Skeletal muscle fibre types, enzyme activities and physical performance in young males and females

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Abstract
Differences in skeletal muscle characteristics, metabolic profiles and functional performance between males and females were investigated using young (15-24 yr) male and female twins as subjects. The comparison included such variables as anthropometry, muscle strength, mechanical power, maximum O2 uptake, electrical activation of muscle, muscle fiber composition (vastus lateralis-muscle) and activities of several skeletal muscle enzymes. In the various functional tests performance of females was from 61.1-84.6% of that in males; distribution of slow twitch fibers in vastus lateralis muscle of the females (49.1 .+-. 7.7%) was lower (P < .05) than that of males (55.9 .+-. 11.9); activities of enzymes Ca2+ stimulated ATPase, CPK [creatine phosphokinase], phosphorylase and LDH [lactate dehydrogenase] were higher (P < .05-.01) in males, whereas the distribution pattern of LDH-1 isozyme was higher (P < .05) in females. A pronounced difference between the 2 groups was an almost 100% longer rise time of isometric force in females. The males, as compared to females, apparently demonstrate higher aerobic and strength performance capacity, more efficient neuromotoric output during contraction, more slow twitch muscle fibers and more pronounced contractile and glycolytic profiles in skeletal muscles.

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