The Effects of Isometric and Isotonic Exercise Upon the Development of Strength, Endurance, and Cross Transfer of the Elbow Flexor Muscles
Authors:   , Gardner Ronald 
Published: February 2023

The purpose of this study was to investigate the effects of isometric and isotonic exercise upon the development of strength, endurance, and cross transfer in the elbow flexor muscles. Thirty-nine male college students served as subjects for this study. A cable tensiometer and associated equipment was utilized as the measuring instrument for the strength tests. The subjects were tested for strength one day prior to the initial endurance tests. Each subject was strapped to an apparatus of the investigator’s own design and tested individually. Each subject was tested for strength in a position with the elbow flexed to form a ninety degree angle. The subjects were given three trials with each arm the best of which was retained as the measure of muscular strength. The endurance test consisted of performing full curls with a load equal to three-eighths that of the initial strength test score. The curls were performed at a cadence of thirty per minute. Each subject was tested for both right and left elbow flexor endurance. Following the pre-tests the subjects were matched into two groups on the basis of their initial strength test scores. An eight weeks training program followed, during which Group I exercised five days a week by performing a six second maximum isometric contraction of the elbow flexor muscles with the elbow flexed at a ninety degree angle. Group II exercised isotonically by performing a maximum of four half curls a day at eighty percent maximum strength, for five days a week. Following the eight weeks training program post-tests of strength and endurance were given. The post-tests were identical to the pre-tests. The t-test for correlated samples showed significant increases in dominant arm strength scores for both Group I and Group II. A significant increase also occurred in strength of the non-dominant arm of Group I. Significant mean increases occurred in endurance for Group I and Group II for both the exercised and unexercised arms. On the basis of the data and within the limitations of this study the following conclusions were drawn: 1. a daily six second maximal isometric contraction of the elbow flexor muscles performed throughout a period of eight weeks, five days a week is sufficient to cause a significant improvement in exercised muscle strength. 2. The same isometric exercise program is sufficient to significantly improve the strength of the contralateral muscles of the opposite limb. 3. A daily isotonic exercising program consisting of performing half curls with a resistance load equal to eighty percent of the dominant arm strength, performed for eight weeks, is sufficient to produce increase in elbow flexor strength of the dominant exercised arm. 4. The same isotonic exercise program does not produce a significant increase in contralateral strength of the muscles of the opposite limb. 5. The results of the reliability tests were such that definite positive conclusions concerning the development of endurance and its cross transfer cannot be drawn. However, it appears that both isometric and isotonic exercise increased endurance in the dominant arm and cross transfer of endurance to the non-dominant arm. 6. Both a daily isometric and a daily isotonic exercise program are equally effective in providing muscle strength increases in the exercised arm. There appears to be no advantage in using one method over the other.