Generation of reaching movements: plausibility and implications of the equilibrium trajectory hypothesis

According to the 'equilibrium trajectory' hypothesis, the generation of multi-joint arm movements by the CNS involves the gradual shifting of the hand equilibrium position between the movement end points. This work presents a model which suggests that reaching movements are explicitly planned in terms of spatially and temporally invariant hand equilibrium trajectories. Implementing the model in computer simulations, and using stiffness parameters which were measured during arm posture, arm trajectories were simulated and compared to measured trajectories. The success of the predicted behavior in capturing the fine kinematic details of measured movements supports the validity of the proposed model for biological trajectory control.