Muscle Function and Physical Activity in the Modern Era of Cystic Fibrosis

Measurement of isometric quadriceps strength (expressed in Newton), performed at René Sabran Hospital (as part of routine clinical practice for people with CF)

Cystic fibrosis (CF) is characterized by various extrapulmonary manifestations, including
 altered skeletal muscle function, with both quantitative (e.g. reduced muscle mass) and
 qualitative (e.g. impaired oxidative function) impairments that may have a negative impact on
 exercise tolerance and quality of life. These abnormalities have traditionally been related
 to disease (e.g. systemic inflammation) or behavioral factors (e.g. increased physical
 inactivity). However, most of the studies that observed these abnormalities and tried to shed
 light on the underlying factors were either small or conducted before the widespread of CFTR
 (Cystic fibrosis transmembrane conductance regulator) modulators that have profound impact on
 the trajectory of the disease. While several studies suggested that the major recent
 improvements in therapeutics, including highly effective CFTR modulators, may have positive
 effects on skeletal muscle function, either directly (e.g. improved mitochondrial function)
 or indirectly (e.g. reduction in physical inactivity), no studies to date have thoroughly
 investigated this issue in a representative sample of people with CF. The absence of recent
 data on muscle function and physical activity levels casts doubt on the relevance of
 recommendations on exercise training in this population that were published before the
 widespread use of highly effective CFTR modulators. This study aims to compare muscle
 function, measured according to the latest recommendations of the European Cystic Fibrosis
 Society (Saynor et al., 2023), and physical activity of children and adults with CF under
 CFTR modulators, compared to age- and sex-matched healthy individuals. We hypothesize that
 the strength, endurance, muscle power, and physical activity levels of individuals with
 cystic fibrosis, treated with CFTR modulators, remain reduced compared to healthy
 individuals.