UC Irvine

To test the hypothesis that O2 uptake (VO2) dynamics are different in adults and children, we examined the response to and recovery from short bursts of exercise in 10 children (7-11 yr) and 13 adults (26-42 yr). Each subject performed 1 min of cycle ergometer exercise at 50% of the anaerobic threshold (AT), 80% AT, and 50% of the difference between the AT and the maximal O2 uptake (VO2max) and 100 and 125% VO2max. Gas exchange was measured breath by breath. The cumulative O2 cost [the integral of VO2 (over baseline) through exercise and 10 min of recovery (ml O2/J)] was independent of work intensity in both children and adults. In above-AT exercise, O2 cost was significantly higher in children [0.25 +/- 0.05 (SD) ml/J] than in adults (0.18 +/- 0.02 ml/J, P less than 0.01). Recovery dynamics of VO2 in above-AT exercise [measured as the time constant (tau VO2) of the best-fit single exponential] were independent of work intensity in children and adults. Recovery tau VO2 was the same in both groups except at 125% VO2max, where tau VO2 was significantly smaller in children (35.5 +/- 5.9 s) than in adults (46.3 +/- 4 s, P less than 0.001). VO2 responses (i.e., time course, kinetics) to short bursts of exercise are, surprisingly, largely independent of work rate (power output) in both adults and children. In children, certain features of the VO2 response to high-intensity exercise are, to a small but significant degree, different from those in adults, indicating an underlying process of physiological maturation.