Evaluation of spasticity in upper limbs of hemiplegic subjects using a mathematical model

The purpose of this study is to propose a new technique for evaluating spasticity in the upper limbs of hemiplegic patients. Each subject lay on a bed, and his forearm was supported with a jig to measure the elbow joint angle. The subject was instructed to relax and not to resist the step-like load which was applied to extend the elbow joint. The elbow joint angle and electromyograms of the biceps muscle, triceps muscle and brachioradialis muscle were measured. The step-like response was approximated with a mathematical model which consisted of elastic components depending on both muscle activities and elbow joint angle. The response of hemiplegic subjects were approximated well with the model. The torque generated by the elastic component was estimated. The normalized elastic torque was approximated with a dumped sinusoid by the least square method. The time constant of the elastic torque showed significant differences between the healthy subjects and the hemiplegic subjects and among the different grades of subjects. These results suggest that the time constant of the elastic torque can be a quantitative index of spasticity.