Midsole structure for a shoe

1. A midsole structure for a shoe comprising:

an upper midsole disposed on an upper side of said midsole structure at a heel region that corresponds to a heel portion of a foot of a wearer of the shoe;

a lower midsole disposed below said upper midsole; and

a wavy sheet interposed between said upper midsole and said lower midsole;

wherein said wavy sheet has a wavy shape with ridge lines and trough lines at least either at a sheet medial side portion or at a sheet lateral side portion of said wavy sheet, and a planar shape area at a sheet central portion of said wavy sheet, wherein said sheet central portion of said wavy sheet is disposed at a heel central region of said midsole structure, and wherein said planar shape area extends across a plurality of said ridge and trough lines at said sheet medial side portion or at said sheet lateral side portion in a substantially longitudinal direction of said midsole structure; and

wherein a lower surface of said upper midsole and an upper surface of said lower midsole respectively have a wavy shape that corresponds to said wavy shape of said wavy sheet at least either at a midsole medial side portion or at a midsole lateral side portion, said lower surface of said upper midsole and said upper surface of said lower midsole respectively have a planar shape area that corresponds to said planar shape area of said wavy sheet at said heel central region of said midsole structure, and at least either said lower surface of said upper midsole or said upper surface of said lower midsole has a plurality of recesses disposed along the substantially longitudinal direction at said heel central region of said midsole structure.

2. The midsole structure according to claim 1 , wherein at least either said lower surface of said upper midsole or said upper surface of said lower midsole has a wavy shape formed of said plurality of recesses at said heel central region of said midsole structure.

3. The midsole structure according to claim 1 , wherein either only said lower surface of said upper midsole or only said upper surface of said lower midsole has a wavy shape formed of said plurality of recesses at said heel central region of said midsole structure.

4. The midsole structure according to claim 1 , wherein both said lower surface of said upper midsole and said upper surface of said lower midsole respectively have a wavy shape formed of said plurality of recesses at said heel central region of said midsole structure.

5. The midsole structure according to claim 4 , wherein said plurality of recesses of said lower surface of said upper midsole at said heel central region and said plurality of recesses of said upper surface of said lower midsole at said heel central region are aligned with one another in an up-down direction.

6. The midsole structure according to claim 4 , wherein said plurality of recesses of said lower surface of said upper midsole at said heel central region and said plurality of recesses of said upper surface of said lower midsole at said heel central region are not aligned with one another in an up-down direction, and are offset from one another in the substantially longitudinal direction, and wherein said wavy shape of said lower surface of said upper midsole and of said upper surface of said lower midsole is formed by said plurality of recesses of both said upper midsole and said lower midsole.

7. The midsole structure according to claim 1 , wherein at least either said lower surface of said upper midsole or said upper surface of said lower midsole has a trough line that extends in a substantially widthwise direction of said midsole structure at a bottom portion of said plurality of recesses.

8. The midsole structure according to claim 1 , wherein at least either said lower surface of said upper midsole or said upper surface of said lower midsole has a trough line that extends inclined relative to a substantially widthwise direction of said midsole structure at a bottom portion of said plurality of recesses.

9. The midsole structure according to claim 1 , wherein said wavy sheet has an opening portion formed thereinto at said sheet central portion.

10. The midsole structure according to claim 1 , wherein said planar shape area of said wavy sheet is a two-dimensional flat planar area that has a flat planar shape extending in said substantially longitudinal direction and in a substantially widthwise direction of said midsole structure at said sheet central portion.

11. The midsole structure according to claim 1 , wherein said ridge lines and said trough lines of said wavy shape of said wavy sheet respectively extend in a substantially widthwise direction of said midsole structure.

12. The midsole structure according to claim 1 , wherein said planar shape area of said wavy sheet does not have a wavy shape.

13. The midsole structure according to claim 1 , wherein said planar shape area of said wavy sheet does not have ridge and trough lines.

14. The midsole structure according to claim 1 , wherein said ridge lines and said trough lines of said wavy shape of said wavy sheet are discontinuous in a substantially widthwise direction and are interrupted and non-existent at said planar shape area of said wavy sheet.

15. The midsole structure according to claim 1 , wherein said planar shape area of said wavy sheet is displaced forwardly away from a rear end of a heel of said midsole structure.

16. The midsole structure according to claim 1 , wherein a rear end of said wavy sheet is displaced forwardly away from a rear end of a heel of said midsole structure.

17. The midsole structure according to claim 1 , wherein said planar shape area of said wavy sheet is displaced transversely inwardly away from a medial side edge and a lateral side edge of said midsole structure.

18. The midsole structure according to claim 1 , wherein a surface of said planar shape area of said wavy sheet extends locally substantially parallel to an upper surface of said upper midsole.