Exercise oxidative skeletal muscle metabolism in adolescents with cystic fibrosis

Introduction: Patients with Cystic Fibrosis (CF) are reported to have limited exercise capacity. There is no consensus about a possible abnormality in skeletal muscle oxidative metabolism in CF. Our aim is to test the hypothesis that abnormalities in oxygenation and/or muscle oxidative metabolism contribute to exercise intolerance in adolescents with mild CF. Methods: Ten adolescents with CF (12-18 years of age, FEV₁>80%_pred, resting oxygen saturation > 94%) and ten healthy age-matched controls (HC) were tested with supine cycle ergometry using near-infrared spectroscopy (NIRS) and ³¹Phosphorus magnetic resonance spectroscopy (³¹P MRS) to study skeletal muscle oxygenation and oxidative metabolism during rest, exercise and recovery. Results: No statistically significant (p>0.1) differences in peak workload and peak oxygen uptake per kilogram lean body mass were found between CF and HC. No differences were found between CF and HC in bulk changes of quadriceps phosphocreatine (PCr) (p = .550) and inorganic phosphate (Pi) (p = .896) content and pH (p = .512) during symptom limited exercise. Furthermore, we found statistically identical kinetics for PCr resynthesis during recovery for CF and HC (p = .53). No statistically significant difference in peak exercise arbitrary unit for total haemoglobin content (tHb_AU) was found between CF and HC (p = .66). Discussion: The results of this study provide evidence that in patients with mild CF and a stable clinical status (without signs of systemic inflammation and /or chronic PA colonisation), no intrinsic metabolic constraints and/or abnormalities in oxygenation and/or muscle oxidative metabolism contribute to exercise intolerance.

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