Skeletal muscle contractile and noncontractile components in young and older women and men

To examine the influences of age, gender, and habitual physical activity le vel on human skeletal muscle composition, we developed a relatively simple magnetic resonance imaging method for the quantitation of leg anterior comp artment contractile and noncontractile content. We studied 23 young (II wom en and 12 men, 26-44 yr old) and 21 older (10 women and II men, 65-83 yr ol d) healthy adults. Analysis was by two-factor fags, gender) ANOVA. Physical activity, quantitated by three-dimensional accelerometer worn about the wa ist for 1 wk, was not different between groups. Men had larger contractile and noncontractile cross-sectional areas (cm(2)) than women, with no gender effect on percent noncontractile area. Young subjects had larger contracti le areas and smaller absolute (cm(2)) and relative (percent total) noncontr actile areas than older subjects. There was a significant linear relationsh ip between physical activity and percent noncontractile area in older (r = -0.68, P = 0.002) but not young subjects. These data demonstrate a more tha n twofold increase in the noncontractile content of locomotor muscles in ol der adults and provide novel support far physical activity as a modulator o f this age-related change in muscle composition.