Skeletal muscle weakness, exercise tolerance and Physical activity in adults with Cystic Fibrosis

¹ Respiratory Rehabilitation and Respiratory Division, University Hospital, Leuven, Leuven, Belgium; and Faculty of Kinesiology and Rehabilitation Sciences, Dept of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium.
² Faculty of Kinesiology and Rehabilitation Sciences, Dept of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium.; and Cystic Fibrosis Centre, Respiratory Division, University Hospital, Leuven, Leuven, Belgium
³ Faculty of Kinesiology and Rehabilitation Sciences, Dept of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium.
⁴ Respiratory Rehabilitation and Respiratory Division, University Hospital, Leuven, Leuven, Belgium
⁵ Cystic Fibrosis Centre, Respiratory Division, University Hospital, Leuven, Leuven, Belgium

^* To whom correspondence should be addressed. E-mail: Thierry.Troosters{at}med.kuleuven.be.

	Abstract

The aim of this study was to investigate the prevalence of muscle weakness and the importance of physical inactivity in CF and its relation to exercise tolerance and muscle strength.

We studied exercise tolerance, skeletal and respiratory muscle strength in a large group of adults with CF (n=64, age 26±8, FEV₁ 65±19%pred) and in 20 age matched controls. Physical activity (PA) was assessed in 20 patients and all controls.

Quadriceps muscle weakness was present in 56% of the patients. Peak oxygen consumption and six minute walking distance was below normal in 89% and 75% of patients, respectively. Respiratory muscle strength was normal. The differences remained after correcting for PA. Quadriceps force was correlated to the six minute walking distance (partial R2 0.08 p<0.01) but not to peak oxygen consumption. "Mild" PA (>3 Metabolic equivalents, METS) and the number of steps overlapped with controls, but patients had less moderate PA (above 4.8METS). Moderate PA was related to VO₂peak (R=0.56; p<0.01) and Quadriceps force (R=0.48; p=0.03).

Conclusion: Skeletal muscle weakness and exercise intolerance are prevalent in CF. Physical inactivity is a factor significantly contributing to exercise tolerance and skeletal muscle force in adults with Cystic Fibrosis, but these impairments are in excess to that expected from physical inactivity only.