Claims:
1. A shoe sole comprising: an outsole having a tread surface and placed at least in a fore foot portion and a rear foot portion; and a midsole placed above the outsole and placed in the fore foot portion, a middle foot portion and the rear foot portion, wherein: the outsole and/or the midsole define: a first transverse groove continuously extending in a transverse direction from a medial edge so as to reach at least a longitudinal axis of a foot at a position of a metatarsal phalangeal joint and/or a base of a proximal phalanx of first to third toes; at least one second transverse groove continuously extending in the transverse direction from the medial edge so as to reach at least the longitudinal axis, in an area between a Chopart's joint of the first toe to a posterior end of a Lisfranc joint; and at least one third transverse groove continuously extending in the transverse direction from the medial edge so as to reach at least the longitudinal axis, in an area between an anterior end to a posterior end of a talus, wherein: the second and third transverse grooves are provided so as to be depressed upwardly from a bottom surface of the shoe sole; each of the grooves to has a front wall surface and a rear wall surface opposing the front wall surface, the front and rear wall surfaces defining each of the grooves; an average value of a width of a flexion area is larger than an average groove width of the first transverse groove and is larger than an average groove width of each of the at least one second transverse groove, wherein the flexion area is an area extending from a most anterior one of the front wall surfaces of the at least one third transverse groove to a most posterior one of the rear wall surfaces of the at least one third transverse groove; and an average depth of the at least one second transverse groove is larger than an average depth of the first transverse groove and is equal to or larger than an average depth of each of the at least one third transverse groove.
2. The shoe sole according to claim 1, wherein an average groove width of at least one of the third transverse groove is larger than the average groove width of the first transverse groove and is larger than the average groove width of each of the at least one second transverse groove.
3. The shoe sole according to claim 2, further comprising an auxiliary transverse groove continuously extending in the transverse direction from the medial edge so as to reach at least the longitudinal axis at a position directly below a base or a shaft of a first metatarsal bone.
4. The shoe sole according to claim 3, wherein an average depth of the auxiliary transverse groove is smaller than the average depth of the second transverse groove, and an average groove width of the auxiliary transverse groove is smaller than the average groove width of at least one of the third transverse groove.
5. The shoe sole according to claim 1, wherein the first transverse groove is depressed upwardly from the tread surface.
6. The shoe sole according to claim 5, wherein: each of the grooves is defined by a front wall surface, a rear wall surface and a ceiling above; a thickness from an upper surface of the midsole to the ceiling of the first transverse groove is set to be 0.5 mm or more and less than 12 mm at a thinnest portion; a thickness from the upper surface of the midsole to the ceiling of the second transverse groove is set to be 0.5 mm or more and 10 mm or less at a thinnest portion; and a thickness from the upper surface of the midsole to the ceiling of the third transverse groove is set to be 0.5 mm or more and 10 mm or less at a thinnest portion.
7. The shoe sole according to claim 1, wherein: a maximum depth of the second and third transverse grooves is 5 mm or more and 40 mm or less; the maximum depth of each of the at least one second transverse groove is larger than a thickness of a portion of the midsole that is directly above an area where the second transverse groove having that maximum depth is provided; and the maximum depth of each of the at least one third transverse groove is larger than a thickness of a portion of the midsole that is directly above an area where the third transverse groove having that maximum depth is provided.
8. The shoe sole according to claim 1, wherein: the average depths of the second and third transverse grooves are 5 mm or more and 40 mm or less; the average depth of at least one of the second transverse groove is larger than an average thickness a of a portion of the midsole that is directly above an area where the at least one second transverse groove is provided; and the average depth of at least one of the third transverse groove is larger than an average thickness a of a portion of the midsole that is directly above an area where the at least one third transverse groove is provided.
9. The shoe sole according to claim 1, wherein: the second transverse groove continuously extends across the shoe sole from the medial edge to a lateral edge of the foot; and the second transverse groove has a larger average depth on a medial side of the foot than an average depth of the second transverse groove on a lateral side of the foot.
10. The shoe sole according to claim 1, wherein: the third transverse groove continuously extends across the shoe sole from the medial edge to a lateral edge of the foot; and the third transverse groove has a larger average depth on a medial side of the foot than an average depth of the third transverse groove on a lateral side of the foot.
11. The shoe sole according to claim 1, wherein the at least one second groove comprises a plurality of second transverse grooves, and the average depth of at least two second transverse grooves is larger than the average depth of the first transverse groove and is equal to or larger than the average depth of each of the at least one third transverse groove.
12. The shoe sole according to claim 2, wherein the at least one third transverse groove comprises a plurality of third transverse grooves, and an average groove width of at least two of the third transverse grooves is larger than the average groove width of the first transverse groove and is larger than the average groove width of each of the at least one second transverse groove.
13. The shoe sole according to claim 1, wherein: the shoe sole is further provided with a longitudinal groove extending from the first transverse groove to the third transverse groove; and the shoe sole further comprises a band portion placed in the longitudinal groove, the band portion extending from the fore foot portion, which is anterior to the first transverse groove, to the rear foot portion, which is posterior to the third transverse groove, the band portion being secured to the shoe sole in the fore foot portion and in the rear foot portion, and the band portion being formed by a material that is less stretchable than the midsole and the outsole
14. The shoe sole according to claim 13, wherein an abrasion-resistant material 34, which is less susceptible to abrasion than the band portion, is attached to a lower surface of the band portion, and the band portion and the abrasion-resistant material together form a band.
15. The shoe sole according to claim 14, wherein a bottom surface of the band is placed above the tread surface.
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