Journal of Applied Physiology, Vol 68, Issue 3 1167-1172, Copyright © 1990 by American Physiological Society

ARTICLES

Operation Everest II: neuromuscular performance under conditions of extreme simulated altitude

S. H. Garner, J. R. Sutton, R. L. Burse, A. J. McComas, A. Cymerman and C. S. Houston
McMaster University, Hamilton, Ontario, Canada.

The force output of the ankle dorsiflexors was studied during a 40-day simulated ascent of Mt. Everest in a hypobaric chamber; both electrically activated and maximal voluntary contractions (MVCs) were employed. The purpose of this study was to establish whether, under conditions of progressive chronic hypoxia, there was a decrease in muscle force output and/or increased fatigability. We also attempted to identify the main site of any failure, i.e., central nervous system, neuromuscular junction, or muscle fiber. Muscle twitch torque (Pt), tetanic torque (Po), MVC torque, and evoked muscle compound action potential (M wave) were monitored during 205-s exercise periods in five subjects at three simulated altitudes (760, 335, and 282 Torr). All three types of torque measurement were well preserved at the three altitudes. In some subjects, the responses to stimuli interpolated during repeated MVCs provided evidence of "central" fatigue at altitude. In addition, the rate of fatigue during 20-Hz electrical stimulation was greater (P less than 0.01) at altitude and there was increased fatigability of the twitch (P less than 0.025); however, the M wave amplitude was maintained. We conclude that central motor drive becomes more precarious at altitude and is associated with increased muscle fatigue at low excitation frequencies; the latter is the result, in part, of chronic hypoxia and occurs in the muscle fiber interior because no impairment in neuromuscular transmission could be demonstrated.

This article has been cited by other articles:

				M. Amann and J. A. L. Calbet Convective oxygen transport and fatigue J Appl Physiol, March 1, 2008; 104(3): 861 - 870. [Abstract] [Full Text] [PDF]

				R. W. Bavis, F. L. Powell, A. Bradford, C. C.W. Hsia, J. E. Peltonen, J. Soliz, B. Zeis, E. K. Fergusson, Z. Fu, M. Gassmann, et al. Respiratory plasticity in response to changes in oxygen supply and demand Integr. Comp. Biol., October 1, 2007; 47(4): 532 - 551. [Abstract] [Full Text] [PDF]

				L. M. Romer, H. C. Haverkamp, M. Amann, A. T. Lovering, D. F. Pegelow, and J. A. Dempsey Effect of acute severe hypoxia on peripheral fatigue and endurance capacity in healthy humans Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2007; 292(1): R598 - R606. [Abstract] [Full Text] [PDF]

				C. Szubski, M. Burtscher, and W. N. Loscher The effects of short-term hypoxia on motor cortex excitability and neuromuscular activation J Appl Physiol, December 1, 2006; 101(6): 1673 - 1677. [Abstract] [Full Text] [PDF]

				M. Amann, L. M. Romer, D. F. Pegelow, A. J. Jacques, C. J. Hess, and J. A. Dempsey Effects of arterial oxygen content on peripheral locomotor muscle fatigue J Appl Physiol, July 1, 2006; 101(1): 119 - 127. [Abstract] [Full Text] [PDF]

				T. D. Noakes, J. A. L. Calbet, R. Boushel, H. Sondergaard, G. Radegran, P. D. Wagner, and B. Saltin Central regulation of skeletal muscle recruitment explains the reduced maximal cardiac output during exercise in hypoxia Am J Physiol Regulatory Integrative Comp Physiol, October 1, 2004; 287(4): R996 - R1002. [Full Text] [PDF]

				M. McGuire, M. MacDermott, and A. Bradford Effects of Chronic Intermittent Asphyxia on Rat Diaphragm and Limb Muscle Contractility Chest, March 1, 2003; 123(3): 875 - 881. [Abstract] [Full Text] [PDF]

				S. C. Gandevia Spinal and Supraspinal Factors in Human Muscle Fatigue Physiol Rev, October 1, 2001; 81(4): 1725 - 1789. [Abstract] [Full Text] [PDF]

				C. S. Fulco, P. B. Rock, S. R. Muza, E. Lammi, B. Braun, A. Cymerman, L. G. Moore, and S. F. Lewis Gender alters impact of hypobaric hypoxia on adductor pollicis muscle performance J Appl Physiol, July 1, 2001; 91(1): 100 - 108. [Abstract] [Full Text] [PDF]

				N. Kinoshita, H. Yamazaki, S. Onishi, Y. Oguma, F. Katsukawa, and M. Horii Physiological Profile of Middle-Aged and Older Climbers Who Ascended Gasherbrum II, an 8035-m Himalayan Peak J. Gerontol. A Biol. Sci. Med. Sci., November 1, 2000; 55(11): 630M - 633. [Abstract] [Full Text]