Gj. Lutz et Lc. Rome, MUSCLE FUNCTION DURING JUMPING IN FROGS .1. SARCOMERE-LENGTH CHANGE, EMG PATTERN, AND JUMPING PERFORMANCE, American journal of physiology. Cell physiology, 40(2), 1996, pp. 563-570
We determined the influence of temperature on muscle function during j
umping to better understand how the frog muscular system is designed t
o generate a high level of mechanical power. Maximal jumping performan
ce and the in vivo operating conditions of the semimembranosus muscle
(SM), a hip extensor, were measured and related to the mechanical prop
erties of the isolated SM in the accompanying paper [Muscle function d
uring jumping in frogs. II. Mechanical properties of muscle: implicati
on for system design. Am. J. Physiol. 271 (Cell Physiol. 40): C571-C57
8, 1996]. Reducing temperature from 25 to 15 degrees C caused a 1.75-f
old decline in peak mechanical power generation and a proportional dec
line in aerial jump distance. The hip and knee joint excursions were n
early the same at both temperatures. Accordingly, sarcomeres shortened
over the same range (2.4 to 1.9 mu m) at both temperatures, correspon
ding to myofilament overlap at least 90% of maximal. At the low temper
ature, however, movements were made more slowly. Angular velocities we
re 1.2- to 1.4-fold lower, and ground contact time was increased by 1.
33-fold at 15 degrees C. Average shortening velocity of the SM was onl
y 1.2-fold lower at 15 degrees C than at 25 degrees C. The low Q(10) o
f velocity is in agreement with that predicted for muscles shortening
against an inertial load.