The effect of exercise intensity on the slow component of VO_2 in persons of different fitness levels

摘要

Objectives. To evaluate the slow component of VO_2 in persons of different fitness levels exercising at different intensities and the contribution of proposed mediators to the slow component of VO_2 using equations from the literature. Experimental design. Cross-sectional. Setting. University. Participants. Low (N=15) and high (N=15) fitness (VO_2max of 37 vs 62 ml·min~(-1)·kg~(-1)). Interventions. None. Measures. Each subject completed, in random order, a series of 12 min cycle ergometer exercise trials corresponding to 50, 60, 70 and 80% of VO_2max. VO_2, minute ventilation (MV), blood lactate (BL), rectal temperature (RT), heart rate and blood pressure were measured. Results. There was a significant (p < 0.05) increase in the slow component of VO_2 for each level of fitness across time and at each workrate. There were no between group differences for any variable. The increase in the slow component of VO_2 ranged from 70 ml·min~(-1) for the lighter workrates to 543 ml·min~(-1) for the high fitness group at 80% of maximal VO_2 (both p < 0.05). The oxygen cost of MV, RT and rate pressure product accounted for about 50% of the observed increase in the slow component of VO_2. MV appears to increase in a pattern most similar to the slow component of VO_2 and the oxygen cost of MV generally accounted for the highest percentage of the observed increase. Conclusions. The slow component of VO_2 needs to be considered when prescribing exercise. These results are not conclusive concerning the primary mediators of the slow component of VO_2.