This study tested the hypothesis that a prolonged decrease in arterial oxygen pressure in resting or contracting skeletal muscles alters their ability to develop force through an impairment of energy-dependent metabolic processes and also through an alteration of electrophysiological events. The experiment was conducted during a 32-day simulated ascent of Mt. Everest (8848 m altitude) (Everest III Comex '97), which also allowed testing of the effects of re-oxygenation on muscle function. Maximal voluntary contractions (MVCs) of the flexor digitorum, and static handgrips sustained at 60% of MVC, were performed by eight subjects before the ascent (control), then during the stays at simulated altitudes of 5000 m, 6000 m and 7000 m, and finally 1 day after the return to 0 m. The evoked muscle compound action potential (M-wave) was recorded at rest and during the manoeuvres at 60% of MVC. The changes in median frequency of electromyographic (EMG) power spectra were also studied during the contraction at 60% of MVC. In four individuals, transient re-oxygenation during the ascent allowed us to test the reversibility of hypoxia-induced MVC and M-wave changes. At rest, a significant decrease in M-wave amplitude was noted at 5000 m. This effect was associated with a prolonged M-wave conduction time at 6000 m and an increased M-wave duration at 7000 m, and persisted after the return to 0 m. Re-oxygenation did not modify the changes in M-wave characteristics. A significant decrease in MVC was measured only during the ascent (-10 to -24%) in the non-dominant forearm of subjects who underwent re-oxygenation; this intervention slightly improved muscle strength at 6000 m and 7000 m. During the ascent and after the return to 0 m, there was a significant reduction of the median frequency decrease throughout contraction at 60% of MVC compared with the EMG changes measured before the ascent. It is concluded that prolonged exposure to hypoxia slows the propagation of myopotentials and alters sensorimotor control during sustained effort. Re-oxygenation did not affect the hypoxia-induced EMG changes and had a modest influence on muscle strength.
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Research Article|
February 10 2000
Effects of prolonged hypobaric hypoxia on human skeletal muscle function and electromyographic events
F. CAQUELARD;
F. CAQUELARD
*Laboratoire de Physiopathologie Respiratoire (EA 2201), Institut Jean Roche, Faculté de Médecine, Université de la Méditerranée, 13916 Marseille, France
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H. BURNET;
H. BURNET
*Laboratoire de Physiopathologie Respiratoire (EA 2201), Institut Jean Roche, Faculté de Médecine, Université de la Méditerranée, 13916 Marseille, France
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F. TAGLIARINI;
F. TAGLIARINI
*Laboratoire de Physiopathologie Respiratoire (EA 2201), Institut Jean Roche, Faculté de Médecine, Université de la Méditerranée, 13916 Marseille, France
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E. CAUCHY;
E. CAUCHY
†ARPE – Laboratoire des Réponses Cellulaires et Fonctionnelles à l'Hypoxie, Faculté de Médecine de Bobigny, Université Paris XIII, Paris, France
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J. P. RICHALET;
J. P. RICHALET
†ARPE – Laboratoire des Réponses Cellulaires et Fonctionnelles à l'Hypoxie, Faculté de Médecine de Bobigny, Université Paris XIII, Paris, France
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Y. JAMMES
*Laboratoire de Physiopathologie Respiratoire (EA 2201), Institut Jean Roche, Faculté de Médecine, Université de la Méditerranée, 13916 Marseille, France
Correspondence: Professor Y. Jammes (e-mail [email protected]).
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Publisher: Portland Press Ltd
Received:
August 23 1999
Accepted:
November 08 1999
Online ISSN: 1470-8736
Print ISSN: 0143-5221
The Biochemical Society and the Medical Research Society © 2000
2000
Clin Sci (Lond) (2000) 98 (3): 329–337.
Article history
Received:
August 23 1999
Accepted:
November 08 1999
Citation
F. CAQUELARD, H. BURNET, F. TAGLIARINI, E. CAUCHY, J. P. RICHALET, Y. JAMMES; Effects of prolonged hypobaric hypoxia on human skeletal muscle function and electromyographic events. Clin Sci (Lond) 1 March 2000; 98 (3): 329–337. doi: https://doi.org/10.1042/cs0980329
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