Absence of calf muscle metabolism alterations in active cystic fibrosis adults with mild to moderate lung disease

Abstract

Background: Specific alterations in skeletal muscle related to genetic defects may be present in adults with cystic fibrosis (CF). Limb muscle dysfunction may contribute to physical impairment in CF.

Aims and objectives: We hypothesized that adults with CF would have altered calf muscle metabolism during exercise.

Methods: Fifteen adults with CF and fifteen healthy controls matched for age, gender and physical activity performed a maximal cycling test and an evaluation of calf muscle energetics by ³¹P magnetic resonance spectroscopy before, during and after plantar flexions to exhaustion.

Results: Maximal cycling test revealed lower exercise capacities in CF (VO_2peak 2.44±0.11 vs. 3.44±0.23L·Min^-1, P=0.03). At rest, calf muscle phosphorus metabolites and pHi were similar in CF and controls (P>0.05). Maximal power output during plantar flexions was significantly lower in CF compared to controls (7.8±1.2 vs. 6.6±2.4W; P=0.013). At exhaustion, PCr concentration was similarly reduced in both groups (CF -33±7%, controls -34±6%, P=0.44), while PCr degradation at identical absolute workload was greater in CF patients (P=0.04). These differences disappeared when power output was normalized for differences in calf size (maximal power output: 0.10±0.02 vs. 0.10±0.03W/cm²; P=0.87). Pi/PCr ratio and pHi during exercise as well as PCr recovery after exercise were similar between groups.

Conclusion: Similar metabolic calf muscle responses during exercise and recovery were found in CF adults and controls. Overall, muscle anabolism rather than specific metabolic dysfunction may be critical regarding muscle function in CF.

Keywords: (31)P MR spectroscopy; Cystic fibrosis; Exercise tolerance; Muscle metabolism.