A single session of Mechanical Insufflation-Exsufflation (with Cough AssistÒ) may improve airway flow and gas exchange in neuromuscular atrophy patients. The goal of this study is to confirm the beneficial effects of this treatment in a larger neuromuscular population, to study its mechanisms of action and to assess whether the effects observed persist over time. A better knowledge of this treatment should help to define its position in the respiratory management of neuromuscular patients.