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J Appl Physiol 100: 1249-1257, 2006. First published December 8, 2005; doi:10.1152/japplphysiol.00361.2005
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Exercise training in normobaric hypoxia in endurance runners. II. Improvement of mitochondrial properties in skeletal muscle

Elodie Ponsot,1 Stéphane P. Dufour,1 Joffrey Zoll,2 Stéphane Doutrelau,1 Benoit N'Guessan,1 Bernard Geny,1 Hans Hoppeler,2 Eliane Lampert,1 Bertrand Mettauer,1,3 Renée Ventura-Clapier,4 and Ruddy Richard1

1Service de Physiologie Clinique et des Explorations Fonctionnelles Respiratoires et de l'Exercice, Département de Physiologie, Équipe d'Accueil 3072, Strasbourg, France; 2Institute of Anatomy, University of Bern, Bern, Switzerland; 3Service de Cardiologie, Hôpitaux Civils de Colmar, Colmar, France; and 4U-446 Institut National de la Santé et de la Recherche Médicale, Faculté de Pharmacie, Châtenay-Malabry, France

Submitted 29 March 2005 ; accepted in final form 1 December 2005

This study investigates whether adaptations of mitochondrial function accompany the improvement of endurance performance capacity observed in well-trained athletes after an intermittent hypoxic training program. Fifteen endurance-trained athletes performed two weekly training sessions on treadmill at the velocity associated with the second ventilatory threshold (VT2) with inspired O2 fraction = 14.5% [hypoxic group (Hyp), n = 8] or with inspired O2 fraction = 21% [normoxic group (Nor), n = 7], integrated into their usual training, for 6 wk. Before and after training, oxygen uptake (VO2) and speed at VT2, maximal VO2 (VO2 max), and time to exhaustion at velocity of VO2 max (minimal speed associated with VO2 max) were measured, and muscle biopsies of vastus lateralis were harvested. Muscle oxidative capacities and sensitivity of mitochondrial respiration to ADP (Km) were evaluated on permeabilized muscle fibers. Time to exhaustion, VO2 at VT2, and VO2 max were significantly improved in Hyp (+42, +8, and +5%, respectively) but not in Nor. No increase in muscle oxidative capacity was obtained with either training protocol. However, mitochondrial regulation shifted to a more oxidative profile in Hyp only as shown by the increased Km for ADP (Nor: before 476 ± 63, after 524 ± 62 µM, not significant; Hyp: before 441 ± 59, after 694 ± 51 µM, P < 0.05). Thus including hypoxia sessions into the usual training of athletes qualitatively ameliorates mitochondrial function by increasing the respiratory control by creatine, providing a tighter integration between ATP demand and supply.

intermittent hypoxia training; skeletal muscle; mitochondria; time to exhaustion; endurance athletes


Address for reprint requests and other correspondence: R. Richard, Hôpital Civil-Service des Explorations Fonctionnelles Respiratoires et de l'Exercice, 1 place de l'Hôpital, BP 426, 67091 Strasbourg Cedex, France (e-mail: Ruddy.Richard{at}physio-ulp.u-strasbg.fr)




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