Muscle strength and exercise kinetics in COPD patients with a normal fat-free mass index are comparable to control subjects

Study objective: This study was designed to investigate the extent of clinical muscle dysfunction in stable patients with COPD who were attending an out-patient pulmonary clinic compared with that of age-matched control subjects without COPD. Design and subjects: Respiratory muscle and hand grip strength, steady-state O-2 kinetics, and body composition were measured in 32 patients with COPD (19 women) [mean (+/- SD) FEV1, 38 +/- 11% predicted] and 36 age-matched control subjects (13 women). Results: Measurements of handgrip force (mean, 97 +/- 32% vs 106 +/- 26% predicted, respectively), maximal expiratory pressure (mean, 57 +/- 33% vs 61 +/- 22% predicted, respectively), steady-state O-2 kinetics (mean tau, 72 +/- 34 s vs 78 +/- 37 s, respectively) and steady-state CO2 kinetics (mean tau, 77 +/- 38 s vs 65 +/- 32 s, respectively) at submaximal exercise were similar in patients and control subjects. All the subjects, except for one female COPD patient, had a normal fat-free mass index (FFMI), although on average the FFMI was lower in male patients (19.8 +/- 2.8) than in male control subjects (23.0 +/- 2.8; p < 0.01). Conclusions: In patients with COPD who were attending a regular outpatient pulmonary clinic, there was no evidence of reduced upper extremity and expiratory muscle strength or prolonged O-2 and CO2 kinetics during isowork submaximal cardiopulmonary exercise compared to healthy, age-matched control subjects. Also, a normal body composition was found in nearly all COPD patients. This argues against the existence of a clinically significant systemic myopathy in most stable patients with severe COPD and normal FFMI.