VELOCITY-DEPENDENT TUNING OF MOTOR STRATEGY DURING 3D ARM MOVEMENT AND ITS RELATIONSHIP TO COMPOSITE COST FUNCTIONS

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The purpose of this study was to investigate the link between composite cost functions, within the framework of optimal control, and the velocity-dependent tuning of motor strategy observed during the control of unconstrained 3D arm movements. We considered an arm pointing task at three different speeds. Experimental results indicated a change of rotation axis for most subjects from the geometrical shoulder-elbow (SE) axis toward the minimum principal inertia (e3) axis as velocity increased. These findings were interpreted based on a numerical inverse optimal control approach, assuming a total cost composed of kinematic, energetic and dynamic elements. While the kinematic cost predominated at low speed, the contribution of energetic/dynamic costs was reinforced for speeded movements, likely to exploit the inertial properties of the arm.