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

Introduction: End-exercise (V) over dot O-2 during heavy, constant-load exercise is reduced after endurance training, due to an attenuated (V) over dot O-2 slow component. Purpose/Methods: To determine whether the training-induced reduction in end-exercise (V) over dot O-2 was associated with reduced muscle use, we measured (V) over dot O-2 and T-2 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 (V) O-2 or active muscle after training in either group during low-intensity cycling, in which no (V) over dot O-2 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 (V) over dot O-2 (2625 +/- 673; 2567 +/- 605 mL.min(-1)) and the T-2 of the vastus lateralis (35.6 +/- 1.4; 34.5 +/- 0.9 ms). Conclusion: These results support the hypothesis that reduction in end-exercise (V) over dot O-2 (and the (V) over dot O-2 slow component) after training is due to reduced muscle use during heavy, constant load cycling.