Impaired skeletal muscle endurance related to physical inactivity and altered lung function in COPD patients

The aims of this work were to determine (1) whether patients with COPD have impaired skeletal muscle performance (ie, maximal strength and endurance) compared with healthy subjects, and (2) whether the level of physical activity, body composition, and lung function are related to skeletal muscle performance in COPD patients.

Seventeen COPD patients and eight healthy age-matched control subjects performed maximum voluntary contraction (MVC) of the quadriceps and an endurance test consisting of dynamic contractions of the quadriceps against 20% of MVC at an imposed regular pace until exhaustion. The endurance test duration determined the muscle "limit time" (Tlim). A score of physical activity (PA score) was obtained using an adapted physical activity questionnaire for the elderly, and body composition was measured by the bioelectrical impedance method. Symptom-limited oxygen uptake (VO2 sl) was also assessed in COPD patients using a maximal incremental exercise test.

The results showed that Tlim and PA score were significantly decreased in COPD patients (p<0.05). Significant positive correlations were found in the COPD group between Tlim and the PA score (r=0.60; p<0.05), FEV1 (r=0.52; p<0.05), and PaO2 (r=0.63; p<0.05). The same results were found between the PA score and VO2 sl (r=0.57; p<0.05) and FEV1 (r=0.63; p<0.05).

These findings indicate impaired skeletal muscle endurance in COPD patients related to altered lung function and associated physical inactivity.