Skeletal muscle weakness is associated with wasting of extremity fat-free mass but not with airflow obstruction in patients with chronic obstructive pulmonary disease

BACKGROUND: Skeletal muscle weakness is a prominent problem in many patients with chronic obstructive pulmonary disease (COPD). OBJECTIVE: The aim of the study was to determine the relation between skeletal muscle function, body composition, and lung function in COPD (emphysema and chronic bronchitis) patients and healthy volunteers. DESIGN: In 50 patients with chronic bronchitis, 49 patients with emphysema, and 28 healthy volunteers, skeletal muscle function was assessed by handgrip and linear isokinetic dynamometry. Whole-body and subregional fat-free mass (FFM) were assessed by dual-energy X-ray absorptiometry. RESULTS: Whole-body and extremity FFM were significantly lower in patients with emphysema (P < 0.001) and chronic bronchitis (P < 0.05) than in healthy volunteers, but trunk FFM was significantly lower only in patients with emphysema (P < 0.001). Extremity FFM was not significantly different between the COPD subtype groups, despite significantly lower values for whole-body and trunk FFM (P < 0.05) in patients with emphysema. Absolute skeletal muscle function (P < 0. 001) and muscle function per kilogram of whole-body FFM were significantly lower in both COPD subtype groups than in healthy volunteers (P < 0.05), but no significant difference was found between patients with chronic bronchitis and those with emphysema. Muscle function per kilogram of extremity FFM was not significantly different between the 3 groups and was not associated with forced expiratory volume in 1 s. CONCLUSION: Skeletal muscle weakness is associated with wasting of extremity FFM in COPD patients, independent of airflow obstruction and COPD subtype.