Figure 1. Experimental protocol and dynamic index measurement.

A and B, sample records that illustrate the experimental protocol used in this study (from top to bottom): the instantaneous firing rate of muscle spindle primary afferent (expressed as impulses (imp) s⁻¹), torque at the wrist joint (expressed as % MVT), rectified EMG (expressed as mV) and joint angle (expressed as deg). Conditioning and test movements were applied to the wrist joint. The test movement consisted of stretch, hold and release with a 16 deg amplitude. It was applied during relaxation (A) and steady voluntary contraction (B). In B, the subject maintained a steady contraction, and EMG level was consistent during the test movement. C, the afferent activity from B (indicated by a dotted line) on an expanded time scale. The instantaneous firing rate in C was determined by averaging over four interspike intervals, to measure the firing rate just before the end of stretch and the dynamic index.