The effect on respiratory drive of a prolonged physical conditioning program.

Nine sedentary men 21 to 35 yr of age took part in a physical conditioning program involving regular aerobic exercise over a period of 6 to 8 wk. There was significant improvement in indexes of cardiorespiratory fitness. Ventilatory and mouth occlusion pressure responses to CO2 at rest and during threadmill exercise was measured before and after training. The slopes of the regression VE/PCO2 increased during exercise (p < 0.05), but not significantly at rest. The slopes of the regression of occlusion pressure at 100 ms versus PCO2, (P100/PCO2) did not change significantly at rest or during exercise. The VE/PCO2 and P100/PCO2 did not change from rest to exercise, and showed no relation to indexes of fitness. It is suggested that the low respiratory drive seen in some athletes is not due to the adaptation that results from short-term training. The possibility that long-term training may result in decreased responsiveness to CO2 cannot be excluded.