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Articles in PresS, published online ahead of print April 5, 2002
J Appl Physiol, 10.1152/jap.01245.2001
Submitted on December 21, 2001
Accepted on March 26, 2002
1 Department of Biology, Marquette University, Milwaukee, WI, USA
2 Human Performance Laboratory, Ball State University, Muncie, IN, USA
3 Department of Cellular Biology and Anatomy, Medical College of Wisconsin, Milwaukee, WI, USA
* To whom correspondence should be addressed. E-mail: robert.fitts{at}mu.edu.
We used Ca2+-activated skinned muscle fibers to test the hypothesis that unilateral lower leg suspension (ULLS) alters cross-bridge mechanisms of muscle contraction. Soleus and gastrocnemius biopsies were obtained from 8 subjects before ULLS, immediately after 12 days of ULLS (post-0 hr), and after 6 hr of re-ambulation (post-6 hr). Post-0 hr soleus fibers expressing type I myosin heavy chain (MHC) showed significant reductions in diameter, absolute and specific peak Ca2+-activated force, unloaded shortening velocity, and absolute and normalized peak power. Fibers obtained from the gastrocnemius were less affected by ULLS, particularly fibers expressing fast MHC isoforms. Post-6 hr soleus fibers produced less absolute and specific peak force than post-0 hr fibers, suggesting that re-ambulation after ULLS induced cell damage. Like bed rest and space flight, ULLS primarily affects soleus over gastrocnemius fibers. However, in contrast to these other models, slow soleus fibers obtained after ULLS showed a decrease in unloaded shortening velocity and a greater reduction in specific force.
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