Purpose: The aim of this study was to compare the muscle deoxygenation measured by near infrared spectroscopy in endurance athletes who presented or not with exercise-induced hypoxemia (EIH) during a maximal incremental test in normoxic conditions. Methods: Nineteen male endurance sportsmen performed an incremental test on a cycle ergometer to determine maximal oxygen consumption ([latin capital V with dot above]O2max) and the corresponding power output (Pmax). Arterial O2 saturation (SaO2) was measured noninvasively with a pulse oxymeter at the earlobe to detect EIH, which was defined as a drop in SaO2 > 4% between rest and the end of the exercise. Muscle deoxygenation of the right vastus lateralis was monitored by near infrared spectroscopy and was expressed in percentage according to the ischemia-hyperemia scale. Results: Ten athletes exhibited arterial hypoxemia (EIH group) and the nine others were nonhypoxemic (NEIH group). Training volume, competition level, [latin capital V with dot above]O2max, Pmax, and lactate concentration were similar in the two groups. Nevertheless, muscle deoxygenation at the end of the exercise was significantly greater in the EIH group (P < 0.05). Conclusion: Greater muscle deoxygenation at maximal exercise in hypoxemic athletes seems to be due, at least in part, to reduced oxygen delivery-that is, exercise-induced hypoxemia-to working muscle added to the metabolic demand. In addition, our finding is also consistent with the hypothesis of greater muscle oxygen extraction in order to counteract reduced O2 availability.
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