Visual control of limb trajectory over obstacles during locomotion: effect of obstacle height and width

Abstract

Abstract The focus of these experiments is to describe the changes in limb trajectory when obstacles of different dimensions are encountered at the normal minimal ground clearance position in the step cycle. Kinematics, ground reaction force data, and EMG signals from four ipsilateral limb muscles were collected and analysed while subjects avoided obstacles placed in their path and maintained their normal step length. The results revealed that the trajectory is substantially modulated for height changes but minimally for the width, provided the width of the obstacle does not force subjects to alter their step length. The average clearance of the toe over the obstacle was ≈10 cm, with three subjects increasing the clearance for higher obstacles. The horizontal toe velocity while going over obstacles was reduced more than the hip velocity as a function of obstacle height, while the hip position was further back and closer to the contralateral limb. Subjects landed with an increase in vertical velocity, while reducing the horizontal velocity. These modifications serve to ensure stability and safety of the subjects by minimizing the dangers due to tripping or slipping. The scaling of the trajectory for different heights was not achieved through linear scaling of muscle activity or ground reaction forces. These results provide insights into the visually observable obstacle properties that can influence the locomotor act.