Relationship between physical activity and muscle mass or quality in chronic obstructive pulmonary disease patients.

BACKGROUND: Physical activity (PA) is an important prognostic factor for chronic obstructive pulmonary disease (COPD). Relationships between PA and the muscle mass and quality have been reported, but whether PA is more strongly associated with the muscle mass or quality remains unclear. METHODS: Baseline data from patients who participated in a randomized controlled trial evaluating the efficacy of providing individual target steps on step count were used. We investigated the relationship between PA measured by accelerometers and muscle mass, evaluated using the skeletal muscle index (SMI), cross-sectional area (CSA) of the pectoralis muscle, CSA of the dorsal muscle group (DMGCSA), and the muscle quality evaluated by phase angle (PhA) in 78 patients with COPD. RESULTS: The step count was correlated with PhA, and the duration of PA at ≥3.0 metabolic equivalents (METs) was correlated with DMGCSA, and PhA. The duration of behavior at 1.0-1.5 METs correlated with DMGCSA and PhA. A multiple regression analysis showed that PhA and modified Medical Research Council dyspnea scale, but not any parameters of muscle mass, were independently associated with step count and duration at ≥3.0 METs. The duration at 1.0-1.5 METs was independently associated with only DMGCSA. CONCLUSION: Although PA and Sedentary behavior (SB) was significantly correlated with both the muscle quality and mass, PA was more strongly influenced by the muscle quality than by muscle mass, whereas SB was strongly influenced by dorsal muscle group mass. CLINICAL TRIAL REGISTRATION: UMIN000046390.