Introduction:

Impaired exercise capacity is common in children with cystic fibrosis (CF), and has been associated with poor quality of life and prognosis. It seems likely that lung function plays a role, but indices of nutritional status and habitual physical activity may also be important. This study examined the influence of these factors on exercise capacity in children with CF and healthy peers.

Methods:

31 children with CF (age 9.6 +/- 0.8 yrs, mean FEV₁ 78% predicted) and 24 control subjects (11.9 +/- 0.7 yrs) were tested on nutritional measures (BMI %, skinfolds, mid-arm circumference) and past year physical activity (mean hr/wk and mean MET hr/wk). Exercise capacity was defined as the heart rate change during the 3-minute step test. T- tests determined between group differences and stepwise multiple regression analysis determined predictors of exercise capacity within each group.

Results:

The CF group had lower FEV₁ and BMI % than their peers (33 +/- 5 vs. 59 +/- 6%), but did not differ in other nutritional indices, exercise capacity, or hr/week of physical activity. Intensity of physical activity was significantly lower for the CF group (31.4 +/- 5.9 vs. 52.0 +/- 6.7 METhr/wk). Activity score (hours/wk) and BMI % significantly predicted exercise capacity in the CF group (R² = 0.25), while subscapular skinfold and BMI % predicted exercise capacity for the controls (R² = 0.18).

Conclusions:

Nutritional indices and intensity of physical activities were predictive of exercise capacity in children with CF, while lung function was not. In addition, these children participate in less vigorous physical activities than their peers. These findings suggest that encouraging physical activity, particularly more intense activities, could improve exercise capacity. The poor prediction outcome suggests that factors other than lung function contribute to exercise capacity. Future research should attempt to define these factors.