In patients with severe Chronic Obstructive Pulmonary Disease (COPD), exercise tolerance is severely impaired due to a ventilatory limitation, levelling off the intensity of exercise. This reduces the physiological benefit of pulmonary rehabilitation. In these patients, it is then proposed to add an Inspiratory Pressure Support (IPS) in order to increase the intensity and the duration of every training session. In a preliminary study, the investigators showed that IPS applied during an exhaustive cycling exercise allowed to prevent the onset of post-exercise quadriceps fatigue evaluated by the endurance time to isotonic quadriceps contractions (TlimQ).