Rationale: Pulmonary rehabilitation (PR) is considered a standard of care for patients with symptomatic lung disease. It has achieved strong evidence for reducing symptoms and improving exercise tolerance. Walking is the most common form of physical activity and most individuals need to walk in the course of their daily activities. Chosen walking speed is a good indicator of the debilitating effects of disease and improvement in usual walk speed has been associated with a substantial reduction in mortality in elderly subjects. Therefore, it is important for clinicians to understand how patients choose to walk in relation to their capabilities as well as to know how this relationship changes with PR.