CALF MUSCLE CROSS-SECTIONAL AREA AND PEAK OXYGEN-UPTAKE AND WORK RATEIN CHILDREN AND ADULTS

It is often assumed that the inherent peak muscle metabolic capacity s cales in direct proportion to muscle cross-sectional area and is the s ame in small and large animals (A. V. Hill. Sci. Frog. 38: 208-230, 19 50). We wondered whether this relationship between size and function w as true during the period of growth and development in humans. Magneti c resonance imaging (MRI) was used to determine calf muscle cross-sect ional area (CSA) in 20 children (6-11 yr old, 11 boys) and in 18 adult s (23-42 yr old, 10 men). Progressive cycle ergometer exercise was per formed to determine peak oxygen uptake (VO2peak) and work rate (WR(pea k)) The scaling factor (determined by allometric analysis) relating ma ximal O-2 uptake (VO2max) to muscle CSA for the whole sample populatio n was 1.04 +/- 0.12 (SE), but the scaling factor relating WR(peak) to muscle CSA was significantly greater (1.37 +/- 0.12). Consistent with this, VO2max/CSA was not affected by body weight, but the WR(peak)/CSA increased as a function of weight both in males (P < 0.005) and femal es (P < 0.05). No differences in VO2max/CSA were found between childre n and adults. WR(peak)/CSA was significantly higher in adults compared with children (P < 0.05). It appears that the inherent peak muscle me tabolic capacity is smaller in children than in adults. Moreover, the coupling of muscle capacity with whole body metabolic rate changes dur ing growth in humans.