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Effects of intermittent hypoxic training on amino and fatty acid oxidative combustion in human permeabilized muscle fibers

¹Unite Propre de Recherche de l’Enseignement Superieur-Équipe d’Accueil 3759 "Multidisciplinary Approach of Doping", Montpellier, France; ²Brunel University, School of Sport and Education, West London, United Kingdom; ³Laboratory of Interaction Physiology, Équipe d’Accueil 701, Biology Institute, Montpellier, France; ⁴Laboratoire d’Etude de la Physiologie de l’Exercice, Department of Sciences and Technology in Sports and Physical Activities, University of Evry Val d’Essonne, Evry, France; ⁵Health and Exercise, School of Medical Sciences, The University of New South Wales, Sydney, Australia; ⁶Department of Human and Health Science, University of Westminster, London, United Kingdom; and ⁷ASPIRE, Academy for Sports Excellence, Doha, Qatar

Submitted 14 October 2005 ; accepted in final form 19 September 2006

The effects of concurrent hypoxic/endurance training on mitochondrial respiration in permeabilized fibers in trained athletes were investigated. Eighteen endurance athletes were divided into two training groups: normoxic (Nor, n = 8) and hypoxic (H, n = 10). Three weeks (W1–W3) of endurance training (5 sessions of 1 h to 1 h and 30 min per week) were completed. All training sessions were performed under normoxic [160 Torr inspired PO₂ (PI)] or hypoxic conditions (100 Torr PI, 3,000 m) for Nor and H group, respectively, at the same relative intensity. Before and after the training period, an incremental test to exhaustion in normoxia was performed, muscle biopsy samples were taken from the vastus lateralis, and mitochondrial respiration in permeabilized fibers was measured. Peak power output (PPO) increased by 7.2% and 6.6% (P < 0.05) for Nor and H, respectively, whereas maximal O₂ uptake (O_{2 max}) remained unchanged: 58.1 ± 0.8 vs. 61.0 ± 1.2 ml·kg^–1·min^–1 and 58.5 ± 0.7 vs. 58.3 ± 0.6 ml·kg^–1·min^–1 for Nor and H, respectively, between pretraining (W0) and posttraining (W4). Maximal ADP-stimulated mitochondrial respiration significantly increased for glutamate + malate (6.27 ± 0.37 vs. 8.51 ± 0.33 µmol O₂·min^–1·g dry weight^–1) and significantly decreased for palmitate + malate (3.88 ± 0.23 vs. 2.77 ± 0.08 µmol O₂·min^–1·g dry weight^–1) in the H group. In contrast, no significant differences were found for the Nor group. The findings demonstrate that 1) a 3-wk training period increased the PPO at sea level without any changes in O_{2 max}, and 2) a 3-wk hypoxic exercise training seems to alter the intrinsic properties of mitochondrial function, i.e., substrate preference.

endurance exercise; substrate preference; hypoxic stress; aerobic adaptation; muscle biopsy