Review question The objective of this systematic review is to identify, appraise and synthesize the best available evidence on the effectiveness of any mode of exercise program on improvement of physical functioning in persons with peripheral arterial disease and symptoms of moderate to severe intermittent claudication. More specifically, the objective is to identify: The effectiveness of any mode of exercise program on the physical functioning of people with moderate to severe intermittent claudication. Inclusion criteria Types of participants This review will consider studies that include adults with moderate to severe intermittent claudication, verified by a validated or a clear classification. There will be no limitation regarding gender or ethnicity. Studies dealing with participants who have co-morbidities, who are in pharmacotherapy or who have had a previous revascularization are included on the basis that these factors are well described and not subject for interventions during the study. Types of intervention This review will consider studies that evaluate any mode of exercise program with clearly prescribed instructions. The exercise may be based in any setting: the hospital, community or home setting. The training may be in the form of individual or group activities, and both supervized as well as non-supervized exercise training will be considered. Types of outcomes This review will consider studies that include outcomes measuring the walking aspect of physical functioning. Outcome must be measured by a standardized and validated test. Both objective performance-based tests as well as self-reported questionnaires assessing walking ability are included. Performance-based tests included are: a treadmill test using a standard protocol and measuring maximal walking time, distance or onset to claudication pain, the Six-minute Walk Test and the Shuttle Walk Test. Included questionnaires are the physical function part of Medical Outcomes Short Form 36 and Walking impairment Questionnaire.