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Impact of weightlessness on muscle functionThe most studied skeletal muscles which depend on gravity, "antigravity" muscles, are located in the posterior portion of the legs. Antigravity muscles are characterized generally by a different fiber type composition than those which are considered nonpostural. The gravity-dependent function of the antigravity muscles makes them particularly sensitive to weightlessness (unweighting) resulting in a substantial loss of muscle protein, with a relatively greater loss of myofibrillar (structural) proteins. Accordingly alpha-actin mRNA decreases in muscle of rats exposed to microgravity. In the legs, the soleus seems particularly responsive to the lack of weight-bearing associated with space flight. The loss of muscle protein leads to a decreased cross-sectional area of muscle fibers, particularly of the slow-twitch, oxidative (SO) ones compared to fast-twitch glycolytic (FG) or oxidative-glycolytic (FOG) fibers. In some muscles, a shift in fiber composition from SO to FOG has been reported in the adaptation to spaceflight. Changes in muscle composition with spaceflight have been associated with decreased maximal isometric tension (Po) and increased maximal shortening velocity. In terms of fuel metabolism, results varied depending on the pathway considered. Glucose uptake, in the presence of insulin, and activities of glycolytic enzymes are increased by space flight. In contrast, oxidation of fatty acids may be diminished. Oxidation of pyruvate, activity of the citric acid cycle, and ketone metabolism in muscle seem to be unaffected by microgravity.
Document ID
20040090016
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Tischler, M. E.
(University of Arizona Tucson 85724, United States)
Slentz, M.
Date Acquired
August 21, 2013
Publication Date
October 1, 1995
Publication Information
Publication: ASGSB bulletin : publication of the American Society for Gravitational and Space Biology
Volume: 8
Issue: 2
ISSN: 0898-4697
Subject Category
Aerospace Medicine
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Number 00-00
NASA Program Flight
NASA Discipline Musculoskeletal
Review
Review, Tutorial
Non-NASA Center

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