抄録
In this paper, impedance characteristics of human arm during isometric muscle contraction are measured experimentally, and relationships between hand impedance and various muscle contraction levels are analyzed. Firstly, while a subject regulates a muscle contraction level or amplitude and direction of hand force to an instructed value, small external disturbances to his hand are applied by a manipulandum. Time changes of the hand displacements and forces caused by the disturbance are measured, and the hand impedance are estimated using a second-order linear model. During the experiments, EMG signals of major muscles acing on shoulder and/or elbow joints are measured in order to estimate a muscle contraction level of the subject. The experimental results in different subjects are summarized as follows: 1) coactivation of agonist and antagonist muscles increases the area of stiffness and viscosity ellipses, 2) spatial characteristics of hand stiffness are changed depending on the amplitude and the direction of the hand force, 3) not only stiffness but also virtual trajectory of the subject's hand change with hand force, 4) it might be possible to predict the arm impedance form EMG signals with sufficient accuracy.
