30> ^0
50 steps per minute so
that environmental stimuli have less effect on the pulse rate (Morehouse and Tuttle, 19^-2).
It was shown also that the reliability of the pulse
rate taken two minutes after exercise was directly related to the stren uousness of the exercise (Morehouse and Tuttle, 19^2). The conclusion reached by most investigators was that all pulse rate tests which employ post-exercise pulse rates, pulse ratio and re covery time of pulse rate after exercise must be sufficiently strenuous to give valid results (Cureton, 19^7) • The Harvard Step Test.
The need in World War II for a simple,
28 valid test of circulatory fitness led to the development of the Harvard Step Test.
This test was proposed as a "simple means of measuring a man’s
efficiency for hard muscular work" (Johnson, Brouha and Darling, 19^-2). Data obtained in general research in the Grant Study at the Harvard Fatigue Laboratory were the basis for this test.
These data
consisted of a series of measurements on 265 college students selected without reference to physical ability. group of athletes for comparison.
Measurements were also made on a
The capacity of each group to perform
hard muscular work was measured by the following determinations:
duration
of run on a treadmill at 7 miles per hour on an 8.6 per cent grade; blood pressure before and after work; pulmonary ventilation and oxygen con sumption during and after work; blood sugar and blood lactate concentra tions.
Of these variables, three were selected as significant measures
of fitness for strenuous exertion:
recovery pulse rate and blood lactate
level at the end of the run, and the duration of the run (Johnson and Brouha, 19^2).
On the basis of these three measures, the subjects were
divided into four categories:
poor, average, good and excellent
(Robinson, Edwards and Dill, 1937) • There was no relation between capa city to perform hard work and basal pulse rate, sitting pulse rate, difference between sitting and recumbent pulse rates, difference between standing and recumbent pulse rates, or differences between systolic blood pressures taken in the standing and recumbent positions.
A close
relationship was found between performance capacity and rate of decel eration of the pulse after work on the treadmill to exhaustion or to a maximum of five minutes (Brouha and Heath, 19^-3)*
29 On the basis of the above results and similar experiments carried on at the Harvard Fatigue Laboratory, an index of fitness for hard mus cular work was computed: Duration of standard exhaustive exercise in seconds X 100 2 x sum of pulses from 1-1.5; 2-2.5; in recovery For practical, administration, stool stepping on a 20 inch bench was pro posed as the standard form of work.
From experimental data, it was
observed that the curves of pulse rate for the first ten minutes of re covery could be sufficiently defined by any three values of the pulse rate taken at different times of recovery (Robinson, Edwards and Dill, 1937)*
Thus, the pulse rates counted at three convenient intervals in
recovery after exercise were an approximation of the whole curve.
The
duration of effort before exhaustion was included to detect the "staying power" in a man, and because the duration and intensity of effort and one other measurement had been shown to approximate the other established differences between fit and unfit subjects.
Also, the duration of work
was shown to differentiate between the poor and the average men, while the pulse rate during recovery distinguished between the superior and the good.
The good men were found to have a relatively slow recovery to
the resting pulse level, while the superior men showed a rapid recovery (Johnson, Brouha and Darling, 19^+2). The index of fitness has been used for two different types of classification:
first, to assess the relative fitness of different men
for hard work; it has been shown to select the best, the poorest and the average men; and, second, to observe quantitatively the improvement of
30 the same man with physical training and to detect physical deterioration in the person who discontinues training (Cureton, 19^7; Brouha, Fradd and Savage, 19^; Johnson, Brouha and Darling, 19^2). A rapid form of the Harvard Step Test index of fitness was devel oped: Index of fitness =
_______ time in stepping in seconds X 100______ 5-5 pulse count (30" period beginning 1 ’ after work)
In this simplified form of the test, the accuracy of the longer form has "been sacrificed for speed, simplicity and ease of administration for large groups (Morehouse and Miller, 19^3).
ARMY AIR FORCE PHYSICAL FITNESS TEST Development of the Army Air Force Test. It was the function of the Army Air Force physical training program to prepare personnel in the organic constituents underlying aviation skills and wartime physical needs.
With this in mind, the Army Air Force physical fitness test was
developed.
The test items included chinning, sit-ups and a 300 yard
shuttle run (Larson, 19^6). Effects of training on the physical fitness rating. A review of the results of a testing program in the Army Air Force show that improve ment in physical fitness resulted from successive stages of training, as depicted hy this test (Larson, 19^6).
31 CHAPTER SUMMARY The main dynamic effect of centrifugal acceleration and of gravity was found to he a redistribution of blood, together with a diminished effective circulation.
Circulatory adjustments to prolonged gravita
tional stress were shown to vary in each individual, according to his own pattern, some patterns showing better adaptation than others.
Physi
cal. training programs improved m an’s adaptation responses to such gravi tational stresses, as measured by the tiltboard test.
Analysis of
exercise tolerance and orthostatic inadequacies revealed the relation ship to be very slight, but consistent.
A review of the literature
failed to show any comparative studies between "blackout” tendencies and tiltboard responses, or between man's exercise tolerance and his Gtolerance.
Studies have been reported which show that after a program
of physical training, a man's basal arterial blood pressure and pulse rate may be lower and may show a more speedy return to the resting level after exercise.
32 CHAPTER III
METHODS
OUTLINE OF THE PROBLEM
The experimental portion of this investigation was divided into three problems:
the first, to determine the relation between the sub
jects’ G-tolerance and fitness for strenuous work; the second, to determine the effects of a six weeks’ training program upon the subjects’ G-tolerance; the third, to investigate the effects of an eight weeks’ non-training period upon the subjects’ G-tolerance.
After the second
test period, in which the subjects' fitness for strenuous work and Gtolerance were determined, the training program was discontinued and the subjects were asked to participate as little as possible in any organized physical training.
The subjects were tested again after a non-training
period lasting eight weeks.
PERSONNEL AND TIME SCHEDULE
Subjects.
In this study twenty-three healthy male, adult students
of the University of Southern California were used as subjects.
The
majority of the subjects were physical education majors and six of these subjects were members of varsity athletic teams.
Eleven of the subjects
had been pilots; five of the subjects had been pilots and were experienc ed centrifuge riders; and seven were neither pilots, nor were they experienced centrifuge riders.
The subjects ranged from nineteen to
33 thirty-two years of age (average, twenty-three years).
The weight range
of the subjects was 125 to 209 pounds (average 168 pounds).
The height
range of the subjects was 5 feet 1 inch to 6 feet 2 inches (average, 5 feet 7 inches). Examiners. All measurements of physical fitness and G-tolerance were administered by six trained graduate students at the University of Southern California under the supervision of a physiologist and a flight surgeon.
The blood pressure measurements taken on tests for G-tolerance
were administered by a flight surgeon.
The reliability of the blood
pressure measurements on the physical, fitness indices was within 5 mm. of mercury.
Pulse rates for physical fitness and G-tolerance tests were
taken by an experienced operator of the electrocardiograph. Time schedule. The first test period was from September 30, 19^9 to October 15, 19^-9*
After all subjects had been tested for G-tolerance
and fitness for strenuous work, a six weeks1 training program was admin istered, from October 17, 19^-9 to December 1, 19^-9• At the end of the training program, the subjects were retested, using the same tests admin istered during the first test period. December 1, 19^9 to December 16, 19^9*
This second test period was from The subjects were then instructed
to forego participation in organized physical conditioning for a period of eight weeks.
This non-training period lasted from December 16, 19^-9
to February 10, 1950> it included the Christmas vacation, final exam ination and registration periods at the University.
At the end of the
non-training period, from February 10, 1950 to March 15, 1950, the
3^ subjects were tested for the third time.
MEASUREMENT OF G-TOLERANCE AND PHYSICAL FITNESS FOR STRENUOUS WORK Fitness for strenuous work. The tests used for this measurement were the Harvard Step Test, the Army Air Force Test and a hand dynamo meter strength test. The Harvard Step Test (Johnson, Brouha, and Darling, 19^-2) represented a test of physical fitness for strenuous exertion.
The test
was performed by stepping on and off a 20 inch bench at the rate of thirty steps per minute for 5 minutes or until the subject was unable to continue.
Each subject was required to maintain a reasonably erect
posture when both feet were on the step. not permitted. the subject.
Exaggerated arm swinging was
A metronome was used in this test to set the pace for The simplified form of the Harvard Step Test was employed.
The Army Air Force Test represented a test of cardiorespiratory endurance, muscular strength, speed, agility and power (Stansbury, 19^3)* Each subject performed three test items in the following order:
a two
minute sit-up test, a pull-up or chinning test and a 250 yard indoor shuttle run.
These were scored on norms prepared by the Army Air Force.
The dynamometer strength test consisted of the hand grip for the dominant hand (Cureton, 19^7) • G-tolerance. The G-tolerance of the subjects at 5 G was determined by responses to visual stimuli, earopacity changes, length of run before
35 loss of vision and pulse rate.
The physical equipment in the Department
of Aviation Medicine at the University of Southern California was em ployed in this phase of the study. For subjects who greyed out or blacked out, the measure of Gtolerance was the length of time (Hallenbeck, Lambert, Wood and McLennan, 19^6).
For subjects who ran 30 seconds, the measure of G-tolerance was
the earopacity change at the end of the run, and earopacity change and pulse rate during the recovery period following exposure to 5 G; this was based on the logical, assumption that the greater the earopacity dis placement at the end of the 30 second run and the greater the earopacity displacement and increase in pulse rate following exposure to 5 G, the poorer the cardiovascular response of the subject. The measure of earopacity was used to determine the circulation at the level of the head (Green, 19^).
I't
been found that the ear
opacity shows the draining of blood from the head at onset of G and that the blood continues to drain from the ear when the acceleration is 3 G or more.
If the acceleration is not beyond the physiologic limit of the
subject and if it is maintained long enough, a change will occur in the subject which will check the downward course of earopacity, and recovery with return, of blood to the ear may take place. The subjects’ responses to visual stimuli were followed by a system of lights which were turned on by the observer and turned off by the subject.
The subjects’ responses were recorded simultaneously with
the other variables.
Peripheral vision was tested by means of two lights
placed on a panel, one at each side, in front of the subject.
These
36 lights subtended an angle of k6 degrees at the subjects’ eyes.
Central
vision was tested by a single light placed in the center of the panel at or near the fixation point of vision (Hallenbeck, Lambert, Wood and McLennan, 19^-6).
Each subject was instructed to fix his gaze on a small,
continuously burning light immediately above the central, test light. Peripheral lights were blue-green in color, the central light red.
The
development of visual symptoms during exposure to G was indicated on the records by the subject’s failure to respond to the peripheral and central light signals. The pulse rate before exposure to 5 G and during an eight minute recovery period following exposure to G was recorded by an electrocard iograph.
In general, investigations have shown that the heart rate
increases at the moment of starting the centrifuge and continues to in crease for some time after the attainment of G.
The rise in heart rate
usually stops, coincident with the levelling off of the earopacity.
The
pulse may show an actual decrease in rate while the force of G is still maintained, and this slowing is usually associated with an upward swing of the earopacity (Code, Wood, Sturm, Lambert and Baldes, 19^5)-
In
this study, the variables measured were loss of peripheral vision or greyout, heart rate during the recovery period after exposure to G, dis placement of earopacity during G and in the recovery period and duration of the run (greyout time or 30 second runs).
The time intervals, accel
eration, subject’s response to light signals and earopacity were recorded by a light camera. For all subjects who responded satisfactorily to the light signals,
37 the length of the run was 30 seconds.
At the end of this designated
time, the centrifuge was automatically stopped; hut if the subject failed to respond to light signals, as noted by the center observer, the run was stopped at that point.
This was considered to be the subject’s
greyout or blackout time.
PROCEDURES USED IN THE THREE TEST PERIODS Determination of physical fitness for strenuous work. The sub jects reported to the Physical Performance Laboratory at the University of Southern California in gym suit and shoes for the Harvard Step Test. The blood pressure measurements were taken with the subject in the sitting position by auscultation on the brachial artery at the bend of the elbow (Best and Taylor, 1950) • All pulse rates for the test were taken by electrocardiograph. On reporting for the test, each subject was required to sit quietly, during which time electrodes were attached and the leads from the electrocardiograph fastened in place.
Five minutes elapsed before
the resting blood pressure and pulse rate were taken.
After completion
of this procedure, the electrocardiographic leads were unfastened and the subject began the Harvard Step Test, as previously described.
After
completing the test, the subject sat down and the blood pressure was taken immediately.
At the same time, the electrocardiographic leads
were again connected.
At the beginning of the first minute after the
test and for a period of 30 seconds, the pulse rate was taken; thereafter,
38 the pulse rate was recorded during recovery for a period of 6 to 10 seconds at the 2, 3>
6, 7 and. 8 minute intervals.
The blood
pressure was taken during the fourth and ninth minutes of the recovery period.
The subject's reactions to the test were noted and recorded and
a comparison of the difficulty in performing the test in the three test periods was made by the subject if possible. The following procedures were used in the administration of the Army Air Force Test and the hand dynamometer strength test.
Each sub
ject reported for the test in a gym suit and rubber soled shoes. 1.
Sit-up test: Subject will assume a supine position with the legs comfortably spread and hands clasped behind head. Legs will be held by an individual at the ankle. Said in dividual will not sit on subject's feet. Subject will lift his trunk upward, touching right elbow to left knee and then lower trunk, touching head to floor. He will continue with out pause, alternating left elbow to right knee and right elbow to left knee. Subject is not to bounce from floor. Recorder will count the number of sit-ups subject completes in two minutes.
2.
Pull-up (Chinning test): Subject will grasp bar with the palms of the hand, facing away from body. Subject will start each pull-up with arms straight. He will lift until chin is over bar; then lower untilarms are straight. Sub ject is not permitted to kick, kip, swing or rest. Partial pull-ups will not be recorded.
3*
250-yard shuttle run (indoors): Subject may use any start ing position. Subject will make ten (10) twenty-five (25) yard trips in the same lane. Total of 250 yards. Any method of turning is permissible. Time will be recorded to next full second. Subject will be started by standard track com mands. Stop watch will be started on command "go" and stopped when subject crosses finish line. (The 250-yard indoor shuttle run was used for ease of administration, r = .91 for the 250 yard indoor shuttle run and 300-yard outdoor shuttle run (Larson, 19^-6) •
The hand dynamometer strength test.
The dynamometer was placed
39 in the dominant hand of the subject so that the fingers would not inter fere with the indicator.
The subject was told to squeeze the instrument
as tightly as possible, using the body in any position to obtain maximum results.
The amount was read from the indicator in kilograms and con
verted into pounds for recording (Cureton, 19^7). The subject’s physical reaction to each test and the after-effects were noted and recorded.
At the end of the third test period, the sub
ject was asked to make a comparison of the difficulty of the tests. Determination of G-tolerance. The University’s physical examin ation records of each subject were examined by a medical doctor.
Each
subject who was not an experienced centrifuge rider was given an indoc trination run, which lasted 3 seconds, at the rate of +3*5 G, +5 G.
G, and
If the subject suffered no ill effects, as determined by a flight
surgeon, and if the subject still desired to participate in the experi ment, he became a centrifuge subject for the duration of the experiment. Before the indoctrination run, each subject was instructed as to how to "fight” G by straining maneuvers.
Also, each subject was given
an opportunity to practice the light signals which were used during the run.
Throughout the indoctrination run and regular test runs, the
center observer gave continuous admonitions to "pull in your belly, tighten your leg muscles and keep breathing." Upon reporting to the centrifuge for the test runs, each subject answered the questions previously described.
He then climbed into the
cab and the belt and shoulder harness were fastened.
The subject was
•'(niuyi ii'mi'i!"!'
98mm V
hi
seated comfortably with his head against a head rest.
The electrodes of
the electrocardiograph were placed on the subject and Leads 1, 2 and 3 were attached.
The subject's helmet and earopacity unit were put on and
he was given a practice period using the light signals.
At this time
also he was cautioned to fight G. When the subject felt he was ready, the door to the centrifuge was closed and the physiologic recordings were begun one minute before the centrifuge began to rotate; the pulse rate was taken for a 10 second interval, the earopacity for the entire minute.
Earopacity, light re
sponses and acceleration were continuously and simultaneously recorded throughout the run.
The maximum length of the test run was 30 seconds
or to greyout time of the subject.
If the subject failed to respond
satisfactorily to the light signals, the center observer motioned for the centrifuge to stop.
Earopacity was recorded for 1 minute during the
third and eighth minutes of recovery.
The arterial blood pressure was
recorded for the second and third test periods only.
The blood pressures,
taken with the subject sitting, were recorded before the run and during the first and ninth minutes. The subject's reactions to each test were recorded; a comparison of the difficulty of the three test periods was made by each subject if possible. The environmental temperature in the centrifuge was maintained at 68 to 71 degrees E.
k-2
THE TRAINING PROGRAM
Each subject participated three times weekly for six and a half weeks in weight lifting and running, which were the basis of the training program because of their similarity to the test items for physical fit ness used in this study, e.g.* strength and cardiovascular endurance. The weight lifting exercises were those described by Morehouse and Rausch (19^7* 19^+8) 9 using the weights prescribed for a man weigh ing 160 pounds.
All subjects lifted the same amount of weight and per
formed the same number of repetitions in each of the weight exercises. Each weight increased 5 pounds per week throughout the complete training period. The number of repetitions per exercise varied.
All arm exercises
included six repetitions for the first work-out of each week, and in creased three repetitions for each of the two succeeding work-outs of the week.
All leg exercises included ten repetitions the first work-out
and increased five repetitions for each of the two succeeding work-outs. The weight training exercises were divided into two sets, utilizing a total of twenty different exercises.
The specific exercises,
the amount of weight and the number of repetitions are shown in Tables I and II (See Appendix A). The exercises in Set I were performed for three weeks, three times weekly.
In addition to the exercises, the
subjects either ran five 4^0-yard laps or performed the Harvard Step Test.
The exercises in Set II were performed three times weekly for three
and a half weeks.
The subjects also ran for 5 minutes on the treadmill,
^3 which was set at a grade of 8.6 degrees and speed of 7 miles per hour. During the last seven days of the training program, each subject was asked to perform the exercises in Set II and to attempt to run the treadmill for 5 minutes every day.
NON-TRAINING PROGRAM The non-training program lasted for a period of eight weeks and included Christmas vacation, final examinations and registration at the University.
During this time the subjects were requested to limit their
activities as much as possible.
CHAPTER SUMMARY
The three phases of this investigation were defined.
The methods
used to measure G-tolerance and fitness for strenuous work were outlined. Administration of the three test periods, the training program and the non-training program were described.
kk
CHAPTER IV
RESULTS
The experimental design of this study required the subjects to undergo a six and a half weeks1 systematic training program, followed by an eight weeks' period, during which time systematic training was dis continued.
Preceding the training program, at the end of the training
program, and at the end of the eight weeks1 period when systematic train ing was not carried on, fitness for strenuous work and G-tolerance measures were taken.
Fitness for strenuous work was measured in terms
of performance scores on the Harvard Step Test, the Army Air Force Phy sical Fitness Test and the hand dynamometer strength test.
Each subject
was exposed to +5 G until he greyed out or for a maximum run of 30 seconds.
G-tolerance was measured in terms of earopacity during and
after the centrifuge run and pulse rates after the centrifuge run for those subjects who endured +5 G for 30 seconds; and duration of the run (time until grey-out) for those subjects who greyed out. These data were analyzed to answer the following questions:
After
the six and a half weeks' systematic training program, was there a change in fitness for strenuous work?
(2) After the six and a half weeks' syste
matic training program, was there a change in G-tolerance?
(3) Eight
weeks after the systematic training stopped, was there a change in fitness for strenuous work?
(k) Eight weeks after systematic training
stopped, was there a change in G-tolerance?
(5) Was there any demonstrable
relationship between fitness for strenuous work and G-tolerance?
^5 In the discussion to follow, measures taken before the training program began are referred to as Test Period I, at the end of the syste matic training program as Test Period II, and eight weeks after the systematic training program stopped as Test Period III.
STATISTICAL ANALYSIS OF THE DATA An outline of the statistical analysis designed to answer the above questions is presented below: 1.
Twenty-three healthy male university students were employed
as subjects.
Of these subjects, twenty-one were used in the comparison
of fitness measures and eighteen were considered in the comparison of G-tolerance measures; fifteen were considered in the comparison of fit ness and G-tolerance measures between Test Periods II and III. 2.
Age, flying and centrifuge experiences and performance of
each subject in the three test periods are shown in Table XX (see Appen dix A).
It is apparent that the subjects fall into two groups:
who endured +5 G for 30 seconds and those who greyed out.
those
This difference
in the measure of G-tolerance makes it necessary to treat these groups separately. 3.
The statistical significance of the obtained differences in
the fitness and G-tolerance measures in Test Periods I, II and III were determined by Fisher's "t" formula (Guilford, 19*^6). 4.
Statistical summaries showing the means, mean differences, "t"
values and level of confidence for statistically significant differences
k6 in fitness and G-tolerance were prepared. 5.
Bank order correlations between the fitness and G-tolerance
measures were computed for:
(l) subjects in each test period who en
dured +5 G for 30 seconds, (2) subjects in all test periods who endured +5 G for 30 seconds, and (3) subjects who greyed out in the test periods. 6.
A rank order correlation between earopacity measures at the
end of the G-test runs in Test Periods I and III was computed. 7 . Graphic illustrations include (l) comparison of G-tolerance in Test Period I, II and III, and (2) the inter-relationship of the Har vard Step Test scores and G-tolerance in each test period.
CONSIDERATION OF RESULTS After the six and a half weeks' systematic training program, was there a change in fitness for strenuous work? 1.
The fitness measures showed a statistically significant
increase after the six and a half weeks1 systematic training program.
In
Test Period I the subjects had a mean score of 65 (range, 32°89) on the Harvard Step Test, in Test Period II, a mean score of 85 (range 62-l4l); on the Army Air Force Test, a mean score of 59 (range 37~83) in Test Period I, in Test Period II, a mean score of 65 (range 41-87).
The
strength test showed a mean score of 118 pounds in Test Period I and a mean score of 125 points in Test Period II (Tables III, V and VII* see Appendix A). 2.
The greatest increase in fitness measures between Test
Periods I and II occurred in those subjects with high initial scores» Subjects were classified as poor, average and good, according to their initial test score on the Harvard Step Test.
In Test Period II the mean
score for the good group was 28.7 points higher; the average group increased 11.1 points, and the poor group 15»1 points.
In Test Period I
the scores for the good group ranged from 32 to 89* for the average group from 64 to 79>
for the poor group from 32 to 46.
In Test
Period II the score for the good group ranged from 8l to 141,. for the average group from 62 to 78> and for the poor group, with only one sub ject, a score of 46.
Two subjects in the good group were training
strenuously in addition to the systematic training program outlined in this study.
If their scores are not considered, the systematic training
program described heretofore would seem to have had more effect on those subjects having low initial scores (Table VII, see Appendix A). Subjects were classified as excellent - very good, average and poor, according to their initial scores on the Army Air Force Test.
In
Test Period II the mean score for the excellent-very good group was 4.28 points higher, for the average group, 8.25 points higher and for the poor group, 15-5 points higher.
In Test Period I scores for the excel
lent-very good group ranged from 64 to 83, for the average group from 49 to 63f and for the poor group from 37 to 42.
In Test Period II scores
for the excellent-very good group ranged from 64 to 87, for the average group from 51 to 63, and for the poor group from 4l to 55 (Table XI, see Appendix A). 3. Pulse rates were recorded during an 8 minute recovery
48 period from the Harvard Step Test in Test Periods I and II.
Pulse rates
at the first minute of the recovery period decreased 16 heats per minute and for the second minute decreased 9 heats per minute.
These decreases
were statistically significant (Tahle XII, see Appendix A). No signifi cant changes in pulse rate were observed at rest or from the third to the eighth minute of recovery in Test Period I and II (Tahle XXV, see Appendix A). 4.
Arterial, hlood pressure measurements were taken du
the first, fourth and ninth minutes of the recovery period after the Harvard Step Test in Test Periods I and II.
The diastolic pressure at
the first minute of recovery decreased 10 mm. of mercury and at the fourth minute decreased 6 mm. of mercury. tically significant.
These decreases were statis
No significant changes in the systolic and pulse
pressures were observed between Test Periods I and II (Table XV, see Appendix A). After the six and a half weeks’ systematic training program was there a change in G-tolerance? 1.
The G-tolerance measures showed definite improveme
in Test Period II.
Earopacity was recorded at the end of the run and at
the first, third and eighth minutes of recovery from exposure to G in Test Periods I and II.
In Test Period II the earopacity showed a statis
tically significant decrease (less blood left the head region) at the end of the run.
Significant changes in earopacity did not occur during
the recovery period, but there was a tendency toward better recovery in Test Period II (Table XXII, see Appendix A).
^9 2.
Pulse rates were taken during the first, third and
eighth minutes during recovery after exposure to G in Test Periods I and II.
Significant changes in pulse rates were not observed in Test Periods
I and II; but pulse rates tended to be slightly lower following exposure to G in Test Period II (Table XXII, see Appendix A). 3.
Group performance on G-test runs showed an increase in
the duration of the centrifuge m m in Test Period II.
Three subjects
who greyed out in about 9 seconds after the onset of +5 G in Test Period I were able to endure 30 seconds in Test Period II without impairment of vision when their fitness for strenuous work was improved.
Two other
subjects who greyed out in about 6 seconds in Test Period I greyed out in about 8 seconds in Test Period II (Table XX and XXI, see Appendix A). Per cent values for duration of runs showed a definite improvement in Test Period II.
In Test Period I, 77 per cent of the
group endured +5 G for 30 seconds and 23 per cent greyed out; in Test Period II, 93 P©** cent of the group endured +5 G for 30 seconds and only 7 per cent greyed out. 5.
Comparison of G-tolerance in Test Periods I and II
graphically presented in Figures 1 and 2.
Mean values and range of earo
pacity changes and pulse rates are shown.
The effect of G in reducing
earopacity (circulation to the head) was diminished during Test Period II. The beneficial effect of frequent and regular exercise varied widely in degree.
Although there were no great differences in pulse rates at rest
and after acceleration, the pulse rates tended to be lower in Test Period II.
50 Eight weeks after systematic training stopped was there a change in fitness for strenuous work? 1.
A statistically significant decrease in fitness was
found in the Army Air Force Test scores.
A slight drop-off in fitness,
as measured hy the Harvard Step Test and hand dynamometer strength test, was observed in Test Period III.
In Test Period II the subjects had a
mean score of 89 (range 62-l4l) on the Harvard Step Test; in Test Period III, their mean score was reduced to 83 (range 46-92).
Scores on the
Army Air Force Test dropped from a mean of 68 (range 41-87) to a mean of 64 (range 45-84) (Tables III, V and VII, see Appendix A). 2.
The greatest drop-off in fitness for strenuous work
was observed in those subjects who had high scores in Test Period II. Classification according to the Harvard Step Test showed the good group to be 8.9 points lower in Test Period III; the average group decreased 4.93 points; the poor group showed no decrease.
In Test Period II the
scores for the good group ranged from 8l to l4l, for the average group from 62 to j8, and for the poor group, with only one subject, a score of 46.
In Test Period III the scores for the good group ranged from 80 to
105, for the average group from 68 to 75 j and for the poor group, with only one subject, a score of 46 (Table IX, see Appendix A). Classification by the Army Air Force Test showed that the mean score for the excellent-very good group was 8 points lower in Test Period III; the mean score for the average group decreased .76 points.
In Test
Period II the scores for the good group ranged from 64 to 87, for the average group from 51 to 63, and for the poor group from 4l to 55*
In
51 Test Period III the scores for the good group ranged from 65 to 84, for the average group from 55 to 62, and for the poor group, with only one subject, a score of 45 (Table XII, see Appendix A). 3.
Pulse rates wererecorded during an 8 minute recovery
period after the Harvard Step Testin Test Periods II and III.
Wo sig
nificant changes in pulse rates were observed following performance of the step test in Test Periods II and III (Table XVI, see Appendix A). 4.
Arterial blood pressure measurements were taken during
the first, fourth and ninth minutes of recovery from the Harvard Step Test in Test Periods II and III.
No significant changes in blood pres
sures after the step test were observed in Test Periods II and III (Table XVII, see Appendix A). Eight weeks after systematic training stopped was there a change in G-tolerance? 1.
A statistically significant drop-off in G-tolerance
measures (earopacity and pulse rates) was noted in Test Period III. Earopacity was recorded during exposure to +G, immediately after G and at the first, third and eighth minutes during recovery from +G in Test Periods II and III.
The earopacity measures during and immediately after
G and during the first minute of recovery showed a statistically signifi cant increase (greater blood displacement from the head region) in Test Period III (Table XXIII, see Appendix A). 2.
Pulse rates were recorded during the first, third and
eighth minutes of recovery from exposure to +G in Test Periods II and III.
Pulse rates showed a statistically significant increase by an
52 average of 13 beats per minute in Test Period III. 3-
Group performance on the +G-test runs showed no signif
icant changes in Test Periods II and III.
One subject greyed out in both
runs; one subject progressed from grey-out to the maximum run of 30 seconds; one subject went from 30 seconds to grey-out; twelve subjects ran 30 sec onds in both test periods (Table XXI, see Appendix A). ^ . Comparison of the per cent values for duration of runs showed no difference between Test Periods II and III.
In both Test Period
II and Test Period III, 77 per cent of the group endured +5 G for 30 seconds and 23 per cent greyed out. 5.
A graphic presentation of the earopacity and pulse
rates for Test Periods II and III is shown in Figures 1 and2 (see Appendix B). In Test Period III there were greater displacements of the earopacity measure and higher pulse rates than in Test Period II. Is there any demonstratable relationship between fitness for stren uous work and G-tolerance? 1.
Comparison of fitness and G-tolerance in subjects
to endure +5 G for 30 seconds. (a)
A slight but consistent relationship was found
between measures of fitness for strenuous work and measures of G-tolerance, as used in this study.
Subjects with high scores, as a group, tended to
have greater G-tolerance also; subjects with low fitness scores, as a group, tended to have less G-tolerance. (b)
Rank order correlation between the Harvard Step
Test and G-tolerance was the highest (rho = .63 and rho = +.6l) in Test
53 Periods II and III.
The Army Air Force Test showed a slightly negative
relationship to G-tolerance in Test Period II, whereas, Test Periods I and III showed a slightly positive relationship (Table XXV, see Appendix A). This would indicate that fitness for strenuous work, as measured by the Harvard Step Test, is more directly related to G-tolerance than is fitness for strenuous work, as measured by the Army Air Force Test. (c)
A graphic presentation of the relationship be
tween fitness, as measured by the Harvard Step Test, and G-tolerance in each test period is shown in Figures 3>
5> 6, 7 and 8 (see Appendix B).
In Test Periods I and III G-tolerance was greater for the good group than for the average and poor groups.
In Test Period II there were better
responses in earopacity for the poor and average groups, but pulse rates did not reflect these differences. (d)
Consideration of all subjects (forty-three)
who endured +5 G for 30 seconds in the three test periods showed the rank order correlation between the Harvard Step Test and G-tolerance to be higher than between the Army Air Force Test and G-tolerance. were:
Correlations
rho = +.^1 for the Harvard Step Test; rho = +.12 for the Army Air
Force Test (Table XXV, see Appendix A). (e)
Figures 9 and 10 show a graphic presentation
of this relationship by combining all forty-three subjects in the three test periods.
The good group, as measured by the Harvard Step Test,
showed better responses in earopacity changes, especially at the end of the run, and immediately after G, and lower pulse rates (average 10 beats per minute after G).
5^ 2.
Comparison of fitness and G-tolerance in subjects
greyed out before 30 seconds. (a)
Consideration of all subjects who greyed out
in the three test periods showed a consistent relationship between fit ness measures and G-tolerance. (b)
The rank order correlation between the Harvard
Step Test and G-tolerance was higher than for the Army Air Force Test and G-tolerance.
Earopacity at the end of the run correlated:
with the Army Air Force Test.
rho = +.10
Pulse rates 1 minute after G correlated:
rho = +.5 with the Harvard Step Test and rho = 0 with the Army Air Force Test. (c)
A graphic presentation of fitness for strenuous
work, as measured by the Harvard Step Test, and G-tolerance, as measured by earopacity changes, is shown in Figures 11 and 12.
Again it is observ
ed that the good fitness group showed better responses to +G. (d)
Of the fifty-six centrifuge runs at +5 G in the
three test periods, grey-out occurred in thirteen subjects.
Of this
group, four subjects were classified by the Harvard Step Test in the good fitness group, with a mean score of
9 k,
and nine subjects in the poor-
average fitness group, with a mean score of 71*
Similarly, of the forty-
three subjects who endured +5 G for 30 seconds, twenty-one were classified by the Harvard Step Test in the good fitness group, with a mean score of 88, and twenty-two subjects in the poor-average fitness group, with a mean score of 71• Subjective comparison of the difficulty of G-runs for the three
55 test periods.
A comparison of the difficulty of the G-test runs in Test
Periods I and II was made by the eighteen subjects.
Three subjects, all
of whom believed their physical condition to be about the same, agreed that the G-test run in Test Period I was more easily accomplished.
Fif
teen subjects believed that the G-test run in Test Period II was more easily accomplished; of these, ten believed they had improved their phy sical condition, three believed their physical condition was about the same and two could not make a comparison. After Test Period III, a comparison of the difficulty of the three G-test runs was made by the fifteen subjects.
One subject believed that
the run in Test Period I was the most difficult, two subjects agreed that the run in Test Period II was the most difficult, four subjects selected the run in Test Period III as the most difficult and eight could make no comparison.
SUMMARY OF KESULTS Changes in fitness and G-tolerance measures after a six and a half weeks’ systematic training program. 1.
Fitness measures showed a statistically significant in
crease, with the greatest increase, in general, being among those sub jects who had high initial scores.
Pulse rates and diastolic blood pres
sure after the Harvard Step Test were lowered after training. 2. increase.
G-tolerance measures showed a statistically significant
In the subjects who endured +5 G for 30 seconds, earopacity
during and after acceleration showed less displacement and pulse rates
56 were lower after the training program.
Group performance on the G-test
runs showed an increase in the duration of the centrifuge run in Test Period II. 3.
Eighteen subjects showed improvement in fitness.
these, sixteen subjects showed improvement in G-tolerance.
Of
Of the thir
teen who endured +5 G for 30 seconds, eleven showed improvement in the earopacity measures and two did not.
Of the five who greyed out in Test
Period I, all showed improved ability to withstand high headward accel eration in Test Period II. 4.
That the proportionate degree of improvement in fitness
and G-tolerance varied from subject to subject is shown by the low rank order correlation.
Eho = +.11 between change in fitness and change in
G-tolerance (earopacity at the end of the run) for the group of subjects who endured +5 G for 30 seconds. Changes in fitness and G-tolerance measures eight weeks after the training program stopped. 1.
A statistically significant drop-off in fitness was
found, as measured by the Army Air Force Test.
No great drop-off was
noted in fitness, as measured by the Harvard Step and hand dynamometer strength tests.
The greatest drop-off in fitness was noted among those
subjects having high scores in Test Period II.
Changes in pulse rates
and blood pressure after the Harvard Step Test were not statistically significant. 2. cant decrease.
G-tolerance measures showed a statistically signifi In the 30 second runs, earopacity showed greater
57 displacement during and after acceleration and pulse rates were higher eight weeks after the systematic training program stopped. 3.
All fifteen subjects showed a statistically signif
decrease in fitness as measured by the Army Air Force Fitness Test.
Four
teen subjects showed a decrease in fitness and one showed an increase in fitness, as measured by the Harvard Step Test.
Of the thirteen subjects
who endured +5 G for 30 seconds, ten showed greater displacement in the earopacity measures, and three did not.
Group performance on the +5 G-
test runs showed no change in duration of the centrifuge runs.
Thirteen
subjects endured +5 G for 30 seconds; one subject greyed out at the same time in both test periods; one subject who endured +5 G for 30 seconds in Test Period II greyed out in Test Period III; and one subject greyed out in Test Period II and ran 30 seconds in Test Period III. Inter-relationship between fitness and G-tolerance. 1.
A slight but consistent relationship was found between
fitness and G-tolerance0 Subjects better fit for exercise tended to be fit for high radial acceleration. 2. A slightly higher relationship was found between the Harvard
Step
Test score and G-tolerance than betweenthe Army Air Force
Fitness Test and G-tolerance. Rank order correlation between earopacity measures at the end of the G-test run in Test Periods I and III. 1. The rank order correlation between G-tolerance (earo pacity during the centrifuge run) for Test Periods I and III was +.l4. 2. Thus, there was a slight tendency for those who ranked
high in G-tolerance in Test Period I to continue to rank high in Gtolerance in
Test Period III, but the relationship was not consistent.
Subjective 1.
comparison of difficulty of G-runs. In comparing Test Periods I and II, mostsubjects agreed
the G-run after training was easier. 2.
There was general agreement among those subject able
to make comparisons of all three test periods that Test Period III was more difficult than either Test Period I or Test Period II.
59 CHAPTER V DISCUSSION EFFECTS OF THE TRAINING PROGRAM ON SUBJECTS1 G-TOLERANCE In this study the effects of the training program showed a positive relationship to the subjects' performance at +5 G.
The subjects, in gen
eral, showed improvement both in fitness for strenuous work and in Gtolerance after a six and a half weeks' systematic training program. At the end of the training program, the subjects showed an in crease of 20 points in their score on the Harvard Step Test. on the Army Air Force Test was increased by
points.
The score
The greatest in
crease in score was found in those subjects having lower (poor-average) initial scores if the two subjects who were training strenuously for athletics are not considered. Improvement in fitness following the systematic training program was shown by higher group scores on the Harvard Step Test, the Army Air Force Test, the hand dynamometer strength test, diminished resting and post-exercise pulse rates and diastolic blood pressure after exercise. Improvement in G-tolerance following the systematic training program was shown by (l) improved circulation to the head during exposure to +G and faster recovery after +G, a lesser increase in pulse rates immediately after +G and faster recovery after +G for those subjects who endured +5 G for 30 seconds before and after training, (2) an increase in the duration of the centrifuge run or time until grey-out for those subjects who
greyed out; three subjects went from grey-out before training to the thirty second centrifuge run after training; two subjects extended their grey-out time after training; thirteen subjects endured +5 G for 30 sec onds in both test periods. It appears that as the subjects’ fitness for strenuous work was increased, G-tolerance also increased.
When the mean level of fitness
for the group was increased by the training program, the group showed increased tolerange to high headward acceleration although the varia bility for individuals was very great. Frequent and regular exercise was found to increase resistance to high headward acceleration, as demonstrated in this study.
Although it
was suggested that the increase in the muscular capillary bed during training for strenuous work might reduce resistance to high headward acceleration by providing a larger reservoir in the lower extremities in which blood could pool, it seems that there are other more beneficial factors of fitness that increase man’s tolerance for high headward acceleration.
INFLUENCE OF THE CESSATION OF SYSTEMATIC TRAINING ON G-TOLERANCE The cessation of regular and frequent exercise for eight weeks after a systematic training program diminished G-tolerance more consis tently than it diminished fitness for strenuous work. There was a definite drop-off in G-tolerance on cessation of frequent and regular exercise for an eight week period following the
6l training program.
Earopacity showed greater displacement during and
after exposure to +5 G and pulse rates were higher after +G following the training program in those subjects who endured +5 G for 30 seconds. A statistically significant drop-off in fitness as measured by the Army Air Force Test was found after training stopped.
The mean
score on the Army Air Force Test was 68 at the end of the training pro gram and
6k
eight weeks after the training program stopped.
The greatest
decrease in fitness scores for the Army Air Force Physical Fitness Test was found, in general, in subjects with higher scores in Test Period II. No statistically significant drop-off in fitness was found as measured by the Harvard Step Test and hand dynamometer strength test. The reduction of frequent and regular exercise, as shown in this study, was found to decrease the group’s resistance to high headward ac celeration.
INTER-RELATION OF SUBJECTS’ FITNESS SCORES TO G-TOLERANCE The relationship between a measure of fitness for strenuous work at any given time and G-tolerance is positive, but slight. tionship is especially evident in the low levels of fitness:
This rela those
subjects who had lower fitness scores tended to exhibit less G-tolerance. Less consistency was found in the relationship for those with higher levels of fitness. Of much greater significance, however, is the relationship demon strated to exist between improvement in fitness for strenuous work and
62
improvement in G-tolerance.
It was shown that improvement in fitness by
systematic training improved G-tolerance.
Fitness, although one factor
in G-tolerance, is not the only determining one.
This was indicated by
the low rank order correlation existing between fitness for strenuous work and G-tolerance, and also by the fact that some subjects classified in the good fitness group, according to the Harvard Step Test, greyed out easily. Men cannot be selected for their ability to tolerate high head ward acceleration on the basis of fitness for strenuous work alone. ever, to maintain G-tolerance at the highest possible level, pilots should be in good physical condition.
How
63 CHAPTER VI
SUMMARY AND CONCLUSIONS
SUMMARY
1.
An investigation was made of the relationship between fitness
for strenuous work and G-tolerance in twenty-three healthy male univer sity students. 2.
The study was designed to determine the relationship between
the subjects' tolerance to +5 G and their fitness for strenuous work; to study the effects of a training program on the subjects’ G-tolerance; and to investigate the influence of cessation of systematic training on G-tolerance. 3.
Fitness for strenuous work was measured by means of perfor
mance tests, namely, the Harvard Step and Army Air Force Tests and the hand dynamometer strength test. J+. Each subject was exposed to +5 G until he greyed out or for a maximum run of 30 seconds.
G-tolerance was measured in terms of earopa
city during acceleration and during an 8 minute recovery period, and pulse rates during an 8 minute recovery period after acceleration for those subjects who endured +5 G for 30 seconds; and time until grey-out for those subjects who greyed out at +5 G. 5*
The basic exercises used in the six and a half weeks’ train
ing program were weight training and running.
These items were selected
because of their high components of muscular strength and cardiovascular
6b
endurance.
Each subject participated at least three times weekly in the
training program. 6.
During the eight weeks’ period after training had ended, the
subjects were requested to participate as little as possible in organi zed physical activity. 7.
Analysis of the fitness measures revealed that most of the
subjects were in "average” physical condition when they started the training program.
The level was raised to "good" after training and
dropped somewhat eight weeks after the program stopped. 8.
A statistically significant increase in the Harvard Step Test
scores, Army Air Force Test scores and hand dynamometer strength was found after a six and a half weeks' systematic training program. 9.
G-tolerance measures showed a significant improvement after
the six and a half weeks ’ systematic training program. 10.
A slight but consistent relationship was found to exist be
tween G-tolerance (earopacity at the end of the run and pulse rates immediately after +5 G) and fitness for strenuous work as measured by the Harvard Step and Army Air Force Tests. 11.
A statistically significant drop-off in fitness as measured
by the Army Air Force Test was found eight weeks after systematic train ing had stopped.
Only a slight drop-off in fitness was observed as
measured by the Harvard Step Test and hand dynamometer strength test. 12.
A statistically significant drop-off in G-tolerance measures
(earopacity and pulse rates) for those subjects who endured +5 G for 30 seconds was noted eight weeks after the training program stopped.
Group
65 performance on the +5 G-test runs showed no change in duration of the centrifuge runs.
CONCLUSIONS Improvement in fitness for strenuous work by systematic training improved G-tolerance. Cessation of frequent and regular exercise de creased G-tolerance.
Fitness scores for strenuous work alone are not a
dependable measure of man’s ability to withstand high headward acceler ation.
Fitness, though one factor in G-tolerance, is not the only
determining factor.
In general, it can be stated that G-tolerance is
increased by improvement in fitness for strenuous work and decreased when fitness for strenuous work is diminished.
A physical training pro
gram designed to maintain a high level of physical condition should aid in obtaining highest individual levels of G-tolerance.
B I B L I O G R A P H Y
66
BIBLIOGRAPHY
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68
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70
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71
Johnson, R. E. and Lucin Brouha, "Pulse, Blood Lactate and Duration of Effort in Relation to Ability to Perform Strenuous Exercise," Rev. Canad. de Biol., 1:171, 1942. Johnson, R. E., Lucin Brouha and R. C. Darling, "A Test of Physical. Fit ness for Strenuous Exertion," Rev. Canad. de Biol., 1:491* June, 1942. Khehr, C. H., D. B. Dill and W. Newfeld* "Training and Its Effects on Man at Rest and Work," Am. J. Physiol., 136:148, 1942. Lambert, E. H., "Physiologic Studies of Man's G. Tolerance in Aircraft," (abstract), Federation Proc., 5:59* March, 1946. ______ , "The Symptoms which Occur in Man during Exposure to Positive Acceleration," Federation Proc., 4:43, 1945. ______ , "Comparison of the Physiologic Effects of Positive Acceleration on a Human Centrifuge and in an Airplane," J. Aviation Med., 20:308, October, 1949. Lambert, E. H. and E. H. Wood, "The Problem of Blackout and Unconscious ness in Aviation," M. Clin. North America, 30:833* July* 1946. ______ , "Direct Determination of Mian's Blood Pressure on the Human Cen trifuge during Positive Acceleration," (abstract), Federation Proc., 5:59* March, 1946. Larson, L. A., "Some Findings Resulting from the Army Air Force’s Phy sical. Training Program," Research Quart., 17:144, May, 1946. Lombard, C. F., "How Much Force Can the Body Withstand," Aviation Week, January 17, 1949. Lowsley, 0. S., "The Effects of Various Forms of Exercise on Systolic, Diastolic and Pulse Pressures and Pulse Rate," Am. J. Physiol., 27:446, 1911. McCurdy, J. H. and L. A. Larson, "The Validity of Circulatory-Respiratory Measures as an Index of Endurance Condition in Swimming," Research Quart., 11:3* October, 1940. Maison, G. L., C. A. Maaske and E. E. Martin, "Sensory Effects of Cen trifugal Force on Man When Seated," Federation Proc., 4:48, 1945* Marshall, G. S., "Physiological. Problems of Human Flight," Brit. M. J., 1 :226, 1940.
72
Mayerson, H. S., "Roentgenkymographic Determination of Cardiac Output in Syncope Induced by Gravity," Am. J. Physiol. , 1 3 8 :6 3 0 , 19^3Mayerson, H. S. and G. E. Burch, "The Influence of Posture on Skin and Subcutaneous Temperatures," Am. J. Physiol., 125:^7^* 1939* Metheny, E. L. et al., "Some Physiologic Responses of Women and Men to Moderate and Strenuous Exercise: A Comparative Study," Am. J. Physiol., 137:318, 19^2. Miller, W. A. and E. R. Elhel, "Effect upon Pulse Rate of Various Cadences in Step-up Test," Research Quart., 17:263* December, 19^6. Morehouse, L. E. and P. J. Rausch, "Weight Training," Scholastic Coach, 17:12, December, 19^+7J 17:13* February* 19^+8. Morehouse, L. E. and W. W. Tuttle, "A Study of the Post Exercise Heart Rate," Research Quart., 13:1* March, 19^2. Patt, H. M . , "Evaluation of Certain Tests of Physical Fitness," J.
Aviation Med., 18:169* April, 19^7Pembrey, M. J. and A. H. Todd, "The Influence of Exercise upon the Pulse and Blood Pressure," J. Physiol.* 66:37* 1908. Phillips, B. E., "Relationship between Certain Aspects of Physical Fitness and Success in Pilot Training," J. Aviation Med., 19:186, June, 19^+8. Phillips, R. B. and Charles Sheard, "Amaurosis Fugax: Effect of Centri fugal Force in Flying," Proc. Staff Meet., Mayo Clin., l4:6l2, 1939* Piorry, P. A., Arch, gen, de med., 12:527* 1826. (Quoted from Britton* S. W . , E. L. Corey and R. F. Stewart, "Effects of High Acceleratory Forces and Their Alleviation," Am. J. Physiol., 1^6:33* 19^6.) Poppen, J. R., "Recent Trends in Aviation Medicine," J. Aviation Med., 12:53, 19^1. Robinson, S. C. and M. Brucer, "Range of Normal Blood Pressure; Statisti cal. and Clinical Study of 11,383 Persons," Arch. Int. Med., 6^:409* September, 1939* Robinson, S. C., H. T. Edwards and D. B. Dill, "New Records in Human Power," Science, 85:^09* 1937Salit, E. P. and W. W. Tuttle, "The Validity of Heart Rate and Blood Pressure Determinations as Measures of Physical Fitness," Research Quart., 15:252, October, 19^.
73 Salit, E. P. and W. W. Tuttle, "Variability of Heart Rate and Blood Pressure in Selected Groups of College and High School Students," J. Lab. & Clin. Med., 29:1139* November, 19^+. Schneider, E. C., "A Cardiovascular Rating as a Measure of Physical Fitness and Efficiency," J. A. M. A., 7^:1507* May 29* 1920. _______ , "Further Observations on Cardiovascular Physical Fitness Test," Mil. Surgeon, 52:18, January, 1923. Schneider, E. C. and C. B. Crampton, "Effect of Posture on Minute Volume of the Heart," A m . J. Physiol., 110:1^, 193^« Schneider, E. C. and D. Truesdell, "A Statistical Study of the Pulse Rate and the Arterial Blood Pressure in Recumbency, Standing and Standard Exercise," Am. J. Physiol., 61:1+29, 1922. Slaughter, 0. L. and E. H. Lambert, "Plethysmographic Study of Leg Volume Changes in Man During Positive Acceleration on a Centrifuge," Federation Proc., 6:203, 19^7* Snell, C. F., "Vasomotor Factors as Applied to Selection of Applicants for Flying Training," J. Aviation Med., 7:12, March, 1936. Stansbury, E. B., "The Physical Fitness Program of the Army Air Forces," J. Health & Phys. Educ., lk:k6^y November, 19^3* Steinhaus, A. H., "Chronic Effects of Exercise," Physiol. Rev., 13:117*
1933Sturm, R. E. and E. H. Wood, "An Instantaneously Recording Cardiotachometer," Federation Proc., 5:102, 19^+6. Taylor, Craig, "Some Properties of Maximal and Submaximal Exercise with Reference to Physiologic Variations and the Measurement of Exercise Tolerance," Am. J. Physiol., 1^2:200, 19^+. "The Army Air Force's Physical Fitness Research Program," Research Quart., 15:12, March, 19^+. Turner, Abbey, H., "The Circulatory Minute Volumes of Healthy Young Women in Reclining, Sitting and Standing Positions," Am. J. Physiol.,
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E.
PUBLICATIONS OF LEARNED ORGANIZATIONS
Baldes, E. J. and C. F. Code, Studies in Aviation Medicine, Vol. 6. Mayo Aero Medical Unit, Acceleration Laboratory. Rochester, Minnesota,
1946, p. 6.
75
Ham, G. C. and E. M. Landis, "Objective Measurement of Circulatory Changes in Man During Acceleration in the Centrifuge and in the Plane,” Office of Scientific Besearch and Development, Committee on Aviation Medicine, Beport No. 67, National. Besearch Council. Washington, D. C.: Government Printing Office. Ham, G. C. and E. M. Landis, "Apparatus for the Study of Changes in the Peripheral. Circulation during Acceleration," Office of Scientific Besearch and Development, Committee on Aviation Medicine, Beport No. **8, National Besearch Council. Washington, D. C.: Government Printing Office, 1942. Second Annual Post-Graduate Course in Aviation Medicine, Proceedings, Feb. 3*7* 19^-1 • Washington, D. C.: United States Printing Press. "U. S. Army Air Forces 'Physical Fitness and Becord Card,1" Beg. No. Sec. k 9 Part 7 C. Washington, D. C.: United States Army Air Force. Wood, E. H., C. F. Code and E. J. Baldes, "Protection Against the Effects of Acceleration Afforded the Human by Assumption of Prone Postion," Studies in Aviation Medicine. Eochester, Minnesota: Mayo Aero Med ical Unit, Acceleration Laboratory, 19^3*
F.
UNPUBLISHED MATERIAL
Mayerson, H. S., "Cardiovascular Besponses to Postural Changes." Unpub lished paper read before the Staff of the School of Aviation Medicine, Bandolph Field, Texas, January 28, 19^-9•
A P P E N D I X
A
FITNESS TABLES FOR THE THREE TEST PERIODS
76
TABLE I
WEIGHT LIFTING EXERCISES SET I
Exercise
Bepetitions
Weight lst wk.
Weight 2nd. wk.
Weight 3rd wk.
Press
6-9-12
1*0#
^5#
50#
Press behind neck
6-9-12
30#
35#
to#
Curl
6-9-12
30#
35#
to#
Push back
6-9-12
10#
15#
20#
Reverse curl
6-9-12
20#
25#
30#
Supine press
6-9-12
50#
55#
60#
Rowing motion to chest
6-9-12
^0#
^5#
50#
Straight arm pull over
6-9-12
25#
30#
35#
Straight leg dead lift
6-9-12
80#
85#
90#
Rise on toes
10-15-20
to#
*15#
50#
Leg raise
10-15-20
ironboot
5#
10#
Straddle lift
10-15-21
80#
85#
90#
77
TABLE II WEIGHT LIFTING EXERCISES SET II
Exercise
Repetitions
Weight Vth wk.
Weight 5th wk.
Weight 6th wk
Press
6-9-12
55#
60#
65#
Side press
6-9-12
15#
20#
25#
One arm rebound press
6-9-12
15#
20#
25#
Lateral raise
6-9-12
5#
10#
15#
Curl
6-9-12
^5#
50#
55#
Reverse curl
6-9-12
35#
>to#
^5#
Straight leg dead lift
6-9-12
90#
95#
100#
Wrestlers bridge
6-9-12
25#
30#
35#
Zottman curl
6-9-12
10#
15#
20#
Rowing motion to abdomen
6-9-12
55#
60#
65#
Bent arm pull over
6-9-12
10#
15#
20#
Supine press
6-9-12
65#
70#
75#
High pull up
6-9-12
30#
35#
Uo#
10-15-20
80#
85#
90#
Deep knee bend
TABLE III HARVARD STEP TEST SCORES
Number of subjects
Mean^
Mean^
Mean difference
t
Level of confidence
Test Period ITest Period II
21
65.80
85.75
+19.95
8.24
1#
Test Period IITest Period III
15
88.68
82.79
- 6.07
1.81
Test Period ITest Period III
15
73.79
82.79
+ 9.00
3.21
l£
NOTE: Mean, refers to first test period listed, and meang, to second test period.
79
TABLE IV CHANGES RECORDED IN THE ARMY AIR FORCE PHYSICAL FITNESS TEST SCORES FROM TEST PERIOD I TO TEST PERIOD II
Tests
Number of subjects
Meani
Mean2
Mean difference
t
Level of confidence
3.40
1*
Sit-ups
21
62.23
67.80
+ 4.57
Pull-ups
21
60.05
60.91
+
.86
.37
250-yard indoor shuttle run
21
59-40
69.59
+10.19
5.51
1*
21
59-40
65.3^
+ 5-94
3.96
1*
Performance rating
NOTE: Period II.
Meanj refers to Test Period I and Meau.2 x to Test
80
TABLE V CHANGES HECOEDED IN THE ARMY AIR FORCE PHYSICAL FITNESS TEST SCORES FROM TEST PERIOD II TO TEST PERIOD III
Number of subjects
Mean^
Mean2
Mean difference
t
Sit-ups
15
68.06
6 k.k6
-3.60
1.66
Pull-ups
15
68.99
62.86
-6.13
2.56
5*
250-yard indoor shuttle run
15
70.80
65.27
-5.53
2.88
5*
Performance rating
15
67.9^
64.27
-3.67
3-3k
1#
Tests
NOTE: Period III.
Level of confidence
Mean^ refers to Test Period II, and Meang* to Test
81
TABLE VI CHANGES RECORDED IN THE ARMY AIR FORCE PHYSICAL FITNESS TEST SCORES FROM TEST PERIOD I TO TEST PERIOD III
Number of subjects
Mean^
Mean^,
Mean difference
Sit-ups
Ik
6 9 .7 1
6 9 .0 7
- .6 k
.3 6
Pull-ups
Ik
6 7 .3 5
6 3 .k9
-3.86
1 .5 1
250-yard indoor shuttle run
Ik
64.35
6 9 .9 2
+5-57
2.11
Ik
6 7 .8 k
68.84
+1.00
•5k
Tests
Performance rating
NOTE: Period III.
t
Level of confidence
Meazij. refers to Test Period I, and Meang, to Test
82
TABLE VII CHANGES RECORDED FOR THE HAND DYNAMOMETER STRENGTH TEST
Number Mean^ of in subjects pounds
Mean^ in pounds
Mean difference
t
Grip strength, Test Period ITest Period II
21
118.17
124.50
+6.33
2.52
Grip strength, Test Period IITest Period III
15
122.07
123.33
+1.26
.05
Grip strength, Test Period ITest Period III
Ik
115.80
123.33
+7.53
1.52
Level of confidence
5#
NOTE: Meai^ refers to first test period listed, and mean2 , to second test period.
TABLE VIII CHANGES IN THE HARVARD STEP TEST GROUPS FROM TEST PERIOD I TO TEST PERIOD II
Groups To Po Io Poor Average Good
Poor
Average
Good
Average amount of increase
1
2 4
2 6 3
M= +15.10 M= +11.12 M= +28.70
TABLE IX CHANGES IN THE HARVARD STEP TEST GROUPS FROM TEST PERIOD II. TO TEST PERIOD III
T. Po III
Average
Groups Poor T. P„ II __ Poor Average Good
Average
Good
amount of increase
1 5
1 8
M= -4.93 M= -8.90
TABLE X
Ill
CHANGES IN THE HARVARD STEP TEST GROUPS FROM TEST PERIOD I TO TEST PERIOD III
Groups Poor Average T0 P. Io_________________
cPoor ^Average Good
1 4
Good
Average amount of increase
1 4 3
M= +26.20 M= + 6.20 M= +10.00
TABLE XI CHANGES IN THE ABMY AIR FORCE PHYSICAL FITNESS TEST GBOUPS FROM TEST PERIOD I TO TEST PERIOD II
Groups To Po Io
Poor
Poor Average Very good Excellent
Average
Very good
2 7
Excellent
1 7 1
Average amount of increase M= M= M= M=
+15.50 + 8.25 + .28 + 4.00
TABLE XII CHANGES IN THE ARMY AIR FORCE PHYSICAL FITNESS TEST GROUPS FROM TEST PERIOD II TO TEST PERIOD III
T. P 0 III
Groups To Po II
Poor
Poor Average Very good Excellent
Average
Very good
2 3
1 5 1
Excellent
1
Average amount of increase M= - .67 M= -6,00 M= -2.00
TABLE XIII CHANGES IN THE ARMY AIR FORCE PHYSICAL FITNESS TEST GROUPS FROM TEST PERIOD I TO TEST PERIOD III
Ill
Groups T. Po I Poor Average Very good Excellent
Poor
Average
Very good
4 1
1 6
Excellent
1 1
Average amount of increase M= M= M== M=
+3.00 +4.60 -3.40 +I0OO
TABLE XIV CHANGES RECORDED IN PULSE RATES FOR HARVARD STEP TEST FROM TEST PERIOD I TO TEST PERIOD II
Pulse rate Resting 1 min. recovery 2 min. recovery 3 min. recovery 4 min. recovery 5 min. recovery 6 min. recovery 7 min. recovery 8 min. recovery NOTE: Period II.
Number of subjects 21 21 20 21 20 21 21 21 21
Level
Mean^ 78.22 148.05 128.20 120.38 115.80 114.43 110.00 107.33 106.95
Mean0
Mean difference - 2.48 75.74 -15.52 132.53 - 8.90 119.30 112.48 - 7.90 109.60 - 6.20 107.38 - 7.05 105.01 - 5.09 103.38 - 3.95 101.76 - 5.19
t .95 4.62 4.23 1.00 .61 1.37 .95 I .63 2.36
of confidence 1* 1*
Mean1 refers to Test Period I, and Meang* to Test
TABLE XV CHANGES RECORDED IN BLOOD PRESSURE MEASUREMENTS FOLLOWING THE HARVARD STEP TEST FROM TEST PERIOD I TO TEST PERIOD II Number of Blood Pressure subjects Systolic 21 Resting 1 min. recovery 20 4 min. recovery 21 9 min. recovery 20 Diastolic 21 Resting 1 min. recovery 20 4 min. recovery 21 9 min. recovery 20 Pulse pressure 20 Resting 1 min. recovery 19 4 min. recovery 20 9 min. recovery 20
NOTE: Period II.
Meanj_
Mean Meaiip difference
118.33 I63.8O 142.62 122.67
115.00 164.65 136.81 119.37
81.71 84.65 80.95 81.05 36.62 79.15 61.67 41.62
t
Level of confidence
- 3.33 + .85 - 5.81 - 3.30
.96 .21 1.14 .92
78.47 7^.85 74.62 77.85
-
1.20 3.63 2.51 1.34
1* 5#
36.53 89.80 62.19 41.52
- .09 +10.75 + .52 - .10
.004 3.85 .11 .003
1*
3-24 9.80 6.33 3.20
Mean.2 refers to Test Period I, and M e a T e s t
TABLE XVI CHANGES RECORDED IN PULSE RATES FOR HARVARD STEP TEST FROM TEST PERIOD II TO TEST PERIOD III
Pulse rate Resting 1 min. recovery 2 min. recovery 3 min. recovery 4 min. recovery 5 min. recovery 6 min. recovery 7 min. recovery 8 min. recovery
Number of subjects 15 15 15 15 15 15 15 15 15
Mean-j_ 76*73 132.07 119.80 111*73 107.73 107.23 105.00 104.00 100.27
Level Meang Mean t of difference confidence 81.93 + 5.20 1.24 137.80 + 5*73 .28 121.60 + 1.80 .61 113.60 + 2.87 .84 108.60 + .87 .30 105.86 - 1.27 .41 .02 104.93 - .07 .41 105.20 + 1.20 103.00 + 2.73 .74 1
H H
NOTE: Mean-]_ refers to Test Period
Meang; to Test
Period III.
TABLE XVII CHANGES RECORDED IN BLOOD PRESSURE MEASUREMENTS FOLLOWING THE HARVARD STEP TEST FROM TEST PERIOD II TO TEST PERIOD III Number Blood of Pressure subjects Systolic Resting 15 1 min. recovery 15 4 min. recovery 15 9 min. recovery 14 Diastolic Resting 15 1 min. recovery 15 4 min. recovery 15 9 min. recovery 14 Pulse pressure
Resting 1 min. recovery 4 min. recovery 9 min. recovery NOTE: Period III.
15 15 15 14
Mean-i
Meanp
Mean difference
t
116.40 163.26 138.33 120.47
113.67 161.73 128.53 113.93
-
2.73 1.53 9.80 6.54
.82 .26 1.45 1.16
78.07 73*73 75.66 77.98
7^.27 70.13 71.13 76.36
-
3.80 3.63 ^.53 1.62
1.22 .89 1.82 .42
38.33 89.53 62.67 kz.k9
39.40 91.60 57*40 37*57
+ + -
I .07 2.07 5.27 4.92
.22 .38 .96 1.10
Level of confidence
Meanj refers to Test Period II, and Meang* to Test
87 TABLE XVIII CHANGES RECORDED IN PULSE RATES FOR HARVARD STEP TEST FROM TEST PERIOD I TO TEST PERIOD III
Number Pulse rate of subjects Resting 15 1 min. recovery 15 2 min. recovery 15 3 min. recovery 15 4 min. recovery 15 5 min. recovery 15 6 min. recovery 15 7 min. recovery 15 8 min. recovery 15 NOTE: Period III.
Mean^
Mean2
8l.80 1^2.87 127.60 118.47 114.17 114.79 111.20 109.13 109.57
81.93 137.80 121.60 113.60 108.60 105.86 104.93 105.20 103.00
Mean difference + .13 - 5.07 - 6.00 - 4.87 - 5.57 - 8.93 - 6.27 - 3.93 - 6.57
Level of confidence
t .05 .95 1.99 1.25 1.98 3.46 2.18 1.42 2.05
1# %
Mean-|_ refers to Test Period I, and Meang* to Test
TABLE XIX CHANGES RECORDED IN BLOOD PRESSURE MEASUREMENTS FOLLOWING THE HARVARD STEP TEST FROM TEST PERIOD I TO TEST PERIOD III Number Blood of pressure subjects Systolic Resting 15 1 min. recovery 15 4 min. recovery 15 9 min. recovery 14 Diastolic Resting 15 1 min. recovery 15 4 min. recovery 15 9 min. recovery 14 Pulse pressure Resting 15 1 min. recovery 15 4 min. recovery 15 9 min. recovery 14 NOTE: Period III.
Level of confidence
Mean^
Mean^
120.67 164.40 148.13 122.20
113.67 161.73 128.53 113.93
- 7.00 - 2.67 -19.60 - 8.27
1.64 .50 2.62 1.56
83.74 87.53 84.26 84.29
74.27 70.13 71.13 76.36
- 9.47 -17.40 -13.13 - 7.93
3.03 3.89 4.88 2.66
1# 1# 1# %
36.93 76.87 63.87 37.91
39-40 91.60 57.40 37.57
+ 2.47 +14.73 - 6.47 - .34
.50 4.74 1.51 .10
1#
Mean difference
t
%
Meani refers to Test Period I, and Meari2 to Test
G-TOLERANCE TABLES FOR THE THREE TEST PERIODS
88 TABLE XX
AGE, HEIGHT, WEIGHT, PLYING AND CENTRIFUGE EXPERIENCE, AND PERFORMANCE ON THE POSITIVE 5G TEST RUNS FOR EACH SUBJECT
Subjects 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Age 28 32 24 23 23 23 23 2k 21 28
25 26 26 23 26 21 2k 2k 25 27 20 30 19
Height in inches 70 l/2 71 1/2 73 70 73 70 7^ 70 1/2 71 1/2 72 68 1/2 73 66 1/2 67 1/2 69 73 60 3 /k 72 70 6k 72 66 71
Weight Flying or Length in seconds of +5G test runs in centrifuge experience Test Period I Test Period II Test Period III pounds F 30 GO 7.9 151 215 F 30 30 30 30 F GO 6 30 195 182 30 C 30 30 F GO 9 30 30 155 l6l 30 NG 30 FC 30 30 30 175 170 GO k F 30 181 1/2 GO 8 30 30 FC 30 30 30 173 30 F 30 30 173 160 GO 8.2 GO 8 F NG 150 C 30 30 30 F 30 30 175 156 1/2 F GO 8.8 GO 7 30 F 209 30 30 30 30 F 125 30 162 GO 6.3 F GO 7-6 F GO 8 GO 7-4 GO 5 131 124 NG GO 5 165 30 30 30 165 30 30 178 30 30 30
NOTE: GO represents grey-out. NG indicates that centrifuge record was not good. Subjects 1 and 19 were not used in the Test Comparisons.
TABLE XXI GROUP PERFORMANCE ON POSITIVE 5G TEST RUNS
Positive 5G test runs Test periods
Number of subjects
Grey-out- Grey-out- 30 second- 30 secondgrey-out 30 second 30 second grey-out
Test period Itest period II
18
2*
3**
13
Test period IItest period III
15
1
1
12
1
Test period Itest period III
13
3
9
1
^Average grey-out time before training, 6.2 seconds; after training, 8.2 seconds.
**Average grey-out time before training, 6 seconds.
TABLE XXII CHANGES RECORDED IN EAROPACITY AND PULSE RATES FOR SUBJECTS WHO ENDURED POSITIVE 50 FOR 30 SECONDS FROM TEST PERIOD I TO TEST PERIOD II
Number of Mean-. subjects
G-tolerance Earopacity During run After run 1 min. recovery 3 min. recovery 8 min. recovery
13 13 13 13 13
- 34.84 + .11 + .99 + 9.54 + 13.77
Pulse rate Resting 1 min. recovery 3 min. recovery 8 min. recovery
13 13 13 13
77.00 102.61 78.77 77.44
NOTE: Period II.
Meanc
+ + + +
Mean difference
t
16.37 15.40 20.43 21.92 24.97
+18.47 +15.29 +19.84 +12.38 +11.20
2.31 1.62 1.47 1.09 .91
70.54 93.30 71.46 73.52
-
1.45 1.14 1.39 .96
6.46 9.31 7.31 3.92
Level of confidence
5#
Mean^ refers to Test Period I, and Meang* to Test
91
TABLE XXIII CHANGES EECOKDED IN EABOPACITY AND PULSE BATES FOB SUBJECTS WHO ENDUHED POSITIVE 5G FOB 30 SECONDS FBOM TEST PEBIOD II TO TEST PEBIOD III Number of Mean^ subjects
G-tolerance Earopacity During run After run 1 min. recovery 3 min. recovery 8 min. recovery
12 12 12 12 11
Pulse rate Besting 1 min. recovery 3 min. recovery 8 min. recovery
12 12 12 12
NOTE: Period III.
Level of confidence
Mean0 d
Mean difference
t
17.70 14.67 20.17 16.08 29.53
- 42.95 + .17 - 2.05 + 4.75 + 21.17
+25.25 -14.50 -22.22 -11.33 - 8.36
2.72 2.21 2.21 1.08 .64
% % %
71.75 103.00 73.08 73.36
87.67 118.50 84.41 80.44
+15.92 +15.50 +11.33 + 7.08
4.21 2.82 4.29 2.81
l* % 1% %
+ + + +
Mean-j_ refers to Test Period II, and Meang, to Test
92
TABLE XXTV CHANGES RECORDED IN EAROPACITY AND PULSE RATES FOR SUBJECTS WHO ENDURED POSITIVE 5G- FOR 30 SECONDS FROM TEST PERIOD I TO TEST PERIOD III Number of Mean^ subjects
G-tolerance
Meang
Mean difference
t
Earopacity During run After run 1 min. recovery 3 min. recovery 8 min. recovery
9 9 9 9 9
- 36.10 - if.56 + 5.11 + IO.78 + 21.00
- ifif.00 .67 - 7.11 + 7.H + 24.90
+ 7.90 + 3.89 -12.22 - 3.67 + 3.90
.61 .ifif if.05 .34 .24
Pulse rate Resting 1 min. recovery 3 min. recovery 8 min. recovery
9 9 9 9
79.31 107.63 81.82 75.89
87.09 122.30 85.38 80.67
+ 8.78 +14.67 + 3.56 + 4.76
1.38 2.37 .51 1.21
NOTE: Period III.
Level of confidence
%
Mean-^ refers to Test Period I, and Meang, to Test
TABLE XXV
BANK ORDER CORRELATION BETWEEN G-TOLERANCE* AND FITNESS FOR THOSE SUBJECTS WHO ENDURED POSITIVE 5G FOR 30 SECONDS
G-tolerance
Number of subjects
Harvard Step Test
Army Air Force Physical Fitness Test
Pulse rates Test Period I Test Period II Test Period III Combined Test Periods
13 17 13 k3
+ .3^ + .08 + .6l + .35
+ .55 + .10 + .17 + .29
Earopacity Test Period I Test Period II Test Period III Combined Test Periods
13 17 13 ^3
+ .31 + .09 + .63 + .kl
+ .20 -.30 + .^3 + .12
*Pulse rate one minute after a 30-second exposure to positive 5G; earopacity change during the 30-second 5G run.
A P P E N D I X
B
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