Identification of the stretch reflex using pseudorandom excitation: Electromyographic response to displacement of the human forearm

System identification techniques are applied to the human stretch reflex by crosscorrelating a random displacement of the forearm with a surface electromyographic signal obtained from biceps muscle. Since the random forcing function is too fast to be tracked by the subject, the resulting responses reflect components of the limb control system which are automatic. Clear responses are obtained for small displacement amplitudes, typically 0·5 mm at the wrist, with a test duration of about 1 minute. The results, which are highly reproducible, are compared with simulations based upon a linear model of the stretch reflex.