SOLE FOR A SHOE

Abstract

In the stable posture, in which path length from the origin to the distal end is L, intersection between the sole bottom surface and line perpendicular to the reference line through position of 0.45×L is C, intersection between the sole bottom surface and line perpendicular to the reference line through position of 0.60×L is D, and sole is in contact with the ground at points C and D, the sole bottom surface at the heel portion is separated from the ground to be in a heel-up state, and an inequality, θ≥5 is satisfied wherein θ is an angle formed by the ground and line that connects the heel central position of 0.15×L with the metatarsophalangeal joints position of 0.68×L. The sole compressive rigidity is relatively lower at the heel-up starting position than at the metatarsophalangeal joints position.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to a sole for a shoe, and more particularly, to an improvement of a sole structure that can achieve a forefoot running in a more natural manner during running without encumbering a forefoot movement by urging an elevation of a heel after landing on the ground.

Recently, when running efficiently in a long-distance race, a forefoot running style that impacts the ground at a forefoot region of a foot has become a mainstream. The forefoot running style has merits that it can reduce the burden on a knee and shorten a ground-contact time to ease the burden on muscles. It is considered that an efficient movement can be attained and a superior running economy can be achieved by skillfully utilizing springy behaviors of an Achilles tendon and calf muscles, i.e. expansion/contraction of the Achilles tendon and contraction/relaxation of the calf muscles, during the forefoot running. Here, the term, “running economy” is an index showing how one can run at a certain speed zone with less energy (or less oxygen consumption). The more superior or higher the running economy is, the smaller oxygen consumption will be and thus an efficient running can be achieved.

However, it requires not less than a certain degree of skill to acquire such a forefoot running. Specifically, first, a contact skill is necessary to allow for a forefoot/midfoot contact with the ground in a phase immediately before a ground contact. Then, a leg strength (or muscular strength and endurance) is necessary to restrain a falling (or sinking/dropping) of a heel to withstand stretching of tendon of muscles in a phase of the ground contact and a lock of an ankle is also necessary. Therefore, it was not easy for a beginner runner to acquire the forefoot running. It mostly depends on an ability of a runner whether he/she can perform the forefoot running continuously.

Incidentally, a sole with a high-rigidity plate (e.g. CFRP (carbon fiber reinforced plastic) plate) incorporated therein has been provided for a practical use in order to support a heel during sinking of the heel. In such a sole, when a load is transferred to a forefoot portion, a forefoot area of the plate is pushed downwardly and thus a heel area of the plate is lifted upwardly through a seesaw action, thereby supporting the heel.

However, since the sole incorporating such a plate is not so structured as to urge a forefoot running naturally as a single piece of sole, it was not sufficient for causing the forefoot running to be sustainable.

Therefore, to achieve the forefoot running, the applicant of the present application proposed a sole for a shoe disclosed in Japanese patent application publication No. 2020-163084 (see paragraphs [0020] to [0024], [0028] to [0030] and FIG. 9). In this sole, inequalities, m2≥m1, m1≥f and m1≥h are satisfied, wherein a position of a rearmost end of a foot-sole-contact-side surface is designated as the origin of a coordinate, a path length measured along the foot-sole-contact-side surface of the sole from the origin to a position of a tip of a toe is designated as L, in a state that the foot-sole-contact-side surface at a heel region is arranged parallel to a horizontal plane, a sole thickness at position Sh of 0.16×L from the origin is h, a sole thickness at position Sm2 of (0.3-0.5)×L from the origin is m2, a sole thickness at position Sm1 of (0.4-0.6)×L from the origin is m1 provided that the position Sm1 is disposed in front of the position Sm2, and a sole thickness at position Sf of 0.7×L from the origin is f. Also, another inequality, θ2≥θ1 is satisfied, wherein an angle between a line connecting the positions Sm1 and Sh and the horizontal plane is θ1, a position where a vertical line drawn from the position Sm1 crosses a ground-contact surface is Sm1′, a position where a vertical line drawn from the position Sh crosses the ground-contact surface is Sh′, and an angle between a line connecting the positions Sm1′ and Sh′ and the horizontal plane is θ2. Furthermore, the ground-contact surface has a downwardly convexly curved shape at a forefoot region.

According to the sole described in the above-mentioned publication, the sole thickness h at the position Sh of 0.16×L from the origin is smaller than the sole thickness m1 at the position Sm1 of (0.4-0.6)×L from the origin, and besides, the angle θ2 between the line connecting the positions Sm1′ and Sh′ and the horizontal plane is greater than the angle θ1 between the line connecting the positions Sm1 and Sh and the horizontal plane. Thereby, at the time of striking onto the ground, the heel portion does not contact the ground, thus not causing a heel strike, thereby promoting a forefoot contact with the ground on landing. Also, the sole thickness m2 at the position of Sm2 is greater than the sole thickness m1 at the position of Sm1, such that thereby when an initial contact with the ground occurs at the position Sm1′ on the sole ground-contact surface, the sole is prevented from leaning rearwardly and thus the heel is restricted from sinking downwardly, thus promptly moving onto a forward rolling of the sole after the initial contact with the ground. Furthermore, the sole thickness f at the position of 0.7×L from the origin is smaller than the sole thickness m1 at the position Sm1, and besides, the sole ground-contact surface has a downwardly convexly curved shape at the forefoot portion, thereby achieving a smooth forward rolling of the sole.

Through further intensive researches on the sole to achieve a forefoot running, the inventors of the present invention have found that there is room for improvement in the sole of the above-mentioned publication to urge a forefoot running naturally during running, to make it sustainable, and to increase a running efficiency during the forefoot running

Accordingly, the applicant of the present application proposed a sole as shown in Japanese patent application publication Nos. 2023-96397 and 2023-95714.

In the sole of Japanese patent application publication No. 2023-96397, in a phase of a ground contact where the sole 1 is in contact with the ground R at point C, a sole reference posture is maintained, in which the sole bottom surface 31 at the heel portion and the toe tip portion is separated from the ground R. Thereby, an intentional ground contact of the heel portion can be prevented, a natural forefoot posture can be promoted and made sustainable. Also, in the reference posture, an inequality, θ≥5 [degrees] is satisfied, wherein the angle θ is set between the ground and a straight line connecting a heel central position 20h of 0.15×L along the sole upper surface 20 from the origin O with a metatarsophalangeal joints position 20j of 0.68×L along the sole upper surface from the origin O. Thereby, the heel portion can be disposed above the forefoot portion of the sole 1 (that is, put at a heel-up state), thus matching it with a forefoot posture (see paragraphs [0025] to [0026], [0033] to [0034], and FIGS. 4, 5, 8(a) of the above-mentioned publication).

Then, in a phase immediately after the ground contact of the sole 1, the heel portion of the sole 1 sinks (or falls) down a distance of d toward the ground R, but the sole 1 is placed in the reference posture (see FIG. 8(a)) in which the sole 1 is in contact with the ground R at the point C of (0.45×L) from the origin O in front of the foot ankle at the time of impacting the ground. Thereby, not only a natural support effect can be developed by the sole bottom surface 31 from the moment of the ground contact but also a shoe wearer can conduct springy behaviors of tendons of the foot. In such a way, an excessive sinking of the heel portion can be prevented to lessen the amount d of sinking/drop, thus relieving a load to the shoe wearer to improve a running efficiency (see paragraph [0035], FIG. 8(b) of the above-mentioned publication). As a result, after the ground contact of the sole 1, the distance to lift up the heel portion can be shortened, thus promptly moving onto the phase of a heel-lift-up of FIG. 8(c). In such a manner, a switching from the heel portion to the forefoot portion after impacting the ground can be conducted smoothly and a smooth shift in center of gravity from the heel portion to the toe portion can be achieved (see paragraph [0036], and FIG. 8(c) of the above-mentioned publication).

Japanese patent application publication No. 2023-96397 describes that a compressive rigidity of the midsole is lower at the metatarsophalangeal joints position and higher at the heel portion. At the time of loading during running, a midsole portion at the metatarsophalangeal joints position deforms downwardly more largely than the heel portion. Thereby, an excessive sinking of the heel portion after the ground contact of the sole can be prevented and a forward load transfer can be smoothly conducted (see paragraphs [0045] to [0047], and FIGS. 10 to 11 of the above-mentioned publication).

On the other hand, in the sole of Japanese patent application publication No. 2023-95714, a curved plate P is disposed inside the sole 1 (see paragraph [0023] and FIG. 1) and a compressed rigidity of the sole body 1A is relatively lower at the metatarsophalangeal joints (MP joints) position 20j (see paragraph [0033], and FIGS. 3, 3A).

In this case, when a maximum load is applied to the sole 1 after the ground contact of the sole 1, the sole forefoot lower portion 2B₁ relatively largely compressive-deforms and the sole 1 sinks downwardly. Then, toes are largely bent and a plantar aponeurosis PF is stretched, thereby elevating an arch SA, promoting a windlass action, and increasing a propulsion force during running. Also, after the ground contact of the sole 1, when the heel is about to sink downwardly, the curved plate P can support the heel portion thus decreasing the amount of drop (or fall) of the heel portion. Moreover, when a maximum load is applied, since a support angle relative to the foot sole is increased, a supporting and elevating effect can be further enhanced at the midfoot portion to the heel portion and the stiffness of the foot can be further increased to further improve a stability. Then, as the toes move to the maximum bending state and the sole 1 reaches a maximum bending phase, the plantar aponeurosis PF is further stretched and the arch SA is further lifted upwardly to further promote the windlass action (see paragraphs [0039] to [0046], and FIG. 3).

Through further intensive researches on the soles of the above-mentioned publications, the inventors of the present invention have found the fact as stated below:

A prior-art shoe aimed to achieve a natural forefoot running by constituting a sole in such a way that as the sole reaches a maximum amount of sinking during running, the angle of the foot relative to the ground can be maintained and the forefoot portion deforms relatively largely without deforming the rearfoot portion (heel portion).

However, when conducting a sensory evaluation through an actual running of a runner who wears shoes, it turns out that in the prior-art shoe, when the sole reaches a maximum amount of sinking during running, an elevation of the heel portion is urged and as a result, a natural forefoot running was rather hindered. It was considered to be the reason that a deviation from a natural forefoot running becomes large by maintaining the angle of the foot relative to the ground till the latter half of the movement stage of a gate cycle (i.e. a running cycle from a ground-contact to a toe-off).

The present invention has been made in view of these circumstances and its object is to provide a sole for a shoe that can achieve a further more natural forefoot running without impeding a forefoot motion by causing an elevation of the heel to be urged after impacting the ground.

Other objects and advantages of the present invention will be obvious and appear hereinafter.

SUMMARY OF THE INVENTION

A sole for a shoe according to the present invention extends from a heel region through a midfoot region to a forefoot region and has a sole upper surface and a sole lower surface. A sole stable posture is proposed in which a line that connects a rearmost end position of the sole upper surface with a distal end position of a toe is defined as a reference line s, the rearmost end position is defined as an origin O, a path length measured along the sole upper surface from the origin O to the distal end position of the toe is defined as L, an intersection point between the sole lower surface and a line perpendicular to the reference line S through a position of 0.45×L from the origin O along the sole upper surface is defined as C, an intersection point between the sole lower surface and a line perpendicular to the reference line S through a position of 0.60×L from the origin O along the sole upper surface is defined as D, and the sole is in contact with the ground at the points C and D. In the sole stable posture, the sole lower surface is separated from the ground at a toe portion and the sole lower surface is separated from the ground at the heel region to be in a heel-up state. In the sole stable posture, an inequality, θ≥5 [degrees] is satisfied in which the angle θ is defined as an angle formed between the ground and a line connecting a heel central position of 0.15×L from the origin O along the sole upper surface and a metatarsophalangeal joints position of 0.68×L from the origin O along the sole upper surface. Also, a sole compressive rigidity in an up-and-down direction is relatively lower at a heel-up starting position of the heel region than at the metatarsophalangeal joints position.

According to the present invention, at the time of a ground contact of the sole with the ground, since the sole contacts the ground at two points, that is, at point C corresponding to the position of 0.45×L from the origin O and at point D corresponding to the position of 0.60×L from the origin O, a stable sole posture can be attained, thereby eliminating a time loss and a power loss.

Also, according to the present invention, since the sole lower surface at the toe portion and the heel portion is separated from the ground (i.e. in a heel-up state for the heel portion) in the sole stable posture, an unintentional heel contact with the ground can be prevented at the time of the ground contact. Moreover, according to the present invention, the line connecting the heel central position and the metatarsophalangeal joints position forms an angle of 5 degrees or more relative to the ground in the sole stable posture, thereby allowing for maintaining a heel-up state of the heel portion and matching a sole posture with a forefoot posture.

Moreover, according to the present invention, since the sole compressive rigidity in the up-and-down direction is relatively lower at the heel-up starting position of the heel region than at the metatarsophalangeal joints position, when the sole reaches a maximum amount of sinking during running, a rearfoot-region side (or a heel-region side) can deform downwardly relatively more largely than a forefoot-region side. Thereby, the angle of the foot relative to the ground can be prevented from being sustained till the latter half of a motion stage of a gate cycle (i.e. a running cycle from a ground-contact to a toe-off), thus preventing the forefoot motion from being hindered by urging an elevation of the heel after the ground contact. As a result, a further more natural forefoot running can be achieved utilizing springy behaviors of tendons of the foot.

Here, in the specification of the present application, “sole compressive rigidity” is a concept that expresses a resistance to compressive deformation of a sole relative to a compressive load. When the same compressive load is applied, a sole of a high compressive rigidity causes a small amount of deformation and a sole of a low compressive rigidity causes a large amount of deformation.

In the sole stable posture, the sole lower surface may be separated from the ground in a rearward region that extends rearward from the position of 0.15×L from the origin O along the sole upper surface, the sole lower surface may be separated from the ground in a forward region that extends forward from the position of 0.68×L from the origin O along the sole upper surface, and the sole lower surface may be in contact with the ground in a forward region that extends forward from the position of 0.15×L from the origin O along the sole upper surface and in a rearward region that extends rearward from the position of 0.68×L from the origin O along the sole upper surface.

The heel-up starting position may be disposed at a backside of an ankle position of 0.27×L from the origin O along the sole upper surface.

In the sole stable posture, in a static upright posture when a shoe is worn by a shoe wearer, the sole compressive rigidity is determined such that θ<5 [degrees] is satisfied. Here, in this specification of the present application, “a static upright posture” is a posture in which a shoe wearer stands up straight with his/her weight evenly distributed on both feet at the time of non-exercise.

The heel region may have an aperture and the forefoot region may not have an aperture.

The heel region and the forefoot region may have an aperture and an open width of the aperture at the heel region may be greater than an open width of the aperture at the forefoot region.

The heel region and the forefoot region may have an aperture and an aperture ratio at the heel region may be greater than an aperture ratio at the forefoot region. Here, in the specification of the present application, “aperture ratio” is a ratio of an aperture volume to an entire volume.

The heel region may be formed by a material of relatively lower hardness and the forefoot region may be formed by a material of relatively harder hardness.

Both the heel region and the forefoot region may have a material area of relatively lower hardness and another material area of relatively harder hardness. An occupancy ratio of the material area of relatively lower hardness at the heel region may be set at a relatively high value and an occupancy ratio of the material area of relatively higher hardness at the forefoot region may be set at a relatively high value. Here, in the specification of the present application, “occupancy ratio” is a ratio of the material area to the entire area.

The points C and D may be disposed at least at a lateral side edge portion of the sole lower surface.

A region extending from the point C to the point D of the sole lower surface may constitute a stable region formed of a flat-shape, and in the sole stable posture, the stable region may be in contact with the ground. In this case, the flat-shaped stable region extending from the point C to the point D can cause a sole posture at the time of the ground contact to be stable and thus the forefoot posture can be made stable.

As above-mentioned, according to the present invention, a sole for a shoe can be achieved that can accomplish a further more natural forefoot running without impeding a forefoot motion by urging an elevation of a heel after a ground contact.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention.

FIG. 1 is a general perspective view of a sole (for a left foot) according to an embodiment of the present invention, as viewed from diagonally above.

FIG. 2 is a general perspective view of the sole of FIG. 1 on a bottom side thereof, as viewed from diagonally below.

FIG. 3 is a general perspective view of the sole of FIG. 1 on a bottom side thereof, as viewed from diagonally below.

FIG. 4 is a general perspective view of the sole of FIG. 1 on a bottom side thereof, as viewed from diagonally below.

FIG. 5 is a rear view of the sole of FIG. 1, as viewed from a heel rear side.

FIG. 6 is a top plan schematic view of the sole of FIG. 1.

FIG. 7 is a bottom schematic view of the sole of FIG. 1.

FIG. 8 is a medial side schematic view of the sole of FIG. 1.

FIG. 9 is a lateral side schematic view of the sole of FIG. 1.

FIG. 10 is a longitudinal sectional view of FIG. 7 taken along line X-X.

FIG. 11 is a cross-sectional view of FIG. 7 taken along line XI-XI.

FIG. 12 is a cross-sectional view of FIG. 7 taken along line XII-XII.

FIG. 13 is a cross-sectional view of FIG. 7 taken along line XIII-XIII.

FIG. 14 is a cross-sectional view of FIG. 7 taken along line XIV-XIV.

FIG. 15 is a cross-sectional view of FIG. 7 taken along line XV-XV.

FIG. 16 is a general perspective view of a plate provided at said sole of FIG. 1, as viewed from diagonally above.

FIG. 17 is a side schematic view of the plate of FIG. 16.

FIG. 18 is a partial perspective view of the plate of FIG. 16 on a bottom side thereof, as viewed from diagonally below.

FIG. 19 is a side schematic view of a shoe employing the sole of the present invention.

FIG. 20 is a side schematic view of the sole of FIG. 19 showing along with a bone structure diagram of a shoe wearer.

FIG. 21 is a bottom schematic view of the sole of FIG. 19.

FIG. 22 is a schematic illustrating the state in a static upright posture in which a load from a foot of a show wearer is applied to the sole of FIG. 20.

FIG. 23 shows the state of the shoe of FIG. 19 during running, illustrating the motion of the shoe relative to the ground in order of (a) to (d) in time-series manner.

FIG. 24 shows the state of a shoe as a comparative example during running, illustrating the motion of the shoe relative to the ground in order of (a) to (d) in time-series manner.

FIG. 25 is a schematic bottom plan view of a sole according to an example of the present invention, corresponding to FIG. 7.

FIG. 26 is a schematic bottom plan view of a sole according to a first variant or alternative example of the present invention.

FIG. 27 is a schematic longitudinal sectional view of a sole according to a second variant of the present invention.

FIG. 28 is a schematic longitudinal sectional view of a sole according to a third variant of the present invention.

FIG. 29 is a schematic longitudinal sectional view of a sole according to a fourth variant of the present invention.

FIG. 30 is a schematic longitudinal sectional view of a sole according to a fifth variant of the present invention.

FIG. 31 is a schematic longitudinal sectional view of a sole according to a sixth variant of the present invention.

FIG. 32 is a schematic longitudinal sectional view of a sole according to a seventh variant of the present invention.

FIG. 33 is a schematic longitudinal sectional view of a sole according to a eighth variant of the present invention.

FIG. 34 is a graph illustrating a negative work by a plantar flexion torque of a foot ankle during running wearing the shoe of the present invention, as compared with a comparative example and a prior-art product.

FIG. 35 is a graph showing a correlation between a deformation rate of a support and an angle θ (11 degrees before deformation) after deformation, in the case that the deformation rate of the forefoot region is 40%.

FIG. 36 is a graph showing a correlation between a deformation rate of a support and an angle θ (11 degrees before deformation) after deformation, in the case that the deformation rate of the forefoot region is 45%.

FIG. 37 is a graph showing a correlation between a deformation rate of a support and an angle θ (4 degrees before deformation) after deformation, in the case that the deformation rate of the forefoot region is 40%.

FIG. 38 is a graph showing a correlation between a deformation rate of a support and an angle θ (4 degrees before deformation) after deformation, in the case that the deformation rate of the forefoot region is 45%.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference to embodiments thereof as illustrated in the accompanying drawings.

FIGS. 1 to 25 show a sole according to an embodiment of the present invention and a shoe incorporating the sole. In these drawings, FIGS. 1 to 5 illustrate an external appearance of the shoe; FIGS. 6 to 15 are a top plan view, a bottom plan view, a side view and a sectional view of the sole; FIGS. 16 to 18 illustrate an external appearance of the plate; FIGS. 19 to 22 are a schematic side view and a schematic bottom plan view illustrating the shape of the sole in detail; FIG. 23 shows the state of the shoe during running in time-series manner; and FIG. 24 shows the state of a shoe as a comparative example during running in time-series manner in comparison with the sole of FIG. 23. Here, an athletic shoe, especially, a running shoe for a middle to long distance is taken for an example as a shoe.

In the following explanation (the same is applicable to the following first to eighth variants), “upward (upper side/upper)” and “downward (lower side/lower)” designate an upward direction and a downward direction, or vertical direction, of the shoe, respectively, “forward (front side/front)” and “rearward (rear side/rear)” designate a forward direction and a rearward direction, or longitudinal direction, of the shoe, respectively, and “a width or lateral direction” designates a crosswise direction of the shoe.

For example, in FIG. 19, a side schematic view of the shoe, “upward” and “downward” designate “upward” and “downward” in FIG. 19, respectively, “forward” and “rearward” designate “right to left direction” in FIG. 19, and “a width direction” designates “out of the page” and “into the page” of FIG. 19.

As shown in FIGS. 1 to 5, Shoe 1 of the present embodiment comprises a midsole 2 that extends longitudinally along the entire length of the sole 1 and an outsole 3 that is disposed below the midsole 2. The midsole 2 includes an upper midsole 2a disposed on an upper side of the sole 1 and a lower midsole 2b disposed below the upper midsole 2a. A top surface (sole top surface) 20 of the upper midsole 2a constitutes a foot-sole contact surface that a foot sole of a shoe wearer comes into a direct contact with or an indirect contact with through an insole and the like. An outer circumferential edge portion of the top surface 20 has an upraised portion 20a that rises upwardly. The outsole 3 is fixedly attached to the bottom surface of the lower midsole 2b through an adhesive and the like.

The midsole 2 (thus, the upper and lower midsoles 2a, 2b) is preferably formed of a soft elastic material, more specifically, thermoplastic synthetic resin and its foamed resin such as ethylene-vinyl acetate copolymer (EVA) or the like, thermosetting synthetic resin and its foamed resin such as polyurethane (PU) or the like, alternatively, rubber material and foamed rubber such as butadiene rubber, chloroprene rubber or the like. The outsole 3 is preferably formed of a hard elastic material, more specifically, thermoplastic resin such as thermoplastic polyurethane (TPU), polyamide elastomer (PAE) and the like, thermosetting resin such as epoxy resin and the like, or solid rubber. In addition, materials for the midsole 2 and the outsole 3 are not limited to the above-mentioned materials. Any other suitable materials can be adopted.

Also, the midsole 2 may be formed not only by a normal injection foam molding method but also by a supercritical foaming method. Here, the “supercritical foaming method” is a method in which resin is made into a super-critical-fluid state under a high temperature and a high pressure and an injection foam molding is conducted. Through such a supercritical foaming method, the midsole 2 can be further lighter in weight.

A plate 4 is inserted between the upper midsole 2a and the lower midsole 2b and sandwiched therebetween. The details of the plate 4 is described below.

At a lower surface (bottom surface) of the sole 1, a vertical hole (aperture) 5 is formed. The hole 5 passes through the outsole 3 but not through the midsole 2. In this exemplification, the hole 5 has a lenticular shape (i.e. a biconvex-lens shape) as viewed from below and extends longitudinally from a heel region to a longitudinally central portion of a midfoot region. Also, in this exemplification, an opening width of the hole is the largest at the lower surface (bottom surface) of the sole 1 and formed in a tapered shape that becomes gradually small toward the inside of the sole 1.

As shown in a sole top plan view of FIG. 6 and a sole bottom plan view of FIG. 7, the sole 1 includes a heel region H, a midfoot region M, and a forefoot region F that respectively correspond to a heel portion, a midfoot portion (plantar arch portion), and a forefoot portion of a foot of a shoe wearer. The sole 1 extends from the heel region H through the midfoot region M to the forefoot region F. The plate 4 extends from the heel region H through the midfoot region M to near the front-end portion (or toe portion) of the forefoot region F of the sole 1. A front-side area of the plate 4 is provided with a plurality of ribs 40 that longitudinally extends curvedly (for more details, see below). In FIG. 7, for illustration purposes, illustration of the ribs 40 of the plate 4 are omitted. Also, in FIG. 7, the bottom surface 50 of the hole 5 appears.

In a sole medial side view of FIG. 8 and a sole lateral side view of FIG. 9, a portion that a design (e.g. uneven patterns) is applied to is shown along with another portion (a white or void portion) that a design is not applied to.

As shown in a sole longitudinal sectional view of FIG. 10, the hole 5 passes through the lower midsole 2b of the midsole 2 in an up-and-down direction (or a right-to-left direction of FIG. 10). The bottom surface 50 of the hole 5 is formed by the lower surface of the plate 4. Also, FIG. 10 and FIGS. 13 to 15 (a sole cross-sectional view) show that the hole 5 has a tapered shape longitudinally and laterally. As shown in FIG. 10, the plate 4 extends curvedly in a longitudinal direction and the ribs 40 are provided at the lower surface of the plate 4. The upper midsole 2a is in contact with the top surface of the plate 4 (see FIGS. 10, 12 to 15) and the lower midsole 2b is in contact with the ribs 40 of the plate 4 (see FIGS. 10 and 12).

As shown in FIGS. 16 to 18, the plate 4 is a thin sheet-like member and its thickness is, for example, 1 to 2 [mm], approximately. For instance, the plate 4 may be disposed inside the midsole 2 through an insert molding, alternatively, may be attached to a boundary surface between the upper midsole 2a and the lower midsole 2b via an adhesive and the like. At a longitudinally central position of the plate 4, a pair of upstanding walls 41 are provided that rise upwardly. The respective ribs 40 disposed at and bulging from the lower surface of the plate 4 protrude downwardly and extend longitudinally. A cross-sectional shape of the respective ribs 40 is not restricted to such a rectangular shape and any suitable shape can be adopted. Also, in the example shown in FIGS. 6 and 18, the respective ribs 40 are provided symmetrically about the longitudinal centerline and formed in a lenticular-shape or a biconvex-lens shape by these ribs 40, as viewed from below. As shown in FIGS. 17 and 10, the plate 4 is curved in a slightly downwardly convex shape on a forefoot-portion side and a heel-portion side, and curved in a slightly upwardly convex shape on a midfoot-portion side.

The plate 4 may be formed of thermoplastic resin comparatively rich in elasticity such as thermoplastic polyurethane (TPU), polyamide elastomer (PAE), acrylonitrile butadiene styrene resin (ABS) and the like, alternatively, thermosetting resin such as epoxy resin, unsaturated polyester resin and the like. Also, as a material for the plate 4, fiber reinforced plastics (FRP) may be adopted in which carbon fibers, aramid fibers, glass fibers or the like are incorporated as a strengthened fiber, and thermosetting resin or thermoplastic resin is incorporated as matrix resin.

Next, the details of the sole according to the present invention and a shoe incorporating the sole will be explained hereinafter in reference to FIGS. 19 to 22.

As shown in FIG. 19, shoe SH includes the sole 1 and is so structured as to fixedly attach an upper U to the top side of the sole 1 via bonding, sewing and the like. In FIG. 19, for simplified illustration and explanation, the sole 1 is formed of a single-layered midsole 2 and an outsole 3 disposed below the midsole 2.

As shown in FIG. 19, a reference line S is defined as a straight line that connects a toe-tip position Se and a rearmost end position (or heel rear end position) S₀ of the sole top surface 20. Here, the sole top surface 20 coincides with a shape of a bottom surface of a last in use for assembly of the shoe SH. Then, the rearmost end position S₀ is set to the origin O, a path length measured along the sole top surface 20 from the origin O to the toe-tip position Se is set to L. An intersection between the sole bottom surface 31 and a line orthogonal to the reference line S through the position 20m of 0.45×L from the origin O along the sole top surface 20 is set to C, and another intersection between the sole bottom surface 31 and a line orthogonal to the reference line S through the position 20n of 0.60×L from the origin O along the sole top surface 20 is set to D. In FIG. 19, an intersection between the reference line S and a line orthogonal to the reference line S through the position 20m is defined as Sp, and an intersection of the reference line S and a line orthogonal to the reference line S through the position 20n is defined as Sq.

When a sole posture in which the sole 1 is in contact with the ground R at points C and D is defined as a sole stable posture, the sole bottom surface 31 at the heel portion and the toe portion is separated (or floated) from the ground R in the sole stable posture. Therefore, the sole bottom surface 31 at the heel portion is in a heel-up state and the position where the sole bottom surface 31 starts a heel-up (i.e. starts to leave from the ground R) at the heel portion is defined as a heel-up starting point.

FIG. 20 is a drawing with a bone structure of a foot of a shoe wearer added to FIG. 19. As shown in FIG. 20, point D of the sole bottom surface 31, which is disposed below position 20n of 0.60×L from the origin O along the sole top surface 20, corresponds to a position of hypothenar eminence (or near the base of a fifth toe) of the foot of the shoe wearer.

Also, as shown in FIG. 20, in the sole stable posture, an inequality, θ≥5 [degrees] is satisfied, wherein an angle (acute angle) between the ground R and a straight-line T connecting the heel central position 20h of 0.15×L from the origin O with the metatarsophalangeal joints position 20j of 0.68×L from the origin O along the sole top surface 20 is set to 0.

Here, a compressive rigidity of the sole 1 in the up-and-down direction (a sole compressive rigidity: a resistance to compressive deformation of a sole relative to a compressive load) is relatively lower at the heel-up starting position of the heel portion than at the metatarsophalangeal joints position 20j. Therefore, when the same compressive load is applied, the amount of compressive deformation of the sole 1 is larger at the heel-up starting position of the heel portion than at the metatarsophalangeal joints position 20j.

The heel-up starting position of the sole bottom surface 31 at the heel portion is preferably the position 20h of 0.15×L from the origin O along the sole top surface 20 in the sole stable posture, as shown in FIG. 20. In this case, at a region rearward from the position 20h, the sole bottom surface 31 is separated from the ground R. Also, preferably, as shown in FIG. 20, at a region forward from the position of 0.68×L from the origin O along the sole top surface 20, the sole bottom surface 31 is separated from the ground R. Moreover, preferably, at a region forward from the position of 0.15×L from the origin O along the sole top surface 20 and a region rearward from the position of 0.68×L from the origin O along the sole top surface 20, the sole bottom surface 31 is in contact with the ground R (see FIG. 20).

More preferably, as shown in FIG. 20, the heel-up starting position of the sole bottom surface 31 at the heel portion is disposed at the back side of the ankle position 20k of 0.27×L from the origin O along the sole top surface 20. In other words, in the sole stable posture, the sole bottom surface 31 is in contact with the ground R at the position (ankle position) 20k of 0.27×L from the origin O along the sole top surface 20. This ankle position 20k corresponds to a generally boundary position between the heel region H and the midfoot region M, as mentioned below. Thereby, in the sole stable posture, a contact area of the sole bottom surface 31 relative to the ground R can be extended in the longitudinal direction, thus allowing for a stabler forefoot posture. In FIG. 20, an area encircled by a dash-and-dot line designates an external ankle LM of the foot. The external ankle LM is disposed below the fibula FB. Also, in FIG. 20, reference characters TB, TL and CC designate a tibia, a talus, and a calcaneus, respectively.

A foot bone structure in FIG. 20 is added for explanation purposes to associate the shape of the sole 1 with the foot bone structure. On the other hand, FIG. 22 shows that state in which the foot of the shoe wearer is actually placed on the sole 1 and the load is applied to the sole 1. At this juncture, in the sole stable posture, at a static upright posture (that is, a posture in which a shoe wearer stands up straight with a weight evenly distributed on both feet at the time of non-exercise when wearing a shoe), the sole compressive rigidity is determined to satisfy an inequality, θ<5 [degrees].

As shown in FIG. 22, in a loaded state that the load from the foot is applied to the sole top surface 20, since the sole compressive rigidity is smaller on the heel side than on the forefoot side, the amount of compressive deformation on the forefoot side is relatively small and the amount of deformation on the heel side is relatively large. Therefore, the sole top surface hardly sinks at the metatarsophalangeal joints position 20j but greatly sinks at the heel central position 20h. As a result, after loading, the heel central position is lowered from the position 20h to the position 20h′ disposed below the position 20h.

Here, when an angle (acute angle) between the ground R and a straight-line (a dash-and-dot line) T′ connecting the heel central position 20h′ with the metatarsophalangeal joints position 20j is set to 0′, in the sole stable posture, an inequality,

θ′<θ

• • is satisfied. That is, an inequality,

θ′<5[degrees]

• • is satisfied. Additionally, in FIG. 22, the straight-line T connecting the heel central position 20h (FIG. 20) with the metatarsophalangeal joints position 20j is shown by a double dotted line.

Then, as shown in FIG. 21, the heel region H, the midfoot region M and the forefoot region F of the sole 1 are designated as follows (by using the path length L measured along the sole top surface 20 from the origin O to the toe-tip end position Se):

• • i) Heel region: 0 to (0.25×L) and the heel rear end edge portion
  • ii) Midfoot region: (0.25×L) to (0.60×L)
  • iii) Forefoot region: (0.60×L) to (1.00×L)

In an example shown in FIG. 21, points C and D on the sole bottom surface 31 are respectively disposed at positions of 0.45×L and 0.60×L from the origin O in the lateral-side edge portion (including the position near the lateral-side edge) and the medial-side edge portion (including the position near the medial-side edge) of the outsole 31.

Preferably, as shown in a hatched area of FIG. 21 and FIGS. 19, 20, a region extending from the position of 0.45×L to the position of 0.60×L from the origin O at the sole bottom surface 31 is formed in a flat shape to constitute a sole stable area. In a sole stable posture in which the sole 1 contacts the ground R at the points C and D, the entire hatched area (or sole stable area) of the sole bottom surface 31 is preferably in contact with the ground R.

Then, effects of the present embodiment will be explained in reference to FIG. 23.

FIG. 23 shows movements of the shoe SH relative to the ground R in order of (a) to (d) in time-series manner. FIG. 23(a) shows a phase at an initial ground contact of the sole 1. At this time, the sole 1 takes a sole posture in which the sole 1 comes into contact with the ground R at the points C and D (see FIGS. 19 to 22) of the sole bottom surface 31, for example, at two points of the lateral-side points C and D (FIG. 21) of the sole bottom surface 31, maintaining a sole stable posture.

As set forth above, in the sole stable posture in which the sole 1 is in contact with the ground R at two points C and D, the sole bottom surface 31 is disposed separately (or floated) away from the ground R at the heel regions and toe portions (see FIG. 19).

Thereby, at the initial ground contact, an unintentional ground contact of the heel region can be prevented, a forefoot running can be naturally promoted, and a forefoot posture can be stabilized. Also, a rolling to the toe portion can be performed smoothly and the forefoot running can be more naturally promoted.

Preferably, at a rearward region extending rearwardly from the position of 0.15×L from the origin O and a forward region extending forwardly from the position of 0.68×L from the origin O, the sole bottom surface 31 is disposed separately (or floated) away from the ground R. More preferably, at the position of 0.27×L from the origin O, the sole bottom surface 31 is in contact with the ground R (see FIG. 20). Thereby, even in the case in which the heel region contacts the ground on the front-end side thereof at the initial ground contact, the sole 1 can be prevented from sinking downwardly toward the heel side to maintain a forefoot posture and a forefoot running can be supported. As a result, the burden on a runner can be lessened to increase a sense of assurance during running.

Also, in the sole stable posture, as above-mentioned, an inequality, θ≥5 [degrees] is satisfied, wherein in FIG. 20 the angle θ is set between the ground and a straight line connecting the heel central position 20h of 0.15×L along the sole top surface 20 from the origin O with the metatarsophalangeal joints position 20j of 0.68×L along the sole top surface 20 from the origin O. Angle α in FIG. 23(a) corresponds to the angle θ (in this exemplification, the angle α is set at an angle greater than the angle θ). Thereby, the heel region of the sole 1 can be disposed above the forefoot region (that is, put at a heel-up state), thus matching it with a forefoot posture.

FIG. 23(b) shows a phase of an intermediate motion after the initial ground contact of the sole 1. At this time, as shown in FIG. 23(b), a maximum load is applied to the sole 1 and the sole 1 is maximally compressed in the up-and-down direction. In this case, the sole 1 contacts the ground R at the points C and D on the medial side of the sole bottom surface 31 as well as at the points C and D on the lateral side of the sole bottom surface 31, thereby maintaining the stable posture of the sole 1 to hold the forefoot posture.

Moreover, at this juncture, as mentioned above, the compressive rigidity of the sole 1 (sole compressive rigidity: a resistance to compressive deformation of a sole relative to a compressive load) in the up-and-down direction is relatively lower at the heel-up starting position (heel central position 20h) of the heel portion than at the metatarsophalangeal joints position 20j. Thereby, when the load is applied to the sole 1 after the initial ground contact, the sole 1 compressive-deforms more largely at the heel central position 20h than at the metatarsophalangeal joints position 20j. Therefore, the angle β in FIG. 23(b) is smaller than the angle α in FIG. 23(a) at the initial ground contact (that is, β<α).

In such a manner, when the sole 1 reaches the maximum amount of sinking at the time of loading after the initial ground contact of the sole 1, the sole 1 deforms downwardly relatively largely at the rearfoot side (heel side) than at the forefoot side. Thereby, the angle of the foot relative to the ground can be prevented from being sustained till the latter half of a motion stage of a gate cycle (i.e. a running cycle from a ground-contact to a toe-off), thus preventing the forefoot motion from being hindered by urging an elevation of the heel after the ground contact, thereby moving onto a natural elevating motion of the heel portion. As a result, a further more natural forefoot running can be achieved utilizing springy behaviors of tendons of the foot.

Then, FIG. 23(c) shows a phase after an elevation of the heel portion has started. At this time, as shown in FIG. 23(c), the toe portion of the sole bottom surface 31 is about to leave the ground R. In the phase of FIG. 23(b) immediately before the phase of FIG. 23(c), since the sole bottom surface 31 is in contact with the ground R at the positions C and D and thus a stable forefoot posture is maintained, a transition from this state to the state of FIG. 23(c) can be smoothly conducted. Thereby, during running, a runner can be directed to a natural elevating motion in a streamlined and effortless manner. Then, in FIG. 23(d), the sole 1 leaves the ground R completely.

Here, FIG. 24 shows the state of a shoe as a comparative example during running. Sole 1′ of this shoe SH′ has a shape similar to the shape of the sole 1 of the shoe SH in FIG. 23 (see FIG. 20), but in contrast to the present invention, a compressive rigidity of the sole 1′ in the up-and-down direction is relatively lower at the metatarsophalangeal joints position 20j than at the heel-up starting position of the heel portion. In this case, when the same compressive load is applied, the amount of compressive deformation of the sole 1′ becomes greater at the metatarsophalangeal joints position 20j than at the heel-up starting position of the heel region.

FIG. 24, similar to FIG. 23, illustrates the motion of the shoe SH′ relative to the ground R in order of (a) to (d) in time-series manner. Respective phases (a) to (d) of FIG. 24 correspond to the respective phases (a) to (d) of FIG. 23, respectively. In FIG. 24, like reference numbers indicate identical or functionally similar elements to those in FIG. 23.

FIG. 24(a) shows a phase of an initial ground contact of the sole 1′. At this time, as with FIG. 23(a), the sole 1′ takes a sole posture in which the sole bottom surface 31′ contacts the ground R at point C′ and D′ (see FIGS. 19 to 22) and maintains a stable posture. The sole bottom surface 31′ is disposed separately (floating) from the ground R at the heel region and the toe portion. Also, angle α′ in FIG. 24(a) corresponds to the angle θ (θ≥5 [degrees]) in FIG. 20. In this case, the angle α′ is equal to the angle α.

FIG. 24(b) shows a phase of an intermediate motion after the initial ground contact of the sole 1′. At this time, a maximum load is applied to the sole 1′ and the sole 1′ is maximumly compressed in the up-and-down direction. Also, at this time, as mentioned above, since the compressive rigidity of the sole 1′ in the up-and-down direction is relatively lower at the metatarsophalangeal joints position 20j than at the heel-up starting position of the heel region (heel central position 20h), when the maximum load is applied to the sole 1′, the sole 1′ compressive-deforms largely at the metatarsophalangeal joints position 20j than at the heel central position 20h. Therefore, the angle β′ in FIG. 24(b) is greater than the angle α′ in FIG. 24(a) at the initial ground contact (i.e. β′>α′)

In this manner, at the time of loading after the initial ground contact of the sole 1′, when the sole 1′ reaches the maximum sinking amount, the forefoot side deforms downwardly relatively more largely than the rearfoot side (heel side). As a result, the angle of the foot relative to the ground is maintained till the latter half of the movement stage of the gate cycle (i.e. a running cycle from a ground-contact to a toe-off), thus urging the elevation of the heel to cause a natural forefoot running to be hindered.

In the phase of FIG. 24(c), after the heel region starts to elevate, the toe portion of the sole bottom surface 31 is about to leave the ground R. Then, in FIG. 24(d), the sole 1′ completely leaves (i.e. toes off) from the ground R.

Next, the following performance test of a shoe (invention product) incorporating the sole of the present invention is conducted to confirm a load relieving effect relative to triceps surae muscle of a shoe wearer. The outline of the test is as follows:

• • i) Two runners (N=2);
    • The breakdown of ground-contact pattern is one forefoot runner and one midfoot runner;
  • ii) Prepared shoes are below three types:
    • (a) Invention product;
    • (b) Comparative example (see paragraph [0070]); and
    • (c) Prior-art product (sole does not have a heel-up shape like the invention product and the comparative example, and a sole bottom surface has a flat shape from a heel region to a forefoot region); and
  • iii) Constant-speed running at the rate of 20.0±1.0[km/h] wearing the respective shoes;
  • iv) Measurement of physical feature points of the runners during running and the ground reaction force, using the motion capture system (MAC 3D system) of Motion Analysis Corporation and the ground reaction force gauge of Kistler Group; and
  • v) Calculation of a negative work of a plantar flexion torque of a foot ankle, which is a general indicator of eccentric contraction of triceps surae muscle after calculating the plantar flexion torque of the foot ankle by inverse dynamics calculation through the physical feature points of the runners and the ground reaction force.

Results of calculation of the plantar flexion torque of the foot ankle regarding the respective shoes are shown in FIG. 34. As is clearly seen from FIG. 34, it is found that the comparative example increases a load relieving effect of triceps surae muscle in comparison with the prior-art product and the invention product further increases a load relieving effect of triceps surae muscle in comparison with the comparative example.

Then, FIGS. 35 to 38 show a correlation between a deformation rate of the forefoot region and the rearfoot portion (heel region) and the above-mentioned angle θ. Here, “deformation rate” is defined as the following formula:

$\mathrm{Deformation}\mathrm{Rate}=$ $\left[\left(\mathrm{deformation}\mathrm{amount}\right)/\left(\mathrm{sole}\mathrm{thickness}\mathrm{before}\mathrm{deformation}\right)\right]\times 100\left[\%\right]$

For example, when the sole thickness before deformation is 50 [mm] and the sole thickness after deformation is 30 [mm], as the deformation amount is 20 [mm],

$\mathrm{Deformation}\mathrm{Rate}=\left(20/50\right)\times 100=40\left[\%\right]$

The greater the deformation rate is, the smaller the compressive rigidity becomes. Also, the support designates a region of the rearfoot portion (heel region) of the sole bottom surface that contacts the ground.

FIGS. 35 and 36 show an example in which before-deformation angle θ is 11 [degrees] (that is, high), and FIGS. 37 and 38 show an example in which before-deformation angle θ is 4 [degrees] (that is, low). Also, FIGS. 35 and 37 show changes of the angle θ when the deformation rate of the support varies from 40[%] to 55[%] in the case of deformation rate 40[%] of the forefoot region. Similarly, FIGS. 36 and 38 show changes of the angle θ when the deformation rate of the support varies from 40[%] to 55[%] in the case of deformation rate 45[%] of the forefoot region. In the respective drawings, an encircled area by a dotted line is determined on the basis of a sensory evaluation that is obtained from the runners after they actually run in a forefoot-style. Such an area shows the border of a range of evaluation of the runners. That is, when the angle θ is situated below such an area, the runners evaluate that a more natural forefoot running is achieved.

As shown in FIG. 35, in the event that the before-deformation angle θ is 11 [degrees] (high) and the deformation rate of the forefoot region is 40[%], as the deformation rate of the support exceeds 47[%] (in the graph, after-deformation angle θ become smaller than approximately 5.5 [degrees]), sensory evaluation becomes better. Also, as shown in FIG. 36, in the event that the before-deformation angle θ is 11 [degrees] (high) and the deformation rate of the forefoot region is 45[%], as the deformation rate of the support exceeds 49[%] (in the graph, after-deformation angle θ become smaller than approximately 5.5 [degrees]), sensory evaluation becomes better. Therefore, in either case, it is found that when the before-deformation angle (initial angle) θ becomes approximately halved after deformation, the sensory evaluation becomes better.

On the other hand, as shown in FIG. 37, in the event that the before-deformation angle θ is 4 [degrees] (low) and the deformation rate of the forefoot region is 40[%], as the deformation rate of the support exceeds 45[%] (in the graph, after-deformation angle θ become smaller than approximately 1.8 [degrees]), sensory evaluation becomes better. Also, as shown in FIG. 38, in the event that the before-deformation angle θ is 4 [degrees] (low) and the deformation rate of the forefoot region is 45[%], as the deformation rate of the support exceeds 49[%] (in the graph, after-deformation angle θ become smaller than approximately 1.8 [degrees]), sensory evaluation becomes better. That is, in either case, it is found that when the before-deformation angle (initial angle) θ becomes approximately halved after deformation, the sensory evaluation becomes better.

Then, FIG. 25 show a general bottom view of the sole 1 (corresponding to FIG. 7). As shown in FIG. 25, an area extending from the heel region H to a generally longitudinally central position of the midfoot region M of the sole 1 is formed with a hole (aperture) 5 that opens to the sole bottom surface 31, but another area extending from the generally longitudinally central position of the midfoot region M to the forefoot region F of the sole 1 is not formed with a hole (aperture). Thereby, the compressive rigidity of the sole 1 in the up-and-down direction is relatively lower at the heel-up starting position of the heel region (heel central position 20h) than at the metatarsophalangeal joints position 20j.

<First Variant>

FIG. 26 shows a sole according to a first variant of the present invention. In FIG. 26, like reference numbers indicate identical or functionally similar elements to those in FIG. 25. As shown in FIG. 26, an area extending from the heel region H to a generally longitudinally central position of the midfoot region M of the sole 1 is formed with a hole (aperture) 50 that opens to the sole bottom surface 31, and another area extending from the generally longitudinally central position of the midfoot region M to the forefoot region F of the sole 1 is formed with a hole (aperture) 51 that opens to the sole bottom surface 31 and that is in connection with the hole 50. An opening width W of the hole 50 is greater than an opening width w of the hole 51 (that is, W>w). Thereby, the compressive rigidity of the sole 1 in the up-and-down direction is relatively lower at the heel-up starting position of the heel region (heel central position 20h) than at the metatarsophalangeal joints position 20j.

<Second Variant>

FIG. 27 shows a general longitudinal sectional view of a sole according to a second variant of the present invention. In the above-mentioned embodiment and the first variant, an example was shown in which the sole 1 has a vertical hole formed therein, but in the second variant, as shown in FIG. 27, the sole 1 has a plurality of lateral or transversal holes (apertures) 52 formed therethrough in a width direction of the sole 1. The respective holes 52 are formed at an area extending from the heel region H to the midfoot region M of the sole 1, but not formed at the forefoot region F and the most part of the midfoot region M of the sole 1. Thereby, the compressive rigidity of the sole 1 in the up-and-down direction is relatively lower at the heel-up starting position of the heel region (heel central position 20h) than at the metatarsophalangeal joints position 20j. In addition, the respective holes 52 may or may not open to the medial side surface and/or the lateral side surface of the sole 1.

<Third Variant>

FIG. 28 shows a general longitudinal sectional view of a sole according to a third variant of the present invention. In the above-mentioned embodiment, an example was shown in which one vertical hole is formed in the sole 1, but in the third variant, as shown in FIG. 28, a plurality of holes (apertures) 53 extending vertically are formed at the midsole 2 of the sole 1. The number of holes 53 is not restricted to this example. The respective holes 53 are formed at an area extending from the heel region H to the midfoot region M of the sole 1, but not formed at the forefoot region F and the large part of the midfoot region M of the sole 1. Thereby, the compressive rigidity of the sole 1 in the up-and-down direction is relatively lower at the heel-up starting position of the heel portion (heel central position 20h) than at the metatarsophalangeal joints position 20j. In addition, the respective holes 53 may open to the bottom surface of the sole 1.

<Fourth Variant>

FIG. 29 shows a generally longitudinal sectional view of a sole according to a fourth variant of the present invention. In the second variant, an example was shown in which a plurality of laterally extending holes is formed only at the area extending from the heel region H to the midfoot region M of the sole 1, but in the fourth variant, as shown in FIG. 29, a plurality of laterally extending holes 52 is formed at an extending from the heel region H to the midfoot region M of the sole 1 and a plurality of laterally extending holes 52′ is formed at the forefoot region F and the large part of the midfoot region M of the sole 1. The number of holes 52, 52′ is not restricted to this example. The diameter of the respective holes 52 is greater than that of the respective holes 52′. In this case, an aperture (or opening) ratio of the hole is greater at the heel-up starting position of the heel region (heel central position 20h) than at the metatarsophalangeal joints position 20j. Here, “aperture ratio” is a ratio of an opening volume relative to the entire volume. In this example, the aperture ratio is a ratio of a total volume of the respective holes 52 (or 52′) relative to the entire volume (i.e. total hole volume plus midsole volume)

Thereby, the compressive rigidity of the sole 1 in the up-and-down direction is relatively lower at the heel-up starting position of the heel region (heel central position 20h) than at the metatarsophalangeal joints position 20j. In addition, the respective holes 52, 52′ may open to the medial side surface and/or the lateral side surface of the sole 1. Also, similarly, in the example of FIG. 26 as well, an aperture (or opening) ratio of the hole is greater at the heel-up starting position of the heel region (heel central position 20h) than at the metatarsophalangeal joints position 20j.

<Fifth Variant>

FIG. 30 shows a generally longitudinal sectional view of a sole according to a fifth variant of the present invention. In the third variant, an example was shown in which a plurality of vertically extending holes 53 is formed only at the area extending from the heel region H to the midfoot region M of the sole 1, but in the fifth variant, as shown in FIG. 30, a plurality of vertically extending holes 53 is formed at an extending from the heel region H to the midfoot region M of the sole 1 and a plurality of vertically extending holes 53′ is formed at the forefoot region F of the sole 1. The number of holes 53, 53′ is not restricted to this example. The diameter of the respective holes 53 is greater than that of the respective holes 53′. In this case, similar to the above-mentioned fourth variant, an aperture (or opening) ratio of the hole is greater at the heel-up starting position of the heel portion (heel central position 20h) than at the metatarsophalangeal joints position 20j.

Thereby, the compressive rigidity of the sole 1 in the up-and-down direction is relatively lower at the heel-up starting position of the heel region (heel central position 20h) than at the metatarsophalangeal joints position 20j. In addition, the respective holes 53, 53′ may open to the bottom surface of the sole 1.

<Sixth Variant>

FIG. 31 shows a generally longitudinal sectional view of a sole according to a sixth variant of the present invention. In the above-mentioned embodiment and the first to fifth variants, an example was shown in which forming a hole (aperture) in the sole 1 makes a difference of the compressive rigidity of the sole 1, but the application of the present invention is not restricted to such an example.

As shown in FIG. 31, the midsole of the sole 1 includes a midsole 21 that is disposed at an area extending from the heel region H to the generally longitudinal central position of the midsole region M and a midsole 2₂ that is disposed at another area extending from the generally longitudinal central position of the midsole region M to the forefoot region F. The midsole 21 is formed of a relatively low-hardness material and the midsole 2₂ is formed of a relatively high-hardness material, and a boundary 2d between the midsoles 2₁ and 2₂ extends substantially upwardly. Thereby, the compressive rigidity of the sole 1 in the up-and-down direction is relatively lower at the heel-up starting position of the heel portion (heel central position 20h) than at the metatarsophalangeal joints position 20j.

<Seventh Variant>

FIG. 32 shows a generally longitudinal sectional view of a sole according to a seventh variant of the present invention. In the above-mentioned sixth variant, an example was shown in which the boundary 2d between the midsoles 2₁ and 2₂ extends substantially upwardly, but in the seventh variant, as shown in FIG. 32, the boundary 2d′ between the midsoles 2₁ and 2₂ extends substantially longitudinally. That is, the respective midsoles 2₁, 2₂ extend from the heel region H through the midfoot region M to the forefoot region F of the sole 1.

Moreover, in this case, at an area extending from the heel region H to the midfoot region M, the thickness of the midsole 2₁ is greater than the thickness of the midsole 2₂. Therefore, the occupancy rate of the midsole 2₁ (relative to the entire midsole) formed of a relatively low-hardness material is relatively higher at such a region. Also, at the forefoot region F, the thickness of the midsole 2₂ is greater than the thickness of the midsoles 2₁. Therefore, the occupancy rate of the midsole 2₂ (relative to the entire midsole) formed of a relatively high-hardness material is relatively higher at such another region.

Thereby, the compressive rigidity of the sole 1 in the up-and-down direction is relatively lower at the heel-up starting position of the heel region (heel central position 20h) than at the metatarsophalangeal joints position 20j.

<Eighth Variant>

FIG. 33 shows a generally longitudinal sectional view of a sole according to an eighth variant of the present invention. In the eighth variant, the boundary 2d′ between the midsoles 2₁ and 2₂ extends substantially longitudinally and the respective midsoles 2₁, 2₂ extend from the heel region H through the midfoot region M to the forefoot region F of the sole 1 as with the above-mentioned seventh variant, but the midsole 2₁ formed of a relatively low-harness material is disposed on the lower side of the sole 1 and the midsole 2₂ formed of a relatively high-harness material is disposed on the upper side of the sole 1.

Also, it is similar to the above-mentioned seventh variant that at an area from the heel region H to the midfoot region M, the thickness of the midsole 2₁ is greater than that of the midsoles 2₂, the occupancy rate of the midsole 2₁ (relative to the entire midsole) of a relatively low-hardness material is thus relatively higher at such a region, at the forefoot region F, the thickness of the midsole 2₂ is greater than the thickness of the midsoles 2₁, and the occupancy rate of the midsole 2₂ (relative to the entire midsole) of a relatively high-hardness material is thus relatively higher at such another region.

Thereby, the compressive rigidity of the sole 1 in the up-and-down direction is relatively lower at the heel-up starting position of the heel portion (heel central position 20h) than at the metatarsophalangeal joints position 20j.

<Ninth Variant>

In the above-mentioned embodiment, an example was shown in which the plate 4 is provided inside the midsole 2 of the sole 1 and the plate 4 is formed with a plurality of ribs 40, but a thin plate without ribs 40 may be adopted by omitting the ribs 40 from the plate 4. Moreover, the plate itself can be omitted. By removing the plate 4, the compressive deformation of the heel region H of the sole 1 can be promoted at the time of loading during running. In addition, by extending the plate 4 along the entire length of a shoe, supportability relative to the foot portion can be improved, bending rigidity of the sole 1 can be increased, and at the time of toe-off, a runner can kick the ground strongly and obtain a propulsive force due to an action of an elastic resilience of the plate 4.

As mentioned above, the present invention is useful for a sole of a shoe that can achieve a further more natural forefoot running without impeding a forefoot motion by causing an elevation of the heel to be urged after impacting the ground during a forefoot running.

Those skilled in the art to which the invention pertains may make modifications and other embodiments employing the principles of this invention without departing from its spirit or essential characteristics particularly upon considering the foregoing teachings. The described embodiments and examples are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. Consequently, while the invention has been described with reference to particular embodiments and examples, modifications of structure, sequence, materials and the like would be apparent to those skilled in the art, yet fall within the scope of the invention.

Claims

1. A sole for a shoe, said sole extending from a heel region through a midfoot region to a forefoot region and having a sole upper surface and a sole lower surface,

wherein a sole stable posture is proposed in which a line that connects a rearmost end position of said sole upper surface with a distal end position of a toe is defined as a reference line S, said rearmost end position is defined as an origin O, a path length measured along said sole upper surface from the origin O to said distal end position of said toe is defined as L, an intersection point between said sole lower surface and a line perpendicular to said reference line S through a position of 0.45×L from the origin O along said sole upper surface is defined as C, an intersection point between said sole lower surface and a line perpendicular to said reference line S through a position of 0.60×L from the origin O along said sole upper surface is defined as D, and said sole is in contact with the ground at said points C and D,

wherein in said sole stable posture, said sole lower surface is separated from the ground at a toe portion and said sole lower surface is separated from the ground at said heel region to be in a heel-up state,

wherein in said sole stable posture, an inequality, θ≥5 [degrees] is satisfied in which said angle θ is defined as an angle formed between the ground and a line connecting a heel central position of 0.15×L from the origin O along said sole upper surface and a metatarsophalangeal joints position of 0.68×L from the origin O along said sole upper surface,

wherein a sole compressive rigidity in an up-and-down direction is relatively lower at a heel-up starting position of said heel region than at said metatarsophalangeal joints position.

2. The sole according to claim 1, wherein in said sole stable posture, said sole lower surface is separated from the ground in a rearward region that extends rearward from the position of 0.15×L from the origin O along said sole upper surface, said sole lower surface is separated from the ground in a forward region that extends forward from the position of 0.68×L from the origin O along said sole upper surface, and said sole lower surface is in contact with the ground in a forward region that extends forward from the position of 0.15×L from the origin O along said sole upper surface and in a rearward region that extends rearward from the position of 0.68×L from the origin O along said sole upper surface.

3. The sole according to claim 1, wherein said heel-up starting position is disposed at a backside of an ankle position of 0.27×L from the origin O along said sole upper surface.

4. The sole according to claim 1, wherein in said sole stable posture, in a static upright posture when a shoe is worn by a wearer, said sole compressive rigidity is determined such that θ<5 [degrees] is satisfied.

5. The sole according to claim 1, wherein said heel region has an aperture and said forefoot region does not have an aperture.

6. The sole according to claim 1, wherein said heel region and said forefoot region have an aperture and an open width of said aperture at said heel region is greater that an open width of said aperture at said forefoot region.

7. The sole according to claim 1, wherein said heel region and said forefoot region have an aperture and an aperture ratio at said heel region is greater that an aperture ratio at said forefoot region.

8. The sole according to claim 1, wherein said heel region is formed by a material of relatively lower hardness and said forefoot region is formed by a material of relatively higher hardness.

9. The sole according to claim 1, wherein both said heel region and said forefoot region have a material area of relatively lower hardness and another material area of relatively higher hardness, and an occupancy ratio of said material area of relatively lower hardness at said heel region is set at a relatively high value and an occupancy ratio of said material area of relatively higher hardness at said forefoot region is set at a relatively high value.

10. The sole according to claim 1, wherein said points C and D are disposed at least at a lateral side edge portion of said sole lower surface.

11. The sole according to claim 1, wherein a region extending from said point C to said point D of said sole lower surface constitutes a stable region formed of a flat-shape, and in said sole stable posture, said stable region is in contact with the ground.