title: Fat metabolism during exercise in patients with McArdle disease.
abstract: OBJECTIVE
  It is known that muscle phosphorylase deficiency restricts carbohydrate utilization, but the implications for muscle fat metabolism have not been studied. We questioned whether patients with McArdle disease can compensate for the blocked muscle glycogen breakdown by enhancing fat oxidation during exercise.
  
  
  METHODS
  We studied total fat oxidation by indirect calorimetry and palmitate turnover by stable isotope methodology in 11 patients with McArdle disease and 11 healthy controls. Cycle exercise at a constant workload of 50% to 60% of maximal oxygen uptake capacity was used to evaluate fatty acid oxidation (FAO) in the patients. Healthy controls were exercised at the same absolute workload.
  
  
  RESULTS
  We found that palmitate oxidation and disposal, total fat oxidation, and plasma levels of palmitate and total free fatty acids (FFAs) were significantly higher, whereas total carbohydrate oxidation was lower, during exercise in patients with McArdle disease vs healthy controls. We found augmented fat oxidation with the onset of a second wind, but further increases in FFA availability, as exercise continued, did not result in further increases in FAO.
  
  
  CONCLUSIONS
  These results indicate that patients with McArdle disease have exaggerated fat oxidation during prolonged, low-intensity exercise and that increased fat oxidation may be an important mechanism of the spontaneous second wind. The fact that increasing availability of free fatty acids with more prolonged exercise did not increase fatty acid oxidation suggests that blocked glycogenolysis may limit the capacity of fat oxidation to compensate for the energy deficit in McArdle disease.
authors.affiliation: Neuromuscular Research Unit, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark. rh10679@rh.dk
authors.forename: M C
authors.initials: MC
authors.lastname: Ørngreen
authors.forename: T D
authors.initials: TD
authors.lastname: Jeppesen
authors.forename: S Tvede
authors.initials: ST
authors.lastname: Andersen
authors.forename: T
authors.initials: T
authors.lastname: Taivassalo
authors.forename: S
authors.initials: S
authors.lastname: Hauerslev
authors.forename: N
authors.initials: N
authors.lastname: Preisler
authors.forename: R G
authors.initials: RG
authors.lastname: Haller
authors.forename: G
authors.initials: G
authors.lastname: van Hall
authors.forename: J
authors.initials: J
authors.lastname: Vissing
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D050260:Carbohydrate Metabolism; D015444:Exercise; D005227:Fatty Acids / Q000378:metabolism*; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D006012:Glycogen Storage Disease Type V / Q000378:metabolism / Q000503:physiopathology*; D006801:Humans; D018482:Muscle, Skeletal / Q000378:metabolism*; D010084:Oxidation-Reduction; D010168:Palmitates / Q000097:blood / Q000378:metabolism; D055815:Young Adult
chemical_list: D005227:Fatty Acids; D005230:Fatty Acids, Nonesterified; D010168:Palmitates