Figure 1. Raw single motor units and kinematic data recorded during ramp-and-hold wrist extension.

A sample trial of a slow wrist extension-flexion movement acquired by direct visual tracking. Records from above: command signal and joint angle, angular velocity (Vel.), acceleration (Acc.), intramuscular recordings of two motor units (MU0 and MU1), the corresponding instantaneous firing rates of the motor units (Inst. frq.), and rectified surface EMG from m. extensor carpi radialis. Horizontal bars indicate periods of movement (M) and position holding (PH) data selected for statistical analyses.