OXYGEN-UPTAKE DYNAMICS DURING HIGH-INTENSITY EXERCISE IN CHILDREN AND ADULTS

We hypothesized that the O2 uptake (VO2) response to high-intensity exercise would be different in children than in adults. To test this hypothesis, 22 children (6-12 yr old) and 7 adults (27-40 yr old) performed 6 min of constant-work-rate cycle-ergometer exercise. Sixteen children performed a single test above their anaerobic threshold (AT). In a separate protocol, six children and all adults exercised at low and high intensity. Low-intensity exercise corresponded to the work rate at 80% of each subject's AT. High-intensity exercise (above the AT) was determined first by calculating the difference in work rate between the AT and the maximal VO2 (DELTA). Twenty-five, 50, and 75% of this difference were added to the work rate at the subject's AT, and these work rates were referred to as 25% DELTA, 50% DELTA, and 75% DELTA. For exercise at 50% DELTA and 75% DELTA, VO2 increased throughout exercise (O2 drift, linear regression slope of VO2 as a function of time from 3 to 6 min) in all the adults, and the magnitude of the drift was correlated with increasing work rates in the above-AT range (r = 0.91, P < 0.0001). In contrast, no O2 drift was observed in over half of the children during above-AT exercise. The O2 drifts were much higher in adults (1.76 +/- 0.63 ml O2.kg-1.min-2 at 75% DELTA) than in children (0.20 +/- 0.42, P < 0.01). The average O2 cost (ml O2.min-1.W-1) was greater in children at all work rates (11.5 +/- 1.2 at 75% DELTA in children, 9.6 +/- 1.0 at 75% DELTA in adults; P < 0.01), and the pattern of the response was different in the two groups. These data suggest that a process of maturation takes place in the integrated adjustment to exercise as reflected in the dynamics of VO2.