Skeletal muscle dysfunction is common in people with COPD, although debate exists as to whether that's simply due to deconditioning, or something more. In people with severe COPD (GOLD stage III and IV), it's known that pulmonary rehabilitation improves some of these muscle abnormalities.
Vogiatzis et al report the results of putting 46 people with stable COPD (GOLD stage II, III, or IV in equal proportions) through a thrice-weekly, high-intensity exercise program for 10 weeks. They all then got a quadriceps muscle biopsy. Sure enough, exercise tolerance, quality of life scores, and salutary remodeling of skeletal muscle occurred in all groups. The new finding here, per the authors, is that those with less-severe COPD (GOLD II) have positive skeletal muscle changes from pulmonary rehab.
Of course, that's not surprising, and the problem isn't proving pulmonary rehab works, it's paying for it.
Vogiatzis I et al. Effect of Pulmonary Rehabilitation on Peripheral Muscle Fiber Remodeling in Patients With COPD in GOLD Stages II to IV. CHEST 2011;140:744-752.