A DYNAMIC NEUROMUSCULAR MODEL FOR DESCRIBING THE PENDULUM TEST OF SPASTICITY

Both dynamic and static thresholds, as well as the gain in the stretch reflex loop, affect the sensitivity of motoneurons to muscle stretch, flow the variation in each parameter will influence the mechanical be havior of patients,vith spasticity. is not well understood because of the difficulty in experimentally isolating individual parameters, A ne uromuscular. dynamic model, based on the pendulum test of spasticity, has been developed to study the specific contribution of individual pa rameter abnormalities in stretch reflex loops to the observed mechanic al abnormalities, The model contains detailed nonlinear dynamics of mu scle force generation and stretch reflexes. A computer simulation of t he model indicates that the stretch reflex thresholds and the gain hav e different influences on the leg swing in the pendulum test of spasti city, Individual changes in the static stretch reflex threshold, in th e dynamic threshold, or in the gain can not stimulate the whole spectr um of spasticity severity, When simultaneous changes in all three para meters of the stretch reflex loop occur, a small variation of the gain coupled with changes in both static and dynamic thresholds can produc e increasing severity of spasticity as the thresholds further decrease , The model is also successful in simulating the effect of posture cha nges on spasticity.