Shoe and foot prosthesis with bending beam spring structures

A sole system which comprises:

• a heel spring formed by upper and lower bending beams attached at a single coupled region;
• wherein each of said bending beams has a fore end and an aft end, a medial edge and a lateral edge, and an upper surface and a lower surface;
• wherein said heel spring has a fore end and an aft end;
• wherein said coupled region has a fore end and an aft end;
• wherein said bending beams are rigidly attached within said coupled region;
• wherein said coupled region is the only region of said heel spring in which a force exerted on one bending beam will influence the other bending beam;
• wherein said heel spring has a single bending beam axis at said coupled region's aft end where the upper surface of the lower bending beam adjoins the lower surface of the upper bending beam along a continuous straight line from the lateral to the medial edges of said bending beams;
• wherein each of said bending beams in use is capable of bending toward the other and storing energy in the region between said bending beam axis and said bending beam's aft end;
• wherein said bending beams are made of a material such that said spring has an energy return of at least 70%;
• and
• wherein at least one of said bending beam surfaces has a concave upward region on its aft end and a concave downward region on its fore end;
• and
• wherein a minimum radius of curvature in said concave upward region is less than a minimum radius of curvature in said concave downward region.