Effects of moderate hyperoxia on oxygen consumption during submaximal and maximal exercise

The present study examined the effect of hyperoxia on oxygen uptake (V˙O2) and on maximal oxygen uptake (V˙O2max) during incremental exercise (IE) and constant work rate exercise (CWRE). Ten subjects performed IE on a bicycle ergometer under normoxic and hyperoxic conditions (30% oxygen). They also performed four 12-min bouts of CWRE at 40, 55, 70 and 85% of normoxic V˙O2max (ex1, ex2, ex3 and ex4, respectively) in normoxia and in hyperoxia. V˙O2max was significantly improved by 15.0 (15.2)% under hyperoxia, while performance (maximum workload, Wmax) was improved by only +4.5 (3.0)%. During IE, the slope of the linear regression relating V˙O2 to work rate was significantly steeper in hyperoxia than in normoxia [10.80 (0.88) vs 10.06 (0.66) ml·min–1·W–1]. During CWRE, we found a higher V˙O2 at ex1, ex2, ex3 and ex4, and a higher V˙O2 slow component at ex4 under hyperoxia. We have shown that breathing hyperoxic gas increases V˙O2max, but to an extent that is difficult to explain by an increase in oxygen supply alone. Changes in metabolic response, fibre type recruitment and V˙O2 of non-exercising tissue could explain the additional V˙O2 for a given submaximal work rate under hyperoxia.