Effects of muscle temperature on the VO2 kinetics at the onset of exercise in man

Abstract

The kinetics (i.e. the rate of readjustment) of O2 uptake (VO2) at the mouth of muscle blood flow in the vastus lateralis muscle (Qm), and the net accumulation of lactate in the rest-to-exercise transient (early lactate) were assessed in 6 untrained men (age 31 +/- 8 (SD) yrs) during constant-load 5-min duration exercises on the cyclo ergometer of 75 and 125 W, performed at muscle temperatures (Tm) of 35.5 +/- 0.9 degrees C (N) and of 28.0 +/- 1.65 degrees C (C). VO2 was measured breath-by-breath; Qm was assessed from 133Xe clearance; early lactate was calculated as the difference between the venous lactate concentrations observed after and before exercise. At both work loads, steady-state VO2 was slightly higher in N than in C (P less than 0.05 at 75 W; NS at 125 W). The half-times of VO2 kinetics were: in N, 36.2 +/- 6.7 s at 75 W and 41.6 +/- 8.6 s at 125 W; in C, 41.4 +/- 10.0 at 75 W and 43.8 +/- 14.0 at 125 W (NS). Mean steady state Qm was 8.5 ml.min-1.100 g-1 in C, and 13.4 in N at 75 W (NS); at 125 W, Qm was 18.3 ml.min-1.100 g-1 in C vs. 25.0 in N (NS). The half-times of the Qm kinetics tended to be slower in C than in N (NS). At both work loads, early lactate was slightly greater in C than in N (NS). It is concluded that, at submaximal exercise, (a) steady state VO2 and the VO2 kinetics are not affected by Tm, and (b) at the onset of exercise Qm does not affect VO2 kinetics.