Functional capacity and body composition in chronic obstructive pulmonary disease: a cross-sectional study of their relationship with disease severity

Chronic obstructive pulmonary disease (COPD) affects the body systemically, not just the lungs — patients often experience diminished functional capacity, greater symptom burden, and loss of muscle mass. This study set out to examine how functional capacity relates to body composition in patients with COPD. We evaluated 101 COPD patients followed at a single pulmonology outpatient clinic in this cross-sectional study. Functional capacity was measured with the Duke Activity Status Index (DASI), from which estimated peak oxygen consumption (VO 2 peak) was derived; symptom burden was captured with the COPD Assessment Test (CAT) and the modified Medical Research Council (mMRC) scale, and body composition was determined via bioelectrical impedance analysis (BIA). Patients were grouped by GOLD 1–4 stage and early-stage (GOLD 1–2) patients were compared against advanced-stage (GOLD 3–4) patients. The mean age was 64.8 ± 10.1 years, and 76.2% of patients were male. DASI scores were lower and CAT and mMRC scores were higher across GOLD stages (all p < 0.001). DASI-derived estimated VO2peak was not an independent functional outcome. Advanced-stage patients had lower FFMI after age and sex adjustment (difference − 1.53 kg/m², 95% CI − 2.52 to − 0.54; p = 0.003); unadjusted fat mass and fat percentage did not differ significantly. In multivariable models with HC3 robust standard errors, DASI was associated with age, FEV₁ (% predicted), albumin and, marginally, male sex ( p = 0.0495; R²=0.377). Only FEV₁ was associated with CAT in the full-sample model (R²=0.281); FFMI was not associated with either score. Exploratory AUCs were 0.720 (95% CI 0.618–0.821) for DASI and 0.717 (0.608–0.827) for CAT. Cronbach’s alpha was 0.893 for DASI and 0.894 for CAT. More advanced COPD was associated with lower functional capacity, greater symptom burden and less favorable muscle-related body composition, but not with fat mass. The DASI, CAT and BIA may complement spirometry in COPD follow-up; longitudinal multicentre studies are needed to confirm their clinical utility. Not applicable.