The investigators know that peripheral muscle weakness and exercise intolerance are prevalent (56%) in cystic fibrosis (Trooster et al, 2009). Physical inactivity is likely to be an important underlying factor. Those conditions are associated with a poor prognosis (Nixon et al, 1992). The effect of intravenous antibiotherapy on peripheral muscle and physical activity remains unclear.

The aim of the study is to evaluate the impact of intravenous antibiotherapy on peripheral muscular strength in patients with cystic fibrosis (adults and children) who receive intravenous antibiotherapy for an acute exacerbation or electively (decline in lung function without exacerbation).

Background Peripheral muscle weakness and exercise intolerance are prevalent (56%) in cystic fibrosis (Trooster et al, 2009). Physical inactivity is likely to be an important underlying factor. Those conditions are associated with a poor prognosis (Nixon et al, 1992). The effect of intravenous antibiotherapy on peripheral muscle and physical activity remains unclear. Wieboldt et al showed that quadriceps strength at the hospital admission for an exacerbation was lower than before and one month after hospitalisation while Burtin et al showed that individual changes in quadriceps force were correlated with daily time spent activities of at least moderate intensity (Wieboldt et al, 2012; Burtin et al, 2013). The effect of intravenous antibiotherapy itself is poorly known in cystic fibrosis. Moreover, they did not study the impact on muscular strength of hospitalisation versus home treatment. In contrast, in COPD, it is well known that exacerbations are associated with a decline of muscle mass and strength and that repeated exacerbations lead to a more rapid decrease in fat free mass (Spruit et al, 2003; Jones et al, 2015; Joppa et al, 2016).

Hypothesis We think that exacerbations aggravate factors underlying muscle weakness as physical inactivity, systemic inflammation and anabolic status. Moreover, hospitalisation itself might be a reason of inactivity as patients spent all the day inside their room compared to patients who follow their treatment at home and continue their usual life.

Aim The aim of our study is to evaluate the impact of an intravenous antibiotherapy on peripheral muscular strength in patients with cystic fibrosis.

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.

Inclusion Criteria:

- patients with cystic fibrosis following the definition of Rosentein et al (1997), who undergo an intravenous antibiotic cure for an acute exacerbation or electively since we notice a decline of respiratory lung function

Exclusion Criteria:

• orthopaedic conditions interfering with mobility or the assessment of skeletal muscle force,
• a pregnancy,
• a pulmonary graft
• a negative response for the informed consent.