 It is well accepted that the exercise training as part of a comprehensive pulmonary rehabilitation program can improve exercise tolerance, functional status and quality of life in patients with COPD. It is feasible that if patients were able to perform a greater volume or intensity of exercise during rehabilitation then the outcomes of the program would be improved. Recent research has demonstrated that breathing a helium-hyperoxic gas mixture can significantly reduce dynamic hyperinflation and dyspnea during exercise in patients with COPD and can increase exercise tolerance to a greater extent than breathing room air or a nitrogen-based hyperoxic gas. If patients with COPD were to breathe a helium-hyperoxic gas during exercise they should be able to tolerate a greater intensity of exercise while maintaining similar levels of exertional symptoms to those observed at lower exercise intensities breathing room air. As a result patients randomized to the helium-hyperoxia condition should obtain greater improvements in exercise tolerance than those receiving usual care i.e. breathing room air 