Peak force and maximal shortening velocity of soleus fibers after
non-weight bearing and resistance exercise.
Widrick, Jeffrey J., and Robert H. Fitts.
Department of Biology, Marquette University, Milwaukee, WI
53201
APStracts 3:0447A, 1996.
This study examined the effectiveness of resistance exercise as a
countermeasure to non-weight bearing induced alterations in the
absolute peak force, normalized peak force (force/fiber cross
-sectional area), peak stiffness, and maximal unloaded shortening
velocity (Vo) of single permeabilized type I soleus muscle fibers.
Adult rats were subjected to one of the following treatments: normal
weight bearing (WB), non-weight bearing (NWB), or NWB with exercise
treatments (NWB+EX). The hindlimbs of the NWB and NWB+EX rats were
suspended for 14 days via tail harnesses. Four times each day, the
NWB+EX rats were removed from suspension and performed 10 climbs ( 15
cm each) up a steep grid with a 500 g mass ( 1.5 times body mass)
attached to their tail harness. NWB was associated with significant
reductions in type I fiber diameter, absolute force, normalized
force, and stiffness. Exercise treatments during NWB attenuated the
decline in fiber diameter and absolute force by almost 60% while
maintaining normalized force and stiffness at WB levels. Type I fiber
Vo increased by 33% with NWB and remained at this elevated level
despite the exercise treatments. We conclude that in comparison to
intermittent weight bearing only (Widrick et al. J. Appl. Physiol.
80: 981-987, 1996), resistance exercise was more effective in
attenuating alterations in type I soleus fiber absolute force,
normalized force, and stiffness, but was less effective in restoring
type I fiber Vo to WB levels.
Received 8 April 1996; accepted in final form 13 September 1996.
APS Manuscript Number A333-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996