Activity limitation and breathlessness are the main clinical features of advanced chronic obstructive pulmonary disease (COPD). During the last few years it has become recognised that this activity limitation relates in some way to peripheral muscle dysfunction that can be partly reversed by the process of pulmonary rehabilitation.^1,2 There is still debate about the detailed nature of the peripheral muscle dysfunction but most investigators would agree that deconditioning through inactivity plays a major role. In health, the age related loss of muscle mass can be prevented by maintained activity or reversed by training. In COPD the contribution of other factors to a specific myopathy such as systemic inflammation, hypoxia, or steroid damage remains uncertain. Physical training is the obvious way of improving the function of deconditioned peripheral muscles, although other options such as electrical stimulation or pharmacological treatment can also have an effect. There is now clear evidence that pulmonary rehabilitation programmes that include individually prescribed but generic physical exercise training are capable of improving functional exercise capacity and health status.³ Rehabilitation programmes generally contain a number of therapeutic elements, but it is also clear that the overall benefits of the process do not occur in the absence of some form of physical training. In addition, it has also been a consistent finding that the resulting improvements in general exercise performance and health status appear to relate poorly to each other. In most cases the magnitude of the improvement in quality of life is greater than the more modest improvements in general exercise capacity.

There are several possible explanations for this apparent dissociation. Firstly, exercise training may be the vector for improvement …