Journal of Applied Physiology, Vol 71, Issue 2 749-757, Copyright © 1991 by American Physiological Society
Dynamic performance of a load-moving skeletal muscle
R. Baratta and M. Solomonow
Department of Orthopaedic Surgery, Louisiana State University Medical Center, New Orleans.
The dynamic response of the tibialis anterior muscle of the cat was
determined while it was subjected to sinusoidally varying orderly
stimulation of motor units and to different isotonic loads in the range of
14-85% of the maximal isometric force. The dynamic response consisted of
three major components: the displacement gain, the displacement
attenuation, and a pure time delay. The displacement gain was dependent on
the passive load applied to the muscle and the active force generated
during contraction, which could be determined from the length-tension
relationships and the corresponding shortening velocity. In general, the
load displacement decreased as the load mass increased from 25 to 85% of
the maximal isometric force. For loads less than 25% of the maximal
isometric force, slight decrease in displacement was consistently observed.
The displacement attenuation was dependent on the contraction frequency but
uniform for all the load masses applied to the muscle. A pure time delay of
5 ms was present and accounted for various physiological processes such as
conduction time in nerve and muscle, neuromuscular junction transmission,
and excitation-contraction coupling. A quantitative equation was developed
to describe the muscle's dynamic response under isotonic conditions and for
a wide range of loads for use in various applications.
