Excess CO2 output independent of hyperventilation during constant-load exercise / 体力科学

ABSTRACT

Gas exchange kinetics during constant-load exercise were measured to investigate the possibility that excess CO<SUB>2</SUB> 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, O<SUB>2</SUB> uptake, and CO<SUB>2</SUB> output were measured breath-by-breath. Excess CO<SUB>2</SUB> output and CO<SUB>2</SUB> 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 CO<SUB>2</SUB> output was observed at levels of WR greater than 40% WRmax after initial CO<SUB>2</SUB> storage, where VC<SUB>O2</SUB>/V<SUB>E</SUB> decreased gradually as though in parallel with the kinetics of CO<SUB>2</SUB> storage. VO<SUB>2</SUB>/V<SUB>E</SUB>, however, appeared to be constant after the initial peak. These data suggest that V<SUB>E</SUB> is closely correlated with V<SUB>O2</SUB> rather than V<SUB>CO2</SUB> during constant-load exercise, indicating that excess CO<SUB>2</SUB> output to compensate lactate production is independent of hyperventilation.