Influence of Hyperoxia on Pulmonary O2 Uptake On-Kinetics During Moderate, Heavy and Supra-Maximal Intensity Exercise in Humans

Abstract

PURPOSE: To examine the influence of hyperoxic gas (50 % O in N) inspiration on pulmonary VO2 kinetics during step transitions to moderate, heavy and supra-maximal intensity cycle exercise. METHODS: Seven healthy male subjects completed repeat transitions to moderate (90 % of the gas exchange threshold, GET), heavy (70 % of the difference between the GET and VO peak) and supra-maximal (105 % VO peak) intensity work rates while breathing either normoxic (N) or hyperoxic (H) gas before and during exercise. RESULTS: As anticipated, hyperoxia resulted in a significant increase in end-tidal PO2 (N: ∼97 ± 4 vs. H: ∼267 ± 3 mmHg during baseline cycling). However, hyperoxia had no significant effect on the Phase II VO2 time constant during moderate (N: 28 ± 3 vs. H: 31 ± 7 s), heavy (N: 32 ± 9 vs. H: 33 ± 6 s) or supra-maximal (N: 37 ± 9 vs. H: 37 ± 9 s) exercise. Hyperoxia resulted in a 45 % reduction in the amplitude of the VO2 slow component during heavy exercise (N: 0.60 ± 0.21 vs. H: 0.33 ±0.17 L−1min-1; p <0.05) and a 15% extension of time to exhaustion during supra-maximal exercise (N: 173 ± 28 vs. H: 198 ± 41 s; p <0.05). CONCLUSION: The Phase II VO2 kinetics are not normally constrained by (diffusional) O2 transport limitations during moderate, heavy or supra-maximal intensity exercise in young healthy subjects performing upright cycle exercise.