The Physiologic Effects of Isometric Work on Man

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THE PHYSIOLOGIC EFFECTS OF ISOMETRIC W W

ON MAN

Clem wj*Thompson

A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physical Education in the Graduate College of the State University of Iowa Adgust 195>0

ProQuest Number: 10907205

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uest ProQuest 10907205 Published by ProQuest LLC(2018). C opyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C o d e M icroform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346

ACKSOWLSIttMEENTS

Th© writer ■wishes to express his sincere appreciation to Professor W* W. Tuttle, Department of Physiology, College of Medicine, State University of Iowa for his direction of this thesis* The writer wishes also to take this opportunity to admit his lack of preparation in the subject of Calculus*

In the beginning the

fact that integration of equations would be necessary was not recognized*

However, when it was found to be necessary, Professor

C» D* Janney, also of the Department of Physiology, to whom I express appreciation, consented to make th© necessary calculations.

ill

TABLE OF CONTENTS

Pag® Introduction

f

..............

1

Technique for Measuring Maximum Strength and Strength Endurance Th© Relation of Maximum Strength to Strength Endurance

• *

The Effect of Isometric Work on Arterial Blood Pressure A Comparison of th© Effect of Isometric Work and Isotonic Work on Arterial Blood Pressure ........ Conclusions

, ........

• « • • • • *

2

20

21*

.

............

28 31

Appendix

33

Bibliography

1*0

iv

TABUS OF FIGURES Figure 1

Page Amplifier, grip dynamometer and recorder. Read from left toright

3

2

Grip dynamometer for men

3

Strain gauge circuit diagram for the grip dyn&raometer ........... . . . . . . .

6

Calibration carve for the grip dynamometer .............................. for men

9

Strength record for a period of one minute made by the Bsterline-Angus recorder. Read from right to l e f t .................

11

Element of the area (Z) used in calculating the relation of average strength for on® minute, to the area under th© strength curve. Read from right to left •

13

Factor for correction of the area, due to curvilinear coordinates, in th© computation of average strength forone minute . . . . . . . .

16

U

5>

6

7

. . . . . . . . . . .

V

TABLE OF TABLES Table I

II

III

IV

V

VI VII

VIII

IX

Pag© Comparison of H Calculated by Using Formula and & Determined by Subdivision of Interval T • • •

19

Calibration Table for Grip Strength Dynamometer for Men , .......................

21

delation of Maximum Strength to Strength Endurance..........................

23

Th© Effect of One Minute of Isometric Work on Arterial Blood Pressure •

2$

The Mean Effect of Isometric Work on Arterial Blood Pressure ........

26

Level of Significance of Isometric Work on Arterial Blood Pressure . » ........ . . . •

27

Comparison of Arterial Blood Pressure Changes Resulting from Isometric and IsotonicWork * •

29

Levels of Significance of the Comparison of Arterial Blood Pressure Change® Resulting from Isometric and Isotonic Work

30

Individual Data Collected from Two Hundred Cases Showing the Maximum Strength, Strength Endurance and Per Cent of Strength Endurance/ Maximum Strength « . ..................

3k

1

Introduction For the purpose of investigating the effects of isometric work on physiologic functions, it seems logical to express the iso­ metric work in term® of strength. The problems investigated included the relation of maximum strength to strength endurancej th© effect of isometric work on arterial blood pressurej and a comparison of the effects of isometric and isotonic work on arterial blood pressure. Strength has been measured by dynamometers of various types since their introduction by Brigham In 1872^.

In general, strength

has been measured either as contraction*^^ or breaking strength^*^ expressed as pounds or kilograms.

Up to the present time the

dynamometers employed provide for measuring maximum strength only. If one wishes to gain a complete picture of strength in man, it seems necessary to record not only maximum strength, but also the tension developed by a group of muscles over a period of time. In order to provide a complete picture of the tension which one is able to develop in a group of muscles and to provide a means of comparing maximum strength with strength endurance, the dynamometer described in th© following discussion was devised.

In this investiga­

tion only grip strength was studied, thus only a grip dynamometer is discussed.

However, the principles employed in the grip strength

technique are equally applicable to the measurement of the strength of almost any other muscle group.

2

Technique for Measuring Maximum Strength and Strength Endurance

General Description of the Grip Dynamometer The grip dynamometer, amplifier, and recorder as arranged for measuring grip strength are shown in Figure 1. th© dynamometer are shown in Figure 2.

The details of

Th© subject places his hand

around the grips A and B with th© little finger against the stop C, This insures that the hand will be in the same position on the dyna­ mometer when repeated tests are made.

When th© subject squeezes,

the lower ends of th© dynamometer are pulled together, thus causing a small bowing in the region above the fulcrum B, a strain gauge (Statham Ifodel G-l) E,

The bowing activates

This arrangement is used since

the force required to actuate the gauge is much smaller than the grip strength. The dynamometer is mad© of tool steel with the dimensions as shown in Figure 2, are secured by screws.

The grips A and B are made of aluminum and As described, this dynamometer provides for a

full-scale reading of 170 pounds.

Other dimensions may be used to

give either larger or smaller full-scale readings, but this is sufficiently large to measure th© grip strength of the majority of men.

Because of possible variations in the modulus of elasticity,

different dynamometers may give somewhat different full-scale readings even though they are made to the same dimensions. It is necessary to protect the strain gauge against movement beyond its normal limit, which in this instance is O.OOlU in.

This

Amplifier, grip dynamosieter and recorder*

Read from left to right.

3

k

To amplifier

'— ICM

-ICM

fO

Fig. 2*

Grip dynamometer for men.

5

limitation of movement is accomplished by inserting between th© handles of th© dynamometer a block (Figure 2) of such thickness that a mechanic1s dial indicator placed at G reads a displacement of slightly less than th© movement limit of the gauge (0.001U in.) when the handles of th© dynamometer are squeezed together.

The range of

th© instrument is then th® fore© required to close the handles of the dynamometer. If th© capacity of th© dynamometer turns out to be different from that desired, various changes can be mad© to alter it.

(a)

Assuming th© gauge contact is above the point at which the bulge is the greatest, moving the gauge contact G up will allow the use of a thinner block at F and increases the range,

(b) Increasing the cross-

section of th© arms of the dynamometer will increase the range. (c) Changing the position of th© fulcrum 0 will change th© range.

The Strain Gauge The strain gauge contains a Wheatstone bridge. resistant elements are stretched wires.

The four

When the pin, which contacts

the side of the dynamometer at (G) is depressed, two wires,

and R^

(Figure 3) are stretched and the other two wires, Rg and %

are allowed

to shorten.

The result is a slight increase in resistance in wires

and R^ and a Slight decrease in resistance in wires Rg and R^. If the bridge was balaneed to begin with, it now is unbalanced.

The

movement of the pin is so slight that th© output voltage is linearly related to th© amount of depression of the pin.

STRAIN GAUGE

o

CD

in CVJ

dynamometer=

CL

7

Any Statham 0-1 strain gauge is suitable as far as we know.

The model G1- 8-130 was selected and found satisfactory#

The

specifications for this model ares range, 8 025.5 maxi.mum input voltage, 5 | nominal resistance, 130 ohms5 and maximum output voltage, 13 m.v.

Amplifier and Recorder Obviously, if one is to record the output of the gauge, an amplifier must be employed#

The amplifier for the output voltage of

the bridge and the supply for the input voltage are mounted as small units in a single cabinet# a U-wire shielded cable*

They are connected to the strain gauge by The input is 2.5 volts, 60 cycle a.c.

supplied by a filament transformer.

The a.c. output for the strain

gauge is fed into an electronic a.c. amplifier, with a characteristic which is linear over most of its range.

The output of th© amplifier

is rectified and operates a 5 m.a* d.c. Esterline-Angus recording meter.

The meter is operated at a chart speed of three inches (h

divisions) per minute.

Th© output signal from the strain gauge is

proportional to the input voltage.

Thus it was necessary to adjust

the input voltage to th© gauge and the gain of the amplifier so that the rang© of the dynamometer corresponds to the full scale deflection of the recorder. Eynamometer Calibration Xf th® same force is applied to different points on th© grip of th© dynamometer different gauge readings will result, due to

8

the variations in th© length of the lever arm involved*

This requires

that calibration force b© applied at some uniform point on th© dynamometer grip, so a® to make calibration values reproducible*

In

order to calibrate the dynamo raster, weights of known quantity are applied to the midpoint of one handle of th© dynamometer.

This Is

accomplished by turning th© dynamometer on its side in a cradle which always holds the lower handle in the same position, thus preventing variations in the point to which the force is applied.

In order to

apply the weight to the desired point a 3/k inch pip© attached to a fulcrum extends over and rests on the upper grip.

Vertical guides

prevent lateral displacement of th© pipe. end of th© pipe supports the weights.

A vertical rod through th© the fulcrum of The distance from/the pip©

to the point of suspension of th© weights is twice the distance from the fulcrum of the pipe to the midpoint of th© handle of th© dyna­ mometer,

The weight of the lever is counterbalanced so that the force

on the gauge is twice the weight applied.

A calibration curve

(Figure h) is established by plotting the weights applied against the Esterline-Angus recorder units.

Th© calibration curve is linear

except in the lower 10—20 per cent of the rang©.

Her© it curves off,

because of th© non-linearity of the amplifier at such low signals. This, however, is unimportant since no one has been found with a strength as small as 20 per cent of the range of the dynamometer used. In this laboratory two grip dynamometers are employed, on© for women and one for men.

Th© one for women has a full scale capacity

9

180

160

140

POUNDS

120

100 80

60

40

20,

Fig, It,

20

40

60 UNITS

80

100

Calibration curve for th© grip dynamometer for men.

10

of 110 pounds, and the one for laen 170 pounds.

It is a simple

matter to change dynamometers since it is necessary only to plug the dynamometer into th© amplifier and secure it by a lock-nut. The dynamometer described not only provides for th© quantitative measure of maximum strength but also for recording th© strength for any desired period of time, thus providing a record of strength endurance.

The Strength Record A strength record is shown in Figure 5,

In this laboratory

it is the practice to record maximum strength over a period of on® minute.

Apparently one minute of maximum effort gives & representa­

tive picture of what an individual will do, since th© output falls off considerably and the subject is well exhausted by the end of this time. In general, all strength records are alike. show that maxiraum strength is quickly attained.

The records

From this point there

is a gradual but irregular falling off in strength.

Strength Endurance Before attempting to measure strength endurance it was necessary to define it.

In this laboratory, strength endurance is

defined as th© average strength for one minute expressed as pounds* If the recording meter mad© a graph in rectangular coordinates the strength endurance index would be found by measuring,

XI

-M A X IM U M

STRENGTH

134 lbs. 70 60-

3.0 2.5-

-50-

2 .0 - ^403 0_^ 20 0.5

60

Fig.

45

30 seconds

Strength record for a period of one minute mad© by the Esterline-Angus recorder. Head from right to left.

12

with a plan lineter, the area under the strength curve, and dividing by th© length of a one-minute time interval on the chart,

In

Ssterline-Angus recorders, however, the ordinate (strength) is measured over the arc of a circle instead of a straight line* thus complicating the problem*

this requires that allowance be made for

this characteristic, th© procedure for making the adjustment is as follows t In the notation of calculus,

(i)

where S' * average strength T *■ length of time interval S(t) represents the curve of strength as a function of time* In order to interpret this integral in terns of the area under the curve, let us refer to Figure 6*

The element of area is a parallelo­

gram (Z, Figure 6) whose area is dA » dt • ds sin*

(2) ■ — R cos (

)

d( p~Y ) dt

For th© present, values of ds, S(t), S, dt, T, and R will be measured in centimeters; and dA and A will be measured in square centimeters* Integrating equation (2) gives 4-

4- \

ro

in Read front right to left

in

curve.

13

CM

(O

M ,T> to

vO

fc.O

whoro f (t) represents the angular deflection of the meter (proportion­ al to strength) as a function of time,

The result of the integration

over (jj-y) can he expanded as a power series in f(t), thus if

/

t-T R

cos p

• f(t) 4* sinp

• £ ^JtX

- cos p

* l^JiX

t«0 - sin p

•

- cos p •

+ cos p

•

+ gin p

*£^£2.

+ * . .J dt

From th© definitions of f(t) and S(t), S(t) ■ R*f(t) so that

/

t»T S(t)

£cos p + sin p •

« cos p • £ ^ £ l

t*0 - sin p • ^ - 2 .

+ cos p •

+ Gin p ,

- cos p * f£ei..X + . . . ^ dt

Let the bracketed expression be represented, for convenience, by F(t) • Then — t»T A -

I

S(t) • F(t) dt

(ii)

J t=0 Because of the dimensions of the meter and the chart, f(t) can vary between th© limits of 0 and 1.030 radians.

This results in

15

a variation of F(t) from 0.859 to 0.951 with a maximum value of 0.965 at f (t) m 0.810 radians (Figure 7) * in F(t) of about 12 per cent.

This la a maximum variation

In any single record, the variation

Is less than this since no single record exploits the entire range of the recording meter. of f(t).

In Figure 7* F(t) has been plotted as a function

The chart reading is directly proportional to th© angular

displacement of the meter needle f(t), so that the abscissa can be plotted either in radians or chart units (1.080 radians * 100 chart units on charts used by authors)• Th© integral in equation (t) can b© evaluated with satis­ factory accuracy by the following approximations

The mean value of

th© chart reading is estimated by inspection of the chart.

The value

of F(t) corresponding to this reading is determined from the graph (Figure

7) • Let us call this mean value F.

for F(t) in equation (U)I

Since F is constant

dt

Substituting In equation (l) we get

Then

F is substituted

0.98

0.96

F(S) and F

0.94

0.92

0.90

0.88 0.86, 0.84

20

40

60

80

100

C H A R T UNITS

S (t) and S Fig, 7*

Factor for correction of th© area, due to curvilinear coordinates, in the computation of average strength for on© minute.

17

3-

----

(5)

tf

A is measured in square centimeters.

If P is the plani-

meter reading and p is the factor for conversion of planimeter reading to square centimeters, then A * Pp.

Since the strength endurance

index is th© average strength for one minute, T is the distance the chart travels in one minute in the recording meter. Since it is more convenient

to measure ST in wchart units”

than in centimeters, we divide the right hand member of (5) by the length of one chart unit in centimeters.

If the length of this unit

is a, then S *

Pp

chart units

aTF or S *

The quantity P aT

p iT

P "IT

chart units

must b© evaluated for each chart, chart recording

speed, and planimeter.

In the author’s case p m 16.77 T »

7.59 cm.

a m

0.120 cm.

cm./planimeter unit

Hence ^ * 18.Ul J L F

0 Kgm, of work was done.

The data collected from the subjects are shown in Table VII. An examination of Table VIII reveals the fact that in th© case of isometric work, the systolic blood pressure increased sharply during the work but returned to th© resting level within on© minute after the end of the work.

In contrast, the isotonic work

caused a sharp rise in systolic blood pressure for more than one minute.

In the case of isometric work the diastolic blood pressure

was sharply elevated during th© work but was not significantly

29

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