Several studies have demonstrated relatively moderate increase in Pdi during exhaustive exercise in COPD patients. The present study was designed to determine whether the small increase in Pdi is due to a central inhibition of respiratory drive, or an inability of the diaphragm to develop pressure. Diaphragm electrical activation (Edi) and transdiaphragmatic (Pdi) pressure were measured in 19 patients with severe COPD using an esophageal catheter. End-expiratory lung volume (EELV) was assessed by inspiratory capacity (IC) maneuvers. Maximal voluntary Edi (Edimax) was obtained during these maneuvers. EELV increased during exercise (p < 0.001) causing end-inspiratory lung volume to attain 98 +/- 5% of TLC at end-exercise. Pdi at rest was 8.4 +/- 2.6 cm H2O. Edi was 19 +/- 4% of Edimax at rest and increased progressively during exercise (p < 0.001) to reach 78 +/- 3% of Edimax at end-exercise. In conclusion, dynamic hyperinflation during exhaustive exercise in patients with COPD, reduces diaphragm pressure generating capacity, promoting near maximal levels of diaphragm activation without evidence of central inhibition.