Electrophysiologic changes during exercise testing in patients with chronic obstructive pulmonary disease.

To determine whether skeletal muscle is involved in the exercise limitation of chronic obstructive pulmonary disease (COPD), we investigated electrical adaptations in muscle during incremental cycling exercise testing. Changes in quadriceps activity were compared using surface electromyography (SEMG) and motor point stimulation in ten COPD patients and ten healthy subjects. Patients showed significantly lower exercise capacity, and M-wave duration was increased from exercise onset (P < 0.