Source: http://patents.com/us-8713821.html
Timestamp: 2018-10-18 17:48:09
Document Index: 626292616

Matched Legal Cases: ['art 51', 'art 50', 'art 3', 'arts 50', 'art 4', 'arts 50', 'arts 50', 'art 3', 'art 4', 'Application No. 112004000536', 'art 50', 'art 50', 'art 50', 'art 50', 'arts 50', 'art 3', 'art 4', 'arts 50', 'arts 50', 'arts 50', 'arts 3', 'arts 50', 'art 3', 'art 4', 'arts 50', 'arts 50', 'arts 50', 'arts 50', 'art 51', 'art 51', 'art 51', 'art 3', 'art 4', 'art 51', 'art 51', 'art 51', 'art 51', 'art 69', 'art 50', 'art 3', 'art 4', 'art 50', 'art 50', 'art 69', 'art 69', 'art 50', 'art 69', 'art 69', 'art 69', 'art 69', 'art 50', 'art 51', 'arts 51', 'art 51', 'art 51', 'art 51', 'art 50', 'art 50', 'art 51', 'art 51', 'art 50', 'art 500', 'art 500', 'art 500', 'art 500', 'art 500', 'art 50', 'art 69', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 3', 'art 4', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50', 'art 50']

US Patent # 8,713,821. Athletic shoes having an upper whose fitting property is improved - Patents.com
United States Patent 8,713,821
Nishiwaki , et al. May 6, 2014
The present invention relates to the upper U of an athletic shoe comprising a first opening 1 out of which the foot sticks upwards during wearing and a second opening 2 which is closed with a tongue. The two openings 1, 2 are continuous with each other, and the upper U comprises a medial side stretchable part 51 which covers a part of a medial side face of an arch of the foot, a lateral side stretchable part 50 which covers a part of a lateral side face of a ball of a little toe (a fifth toe), a front part 3 located forward of the two stretchable parts 50, 51 and a rear part 4 located backward of the two stretchable parts. Each of the stretchable parts 50, 51 is provided so as to essentially cross one of side faces of the upper U from a top surface of a sole S to the second opening 2. Young's modulus along the lengthwise direction L of the foot of each of the stretchable parts 50, 51 is set smaller than that of the front part 3 and the rear part 4.
Nishiwaki; Tsuyoshi (Kobe, JP), Nakabe; Noboru (Kobe, JP), Kurosaki; Kiyomitsu (Kobe, JP), Kayano; Toshikazu (Kobe, JP)
Nishiwaki; Tsuyoshi
Nakabe; Noboru
Kurosaki; Kiyomitsu
Kayano; Toshikazu
Asics Corporation (Hyogo, JP)
Family ID: 1000000507344
12/915,369
US 20110041362 A1 Feb 24, 2011
10547645 7823298
PCT/JP2004/005335 Apr 14, 2004
Apr 24, 2003 [JP] 2003-119887
Oct 31, 2003 [JP] 2003-371830
Current U.S. Class: 36/88 ; 36/50.1; 36/93; 36/97
Current CPC Class: A43B 23/045 (20130101); A43B 23/047 (20130101); A43B 5/10 (20130101)
Current International Class: A43C 11/00 (20060101); A43B 3/26 (20060101)
Field of Search: ;36/88,93,103,102,51,50.1
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Catalog#1 Kayano 10th Anniversary, New Biomorphic Fit Technology, May 2003. cited by applicant .
Catalog#2 ASICS Spring 2004 Footwear, May 2003. cited by applicant .
Catalog #3 ASICS 2004 Spring & Summer Shoes Lineup, Jul. 2003. cited by applicant .
Office Action dated Sep. 13, 2011, issued by the German Patent Office, in connection with corresponding German Patent Application No. 112004000536.1. cited by applicant.
This is a continuation application of U.S. application Ser. No. 10/547,645 filed on Sep. 1, 2005, now U.S. Pat. No. 7,823,298 which is a national phase application based on PCT/JP04/05335 filed Apr. 14, 2004, which claims priorities of Japanese 2003-119887 filed on Apr. 24, 2003 and Japanese 2003-371830 filed on Oct. 31, 2003. The entire disclosures of these applications are incorporated herein by reference.
1. An athletic shoe suitable for exercise comprising a sole for absorbing shock of landing and an upper for covering an instep of a foot, the sole comprising a plurality of layers, wherein: the upper defines a first opening out of which the foot sticks upwards during wearing and a second opening being placed anterior to the first opening and opening in an upper surface of the instep and covered with a tongue, the two openings being continuous with each other in a longitudinal direction, and the upper comprises: a medial side surface of the upper which covers a medial side of the foot; a lateral side surface of the upper which covers a lateral side of the foot; and a medial side stretchable part formed on the medial side surface of the upper from a top surface of the sole to the second opening, wherein the medial side stretchable part has a Young's modulus along a lengthwise direction of the foot less than a Young's modulus of a remaining portion of the medial side surface of the upper, wherein all remaining portions of the medial side surface of the upper and a part opposite to the medial side stretchable part in the lateral side surface are covered by a material whose stretching and contracting property is less than that of the medial side stretchable part, wherein the medial side stretchable part is provided on the medial side of the foot at a location corresponding substantially to Lisfranc's joint, and wherein both a front edge and rear edge enclosing respective sides of the medial stretchable part extend in a rear direction of the foot as the front edge and rear edge get close to the sole from the second opening, and upper ends of the front edge and rear edge are positioned anterior to a front end of the first opening, wherein a part corresponding to a distal caput of a fifth metatarsal bone in the lateral side surface is covered with a material being substantially more difficult to stretch than the medial side stretchable part, and wherein the medial side stretchable part is provided from the top surface of the sole to the second opening and is in contact with the second opening.
2. An athletic shoe according to claim 1, wherein a roll-up portion in which the sole rolls up upwards is provided below the part corresponding to the distal caput of the fifth metatarsal bone.
3. An athletic shoe according to claim 1, wherein: the upper further comprises a lateral side stretchable part on a lateral side surface of the upper; and a Young's modulus of the lateral side stretchable part along the lengthwise direction of the foot is less than a Young's modulus of a remaining portion of the lateral side surface of the upper.
4. An athletic shoe according to claim 1, wherein the sole comprises an outsole that is continuous from a front portion of the sole to a rear portion of the sole.
FIG. 16(a) shows the shoe disclosed in the first patent document. In this shoe, a part of the lateral side of an upper U is formed with elastic member 100.
FIG. 16(b) shows the shoe disclosed in the second patent document. In this shoe, a part of both sides of an upper U is formed with elastic member 100.
FIG. 16(c) and FIG. 16(d) show the third patent document. In this shoe, both sides of a front part of an upper U are formed with elastic member 100.
FIG. 17(a) shows the shoe disclosed in the fourth patent document. In this shoe, a part of an upper U anterior to an opening is formed with bendable member 100.
FIG. 17(b) shows the shoe disclosed in the fifth patent document. In this shoe, a notched portion 102 in wedge shape is formed with stretchable member 100. The notched portion 102 extends shortly from the opening 103 of the upper U.
FIG. 2(a) and FIG. 2(b) are perspective views of the foot.
Generally, during running, runners raise their heel so as to kick the ground. At this time, the behavior of a front portion of the foot, which is located forward of a vicinity 81 of the arch in the medial side of the foot and a vicinity 80 of the ball of the little toe (the fifth toe) shown in FIG. 2(a) and FIG. 2(b), is quite different from that of a rear portion of the foot which is located backward thereof. This difference in behavior is not evident when the foot is in a stationary state.
In the present invention, by the use of the term "the region essentially corresponding to a top edge of distal caput (head) of a fifth metatarsal bone", it is meant to include not only the region just corresponding to the top edge of the distal caput of the fifth metatarsal bone but also its surrounding vicinity. Accordingly, for example, even if the lateral side stretchable part extends from a location slightly above the region just corresponding the top edge of the distal caput of the fifth metatarsal bone to the second opening, the lateral side stretchable part is provided in the area from the region essentially corresponding to the top edge of the distal caput of the fifth metatarsal bone to the second opening.
In the present invention by the use of the term "essentially cross one of side faces of the upper from the top surface of the sole to the second opening" it is meant that a stretchable member is provided from the top surface of the sole to the second opening on the side face of the upper so as to allow a part of the upper along a rim of the second opening to stretch and contract. Therefore, for example, even if an eyelet stay is provided with the upper along the rim of the second opening, a part of the eyelet stay is notched and the lateral side face of the notched portion is merely covered with cloth and so on, the stretchable member "essentially cross" the side of the upper.
In the present invention, by the use of the term "material which is substantially difficult to stretch" or "material which is substantially inelastic", it is meant to include the materials of which ordinary athletic shoes uppers are formed, and which have a Young's modulus greater than the stretchable parts.
By the use of the term "cloth" herein it is meant a sheet-like material of which the upper of the shoe is formed and can include a sheet of rubber or resin, woven fabric, knitted fabric and/or nonwoven fabric.
FIG. 2(a) and FIG. 2(b) are perspective views of the foot showing locations on the foot where strains occur (80, 81, 82) at the time of running.
FIG. 7(a) is a sectional view showing a base material, FIG. 7(b) is a sectional view showing a stretchable part on which an elastic member is laminated and FIG. 7(c) is a sectional view showing a part of the upper at a rear edge of a front part.
FIG. 10(a) is a perspective view showing a medial side stretchable part and its vicinity of a third embodiment and FIG. 10(b) is an exploded perspective view of the same.
FIG. 11(a) is a perspective view showing a medial side stretchable part and its vicinity of a fourth embodiment and FIG. 11(b) is an exploded perspective view of the same.
FIG. 12(a) and FIG. 12(b) are side views of a shoe of a fifth embodiment, medial side and lateral side view respectively, and FIG. 12(c) is a schematic side view (lateral side) showing the relationship between bones of the foot and the shoe.
FIG. 13(a) and FIG. 13(b) are side views showing a lateral side stretchable part and its vicinity.
FIG. 14(a) and FIG. 14(b), are side views of a shoe of a sixth embodiment, medial side and lateral side view respectively, and FIG. 14(c) is a schematic side (lateral side) view showing the relationship between bones of the foot and the shoe
FIG. 15(a), FIG. 15(b), FIG. 15(c), and FIG. 15(d) are side views showing the action of the stretchable part of the invention and FIG. 15(e) is a side view showing the related art.
FIG. 16(a), FIG. 16(b), FIG. 16(c), and FIG. 16(d) are perspective views and plan views showing conventional shoes.
FIG. 17(a) is a plan view and FIG. 17(b) is a side view showing another conventional shoes.
As described above and referring to FIGS. 2(a) and 2 (b), during running, the behavior of a front portion of the foot, which is located forward of the medial side face 81 of the arch in the medial side of the foot and located forward of the lateral side face 80 of the ball of the little toe, is quite different from that of the rear portion of the foot which is located backward thereof.
Still referring to FIG. 1, in addition, the lateral side stretchable part 50, covers the distal caput (head) 90 of a fifth metatarsal bone and its neighboring region and is provided in an area from the region to the second opening 2. The area where the lateral side stretchable part 50 is provided includes a line which extends forwardly and obliquely upward from the rear end 90b of the distal caput (head) 90 of a fifth metatarsal bone to the second opening 2. The lateral side stretchable part 50 has a length along the lengthwise direction L of the foot in the neighboring region of the distal caput (head) 90 of a fifth metatarsal bone so that the lateral side stretchable part 50 can stretch and contract along the lengthwise direction L of the foot.
Each of the two stretchable parts 50, 51 comprise a base material shown in cross section view in FIG. 7(a). The base material is formed by stacking or layering cloths 57, 58 which have stretching and contracting properties. Referring to FIG. 3, the cloths 57, 58 are sewn to each other at the rear edge 33 of the front part 3 and at the front edge 43 of the rear part 4. In the central region of each of the stretchable parts 50, 51, the cloths 57, 58 are neither bonded to each other nor sewn to each other, and so the cloths 57, 58 can freely slide over each other and deform separately from each other.
As shown in cross section view in FIG. 7(b), an elastic material 56 is provided on a part of the upper cloth 57 of the base material 55. The elastic material 56 gets into and adheres to the surface of a part of the upper cloth 57. The elastic material provides a means for controlling the direction of the stretch of the stretchable parts 50, 51.
On the other hand, as shown in cross section view in FIG. 7(c), at the position of the reinforcing members 6, 7 (FIG. 5), the cloths 57, 58 of the stretchable parts 50, 51 and materials 37, 38 of the front and rear parts 3, 4 are sewn to the belt-like material of the reinforcing member 6, 7.
At the time of putting on the shoe on the foot, after unfastening the lace R shown in FIG. 6, the foot is inserted into the shoe from the first opening 1 and the rear portion of the second opening 2. At this time, the medial side and lateral side stretchable parts 50, 51 become stretched a little so that the front part 3 fits the toe, of the foot and that the rear part 4 fits the heel of the foot.
Referring to FIG. 2a, at the time of running as the foot bends with the heel raised upward, the behavior of the foot differs very much between the front foot portion and the rear foot portion about a vicinity 81 of the arch in the medial side of the foot and a vicinity 80 of the ball of the little toe (the fifth toe). At this time, the upper U stretches in the vicinity of the top surface of the sole S (FIG. 3), and, contracts in the vicinity of the second opening 2. Since the stretchable parts 50 and 51 of this athletic shoe in the vicinity of the sole S are longer in the lengthwise direction L of the foot, and Young's modulus thereof along the lengthwise direction L of the foot is set small, the stretchable parts 50 and 51 can stretch easily in the vicinity of the sole S. On the other hand, since the notched portions 63 and 64 are formed in the stretchable parts 50 and 51 in the vicinity of the second opening 2, the stretchable parts 50 and 51 can contract easily in the vicinity of the second opening 2. Accordingly, the upper U can fit the foot.
Referring to FIG. 2 and the lateral side foot portion 82, which is located under the ankle of the foot, the behavior of the foot differs substantially between the front and the rear about said lateral side foot portion 82. Accordingly, it is preferable to provide the stretchable member proximate to said lateral side foot portion 82 as well as in the vicinity 80 of the little toe and the vicinity 81 of the arch in the medial side of the foot.
As shown in FIG. 8, in this embodiment, the elastic material 56 of the medial side-stretchable part 51 is separated in the vertical direction.
FIG. 10 shows a third embodiment of the shoe of this invention. FIG. 10(a) is a perspective view showing a medial side stretchable part 51 and its vicinity and FIG. 10(b) is an exploded perspective view thereof.
In this embodiment, as shown in FIG. 10(a), a loop P covers the medial side notched portion 63. As shown by the broken line, the ends of the loop P are sewn to the top edge of the first medial side stay portion 71 and the second medial side stay portion 61, but are not sewn to the eyelet stay portions 62, 72B. Accordingly, the loop P allows the medial side stretchable part 51 to stretch and contract.
Further, as shown in the exploded perspective view of FIG. 10(b), the stay portions 61, 62 of the front reinforcing member 6 and the stay portions 71, 72B of the rear reinforcing member 7 are formed separately with each other, respectively. The top edges of the medial side stay portions 61, 71 of the reinforcing members 6, 7 are provided in proximity with the eyelet stay portions 62, 72B, respectively. Thereby, it becomes unnecessary to form each of the reinforcing members 6, 7 integrally, thus costs can be reduced.
As shown by the broken line in FIG. 10(a), the first medial side stay portion 61 and the second medial side stay portion 71 are sewn to the rear edge of the front part 3 and the front edge of the rear part 4, respectively, together with cloths 57, 58 of the medial side stretchable part 51.
FIG. 11 show a fourth embodiment. FIG. 11(a) is a perspective view showing a medial side stretchable part and its vicinity and FIG. 11(b) is an exploded perspective view thereof.
In this embodiment, as shown in FIG. 11(b); the loop P is formed integrally with the first medial side stay portion 61 and the second medial side stay portion 71. The loop P is not sewn to the eyelet stay portions 62, 72B. Accordingly, the loop P allows the medial side stretchable part 51 to stretch and contract, similarly to the third embodiment.
FIG. 12 and FIG. 13 show a athletic shoe for court (for example volleyball) according to a fifth embodiment. FIG. 12(a) shows a medial side face of a shoe (for a right foot) and FIG. 12(b) shows a lateral side face of such shoe. FIG. 12(c) shows the relationship between the bones of the foot and the lateral side face of the shoe. FIG. 13(a) and FIG. 13(b) are enlarged side views showing a lateral side stretchable part and its vicinity.
In FIG. 12(a), FIG. 12(b), FIG. 13(b), FIG. 14(a) and FIG. 14(b), in order to understand easily the area where the stretchable part is provided, the stretchable parts are dot-meshed.
As shown in FIG. 12(a), the medial side stretchable part 51 of the shoe of this embodiment is provided so as to essentially cross medial side face 31 of the upper U from a top surface of the sole S to the second opening 2. This structure is similar to the first embodiment. The stretchable part 51 is formed to be approximately rectangular or square-shaped. The front eyelet stay portion 62 is provided separately on the medial side and the lateral side of the second opening 2 and is not provided in front of the second opening 2.
As shown in FIG. 12(b), on the lateral side face of the upper U, a connecting part 69 is provided below the lateral side stretchable part 50, continuously extending from the front part 3 to the rear part 4. The lateral side stretchable part 50 does not extends to the top surface of the sole S in appearance. The lateral side stretchable part 50 is provided so as to be over an approximately half of the upper U in height, extending downwards from the second opening 2. The connecting part 69 is formed of the same or similar material as second medial side stay portion 70, and the Young's modulus along the lengthwise direction L of the foot of the connecting part 69 is set larger than that of the lateral side stretchable part 50. Below the connecting part 69, a roll-up portion 68 is formed by making the sole S project upwards so as to be rolled up.
Referring to FIGS. 13(a) and 13(b), a stretchable member 54 having stretching and contracting property is placed in an area surrounded by the first medial side stay portion 60, the second medial side stay portion 70 and the sole S (the area shown by one-dot chain line). Next, the connecting part 69 is sewn so as to cover the lower portion of the stretchable member 54 placed in above-described manner. This connecting part 69 is formed of material which is substantially difficult to stretch. On the other hand, a rectangular or square-shaped section, which is surrounded by the first lateral side stay portion 60, the second lateral side stay portion 70, the connecting part 69 and the rim 35 of the second opening 2, can stretch and contract, and this section defines the lateral side stretchable part 50.
FIG. 14 shows a trail shoe according to a sixth embodiment. FIG. 14(a) shows a medial side face of the shoe (for a left foot) of this embodiment, FIG. 14(b) shows a lateral side face of the same shoe, and FIG. 14(c) shows the relationship between bones of the foot and the lateral side face of the shoe.
The medial side stretchable part 51 of this embodiment, as shown in FIG. 14(a) is provided so as to be approximately half of the upper U in height, extending downwards from the second opening 2. This medial side and lateral side stretchable parts 51, 50 are arranged on opposite sides of the second opening 2. That is, the medial side stretchable part 51 faces opposite to the lateral side stretchable part 51 via the second opening 2. Such an arrangement of the stretchable parts is different from that in the above-described embodiments. A member formed of material which is substantially difficult to stretch is provided between the medial side stretchable part 51 and the sole S.
On the other hand, the lateral side stretchable part 50, as shown in FIG. 14(c), is provided in the same area as in the first embodiments (the area from a region corresponding to distal caput 90 of a fifth metatarsal bone to the second opening 2). The lateral side stretchable part 50 is longitudinally separated by a protecting member 55, similar to the medial side stretchable part 51. A front region of the separated lateral side stretchable part 51, as shown in FIG. 14(b), crosses a lateral side face 30 of the upper U from a top surface of the sole S to the second opening 2.
In the above-described six embodiments, the lateral side stretchable part 50 is formed to be substantially rectangular, square-shaped or trapezoid-shaped resembling triangle, and to have a longitudinal length in a region corresponding to distal caput 90 of a fifth metatarsal bone and in its neighborhood, as shown in FIG. 14(c). The action caused by such formation of the lateral side stretchable part will be described below referring to the schematic views of the lateral side stretchable part (FIG. 15(a) to FIG. 15(e)). In FIG. 15(a) to FIG. 15(e), in order to understand easily the area where the stretchable parts are provided, the stretchable parts are dot-meshed.
In the prior art (FIG. 15(e)), a small stretchable part 500 which is formed to be an inverted triangle is provided on the lateral side of the foot. When a force in the lengthwise direction L of the foot is applied to the stretchable part 500, the stretchable part 500 stretches as shown by two-dot line M of the same figure. In this case, elongation percentage at a bottom point 501 of the stretchable part 500 is zero. That is, since the inverted triangular stretchable part 500 has no certain length in the lengthwise direction L of the foot at its bottom, it can stretch little at the bottom. Accordingly, the upper can stretch little in the lengthwise direction L of the foot in almost all of the lateral side face of the upper.
Referring to this invention, as shown in FIG. 15(a), wherein the lateral side stretchable part 50 is formed to be substantially rectangular or square-shaped. A connecting part 69 which is hard to stretch and contract is provided between the lateral side stretchable part 50 and the sole S. In such a structure, when a force in the lengthwise direction L of the foot is applied to the lateral side stretchable part 50, the lateral side stretchable part 50 stretches as shown by two-dot line M1 of the same figure. In this case, since the lateral side stretchable part 50 has a certain length in the lengthwise direction L of the foot at a region (a point) O which is in the vicinity of said distal caput 90 of a fifth metatarsal bone, this region can stretch in the lengthwise direction L of the foot. That is, the lateral side stretchable part 50 can stretch and contract longitudinally in an area from a region to the second opening 2.
On the other hand, as shown in FIG. 15(b), the lateral side stretchable part 50, which is formed to be substantially trapezoidal resembling to a triangle, is provided from the second opening 2 to the top surface of the sole S.
Thus, the lateral side stretchable part 50, substantially in the shape of a trapezoid, rectangle or square, can deform to various shapes according to external force. Therefore, at the time of exercise, the lateral side stretchable part 50 stretches according to the deformation of the foot so that the front part 3 and the rear part 4 of the upper U can move independently from each other about a boundary near the distal caput (head) 90 of a fifth metatarsal bone. As a result, the upper can deform in accordance with the motions of the front foot portion and the rear foot portion, which are different from each other.
In the lateral side stretchable part 50 formed to be substantially rectangular or square-shaped, a member 59 which is hard to stretch and contract may be provided isolated in the central region of the lateral side stretchable part 50, as shown in FIG. 15(c). The lateral side stretchable part 50 may be formed to be in the shape constricted in the middle in the vertical direction, as shown in FIG. 15(d).
Further, in order to prevent unnecessary stretching and to provide sufficient stretch of the lateral side stretchable part 50, the "elastic constant" k per unit height W (FIG. 15(a)) of the lateral side stretchable part 50 is preferably set between about 0.1 N/mm and 50 N/mm. Said "elastic constant" is defined as a value obtained by cutting the stretchable part into a test piece which is slender and long in the lengthwise direction of the foot, applying a load f in the longitudinal direction to the test piece and dividing the load f by a strain .epsilon. of the test piece and a width W of the test piece. That is, this "elastic constant" k is given by the following expression (1). k=f/(.epsilon.W) (1)
The reason why conception of above "elastic constant" is introduced is that thickness of material of the upper cannot be ambiguous. That is, the correct thickness of the upper is difficult to measure. Therefore, it is different to obtain the correct value of the following Young's modulus of the material of the upper. The "elastic constant" k can be obtained without measuring the correct thickness of the material of the upper.
Young's modulus is obtained by dividing the load f by a strain .epsilon. of the test piece and a transverse sectional area S of the test piece. That is, Young's modulus E is given by the following expression (2). k=f/(.epsilon.S) (2)
Preferred values of the "elastic constant" k vary with the shape, size and type of shoe and the shape and size of the stretchable parts. For example, it is preferable to set said "elastic constant" k approximately between 0.1 N/mm and 7.0 N/mm in the shoes shown in FIG. 1 to FIG. 11(b), FIG. 14(a) to FIG. 14(c). In the running shoes shown in FIG. 1 to FIG. 11(b), it is preferred to set the "elastic constant" k approximately between 0.1 N/mm and 3.0 N/mm. In the athletic shoes for court sports shown in FIG. 12(a) to FIG. 13(b), it is preferable to set the "elastic constant" k approximately between 10 N/mm and 30 N/mm. In the trail shoe shown in FIG. 14(a) to FIG. 14(c), it is preferable to set the "elastic constant" k approximately between 1.0 N/mm and 7.0 N/mm.
These specific values of the "elastic constant" k are supposed to be set larger than the "elastic constant" k of conventional stretchable material. In the present invention, the stretchable part 50 is necessarily formed to have a certain length in the lengthwise direction L of the foot. Accordingly, when the stretchable part 50 is formed to be too stretchable, the function of the upper U to keep the stability of the foot decrease too much. Because of this, the "elastic constant" k of the stretchable part 50 is set large to a certain extent, according as the stretchable part 50 is formed to have said length in the lengthwise direction L of the foot.
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