Reciprocal reflex control of equilibrium joint position by antagonistic muscles

This paper describes a movement control model that integrates the spring-like property of muscles and their reciprocal reflex control circuit. The descending commands specify an equilibrium position of the joint and an excitation signal for antagonist muscles. The equilibrium signal activates γ motor neurons of muscle spindles, and the excitation signal activates α motor neurons of extrafusal muscle fibers. The equilibrium position is achieved through reciprocal inhibition, which balances the action of the antagonists at the joint. A movement is produced by shifting the equilibrium position and altering the intensity of excitation signal. Simulation results show that a smooth movement with a bell shaped velocity profile, and triphasic flexor/extensor activities can be reproduced with proper choice of reflex gains