Abstract
IntroductionWhile hypoxia is known to decrease peak oxygen uptake (2 max) and maximal power output in both adults and children its influence on submaximal exercise cardiorespiratory and, especially, muscle oxygenation responses remains unclear.MethodsEight pre-pubertal boys (age = 8 ± 2 years.; body mass (BM) = 29 ± 7 kg) and seven adult males (age = 39 ± 4 years.; BM = 80 ± 8 kg) underwent graded exercise tests in both normoxic (PiO2 = 134 ± 0.4 mmHg) and hypoxic (PiO2 = 105 ± 0.6 mmHg) condition. Continuous breath-by-breath gas exchange and near infrared spectroscopy measurements, to assess the vastus lateralis oxygenation, were performed during both tests. The gas exchange threshold (GET) and muscle oxygenation thresholds were subsequently determined for both groups in both conditions.ResultsIn both groups, hypoxia did not significantly alter either GET or the corresponding 2 at GET. In adults, higher E levels were observed in hypoxia (45 ± 6 l/min) compared to normoxia (36 ± 6 l/min, p < 0.05) at intensities above GET. In contrast, in children both the hypoxic E and 2 responses were significantly greater than those observed in normoxia only at intensities below GET (p < 0.01 for E and p < 0.05 for 2). Higher exercise-related heart rate (HR) levels in hypoxia, compared to normoxia, were only noted in adults (p < 0.01). Interestingly, hypoxia per se did not influence the muscle oxygenation thresholds during exercise in neither group. However, and in contrast to adults, the children exhibited significantly higher total hemoglobin concentration during hypoxic as compared to normoxic exercise (tHb) at lower exercise intensities (30 and 60 W, p = 0.01).ConclusionThese results suggest that in adults, hypoxia augments exercise ventilation at intensities above GET and might also maintain muscle blood oxygenation via increased HR. On the other hand, children exhibit a greater change of muscle blood perfusion, oxygen uptake as well as ventilation at exercise intensities below GET.
Highlights
While hypoxia is known to decrease peak oxygen uptake (Vo2 max ) and maximal power output in both adults and children its influence on submaximal exercise cardiorespiratory and, especially, muscle oxygenation responses remains unclear.Edited by: Gregoire P
The nocturnal exposure to normobaric hypoxia resulted in a significant reduction in SpO2 and PET O2 in adults and children
Seems to increase in adults across all intensities while it was only slightly increased at lower intensities in children; (b) the significant increase in ventilation was only observed at lower intensities in children and only at higher intensities in adults; and (c) muscle blood volume was only augmented in children at lower exercise intensities
Summary
While hypoxia is known to decrease peak oxygen uptake (Vo2 max ) and maximal power output in both adults and children its influence on submaximal exercise cardiorespiratory and, especially, muscle oxygenation responses remains unclear.Edited by: Gregoire P. Increased perfusion of organs or tissues, such as skeletal muscle, is a well-established mechanism that can alleviate local hypoxaemia (Wolfel and Levine, 2001; Joyner and Casey, 2014) While these responses have previously been documented in both adults and children (Kriemler et al, 2016), full compensation is only achieved after prolonged acclimatization and only at moderate altitude/hypoxic levels (West et al., 2007). The aforementioned mechanisms do not seem to acutely counteract the hypoxia-related decrement in maximal endurance performance as this is mostly underlined by decreased Vo2max (Roach and Kayser, 2001; Astrand et al., 2003) They may importantly modulate responses to submaximal exercise, which is even more pertinent, as both children and adults most often engage in submaximal activities at elevated altitudes (e.g., family mountaineering, skiing and/or trekking)
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