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Disproportionate loss of thin filaments in human soleus muscle after 17-day bed restPreviously we reported that, after 17-day bed rest unloading of 8 humans, soleus slow fibers atrophied and exhibited increased velocity of shortening without fast myosin expression. The present ultrastructural study examined fibers from the same muscle biopsies to determine whether decreased myofilament packing density accounted for the observed speeding. Quantitation was by computer-assisted morphometry of electron micrographs. Filament densities were normalized for sarcomere length, because density depends directly on length. Thick filament density was unchanged by bed rest. Thin filaments/microm2 decreased 16-23%. Glycogen filled the I band sites vacated by filaments. The percentage decrease in thin filaments (Y) correlated significantly (P < 0.05) with the percentage increase in velocity (X), (Y = 0.1X + 20%, R2 = 0.62). An interpretation is that fewer filaments increases thick to thin filament spacing and causes earlier cross-bridge detachment and faster cycling. Increased velocity helps maintain power (force x velocity) as atrophy lowers force. Atrophic muscles may be prone to sarcomere reloading damage because force/microm2 was near normal, and force per thin filament increased an estimated 30%.
Document ID
20040172572
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Riley, D. A.
(Medical College of Wisconsin Milwaukee, United States)
Bain, J. L.
Thompson, J. L.
Fitts, R. H.
Widrick, J. J.
Trappe, S. W.
Trappe, T. A.
Costill, D. L.
Date Acquired
August 22, 2013
Publication Date
October 1, 1998
Publication Information
Publication: Muscle & nerve
Volume: 21
Issue: 10
ISSN: 0148-639X
Subject Category
Life Sciences (General)
Funding Number(s)
CONTRACT_GRANT: UO1NS33472
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
NASA Discipline Musculoskeletal

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