In this issue of CHEST (page 370), Dolmage et al9extend this concept. They reasoned that single-leg cycling would require less ventilation (smaller muscle mass) and allow subjects to exercise at a higher muscle-specific intensity than conventional stationary cycling, potentially leading to a greater training response. They showed first that it is relatively simple to adapt a bike for single-leg cycling, and that impaired patients with COPD can successfully perform and tolerate this exercise without much instruction. In a prior study,10 they compared single-leg and two-leg cycle exercise in healthy control subjects and patients with COPD. In healthy control subjects during single-leg incremental exercise, subjects were able to generate approximately 50% of the power that they could generate during two-leg cycling, indicating that muscle-specific intensity was similar for the two forms of exercise. In contrast, in patients with COPD, during single-leg exercise patients were able to generate 80% of the power that they generated during two-leg cycling, suggesting that the exercising muscle was not maximally stressed during two-leg exercise. All patients with COPD in this study showed evidence of ventilatory limitation during two-leg exercise and complained prominently of dyspnea. During endurance constant workload exercise, healthy subjects performed single-leg exercise for roughly twice as long as two-leg exercise, so that total work was roughly the same during the two exercises. In contrast, patients with COPD exercised for almost four times as long during single-leg exercise compared with two-leg exercise, so that total work was significantly greater during single-leg exercise. Minute ventilation was lower during single-leg exercise, allowing the patients to exercise for longer at the same muscle-specific intensity.