Arm stiffness and movement adaptation to external loads

In this study we have combined kinematic recording and analysis of movement trajectories with computer simulations, based on the equilibrium trajectory control scheme, in order to investigate what mechanisms underlie motor adaptation to unexpectedly introduced external loads. The static arm stiffness field while maintaining posture against externally 1m posed forces was measured and a mathematical model to account for the variations in joint sti!fnesses with external forces was developed. Our results have indicated that the observed motor behavwr m the loaded case can be well accounted for within the framework of the equilibrium trajectory control hypothesis.