The effect of exercise intensity on the slow component of VO2 in persons of different fitness levels.

OBJECTIVES

To evaluate the slow component of VO2 in persons of different fitness levels exercising at different intensities and the contribution of proposed mediators to the slow component of VO2 using equations from the literature.

EXPERIMENTAL DESIGN

Cross-sectional.

SETTING

University.

PARTICIPANTS

Low (N = 15) and high (N = 15) fitness (VO2max 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 VO2max. VO2, 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 VO2 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 VO2 ranged from 70 ml.min-1 for the lighter workrates to 543 ml.min-1 for the high fitness group at 80% of maximal VO2 (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 VO2. MV appears to increase in a pattern most similar to the slow component of VO2 and the oxygen cost of MV generally accounted for the highest percentage of the observed increase.

CONCLUSIONS

The slow component of VO2 needs to be considered when prescribing exercise. These results are not conclusive concerning the primary mediators of the slow component of VO2.