Neural, mechanical, and geometric factors subserving arm posture in humans

摘要: When the hand is displaced from an equilibrium posture by external disturbance, a force generated to restore original position. We developed new experimental method measure and represent field of elastic forces associated with in horizontal plane. While subjects maintained given posture, small displacements along different directions were delivered torque motors. The was held positions and, at that time, we measured corresponding restoring before onset any voluntary reaction. stiffness vicinity position estimated analyzing displacement vectors. chose both numerically, as matrix, graphically, ellipse characterized three parameters: magnitude (the area), shape ratio axis) orientation (direction major axis). latter representation captures main geometrical features posture. also evaluated conservative nonconservative components this field. found former much larger than concluded behavior neuromuscular system multiarticular arm predominantly spring-like. Our data indicated invariant over time. investigated ability our produce adaptive changes stiffness. findings that, when disturbance acting fixed predictable direction imposed, increased but only minor occurred. Taken together, all these experiments step toward understanding interactions between neural factors involved maintaining its environment.