Spatial characteristics of human hand impedance in multi-joint arm movements

The present paper examines spatial characteristics of human hand impedance in multi-joint arm movements. While a subject maintains a hand location, small external disturbance to his hand is applied by a manipulandum. Time changes of the hand displacements and forces caused by the disturbance are measured and the hand impedance is estimated using a second-order linear model. The estimated hand impedance in different subjects and hand locations are summarized as follows: (1) spatial variations of the estimated hand impedance ellipses approximately agree with the experimental results of other researchers (Mussa-Ivaldi et at, 1985: Dolan et al., 1993), (2) the human hand inertia characteristics can be explained from basic biomechanics of the passive inertial effects (3) the grip force of the subject increases the size of the stiffness and viscosity ellipses, and (4) spatial features of the orientation. And the shape characteristics of the stiffness and viscosity ellipses are mostly explained from the kinematics point of view of the human arm