Acceleration of (V)over-dot-O-2 kinetics in heavy submaximal exercise by hyperoxia and prior high-intensity exercise

We examined the hypothesis that O-2 uptake ((V) over dotO(2)) would change more rapidly at the onset of step work rate transitions in exercise with hyperoxic gas breathing and after prior high-intensity exercise. The kinetics if (V) over dotO(2) were determined from the mean response time (MRT; time to 63% of total change in (V) over dotO(2)) and calculations of O-2 deficit and slow component during normoxic and hyperoxic gas breathing in one group of seven subjects during exercise below and above ventilatory threshold (VT) and in another group of seven subjects during exercise above VT with and without prior high-intensity exercise. In exercise transitions below VT, hyperoxic gas breathing did not affect the kinetic response of (V) over dotO(2) at the onset or end of exercise. At work rates above VT, hyperoxic gas breathing accelerated both the on-and off-transient MRT, reduced the O-2 deficit, and decreased the (V) over dotO(2) slow component from minute 3 to minute 6 of exercise, compared with normoxia. Prior exercise above VT accelerated the on-transient MRT and reduced the (V) over dotO(2) slow component from minute 3 to minute 6 of exercise in a second bout of exercise with both normoxic and hyperoxic gas breathing. However, the summated O-2 deficit in the second normoxic and hyperoxic steps was not different from that of the first steps in the same gas condition. Faster on-transient responses in exercise above, but not below, VT with hyperoxia and, to a lesser degree, after prior high-intensity exercise above VT support the theory of an O-2 transport limitation at the onset of exercise for workloads >VT.