SKELETAL MUSCLE IMPEDANCE IN THE CONTROL OF MOTOR ACTIONS

Abstract

Unlike ideal engineering actuators, skeletal muscle has neither zero nor infinite mechanical impedance. Non-zero neuro-motor mechanical impedance is required to stabilize posture; its possible contribution to movement will briefly be considered. The essential role of variable mechanical impedance to control physical interaction with objects will be described. Evidence that humans voluntarily control impedance to achieve task goals will be reviewed. Robot impedance control is a biologically-inspired approach to controlling robot interaction. How robust contact stability may be achieved by constraining mechanical impedance will be detailed. One robot application requiring contact and cooperation between robots and humans is robotic physiotherapy. Experience to date demonstrating the success of robotic neuro-rehabilitation of patients recovering from stroke will be summarized. Analysis of the geometry of musculo-skeletal attachment reveals that force control may require synergistic co-contraction of apparently antagonist muscles, rendering the conventional anatomical definition of synergist and antagonist muscles ambiguous. Analysis of workless constraint forces show that they may be used to economize muscle effort; exerting force components normal to a kinematic constraint never requires more muscle effort than exerting purely tangential forces.