OBJECTIVE: To investigate the association between physical activity and exercise-induced bronchoconstriction (EIB) in an urban population sample of schoolchildren, taking into account potential confounders such as asthma symptoms and overweight. METHODS: Children aged 10-12 years answered validated questionnaires on physical activity (Physical Activity and Lifestyle Questionnaire) and asthma symptoms (ISAAC questionnaire), and were categorized according to their body mass index (BMI). EIB (FEV(1) decrease from baseline ≥13%) was assessed by a standardized free running Exercise Challenge Test (ECT). RESULTS: Six hundred seven children completed the ECT. There were no differences among asthma groups (diagnosed asthma, asthma-related symptoms not diagnosed as asthma, no asthma-related symptoms) regarding total daily energy expenditure and time spent in mild (1.1-2.9 metabolic equivalents-METs), moderate (3-6 METs), and vigorous (>6 METs) activities. Only overweight/obese EIB-positive children had shorter duration of vigorous activity as compared to their EIB-negative or non-overweight/obese EIB-positive peers. Total daily energy expenditure and duration of mild- and moderate-intensity activity were negatively associated with EIB independently of BMI status or asthma-related symptoms. CONCLUSIONS: Decreased levels of physical activity are associated with EIB irrespectively of BMI status and asthma-related symptoms. Longitudinal studies are needed to confirm the negative impact of sedentary lifestyle on the development of EIB suggested by these findings.