Muscle weakness and early fatigue are common symptoms of chronic organ diseases, like chronic obstructive pulmonary disease (COPD), chronic heart failure (CHF) and chronic renal failure (CRF). It is becoming more and more clear that symptom intensities and exercise intolerance are related to muscle wasting and intrinsic alterations in peripheral skeletal muscle in these patient populations, while correlations with parameters of organ functioning are poor. Also, changes in muscle structure and function in COPD, CHF and CRF show much resemblance. Semi-starvation, reduced physical activity and ageing are external factors possibly confounding a direct relationship between the primary organ impairments and alterations in peripheral skeletal muscle and exercise capacity. Reducing the catabolic effects of the various contributing factors might improve muscle function and health status in chronic disease. In this review, we present a systematic overview of human studies on alterations in skeletal muscle function, morphology and energy metabolism in COPD, CHF, CRF and we compare the results with comparable studies in anorexia nervosa, disuse or inactivity and ageing. Unravelling the relative contributions of these external factors to the observed alterations in the various diseases may contribute to targeted intervention strategies to improve muscle function in selected groups of patients.
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