Figure 3.

Exemplary spindle afferent responses across movement cycles. Responses of the afferent 5701 (also shown in Fig. 2) and of another type Ia afferent recorded from the extensor digitorum muscle of a different subject. Also shown are the simultaneously recorded EMG signals, MCP joint torque, and kinematics from the two individuals (left and right columns, respectively) from which each afferent was recorded. Each trace represents the average across 10 continuous movement cycles. Shaded colored areas represent ±1 SEM, and the coloring scheme is the same as in Figure 1B. In addition to any bias load, the same viscous load was experienced across all conditions for damping. Despite the very similar kinematics during the initial 250 ms of muscle stretch (gray background bars), large differences in afferent firing rate were observed as a function of bias load condition, with even no clear difference in extensor muscle EMG between the no bias load (red) and the bias load resisting flexion (blue) over most of this period. For comparison, extensor EMG during equivalent passive motion of the finger is also shown (dashed colored lines).