Thigh muscle strength and endurance in patients with COPD compared with healthy controls

The aim of this study was to evaluate thigh muscle strength and endurance in patients with COPD compared with healthy controls. Forty-two patients (26 women; 16 men) with moderate to severe COPD and 53 (29 women; 24 men) age-matched healthy controls participated in the study. The subjects were tested for maximum voluntary contractions (MVC), endurance and fatigue of the thigh muscles on an isokinetic dynamometer (KinCom). Endurance was expressed as the number of attained repetitions of knee extension and muscle fatigue as a fatigue index (FI). MVC in knee extension was 17% lower in female patients (P=0.017) but no difference was found in male patients (P=0.56) compared to controls. MVC in knee flexion was lower both in female (51%) (P<0.001) and male patients (40%) (P<0.001) compared to controls. Both female and male patients had significantly lower muscle endurance compared to controls. Female patients had a higher FI (22.5%) than female controls (10%) (P=0.001) while no difference was found regarding FI between male patients (15%) and male controls (10%) (P=0.103). The level of self-reported everyday physical activity did not differ between groups. The results showed impaired skeletal muscle function in COPD, except for MVC in knee extension in male patients. Female patients seemed to be more prone to decrease in thigh muscle function. More focus on improving muscle strength and muscle endurance should be considered when designing pulmonary rehabilitation programs. Patients with preserved level of physical activity can be included in exercise programs and gender-related differences should be taken into account.