Relationship between velocity and curvature of a human locomotor trajectory.

Human locomotion involves the coordination of the movements of the limbs to allow the subject to navigate in the environment. Here we study some curved locomotor paths with the hypothesis that, also during locomotion, movement obey the so-called 'two-thirds power law' stating that the angular velocity of the end effector (here the entire body) is proportional to the two-thirds root of its curvature. We recorded the path of subjects who had to reproduce by mean of displacements of their entire body some circular or elliptical shapes drawn on the ground. Our results clearly show that human subjects adapt their locomotor velocity to the radius of curvature of the path they are following in accordance with the prediction of the power law. These results suggest that for the locomotor system, the central nervous system computes motor strategies in 2D navigational space by taking into account the shape of the path to be followed.