VE and VCO2 remain tightly coupled during incremental cycling performed after a bout of high-intensity exercise

The purpose of the present study was to determine whether the linear relationship between CO2 output (VCO2) and pulmonary ventilation (VE) is altered during incremental cycling performed after exercise-induced metabolic acidosis. Ten untrained, female subjects performed two incremental cycling tests (15 W x min(-1) up to 165 W) on separate days. One incremental exercise test was conducted without prior exercise, whereas the other test was preceded by a 1-min bout of maximal cycling. The ventilatory equivalent for O2 (VE/VO2) was only elevated above control values at 15-60 W during incremental cycling performed after high-intensity exercise. In contrast, the ventilatory equivalent for CO2 (VE/VCO2) was significantly increased above control levels at nearly every work stage of incremental work (all except 165 W). Hyperventilation relative to VCO2 was confirmed by the significantly lower end-tidal CO2 tension (P(ET)CO2) obtained throughout the incremental cycling that was performed after high-intensity exercise (except at 165 W). VE and VCO2 were significantly correlated under both treatment conditions (r > 0.99; P < 0.001). Moreover, both the slope and y-intercept of the linear regression were found to be significantly elevated during the incremental cycling performed after high-intensity cycling compared to control conditions (P < 0.01). The increase in the slope of the VE-VCO2 relationship during incremental exercise performed under these conditions does not represent an uncoupling of VE from VCO2, but could be accounted for by the significantly lower P(ET)CO2 observed during exercise.