This randomized control trial will investigate whether a modality that generates more contractile muscle fatigue with lower ventilatory requirements render better results after a 12-week exercise training program in subjects with COPD.

Subjects will be randomized to either exercise in a training program including downhill walking or to exercise in a training program including conventional walking.

Inclusion Criteria:

• Patients with a primary diagnosis of COPD according to internationally accepted guidelines
• Patients referred to the outpatient PR program of Gasthuisberg University Hospital(Leuven, Belgium)

Exclusion Criteria:

• Any underlying disease or musculoskeletal limitation that could impair the ability to perform any of the exercise training modalities
• Absence of exacerbations in the previous month before entering the present study
• Patients included on the waiting list for lung transplantation