title: Impaired mitochondrial function and reduced energy cost as a result of muscle damage.
abstract: OBJECTIVE
  Although it has been largely acknowledged that isometric neuromuscular electrostimulation (NMES) exercise induces larger muscle damage than voluntary contractions, the corresponding effects on muscle energetics remain to be determined. Voluntary exercise-induced muscle damage (EIMD) has been reported to have minor slight effects on muscle metabolic response to subsequent dynamic exercise, but the magnitude of muscle energetics alterations for NMES EIMD has never been documented.
  
  
  METHODS
  ³¹P magnetic resonance spectroscopy measurements were performed in 13 young healthy males during a standardized rest-exercise-recovery protocol before (D0) and 2 d (D2) and 4 d (D4) after NMES EIMD on knee extensor muscles. Changes in kinetics of phosphorylated metabolite concentrations (i.e., phosphocreatine [PCr], inorganic phosphate [Pi], and adenosine triphosphate [ATP]) and pH were assessed to investigate aerobic and anaerobic rates of ATP production and energy cost of contraction (Ec).
  
  
  RESULTS
  Resting [Pi]/[PCr] ratio increased at D2 (+39%) and D4 (+29%), mainly owing to the increased [Pi] (+43% and +32%, respectively), whereas a significant decrease in resting pH was determined (-0.04 pH unit and -0.03 pH unit, respectively). PCr recovery rate decreased at D2 (-21%) and D4 (-23%) in conjunction with a significantly decreased total rate of ATP production at D4 (-18%) mainly owing to an altered aerobic ATP production (-19%). Paradoxically, Ec was decreased at D4 (-21%).
  
  
  CONCLUSIONS
  Overall, NMES EIMD led to intramuscular acidosis in resting muscle and mitochondrial impairment in exercising muscle. Alterations of noncontractile processes and/or adaptive mechanisms to muscle damage might account for the decreased Ec during the dynamic exercise.
authors.affiliation: 1Aix-Marseille University, Centre National de la Recherche Scientifique (CNRS), Centre de Résonance Magnétique Biologique et Médicale (CRMBM), Unité Mixte de Recherche 7339, Marseille, FRANCE; 2Assistance Publique des Hôpitaux de Marseille (APHM), Sainte Marguerite Hospital, Department of Rheumatology, Marseille, FRANCE; and 3APHM, La Timone Hospital, Centre d'Exploration Métabolique par Résonance Magnétique (CEMEREM), Imaging Center, Marseille, FRANCE.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Fouré
authors.forename: Jennifer
authors.initials: J
authors.lastname: Wegrzyk
authors.forename: Yann
authors.initials: Y
authors.lastname: Le Fur
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Mattei
authors.forename: Hélène
authors.initials: H
authors.lastname: Boudinet
authors.forename: Christophe
authors.initials: C
authors.lastname: Vilmen
authors.forename: David
authors.initials: D
authors.lastname: Bendahan
authors.forename: Julien
authors.initials: J
authors.lastname: Gondin
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007719:Knee Joint / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000378:metabolism*; D063806:Myalgia / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D055815:Young Adult
chemical_list: D010710:Phosphates; D010725:Phosphocreatine; D000255:Adenosine Triphosphate