Visuomotor control of leaping over a raised obstacle is sensitive to small baseline displacements

Abstract

The limb kinematics used for stepping or leaping over an obstacle are determined primarily by visual sensing of obstacle position and geometry. In this study, we demonstrate that changes are induced in limb kinematics even when obstacle geometry is manipulated in a way that does not introduce a mechanical requirement for a change of limb trajectory nor increase risk of collision. Human participants performed a running leap over a single raised obstacle bar. Kinematic changes were measured when an identical second bar was introduced at a ground level underneath the obstacle and displaced by a functionally insignificant distance along the axis of travel. The presence or absence of a baseline directly beneath the highest extremity had no significant effect on limb kinematics. However, displacing the baseline horizontally induced a horizontal translation of limb trajectory in the direction of the displacement. These results show that systematic changes to limb trajectories can occur in the absence of a change in sensed mechanical constraints or optimization. The nature of visuomotor control of human leaping may involve a continuous mapping of sensory input to kinematic output rather than one responsive only to information perceived to be mechanically relevant.

Human locomotion over obstacles reveals real-time prediction of energy expenditure for optimized decision-making

“…The ground underfoot can hence change from step to step, necessitating a cascade of adaptations to steady-state gait. Animals have evolved a set of manoeuvres for negotiating such terrain, including leaping [14], changing direction [15], stepping onto raised/lowered ground [16], elevating the swing limb [17], and locally modifying step length and step width [18][19][20][21]. The energetic implications of these manoeuvres are considerable: human gross metabolic energy expenditure when walking over challenging rocky terrain can be more than twice that of walking over level ground [22], and even small variations (up to 2.5 cm) in terrain substrate height have been shown to increase energy expenditure by over 20% [23].…”