INT’L. J. AGING AND HUMAN DEVELOPMENT, Vol. 6(4), 1975
STRENGTH AND AGING: AN EXPLORATORY STUDY*
WENDELL P. LIEMOHN, PH.D. Developmental Training Center University of Indiana Bloomington, Indiana
ABSTRACT
Strength measurements were administered to 52 men ranging in age from 4 2 to 83 years, who were then randomly assigned within their respective age group to either the Isometric-training Group (ITG) or to the Control-exercise Group (CEG). At the conclusion of a six-week training program all initial measurements were again administered. No significant differences were found in (1) strength trainability by age group, and (2) in strength trainability by muscle group when the upperextremity-strength ratios were compared with the lower-extremitystrength ratios. When the initial and final strength scores of the ITG were subjected to a t test for correlated samples, the fiidings included: (1) the four age groups of the ITG experienced statistically significant gains in strength for six of the eight strength measurements, and (2) as age increased, strength trainability appeared to decrease.
Astrand [ 11 and Bosco [2] have listed many of the physiological involutions associated with aging. Karvonen [3] and Mateef [4] are of the opinion that exercise may delay some of these physiological changes. Strength is one parameter known to be adversely affected by age (Ruger [S] ; Ufland [6] ; Fisher and Birren 171 ;Asmussen and Heeboll-Neilson [8] ; and Shock 191). Muller [lo] states that “the gift however to increase strength by training is lost in the course of aging.” Mitolo [ 111 , using electromyographic techniques, found that the biceps brachii of two male subjects in their seventies “displayed
*
This paper is based upon part of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physical Education for Men in the Graduate College of The University of Iowa, August, 1970. Dissertation Chairmen: Associate Professor Gene M. Asprey, Department of Physical Education for Men; and Associate Professor H. Lee Jacobs, Institute of Gerontology. 347 @ 1976. Baywood Publishing Co.
doi: 10.2190/PG7M-4Y15-Q5A5-3KL6 http://baywood.com
348
I
WENDELL P. LIEMOHN
ability in man differs significantly from decade to decade, and that this variation is influenced by variations in the output of testosterone. Allen [14] and Rodriguez, DePalma and Daykin [ 151 found that men in their seventies and eighties experienced gains in strength from following an isometric training program. The latter investigators found their six-week training program to be especially appropriate for elderly, languid patients. The ability to experience strength gains from following a strength training program is believed to be affected by histological changes with age as well as the previously cited hormonal factor. Gardner [I61 found a reduction in the counts of ventral root fibers with an increase with age; this suggests a degeneration of the anterior horn cells, which could cause a decrease in the number of motor units that function. Drahota and Gutmann [17] and Rubenstein [18] are of the opinion that a decline in the trophic function of the nervous system may be responsible for the characteristics of aging in skeletal muscle. Asmussen and Heeboll-Neilson [8] , after noting greater decrements from aging in trunk and lower-limb strength than decrements in arm and finger strength, credit this fmding to a disproportionate decreased usage of the lower limbs as the individual ages. This would perhaps explain the findings of Simonson, Kerns, and Enzer [ 191. The latter investigators found that testosterone produced increases in back strength but did not produce significant increases in upper-limb strength. Kraut, Muller, and Muller-Wecker [20] found that muscles of the lower extremity usually benefited more from an isometric training program than muscles of the upper extremity. The purposes of this study included:' (1) comparing the ability of members of different age groups to gain strength from participating in an isometric-training program three times a week for a period of six weeks, (2) determining if in the elderly the proportional gains in strength from following an isometric-training program are greater in the lower extremity than in the upper extremity. The hypotheses chosen were: (1) strength trainability does not differ between age groups, (2) there is n o difference between the strength trainability of the upper and lower limbs.
Methods The participants were male residents of the Iowa Soldiers' Home, Marshalltown, Iowa. One hundred and ten men, ranging in age from 41 to 98 years, originally volunteered to take part in the experiment. From the group of volunteers, 88 were selected and expected to be involved and they were Parameters of measurement made also included a circulatory test and a personality test.
STRENGTH AND AGING / 349
advised by letter of the time that they were to report for initial measurements. Twenty-seven men reported and completed the testing (including a retest on a second day for the future determination of reliability coefficients) during the initial test week. The investigator, believing this group to be representative of those to be tested during the second and third weeks of testing, (1) chose the following age groups: 41-50, 51-60, 61-70, 71-80, and 81-90; and (2) randomly assigned these 27 subjects to one of two training programs. At the conclusion of the three weeks of testing, only 49 of the 88 volunteers completed the testing; five men would and/or could not complete the testing after reporting for measurement, and 34 refused to report. A cable tensiometer was used to obtain the measurements for four strength tests administered to each subject. Using the measurement procedures outlined by Clarke [21, 221, the following strength tests were administered bilaterally in the order listed: (1) knee extension, (2) knee flexion, (3) forearm flexion, and (4) forearm extension. The subjects were given three trials for each test, with a one-minute interval between trials. Because of the trend noted in the strength scores obtained during the pilot project, the mean of the second and third trials was used as the criterion score for each of the four strength tests. The volunteers assigned to the isometric-training group (ITG) were scheduled for a 15-minute period in which to exercise, three days a week, for a period of six weeks. The training program was an exact replication of the strength tests in terms of the positions used for muscle contraction, but the contractions were held for a duration of five seconds. The investigator worked individually with each subject during the exercise sessions. Those assigned to the control-exercise group (CEG) were scheduled for a 15-minute period in which to exercise, three days a week, for a period of six weeks. The exercise program consisted primarily of exercises taken from The Fitness Challenge in the Later Years-An Exercise Program for Older Americans. The exercises stressed balance, flexibility, and coordination; overload was avoided. The investigator worked individually with each man during the exercise sessions.
Results At the conclusion of the training programs, 23 members of the ITG and 16 members of the CEG were retested. The final measurements were made at the same hour of the day as the initial measurements. Six participants in the ITG and four in the CEG did not complete the training program for reasons including furlough, loss of interest, and health. A simple-randomized design, as outlined by Lindquist [23] was used to: an ability to get trained.” Hettinger [12, 131 believes that strength train-
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(1) compare the strength trainability among four different age groups,' and (2) compare the strength gains between the training programs followed. A Type I mixed design, as outlined by Lindquist [23], was used to compare the strength trainability of the upper extremities with the lower extremities in relation to age. Two men in the ITG and five in the CEG were not measured for knee-joint-flexion strength, hence comparisons for knee-flexion strength were based on 8 smaller N than for the other strength tests. A comparison of the means in strength trainability for the four age groups yielded no significant differences for any of the eight strength measurements obtained from the men in the ITG. When the same comparison was made for the men in the CEG,a significant difference was found. The three subjects in the 41-50 age group had statistically significant greater right-kneeextension strength gains than did the men in the other age groups of the CEG;however, their initial means were also lower than the initial means of the men in the other age groups of the CEG (Table 1). Table 1. Initial and Final Strength Means, t Test Comparisons, F Test Comparisons Between Age Groups of Respective Training Groups ( F l ) , and F Test Comparisons Between Training Groups (F2) Control Exercise Group ITG-CEG
Isometric Training Group InitiarFinal
N
t
F1
Age InitialGroups Final
N
t
F1
Right-knee Extension
41-50 51-60 61-70 71-80 41-80
76-84 5 66-85 6 49-62 6 5 49-69 60-75 22
0.765 2.159 1.298 1.834 1.986a
0.546
41-50 51-60 61-70 71-80 41-80
46-63 3 71-82 4 100-95 4 49-51 4 68-73 15
3.209 1.591 0.984 2.386 1.818
0.536
41-50 51-60 61-70 71-80 41-80
4864 3 67-75 4 99-98 4 57-58 4 69-74 15
3.1 12 1.013 0.208 0.31 0 1.804
2.144
41-50 51-60 61-70 71-80 41-80
40-53 2 48-52 3 59-64 3 35-33 2 47-52 10
4.853 1.369 0.873 0.481 1.972
1.081 1.400 2.927 2.197 4.617a-b
Left-knee Extension
41-50 51-60 61-70 71-80 41-80
5 7576 68-85 6 51-62 6 52-64 5 61-72 22
0.141 1.715 1.324 1.418 2.300a
1.176 1.042 2.644 1.339 2.627
Right-knee Flexion
41-50 51-60 61-70 71-80 41-80
57-62 4 6 42-54 37-42 5 5 3040 41-49 20
1.738 3.080a 0.826 2.526 3.940a
11.097a'c 2.597 0.026 2.198 2.771
AU data relative to the two men in the 81-90 age group were not included in the statistical analysis. The average strength gains of the 81-year-old in the ITG for the eight tests was 57 per cent; the average strength gains of the 8 2 year old in the CEG for the eight tests was 21 per cent.
STRENGTH A N D AGING
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Table 1. (cont.) Isometric Training Group lnitialFinal
N
Left-knee Flexion 4 41-50 56-58 6 51-60 46-54 61-70 30-36 5 71-80 33-38 5 41-80 41-46 20 Right-elbow Extension 5 41-50 37-50 51-60 35-42 6 61-70 29-33 6 5 71-80 29-39 41-80 33-41 22 Left-elbow Extension 41-50 41-48 5 51-60 39-43 6 61-70 28-30 6 71-80 30-42 5 41-80 3440 22 Right-elbow Flexion 41-50 78-84 5 51-60 71-74 6 61-70 50-56 6 71-80 41-62 5 41-80 60-69 22 Left-elbow Flexion 41-50 75-89 5 51-60 69-76 6 61-70 48-56 6 71-80 42-65 5 41-80 59-71 22
t
0.285 1.724 1.478 0.997 2.468a 3.53Za 2.906a 1.836 1.421 3.990a 3.745a 1.159 4.025 2.2ooa 2.921 1.467 0.678 2.273 1.854 2.730a 3.014a 1.433 1.488 1.445, 3.881
Control Exercise Group Age InitialGroups Final
N
t
0.437
41-50 51-60 61-70 71-80 41-80
43-49 50-51 6463 29-28 49-49
2 3 3 2 10
19.080a 0.082 0.316 3.544 0.472
0.720
41-50 5 1-60 61-70 71-80 41-80
41-45 39-49 48-55 30-31 40-45
3 4 4 4 15
16.787a 2.671 2.177 0.133 3.1 77a
1.066
41-50 51-60 61-70 71-80 41-80
42-46 42-47 46-52 32-33 41-45
3 4 4 4 15
3.045 4.472a 0.648 0.523 2.064
1.563
41-50 51-60 61-70 71-80 41-80
73-75 72-78 86-86 42-50 68-72
3 4 4 4 15
0.321 1.623 0.022 2.836 1.714
1.629
41-50 5 1-60 61-70 7 1-80 41-80
62-72 3 70-81 4 86-90 4 5054 4 68-74 15
1.223 0.838 1.935 0.420 2.664
F1
~
~
~
~
F1
ITG-CEG
F2 0.667 1.382 3.827 0.677
1.510 3.652 0.217 0.006 0.949 1.071 1.859 0.029
0.069 0.877 0.1 18 0.066 0.000 1.581 0.926 0.828 0.014 0.015 2.544 1.361 0.305
~~~~~~~
a Significant at the .05 level or greater.
Strength gains of the 41-50 age group of the CEG significantly greater than the strength gains of the other age groups of the CEG for Right-knee Extension. Strength gains of the 41-50 age group of the CEG significantly greater than the strength gains of the 41-50age group of the ITG for Right-knee Flexion.
When, for each age group, a comparison was made between the means of the ITG and the CEG for strength trainability, a significant difference was obtained for only one of the eight strength measurements. For right-knee-flexion strength, the men in the 41-50 age group of the CEG (N = 2) had significantly greater strength gains at the .05level than did the subjects in the ITG ( N = 4). The results of this analysis are presented in Table 1. When the means of the upper-extremity-strength ratios (final strength score divided by initial strength score) were compared with the means of the lowerextremity-strength ratios for the men in the ITG, no significant differences in
352 / WENDELL P. LIEMOHN
strength trainability by muscle group were found (Table 2). When the same comparison was made for the men in the CEG, a significant difference was found. The strength ratios for left-elbow-flexion strength and left-elbowextension strength were significantly greater than the ratios for left-kneeflexion strength (Table 2). However, 50 per cent of the CEG participants scored lower on the final left-knee-flexion test than they did on the initial test. Table 2. Strength Ratio Comparisonsa 41-50
Test/Group ~~
Nb
Nb
51-60
~
~~
61-70
71-80
Nb
~
Nb
41-80
~~~
Nb
~~
Knee Extension Right: I T G CEG Left: I T G CEG Knee Flexion Right: I T G CEG Left: I T G CEG Elbow Extension Right: I T G CEG Left: I T G CEG Elbow Flexion Right: I T G CEG Left: I T G CEG
1.070 1.409 0.997 1.365
4 3 4 3
1.435 1.127 1.338 1.096
6 4 6 4
1.300 0.946 1.241 0.988
5 4 4
1.527 1.056 1.435 1.048
5 4 5 4
1.351 1.116 1.270 1.108
20 10 20 10
1.078 1.315 1.039 1.150
4 2 4
2
1.383 1.064 1.230 1.011
6 3 6 3
1.046 1.069 1.254 0.978
5 3 5 3
1.362 0.968 1.237 0.953
5 2 5 2
1.232 1.151 1.200 1.017'
20 10 20 10
1.285 1.116 1.131 1.065
4 3 4 3
1.201 1.249 1.156 1.129
6 4 6 4
1.057 1.129 1.075 1.138
5 4 5 4
1.592 1.037 1.663 1.078
5 4 5 4
1.279 1.134 1.257 1.105'
20 10 20 10
1.050 1.114 1.139 1.195
4 3 4 3
1.098 1.100 1.175 1.156
6 4 6 4
1.090 0.999 1.192 1.044
5
1.961 1.191 1.882 1.124
5 4 5 4
1.302 1.150 1.349 1.191
20
5
4 5 4
10 20
10
a The ratio is the final mean divided by the initial mean. Only those individuals that were able to take all of the strength tests are included in this comparison. The strength gains for Left-elbow Extension and Flexion were significantly greater than the strength gains for Left-knee Flexion in the CTG.
'
To further elucidate the value of isometrics for the elderly, examination of individual gains and losses was made. The initial and final strength scores (in pounds) were also subjected to a Fisher f test for correlated samples t o determine if the strength gains or losses were significant. These results are summarized in Table 1.
Discussion Based on the analysis of the data, the hypothesis that strength trainability does not differ among the age groups remains tenable. The fact that agerelated trends in strength trainability were not found between the various
STRENGTH AND AGING / 353
age groups is in disagreement with the findings of Hettinger [13]. However, when initial and final strength scores were, for each age group, subjected to a f test for correlated samples, the following possible age-related trends for strength trainability were noted:
1. the 41-50 age group in the ITG experienced statistically significant gains in strength for three of the eight tests, 2. the 51-60 age group in the ITG experienced statistically significant gains in strength for two of the eight tests, 3. the 61-70 age group in the ITG experienced statistically significant gains in strength for one of the eight tests, and 4. the 71-80 age group in the ITG did not experience statistically significant gains in strength for any of the eight tests. Variance analysis revealed that the two men in the 41-50 age group in the CEG had greater gains (significant at the .05 level) in strength for right-kneeflexion than did the four men in the ITG for the same age group. This was not expected; however, two of the men in this age group in the ITG scored lower on the final measurements than they did on the initial measurements for more than 50 per cent of the strength tests. The fact that on occasion men in the CEG appeared to gain in strength from the participation in a training program which avoided overload might be explained by:
1. the possibility that some overload occurred; 2. the apprehensiveness during the initial testings which resulted in submaximal effort for criterion as well as reliability scores; and 3. the usage, not necessarily overload, of relatively unused muscles during the training program gave the men in the CEG the realization that their muscles were more functional than they had realized-possibly , muscle re-education following disuse atrophy. It seems plausible that participation in the CEG, although not providing specificity of training and overload, resulted in muscle reeducation that may have enabled some of the men to exert a greater effort on the final measurements. Reasons ( 2 ) and (3) above cannot be ruled out as reasons for some of the gains in strength experienced by the men in the ITG. In one instance in particular, a 71-year-old in the ITG experienced exceptional gains in strength; even though he stated that he felt stronger, it is evident that a great percentage of his strength gains must be attributed to the removal of gross inhibitions or muscle re-education rather than the neural learning usually associated with the acquisition of strength. Because only initial and final measurements were made, the relative weights of the “re-education factor” and the “true strength-gain factor” cannot be discerned.
354 / W E N D E L L P. LIEMOHN
Individual variability in strength trainability within an age group was noted frequently. Factors that might be responsible for this include:
1. 2. 3. 4.
training stimulus too small to elicit a training effect in some men, some men possessing little or n o strength trainability, failure of some men to cooperate, and variability in post-contraction periods.
The findings of this study would tend to support the idea that strength trainability in some elderly men might be more of an individual phenomenon than an age-related phenomenon. The relationship between strength trainability and chronological age cannot be discounted; however, i t is likely that physiological age may be a more important factor than chronological age. In young men strength gains are, at least in part, dependent upon (1) neural learning-this may be adversely affected by neuromuscular degeneration, and (2) an increase in muscle protein-this may be adversely affected by a decrease in hormonal output. In the elderly and debilitated perhaps a third factor, muscle re-education, might be added-a more gross neural learning than that usually associated with the acquisition of strength from following a strengthtraining program. In Table 3 is presented a comparison between the mean scores that men in the ITG and the CEG received on the final strength tests and also the mean scores that Clarke [22] reported for the same strength tests.3 Of the four tests compared, Clarke and the investigator found that subjects tended to register their greatest strength on the knee-extension test. Clarke found that the second strongest muscle group of the four compared was the knee flexors; whereas the four age groups in this study had elbow flexion as their second highest strength score, with knee flexion ranking third. When the mean scores reported by Clarke for elbow-flexion strength are compared with the same scores for the 41-50 age group of this study, little difference is noted in actual scores or in percentage scores. However, when the other strength scores of this age group are compared with Clarke’s means, considerable difference is noted, particularly in the scores for knee extension and knee flexion. On the basis of these comparisons, it would appear that agerelated strength decrements are the greatest in muscles which extend and flex the knee, and least in the muscles that flex the elbow. This is in agreement with the findings of Asmussen and Heeboll-Nielson [ S ] . The latter investigators crcdit this to the belief that there is a disproportionate decreased usage of the lower limbs as the individual ages. Based on the analysis of the data, the hypothesis that strength trainability does not differ between the upper and lower limbs remains tenable. The failure to observe statistically significant differences in proportional gains Clarke’s participants were college age men.
STRENGTH AND AGING / 355
Table 3. Final Strength Meansa of ITG and CEG Compared with Means Reported by Clarke (1 966)in College Age Men for Four Strength Tests Test/Group
Knee Extension Clarke IT G CEG Mean (ITG, CEG) Per centb Knee Flexion Clarke IT G CEG Mean (ITG, CEG) Per cent Elbow Extension Clarke ITG CEG Mean (ITG, CEG) Per cent El bow Flexion Clarke IT G CEG Mean (ITG, CEG) Per cent
Clarke
47-50
51-60
61-70
71-80
80 64 74 50
85 78 82 56
62 97 76 51
67 55 61 41
60 50 57 57
54 51 53 54
39 63 48 49
39 30 36 37
49 46 48 70
43 48 45 66
31 53 40 59
41 32 37 54
87 84 86 93
75 80 77 88
56 88 69 78
63 52 58 66
148
99
68
88
'
a All means are in pounds.
Per cent that ITG-CEG mean is of Clarke's mean.
between the different muscle groups from following an isometric-training program in context is not in agreement with the findings of Kraut, Muller, and Muller-Wecker [ 2 0 ] .It is possible that a disproportionate degree of neuromuscular deterioration in the lower extremities as a concomitant effect of advanced age and/or disuse precluded the finding of statistically significant differences (1) between muscle groups in general, and (2) in proportional strength gains in favor of the lower extremities over the upper extremities. If the neuromuscular deterioration is more of a concomitant effect of aging rather than disuse, differences in atrophy and/or trainability in the flexors and extensors of the knee might be explained by the fact that the extensors receive their innervation from the femoral plexus, whereas the flexors receive their innervation from the sacral plexus.
356 I WENDELL P. LIEMOHN
Summary Strength measurements were administered to 52 men ranging in age from 42 to 83 years. The men were then randomly assigned within their respective age groups to either the Isometric-training Group (ITG) or to the Control-exercise Group (CEG). At the conclusion of a six-week training program, the strength measurements were again administered. When the data relative to the strength scores of the ITG were subjected to analysis of variance comparisons, n o significant differences were found in (1) strength trainability by age groups, and ( 2 ) in strength trainability by muscle group when the upper-extremity-strength ratios were compared with the lowerextremity-strength ratios. When the initial and final strength scores of the ITG were subjected to a r test for correlated samples, it was noted that the ITG experienced statistically significant gains in strength for all of the eight strength measurements. REFERENCES
1. Per-Olof Astrand, “Human Physical Fitness with Special Reference to Sex and Age,” Physiological Reviews, 36, pp. 307-335, 1956. 2. J. S . Bosco, “Can Adult Physical Fitness Be Improved?” Journal o f the Association f o r Physical and Mental Rehabilitation, pp. 115-1 16, 1962. 3. M. J. Karvonen, “Exercise-Physiological Aging,” Health and Fitness in the Modern World, Athletic Institute, Chicago, 196 1. 4. D. Mateef, “Materials of the All-Union and Let Transcaucasus Conference Devoted to Problems of Clinical Gerontology and Geriatrics,” (trans. and ed. by Office of Technical Services, U.S. Department of Commerce), Joint Publication Research Services, Washington, D.C., pp. 1-13, 1966. 5. H. A. Ruger, “On the Growth Curves of Certain Characters in Man (Males),” Annals o f Eugenics, 2, pp. 76-1 10, 1927. 6. J. M. Ufland, “Einfluss des Lebensalters, Geschlechts, der Konstitution und des Berufs auf die Kraft verschiederner Muskelgruppen,” Arbeitsphysiologie, 7, pp. 251-258, 1933. 7. M. B. Fisher and J. E. Birren, “Age and Strength,” Journal o f Applied Psychology, 31, pp. 490-97, 1947. 8 . E. Asmussen and K. Heeboll-Nielson, “Isometric Muscle Strength in ReIation to Age in Men and Women,” Ergonomics, pp. 167-169, 1962. 9. N. W. Shock, “The Physiology of Aging,” Scientific American, 206, pp. 100-1 10, 1962. 10. E. A. Muller, “The Regulation of Muscular Strength,” Journal of the Association f o r Physical and Mental Rehabilitation, 11, pp. 41-47, 1957. 11. M. Mitolo, “Physical Training Capacity of Aged Skeletal Muscle,” Acta Physiologica Academiae Scientiarum Hungaricae, 31, pp. 199-208, 1967. 12. T. Hettinger, “Die Trainierbarkeit menschlicher Muskeln in Abhangigkeit vom Alter und Geschlecht,” Internationale Zeitschrift Fur Angewandt Physiologie, 17, pp. 371-377, 1958.
STRENGTH A N D AGING / 357
13. T. Hettinger, Physiology of Strength, Charles C. Thomas, Springield, Illinois, 1961. 14. J. Allen, “The Use of Isometric Exercises in a Geriatric Treatment Program,” Geriatrics, 20, pp. 346-347, 1965. 15. M. J. Rodriguez, 5 . J. DePalma and H. P. Daykin, “Isometric Exercise in General Practice,” The Journal of the Association for Physical and Mental Rehabilitation, 19, pp. 197-200, 1965. 16. E. D. Gardner, “Decrease in Human Neurones with Age,” Anatomical Record, 77, pp. 529-536, 1940. 17. Z. Drahota and E. Gutmann, “The Influence of Age on the Course of Reinnervation of Muscle,” Gerontologia, 5, pp. 88-109, 1961. 18. L. J. Rubinstein, “Aging Changes in Muscle,” in G. H. Bourne (ed.), The Structure and Function of Muscle, III Pharmacology and Disease, Academic Press, New York, 1960. 19. E. Simonson, W. M. Kearns, and N. Enzer, “Effect of Methyl Testosterone Treatment on Muscular Performance and the Central Nervous System of Older Men,” Journal of Clinical Endocrinology, 4 , pp. 528-534, 1944. 20. H. Kraut, E. A. Muller and H. Muller-Wecker, “Die Abhangigkeit des Muskeltrainings und des Eiweinssansatzes von der Eiweissaufnahme und vom Eiweissbestand des Korpers,” Biochemische Zeitschrift, 324, pp. 280294, 1953. 21. H. H. Clarke and D. H. Clarke, Developmental and Adapted Physical Education, Prentice-Hall, Inc., Englewood Cliffs, N.J., 1963. 22. H. H. Clarke, Muscular Strength and Endurance in Man, Prentice-Hall, Inc., Englewood Cliffs, N.J., 1966. 23. E. F. Lindquist, Design and Analysis o f Experiments in Psychology and Education, Houghton Mifflin Company, Boston, 1953.
Address reprint request to:
W.P. Liemohn, Ph.D. Developmental Training Center University of Indiana 2858 East 10th Street Bloomhgton, Indiana 47401
STRENGTH AND AGING: AN EXPLORATORY STUDY*
WENDELL P. LIEMOHN, PH.D. Developmental Training Center University of Indiana Bloomington, Indiana
ABSTRACT
Strength measurements were administered to 52 men ranging in age from 4 2 to 83 years, who were then randomly assigned within their respective age group to either the Isometric-training Group (ITG) or to the Control-exercise Group (CEG). At the conclusion of a six-week training program all initial measurements were again administered. No significant differences were found in (1) strength trainability by age group, and (2) in strength trainability by muscle group when the upperextremity-strength ratios were compared with the lower-extremitystrength ratios. When the initial and final strength scores of the ITG were subjected to a t test for correlated samples, the fiidings included: (1) the four age groups of the ITG experienced statistically significant gains in strength for six of the eight strength measurements, and (2) as age increased, strength trainability appeared to decrease.
Astrand [ 11 and Bosco [2] have listed many of the physiological involutions associated with aging. Karvonen [3] and Mateef [4] are of the opinion that exercise may delay some of these physiological changes. Strength is one parameter known to be adversely affected by age (Ruger [S] ; Ufland [6] ; Fisher and Birren 171 ;Asmussen and Heeboll-Neilson [8] ; and Shock 191). Muller [lo] states that “the gift however to increase strength by training is lost in the course of aging.” Mitolo [ 111 , using electromyographic techniques, found that the biceps brachii of two male subjects in their seventies “displayed
*
This paper is based upon part of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physical Education for Men in the Graduate College of The University of Iowa, August, 1970. Dissertation Chairmen: Associate Professor Gene M. Asprey, Department of Physical Education for Men; and Associate Professor H. Lee Jacobs, Institute of Gerontology. 347 @ 1976. Baywood Publishing Co.
doi: 10.2190/PG7M-4Y15-Q5A5-3KL6 http://baywood.com
348
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WENDELL P. LIEMOHN
ability in man differs significantly from decade to decade, and that this variation is influenced by variations in the output of testosterone. Allen [14] and Rodriguez, DePalma and Daykin [ 151 found that men in their seventies and eighties experienced gains in strength from following an isometric training program. The latter investigators found their six-week training program to be especially appropriate for elderly, languid patients. The ability to experience strength gains from following a strength training program is believed to be affected by histological changes with age as well as the previously cited hormonal factor. Gardner [I61 found a reduction in the counts of ventral root fibers with an increase with age; this suggests a degeneration of the anterior horn cells, which could cause a decrease in the number of motor units that function. Drahota and Gutmann [17] and Rubenstein [18] are of the opinion that a decline in the trophic function of the nervous system may be responsible for the characteristics of aging in skeletal muscle. Asmussen and Heeboll-Neilson [8] , after noting greater decrements from aging in trunk and lower-limb strength than decrements in arm and finger strength, credit this fmding to a disproportionate decreased usage of the lower limbs as the individual ages. This would perhaps explain the findings of Simonson, Kerns, and Enzer [ 191. The latter investigators found that testosterone produced increases in back strength but did not produce significant increases in upper-limb strength. Kraut, Muller, and Muller-Wecker [20] found that muscles of the lower extremity usually benefited more from an isometric training program than muscles of the upper extremity. The purposes of this study included:' (1) comparing the ability of members of different age groups to gain strength from participating in an isometric-training program three times a week for a period of six weeks, (2) determining if in the elderly the proportional gains in strength from following an isometric-training program are greater in the lower extremity than in the upper extremity. The hypotheses chosen were: (1) strength trainability does not differ between age groups, (2) there is n o difference between the strength trainability of the upper and lower limbs.
Methods The participants were male residents of the Iowa Soldiers' Home, Marshalltown, Iowa. One hundred and ten men, ranging in age from 41 to 98 years, originally volunteered to take part in the experiment. From the group of volunteers, 88 were selected and expected to be involved and they were Parameters of measurement made also included a circulatory test and a personality test.
STRENGTH AND AGING / 349
advised by letter of the time that they were to report for initial measurements. Twenty-seven men reported and completed the testing (including a retest on a second day for the future determination of reliability coefficients) during the initial test week. The investigator, believing this group to be representative of those to be tested during the second and third weeks of testing, (1) chose the following age groups: 41-50, 51-60, 61-70, 71-80, and 81-90; and (2) randomly assigned these 27 subjects to one of two training programs. At the conclusion of the three weeks of testing, only 49 of the 88 volunteers completed the testing; five men would and/or could not complete the testing after reporting for measurement, and 34 refused to report. A cable tensiometer was used to obtain the measurements for four strength tests administered to each subject. Using the measurement procedures outlined by Clarke [21, 221, the following strength tests were administered bilaterally in the order listed: (1) knee extension, (2) knee flexion, (3) forearm flexion, and (4) forearm extension. The subjects were given three trials for each test, with a one-minute interval between trials. Because of the trend noted in the strength scores obtained during the pilot project, the mean of the second and third trials was used as the criterion score for each of the four strength tests. The volunteers assigned to the isometric-training group (ITG) were scheduled for a 15-minute period in which to exercise, three days a week, for a period of six weeks. The training program was an exact replication of the strength tests in terms of the positions used for muscle contraction, but the contractions were held for a duration of five seconds. The investigator worked individually with each subject during the exercise sessions. Those assigned to the control-exercise group (CEG) were scheduled for a 15-minute period in which to exercise, three days a week, for a period of six weeks. The exercise program consisted primarily of exercises taken from The Fitness Challenge in the Later Years-An Exercise Program for Older Americans. The exercises stressed balance, flexibility, and coordination; overload was avoided. The investigator worked individually with each man during the exercise sessions.
Results At the conclusion of the training programs, 23 members of the ITG and 16 members of the CEG were retested. The final measurements were made at the same hour of the day as the initial measurements. Six participants in the ITG and four in the CEG did not complete the training program for reasons including furlough, loss of interest, and health. A simple-randomized design, as outlined by Lindquist [23] was used to: an ability to get trained.” Hettinger [12, 131 believes that strength train-
350
I
WENDELL P. LIEMOHN
(1) compare the strength trainability among four different age groups,' and (2) compare the strength gains between the training programs followed. A Type I mixed design, as outlined by Lindquist [23], was used to compare the strength trainability of the upper extremities with the lower extremities in relation to age. Two men in the ITG and five in the CEG were not measured for knee-joint-flexion strength, hence comparisons for knee-flexion strength were based on 8 smaller N than for the other strength tests. A comparison of the means in strength trainability for the four age groups yielded no significant differences for any of the eight strength measurements obtained from the men in the ITG. When the same comparison was made for the men in the CEG,a significant difference was found. The three subjects in the 41-50 age group had statistically significant greater right-kneeextension strength gains than did the men in the other age groups of the CEG;however, their initial means were also lower than the initial means of the men in the other age groups of the CEG (Table 1). Table 1. Initial and Final Strength Means, t Test Comparisons, F Test Comparisons Between Age Groups of Respective Training Groups ( F l ) , and F Test Comparisons Between Training Groups (F2) Control Exercise Group ITG-CEG
Isometric Training Group InitiarFinal
N
t
F1
Age InitialGroups Final
N
t
F1
Right-knee Extension
41-50 51-60 61-70 71-80 41-80
76-84 5 66-85 6 49-62 6 5 49-69 60-75 22
0.765 2.159 1.298 1.834 1.986a
0.546
41-50 51-60 61-70 71-80 41-80
46-63 3 71-82 4 100-95 4 49-51 4 68-73 15
3.209 1.591 0.984 2.386 1.818
0.536
41-50 51-60 61-70 71-80 41-80
4864 3 67-75 4 99-98 4 57-58 4 69-74 15
3.1 12 1.013 0.208 0.31 0 1.804
2.144
41-50 51-60 61-70 71-80 41-80
40-53 2 48-52 3 59-64 3 35-33 2 47-52 10
4.853 1.369 0.873 0.481 1.972
1.081 1.400 2.927 2.197 4.617a-b
Left-knee Extension
41-50 51-60 61-70 71-80 41-80
5 7576 68-85 6 51-62 6 52-64 5 61-72 22
0.141 1.715 1.324 1.418 2.300a
1.176 1.042 2.644 1.339 2.627
Right-knee Flexion
41-50 51-60 61-70 71-80 41-80
57-62 4 6 42-54 37-42 5 5 3040 41-49 20
1.738 3.080a 0.826 2.526 3.940a
11.097a'c 2.597 0.026 2.198 2.771
AU data relative to the two men in the 81-90 age group were not included in the statistical analysis. The average strength gains of the 81-year-old in the ITG for the eight tests was 57 per cent; the average strength gains of the 8 2 year old in the CEG for the eight tests was 21 per cent.
STRENGTH A N D AGING
I 351
Table 1. (cont.) Isometric Training Group lnitialFinal
N
Left-knee Flexion 4 41-50 56-58 6 51-60 46-54 61-70 30-36 5 71-80 33-38 5 41-80 41-46 20 Right-elbow Extension 5 41-50 37-50 51-60 35-42 6 61-70 29-33 6 5 71-80 29-39 41-80 33-41 22 Left-elbow Extension 41-50 41-48 5 51-60 39-43 6 61-70 28-30 6 71-80 30-42 5 41-80 3440 22 Right-elbow Flexion 41-50 78-84 5 51-60 71-74 6 61-70 50-56 6 71-80 41-62 5 41-80 60-69 22 Left-elbow Flexion 41-50 75-89 5 51-60 69-76 6 61-70 48-56 6 71-80 42-65 5 41-80 59-71 22
t
0.285 1.724 1.478 0.997 2.468a 3.53Za 2.906a 1.836 1.421 3.990a 3.745a 1.159 4.025 2.2ooa 2.921 1.467 0.678 2.273 1.854 2.730a 3.014a 1.433 1.488 1.445, 3.881
Control Exercise Group Age InitialGroups Final
N
t
0.437
41-50 51-60 61-70 71-80 41-80
43-49 50-51 6463 29-28 49-49
2 3 3 2 10
19.080a 0.082 0.316 3.544 0.472
0.720
41-50 5 1-60 61-70 71-80 41-80
41-45 39-49 48-55 30-31 40-45
3 4 4 4 15
16.787a 2.671 2.177 0.133 3.1 77a
1.066
41-50 51-60 61-70 71-80 41-80
42-46 42-47 46-52 32-33 41-45
3 4 4 4 15
3.045 4.472a 0.648 0.523 2.064
1.563
41-50 51-60 61-70 71-80 41-80
73-75 72-78 86-86 42-50 68-72
3 4 4 4 15
0.321 1.623 0.022 2.836 1.714
1.629
41-50 5 1-60 61-70 7 1-80 41-80
62-72 3 70-81 4 86-90 4 5054 4 68-74 15
1.223 0.838 1.935 0.420 2.664
F1
~
~
~
~
F1
ITG-CEG
F2 0.667 1.382 3.827 0.677
1.510 3.652 0.217 0.006 0.949 1.071 1.859 0.029
0.069 0.877 0.1 18 0.066 0.000 1.581 0.926 0.828 0.014 0.015 2.544 1.361 0.305
~~~~~~~
a Significant at the .05 level or greater.
Strength gains of the 41-50 age group of the CEG significantly greater than the strength gains of the other age groups of the CEG for Right-knee Extension. Strength gains of the 41-50 age group of the CEG significantly greater than the strength gains of the 41-50age group of the ITG for Right-knee Flexion.
When, for each age group, a comparison was made between the means of the ITG and the CEG for strength trainability, a significant difference was obtained for only one of the eight strength measurements. For right-knee-flexion strength, the men in the 41-50 age group of the CEG (N = 2) had significantly greater strength gains at the .05level than did the subjects in the ITG ( N = 4). The results of this analysis are presented in Table 1. When the means of the upper-extremity-strength ratios (final strength score divided by initial strength score) were compared with the means of the lowerextremity-strength ratios for the men in the ITG, no significant differences in
352 / WENDELL P. LIEMOHN
strength trainability by muscle group were found (Table 2). When the same comparison was made for the men in the CEG, a significant difference was found. The strength ratios for left-elbow-flexion strength and left-elbowextension strength were significantly greater than the ratios for left-kneeflexion strength (Table 2). However, 50 per cent of the CEG participants scored lower on the final left-knee-flexion test than they did on the initial test. Table 2. Strength Ratio Comparisonsa 41-50
Test/Group ~~
Nb
Nb
51-60
~
~~
61-70
71-80
Nb
~
Nb
41-80
~~~
Nb
~~
Knee Extension Right: I T G CEG Left: I T G CEG Knee Flexion Right: I T G CEG Left: I T G CEG Elbow Extension Right: I T G CEG Left: I T G CEG Elbow Flexion Right: I T G CEG Left: I T G CEG
1.070 1.409 0.997 1.365
4 3 4 3
1.435 1.127 1.338 1.096
6 4 6 4
1.300 0.946 1.241 0.988
5 4 4
1.527 1.056 1.435 1.048
5 4 5 4
1.351 1.116 1.270 1.108
20 10 20 10
1.078 1.315 1.039 1.150
4 2 4
2
1.383 1.064 1.230 1.011
6 3 6 3
1.046 1.069 1.254 0.978
5 3 5 3
1.362 0.968 1.237 0.953
5 2 5 2
1.232 1.151 1.200 1.017'
20 10 20 10
1.285 1.116 1.131 1.065
4 3 4 3
1.201 1.249 1.156 1.129
6 4 6 4
1.057 1.129 1.075 1.138
5 4 5 4
1.592 1.037 1.663 1.078
5 4 5 4
1.279 1.134 1.257 1.105'
20 10 20 10
1.050 1.114 1.139 1.195
4 3 4 3
1.098 1.100 1.175 1.156
6 4 6 4
1.090 0.999 1.192 1.044
5
1.961 1.191 1.882 1.124
5 4 5 4
1.302 1.150 1.349 1.191
20
5
4 5 4
10 20
10
a The ratio is the final mean divided by the initial mean. Only those individuals that were able to take all of the strength tests are included in this comparison. The strength gains for Left-elbow Extension and Flexion were significantly greater than the strength gains for Left-knee Flexion in the CTG.
'
To further elucidate the value of isometrics for the elderly, examination of individual gains and losses was made. The initial and final strength scores (in pounds) were also subjected to a Fisher f test for correlated samples t o determine if the strength gains or losses were significant. These results are summarized in Table 1.
Discussion Based on the analysis of the data, the hypothesis that strength trainability does not differ among the age groups remains tenable. The fact that agerelated trends in strength trainability were not found between the various
STRENGTH AND AGING / 353
age groups is in disagreement with the findings of Hettinger [13]. However, when initial and final strength scores were, for each age group, subjected to a f test for correlated samples, the following possible age-related trends for strength trainability were noted:
1. the 41-50 age group in the ITG experienced statistically significant gains in strength for three of the eight tests, 2. the 51-60 age group in the ITG experienced statistically significant gains in strength for two of the eight tests, 3. the 61-70 age group in the ITG experienced statistically significant gains in strength for one of the eight tests, and 4. the 71-80 age group in the ITG did not experience statistically significant gains in strength for any of the eight tests. Variance analysis revealed that the two men in the 41-50 age group in the CEG had greater gains (significant at the .05 level) in strength for right-kneeflexion than did the four men in the ITG for the same age group. This was not expected; however, two of the men in this age group in the ITG scored lower on the final measurements than they did on the initial measurements for more than 50 per cent of the strength tests. The fact that on occasion men in the CEG appeared to gain in strength from the participation in a training program which avoided overload might be explained by:
1. the possibility that some overload occurred; 2. the apprehensiveness during the initial testings which resulted in submaximal effort for criterion as well as reliability scores; and 3. the usage, not necessarily overload, of relatively unused muscles during the training program gave the men in the CEG the realization that their muscles were more functional than they had realized-possibly , muscle re-education following disuse atrophy. It seems plausible that participation in the CEG, although not providing specificity of training and overload, resulted in muscle reeducation that may have enabled some of the men to exert a greater effort on the final measurements. Reasons ( 2 ) and (3) above cannot be ruled out as reasons for some of the gains in strength experienced by the men in the ITG. In one instance in particular, a 71-year-old in the ITG experienced exceptional gains in strength; even though he stated that he felt stronger, it is evident that a great percentage of his strength gains must be attributed to the removal of gross inhibitions or muscle re-education rather than the neural learning usually associated with the acquisition of strength. Because only initial and final measurements were made, the relative weights of the “re-education factor” and the “true strength-gain factor” cannot be discerned.
354 / W E N D E L L P. LIEMOHN
Individual variability in strength trainability within an age group was noted frequently. Factors that might be responsible for this include:
1. 2. 3. 4.
training stimulus too small to elicit a training effect in some men, some men possessing little or n o strength trainability, failure of some men to cooperate, and variability in post-contraction periods.
The findings of this study would tend to support the idea that strength trainability in some elderly men might be more of an individual phenomenon than an age-related phenomenon. The relationship between strength trainability and chronological age cannot be discounted; however, i t is likely that physiological age may be a more important factor than chronological age. In young men strength gains are, at least in part, dependent upon (1) neural learning-this may be adversely affected by neuromuscular degeneration, and (2) an increase in muscle protein-this may be adversely affected by a decrease in hormonal output. In the elderly and debilitated perhaps a third factor, muscle re-education, might be added-a more gross neural learning than that usually associated with the acquisition of strength from following a strengthtraining program. In Table 3 is presented a comparison between the mean scores that men in the ITG and the CEG received on the final strength tests and also the mean scores that Clarke [22] reported for the same strength tests.3 Of the four tests compared, Clarke and the investigator found that subjects tended to register their greatest strength on the knee-extension test. Clarke found that the second strongest muscle group of the four compared was the knee flexors; whereas the four age groups in this study had elbow flexion as their second highest strength score, with knee flexion ranking third. When the mean scores reported by Clarke for elbow-flexion strength are compared with the same scores for the 41-50 age group of this study, little difference is noted in actual scores or in percentage scores. However, when the other strength scores of this age group are compared with Clarke’s means, considerable difference is noted, particularly in the scores for knee extension and knee flexion. On the basis of these comparisons, it would appear that agerelated strength decrements are the greatest in muscles which extend and flex the knee, and least in the muscles that flex the elbow. This is in agreement with the findings of Asmussen and Heeboll-Nielson [ S ] . The latter investigators crcdit this to the belief that there is a disproportionate decreased usage of the lower limbs as the individual ages. Based on the analysis of the data, the hypothesis that strength trainability does not differ between the upper and lower limbs remains tenable. The failure to observe statistically significant differences in proportional gains Clarke’s participants were college age men.
STRENGTH AND AGING / 355
Table 3. Final Strength Meansa of ITG and CEG Compared with Means Reported by Clarke (1 966)in College Age Men for Four Strength Tests Test/Group
Knee Extension Clarke IT G CEG Mean (ITG, CEG) Per centb Knee Flexion Clarke IT G CEG Mean (ITG, CEG) Per cent Elbow Extension Clarke ITG CEG Mean (ITG, CEG) Per cent El bow Flexion Clarke IT G CEG Mean (ITG, CEG) Per cent
Clarke
47-50
51-60
61-70
71-80
80 64 74 50
85 78 82 56
62 97 76 51
67 55 61 41
60 50 57 57
54 51 53 54
39 63 48 49
39 30 36 37
49 46 48 70
43 48 45 66
31 53 40 59
41 32 37 54
87 84 86 93
75 80 77 88
56 88 69 78
63 52 58 66
148
99
68
88
'
a All means are in pounds.
Per cent that ITG-CEG mean is of Clarke's mean.
between the different muscle groups from following an isometric-training program in context is not in agreement with the findings of Kraut, Muller, and Muller-Wecker [ 2 0 ] .It is possible that a disproportionate degree of neuromuscular deterioration in the lower extremities as a concomitant effect of advanced age and/or disuse precluded the finding of statistically significant differences (1) between muscle groups in general, and (2) in proportional strength gains in favor of the lower extremities over the upper extremities. If the neuromuscular deterioration is more of a concomitant effect of aging rather than disuse, differences in atrophy and/or trainability in the flexors and extensors of the knee might be explained by the fact that the extensors receive their innervation from the femoral plexus, whereas the flexors receive their innervation from the sacral plexus.
356 I WENDELL P. LIEMOHN
Summary Strength measurements were administered to 52 men ranging in age from 42 to 83 years. The men were then randomly assigned within their respective age groups to either the Isometric-training Group (ITG) or to the Control-exercise Group (CEG). At the conclusion of a six-week training program, the strength measurements were again administered. When the data relative to the strength scores of the ITG were subjected to analysis of variance comparisons, n o significant differences were found in (1) strength trainability by age groups, and ( 2 ) in strength trainability by muscle group when the upper-extremity-strength ratios were compared with the lowerextremity-strength ratios. When the initial and final strength scores of the ITG were subjected to a r test for correlated samples, it was noted that the ITG experienced statistically significant gains in strength for all of the eight strength measurements. REFERENCES
1. Per-Olof Astrand, “Human Physical Fitness with Special Reference to Sex and Age,” Physiological Reviews, 36, pp. 307-335, 1956. 2. J. S . Bosco, “Can Adult Physical Fitness Be Improved?” Journal o f the Association f o r Physical and Mental Rehabilitation, pp. 115-1 16, 1962. 3. M. J. Karvonen, “Exercise-Physiological Aging,” Health and Fitness in the Modern World, Athletic Institute, Chicago, 196 1. 4. D. Mateef, “Materials of the All-Union and Let Transcaucasus Conference Devoted to Problems of Clinical Gerontology and Geriatrics,” (trans. and ed. by Office of Technical Services, U.S. Department of Commerce), Joint Publication Research Services, Washington, D.C., pp. 1-13, 1966. 5. H. A. Ruger, “On the Growth Curves of Certain Characters in Man (Males),” Annals o f Eugenics, 2, pp. 76-1 10, 1927. 6. J. M. Ufland, “Einfluss des Lebensalters, Geschlechts, der Konstitution und des Berufs auf die Kraft verschiederner Muskelgruppen,” Arbeitsphysiologie, 7, pp. 251-258, 1933. 7. M. B. Fisher and J. E. Birren, “Age and Strength,” Journal o f Applied Psychology, 31, pp. 490-97, 1947. 8 . E. Asmussen and K. Heeboll-Nielson, “Isometric Muscle Strength in ReIation to Age in Men and Women,” Ergonomics, pp. 167-169, 1962. 9. N. W. Shock, “The Physiology of Aging,” Scientific American, 206, pp. 100-1 10, 1962. 10. E. A. Muller, “The Regulation of Muscular Strength,” Journal of the Association f o r Physical and Mental Rehabilitation, 11, pp. 41-47, 1957. 11. M. Mitolo, “Physical Training Capacity of Aged Skeletal Muscle,” Acta Physiologica Academiae Scientiarum Hungaricae, 31, pp. 199-208, 1967. 12. T. Hettinger, “Die Trainierbarkeit menschlicher Muskeln in Abhangigkeit vom Alter und Geschlecht,” Internationale Zeitschrift Fur Angewandt Physiologie, 17, pp. 371-377, 1958.
STRENGTH A N D AGING / 357
13. T. Hettinger, Physiology of Strength, Charles C. Thomas, Springield, Illinois, 1961. 14. J. Allen, “The Use of Isometric Exercises in a Geriatric Treatment Program,” Geriatrics, 20, pp. 346-347, 1965. 15. M. J. Rodriguez, 5 . J. DePalma and H. P. Daykin, “Isometric Exercise in General Practice,” The Journal of the Association for Physical and Mental Rehabilitation, 19, pp. 197-200, 1965. 16. E. D. Gardner, “Decrease in Human Neurones with Age,” Anatomical Record, 77, pp. 529-536, 1940. 17. Z. Drahota and E. Gutmann, “The Influence of Age on the Course of Reinnervation of Muscle,” Gerontologia, 5, pp. 88-109, 1961. 18. L. J. Rubinstein, “Aging Changes in Muscle,” in G. H. Bourne (ed.), The Structure and Function of Muscle, III Pharmacology and Disease, Academic Press, New York, 1960. 19. E. Simonson, W. M. Kearns, and N. Enzer, “Effect of Methyl Testosterone Treatment on Muscular Performance and the Central Nervous System of Older Men,” Journal of Clinical Endocrinology, 4 , pp. 528-534, 1944. 20. H. Kraut, E. A. Muller and H. Muller-Wecker, “Die Abhangigkeit des Muskeltrainings und des Eiweinssansatzes von der Eiweissaufnahme und vom Eiweissbestand des Korpers,” Biochemische Zeitschrift, 324, pp. 280294, 1953. 21. H. H. Clarke and D. H. Clarke, Developmental and Adapted Physical Education, Prentice-Hall, Inc., Englewood Cliffs, N.J., 1963. 22. H. H. Clarke, Muscular Strength and Endurance in Man, Prentice-Hall, Inc., Englewood Cliffs, N.J., 1966. 23. E. F. Lindquist, Design and Analysis o f Experiments in Psychology and Education, Houghton Mifflin Company, Boston, 1953.
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W.P. Liemohn, Ph.D. Developmental Training Center University of Indiana 2858 East 10th Street Bloomhgton, Indiana 47401
