Cardiorespiratory Responses of Adults and Children during Normoxic and Hypoxic Exercise

We aimed to elucidate potential differential effects of hypoxia on cardiorespiratory responses during submaximal cycling and simulated skiing exercise between adults and pre-pubertal children. Healthy, low-altitude residents (adults, N=13, Age=40±4yrs.; children, N=13, age=8±2yrs.) were tested in normoxia (Nor: P_iO₂=134±0.4 mmHg; 940 m) and normobaric hypoxia (Hyp: P_iO₂=105±0.6 mmHg; ~3 000 m) following an overnight hypoxic acclimation (≥12-hrs). On both days, the participants underwent a graded cycling test and a simulated skiing protocol. Minute ventilation (V_E), oxygen uptake (VO₂), heart rate (HR) and capillary-oxygen saturation (SpO₂) were measured throughout both tests. The cycling data were interpolated for 2 relative workload levels (1 W·kg^-1 & 2 W·kg^-1). Higher resting HR in hypoxia, compared to normoxia was only noted in children (Nor:78±17; Hyp:89±17 beats·min^-1; p<0.05), while SpO₂ was significantly lower in hypoxia (Nor:97±1%; Hyp:91±2%; p<0.01) with no between-group differences. The V_E, VO₂ and HR responses were higher during hypoxic compared to normoxic cycling test in both groups (p<0.05). Except for greater HR during hypoxic compared to normoxic skiing in children (Nor:155±19; Hyp:167±13 (beats·min^-1); p<0.05), no other significant between-group differences were noted during the cycling and skiing protocols. In summary, these data suggest similar cardiorespiratory responses to submaximal hypoxic cycling and simulated skiing in adults and children.