Abstract

Gas exchange kinetics during constant-load exercise were measured to investigate the possibility that excess CO2 output during exercise might not be dependent on hyperventilation. Five healthy males performed twelve minutes of cycle exercise, including two minutes of 0 W pedaling, at 20, 40, 50, 60, 70, and 80 of their maximal work rate (WRmax) determined on the basis of preliminary ramp exercise of 30 W/min. Minute ventilation, O2 uptake, and CO2 output were measured breath-by-breath. Excess CO2 output and CO2 stores were calculated, assuming that the respiratory quotient (RQ) in tissue is constant during constant-load exercise and that the respiratory exchange ratio at the mouth level is equal to the RQ during the steady-state phase. Excess CO2 output was observed at levels of WR greater than 40 WRmax after initial CO2 storage, where VCO2/VE decreased gradually as though in parallel with the kinetics of CO2 storage. VO2/VE, however, appeared to be constant after the initial peak. These data suggest that VE is closely correlated with VO2 rather than VCO2 during constant-load exercise, indicating that excess CO2 output to compensate lactate production is independent of hyperventilation. Verf.-Referat