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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; 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 ( _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 …