Journal of Applied Physiology, Vol 80, Issue 6 2243-2249, Copyright © 1996 by American Physiological Society
Load, length, and velocity of load-moving tibialis anterior muscle of the cat
R. V. Baratta, M. Solomonow, G. Nguyen and R. D'Ambrosia
Bioengineering Laboratory, Louisiana State University Medical Center, New Orleans 70112, USA.
Three-dimensional relationships of load, length, and velocity of shortening
of the tibialis anterior muscle in the cat were derived experimentally and
fitted with an analytic model. Gravitational loads were applied to the
isolated muscle, which arrived at an equilibrium with the passive forces
before supramaximal tetanic stimulation was delivered to its nerve.
Recordings of initial passive muscle length at equilibrium and length
changes throughout the shortening phase up to the final length at active
equilibrium were taken and numerically differentiated to obtain each load's
instantaneous velocity. A three-dimensional surface was constructed by
using instantaneous length and the corresponding velocity for each of
several loads. Maximal velocity of shortening was shown to gradually
decrease, occurring earlier in the shortening phase (at larger muscle
lengths) as loads increased. Whereas load-velocity curves were hyperbolic
for middle and short muscle lengths, they were nonmonotonic during
shortening above the optimal length. The model was found to correlate well
with the experimental data (R = 0.98) and allowed for prediction of both
muscle performance boundaries and instantaneous shortening velocity for a
given length across the physiological load spectrum, thus offering a
realistic estimation of the contractile properties exhibited by the
tibialis anterior muscle in functions similar to naturally occurring
movements against gravitational loads, which are accelerated and
decelerated during the movement.
