The Force-Velocity Relationship of the Soleus Muscles of Mice During After-Loaded Isotonic Contractions and After-Loaded Isotonic Releases
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Authors
Ward, Christine E.
Issue Date
1988
Type
Thesis
Language
en_US
Keywords
Alternative Title
Abstract
Hypotheses were tested that a muscle stimulated at a frequency that
elicited a maximal rate of force development (dP/dto) was fully activated
during after-loaded isotonic contractions by the time the muscle developed
the force necessary to displace the after-load and consequently the
shortening velocity was maximum. whereas a muscle stimulated at a rate
that elicited maximum tetanic force (Po) was not fully activated and under
similar circumstances could not displace after-loads at maximum velocities.
As controls for fully activated muscle, the same muscles were stimulated to
develop Po and were then released to each after-load. Soleus muscles from
14 mice were stimulated directly in vitro at 25º C. Shortening velocities of
each muscle were measured at 13 different after-loads using 4 different
protocols: stimulation at a frequency that produced Po (approximately 90 Hz)
with an after-loaded isotonic contraction: stimulation at 90 Hz to Po with a
quick-release to each after-load; stimulation at a frequency that produced
dP/dto (approximately 250 Hz) with an after-loaded isotonic contraction; or
stimulation at 250 Hz to Po with a quick-release to each after-load. The
maximum velocity of unloaded shortening (V max) was extrapolated from the
force-velocity relationship. A significant difference was observed between
the V max of isotonic contractions at 90 Hz (V max=4.17±0.l4 Lf/s) and that
at 250 Hz (V max=4.82±O.l4 Lf/s). Based on a repeated measures analysis of
variance of the velocities at 13 after-loads, I concluded that soleus muscles
were not fully activated when stimulated at a frequency that produced Po
unless stimulated to Po and subsequently quick-released to the after-loads.
whereas muscles stimulated at a frequency that produced dP/dto were fully
activated in all cases except during isotonic contractions at after-loads above
0.40. Furthermore, the extrapolation of measured velocities of a whole
muscle to V max is not valid and the practice should be discontinued.
Description
19 p.
Citation
Publisher
Kalamazoo College
License
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