Cardio-Respiratory and Muscle Oxygenation Responses to Submaximal and Maximal Exercise in Normobaric Hypoxia: Comparison between Children and Adults

SIMPLE SUMMARY: Exposure to altitude (hypoxia) is known to importantly challenge human physiology—particularly during physical exercise. While the effects of hypoxia on exercise performance have been extensively investigated in the last century, the effect of maturation remains poorly explored. In the present work, we aimed to compare the various physiological (cardiorespiratory and muscle oxygenation) responses to moderate- and high-intensity exercise in hypoxic condition in children as compared to adults to directly delineate the effects of aging. For this purpose, healthy prepubertal children and healthy adults underwent exercise testing in the laboratory under normal (normoxic) and simulated altitude (hypoxic) conditions with several physiological measures conducted continuously throughout both testing sessions. The comparison of the outcomes showed that hypoxia provoked similar exercise-related responses in most, but not all physiological responses in children and adults. From a practical point, these data suggest the comparable effects of hypoxia in children and adults with the observed differences warranting further investigation. ABSTRACT: As differential physiological responses to hypoxic exercise between adults and children remain poorly understood, we aimed to comprehensively characterise cardiorespiratory and muscle oxygenation responses to submaximal and maximal exercise in normobaric hypoxia between the two groups. Following familiarisation, fifteen children (Age = 9 ± 1 years) and fifteen adults (Age = 22 ± 2 years) completed two graded cycling exercise sessions to exhaustion in a randomized and single-blind manner in normoxia (NOR; F(i)O(2) = 20.9) and normobaric hypoxia (HYP; F(i)O(2) = 13.0) exercises conditions. Age-specific workload increments were 25 W·3 min(−1) for children and 40 W·3 min(−1) for adults. Gas exchange and vastus lateralis oxygenation parameters were measured continuously via metabolic cart and near-infrared spectroscopy, respectively. Hypoxia provoked significant decreases in maximal power output P(MAX) (children = 29%; adults 16% (F = 39.3; p < 0.01)) and power output at the gas exchange threshold (children = 10%; adults:18% (F = 8.08; p = 0.01)) in both groups. Comparable changes were noted in most respiratory and gas exchange parameters at similar power outputs between groups. Children, however, demonstrated, lower P(ET)CO(2) throughout the test at similar power outputs and during the maintenance of [Formula: see text] (2) at the maximal power output. These data indicate that, while most cardiorespiratory responses to acute hypoxic exercise are comparable between children and adults, there exist age-related differential responses in select respiratory and muscle oxygenation parameters.