Effect of phase of stimulation on acute damage caused by eccentric
contractions in mouse soleus muscle..
Don, E., Stevens.
Department of Zoology, University of Guelph, Guelph, Ontario N1G
2W1, Canada
APStracts 3:0059A, 1996.
Stevens, E. Don. Effect of phase of stimulation on the amount of acute
damage caused by eccentric contractions in mouse soleus muscle.
Eccentric contractions (activation during muscle lengthening) can
cause muscle damage. The effect of phase of stimulation on the extent
of muscle damage was studied using the work-loop method. For the work
loop method the muscle was subjected to sinusoidal length changes at
2 Hz. The muscle was activated at different times during the imposed
length change cycle; this time is called the phase of stimulation.
Work was calculated from the loop formed when force was plotted
against length. Work done was positive when the muscle was shortening
and was negative when the muscle was lengthening; net work was the
difference. One complete length change cycle was 100 (i.e., given as
percent of the cycle); shortening occurred from 25 to 75. The muscle
did the most net work when stimulated at phase 20, that is, when
activation started just before shortening. Damage was defined as a
decrease in work. Significant damage occurred after a single trial of
three consecutive eccentric contractions; the muscle did less
positive and less net work because of the damage. Maximal damage
occurred at phase of stimulation 90 and 0, the center of the
lengthening part of the length change cycle (work decreased 10%).
Negligible damage occurred at phase of stimulation 20 to 40. Negative
work (work required to lengthen the muscle) also decreased because of
the damage. Eccentric contractions caused much more damage than
concentric contractions during oscillatory work.
Received 1 August 1995; accepted in final form 16 January 1996.
APS Manuscript Number A845-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96