Abstract
BACKGROUND: Children with uncontrolled asthma are less tolerant to exercise due to ventilatory limitation, exercise-induced bronchoconstriction (EIB), or physical deconditioning. The contribution of these factors in children with controlled mild-to-moderate asthma is unknown. OBJECTIVE: To explore the underlying mechanisms of reduced exercise capacity in children with controlled mild-to-moderate asthma. METHODS: This was a cross-sectional study of 45 children and adolescents (age 8-18 years) with controlled mild-to-moderate asthma (asthma control test score 21-25) and 61 age-matched healthy controls. All participants completed a physical activity questionnaire and performed spirometry and cardiopulmonary exercise testing (CPET; maximal incremental protocol). Spirometric indices and CPET parameters were compared between the two groups. The effect of EIB (FEV(1) decrease >10% post CPET), ventilatory limitation and physical deconditioning on maximum oxygen uptake (O(2)peak), was assessed by multivariable linear regression. RESULTS: 62.2% of children with asthma and 29.5% of controls (P = 0.002) were categorized as inactive. Reduced exercise capacity (O(2)peak <80%) was noted in 53.3% of asthmatics and 16.4% of controls (P < 0.001). EIB was documented in 11.1% of participants with asthma. Physical deconditioning was noted in 37.8% of children with asthma and in 14.8% of controls (P = 0.013). Physical deconditioning emerged as the only significant determinant of O(2)peak, irrespective of asthma diagnosis, body mass index, ventilatory limitation and EIB. CONCLUSION: Children with controlled mild-to-moderate asthma are less tolerant to strenuous exercise than their healthy peers. The decreased exercise capacity in this population should mainly be attributed to physical deconditioning, while the contribution of ventilatory limitation and EIB is rather small.