Some progress toward a quantitative description of human neuromuscular dynamics

Abstract

s $71 SOME PROGRESS TOWARD A QUANTITATIVE DESCRIPTION OF HUMAN NEUROMUSCULAR DYNAMICS GEORGE I. ZAHALAK (Department of Mechanical Engineering, Washington University, St. LOUIS. MO 63130, U.S.A.) The quantitative description of the dynamic behavior of human skeletal muscle as it functions normally in-t-it-o is a very difficult problem for which only limited results have been obtained to date. Some progress has been made recently by the author and his associates via extensive frequency-response tests of the forearm flexion/extension system in normal adult males. These experiments invrolved both voluntary and externally forced oscillations. but were restricted to smnfl fractional variations in muscle length, and suggested mathematical models for bo!h (1) the dynamic relation between force, length and EMG in muscle, and (2) the dynamic relation between reflex EMG and muscle stretch. A new versatile testing device, dubbed the Programmable Limb Testing System (PLTS). has made possible the extension of these experiments to large variations in muscle length and wider dynamic ranges: experiments are currently in progress to verify and generalize the small-amplitude frequency-response results. A new approach to formulating a whole muscle model valid for large variations in muscle length, both in shortening and in stretch, has been proposed by the author. This model, termed the Distribution-Moment Model, is based directly on current biophysical theories of molecular contraction dynamics and appears o olfer several advantages over the classic A. V. Hill model while retaining much of the latter’s simplicity. EFFECT OF IMMOBILIZATlON AND REMOBILIZATION ON THE PROPERTIES OF THE MEDIAL COLLATERAL LIGAMENTS SAVIO L-Y. WOO, PETER 0. NEWTON and MARK A. GOMEZ (San Diego Veterans Administration Medical Center and University of California, San Diego, La Jolla, CA 92093, U.S.A.) Twenty-two New Zealand white rabbits were divided into four groups: (1) 9 weeks of immobilization, (2) 12 weeks of immobilization, (3) 9 weeks immobilization + 9 weeks remobilization and (4) 12 weeks immobilization + 9 weeks remobilization. At sacrifice, the medial collateral ligament (MCL) specimen including the bones were tested following Woo et al. The load-deformation curve for the MCL-bone complex and the load-strain curve of the MCL substance were obtained. With immobilization, the strength characteristics of the MCL-bone complex reduced to approximately l/3 that of the controls. There were Iarge differences in the load-strain curves between the control and experimental MCL’s indicating that changes in the ligament mechanical properties had possibly occurred. Interestingly, the load-strain curves of the experimental and control MCL from the remobilization groups were similar, indicating recovery of the properties of the MC substance. The structural strength of the MCL-bone complexes from the experimental knees, however, continued to be inferior (Noyes er 01.. 1974).