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

Abstract

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; VO2 max 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 (ThCOx) and to the respiratory compensation point (RCP) were determined. Power output (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 ThCOx (259 ± 23 vs. 288 ± 30 W) were, however, improved (P < 0.05) with hyperoxia and the ThCOx shift was related to the 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.

Mechanisms of Improved Exercise Performance under Hyperoxia

“…The modest increase in W max under hyperoxia found in the current study is in line with previous studies performed mostly in young athletes breathing oxygen- enriched air with various fractions of O 2 of 0.3-1.0 [11,17,18,19,20,21]. Our data extend these findings by showing a similar effect of hyperoxia on exercise performance in nonathletic - albeit relatively fit - subjects of both genders and of a broad age range (24-66 years).…”

“…Accordingly, reduced cerebral tissue oxygenation (CTO) during exercise was associated with cessation of motor tasks [6,7]. Moreover, the exercise-induced decline in CTO was aggravated by hypoxia [8,9,10], but reduced by hyperoxia along with a better exercise capacity [11]. …”

Effect of hypoxia and hyperoxia on exercise performance in healthy individuals and in patients with pulmonary hypertension: a systematic review

“…Further studies in a limited number of mostly healthy young athletes found an unchanged or increased maximal performance with higher FI O 2 (22,42,45).…”

“…In a systematic review of the literature, we identified four randomized-controlled trials, which included a least eight subjects and provided data on the effect of hyperoxia vs. normoxia air on maximal exercise performance in terms of workload or V O 2 (Table A2). All revealed an increased workload of V O 2 under hyperoxia (20,42,48,68).…”

“…Since the end-tidal PCO 2 (PET CO 2 ) was increased in hyperoxia compared with normoxia, these findings are consistent with a reduction in peripheral chemoreceptor sensitivity by hyperoxia with relative reduction in alveolar ventilation and a rise in the alveolar PCO 2 (and, hence, PET CO 2 ) (12). The higher CTO with postponed drop toward endexercise under hyperoxia may suggest a role of the brain in exercise limitation (42,66,68). The higher V O 2 under hyperoxia is not entirely understood, but may be related in part to changes in metabolism, redistribution of blood flow, differences in type and recruited muscle fibers, and in metabolism of nonexercising tissues (47,48,68), Higher blood lactate levels due to increased exercise under hyperoxia seem not to play a role (14).…”