At visits 4 - 7, patients will perform PFTs at baseline and at 30 and 120 minutes after inhaling arformoterol or normal saline (randomized order) and then constant work exercise on the treadmill or cycle ergometer (randomized order). Metabolic measurements will be made throughout exercise, and patients will provide continuous ratings of breathlessness and leg discomfort using a system consisting of a computer, monitor, and a mouse.