title: Skeletal muscle endurance and muscle metabolism in patients with chronic heart failure.
abstract: BACKGROUND
  Alterations in skeletal muscle function are known to contribute to exercise intolerance in patients with chronic heart failure (CHF).
  
  
  OBJECTIVE
  To evaluate whether muscle isometric endurance can be objectively measured and whether it is related to skeletal muscle metabolism in CHF.
  
  
  METHODS
  Isometric endurance of the vastus lateralis, measured as time to fatigue (T(F)), was evaluated in 25 patients with CHF (55+/-8 years of age [mean +/- SD]) and 18 healthy subjects (HS) (62+/-6 years of age [mean +/- SD]). Median frequency of surface electromyography was obtained from spectral analysis using a fast Fourier transformation. Citrate synthase (CS), 3-hydroxyacyl-CoA dehydrogenase (HADH), hexokinase (HK) and phosphofructokinase (PFK) activities were determined from the right vastus lateralis muscle.
  
  
  RESULTS
  T(F) was lower in CHF patients than in HS (49+/-4 s and 80+/-7 s, respectively; P<0.01). Muscle fatigue was present at the end of the endurance test in both groups (median frequency breakpoint at mid-exercise for both groups [P<0.05]). CS (P<0.01) and HK (P<0.01) activities were lower in CHF patients than in HS, but PFK activity was higher (P<0.05). T(F) correlated significantly with CS (r=0.50), HADH (r=0.42), PFK (r=-0.47) and HK (r=0.41) activities and the PFK/CS ratio (r=-0.39) when both groups were considered, and with HADH (r=0.47) and PFK (r=-0.57) activities for the CHF group alone (all P<0.05).
  
  
  CONCLUSIONS
  These results suggest that isometric endurance of the vastus lateralis muscle is reduced in patients with CHF and that it is related to a reduced muscle oxidative capacity.
authors.affiliation: Centre de recherche, Hôpital Laval, Institut universitaire de cardiologie et de pneumologie, Université Laval, Ste-Foy, Québec, Canada.
authors.forename: Patrice
authors.initials: P
authors.lastname: Brassard
authors.forename: Francois
authors.initials: F
authors.lastname: Maltais
authors.forename: Martin
authors.initials: M
authors.lastname: Noel
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Doyon
authors.forename: Pierre
authors.initials: P
authors.lastname: LeBlanc
authors.forename: Joakim
authors.initials: J
authors.lastname: Allaire
authors.forename: Clermont
authors.initials: C
authors.lastname: Simard
authors.forename: Marie-Hélène
authors.initials: MH
authors.lastname: Leblanc
authors.forename: Paul
authors.initials: P
authors.lastname: Poirier
authors.forename: Jean
authors.initials: J
authors.lastname: Jobin
mesh_terms: D049628:Body Size / Q000502:physiology; D015444:Exercise / Q000502:physiology; D005260:Female; D006333:Heart Failure / Q000378:metabolism* / Q000503:physiopathology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008875:Middle Aged; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000503:physiopathology*; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology