Cerebral oxygenation during hyperoxia-induced increase in exercise tolerance for untrained men

This study aimed to investigate the involvement of cerebral oxygenation in limitation of maximal exercise. We hypothesized that O₂ supplementation improves physical performance in relation to its effect on cerebral oxygenation during exercise. Eight untrained men (age 27 ± 6 years; \({\dot{\text{V}}}\)O_2max 45 ± 8 ml min⁻¹ kg⁻¹) performed two randomized exhaustive ramp exercises on a cycle ergometer (1 W/3 s) under normoxia and hyperoxia (FIO₂ = 0.3). Cerebral (ΔCOx) and muscular (ΔMOx) oxygenation responses to exercise were monitored using near-infrared spectroscopy. Power outputs corresponding to maximal exercise intensity, to threshold of ΔCOx decline (Th_COx) and to the respiratory compensation point (RCP) were determined. Power output (\({\dot{\text{W}}}\) _max = 302 ± 20 vs. 319 ± 28 W) and arterial O₂ saturation estimated by pulse oximetry (SpO₂ = 95.7 ± 0.9 vs. 97.0 ± 0.5 %) at maximal exercise were increased by hyperoxia (P < 0.05). However, the ΔMOx response during exercise was not significantly modified with hyperoxia. RCP (259 ± 17 vs. 281 ± 25 W) and Th_COx (259 ± 23 vs. 288 ± 30 W) were, however, improved (P < 0.05) with hyperoxia and the Th_COx shift was related to the \({\dot{\text{W}}}\) _max improvement with hyperoxia (r = 0.71, P < 0.05). The relationship between the change in cerebral oxygenation response to exercise and the performance improvement with hyperoxia supports that cerebral oxygenation is limiting the exercise performance in healthy young subjects.