Endurance training reduces end-exercise VO₂ and muscle use during submaximal cycling

Introduction: End-exercise VO₂ during heavy, constant-load exercise is reduced after endurance training, due to an attenuated VO₂ slow component. Purpose/Methods: To determine whether the training-induced reduction in end-exercise VO₁ was associated with reduced muscle use, we measured VO₂ and T₂ changes in magnetic resonance images in the final minute of two 15-min constant-load cycle rides, one above lactate threshold and the other below lactate threshold. These measures were repeated after a 4-wk period in eight subjects who trained on a cycle ergometer and seven controls. Results: There were no changes in end-exercise VO₂ or active muscle after training in either group during low-intensity cycling, in which no VO₂ slow component was present. During high-intensity cycling, in which there was a slow component before training, the training group experienced a significant reduction (P < 0.05) in end-exercise VO₂ (2625 ± 673; 2567 ± 605 mL·min^-1) and the T₂ of the vastus lateralis (35.6 ± 1.4; 34.5 ± 0.9 ms). Conclusion: These results support the hypothesis that reduction in end-exercise VO₂ (and the VO₂ slow component) after training is due to reduced muscle use during heavy, constant load cycling.