Muscle function during jumping in frogs (ii): the influence of
temperature on the mechanical properties of muscle; implications for
the design of the muscular system.
Lutz, Gordon J., and Lawrence C. Rome.
Department of Biology, University of Pennsylvania, Philadelphia PA
19104, (215) 898-9915, (215) 898-8780 (fax)
APStracts 3:0060C, 1996.
We characterized the design of the frog muscular system for jumping by
comparing the properties of isolated muscle with the operating
conditions of muscle measured during maximal jumps. During jumping
the semimembranosus muscle (SM) shortened with a V/Vmax (where V is
the shortening velocity and Vmax is the maximal shortening velocity)
where 90% and 100% of maximal power would be generated at 15 and 25oC
respectively. To assess the level of activation during jumping the SM
was driven through the in vivo length change and stimulus conditions
while measuring the resulting force. The force exerated under the in
vivo conditions at both temperatures was at least 90% of the force
generated at that same V under maximally activated conditions. Thus,
the SM was nearly maximally activated and shortening deactivation was
minimal. The initial sarcomere length (SL) and duration of the
stimulus prior to shortening were important factors which minimized
shortening deactivation during jumping. Thus, the frog muscular
system appears designed to meet the 3 necessary conditions for
maximal power generation during jumping: optimal myofilament overlap,
optimal V/Vmax and maximal activation.
Received 21 September 1995; accepted in final form 7 February
1996.
APS Manuscript Number C571-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 24 February 96