Effects of prior heavy-intensity exercise during single-leg knee extension on Vo2 kinetics and limb blood flow

The effects of prior heavy-intensity exercise on O-2 uptake ((V) over dot o(2)) kinetics of a second heavy exercise may be due to vasodilation (associated with metabolic acidosis) and improved muscle blood flow. This study examined the effect of prior heavy-intensity exercise on femoral artery blood flow (Qleg) and its relationship with (V) over dot o(2) kinetics. Five young subjects completed five to eight repeats of two 6-min bouts of heavy-intensity one-legged, knee-extension exercise separated by 6 min of loadless exercise. (V) over dot o(2) was measured breath by breath. Pulsed-wave Doppler ultrasound was used to measure Qleg. (V) over dot o(2) and blood flow velocity data were fit using a monoexponential model to identify phase II and phase III time periods and estimate the response amplitudes and time constants (tau). Phase II (V) over do o(2) kinetics was speeded on the second heavy-intensity exercise [mean tau (SD), 29 (10) s to 24 (10) s, P < 0.05] with no change in the phase II (or phase III) amplitude. Qleg was elevated before the second exercise [1.55 (0.34) l/min to 1.90 (0.25) l/min, P < 0.05], but the amplitude and time course [tau, 25 (13) s to 35 (13) s] were not changed, such that throughout the transient the Qleg (and Delta Qleg/Delta(V) over dot o(2)) did not differ from the prior heavy exercise. Thus (V) over do o(2) kinetics were accelerated on the second exercise, but the faster kinetics were not associated with changes in Qleg. Thus limb blood flow appears not to limit (V) over dot o(2) kinetics during single-leg heavy-intensity exercise nor to be the mechanism of the altered (V) over dot o(2) response after heavy-intensity prior exercise.