Dynamic and Loaded Impedance Components in the Maintenance of Human Arm Posture

Document Type




Publication Date



Institute of Electrical and Electronics Engineers (IEEE)

Source Publication

IEEE Transactions on Systems, Man, and Cybernetics

Source ISSN



The postural stiffness of the human arm has previously been estimated by displacing the hand from a series of equilibrium positions and correlating the resultant displacements and restoring forces. We extend this experimental methodology to include measurement of dynamic components of impedance. The stiffness-damping-mass characteristics are represented numerically as matrices and graphically as ellipses characterized by size, shape, and orientation. The latter depict the predominant nonrotational component of the impedance force fields. The results suggest: (1) joint damping is related to both joint stiffness and joint inertia; and (2) two-joint impedances, i.e., impedances associated with muscles connected across both the elbow and shoulder joints, play a relatively smaller role in damping than in stiffness. The ability to modulate stiffness in the face of initial static bias forces, i.e., "loading", is also examined. We observe regular shifts in the human arm endpoint's "spring center" corresponding to the bias force directions and magnitudes.


IEEE Transactions on Systems, Man, and Cybernetics, Vol. 23, No. 3 (May/June 1993): 698-709. DOI.

Mark Nagurka was affiliated with Carnegie Mellon University at the time of publication.