MATURATION OF VENTILATORY RESPONSES TO 1-MINUTE EXERCISE

To test the hypothesis that ventilatory responses to exercise mature during growth in healthy children, we examined CO2 production (VCO2) and minute ventilation (V(E)) before, during, and for 10 min after 1-min bursts of cycle ergometry exercise. Ten children (range: 7-11 y old) and 13 adults (26-42 y old) exercised at work rates corresponding to 50 and 80% of the anaerobic or lactate threshold, 50% of the difference between anaerobic threshold and maximum O2 consumption, 100% of maximum O2 consumption, and 125% of maximum O2 consumption (125% max). Gas exchange was measured breath by breath. Children recovered faster from high-intensity (above anaerobic threshold) exercise as judged by the time constant of single exponential curve-fits to postexercise VCO2 [55 +/- 10 s (1 SD) at 125%. max in children compared with 92 +/- 17 s at 125% max in adults; p < 0.001] and V(E) (58 +/- 10 s at 125% max in children compared with 125 +/- 37 s in adults, p < 0.001). Although we found no significant difference between VCO2 and V(E) recovery times in children, V(E) was significantly slower than VCO2 in adults for high-intensity exercise. Moreover, recovery times in adults increased with work intensity but were independent of them in children. Whereas the CO2 costs [calculated as total CO2 produced above baseline per unit work done (mL.J-1)] increased with work intensity in adults, no similar significant relationship was observed in children. Finally, at 125% max, the ratio of CO2 cost to O2 cost was 1.48 +/- 0.07, less than the ratio in adults (1.83 +/- 0.07, p < 0.01). These results demonstrate marked differences in dynamic ventilatory response to short bursts of exercise reflecting maturation of both respiratory control and cellular metabolic factors.