Inclusion Criteria:  7-10 years of age The ability to ride stationary bicycles as assessed by the parents.  Exclusion Criteria:  Immobility An acute febrile or upper respiratory illness in the last 2 weeks The use systemic or inhaled steroids or antiepileptic drugs in the previous month Inhaled bronchodilator use in the previous 24 hours A chronic lung illness (with the exception of BPD and asthma) Congenital cardiac defect (with the exception of atrial septal defect and patent foramen ovale).