Characterization of neuro-musculoskeletal model with spinal reflex regulation

A human being can perform many different movements to adapt to variable environment, all these skills are extraordinary feats of coordination and control. It is believed that they result from the human hierarchical motor control system. This system is a complex nonlinear system including highly integrated neural centers in the brain and the spinal cord, many actuators constructed by muscles and bones and numerous sensory receptors. It is believed that the neuro-musculoskeletal model of human motor control system is very important to understand the characteristics of the system and many neuro-musculoskeletal models were presented over the past decades. In this paper, dynamic behavior and mechanism of the neuro-musculoskeletal model presented in are investigated. It is a single joint reflex model with agonist and antagonist muscles. Some intrinsic properties of the system model such as behavior of the moment arms, characteristics of force and stabilization are presented. The results reveal some inherit properties in the system. Firstly, to guarantee a unique equilibrium point of the system, the descending neuron control commands must be selected in special range; Secondly, the reflex regulation in spinal control circuit, i.e., the feedback from Renshaw cells and gamma motor neurons, are not absolutely necessary to ensure the system stable, the system can still converge to a equilibrium point with the constant muscle activations.