抄録
The mechanical impedance of the human multi-joint arm during point-to-point movement in horizontal plane was investigated by using a high-performance manipulandum and an estimation algorithm newly developed. Ratios of the elbow, shoulder, and two-joint stiffness were greatly altered during movements. As a result, the shape and direction of a hand stiffness ellipse were changed, and the stiffness in a certain direction was sometimes lower than that of posture maintenance. Although the joint stuffiness during movements was increased, it was still lower than that previously assumed in the equilibrium-point control hypothesis. This revealed that the equilibrium trajectory (especially, in the velocity profile) was quite different from the minimum jerk trajectory, indicating that the minimum jerk trajectory could not be a reference trajectory sent to neuro-muscular servo controller based on the equilibrium-point control hypothesis. Rather it suggests that the central nervous system regulates muscle activations to produce appropriate torque patterns based on an internal model of arm dynamics, and to form the arm impedance adequately for interactions with environments.
