Effect of Body Weight and Adiposity on Physical Fitness in Healthy Adolescent Females. 1

Decreased physical activity and increased adiposity are commonly found in adolescent females and contribute to the pathological manifestations of syndromes like obesity, noninsulin dependent diabetes, and/or polycystic ovarian syndrome. But the important relationship between fitness and fatness has not been adequately studied in large part because of confounding effects of adiposity on the determinants of traditional indexes of fitness like maximal oxygen uptake (VdotO₂max). We used serial, magnetic resonance images of the right thigh to noninvasively measure muscle and fat volume of 44 healthy females (age 15-17 y.o.). VdotO₂max was measured using standard progressive cycle ergometer protocols. As expected, when normalized to body weight VdotO₂max/kg decreased as thigh fat increased. In contrast, VdotO₂max normalized to muscle mass was independent of thigh fat. In healthy adolescent females, adiposity is not associated with muscle size-independent components of fitness (such as mitochondrial or capillary density). If fitness declines with increasing adiposity, the mechanism is likely related to a decrease in muscle volume relative to fat Figure

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