Muscle fatigue and exhaustion during dynamic leg exercise in normoxia and hypobaric hypoxia
Charles S. Fulco, Steven F. Lewis, Peter N. Frykman, Robert Boushel, Sinclair Smith, Everett A. Harman, Allen Cymerman, and Kent B. Pandolf Environmental Physiology and Medicine Directorate and Occupational Health and Performance Directorate, US Army Research Institute of Environmental Medicine, Nat...
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Published in | Journal of applied physiology (1985) Vol. 81; no. 5; pp. 1891 - 1900 |
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Main Authors | , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Bethesda, MD
Am Physiological Soc
01.11.1996
American Physiological Society |
Subjects | |
Online Access | Get full text |
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Summary: | Charles S.
Fulco,
Steven F.
Lewis,
Peter N.
Frykman,
Robert
Boushel,
Sinclair
Smith,
Everett A.
Harman,
Allen
Cymerman, and
Kent B.
Pandolf
Environmental Physiology and Medicine Directorate and Occupational
Health and Performance Directorate, US Army Research Institute of
Environmental Medicine, Natick 01760-5007; and Department of Health
Sciences, Sargent College of Allied Health Professions, Boston
University, Boston, Massachusetts 02215
Received 23 October 1995; accepted in final form 16 April 1996.
Fulco, Charles S., Steven F. Lewis, Peter N. Frykman, Robert
Boushel, Sinclair Smith, Everett A. Harman, Allen Cymerman, and Kent B. Pandolf. Muscle fatigue and exhaustion during dynamic leg exercise
in normoxia and hypobaric hypoxia. J. Appl. Physiol. 81(5): 1891-1900, 1996. Using an
exercise device that integrates maximal voluntary static contraction
(MVC) of knee extensor muscles with dynamic knee extension, we compared
progressive muscle fatigue, i.e., rate of decline in force-generating
capacity, in normoxia (758 Torr) and hypobaric hypoxia (464 Torr).
Eight healthy men performed exhaustive constant work rate knee
extension (21 ± 3 W, 79 ± 2 and 87 ± 2% of 1-leg knee
extension O 2 peak uptake for
normoxia and hypobaria, respectively) from knee angles of
90-150° at a rate of 1 Hz. MVC (90° knee angle) was
performed before dynamic exercise and during 5-s pauses every 2 min
of dynamic exercise. MVC force was 578 ± 29 N in normoxia and 569 ± 29 N in hypobaria before exercise and fell, at exhaustion, to similar levels (265 ± 10 and 284 ± 20 N for normoxia and
hypobaria, respectively; P > 0.05)
that were higher ( P < 0.01) than
peak force of constant work rate knee extension (98 ± 10 N, 18 ± 3% of MVC). Time to exhaustion was 56% shorter for hypobaria
than for normoxia (19 ± 5 vs. 43 ± 7 min, respectively;
P < 0.01), and rate of right leg MVC fall was
nearly twofold greater for hypobaria than for normoxia (mean slope = 22.3 vs. 11.9 N/min, respectively;
P < 0.05). With increasing duration
of dynamic exercise for normoxia and hypobaria, integrated
electromyographic activity during MVC fell progressively with MVC
force, implying attenuated maximal muscle excitation. Exhaustion, per
se, was postulated to relate more closely to impaired shortening
velocity than to failure of force-generating capacity.
muscle endurance; strength; electromyography; quadriceps femoris
muscles; hypoxia; muscle contraction; oxygen uptake; perceived
exertion; muscle ischemia |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 |
ISSN: | 8750-7587 1522-1601 |
DOI: | 10.1152/jappl.1996.81.5.1891 |