Closed-loop recruitment and frequency modulation of antagonistic muscles during co-activation in FNS

Coactivation of electrically antagonistic muscles provides resistance to external disturbances and continuity of bidirectional activation. A closed-loop controller for simultaneous pulse-width (PW) and stimulus-period (SP) modulation during cocontraction of antagonists has been developed. This PW+SP controller consists of a modified proportional-plus-integral (PI) control law and an SP modulation algorithm that modulates the stimulus frequency of the antagonists in a push-pull manner. The control algorithm is evaluated for the control of joint position and load transition using a cat hindlimb. Faster net force production in the desired direction and improved performance were achieved when compared with the PI controller with PW modulation alone.<>