 To circumvent these difficulties, the investigators have recently developed a strong and simple exercise methodology whose primary objective is to assess exertional dyspnea in patients with COPD: the 3-min constant rate shuttle walking test. During this test, which is a modification of the endurance shuttle walking test, patients are asked to walk around two cones set-up in a flat corridor and separated by 10m. An audio signal is used to impose the walking speed and the test ends at a fixed duration of 3 minutes or until symptoms become intolerable. At pre-specified time point during the test, and at the end of the test 3 min, patients are asked to score their perception of dyspnea on a Borg scale. The feasibility and reproducibility of this test in providing a standardized physical stimulus and a measurable level of dyspnea in patients with moderate to severe COPD has been reported. In one study, the investigators also confirmed the responsiveness of this test to bronchodilation, reporting statistically and clinically significant reduction in Borg dyspnea score with ipratropium bromide compared to placebo. 