Isokinetic endurance of men of high and low strength.

Abstract

Generally, isometric and isotonic muscular strength are believed unrelated to relative muscular endurance. If, however, randomly selected subjects are first divided into groups high and low in maximum strength, there often exists an inverse relationship between strength and endurance (1). This appears to be based, in part, on varying intramuscular circulatory occlusion resulting from the contraction tensions produced (2). Recently, the relationship between maximum isokinetic strength and isokinetic endurance was studied in a large, random sample (3). Similar to other types of strength, nonsignificant correlations of -0.03 and 0.04 were calculated between maximum isokinetic strength and selected measures of isokinetic endurance. Since the mechanics of isokinetic contractions differ somewhat from isometric and isotonic contractions, ic was unclear whether blood flow affects the strength/endurance relationship in similar ways. Thirty-seven untrained but healthy male subjects were tested on a Cybex I1 isokinetic dynamometer for strength of extension of the dominant knee at a contraction velocity of 12O0/sec. Mean subject age was 21.8 yr., mean height was 70.6 in. and mean body weight was 174.3 Ib. Subjects whose maximal strength was .25 standard deviation above or below the group mean of 123.78 ft-lb. 2 27.31 were called high in strength (149.47 ft-lb. f 14.89, n = 15) and low in strength (95.71 ft-lb. f 13.31, n = 14), respectively. To assess isokinetic endurance, subjects performed a series of maximal knee extensions (one/sec.) until peak torque production dropped below 75% of initial strength. Two measures representing endurance capacity were obtained from the raw data, the maximum number of repetitions performed in excess of 75 % of peak torque and the total work accomplished by contractions in excess of 75 0/0 of peak torque. Groups high and low in strength differed significantly in the total amount of work done (2006.87 f 643.71 ft-lb. vs 1181.18 & 200.50 ft-lb., respectively) but not in the total number of repetitions performed ( 15.32 & 4.28 vs 14.00 f 2.67, respectively). When Pearson product-moment correlations were calculated between isokinetic strength and total work performed, coefficients of 0.39 and -0.02 were nonsignificant for both groups, respectively. When correlated with the total number of repetitions performed, strength was not significantly related to endurance for the group high in strength (r = 0.06). Strength was inversely related to endurance in those low in strength (r = -0.54, p < .01). These results suggest that, depending how endurance is defined, the isokinetic strength/endurance relationship is influenced by maximum strength in a manner similar to that observed for isometric and isotonic contractions. REFERENCES 1. BARNES. W. S. The relationship between static muscular strength, relative static muscular endurance and intramuscular occlusion in the human forearm. Unpublished doctoral dissertation, Univer. of Southern California, 1977.