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Effect of a 17 day spaceflight on contractile properties of human soleus muscle fibres1. Soleus biopsies were obtained from four male astronauts 45 days before and within 2 h after a 17 day spaceflight. 2. For all astronauts, single chemically skinned post-flight fibres expressing only type I myosin heavy chain (MHC) developed less average peak Ca2+ activated force (Po) during fixed-end contractions (0.78 +/- 0. 02 vs. 0.99 +/- 0.03 mN) and shortened at a greater mean velocity during unloaded contractions (Vo) (0.83 +/- 0.02 vs. 0.64 +/- 0.02 fibre lengths s-1) than pre-flight type I fibres. 3. The flight-induced decline in absolute Po was attributed to reductions in fibre diameter and/or Po per fibre cross-sectional area. Fibres from the astronaut who experienced the greatest relative loss of peak force also displayed a reduction in Ca2+ sensitivity. 4. The elevated Vo of the post-flight slow type I fibres could not be explained by alterations in myosin heavy or light chain composition. One alternative possibility is that the elevated Vo resulted from an increased myofilament lattice spacing. This hypothesis was supported by electron micrographic analysis demonstrating a reduction in thin filament density post-flight. 5. Post-flight fibres shortened at 30 % higher velocities than pre-flight fibres at external loads associated with peak power output. This increase in shortening velocity either reduced (2 astronauts) or prevented (2 astronauts) a post-flight loss in fibre absolute peak power (microN (fibre length) s-1). 6. The changes in soleus fibre diameter and function following spaceflight were similar to those observed after 17 days of bed rest. Although in-flight exercise countermeasures probably reduced the effects of microgravity, the results support the idea that ground-based bed rest can serve as a model of human spaceflight. 7. In conclusion, 17 days of spaceflight decreased force and increased shortening velocity of single Ca2+-activated muscle cells expressing type I MHC. The increase in shortening velocity greatly reduced the impact that impaired force production had on absolute peak power.
Document ID
20040142002
Document Type
Reprint (Version printed in journal)
Authors
Widrick, J. J. (Marquette University Milwaukee, WI 53201, United States)
Knuth, S. T.
Norenberg, K. M.
Romatowski, J. G.
Bain, J. L.
Riley, D. A.
Karhanek, M.
Trappe, S. W.
Trappe, T. A.
Costill, D. L.
Fitts, R. H.
Date Acquired
August 22, 2013
Publication Date
May 1, 1999
Publication Information
Publication: The Journal of physiology
Volume: 516 ( Pt 3)
ISSN: 0022-3751
Subject Category
Life Sciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
Clinical Trial
STS-78 Shuttle Project
manned
short duration
Non-NASA Center
NASA Discipline Musculoskeletal
Flight Experiment
NASA Experiment Number 8913020 1/2