Effect of increased muscle temperature on oxygen uptake kinetics during exercise

To test whether increased muscle temperature (T-m) would improve O-2 uptake ((V) over dotO(2)) kinetics, seven men performed transitions from rest to a moderate work rate [below the estimated lactate threshold (LTest)] and a heavy work rate ((V) over dotO(2) = 50% of the difference between LTest and peak (V) over dotO(2)) under conditions of normal T-m (N) and increased T-m (ii), produced by wearing hot water-perfused pants before exercise. Quadriceps T-m 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 (V) over dotO(2) or in the time constants of the on and off transients for moderate and heavy exercise between the two conditions. The increment in (V) over dotO(2) between the 3rd and 6th min of heavy exercise was slightly but significantly smaller for Il than for N. These data suggest that elevated T-m before exercise onset, which would have been expected to increase O-2 delivery and off-loading to the muscle, had no appreciable effect on the fast exponential component of (V) over dotO(2) kinetics (invariant time constant). These data further suggest that elevated T-m does not contribute to the slow component of (V) over dotO(2) during heavy exercise.