We compared dynamic hand stiffness during discrete multi-joint arm movement and static stiffness during posture control in order to investigate computational strategy for arm control by the central nervous system. Estimated stiffness during movement obtained by applying small perturbations were lower than those during static posture near the end of the movement. This result supports our simulation study that the virtual equilibrium trajectory of the hand is complicated in its shape to compensate nonlinear interaction forces of the multi-joint arm especially for fast movements.
Gomi et al. (Thu,) studied this question.