AU2011236925A1

AU2011236925A1 - Sole structure for shoe

Info

Publication number: AU2011236925A1
Application number: AU2011236925A
Authority: AU
Inventors: Kazunori Iuchi; Natsuki Sato; Takeshi Takeshita
Original assignee: Mizuno Corp
Current assignee: Mizuno Corp
Priority date: 2010-04-02
Filing date: 2011-03-28
Publication date: 2012-08-30
Also published as: TW201201727A; WO2011125959A1; CA2787326A1; JP5392954B2; US20110239489A1; CN102821633A; JPWO2011125959A1; BR112012020621A2; EP2554070A1

Abstract

Disclosed is a sole structure which can reduce energy loss while running. A sole structure (1) for a shoe is provided with: an upper plate (3) which is disposed in the upper part of the sole structure (1) and which stretches from the front to the back of the sole; a lower mid-sole (4) which is made from a soft elastic member, is disposed below the upper plate (3), is fixed to the lower surface of the upper plate (3), and has a groove (41) which opens downwards and which stretches in the width direction of the sole; and bend restriction sections (10) which are provided in a bent state in the length direction of the sole between edge sections of the opening of the groove (41), and which connect the edge sections of the opening. When the sole starts bending, the bend restriction sections (10) allow the sole to bend from when the bend restriction sections (10) are in a bent state up until the bend restriction sections (10) are gradually stretched into a straight line between the edge sections of the opening, and when the sole has been bent, the bend restriction sections (10) restrict the bending of the sole by receiving force in the extension direction when the straight line is stretched between the edge sections of the opening.

Description

DESCRIPTION Sole Structure for a Shoe 5 TECHNICAL FIELD The present invention relates generally to a sole structure for a shoe, and more particularly, to an improved sole structure for decreasing an energy loss during running. 10 BACKGROUND ART The applicant proposed a sole structure such as shown in WO 2006/070549 for improving bendability of a sole forefoot region of a shoe. The sole structure is comprised 15 ofalongitudinallyextendingupperplate disposedonanupper side of the sole forefoot region and a longitudinally extending lower plate disposed under and located away from the upper plate and having an undulated shape such that a longitudinal path length of the lower plate is greater than 20 a longitudinal path length of the upper plate. In this case, during bending deformation of the sole forefoot region, the lower plate can further extend due to the undulated shape of a greater longitudinal path length and as a result the lower plate does not hinder bending 25 deformation of the sole forefoot region, thus improving - 1bendability of the sole forefoot region Also, the applicant proposed a sole structure such as shown in Japanese patent application publication No. 2005-013718 for conducting a push off motion of the sole 5 forefoot region in a smooth manner. The sole structure has a longitudinally extending void in a flat shape at the sole forefoot region. The void is formed of a first curved surface and a second curved surface and a longitudinal path length between a front end and a rear end of the first curved surface 10 is substantially equal to a longitudinal path length between a front end and a rear end of the second curved surface. In this case, when a ball of a foot of a shoe wearer pushes the sole forefoot region, the first curved surface deforms so as to come close to the second curved surface 15 and as a result a sole rear foot region located behind the void is deformed so as to be lifted upwardly. From such a state, as the sole forefoot region is further compressed and the void is closed, the bending rigidity of the sole forefoot region is increased, thus conducting the push off motion of 20 the sole forefoot region in a smoother manner. In the above-mentioned sole structure shown in WO 2006/070549, it is possible to improve the bending properties of the sole forefoot region. However, during bending of the sole forefoot region, since the lower plate 25 still has an undulated shape to allow for a longitudinal - 2 extension, the sole forefoot region still has a longitudinal flexibility during the push off motion of the sole forefoot region. As a result, the push off motion of the sole forefoot region cannot be conducted in a smooth (i.e. rapid, secure 5 and efficient) manner. Also, in the above-mentioned sole structure shown in Japanese patent application publication No. 2005-013718, it is possible to cause the push off motion of the sole forefoot region to be conducted in a smooth manner. 10 However, since the sole structure is so constructed as to make the sole rear foot region bend relative to the sole forefoot region, the bending properties of the sole forefoot region itself is not necessarily preferable. On the other hand, the inventors of the present 15 application paid attention to the energy due to the metatarsophalangeal (or MP) joint torque during the push off motion in order to improve a ride feeling due to a weight transfer from the ground contact phase to the toe off phase of the sole forefoot region, i.e. to attain a smoother ride 20 feeling in sensual evaluation. FIG. 12 schematically illustrates a state in which a shoe wearer is running and especially shows a push off phase of running. In FIG. 12, (a) is a state in which the entire sole surface including the sole forefoot region 25 is in contact with the ground; (b) is a heel-off state in -3which the heel region of the sole begins to leave the ground and also the sole forefoot region begins to bend; (c) and (d) are states in which bending of the sole forefoot region gradually proceeds; (e) is a state in which the sole forefoot 5 region is bent at a maximum angle, in other words, the push off motion of the sole forefoot region is going to start; and (f) is a state in which the push off motion of the sole forefoot region ends and the sole forefoot region is about to leave the ground. In each of the drawings, an upward arrow 10 mark shows a ground reaction force vector that the sole receives from the ground. FIG. 13 illustrates alegofarunner in aschematicmanner, in whichMPshows ametatarsophalangeal (or MP) joint. Fig. 14 is a graph that shows a torque around 15 the MP joint (or MP joint torque), which is fluctuated during the push off phase shown in FIG. 12. FIG. 15 is a graph that shows a fluctuation of an angular velocity. FIG. 16 is a graph that shows a fluctuation of a power due to the MP joint torque during the push off phase, the power being calculated based 20 on the MP joint torque and the angular velocity. As shown in FIG. 16, during the toe off phase including from the state in which the power becomes zero (or MP joint torque becomes zero; see FIG. 14) to the state in which a toe of a foot has left the ground completely, the 25 energy due to the MP joint torque is negative and an energy - 4 loss is generated (see a hatched region of FIG. 16). The inventors assumed that when such energy loss can be made as close to zero as possible a force during the push off motion can be transmitted to the ground efficiently and a smooth 5 ride feeling can be achieved. On the other hand, it is known that a bending resistance of a sole influences a ride feeling in sensory evaluation. Two kinds of shoes were provided, one had a great bending resistance and the other had a small bending 10 resistance. The same runner wore these shoes and did running. A graph on the bottom side of FIG. 17 shows a power due to theMPjoint torque duringthepushoffphase, whichfluctuates as time elapses. Drawings (b)-(f) on the top side of FIG. 17 correspond to the drawings (b) - (f) of FIG. 12, respectively. 15 Also, the drawings (b) - (f) on the top side of FIG. 17 correspond to the graph on the bottom side of FIG. 17. In the graph of FIG. 17, a negative region in the vertical axis indicates generation of a power loss and thus as the graph goes down from zero in the vertical axis a power loss becomes great. 20 As can be seen from FIG. 17, in the case of the shoe of a great bending resistance, an energy loss is great in the middle of (b) and (c) to (d) in the beginning of the push off phase, whereas in the case of the shoe of a small bending resistance, an energy loss is great at (e) - (f) 25 in the latter half of the push off phase. Additionally, during - 5 the period from (b) to the middle of (b) and (c) of the push off phase, the shoe of a small bending resistance also generates an energy loss, but such an energy loss is neglectable. 5 In view of the above-mentioned consideration, the inventors have come to the following conclusion: If advantages of the above-mentioned two kinds of shoes can be adopted, that is, during the periods of (b) - (d) of the firsthalfof thepushoffphase, thebendingresistance 10 is made smaller, and at the same time during the periods of (e) - (f) of the latter half of the push off phase, the bending resistance is made greater, a smoother ride feeling during running can be achieved. The present invention has been made based on 15 the result of the above-mentioned consideration and it is directed to providing a sole structure for a shoe that can decrease an energy loss during running. In other words, the present invention is directed to providing a sole structure that can attain a smooth ride feeling during running by 20 decreasing en energy loss. DISCLOSURE OF INVENTION A sole structure for a shoe according to a first aspect of the present invention as claimed in claim 1 comprises 25 a sole having a laterally extending groove that is formed - 6 on a bottom surface of the sole, and a bending restriction member that is formed in a bent shape and that spans the groove longitudinally between a front edge and a rear edge of an opening of the groove. In the beginning phase of bending of 5 the sole, the bending restriction member allows for the sole to bend till the bending restriction member gradually extends toward a straight shape from the bent shape and becomes taut between the front edge and the rear edge of the opening of the groove. Thereafter, in an advanced phase of bending of 10 the sole, when the bending restriction member experiences a force that pulls the bending restriction member in a longitudinal direction from its taut state, it functions so as to restrict bending of the sole. According to the first aspect of the present 15 invention, in thebeginningphaseof sole bending, the bending restriction member in the bent shape spanning the groove longitudinally between the front and rear edge of the groove allows for the sole to bend till the bending restriction member gradually extends toward the straight shape from the bent 20 shape and becomes taut between the front and rear edge of the groove. Therefore, in the beginning of the push off phase of running, bending resistance of the sole becomes relatively small thus allowing for the sole to bend smoothly. As a result, an energy loss at the beginning of the push off phase can 25 be decreased. -7- Thereafter, in the advanced phase of bending of the sole, the bending restriction member experiences a force that pulls it in the longitudinal direction from its taut state and the bending restriction member functions so 5 as to restrict bending of the sole. Therefore, in the latter half of the push off phase of running, bending resistance of the sole becomes relatively large thus restraining the sole from bending. As a result, an energy loss in the latter half of the push off phase can be decreased. 10 In such a manner, a shoe can be achieved that can decrease an energy loss during running and can thus attain a smooth ride feeling during running. The groove may be provided at a sole forefoot region as claimed in claim 2. 15 The bending restriction member may have an upwardly bent portion in the groove and its longitudinal sectional shape may be inverted V-shaped or U-shaped as claimed in claim 3. In the beginning of sole bending, the upwardly 20 bent portion deforms in suchawaythat itsheight is gradually lowered, i.e. the upwardly bent portion gradually becomes flatter, and thus it gradually extends in the longitudinally direction. Preferably, the bending restriction member is 25 not fixedly attached to a surface of the groove as claimed -8 in claim 4. In this case, during bending of the sole, the bending restriction member can deform independently from the groove without being directly influenced by deformation of the groove. 5 More preferably, the bending restriction member is located away from the surface of the groove as claimed in claim 5. In this case, during bending of the sole, the bending restriction member is less influenced by deformation of the groove and can deformmore independently from the groove. 10 Also, in this case, a bottom of the groove that is a bending or flex point during bending of the sole can be located at an upper position away from the bending restriction member. In other words, a neutral axis of sole bending can be located at an upper position. As a result, during bending of the sole, 15 the amountofdeformation ofa span of the bending restriction member between the front and rear edge of the groove can be enlarged. Thereby, the amount of restraint of the bending restriction member relative to bending of the sole can be easily enlarged thus facilitating adjustment of the amount 20 of restraint. The bending restriction member may have a downwardly bent portion in the groove and its longitudinal sectional shape may be V-shaped or U-shaped as claimed in claim 6. 25 Inthebeginningofsolebending, the downwardly - 9 bent portion deforms in such a way that its height is gradually lowered, i.e. the downwardly bent portion gradually becomes flatter, and thus it gradually extends in the longitudinally direction. 5 The bending restriction member may be band-shaped or tape-like member as claimed in claim 7. In the event that the bending restriction member is flexible, it can be easily installed at the opening of the groove with its bent shape maintained. Also, in this case, a variation 10 of width or thickness of the bending restriction member causes its tensile modulus of elasticity and modulus in bending to vary with ease. Thereby, a restraining action of the bending restriction member relative to bending of the sole can be adjusted easily. 15 The bending restriction member may have a sideway bent portion in the groove as claimed in claim 8. In the beginning of sole bending, the sideway bent portion deforms in such a way that the amount of bending of the sideway bent portion is gradually lessened, and it thus gradually 20 extends in the longitudinally direction. The bending restriction member may be wire-shaped such as a string, thread or a wire as claimed in claim 9. In this case, a variation of size or diameter of a section of the bending restriction member causes its 25 modulus of elasticity to vary with ease. Thereby, a - 10 restraining action of the bending restriction member relative to bending of the sole can be adjusted easily. The bending restriction member may be made of fabric as claimed in claim 10. In this case, since the bending 5 restriction member is made of a material with less flexibility, when the bending restriction member is pulled in the longitudinal direction from its taut state in the advanced phase of sole bending, it effectively functions to restrain sole bending. Thereby, in the latter half of the push off 10 phase during running, bending resistance of the sole can be effectively enlarged. Moreover, in this case, since the bending restriction member made of fabric has a very small bending resistance and is very flexible, there is little power to bend it when it is in a bent shape. Therefore, the bending 15 restriction member made of fabric does not cause any bending resistance to the sole in the beginning of sole bending. The bending restriction member may be a sheet-shaped member that covers a ground contact side surface of the sole, and the sheet-shaped member may have a plurality 20 of outsole pieces fixedly attached on a ground contact side surface of the sheet-shaped member as claimed in claim 11. In this case, since the sheet-shaped bending restriction member is used as a base sheet for a plurality of outsole pieces that are separately provided from each other, 25 the bending restriction member and the outsole pieces are - 11 integrally formed with each other and can be made unitary. Thus, an assembly process of the sole structure can be simplified and the weight of the sole structure can be decreased. 5 The bending restriction member may be located on a medial side or a lateral side of the sole as claimed in claim 12. In the event that the bending restriction member is locatedon themedial sideofthesole, ashoecanbeachieved 10 that is suitable for a runner who has a tendency of pronation during running. In this case, in the latter half of the push off phase of running, bending resistance of the medial side region of the sole becomes relatively great and bending of the sole medial side region is restrained. Thereby, an energy 15 loss in the latter half of the push off phase can be reduced. In the event that the bending restriction member is located on the lateral side of the sole, a shoe can be achieved that is suitable for a runner who has a tendency of supination during running. In this case, in the latter 20 half of the push off phase of running, bending resistance of the lateral side region of the sole becomes relatively great and bending of the sole lateral side region is restrained. Thereby, an energy loss in the latter half of the push off phase can be reduced. 25 The bending restriction member may be located - 12 on the lateral side and the medial side of the sole as claimed in claim 13. In this case, a shoe can be attained that is suitable for a runner who has a tendency of pronation as well 5 as forarunnerwhohasatendencyof supination during running. Also, in this case, when the tensile modulus of elasticity or modulus in bending of the bending restriction member on the medial side is made different from the tensile modulus of elasticity or modulus in bending of the bending restriction 10 member on the lateral side, a fine adjustment of the sole bending resistance is made possible between the medial side and the lateral side. An elastic cover member may be disposed between the front and rear edge of the opening of the groove to cover 15 the bending restriction member from below as claimed in claim 14. The elastic cover member extends longitudinally along the bent shape of the bending restriction member. In this case, provision of the elastic cover member prevents the bending restriction member from being 20 exposed to the ground thereby improving durability of the bending restriction member. Also, in this case, since the elastic cover member has a longitudinal elasticity it does not hinder bending of the sole. An outsole member with a ground contact surface 25 may be disposed on a bottom surface of the sole and the cover - 13 member may be formed of the outsole member as claimed in claim 15. In this case, since the elastic cover member does not need to be provided separately from the outsole member 5 the number of components of the sole structure can be reduced and the structure can be simplified. The sole structure may further include a longitudinally extending upper plate disposed on an upper sideof the sole, andamidsole that is formedof a soft elastic 10 material, that is disposed under the upper plate and that has a groove formed on a bottom surface of the midsole as claimed in claim 16. In this case, a downward force imparted from a shoe wearer's foot at the time of sole contact with the 15 ground can be supported by the upper plate. Also, in this case, since the upper plate is disposed above the bottom portion of the groove, the bottom portion of the groove can be prevented from being deformed by the downward force imparted from the shoe wearer's foot and a neutral axis during 20 sole bending can be located at an upper position. As a result, during bending of the sole, the amount of deformation of a span of the bending restriction member between the front and rear edge of an opening of the groove can be enlarged, thereby increasing the amount of restraint easily by the bending 25 restriction member relative to sole bending to facilitate - 14 an adjustment of the amount of restraint. Moreover, in this case, since the midsole is disposed under the upper plate, the midsole can prevent the upper plate from sinking downwardly as the downward force 5 is exerted. Thus, the neutral axis during sole bending can be maintained at an upper position. The sole structure may further include a longitudinally extending lower plate disposed on a lower side of the midsole and the bending restriction member may be formed 10 of the lower plate that extends beyond the groove as claimed in claim 17. In this case, it does not need to provide the bending restriction member discretely from the lower plate, the number of components of the sole structure can be reduced 15 and the structure can be simplified. A sole structure for a shoe according to a second aspect of the present invention as claimed in claim 18 comprises a longitudinally extending plate disposed on an upper side ofasole, amidsole that is formed ofasoft elastic 20 material, that is disposed under and fixedly attached to the plate, and that has a laterally extending groove formed on a bottom surface of the midsole, and a bending restriction member formed in a bent shape and spanning the groove longitudinally between a front and rear edge of an opening 25 of the groove. In the beginning phase of bending of the sole, - 15 the bending restriction member allows for the sole to bend till the bending restriction member gradually extends toward a straight shape from a bent shape and becomes taut between the front and rear edge of the opening of the groove. In an 5 advanced phase of bending of the sole, when the bending restriction member experiences a force that pulls the bending restriction member in a longitudinal direction from its taut state, it functions so as to restrain the sole from bending. According to the second aspect of the present 10 invention, the bending restriction member in the bent shape spanning the groove longitudinally between the front and rear edge of the groove allows for the sole to bend till the bending restriction member gradually extends toward the straight shape from the bent shape and becomes taut between the front 15 and rear edge of the groove in the beginning phase of sole bending. Therefore, in the beginning of the push off phase of running, bending resistance of the sole becomes relatively small thus allowing for the sole tobend smoothly. As a result, an energy loss in the beginning of the push off phase can 20 be decreased. Thereafter, the bending restriction member experiences a force that pulls it in the longitudinal direction from its taut state and the bending restriction member functions so as to restrict bending of the sole in 25 the advanced phase of bending of the sole. Therefore, in the - 16 latter half of the push off phase of running, bending resistance of the sole becomes relatively large thus restraining the sole from bending. As a result, an energy loss in the latter half of the push off phase can be decreased. 5 In such a manner, a shoe can be achieved that can decrease an energy loss during running and can thus attain a smooth ride feeling during running. In this case, a downward force imparted from a shoe wearer's foot at the time of sole contact with the 10 ground can be supported by the plate. Also, in this case, since the plate is disposed above the bottom portion of the groove, the bottom portion of the groove can be prevented from being deformed by the downward force imparted from the foot and a neutral axis during sole bending can be located 15 at an upper position. As a result, during bending of the sole, the amount of deformation of a span of the bending restriction member between the front and rear edge of an opening of the groove can be enlarged, thereby increasing the amount of restraint easily by the bending restriction member relative 20 to sole bending and thus facilitating an adjustment of the amount of restraint. Moreover, in this case, since the midsole is disposed under the plate, the midsole can prevent the plate from sinking downwardly as the downward force is exerted. 25 Thus, the neutral axis during sole bending can be maintained - 17 at an upper position. A length L of the bending restriction member along the bent shape thereof between the front and rear edge of the opening of the groove satisfies the following 5 inequality as claimed in claim 19: S+Dxsinl5 0 L ! S+Hxsinl5* wherein S designates a distance between the front and rear edge of the opening of the groove; D designates a depth of the groove; and H designates a thickness of the midsole above 10 the bottom of the groove. The reason why the length L is provided by the above-mentioned inequality is hereinafter explained. FIG. 4 schematically shows a structure in which a bending restriction member Br is provided in a bent shape 15 between a front and rear edge of an opening of a groove G formed in a midsole M. From the state shown in FIG. 4, suppose the midsole M to be bent 15 degrees. At this juncture, the midsole M is bent around a bottom position Ga of the groove G. In this case, the bottom position Ga is a bending or flex 20 point. Alternatively, the midsole M is bent around the uppermost position Ha of the midsole M located above the bottom position Ga of the groove G. In this case, the uppermost position Ha is a bending or flex point. Actual flex point is located between the bottom position M and the uppermost 25 position Ha. This is also true of the structure having a hard - 18 plate fitted to the midsole M. In the event of the midsole having a hard plate, the neutral axis of sole bending tends to be transferred to the position in the vicinity of the hard plate. 5 When the midsole M is bent around the bottom position Ga of the groove G, the central angle of the groove G around the bottom position Ga is increased by 15 degrees. Suppose such an increase in the central angle of the groove G around the bottom position Ga to cause the bending 10 restriction member Br to extend in a linear taut shape from the bent shape between the front and rear edge of the opening of the groove G. An increment AS of the distance between the front and rear edge of the opening of the groove G is approximately represented by 15 AS ~ Dxsinl5 0 Therefore, the length L of the bending restriction member Br along the bent shape is represented by L ~ S+AS = S+Dxsinl5 0 (1) 20 On the other hand, when the midsole M is bent around the uppermost position Ha of the midsoleM, the central angle of the groove G around the position Ha is increased by 15 degrees. Suppose such an increase in the central angle of the groove G around the position Ha to cause the bending 25 restriction member Br to extend in a linear taut shape from - 19 the bent shape between the front and rear edge of the opening of the groove G. An increment AS of the distance between the front and rear edge of the opening of the groove G is approximately represented by 5 AS' ~ Hxsinl5* Therefore, the length L of the bending restriction member Br along the bent shape is represented by L ~ S+AS' = S+Hxsinl5 0 (2) 10 In view of the equations (1) and (2), the length L of the bending restriction member Br along the bent shape is an intermediate value between the value of the equation (1) andthevalueoftheequation (2) andcanthusberepresented by the above-mentioned inequality. 15 Next, the reason why the bending angle of 15 degrees was adopted is explained below: FIG. 5 is a graph showing a fluctuation of a kick force imparted backward to the ground by a runner during running and also a fluctuation of a bending angle of the sole 20 during running. This graph is obtained by a bio mechanics experiment. A graph on the upper side of FIG. 5 indicates avariation of the kickforce Fyas time elapses. Thehorizontal axis shows time [ms] and the vertical axis shows the kick 25 force Fy [N] imparted backward to the ground by the runner - 20 in the period from heel contact with the ground to toe off phase during running. A graph on the lower side of FIG. 5 indicates a variation of the bending angle [0] of the sole as time elapses. These graphs on the upper and lower side 5 of FIG. 5 correspond to each other. As can be seen from FIG. 5, when the kick force Fy reaches the maximum value Fymax, the bending angle of the sole is 15*. The bending angle of the sole is determined by an increment of the angle measured from the state in which 10 the entire sole surface is in contact with the ground, i.e. the bending angle of the sole is zero. On the other hand, as was found from FIG. 17, during the phase of (c) - (d) in which the sole forefoot region is in the middle of bending the sole of a small bending 15 resistance has a smaller energy loss, whereas around thephase of (e) in which the sole forefoot region is bent at the maximum angle the sole of a great bending resistance has a smaller energy loss. Consequently, it is found that with regard to 20 sole bending the sole should be bent before the state in which the sole can kick the ground backward at the maximum power and afterward the sole preferably should not be bent. Therefore, the angle of 15* was adopted as a sole bending angle. 25 According to the present invention, in the state - 21 where the sole bending angle is less than 15 degrees the bending restriction member is bent between the front and rear edge of the groove, in the state where the sole bending angle is equal to 15 degrees the bending restriction member is linearly 5 taut between the front and rear edge of the groove, and in the state where the sole bending angle is more than 15 degrees the bending restriction member is pulled in the longitudinal directionfromthe tautstate, i.e. atensile forceisimparted to the bending restriction member in a taut state. 10 The bending restriction member is preferably formed of a material that has the Young's modulus of 400 MPa or more at a strain of 10% or less as claimed in claim 20. The reason why the Young's modulus is determined at such a value is explained below using FIG. 6. 15 First, bending restrictionmembersmade of four kinds of materials of dif ferent Young's modulus were prepared. The same runner wore four kinds of shoes with these four kinds of bending restriction members and took a running test. During the test an energy loss due to the MP joint torque was calculated 20 for each of the shoes. FIG. 6 shows the result of calculation of the energy loss during running. In addition, the above-mentioned four kinds of materials were solid rubber, PEBAX ®, polyester tape, and nylon tape. The Young's modulus of each of these four kinds 25 of materials was measured by the following test: - 22 i) Method of Test; Tensile test prescribed in JIS K 7113 ii) Shape of Test Piece; Shape prescribed in JIS K 7113 5 iii)Test Rate; 500 mm/min. iv) Distance of Grasp of Test Piece: 50 mm v) Tensile Condition; Less than 10% of strain The order of the Young's modulus of four kinds of materials was as follows: 10 SolidRubber<PEBAX*<PolyesterTape<NylonTape A concrete value of each of the Young's modulus is plotted in FIG. 6. As can be seen from FIG. 6, the greater the Young's modulus is, the smaller the energy loss is. Especially, 15 when the Young's modulus reaches at 400[MPa] the energy loss sharply decreases. Also, when the Young's modulus exceeds 400[MPa] the energy loss is little varied. Such being the case, as the Young's modulus of material to compose thebending restrictionmember, thevalue 20 of 400 MPa or more at strain of 10% or less is determined. The materials suited for this condition are polyester or nylon in the example of FIG. 6. The bending restriction member functions such that it allows for the sole to bend till sole bending angle 25 reaches 15 degrees and it restrains the sole from bending - 23 when sole bending angle exceeds 15 degrees as claimed in claim 21. As mentioned above, according to the first aspectof thepresent invention, since thebendingrestriction 5 member in the bent shape is provided so as to span the groove longitudinally between the front and rear edge of the opening of the groove, the sole is allowed to bend till the bending restriction member gradually extends toward the straight shape from the bent shape and becomes taut between the front 10 and rear edge of the groove during the beginning phase of sole bending. Therefore, in the beginning of the push off phase of running, bending resistance of the sole becomes relatively small thus allowing for the sole to bend smoothly. As a result, an energy loss in the beginning of the push off 15 phase can be decreased. Also, during the advanced phase of bending of the sole, the bending restriction member experiences a force that pulls it in the longitudinal direction from its taut state and the bending restriction member functions so as to 20 restrict bending of the sole. Therefore, in the latter half of the push off phase of running, bending resistance of the sole becomes relatively large thus restraining the sole from bending. As a result, an energy loss in the latter half of the push off phase can be decreased. 25 In such a manner, a shoe can be achieved that - 24 can decrease an energy loss during running and can thus attain a smooth ride feeling during running. According to the second aspect of the present invention, as with the first aspect of the present invention, 5 due to the function of the bending restriction member, not only an energy loss during running can be decreased and a smooth ride feeling during running can be achieved but also a downward force imparted from a shoe wearer's foot at the time of sole contact with the ground can be supported by the 10 plate. Moreover, since the plate is disposed above the bottom portion of the groove, the bottom portion of the groove can be prevented from being deformed by the downward force imparted from the shoe wearer's foot and a neutral axis during sole bending can thus be located at an upper position. As 15 a result, duringbending of the sole, the amount of deformation of a span of the bending restriction member between the front and rear edge of the opening of the groove can be enlarged, thereby increasing the amount of restraint easily by the bending restriction member relative to sole bending and thus 20 facilitating an adjustment of the amount of restraint. Also, since the midsole is disposed under the plate, the midsole can prevent the plate from sinking downwardly as the downward force is exerted. Thus, the neutral axis during sole bending can be maintained at an upper position. 25 - 25 - BRIEF DESCRIPTION OF DRAWINGS FIG. 1A is a bottom view of a sole structure for a shoe according to a first embodiment of the present invention; 5 FIG. 1B is a medial side view of FIG. 1A; Fig. 2 is a cross sectional view of FIG. 1A taken along line II-II; Fig. 3 is a longitudinal sectional view of FIG. 1A taken along line III-III; 10 Fig. 4 is a schematic view corresponding to FIG. 3; FIG. 5 is a graph showing a variation of a kick force imparted rearward to the ground by a runner during running and also a bending angle of the sole as time elapses; 15 Fig. 6 is a graph showing a correlation between an energy loss and Young's modulus of the bending restriction member; FIG. 7A is a schematic illustrating the bending motion of the sole structure according to the first 20 embodiment; FIG. 7B is a schematic illustrating the bending motion of the sole structure according to the first embodiment; FIG. 7C is a schematic illustrating the bending 25 motion of the sole structure according to the first - 26 embodiment; FIG. 8 is an enlarged longitudinal sectional view of the bending restriction member in use for a sole structure for a shoe according to a third embodiment of the 5 present invention, corresponding to FIG. 3 of the first embodiment; FIG. 9 is a partial bottom view of a sole structure for a shoe according to a fifth embodiment of the present invention; 10 FIG. 10 is a longitudinal sectional view of FIG. 9 taken along line X-X; FIG. 11 is a partial bottom view of a sole structure for a shoe according to a sixth embodiment of the present invention; 15 FIG. 12 is a schematic illustrating the state of running of a runner or a shoe wearer; FIG. 13 is a schematic illustrating a leg of the runner; FIG. 14 is a graph showing a variation of a 20 torque around a MP joint (or MP joint torque) in the push off phase of FIG. 12; FIG. 15 is a graph showing a variation of an angular velocity in the push off phase of FIG. 12; FIG. 16 is a graph showing a variation of a 25 power generated by the MP joint in the push off phase of FIG. - 27 - 12, which is calculated based on the MP joint torque of FIG. 14 and the angular velocity of FIG. 15; and FIG. 17 is a graph showing a variation of a power generated by the MP joint in the push off phase of a 5 shoe of a small bending resistance and another shoe of a great bending resistance, and schematics (b)-(f) above the graph corresponds to schematics (b)-(f) of FIG. 12, respectively. BEST MODE FOR CARRYING OUT THE INVENTION 10 Embodiments of the present invention will be hereinafter described in accordance with the appended drawings. <First Embodiment> Referring now to the drawings, FIGS. 1A to 7C 15 show a sole structure or a sole assembly for a shoe according to a first embodiment of the present invention. In these drawings, like reference numbers indicate identical or functionally similar elements. As shown in FIGS. 1A and 1B, a sole structure 20 1 for a shoe comprises an upper midsole 2 formed of a soft elastic material and extending longitudinally from a heel region H through a midfoot region M to a forefoot region F of the shoe, anupperplate3 formedofahardelasticmaterial, fixedly attached to the bottom of the upper midsole 2 and 25 extending longitudinally from the heel region H through the - 28 midfoot region M to the forefoot region F of the shoe, a lower midsole 4 formed of a soft elastic material, fixedly attached to the bottom of the upper plate 3 and disposed mainly at the forefoot region F of the shoe, and a lower plate 5 of 5 hard elasticity which extends longitudinally mainly from the heel region H to the midfoot region M and whose front end portion is fixedly attached to the bottom of the lower midsole 4. The upper midsole 2, as shown in FIG. 2, has 10 a foot sole contact surface 20 that a sole of a shoe wearer's foot contacts and a pair of upraised portions 21 extending obliquely upwardly from opposite side edges of the foot sole contact surface 20. The upper plate 3 has a support portion 30 to support the foot sole contact surface 20 of the upper 15 midsole 2 and a pair of upraised portions 31 extending obliquely upwardly from opposite side edges of the support portion 30. The lower midsole 4, as shown in FIGS. 1A and 1B, has grooves 40, 41 formed on a bottom surface of the lower 20 midsole 4 at the forefoot region F and extending laterally or substantially along the width of the shoe. These grooves 40, 41 are provided to facilitate bending of the forefoot region F of the sole. The groove 40 is disposed on the front side of the forefoot region F and the groove 41 is disposed 25 on the rear side of the forefoot region F, preferably, at - 29 the slightly rear of a thenar eminence of a ball of the foot of the shoe wearer. Vent holes 4a are formed in the groove 41 to pass through the lower midsole 4 upwardly. The upper midsole 2 and the upper plate 3 also have vent holes (not 5 shown) to pass through them, which provide a connection with the vent holes 4a. The lower plate 5 has a wavy corrugation that progresses forwardly and has protrusions 50 protruding upwardly in a convex shape at the heel region H and the midfoot 10 region M. In FIG. lA, dotted lines L indicate ridge lines of the protrusions 50. Each of the protrusions 50 is coupled to the upper plate 3 via an elastic block member 6. There is formed a void C between the upper plate 3 and the lower plate 5. 15 Outsole plates 7 that contact the ground are fixedly attached to each of bottom surfaces of the lower midsole 4 and the lower plate 5. The upper midsole 2 and the lower midsole 4 are formed of a soft elastic material such as thermoplastic 20 synthetic resin or its foam, e.g. ethylene-vinyl acetate copolymer (EVA); thermosetting resin or its foam, e.g. polyurethane (PU); or rubber material or its foam, e.g. butadiene or chloroprene rubber. The upper plate 3 and the lower plate 5 is formed 25 of a hard elastic material such as thermoplastic resin, e.g. - 30 thermoplastic polyurethane (TPU), polyamide elastomer (PAE); or thermosetting resin, e.g. epoxy resin, unsaturated polyester resin. Also, the upper plate 3 may be integrally formed with the lower plate 5 using EVA or rubber. The outsole 5 plate 7 is formed of rubber material or the like. As shown in FIG. 3, the groove 41 formed on the bottom surface of the lower midsole 4 has a cross sectional shape of an inverted V-shape that opens to the ground contact side. 10 A bending restriction member 10 spans an opening of the groove 41 longitudinally between a front end edge and a rear end edge of the opening of the groove 41. The bending restricting member 10 is a bend-shaped member and forms an inverted V-shape between the front and rear end edge of the 15 opening of the groove 41. The bending restriction member 10 has an upwardly bent portion 10a in an inverted V-shape and its longitudinally opposite ends are coupled to the front and rear end edge of the opening of the groove 41. Here, as the bending restriction member 10, for example, a nylon tape 20 is used. A thickness t of the bending restriction member 10 is less than 1 mm, and for example, t=0.5 mm is used. The bending restriction member 10, as shown in FIG. 1A, is provided on the medial side and the lateral side of the sole, respectively. 25 A length L of the bending restriction member - 31 - 10 along its bent shape between the front and rear edge of the opening of the groove 41 satisfies an inequality, S+Dxsinl5* L S+Hxsinl5 wherein S designates a distance between the front and rear 5 edge of the opening of the groove; D designates a depth of the groove; and H designates a thickness of the midsole above a bottom of the groove. The reason why the length L is provided by the above-mentioned inequality is hereinafter explained. 10 FIG. 4 schematically shows a structure in which a bending restriction member Br is provided in a bent shape between a front and rear edge of an opening of a groove G formed in a midsole M. From the state shown in FIG. 4, suppose the midsole M to be bent 15 degrees. At this juncture, the 15 midsole M is bent around a bottom position Ga of the groove G. In this case, the bottom position Ga is a bending or flex point. Alternatively, the midsole M is bent around the uppermost position Ha of the midsole M located above the bottom position Ga of the groove G. In this case, the uppermost 20 position Ha is a bending or flex point. Actual flex point is located between the bottom position Ga and the uppermost position Ha. This is also true of the structure having a hard plate fitted to the midsole M. In the event of the midsole having a hard plate, the neutral axis of sole bending tends 25 to be transferred to the position in the vicinity of the hard - 32 plate. When the midsole M is bent around the bottom position Ga of the groove G, the central angle of the groove G around the bottom position Ga is increased by 15 degrees. 5 Suppose such an increase in the central angle of the groove G around the bottom position Ga to cause the bending restriction member Br to extend in a linear taut shape from the bent shape between the front and rear edge of the opening of the groove G. An increment AS of the distance between the 10 front and rear edge of the opening of the groove G is approximately represented by AS = Dxsinl5* Therefore, the length L of the bending restriction member Br along the bent shape is represented 15 by L ; S+AS = S+Dxsinl5 0 (1) On the other hand, when the midsole M is bent around the uppermost position Ha of themidsole M, the central angle of the groove G around the position Ha is increased 20 by 15 degrees. Suppose such an increase in the central angle of the groove G around the position Ha to cause the bending restriction member Br to extend in a linear taut shape from the bent shape between the front and rear edge of the opening of the groove G. An increment AS' of the distance between 25 the front and rear edge of the opening of the groove G is - 33 approximately represented by AS' ~ Hxsinl5* Therefore, the length L of the bending restriction member Br along the bent shape is represented 5 by L ~ S+AS' = S+Hxsinl5 0 (2) In viewofthe equations (1) and (2), the length L of the bending restriction member Br along the bent shape should be an intermediate value between the value of the 10 equation (1) and the value of the equation (2) and can thus be represented by the above-mentioned inequality. Next, the reason why the bending angle of 15 degrees was adopted is explained below: FIG. 5 is a graph showing a fluctuation of a 15 kick force imparted backward to the ground by a runner during running and also a fluctuation of a bending angle of the sole during running. This graph is obtained by a bio mechanics experiment. A graph on the upper side of FIG. 5 indicates 20 avariationofthekickforce Fyas timeelapses. Thehorizontal axis shows time [ms] and the vertical axis shows the kick force Fy [N] imparted backward to the ground by a runner in the period from heel contact with the ground to toe off phase during running. A graph on the lower side of FIG. 5 indicates 25 avariationofthebendingangle [0] ofthesoleas timeelapses. - 34 - These graphs on the upper and lower side of FIG. 5 correspond to each other. As can be seen from FIG. 5, when the kick force Fy reaches the maximum value, Fymax, the bending angle of 5 the sole is 150. The bending angle of the sole is determined by an increment of the angle measured from the state in which the entire sole surface is in contact with the ground, i.e. the bending angle of the sole is zero. On the other hand, as can be seen from FIG. 10 17, during the phase of (c)-(d) in which the sole forefoot region is in the middle of bending, the sole of a small bending resistance has a smaller energy loss, whereas around the phase of (e) inwhichthe sole forefootportionisbentatthemaximum angle, the sole of a great bending resistance has a smaller 15 energy loss. Consequently, it is found that with regard to sole bending the sole should be bent before the state in which the sole can kick the ground backward at the maximum power and afterward the sole preferably should not be bent. 20 Therefore, the angle of 150 was adopted as a sole bending angle. According to this embodiment, in the state where the sole bending angle is less than 15 degrees the bending restriction member is bent between the front and rear edge 25 of the groove, in the state where the sole bending angle is - 35 equal to 15 degrees the bending restriction member is linearly taut between the front and rear edge of the groove, and in the state where the sole bending angle is more than 15 degrees the bending restriction member is pulled in the longitudinal 5 directionfromthe taut state, i.e. atensile force is imparted to the bending restriction member in a taut state. The bending restriction member is preferably formed of a material that has the Young's modulus of 400 MPa or more at a strain of 10% or less. 10 The reason why the Young's modulus is determined at such a value is explained below using FIG. 6. First, four kinds of bending restriction members formed of materials of different Young's modulus were prepared. The same runner wore these four shoes and took a 15 running test. During the test an energy loss due to the MP joint torque was calculated for each of the shoes. FIG. 6 shows the result of calculation of the energy loss during running. The above-mentioned four kinds of materials 20 were solid rubber, PEBAX*, polyester tape, and nylon tape. The Young's modulus of each of these materials was measured by the following test: i) Method of Test; Tensile test prescribed in JIS K 7113 25 ii) Shape of Test Piece; Shape prescribed in - 36 - JIS K 7113 iii)Test Rate; 500 mm/min. iv) Distance of Grasp of Test Piece: 50 mm v) Tensile Condition; Less than 10% of strain 5 The order of the Young's modulus of these materials was as follows: Solid Rubber<PEBAX*<Polyester Tape< Nylon Tape A concrete value of each of the Young's modulus is plotted in FIG. 6. 10 As can be seen from FIG. 6, the greater the Young's modulus is, the smaller the energy loss is. Especially, when the Young's modulus reaches at 400 [MPa] the energy loss sharply decreases. Also, when the Young's modulus exceeds 400[MPa] the energy loss is little varied. 15 Such being the case, as the Young's modulus of material to compose the bending restriction member, the value of 400 MPa or more at strain of 10% or less is determined. The materials suited for this condition are polyester or nylon in the example of FIG. 6. 20 The upwardly protruding bent or curved portion 10a of the bending restriction member 10 is not fixedly attached to the bottom of the groove 41. Preferably, the bending restriction member 10 is not fixed to nor even contacted with a sidewall of the groove 41 and it is located 25 away from the sidewall of the groove 41. - 37 - As shown in FIG. 3, an elastic cover member 8 is provided under the bending restriction member 10. The elastic cover member 8 spans the groove 41 between the front and rear edge of the opening of the groove 41 and covers a 5 lower surface of the bending restriction member 10. In FIG. 3, the elastic cover member 8 is formed of the outsole plate 7. In this case, the elastic cover member 8 does not need to be provided discretely from the outsole plate 7 the number of components of the sole assembly can be reduced thus 10 simplifying the structure. Alternatively, the elastic cover member 8 may be formed of rubber material provided separately from the outsole plate 7. The elastic cover member 8 extends along the bent shape of the bending restriction member 10 between the front and rear edge of the opening of the groove 15 41andisfittedtothelowersurfaceofthebendingrestriction member 10. Since the elastic cover member 8 is provided at the position corresponding to the position of the bending restriction member 10, the elastic cover member 8 is also disposed at both the medial side and the lateral side of the 20 sole as with the bending restriction member 10. Here, the opposite ends of the bending restriction member 10 are sandwiched between the lower midsole 4 and the elastic cover member 8 and the outsole plate 7. An extent of a sandwiched portion of the end of the bending 25 restriction member 10, which is shown in FIG. 4 as an extent - 38 of 5 in the bending restriction member Br that is sandwiched between the midsole M and the cover member P, is preferably more than or equal to 10 mm, i.e. 5 10 [mm], in order to secure a sufficient bonding area of the bending restriction member 5 to prevent a separation of the bending restriction member from the sole structure. Next, the action of the sole structure during bending according to this embodiment will be explained in accordance with FIGS. 7A to 7C. 10 FIGS. 7A to 7C. schematically illustrate the sectional structure of the above-mentioned sole assembly. In these drawings, like reference numbers indicate identical or functionally similar elements. Here, the bending restriction member 10 extends along the left to right 15 direction in the drawings. FIG. 7A shows the state before bending, FIG. 7B the state in which the sole is bent at 15 degrees, and FIG. 7C state in which the sole is bent at 30 degrees. As shown in FIG. 7A, before bending of the sole, 20 a distance between the front and rear edge of the opening of the groove 41 is 10 mm and a path length L of the bending restriction member 10 along its bent shape is equal to 12.5 mm. In FIG. 7A, point P that indicates the bottom of the groove 41 is a bending or flex point of sole bending. 25 From the state of FIG. 7A, when the sole bends - 39 - 15 degrees as shown in FIG. 7B, it bends around point P at the bottom of the groove 41. During this bending motion, the bending restriction member 10 deforms in such a way that its height of the upwardly protruded bent portion 10a gradually 5 decreases, that is, the upwardly protruded bent portion 10a is gradually flatter and the bending restriction member 10 gradually extends from the bent shape. As a result, the distance between the front and rear edge of the opening of the groove 41 reaches 12.5 mm. Such a length is the same as 10 the path length L of the bending restriction member 10 along its bent shape. At this juncture, the bending restriction member 10 is taut in a linear shape between the front and rear edge of the opening of the groove 41 but is not elongated. Therefore, in the beginning stage of sole 15 bending as shown in FIGS. 7A-7B, the bending restriction member 10 gradually extends from the bent shape and then becomes taut or tight on the straight between the front and rear edge of the opening of the groove 41. As a result, the bending restriction member 10 allows the sole to bend and 20 does not hinder sole bending. Thereby, in the first stage of push off phase during running, bending resistance of the sole becomes relatively small and the sole can be bent in a smooth manner thus reducing an energy loss in the first stage of the push 25 off phase. - 40 - Then, as shown in FIG. 7C, when the sole further bends around point P at the bottom of the groove 41 and the bending angle of the sole becomes 30 degrees the distance between the front and rear edge of the opening of the groove 5 41 further extends and reaches 14.8 mm. At this juncture, the bending restriction member 10 is pulled and elongated by a length of 5(=14.8-12.5) from the taut state shown in FIG. 7B. Therefore, as shown in FIGS. 7B-7C, in the 10 advanced stage of sole bending, the bending restriction member 10 functions to restrict bending of the sole. Thereby, in the latter half of the push off phase during running, bending resistance of the sole becomes relatively large and bending of the sole is restrained thus 15 reducing an energy loss in the latter half of the push off phase during running. In such a manner, according to the first embodiment of the present invention, a sole structure can be achieved that can reduce an energy loss during running 20 and thus can attain a smooth ride feeling during running. Also, in this case, since the bending restriction member 10 is not fixedly attached to the wall surface of the groove 41 it can bend independently from the groove41andwithoutbeingdirectlyinfluencedbydeformation 25 of the groove 41 during bending of the sole. - 41 - Moreover, in this case, since the bending restriction member 10 is located away from the wall surface of the groove 41 the bending restriction member 10 can bend more independently from the groove 41 and without being 5 influenced by deformation of the groove 41 during bending of the sole. At this juncture, the bottom of the groove that is the bending or flex point of the sole during bending of the sole can be located at the position located upwardly away from the bending restriction member 10. In other words, the 10 neutral axis during bending of the sole can be located at the upper position. Thereby, the amount of deformation of the bending restriction member 10 spanning the groove 41 between the front and rear edge of the groove 41 can be enlarged duringbendingofthesole.Asaresult, theamountof restraint 15 of the bending restriction member 10 relative to bending of the sole can be easily increased thus facilitating an adjustment of the restriction. Also, in this case, as the bending restriction member 10, a band-shaped or tape-like member is adopted and 20 thus the bending restriction member 10has flexibility thereby facilitating a provision of the bending restriction member 10 in a bent shape between the front and rear edge of the groove 41. In this case, a variation of a width or thickness of the bending restriction member 10 can vary the tensile 25 modulus of elasticity and modulus in bending of the bending - 42 restriction member 10. Thus, the action of restraint of the bending restriction member 10 relative to bending of the sole can be adjusted with ease. In addition, since the elastic cover member 5 8 is provided under the bending restriction member 10 the bending restriction member 10 can be prevented from being exposed to the ground contact side and durability of the bending restriction member 10 can be improved. Also, in this case, the elastic cover member 8 has elasticity and thus it 10 does not hinder bending of the sole. Also, in this case, the upper plate 3 can support the downward force imparted from the wearer's foot at the time of sole contact with the ground, prevent the bottom of the groove 41 from being deformed and maintain the neutral 15 axisduringbendingofthe soleat theupperposition. Thereby, the amount of deformation of the bending restriction member 10 spanning the groove 41 between the front and rear edge of the groove 41 can be enlarged during bending of the sole. Asaresult, the amount of restraintof thebendingrestriction 20 member 10 relative to bending of the sole can be easily increased thus facilitating an adjustment of the restriction Furthermore, in this case, the lower midsole 4 can prevent the upper plate 3 from being lowered when the downward force is exerted to the upper plate 3, thereby 25 maintaining the neutral axis at an upper position during - 43 bending of the sole. The bending restriction member 10 may be formed by extending the lower plate 5. In this case, the bending restriction member 10 does not need to be provided discretely 5 from the lower plate 5 thus decreasing the number of components and simplifying the structure of the sole assembly. <Second Embodiment> In the first embodiment, the groove 41 formed 10 on the lowermidsole 4 has an inverted V-shape in cross section but the present invention is not limited to such an example. The cross sectional shape of the groove 41 may be inverted U-shaped or circular shaped. Any suitable shape can be adopted as long as the groove 41 opens to the ground contact side. 15 In all cases, the sole bends around the bottom of the groove of an inverted V-shape, inverted U-shape, circular shape or any other shape as the bending or flex point during bending of the sole. In any of the cases where the groove 41 has 20 a different shape in cross section, the bending restriction member 10 disposed in the groove 41 has the upwardly protruding bent portion 10a, which is not fixedly attached to the bottom of the groove 41. Preferably, the bending restriction member 10 is not fixed to the sidewall of the groove 41 either and 25 located away from the sidewall of the groove 41. - 44 - <Third Embodiment> In the first embodiment, the bending restriction member 10 has an inverted V-shape in longitudinal 5 section but the present invention is not limited to such an example. The longitudinal sectional shape of the bending restriction member 10 may be inverted U-shaped or circular shaped. Any suitable shape can be adopted in accordance with the cross sectional shape of the groove 41. 10 Also, as shown in FIG. 8, the bending restriction member may have a downwardly protruding bent portion 10'a in a V-shape or U-shape. In this case, an elastic cover member 8' that covers the downwardly protruding bent portion 10'a of the bending restriction member 10' from below 15 also has a downwardly protruding bent shape along the bent shape of the bending restriction member 10'. In FIG. 8, reference numbers similar to those of the first embodiment indicate identical or functionally similar elements. In this case, in the beginning stage of bending 20 of the sole, the bending restriction member 10' gradually extends from the bent shape in such a way that the height of the downwardly protruding bent portion 10'a gradually decreases or the downwardly protruding bent portion 10'a gradually flattened. 25 - 45 - <Fourth Embodiment> In the first embodiment, a nylon tape was shown by way of example as the bending restriction member 10 but the present invention is not limited to such an example. Other 5 kinds of tapes such as polyester tape or the like may be used. Alternatively, fabric such as textile, non-woven material or the like, knitting, or artificial leather may be used. In the event that the bending restriction member is made of material with less flexibility such as fabric 10 or artificial leather, when the bending restriction member is pulled in the longitudinal direction from its taut state in the advancedphase of sole bending, the bending restriction member effectively functions to restrain sole bending. Thereby, in the latterhalf of thepushoffphaseduringrunning, 15 bending resistance of the sole can be effectively enlarged. Moreover, when the bending restriction member is made of fabric, which has a very small bending resistance and is very flexible, there is little power to bend it when it is in a bent shape. Therefore, the bending restriction member made 20 of fabric does not cause any bending resistance to the sole in the beginning of sole bending. Also, the bending restriction member 10 may be formed by extending the lower plate 5 to the opening of the groove 41. 25 - 46 - <Fifth Embodiment> In the first to fourth embodiment, a band-shaped or tape-like member was used as the bending restriction member 5 10, but the present invention is not limited to such an embodiment. As shown in FIGS. 9 and 10, a wire-like member may be used as the bending restriction member. In these drawings, reference numbers similar to those in the first to fourth embodiment indicate identical or functionally 10 similar elements. The bending restriction member 10", as shown in FIGS. 9 and 10, is a wire-like member that spans the groove 41 between the front and rear edge of the groove 41 and that is crooked sideways or in the width direction (i.e. the left 15 to rightdirection in FIG. 9) inagenerallyV-shape orU-shape between the front and rear edge of the groove 41. The bending restriction member 10" has a sideway crook or laterally bent portion 10"a that is crooked sideways in a generally V-shape or U-shape and opposite ends of the bending restriction member 20 10" couple the front edge to the rear edge of the groove 41. As the bending restriction member 10", for example, a nylon wire, otherwiresmadeofresindifferent fromnylon, thread, twisted yarn or the like may be used. In the beginning stage of bending of the sole, 25 the bending restriction member 10" gradually extends to a - 47 linear shape from the crooked shape in such a way that the amount of a sideway crook 10"a of the bending restriction member 10" gradually decreases. In this case, a variation of the size of the 5 section or the diameter of the bending restriction member 10" can vary the tensile modulus of elasticity and modulus in bending of the bending restriction member 10", thereby facilitating an adjustment of restricting action of the bending restriction member 10" relative to bending of the 10 sole. <Sixth Embodiment> In the fourth embodiment, when forming the bending restriction member 10 of fabric of a poor elasticity, 15 the bending restriction member maybe formed of a fabric sheet that covers the ground contact side surface of the lower midsole 4 and a multiple of outsole pieces that are separately disposed from each other may be fixedly attached to a ground contact side surface of the fabric sheet. 20 FIG. 11 shows a sixth embodiment of the present invention that employs such a fabric sheet. In FIG. 11, the same reference number as those in the first embodiment indicate identical or similar elements. As shown in FIG. 11, on the bottom surface of the lower midsole 4, fabric sheets 25 10A, 10B and 10C are attached. The fabric sheet 10A is disposed - 48 at a front side region Fi of the forefoot portion of the shoe, the fabric sheet 1OB at a central side region F 2 of the forefoot portion of the shoe, and the fabric sheet 10C at a region

F

3 extending from the rear side region to the midfoot region 5 of the forefoot portion of the shoe. The fabric sheets 10B and 10C are disposed at opposite sides of the groove 41. The rear end of the fabric sheet 1OBand the front endof the fabricsheet 1OCare coupled to each other via a pair of band-shaped sheet connections 10 l0e each spanning the groove 41. The sheet connection l0e is also formedof fabric and integrated with the fabric sheets 10B and 10C. The sheet connection l0e has upwardlybent portion in an inverted U-shape in the groove 41. On ground contact side surfaces of the fabric 15 sheets 10A, 10B and 10C, a multiple of outsole pieces 7p are fixedly attached. The outsole pieces 7p are, for example, hexagonal or rectangular shaped small pieces and formed integrally with the fabric sheets 10A, 10B and 10C through insert molding or the like. 20 In this case, since the fabric sheets 10A, 10B and 10C are used as base members of the outsole pieces 7p, the fabric sheets 10A, 10B and 10C and the outsole pieces 7pareintegratedwitheachother tobeaunitarypart. Thereby, an assembly process of the sole structure can be simplified 25 and the weight of the sole structure can be decreased. - 49 - <Seventh Embodiment> In the first embodiment of the present invention, the bending restriction member 10 was provided on both the 5 medial side and the lateral side of the sole, but the present invention is not limited to such an example. The bending restriction member 10 may be provided on either the medial side or the lateral side of the sole. In the event that the bending restriction member 10 10 is located on the medial side of the shoe, a shoe can be achieved that is suitable for a runner who has a tendency of pronation during running. In this case, in the latter half of the push off phase of running, bending resistance of the medial side region of the sole becomes relatively great and 15 bendingof the sole medial side region is restrained. Thereby, an energy loss in the latter half of the push off phase can be reduced. In the event that the bending restriction member 10 is located on the lateral side of the shoe, a shoe can 20 be achieved that is suitable for a runner who has a tendency of supination during running. In this case, in the latter half of the push off phase of running, bending resistance of the lateral side region of the sole becomes relatively great and bending of the sole lateral side region is restrained. 25 Thereby, an energy loss in the latter half of the push off - 50 phase can be reduced. Additionally, in the event that the bending restriction member 10 is located on the medial side and the lateral side of the shoe shown in the first embodiment, a 5 shoe can be attained that is suitable for a runner who has a tendency of pronation as well as for a runner who has a tendency of supination during running. Also, in this case, when the tensile modulus of elasticity and modulus in bending of the bending restriction member 10 on the medial side is 10 made different from the tensile modulus of elasticity and modulus in bending of the bending restriction member on the lateral side, a fine adjustment of the sole bending resistance is made possible between the medial side and the lateral side. Also, the bending restriction member 10 disposed on the medial 15 side or/and the lateral side of the sole may be composed of a plurality of members. <Eighth Embodiment> In the first embodiment, the bending 20 restriction member 10 disposed on the medial side of the sole had generally the same width as the bending restriction member 10 disposed on the lateral side of the sole. In the present invention, the width of the bending restriction member 10 on the medial side may be greater than the width of the bending 25 restriction member 10 on the lateral side. At this juncture, - 51 in the event that a plurality of bending restriction members 10 are provided, the width of the bending restriction member 10 that is herein referred to means the total amount of the widths of the bending restriction members. Also, in the event 5 that each of the bending restriction members 10 has generally the same width, the number of bending restriction members 10 disposed on the medial side may be greater than the number of bending restriction members 10 disposed on the lateral side. 10 Generally, during running, the medial side region of the sole forefoot portion is in contact with the ground for a longer time than the lateral side region of the sole forefoot portion and thus the bending angle of the MP joint on the medial side is generally greater than the bending 15 angle of the MP joint on the lateral side. That is the reason why the width/number of bending restriction members 10 on the medial side where a greater bending restriction action needs to be imparted during sole bending is greater than the width/number of bending restriction members 10 on the lateral 20 side. INDUSTRIAL APPLICABILITY As above-mentioned, the present invention is useful for a sole assembly for a shoe, and suitable especially 25 to a running shoe that can attain smooth ride feelings during - 52 running by decreasing energy loss. 5 10 15 20 25 - 53 -

Claims

1. A sole structure for a shoe comprising: a sole having a laterally extending groove, 5 said groove being formed on a bottom surface of said sole; and a bending restriction member formed in a bent shape and spanning said groove longitudinally between a front edge and a rear edge of an opening of said groove, wherein during a beginning phase of bending 10 of said sole, saidbending restriction member allows for said sole to bend till said bending restriction member gradually extends toward a straight shape from a bent shape and becomes taut between said front edge and said rear edge of said opening of said groove, and during an advanced phase of bending of 15 said sole, when said bending restriction member experiences a force that pulls said bending restriction member in a longitudinal direction from its taut state, it functions so as to restrict said sole from bending. 20

2. The sole structure according to claim 1, wherein said groove is disposed at a forefoot region of said sole.

3. The sole structure according to claim 1, 25 wherein said bending restriction member has an upwardly - 54 - protruded bent portion in said groove.

4. The sole structure according to claim 3, wherein said bending restriction member is not fixedly 5 attached to a wall surface of said groove.

5. The sole structure according to claim 3, wherein said bending restriction member is located away from a wall surface of said groove. 10

6. The sole structure according to claim 1, wherein said bending restriction member has a downwardly protruded bent portion in said groove. 15

7. The sole structure according to claim 3 or 6, wherein said bending restriction member is band-shaped.

8. The sole structure according to claim 1, wherein said bending restriction member has a sideway 20 protruded bent portion in said groove.

9. The sole structure according to claim 8, wherein said bending restriction member is wire-shaped. 25

10. The sole structure according to claim 1, - 55 - wherein said bending restriction member is made of fabric.

11. The sole structure accordingto claim 10, wherein said bending restriction member is a sheet-shaped 5 member that covers a ground contact side surface of said sole, said sheet-shaped member has a plurality of outsole pieces fixedly attached on a ground contact side surface of said sheet-shaped member. 10

12. The sole structure according to claim 1, wherein said bending restriction member is located on a medial side or a lateral side of said sole.

13. The sole structure according to claim 1, 15 wherein said bending restriction member is located on a medial side and a lateral side of said sole.

14. The sole structure according to claim 1, wherein an elastic covermember is disposedbetween said front 20 edge and said rear edge of said opening of said groove, said cover member extends longitudinally along said bent shape of said bending restriction member and covers said bending restriction member from below. 25

15. The sole structure according to claim 14, - 56 - wherein an outsole member having a ground contact surface is disposed on a bottom surface of said sole, said cover member being formed of said outsole member. 5

16. The sole structure according to claim 1 further comprising a longitudinally extending upper plate disposed on an upper side of said sole and a midsole formed of a soft elastic material and disposed under said upper plate, said groove being formed on a bottom surface of said midsole. 10

17. The sole structure according to claim 16 further comprising a longitudinally extending lower plate disposed on a lower side of said midsole, said bending restriction member being formed of said lower plate that 15 extends beyond said groove.

18. A sole structure for a shoe comprising: a longitudinally extending plate disposed on an upper side of a sole; 20 a midsole that is formed of a soft elastic material, that is disposed under and fixedly attached to said plate and that has a laterally extending groove formed on a bottom surface of said midsole; and a bending restriction member formed in a 25 bent shape and spanning said groove longitudinally between - 57 - a front edge and a rear edge of an opening of said groove, wherein during a beginning phase of bending of said sole, said bending restriction member allows for said sole to bend till said bending restriction member gradually 5 extends toward a straight shape from a bent shape and becomes taut between said front edge and said rear edge of said opening of said groove, and during an advanced phase of bending of said sole, when said bending restriction member experiences a force that pulls said bending restriction member in a 10 longitudinal direction from its taut state, it functions so as to restrain said sole from bending.

19. The sole structure according to claim 18, wherein a length L of the bending restriction member along 15 the bent shape thereof between said front edge and said rear edge of said opening of said groove satisfies an inequality, S+Dxsinl5 0 L S+Hxsinl5 0 in which S designates a distance between said front edge and said rear edge of said opening of said groove; 20 D designates a depth of said groove; and H designates a thickness of said midsole above a bottom of said groove.

20. The sole structure according to claim 1 or 18, wherein said bending restriction member is formed of 25 a material that has the Young's modulus of 400 MPa or more - 58 - at a strain of 10% or less.

21. The sole structure according to claim 1 or 18, wherein said bending restriction member functions such 5 that it allows for saidsole tobendtill thebentanglebecomes 150 and restricts bending of said sole when the bent angle exceeds 15*. 10 15 20 25 - 59 -