title: Opposite effects of hyperoxia on mitochondrial and contractile efficiency in human quadriceps muscles.
abstract: Exercise efficiency is an important determinant of exercise capacity. However, little is known about the physiological factors that can modulate muscle efficiency during exercise. We examined whether improved O2 availability would 1) impair mitochondrial efficiency and shift the energy production toward aerobic ATP synthesis and 2) reduce the ATP cost of dynamic contraction owing to an improved neuromuscular efficiency, such that 3) whole body O2 cost would remain unchanged. We used (31)P-magnetic resonance spectroscopy, surface electromyography, and pulmonary O2 consumption (V̇o2p) measurements in eight active subjects during 6 min of dynamic knee-extension exercise under different fractions of inspired O2 (FiO2 , 0.21 in normoxia and 1.0 in hyperoxia). V̇o2p (755 ± 111 ml/min in normoxia and 799 ± 188 ml/min in hyperoxia, P > 0.05) and O2 cost (P > 0.05) were not significantly different between normoxia and hyperoxia. In contrast, the total ATP synthesis rate and the ATP cost of dynamic contraction were significantly lower in hyperoxia than normoxia (P < 0.05). As a result, the ratio of the rate of oxidative ATP synthesis from the quadriceps to V̇o2p was lower in hyperoxia than normoxia but did not reach statistical significance (16 ± 3 mM/ml in normoxia and 12 ± 5 mM/ml in hyperoxia, P = 0.07). Together, these findings reveal dynamic and independent regulations of mitochondrial and contractile efficiency as a consequence of O2 availability in young active individuals. Furthermore, muscle efficiency appears to be already optimized in normoxia and is unlikely to contribute to the well-established improvement in exercise capacity induced by hyperoxia.
authors.affiliation: Aix-Marseille Université, Centre National de la Recherche Scientifique, Center for Magnetic Resonance in Biology and Medicine, UMR 7339, Marseille, France; Division of Geriatrics, Department of Medicine, University of Utah, Salt Lake City, Utah; Geriatric Research, Education, and Clinical Center, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, Utah; gwenael.layec@utah.edu.
authors.forename: Gwenael
authors.initials: G
authors.lastname: Layec
authors.affiliation: Département des Neurosciences Fondamentales, Centre Médical Universitaire, University of Geneva, Geneva, Switzerland;
authors.forename: Aurélien
authors.initials: A
authors.lastname: Bringard
authors.affiliation: Aix-Marseille Université, Centre National de la Recherche Scientifique, Center for Magnetic Resonance in Biology and Medicine, UMR 7339, Marseille, France;
authors.forename: Yann
authors.initials: Y
authors.lastname: Le Fur
authors.affiliation: Movement To Health (M2H), EuroMov, Montpellier-1 University, Montpellier, France; and Institut National de la Santé et de la Recherche Médicale ADR 08, Montpellier, France.
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Micallef
authors.affiliation: Aix-Marseille Université, Centre National de la Recherche Scientifique, Center for Magnetic Resonance in Biology and Medicine, UMR 7339, Marseille, France;
authors.forename: Christophe
authors.initials: C
authors.lastname: Vilmen
authors.affiliation: Movement To Health (M2H), EuroMov, Montpellier-1 University, Montpellier, France; and.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Perrey
authors.affiliation: Aix-Marseille Université, Centre National de la Recherche Scientifique, Center for Magnetic Resonance in Biology and Medicine, UMR 7339, Marseille, France;
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Cozzone
authors.affiliation: Aix-Marseille Université, Centre National de la Recherche Scientifique, Center for Magnetic Resonance in Biology and Medicine, UMR 7339, Marseille, France;
authors.forename: David
authors.initials: D
authors.lastname: Bendahan
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D001642:Bicycling; D004576:Electromyography; D004734:Energy Metabolism; D015444:Exercise; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D018496:Hyperoxia / Q000378:metabolism / Q000503:physiopathology*; D007537:Isometric Contraction; D008168:Lung / Q000378:metabolism / Q000503:physiopathology*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008931:Mitochondria, Muscle / Q000378:metabolism*; D018763:Muscle Fatigue; D053580:Muscle Strength; D010101:Oxygen Consumption; D052097:Quadriceps Muscle / Q000378:metabolism / Q000503:physiopathology*; D013997:Time Factors
chemical_list: D000255:Adenosine Triphosphate
keywords: 31P-magnetic resonance spectroscopy; O2 availability; mitochondria; muscle efficiency; muscle energetics