Roll-over geometry, a leading design objective for passive prosthetic feet, does not provide enough information to find the lower leg segment orientation in the laboratory reference frame. The physical behavior of a prosthetic foot adds a constraint which makes finding this orientation possible. A novel optimization parameter for prosthetic feet that incorporates both the roll-over geometry and the orientation of the lower leg, the Lower Leg Trajectory Error, is introduced. Ground reaction forces and locations of the center of pressure from published gait data for physiological, able-bodied walking are applied to a biologically inspired conceptual prosthetic foot to calculate the resulting lower leg trajectory from foot flat to toe off. The stiffnesses of this conceptual foot are optimized using the Lower Leg Trajectory Error. To further investigate the role of roll-over geometry and physical behavior, the lower leg trajectories of the optimized foot, a rigid foot with roll-over geometry identical to this optimized foot, and a rigid foot with physiological roll-over geometry are compared.
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