Fig. 2

Sagittal positions of the tripped foot throughout strides representative of recovery strategies during treadmill walking. Trajectories of the tripped foot during able-bodied (red), amputee sound side (green) and amputee prosthesis side (blue) recoveries are shown during elevating (left), delayed-lowering (middle) and lowering (right) strategies. Undisturbed walking of the able-bodied subject is also illustrated for reference (dashed line); note that differences in trajectories before the trip occurs are due to different baseline trajectories and not early trajectory deviations. Arrows indicate the direction of foot movement throughout a gait cycle from foot strike to the subsequent foot strike. Positions are defined with respect to a global reference frame. Hence, the foot moves posteriorly during stance, due to movement of the treadmill belt. Dots indicate where the foot was arrested in trip trials. Relative to the position at foot arrest, there were no significant differences across limbs in the elevating strategy. In delayed-lowering strategies, the prosthetic foot was elevated more than in able-bodied recoveries. Lowering strategies on the prosthesis side were achieved with less foot elevation than in able-bodied subjects. Vertical and horizontal axes were scaled to the undisturbed walking amplitude for each subject. Horizontal (vertical) foot position of each stride was zeroed at its most posterior (inferior) position