Effect of 17 Days of Bed Rest on Peak Isometric Force and Unloaded Shortening Velocity of Human Soleus Fibers

Authors

Jeffrey J. Widrick, Marquette University
Janell Romatowski, Marquette UniversityFollow
James L. W. Bain, Medical College of Wisconsin
Scott W. Trappe, Ball State University
Todd A. Trappe, Ball State University
Joyce L. Thompson, Medical College of Wisconsin
David L. Costill, Ball State University
Danny A. Riley, Medical College of Wisconsin
Robert H. Fitts, Marquette UniversityFollow

Document Type

Article

Language

eng

Format of Original

10 p.

Publication Date

11-1997

Publisher

American Physiological Society

Source Publication

American Journal of Physiology - Cell Physiology

Source ISSN

0002-9513

Original Item ID

DOI: 10.1152/ajpcell.1997.273.5.C1690

Abstract

The purpose of this study was to examine the effect of prolonged bed rest (BR) on the peak isometric force (P_o) and unloaded shortening velocity (V_o) of single Ca²⁺-activated muscle fibers. Soleus muscle biopsies were obtained from eight adult males before and after 17 days of 6° head-down BR. Chemically permeabilized single fiber segments were mounted between a force transducer and position motor, activated with saturating levels of Ca²⁺, and subjected to slack length steps. V_o was determined by plotting the time for force redevelopment vs. the slack step distance. Gel electrophoresis revealed that 96% of the pre- and 87% of the post-BR fibers studied expressed only the slow type I myosin heavy chain isoform. Fibers with diameter >100 μm made up only 14% of this post-BR type I population compared with 33% of the pre-BR type I population. Consequently, the post-BR type I fibers (n = 147) were, on average, 5% smaller in diameter than the pre-BR type I fibers (n = 218) and produced 13% less absolute P_o. BR had no overall effect on P_o per fiber cross-sectional area (P_o/CSA), even though half of the subjects displayed a decline of 9–12% in P_o/CSA after BR. Type I fiber V_o increased by an average of 34% with BR. Although the ratio of myosin light chain 3 to myosin light chain 2 also rose with BR, there was no correlation between this ratio and V_o for either the pre- or post-BR fibers. In separate fibers obtained from the original biopsies, quantitative electron microscopy revealed a 20–24% decrease in thin filament density, with no change in thick filament density. These results raise the possibility that alterations in the geometric relationships between thin and thick filaments may be at least partially responsible for the elevated V_o of the post-BR type I fibers.

Comments

Accepted version. American Journal of Physiology - Cell Physiology, Vol. 273, No. 5 (November 1997): C1690-C1699. DOI. © 1997 American Physiological Society. Used with permission.

Recommended Citation

Widrick, Jeffrey J.; Romatowski, Janell; Bain, James L. W.; Trappe, Scott W.; Trappe, Todd A.; Thompson, Joyce L.; Costill, David L.; Riley, Danny A.; and Fitts, Robert H., "Effect of 17 Days of Bed Rest on Peak Isometric Force and Unloaded Shortening Velocity of Human Soleus Fibers" (1997). Biological Sciences Faculty Research and Publications. 452.
https://epublications.marquette.edu/bio_fac/452