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Impact of weightlessness on muscle function.

M E Tischler1, M Slentz

  • 1Department of Biochemistry, University of Arizona, Tucson 85724, USA.

ASGSB Bulletin : Publication of the American Society for Gravitational and Space Biology
|October 1, 1995
PubMed
Summary

Spaceflight causes significant muscle protein loss, particularly in antigravity muscles like the soleus. This leads to reduced muscle fiber size and altered fiber type composition, impacting muscle function.

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Area of Science:

  • Skeletal muscle physiology
  • Spaceflight adaptation
  • Muscle protein metabolism

Background:

  • Antigravity muscles, crucial for posture, are sensitive to microgravity.
  • Weightlessness leads to substantial muscle protein loss, especially myofibrillar proteins.
  • Soleus muscle in the legs is highly responsive to unweighting during spaceflight.

Purpose of the Study:

  • To investigate the effects of microgravity on skeletal muscle composition and function.
  • To analyze changes in muscle fiber types, protein content, and metabolic pathways.
  • To understand the adaptation of antigravity muscles to spaceflight conditions.

Main Methods:

  • Analysis of muscle protein and mRNA levels (e.g., alpha-actin).
  • Assessment of muscle fiber cross-sectional area and type composition (SO, FOG, FG).
Keywords:
NASA Discipline MusculoskeletalNASA Discipline Number 00-00NASA Program FlightNon-NASA Center

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  • Measurement of maximal isometric tension (Po) and shortening velocity.
  • Evaluation of fuel metabolism, including glucose uptake, fatty acid oxidation, and enzyme activities.

    • Main Results:

    • Microgravity exposure caused decreased alpha-actin mRNA and substantial muscle protein loss.
    • Soleus muscle showed significant atrophy, particularly in slow-twitch oxidative fibers.
    • A shift in fiber composition from SO to FOG was observed in some muscles.
    • Maximal isometric tension decreased, while maximal shortening velocity increased.
    • Glucose uptake and glycolytic enzyme activity increased, but fatty acid oxidation may decrease.

    Conclusions:

    • Spaceflight induces significant alterations in antigravity muscle structure and function.
    • Adaptation to microgravity involves muscle atrophy, fiber type shifts, and altered fuel metabolism.
    • These changes highlight the vulnerability of postural muscles to unweighting and the need for countermeasures.