Changes in ventilation at the start and end of moderate and heavy exercise of short and long duration.

These experiments examined the effect of exercise intensity and duration on the magnitude of the abrupt change in ventilation at the start (VE,start) and end (VE,end) of exercise. Five subjects performed constant load treadmill exercise at 50% and 80% of their maximum oxygen consumption (VO2max) for 6 and 10 min while inspiring atmospheric air. The subjects also completed additional exercise tests at 80% VO2max for 10 min while inspiring an oxygen-enriched gas mixture. During each exercise trial ventilation was measured breath-by-breath. The VE,start and VE,end were determined by using non-linear curve-fitting techniques. The results showed that VE,start was greater at the start of the 80-% exercise tests compared to the 50-% tests and that VE,start at each level of exercise was greater than VE,end. The results also demonstrated that VE,end was inversely related to the intensity and duration of exercise. Furthermore, the VE,end was not altered subsequent to the inspiration of oxygen-enriched air. These findings have led us to postulate that the stimulus responsible for VE,start is reduced during exercise and that the degree of reduction is related to the intensity and duration of exercise. In addition, it was concluded that these changes might occur independently of peripheral chemoreceptor activity.