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Modulation of exercise-induced spinal loop properties in response to oxygen availability.
Thomas Rupp1, Sébastien Racinais, Aurélien Bringard
1Laboratoire de Physiologie de l'Exercice, Université Savoie Mont Blanc, Campus Scientifique Technolac, 73376, Chambéry, Le Bourget Du Lac Cedex, France, thomas.rupp@univ-savoie.fr.
European Journal of Applied Physiology
|November 2, 2014
Summary
Acute hypoxia alters spinal reflexes and muscle function after fatigue. While central adaptations were similar, differing recovery patterns suggest distinct neural regulation under hypoxia versus normoxia.
Area of Science:
- Exercise Physiology
- Neuroscience
- Muscle Physiology
Background:
- Sustained submaximal contractions induce fatigue, altering neuromuscular function.
- Hypoxia, or low oxygen levels, can impact physiological responses during exercise.
- Understanding neural control adaptations during fatigue under varying oxygen availability is crucial.
Purpose of the Study:
- To investigate the effects of acute hypoxia on spinal reflexes and soleus muscle function following fatiguing plantar flexor contractions.
- To compare neuromuscular responses during and after fatigue under normoxic and hypoxic conditions.
- To explore the role of central and peripheral adaptations in response to exercise-induced fatigue under different oxygen levels.
Main Methods:
- Fifteen healthy males performed a sustained submaximal contraction task under normoxia (FiO₂=0.21) and hypoxia (FiO₂=0.11).
- Hoffman reflex (H-reflex) and M-wave were measured at rest; voluntary activation (VA), surface EMG, and V-wave were assessed during maximal voluntary contractions (MVC).
- Measurements were taken before exercise, at task failure, and during 6, 12, and 18 minutes of recovery.
Main Results:
- Normalized H-reflex was depressed pre-exercise in hypoxia compared to normoxia.
- Time to task failure and MVC reduction at task failure were not affected by hypoxia.
- At task failure, VA, RMSmax/M sup, H max/M max, and V sup/M sup decreased similarly in both conditions.
- H max/M max recovered faster in hypoxia, while V sup/M sup recovered faster in normoxia.
Conclusions:
- Central adaptations to sustained submaximal fatiguing contractions are similar in hypoxia and normoxia at task failure.
- Hypoxia-induced differences in spinal loop properties suggest mediation by muscle afferents and distinct supraspinal versus spinal regulation.
- These findings highlight the complex interplay between oxygen availability and neural control of muscle function during and after fatigue.
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