Influence of mild hypoxia on cardiorespiratory responses and muscle oxygenation during incremental exercise
This study investigated the influence of cardiorespiratory responses, blood lactate concentration and muscle oxygenation during incremental exercise tests in normoxia and hypoxia. Seven healthy subjects performed an incremental cycle ergometer exercise test breathing in random order either room air or a 15% O2 gas mixture. Ventilation and pulmonary gas exchange were measured and computed breath-bybreath. Arterial oxygen saturation (SaO2) was estimated continuously via pulse oxymeter. Forearm venous blood for measurement of blood lactate was collected every minute. Continuous-wave near infrared spectroscopy measured peripheral tissue saturation (SO2NIRS) in the vastus lateralis muscle. Significant reduction in oxygen uptake (p<0.01), power output (p<0.01) and SaO2 (p<0.001) was found in peak incremental exercise during hypoxia compared with normoxia. For the same power output in the twoconditions, hypoxia significantly decreased SaO2 (ANOVA: p<0.001) and blood lactate concentration (ANOVA: p<0.05) and increased minute ventilation (ANOVA: p<0.01). In the hypoxic condition, oxygen uptake and SO2NIRS were not found when exercising at the same power output compared with normoxia. This study would suggest that mild hypoxia may be avoided through ventilatory compensation at the alveolar level, and oxygen consumption in alveolar and peripheral tissue oxygenation can be maintained while exercising for the same power output.
Graduate School of Health Sciences, Hiroshima University