Physical activity in COPD
Even mild-to-moderate COPD is associated with a decrease in physical activity [31], which is thought to occur primarily as a consequence of dyspnoea induced by increased ventilatory constraints. Indeed, dynamic hyperinflation has been demonstrated in symptomatic patients with mild airflow limitation [32]. Exercise intolerance also relates to skeletal muscle dysfunction, characterised by both quantitative (loss of muscle mass) and qualitative (reduced enzymatic capacities) features resulting from sedentariness and probably from systemic consequences of COPD, including inflammation and oxidative stress [33]. Low levels of activity are related to poorer survival in COPD patients, as well as in the general population [33]. Some COPD-specific outcomes (e.g. exacerbations and hospitalisations) are also impaired in patients with low levels of physical activity.