Am. J. Respir. Crit. Care Med., Volume 159, Number 3, March 1999, 748-754

Peripheral Muscle Weakness and Exercise Capacity in Children with Cystic Fibrosis

KEES de MEER, VINCENT A. M. GULMANS, and JOHAN van der LAAG

Departments of Gastroenterology, Physiotherapy, and Respiratory Diseases, University Children's Hospital "Het Wilhelmina Kinderziekenhuis", Utrecht, The Netherlands

Exercise intolerance in cystic fibrosis (CF) is attributed to diminished nutritional and pulmonary function. We studied the pathophysiology of such intolerance in relation to muscle force and fat-free mass (FFM), in 15 children with moderately severe symptoms of CF (FEV₁ < 80% predicted and/or weight for age < 1 SD of reference median), 13 children with mild symptoms of CF (FEV₁ and weight above these thresholds), and 13 healthy controls. Cycle maximal workload (Wmax) and O₂max were assessed. Maximal peripheral muscle force was measured, and FFM was calculated from skinfolds. Patients with mild CF, as compared with matched controls, had lower values of Wmax per kilogram of FFM (3.9 ± 0.5 versus 4.6 ± 0.3 W/kg [mean ± SD], respectively; difference = 0.7 [95% CI = 0.4 to 1.1]), and diminished maximal muscle force (2.7 ± 0.4 kN versus 3.1 ± 0.7 kN; difference = 0.44 [95% CI = 0.03 to 0.87]), but similar O₂max. Patients with moderate CF had lower FFM, muscle force, and exercise tolerance than did the other groups. Oxygen cost of work was elevated in both groups of CF patients. Muscle force showed a strong positive correlation with Wmax in patients and controls, with disproportionately lower regression slopes in the CF patients. In children with CF, muscle force is decreased and associated with diminished maximal work load, even in the absence of diminished pulmonary or nutritional status.

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