The file associated with this record is embargoed while permission to archive is sought from the publisher. The final published version may be available through the links above. ; The inability to be physically active is one of the key complaints expressed by patients with COPD. This is best considered as an exercise problem because it is the quantitative restriction to physical capacity more than the sensation of breathlessness or fatigue during exercise (something we all experience) that is the abnormal symptom. There is now a convincing body of evidence indicating that skeletal muscle dysfunction is a frequent and clinically relevant feature of COPD that contributes significantly to reduced exercise performance and, indeed, mortality independently from the severity of lung function impairment.1 The cause of this dysfunction has been debated, but a long-term downward spiral of inactivity and deconditioning is the key feature of its natural history, although other disease-related factors (eg, hypoxia, drug therapy, systemic inflammation) may contribute in selected patients.[opening paragraph] ; Peer-reviewed ; Publisher Version