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Muscle Function and Resting Energy Expenditure in Female Athletes with Cystic Fibrosis

Division of Respiratory Medicine, Hospital for Sick Children, Toronto, and Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada; James Fairfax Institute for Nutrition, and Department of Respiratory Medicine, Childrens Hospital at Westmead, Westmead; and Rayscan Radiology, Liverpool, Sydney, Australia

Correspondence and requests for reprints should be addressed to H.C. Selvadurai, M.D., Department of Respiratory Medicine, Hospital for Sick Children, 555 University Avenue, Toronto, ON, M5G 1X8 Canada. E-mail: Hiran.Selvadurai{at}sickkids.ca

The pathophysiology of impaired exercise tolerance in patients with cystic fibrosis (CF) is not completely understood. The objective of this study was to compare exercise ability (at clinical and cellular levels) and resting energy expenditure in female athletes with CF compared with matched control subjects. Sixteen subjects and matched control subjects participated in the study. The girls with CF not only had a significantly greater resting energy expenditure (7.6% higher; p < 0.05), their habitual daily activity was also significantly greater than that of control subjects (15% greater; p < 0.01). Peak aerobic capacity was similar in both groups. However, peak anaerobic power was 20% less (p < 0.05) in girls with CF. The ³¹P magnetic resonance spectroscopy studies demonstrated that there were no differences between the groups at rest, but at 25% total work output the girls with CF were less acidotic (CF, pH 6.99 [0.06]; control subjects, 6.90 [0.05]) and had a significantly lower inorganic phosphorus-to-phosphocreatine ratio (CF, 0.34 [0.07]; control subjects, 0.41 [0.08]). These differences continued to increase to maximal exercise. This study demonstrates that in spite of normal lung function and good nutritional status, females athletes with CF still had significant deficiencies in some measures of fitness and muscle metabolism compared with healthy athletes.

Key Words: exercise tolerance • aerobic capacity • anaerobic power

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