FITNESS, FATNESS, AND THE EFFECT OF TRAINING ASSESSED BY MAGNETIC-RESONANCE-IMAGING AND SKINFOLD-THICKNESS MEASUREMENTS IN HEALTHY ADOLESCENT FEMALES

The relation between fitness and adiposity is particularly relevant to adolescent females in whom fitness is known to decrease and fatness t o increase. However, little is known about the interaction of these va riables in normally active, nonobese subjects. Our major hypotheses we re that adiposity would be inversely correlated with physical fitness and that even a relatively brief intervention would lead to measurable , site-specific changes in body fat. We used a cross-sectional protoco l to correlate body adiposity with indexes of fitness and a prospectiv e study design to examine body adiposity before and after a 5-wk perio d of endurance training in 44 nonobese females aged 15-17 y (control g roup, n = 22; training group, n = 22). Adiposity was assessed by magne tic resonance imaging of the abdomen and thigh as well as by standard skinfold-thickness measuring techniques. Fitness was assessed by using cycle ergometer measurements of maximal oxygen uptake (VO2 max). Ther e were significant negative correlations between VO2 max normalized to body weight and subcutaneous abdominal, thigh, and skinfold estimates of fat. However, when VO2 max was normalized to muscle volume these c orrelations were not significant. Abdominal fat increased in direct pr oportion to body weight (scaling factor = 1.14 +/- 0.16) but thigh fat increased proportionately less (scaling factor = 0.38 +/- 0.12, P < 0 .05). Training increased thigh muscle mass significantly only in the m idmuscle region and prevented the observed fat increase in the distal thigh of the control subjects. Body fat distribution in adolescent fem ales appeared to be affected by many factors, including overall body w eight and the level of physical activity.