Upper and Lower Limb Skeletal Muscle Mass Index as a Novel Evaluation Index in Patients with Chronic Obstructive Pulmonary Disease.

Objectives: The objective of this study was to examine the relationships and usefulness of physical activity, physical performance, and physical function in patients with chronic obstructive pulmonary disease (COPD), focusing on 2 newly proposed skeletal muscle indices: the upper limb skeletal muscle mass index (USMI) and lower limb skeletal muscle mass index (LSMI). Methods: A total of 80 stable patients with COPD who participated in outpatient pulmonary rehabilitation at Osaka Fukujuji Hospital were enrolled. The primary measurements were the USMI, LSMI, and skeletal muscle index (SMI). The explanatory measurements included physical activity, incremental shuttle walking distance (ISWD), quadriceps strength, handgrip strength, the Nagasaki University Respiratory Activities of Daily Living Questionnaire, and pulmonary function. Pearson’s correlation coefficient and stepwise multiple regression analysis were used for the statistical analyses. Results: USMI showed no significant correlations with physical activity parameters or ISWD. In contrast, LSMI was significantly correlated with weekly exercise volume (r=0.42, p<0.01), daily exercise volume (r=0.42, p<0.01), time spent in activities ≥3 metabolic equivalents of task (r=0.40, p<0.01), and ISWD (r=0.46, p<0.01). Multiple regression analysis identified ISWD as an independent factor for USMI, LSMI, and SMI. Conclusions: This study demonstrated that LSMI, similar to SMI, was associated with physical activity and exercise capacity in patients with COPD. These findings highlight the importance of evaluating, maintaining, and strengthening lower limb skeletal muscle mass and suggest that LSMI may serve as a useful clinical evaluation index.