A high blood lactate induced by heavy exercise does not affect the increase in submaximal $\dot V{\text{O}}_2$ with hyperoxia

Abstract

Few studies evidenced an enhancement in oxygen uptake $\left( {\dot V{\text{O}}_2 } \right)$ during submaximal exercise in hyperoxia. This O₂ “overconsumption” seems to increase above the lactate threshold. The aim of this study was to determine whether the hyperoxia-induced enhancement in $\dot V{\text{O}}_2$ may be related to a higher metabolism of lactate. Nine healthy males (aged 23.1 years, mean $\dot V{\text{O}}_2 \max$ = 53.8 ml min⁻¹ kg⁻¹) were randomized to two series of exercise in either normoxia or hyperoxia corresponding to an inspired O₂ fraction (F_IO₂) of 30%. Each series consisted of 6 min cycling at 50% $\dot V{\text{O}}_2 \max$ (Moderate1), 5 min cycling at 95% $\dot V{\text{O}}_2 \max$ (Near Max) and then 6 min at 50% $\dot V{\text{O}}_2 \max$ (Moderate2). In both series Near Max was performed in normoxia. $\dot V{\text{O}}_2$ was significantly greater under hyperoxia than in normoxia during Moderate1 (2192±189 vs. 2025±172 ml min⁻¹) and during Moderate2 (2352±173 vs. 2180±193 ml min⁻¹). However, the effect of the high F_IO₂ was not significantly different on $\dot V{\text{O}}_{2{\text{Moderate}}2}$ (+172±137 ml min⁻¹ with [La] ~ 6 mmol l⁻¹) compared to $\dot V{\text{O}}_{2{\text{Moderate}}1}$ (+166±133 ml min⁻¹ with [La] ~ 2.4 mmol l⁻¹). [La] at the onset of Moderate2 was not different between normoxia and hyperoxia (10.1±2.2 vs. 10.9±1.6 mmol l⁻¹). The results show that $\dot V{\text{O}}_2$ is significantly increased during moderate exercise in hyperoxia. But this O₂ overconsumption was not modified by a high [La] induced by a prior heavy exercise. It could be concluded that lactate accumulation is not directly responsible for the increase in O₂ overconsumption with intensity during exercise in hyperoxia.