Effects of prior heavy exercise on phase II pulmonary oxygen uptake kinetics during heavy exercise

We tested the hypothesis that heavy-exercise phase II oxygen uptake ((V)over dot o(2)) kinetics could be speeded by prior heavy exercise. Ten subjects performed four protocols involving 6-min exercise bouts on a cycle ergometer separated by 6 min of recovery: 1) moderate followed by moderate exercise; 2) moderate followed by heavy exercise; 3) heavy followed by moderate exercise, and 4) heavy followed by heavy exercise. The (V)over dot o(2), responses were modeled using two (moderate exercise) or three (heavy exercise) independent exponential terms. Neither moderate- nor heavy-intensity exercise had an effect on the Tio, kinetic response to subsequent moderate exercise. Although heavy-intensity exercise significantly reduced the mean response time in the second heavy exercise bout (from 65.2 +/- 4.1 to 47.0 +/- 3.1 s; P < 0.05), it had no significant effect on either the amplitude or the time constant (from 23.9 +/- 1.9 to 25.3 +/- 2.9 s) of the (V)over dot o(2), response in phase II. Instead, this "speeding" was due to a significant reduction in the amplitude of the (V)over dot o(2) slow component. These results suggest phase II (V)over dot o(2) kinetics are not speeded by prior heavy exercise.