BACKGROUND: Skeletal muscle wasting is related to muscle dysfunction, exercise intolerance, and increased mortality risk in patients with COPD. STUDY OBJECTIVES: The aims of this study were to investigate the effects of whole-body exercise training on body composition in normal-weight patients with COPD, and to study the relationship between changes in body composition and functional capacity. SETTING AND PARTICIPANTS: Fifty patients with COPD (FEV(1), 39% of predicted [SD, 16]) admitted to the pulmonary rehabilitation center at Hornerheide, and 36 healthy age-matched control subjects (for baseline comparison) were included. INTERVENTIONS: Patients participated in a standardized inpatient exercise training program consisting of daily submaximal cycle ergometry, treadmill walking, weight training, and gymnastics during 8 weeks. MEASUREMENTS: Fat-free mass (FFM) was measured by bioelectrical impedance analysis. None of the patients met the criteria for nutritional supplementation (body mass index </= 21, or FFM index </= 15 kg/m(2) in women and </= 16 kg/m(2) in men). Exercise capacity was measured using incremental cycle ergometry. Isokinetic quadriceps strength was measured with a Biodex dynamometer (Biodex Medical Corporation; Shirley, NY). RESULTS: At baseline, patients were characterized by a significantly lower FFM than the control subjects. Age and FFM were independent predictors of skeletal muscle function and exercise capacity in patients. After rehabilitation, weight (72.4 +/- 9.8 to 73.0 +/- 9.4 kg, p < 0.05) significantly increased, as a result of increased FFM (52.4 +/- 7.3 to 53.4 +/- 7.7 kg, p < 0.05), while fat mass (20.0 +/- 6.1 to 19.6 +/- 5.7 kg) tended to decrease. Peak work rate (63 +/- 29 to 84 +/- 42 W, p < 0.001), maximal oxygen consumption (O(2)max) [1,028 +/- 307 to 1,229 +/- 421 mL/min, p < 0.001], and isokinetic quadriceps strength (82.5 +/- 36.4 to 90.3 +/- 34.9 Newton-meters, p < 0.05) all improved. Changes in FFM were proportionally smaller than functional improvements, and were related to changes in O(2)max (r = 0.361, p < 0.05), but not to other changes in functional capacity. CONCLUSIONS: Intensive exercise training per se is able to induce an anabolic response in normal-weight patients with COPD classified into Global Initiative for Chronic Obstructive Lung Disease stages III-IV. Improvements in exercise performance and muscle function are proportionally larger than increases in FFM.