The effect of exercise intensity on the slow component of V̇O₂ in persons of different fitness levels

Objectives. To evaluate the slow component of V̇O₂ in persons of different fitness levels exercising at different intensities and the contribution of proposed mediators to the slow component of V̇O₂ using equations from the literature. Experimental design. Cross-sectional. Setting. University. Participants. Low (N=15) and high (N=15) fitness (V̇O₂max of 37 vs 62 ml · min^-1 · kg^-1). Interventions. None. Measures. Each subject completed, in random order, a series of 12 rain cycle ergometer exercise trials corresponding to 50, 60, 70 and 80% of V̇O₂max. V̇O₂, 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 V̇O₂ 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 V̇O₂ ranged from 70 ml · min^-1 for the lighter workrates to 543 ml · min^-1 for the high fitness group at 80% of maximal V̇O₂ (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 V̇O₂. MV appears to increase in a pattern most similar to the slow component of V̇O₂ and the oxygen cost of MV generally accounted for the highest percentage of the observed increase. Conclusions. The slow component of V̇O₂ needs to be considered when prescribing exercise. These results are not conclusive concerning the primary mediators of the slow component of V̇O₂.