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Energy metabolism during anaerobic exercise in children with cystic fibrosis and asthma. Med. Sci. Sports Exerc., Vol. 31, No. 9, pp. 1242-1249, 1999.The nature of a child's daily physical activity requires both aerobic and anaerobic energy metabolism. Aerobic exercise becomes compromised with advancing airway obstruction in children with cystic fibrosis (CF) and asthma (AS). Whether children with CF will have altered metabolic responses to supramaximal exercise when compared with asthmatics or healthy controls is still undetermined.Twenty-five children with CF, 22 with AS, and 23 healthy controls (CN) performed an incremental graded aerobic and Wingate anaerobic test (WAnT) on a cycle ergometer. Analysis of gas exchange and ventilatory data was collected and averaged every 5 s to estimate ventilatory kinetics and energy system contributions during both tests.The CF and AS groups had mild lower airway obstruction (FEF25-75% < 80%) as compared with the CN. All three groups demonstrated similar anaerobic (mean and peak power during the WAnT) and aerobic exercise performance (peak oxygen consumption). In contrast to the AS or CN groups, children with CF used a lower percentage of their peak V̇O2 and V̇E during each phase of the WAnT, suggesting a preferential use of ATP/phosphocreatine and glycolytic energy stores compared with aerobic pathways. Greater reliance on anaerobic pathways during the WAnT in children with CF could be due to the physiologic sequelae underlying chronic obstructive lung disease.Oxygen uptake kinetics appeared similar for all three groups. Although the energy needed to perform the WAnT can be met by subjects with CF, abnormalities in energy metabolism may exist for this group during exercise.