Isometric and dynamic endurance as a function of age and skeletal muscle characteristics.

The aim of the study was to investigate the influence of age on endurance of human skeletal muscle. An attempt was made to correlate muscular performance at various ages with some morphological and enzymatic characteristics of the muscle. Fifty healthy men, 22-65 years of age, with low daily physical activity (clerks) volunteered for the study. Isometric and dynamic endurance were determined under standardized conditions and measured in relation to maximum strength, thereby correcting for individual as well as age differences in maximum strength. Biopsies taken from the quadriceps muscle were used for muscle fibre classification, fibre area determinations, and measurements of some enzyme activities (Mg2+ stimulated ATPase, myokinase (MK), lactate dehydrogenase (LDH),LDH isozymes). Maximum isometric and dynamic strength decreased in the older groups while no significant change was seen in isometric or dynamic endurance. Significant correlations were observed between endurance and fibre type distribution, fibre areas, and LDH isozyme activities.