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Chronic obstructive pulmonary disease (COPD) has long been recognised to affect the pulmonary system. However, a growing body of evidence is now emerging, which indicates that skeletal muscle dysfunction (SMD) is becoming a key feature of COPD.1 SMD is related to the loss of muscle mass and strength, which are significant predictors of poor healthrelated quality of life (HRQoL), mortality and subsequent increased healthcare costs in COPD patients.2,–,4 SMD usually affects the muscles of ambulation by altering their structure and biochemical function.1 Tissue biopsies taken from the quadriceps muscles have shown a greater predominance towards fatiguable Type IIb muscle fibres and a reduction in Type I muscle fibres, along with lower oxidative enzyme concentrations, mitochondria and lower muscle fibre-to-capillary ratios.1 5,–,7 The shift in Type IIb muscle fibres along with lower oxidative enzyme concentrations cause early lactic acid production at lower exercise levels due to anaerobic metabolism.8
Despite the greater predominance of Type IIb muscle fibres, there also appears to be a deficit in muscle strength in COPD patients. An observational study has demonstrated that respiratory disease patients have on average a 19% overall lower muscle strength score on four resistance exercises (knee extensions, leg curls, chest press and seated row) when compared with healthy subjects.9
Traditionally, most …
Competing interests None.
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