THE EFFECT OF EXERCISE INTENSITY ON ??VO2 DRIFT IN PERSONS OF DIFFERENT FITNESS LEVELS 1027

Abstract

Previous research suggests that the increase in ˙VO2 is more rapid in fit vs unfit subjects in response to increasing workloads and therefore the fit subjects would demonstrate less ˙VO2 drift. However, the magnitude and the mechanism has not been studied. Therefore, the purpose of this study was to compare the ˙VO2 drift in persons of different fitness levels exercising at different relative intensities. In addition, the contribution of proposed mediators of ˙VO2 drift was estimated using equations from the literature. Low (N = 15) and high (N = 15) fitness ([horizontal bar over]x ˙VO2 max 37 vs 62 ml·min-1·kg-1) males were recruited. Each subject completed, in random order, a series of 12 min stationary bicycle ergometer exercise trials corresponding to 50, 60, 70 and 80% of ˙VO2 max.˙VO2, minute ventilation, blood lactate, rectal temperature, heart rate and blood pressure were measured throughout each trial. A three factor(fitness, workload, time) repeated measures MANOVA found significant interactions. Subsequent follow up procedures indicated that there was a significant ˙VO2 drift for each level of fitness across time and at each workload. There were no differences between the fitness levels for˙VO2 drift or any of the proposed mediators. The ˙VO2 drift ranged from 70 ml·min-1 for the lighter workloads to 543 ml·min-1 for the high fitness group at 80% of maximal˙VO2. The oxygen cost of minute ventilation, body temperature and rate pressure product accounted for about 50% of the observed ˙VO2 drift. Of these, minute ventilation appears to increase in a pattern most similar to the ˙VO2 drift and the oxygen cost of minute ventilation generally accounted for the highest percentage of the observed ˙VO2 drift. These results suggest that minute ventilation appears to be the primary mediator of ˙VO2 drift. However, the contributions of body temperature, blood lactate and work of the heart can not be neglected.