title: Accurate work-rate measurements during in vivo MRS studies of exercising human quadriceps.
abstract: BACKGROUND
  Given that we have reached a point in the field of muscle energetics where absolute measurements are warranted to take the area forward, we designed an ergometer, including two force and two displacement transducers, allowing dynamic and isometric knee extension within a MR system and accurate measurements of power output.
  
  
  METHODS
  On the basis of repeated measurements, the force and displacement transducers accuracy was 1% for values ranging from 0 to 394 N and 4% for values ranging from 0 to 20 cm. In addition, measurements were not affected by magnetic field. MRS experiments in exercising muscle were conducted in eight subjects. They performed two standardized dynamic alternate leg extension exercises (25 and 35% of MVC) while the corresponding metabolic changes were measured using (31)P-MRS.
  
  
  RESULTS
  The mean power output produced during both exercises were 63 +/- 16 and 81 +/- 15 W while the eccentric work was reduced i.e. 12 +/- 14 and 21 +/- 6 W for the moderate and heavy exercise respectively. The corresponding metabolic changes were significant with a 20-40% PCr depletion and an end of exercise pH ranging from 0.02 to 0.70 pH units.
  
  
  CONCLUSIONS
  Overall, the present ergometer allows quadriceps exercise in a MR system and should be useful for future metabolic studies for which reliable and absolute quantification of power output is warranted.
authors.affiliation: Centre de Resonance Magnetique Biologique et Medicale, UMR CNRS 6612, Faculté de Médecine de Marseille, 27Bd Jean Moulin, 13005 Marseille, France.
authors.forename: Gwenael
authors.initials: G
authors.lastname: Layec
authors.forename: Aurélien
authors.initials: A
authors.lastname: Bringard
authors.forename: Christophe
authors.initials: C
authors.lastname: Vilmen
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Micallef
authors.forename: Yann Le
authors.initials: YL
authors.lastname: Fur
authors.forename: Stéphane
authors.initials: S
authors.lastname: Perrey
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Cozzone
authors.forename: David
authors.initials: D
authors.lastname: Bendahan
mesh_terms: D016552:Ergometry / Q000379:methods; D015444:Exercise / Q000502:physiology*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D052097:Quadriceps Muscle / Q000502:physiology*