Methods We would compare patients (adults and children) who receive intravenous antibiotherapy for an acute exacerbation, with patients who receive elective intravenous antibiotherapy (decline in lung function without exacerbation). We will also compare hospitalised patients who receive specific exercise training, with patients who follow their antibiotherapy at home without specific exercise training. We will have a stable patients group as control. To evaluate muscular strength we plan to measure quadriceps force at the beginning of the cure and at the end with a functional test, the 1-minute Sit-to-Stand test and a strength (isometric) test, with the Microfet2dynamometer. Those test are not invasive, easy to realise and have already been used in other studies (Ozalevli, 2005). We will quantify the physical activity level of the patients with an accelerometer that they will carry during 72 hours, during the first week of the treatment.