Fig 1. Similarity of muscle spindle IFRs and musculotendon force-related variables in during stretch.

(A) An example ramp-hold-release length profile applied to the triceps surae at the calcaneus, and response of the musculotendon force and muscle spindle primary afferent spiking. The spike train from a single trial and corresponding instantaneous firing rate (IFR) are shown in black at the top as an example of a typical response. Perturbation kinematics (i.e. muscle length, velocity, and acceleration) are shown in red. The musculotendon response to this stretch (i.e. force and dF/dt) is shown in blue. (B) The similarities between muscle spindle IFR shown in black at the top (ensemble average of 20 trials with bin size of 20 ms) and the muscle force-related variables shown in A. Specifically, note the similarities between force (green box) and the plateau response of the muscle spindle (yellow box), and between rate change in force (light blue box) and the dynamic response of the muscle spindle afferent (magenta box). The examples shown are from afferent 2.