Effect of increased muscle temperature on oxygen uptake kinetics during exercise.

To test whether increased muscle temperature (Tm) would improve O2 uptake (VO2) kinetics, seven men performed transitions from rest to a moderate work rate [below the estimated lactate threshold (LTest)] and a heavy work rate (VO2 = 50% of the difference between LTest and peak VO2) under conditions of normal Tm (N) and increased Tm (H), produced by wearing hot water-perfused pants before exercise. Quadriceps Tm was significantly higher in H, but rectal temperature was similar for the two conditions. There were no significant differences in the amplitudes of the fast component of VO2 or in the time constants of the on and off transients for moderate and heavy exercise between the two conditions. The increment in VO2 between the 3rd and 6th min of heavy exercise was slightly but significantly smaller for H than for N. These data suggest that elevated Tm before exercise onset, which would have been expected to increase O2 delivery and off-loading to the muscle, had no appreciable effect on the fast exponential component of VO2 kinetics (invariant time constant). These data further suggest that elevated Tm does not contribute to the slow component of VO2 during heavy exercise.