Gj. Lutz et Lc. Rome, MUSCLE FUNCTION DURING JUMPING IN FROGS .2. MECHANICAL-PROPERTIES OF MUSCLE - IMPLICATIONS FOR SYSTEM-DESIGN, American journal of physiology. Cell physiology, 40(2), 1996, pp. 571-578
We characterized the design of the frog muscular system for jumping by
comparing the properties of isolated muscle with the operating condit
ions of muscle measured during maximal jumps. During jumping, the semi
membranosus muscle (SM) shortened with a V/V-max (where V is shortenin
g velocity and V-max is maximal shortening velocity) where 90 and 100%
of maximal power would be generated at 15 and 25 degrees C, respectiv
ely. To assess the level of activation during jumping, the SM was driv
en through the in vivo length change and stimulus conditions while the
resulting force was measured. The force generated under the in vivo c
onditions 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. T
he initial sarcomere length and duration of the stimulus before shorte
ning were important factors that minimized shortening deactivation dur
ing jumping. Thus the frog muscular system appears to be designed to m
eet the three necessary conditions for maximal power generation during
jumping: optimal myofilament overlap, optimal V/V-max, and maximal ac
tivation.