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Modulation of exercise-induced spinal loop properties in response to oxygen availability

Rupp, Thomas
Racinais, Sébastien
Lapole, Thomas
Perrey, Stéphane
Published in European journal of applied physiology. 2015, vol. 115, no. 3, p. 471-82
Abstract This study investigated the effects of acute hypoxia on spinal reflexes and soleus muscle function after a sustained contraction of the plantar flexors at 40% of maximal voluntary isometric contraction (MVC). Fifteen males (age 25.3 ± 0.9 year) performed the fatigue task at two different inspired O₂ fractions (FiO₂ = 0.21/0.11) in a randomized and single-blind fashion. Before, at task failure and after 6, 12 and 18 min of passive recovery, the Hoffman-reflex (H max) and M-wave (M max) were recorded at rest and voluntary activation (VA), surface electromyogram (RMSmax), M-wave (M sup) and V-wave (V sup) were recorded during MVC. Normalized H-reflex (H max/M max) was significantly depressed pre-exercise in hypoxia compared with normoxia (0.31 ± 0.08 and 0.36 ± 0.08, respectively, P < 0.05). Hypoxia did not affect time to task failure (mean time of 453.9 ± 32.0 s) and MVC decrease at task failure (-18% in normoxia vs. -16% in hypoxia). At task failure, VA (-8%), RMSmax/M sup (-11%), H max/M max (-27%) and V sup/M sup (-37%) decreased (P < 0.05), but with no FiO2 effect. H max/M max restored significantly throughout recovery in hypoxia but not in normoxia, while V sup/M sup restored significantly during recovery in normoxia but not in hypoxia (P < 0.05). Collectively, these findings indicate that central adaptations resulting from sustained submaximal fatiguing contraction were not different in hypoxia and normoxia at task failure. However, the FiO₂-induced differences in spinal loop properties pre-exercise and throughout recovery suggest possible specific mediation by the hypoxic-sensitive group III and IV muscle afferents, supraspinal regulation mechanisms being mainly involved in hypoxia while spinal ones may be predominant in normoxia.
Keywords AdultExerciseHumansHypoxia/physiopathologyMaleMuscle ContractionMuscle FatigueMuscle, Skeletal/physiologyOxygen/metabolismReflexSpinal Cord/physiology
PMID: 25361617
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RUPP, Thomas et al. Modulation of exercise-induced spinal loop properties in response to oxygen availability. In: European journal of applied physiology, 2015, vol. 115, n° 3, p. 471-82. doi: 10.1007/s00421-014-3032-5 https://archive-ouverte.unige.ch/unige:93326

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Deposited on : 2017-04-07

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