title: Mitochondrial Coupling and Contractile Efficiency in Humans with High and Low V˙O2peaks.
abstract: BACKGROUND
  Endurance training elicits tremendous adaptations of the mitochondrial energetic capacity. Yet, the effects of training or physical fitness on mitochondrial efficiency during exercise are still unclear. Accordingly, the purpose of the present study was to examine in vivo the differences in mitochondrial efficiency and ATP cost of contraction during exercise in two groups of adults differing in their aerobic capacity.
  
  
  METHODS
  We simultaneously assessed the ATP synthesis and O2 fluxes with P-magnetic resonance spectroscopy and pulmonary gas exchange measurements in seven endurance-trained (ET, V˙O2max: 67 ± 8 mL·min⁻¹·kg⁻¹) and seven recreationally active (RA, V˙O2max: 43 ± 7 mL·min⁻¹·kg⁻¹) subjects during 6 min of dynamic moderate-intensity knee extension.
  
  
  RESULTS
  The ATP cost of dynamic contraction was not significantly different between ET and RA (P > 0.05). Similarly, end-exercise O2 consumption was not significantly different between groups (ET: 848 ± 155 mL·min⁻¹ and RA: 760 ± 131 mL·min⁻¹, P > 0.05). During the recovery period, the PCr offset time constant was significantly faster in ET compared with RA (ET: 32 ± 8 s and RA: 43 ± 10 s, P < 0.05), thus indicating an increased mitochondrial capacity for ATP synthesis in the quadriceps of ET. In contrast, the estimated mitochondrial efficiency during exercise was not significantly different (P/O, ET: 2.0 ± 1.0 and RA: 1.8 ± 0.4, P > 0.05). Consequently, the higher mitochondrial capacity for ATP synthesis in ET likely originated from an elevated mitochondrial volume density, mitochondria-specific respiratory capacity, and/or slower postexercise inactivation of oxidative phosphorylation by the parallel activation mechanism.
  
  
  CONCLUSIONS
  Together, these findings reveal that 1) mitochondrial and contractile efficiencies are unaltered by several years of endurance training in young adults, and 2) the training-induced improvement in mitochondrial energetic capacity appears to be independent from changes in mitochondrial coupling.
authors.affiliation: 1Aix-Marseille University, Centre National de la Recherche Scientifique, Center for Magnetic Resonance in Biology and Medicine, Unite Mixte de Recherche 7339, Marseille, FRANCE; 2Department of Internal Medicine, Division of Geriatrics, University of Utah, Salt Lake City, UT; 3Geriatric Research, Education, and Clinical Center, George E. Whalen VA Medical Center, Salt Lake City, UT; 4Department of Anesthesiology, Pharmacology and Intensive Care and Department of Fundamental Neurosciences, University of Geneva, SWITZERLAND; 5Motricity Efficiency and Deficiency, EA 2991, Faculty of Sport Science, Unite de Formation et de Recherche en Sciences et Techniques des Activites Physiques et Sportives, Montpellier, FRANCE; 6INSERM ADR 08, Montpellier, FRANCE.
authors.forename: Gwenael
authors.initials: G
authors.lastname: Layec
authors.forename: Aurélien
authors.initials: A
authors.lastname: Bringard
authors.forename: Yann
authors.initials: Y
authors.lastname: Le Fur
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Micallef
authors.forename: Christophe
authors.initials: C
authors.lastname: Vilmen
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: D000255:Adenosine Triphosphate / Q000502:physiology; D000328:Adult; D015444:Exercise / Q000502:physiology; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008931:Mitochondria, Muscle / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D011659:Pulmonary Gas Exchange; D052097:Quadriceps Muscle / Q000502:physiology*
chemical_list: D000255:Adenosine Triphosphate