Control of ventilation and heart rate during exercise appears to undergo maturation, while aerobic metabolism ([latin capital V with dot above]O2) may not. Since we had previously found that hypoxia during exercise produced different ventilatory responses in children (C) compared to adults (A), we hypothesized that [latin capital V with dot above]O2 and heart rate kinetics during exercise would show similar maturational responses to hypoxia. To test this hypothesis, we examined the responses during progressive (ramp) and constant work rate tests in children and adults breathing either room air or hypoxic gas (FiO2 = 0.15). When corrected for body weight, children and adults had similar values for lacticacidosis threshold (LAT) (C: 29.1 +/- 5.0 ml[middle dot];min-1 [middle dot]kg-1; A: 27.9 +/- 4.3) and [latin capital V with dot above]O2max (C: 40.7 +/- 8.6 ml[middle dot]min-1[middle dot]kg-1; A: 45.2 +/- 6.7) during normoxia. Hypoxia significantly lowered LAT (C: 27.5 +/- 5.4 ml[middle dot]min-1[middle dot]kg-1; A: 23.2 +/- 3.8; both P < 0.05) and [latin capital V with dot above]O2max (C: 37.7 +/- 8.3 ml[middle dot]min-1[middle dot]kg-1; A: 40.1 +/- 5.3; both P < 0.05) in both children and adults. Metabolic efficiency ([DELTA][latin capital V with dot above]O2/[DELTA]work rate) and the [latin capital V with dot above]O2-heart rate relationship ([DELTA][latin capital V with dot above]O2/[DELTA]HR/kg) were similar in the two groups and unaffected by hypoxia. During the constant work rate exercise, [latin capital V with dot above]O2 kinetics (time constant during phase 2 of the response ([tau]1) and the O2 deficit) were similar between children and adults and were significantly slowed by hypoxia, consistent with current understanding of the control of oxidative metabolism. Finally, heart rate was increased at rest and during exercise with hypoxia, while the time to reach 75% of the end-exercise response was delayed significantly, in both groups. The dynamic adjustments of metabolism and heart rate during exercise are slowed with hypoxia to a similar degree in children and adults.
(C)1991The American College of Sports Medicine