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 VO2 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.