Mechanisms of Improved Exercise Performance under Hyperoxia

Abstract

<b><i>Background:</i></b> The impact of hyperoxia on exercise limitation is still incompletely understood. <b><i>Objectives:</i></b> We investigated to which extent breathing hyperoxia enhances the exercise performance of healthy subjects and which physiologic mechanisms are involved. <b><i>Methods:</i></b> A total of 32 healthy volunteers (43 ± 15 years, 12 women) performed 4 bicycle exercise tests to exhaustion with ramp and constant-load protocols (at 75% of the maximal workload [W<sub>max</sub>] on FiO<sub>2</sub> 0.21) on separate occasions while breathing ambient (FiO<sub>2</sub> 0.21) or oxygen-enriched air (FiO<sub>2</sub> 0.50) in a random, blinded order. Workload, endurance, gas exchange, pulse oximetry (SpO<sub>2</sub>), and cerebral (CTO) and quadriceps muscle tissue oxygenation (QMTO) were measured. <b><i>Results:</i></b> During the final 15 s of ramp exercising with FiO<sub>2</sub> 0.50, W<sub>max</sub> (mean ± SD 270 ± 80 W), SpO<sub>2</sub> (99 ± 1%), and CTO (67 ± 9%) were higher and the Borg CR10 Scale dyspnea score was lower (4.8 ± 2.2) than the corresponding values with FiO<sub>2</sub> 0.21 (W<sub>max</sub> 257 ± 76 W, SpO<sub>2</sub> 96 ± 3%, CTO 61 ± 9%, and Borg CR10 Scale dyspnea score 5.7 ± 2.6, <i>p</i> < 0.05, all comparisons). In constant-load exercising with FiO<sub>2</sub> 0.50, endurance was longer than with FiO<sub>2</sub> 0.21 (16 min 22 s ± 7 min 39 s vs. 10 min 47 s ± 5 min 58 s). With FiO<sub>2</sub> 0.50, SpO<sub>2</sub> (99 ± 0%) and QMTO (69 ± 8%) were higher than the corresponding isotime values to end-exercise with FiO<sub>2</sub> 0.21 (SpO<sub>2</sub> 96 ± 4%, QMTO 66 ± 9%), while minute ventilation was lower in hyperoxia (82 ± 18 vs. 93 ± 23 L/min, <i>p</i> < 0.05, all comparisons). <b><i>Conclusion:</i></b> In healthy subjects, hyperoxia increased maximal power output and endurance. It improved arterial, cerebral, and muscle tissue oxygenation, while minute ventilation and dyspnea perception were reduced. The findings suggest that hyperoxia enhanced cycling performance through a more efficient pulmonary gas exchange and a greater availability of oxygen to muscles and the brain (cerebral motor and sensory neurons).