Patent Publication Number: US-2021161684-A1

Title: Sole of athletic prosthetic leg

Description:
TECHNICAL FIELD 
     The present disclosure relates to a sole attached to a ground contact region of an athletic prosthetic leg, in particular, to a sole of an athletic prosthetic leg which inhibits slip of the prosthetic leg during a competition. 
     BACKGROUND 
     Conventionally, a prosthetic leg for a competition (hereinafter, it is referred to as an athletic prosthetic leg or simply referred to as a prosthetic leg) having a leaf-spring-like leg portion which extends via a curved portion to a side of a toe and in which a ground contact region extends from the toe to a side of the curved portion in an arc has been well-known. In such an athletic prosthetic leg having the leaf-spring-like leg portion, generally, a sole which abuts a road surface is attached to a bottom surface of the ground contact region. 
     For example, Patent Literature 1 illustrates a sole which is attached to a lower surface of a curved leaf-spring-like athletic prosthetic leg to correspond to sporting events such as jogging or running. In other words, Patent Literature 1 discloses a sole to which a spike is attached at a lower surface of the sole contacting a road surface or a sole provided with a number of outsole portions each having a hexagonal contact patch. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Patent Laid-Open No. 2016-150189 
     SUMMARY 
     Technical Problem 
     However, in the sole illustrated in Patent Literature 1, due to early abrasion of a part of the sole, especially a portion at a side of a toe, a service life of the sole itself has been made shorter. 
     Also, in the sole illustrated in Patent Literature 1, inhibiting slip of the prosthetic leg, that is, anti-slip property is not at all considered. For example, running on a wet road surface is required in a case of a competition in rainfall etc. At that time, when a water film exists on the road surface, the water film is interposed between a bottom surface of the sole and the road surface while hindering ground contact of the bottom surface, resulting that slip is caused. Especially, on a road with a low coefficient friction μ such as asphalt and a stone pavement, there has been a case where a wearer of the prosthetic leg hesitates further acceleration. Accordingly, a sole having a high anti-slip property has been required for the wearer of the prosthetic leg to satisfactorily exert his running skill as athletes. 
     An object of the present disclosure is to provide a sole of athletic prosthetic leg achieving both wear resistance performance and anti-slip property. 
     Solution to Problem 
     The inventor earnestly studied means to solve the problem. In other words, while a bottom surface of an athletic prosthetic leg has been reviewed in detail, the inventor new 1 y found that an especially severe abrasion tends to occur at a portion at a side of a toe of the bottom surface of the sole. Moreover, the inventor conceived that anti-slip property can be improved by providing recesses and protrusions at the bottom surface of the sole, and completed the present disclosure. 
     According to the present disclosure, there is provided a sole of an athletic prosthetic leg, the athletic prosthetic leg having a leaf-spring-like leg portion extending to a side of a toe via at least one curved portion, the sole being configured to be attached to a ground contact region of the athletic prosthetic leg, the ground contact region extending from the toe to a side of the curved portion in an arc, wherein the sole includes a bottom surface having a shape conforming to an extending shape of the ground contact region, and the bottom surface includes at least one sipe linearly extending at a portion which continues at a constant radius of curvature from the toe, and the sipe terminates in the bottom surface. 
     Advantageous Effect 
     Due to the present disclosure, a sole of an athletic prosthetic leg achieving both wear performance resistance and anti-slip property can be provided. By attaching this sole to the athletic prosthetic leg, an athlete&#39;s skill can be satisfactorily exerted and a long service life of the sole can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a side view of an athletic prosthetic leg to which a sole according to a first embodiment of the present disclosure is attached; 
         FIG. 2A  is a drawing for explaining in stages movement of a leg portion and a ground contact form in a case where the athletic prosthetic leg is worn and a wearer executes straight running; 
         FIG. 2B  is a drawing for explaining in stages the movement of the leg portion and the ground contact form in a case where the athletic prosthetic leg is worn and the wearer executes straight running; 
         FIG. 2C  is a drawing for explaining in stages the movement of the leg portion and the ground contact form in a case where the athletic prosthetic leg is worn and the wearer executes straight running; 
         FIG. 2D  is a drawing for explaining in stages the movement of the leg portion and the ground contact form in a case where the athletic prosthetic leg is worn and the wearer executes straight running; 
         FIG. 3  is a drawing which illustrates a pattern of a sole bottom surface of the sole of the athletic prosthetic leg according to the first embodiment; 
         FIG. 4A  is a drawing illustrating variation of the shape of a sipe; 
         FIG. 4B  is a drawing illustrating variation of the shape of a sipe; 
         FIG. 4C  is a drawing illustrating variation of the shape of a sipe; 
         FIG. 5  is a drawing illustrating a portion Q of the sole bottom surface of  FIG. 1 ; 
         FIG. 6  is a drawing which illustrates a pattern of a sole bottom surface of a sole of an athletic prosthetic leg according to a second embodiment; 
         FIG. 7  is a drawing illustrating one shape of a width direction land portion of  FIG. 6 ; 
         FIG. 8  is a drawing illustrating one shape of the width direction land portion of  FIG. 6 ; 
         FIG. 9A  is a drawing for explaining a mutual arrangement in which an arrangement phase of line-symmetric sipe pairs is synchronized with a phase of waves of a width direction land portion; 
         FIG. 9B  is a drawing for explaining a mutual arrangement in which the arrangement phase of the line-symmetric sipe pairs is different from the phase of the waves of the width direction land portion; 
         FIG. 10A  is a drawing illustrating variation of a pair of sipes; 
         FIG. 10B  is a drawing illustrating variation of the pair of sipes; and 
         FIG. 10C  is a drawing illustrating variation of the pair of sipes. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, with reference to the drawings, a sole of an athletic prosthetic leg of the present disclosure (hereinafter, it is also referred to as a sole) will be explained in detail with illustration of embodiments thereof. 
       FIG. 1  is a side view of an athletic prosthetic leg  1  to which a sole  5  according to a first embodiment of the present disclosure is attached. The athletic prosthetic leg  1  has a leaf-spring-like leg portion  2 , and the sole  5  is attached to a ground contact region at its tip side. Additionally, while illustration is omitted, a base end portion of the leg portion  2  is connected to a socket via an adapter and the socket houses a stump of a wearer&#39;s leg, whereby the wearer can wear the prosthetic leg. The adapter and the socket which correspond to the position of the stump of the leg, such as an above-knee prosthesis and a below-knee prosthesis, are used.  FIG. 1  illustrates the leg portion  2  and the sole  5  in a standing state of the wearer who wears the athletic prosthetic leg  1 . 
     Hereinafter, in this embodiment, in a height direction of the athletic prosthetic leg, a side where the leg portion  2  is connected to the adapter is referred to as a connection side, and a side where the leg portion  2  contacts a road surface S is referred to as a ground contact side. Also, a toe T of the athletic prosthetic leg  1  refers to a point at the forefront as a termination of the leg portion  2  extending from the connection side. Further, a direction extending from the toe T in parallel with the road surface S is referred to as a leg portion front-rear direction Y. Further, a widthwise direction of the leg portion  2  is referred to as a width direction W. 
     In this embodiment, the leg portion  2  of the athletic prosthetic leg  1  has a plate-like extending shape to the side of the toe T via at least one curved portion, in the illustrated example, one curved portion  3 . In  FIG. 1 , the leg portion  2  is constituted by, in the order from the connecting side to the ground contact side, a straight portion  2   a , a curved portion  2   b  which is convex to the side of the toe T, the curved portion  3  which is convex to a rear side in the leg portion front-rear direction Y, a curved portion  2   c  which is concave to the ground contact side and a ground contact portion  4  which is convex to the ground contact side to extend to the side of the toe T in an arc. 
     Additionally, although the material of the leg portion  2  is not limited, from a viewpoint of strength and weight saving, fiber reinforced plastic etc. is preferably used. 
     The ground contact portion  4  includes a ground contact region  4   s  extending from the toe T to the side of the curved portion  3  in an arc at the ground contact side, and the sole  5  is attached to the ground contact region  4   s . The ground contact region  4   s  refers to the entire region abutting the road surface S when the wearer who wears the athletic prosthetic leg  1  executes straight running movement, and in a state that sole  5  is attached, the ground contact region  4   s  abuts the road surface S via the sole  5 . 
     The sole  5  has a shape conforming to an extending shape of the ground contact region  4   s . Also, the ground contact side of the sole  5  is a bottom surface  5   s . As illustrated in  FIG. 1 , the bottom surface  5   s  has a shape in which an arc X 1  and an arc X 2  are continued from the toe T side to the curved portion  3  side. While the arc X 1  and the arc X 2  have a different radius of curvature to each other in this embodiment, they may include the same radius of curvature. 
     A pattern of the bottom surface  5   s  of the sole of the athletic prosthetic leg according to the first embodiment of the present disclosure is based on a finding related to a ground contact form obtained from an experiment which will be described later. Accordingly, an experiment result of the ground contact form of the bottom surface  5   s  as described above will be explained below using  FIGS. 2A, 2B, 2C and 2D .  FIGS. 2A, 2B, 2C and 2D  are drawings for explaining in stages movement of the leg portion  2  and the ground contact form of the bottom surface  5   s  when the wearer who wears the athletic prosthetic leg  1  executes straight running. In each drawing, an upper portion is a side view of the leg portion  2  and the sole  5 , and a lower portion illustrates a transition of the ground contact form of the bottom surface  5   s  when the wearer who wears the athletic prosthetic leg  1  executes straight running. 
     In other words,  FIG. 2A  illustrates a state that the wearer lowers the raised athletic prosthetic leg  1  to the road surface S and the entire weight is loaded on the athletic prosthetic leg  1 . As illustrated in the lower portion of the drawing, at an initial stage of lowering the prosthetic leg  1  on the road surface S, a ground contact region of the bottom surface  5   s  is located to be adjacent to a center portion of the bottom surface, which is a region spaced from both the curved portion  3  and a side of the toe T in the leg portion front-rear direction. 
       FIG. 2B  illustrates a state that the wearer steps forward while the entire weight remains to be loaded on the athletic prosthetic leg  1 . In a case of running of a healthy person, such a step form is generally applied that ground contact is sequentially executed from a heel side which firstly contacts the ground toward a toe side of a shoe sole, while in the athletic prosthetic leg  1 , the ground contact region is moved to the side of the curved portion  3  from a portion which firstly contacts the ground. 
       FIG. 2C  illustrates a state that the wearer starts a kick-out movement of the athletic prosthetic leg  1  by shaking an opposite leg from the leg wearing the athletic prosthetic leg  1  forward. Entering into this kick-out movement, the athletic prosthetic leg  1  contacts the ground at a region at the side of the toe T of the bottom surface  5   s  from the regions illustrated in  FIGS. 2A and 2B . 
       FIG. 2D  illustrates a state that the wearer is in a final stage of kicking out the athletic prosthetic leg  1  just before separating from the road surface S. To kick out from the toe T of the bottom surface  5   s , ground contact is executed further at the side of the toe T than in  FIG. 2C . 
     The bottom surface  5   s  based on the experiment result illustrated in  FIGS. 2A, 2B, 2C and 2D  will be explained below. 
     As illustrated in  FIG. 3 , the bottom surface  5   s  includes at least one, ten in the illustrated example, sipes  13 A and  13 B linearly extending at a portion Q corresponding to the arc X 1  which continues at a constant radius of curvature from the toe. The sipes  13 A and  13 B terminate in a land portion of the portion Q of the bottom surface  5   s . Here, in this embodiment, terminating in the bottom surface  5   s  means that the sipes  13 A and  13 B are not open at an end edge of the sole  5 , which refers to a sipe having both ends which terminate in the portion Q of the bottom surface  5   s.    
     In other words, as illustrated in  FIG. 2D , the portion Q is a region where the wearer shakes an opposite leg from a leg wearing the athletic prosthetic leg  1  forward to execute the kick-out movement of the athletic prosthetic leg  1 . The portion Q and a portion adjacent thereto sequentially contact the ground toward the toe T, and the wearer presses the road surface S by the bottom surface  5   s  to slidingly contact the ground, so that these portions are a region which easily develops abrasion in particular. Especially, the portion Q finally contacts the ground when the wearer wearing the athletic prosthetic leg  1  executes the kick-out movement, so that a severer abrasion has been inclined to occur. Further, in this region, it is vital that slip prevention is maintained in addition to improving wear resistance performance. Moreover, the sipes  13 A and  13 B with a groove width of less than 1 mm terminating in the bottom surface  5   s  are formed, and edge components are distributed without deteriorating rigidity of the bottom surface  5   s , so that both wear resistance performance and anti-slip property can be achieved. Further, according to the configuration of the sipes  13 A and  13 B, occurrence of cracking at the portion Q can also be inhibited. 
     As illustrated in  FIG. 3 , the sipes  13 A and  13 B are preferably linear without any bent portion. In other words, with the sipe being linear, not in a bending shape by a bent portion, occurrence of cracking starting from the bent portion can be inhibited. 
     Additionally, the sipes  13 A and  13 B are not limited to the shape shown in  FIG. 3 , and may have the shape illustrated in  FIGS. 4A, 4B and 4C . A sipe  13 C illustrated in  FIG. 4A  is linear along the leg portion front-rear direction Y. Also, a sipe  13 D illustrated in  FIG. 4B  is linear along the width direction W. Further, a sipe  13 E illustrated in  FIG. 4C  has a shape inclined from the leg portion front-rear direction Y. 
     Also, as illustrated in  FIG. 3 , a plurality of sipes  13 A and  13 B are preferably used. By using the plurality of sipes  13 A and  13 B, sufficient drainage performance can be achieved. On the other hand, from a viewpoint of inhibiting rigidity deterioration, the total number of the sipes  13 A to  13 E formed at the portion Q is preferably less than 20. 
     Regarding the shape of the sipes  13 A and  13 B, an explanation will be made in more detail with reference to  FIG. 5 . 
     As illustrated in  FIG. 5 , the plurality of sipes  13 A and  13 B preferably include at least one line-symmetric sipe pair  130  constituted by two line-symmetric sipes in a line-symmetric relation with a line along the leg portion front-rear direction Y being set to an axis of symmetry a 1 , and in the illustrated example, five pairs are included. By including the line-symmetric sipe pair  130 , an edge function can be evenly applied to a toe portion of the bottom surface  5   s.    
     Also, from a viewpoint of exerting a fully edge function to various input of force, as illustrated in  FIG. 5 , the sipes  13 A and  13 B preferably extend in a direction inclined to the axis of symmetry a 1 . More specifically, an inclination angle θ 1  or θ 2  to the axis of symmetry a 1  of each of the sipes  13 A and  13 B is more preferably 20° to 50°. 
     Also, the line-symmetric sipe pair  130  preferably has an arrangement that each of the sipes  13 A and  13 B constituting the line-symmetric sipe pair  130  extends in a direction converging to a side of the toe T of the axis of symmetry a 1 . With this configuration, since the sipe  13 A and the sipe  13 B extend in different directions, a land portion adjacent to each sipe produces a different response to an input of force from a certain direction, thereby inhibiting deformation as the entire Q portion. Further, an edge function can be efficiently exerted along the direction that the sipes  13 A and  13 B converge. 
     Also, such a relation is preferably satisfied that a length h 2  of the sipes  13 A and  13 B along the leg portion front-rear direction Y, to a length h 1  of the portion Q in the leg portion front-rear direction Y, has a ratio h 2 /h 1  of 0.4 to 0.9, while a length n 2  along the width direction W, to a length n 1  of the portion Q in the width direction W, has a. ratio of n 2 /n 1  of 0.075 to 0.095. With this configuration, the drainage performance and the wear resistance performance can be balanced. 
     Additionally, in this embodiment, an aspect of recesses and protrusions formed at regions other than the portion Q of the bottom surface  5   s  is not especially limited. 
     Further, based on the experiment result illustrated in  2 A,  2 B,  2 C and  2 D, the inventor obtained the finding that separating functions of a bottom surface  50   s  in accordance with the transition of the ground contact region is advantageous to property improvement of the sole of the prosthetic leg, and conceived the following groove pattern. 
     As illustrated in  FIG. 6 , the bottom surface  50   s  has an array of the sipe pairs in which the line-symmetric sipe pairs  130  are arranged at the portion Q in the width direction W and, at the side of the curved portion  3  from the portion Q, a plurality of width direction land portions extending to be wavy-shaped in the width direction W defined by a plurality of width direction grooves extending in the width direction W. In other words, in the groove pattern illustrated in  FIG. 6 , at the portion Q of the bottom surface  50   s , five line-symmetric sipe pairs  130  are arranged in the width direction W. Further, in this groove pattern, at the side of the curved portion  3  from the portion Q, a plurality of width direction land portions  12 ,  14 ,  10  and  11  extending to be wavy-shaped in the width direction W defined by the plurality of width direction grooves extending in the width direction W are sequentially arranged. 
     The wave described herein refers to, not merely a sinusoidal wave, one in which a substantially identical shape executes phase variation with a substantially identical cycle such as zigzag and recesses and protrusions, and among these, a sinusoidal wave or a zig-zag shape with an identical phase is preferable. 
     The shape of the width direction land portions  10 ,  11 ,  12  and  14  will be explained with reference to  FIGS. 6 and 7 . 
     As illustrated in  FIG. 7 , the width direction land portion  10  is a land portion extending with a predetermined width along a wavy line P 1  which is wavy-shaped as described above. By allowing the width direction land portion  10  to be wavy-shaped in this way, an edge component in the width direction W increases and also an edge component in a front-rear direction can be applied, and comprehensively, a higher edge effect can be obtained. In other words, even if a direction of the input of force is shifted from the width direction W at the time of running of the wearer of the athletic prosthetic leg  1 , the edge effect can be fully exerted. 
     Additionally, the width direction land portion  10  is wavy-shaped, which means that, as illustrated in  FIGS. 6 and 7 , a toe side protruding portion  10   b  and a curved portion side protruding portion  10   c  which protrude to one side or the other side in the leg portion front-rear direction from a position of a ridge M 1  or a valley V 1  of the wavy line P 1  may be included. Due to the inclusion of the toe side protruding portion  10   b  and the curved portion side protruding portion  10   c , the edge component is further increased and the edge effect in both the leg portion front-rear direction Y and the width direction W can be improved. 
     Further, the width direction land portion  10  is preferably line-symmetric about a line extending in the leg portion front-rear direction Y through the ridge M 1  or the valley V 1  of a wave in one wavelength of the wave (from one ridge to another ridge or from one valley to another valley of a wave). As illustrated in  FIG. 7 , the width direction land portion  10  is line-symmetric about a line b 1  extending in the leg portion front-rear direction Y through the ridge M 1  of the wavy line P 1  in one wavelength λ 1  of a wave, and line-symmetric about a line b 2  extending in the leg portion front-rear direction Y through the valley V 1  in one wavelength λ 2  of the wave. With this configuration, even if a direction of the input of force is shifted from the width direction W at the time of running of the wearer of the athletic prosthetic leg  1 , the edge effect can be fully exerted. 
     The width direction land portions  11  and  14  have the shape extending to be wavy-shaped with the same phase as in the width direction land portion  10 . Consequently, in the same manner as the width direction land portion  10 , the width direction land portions  11  and  14  are land portions extending with a predetermined width along a line which is wavy-shaped following the above-described definition. Additionally, the difference between the width direction land portions  11 ,  14  and the width direction land portion  10  is as described later, and the other configurations follow the above-described configuration of the width direction land portion  10 . 
     Here, a region where the width direction land portions  10 ,  11  and  14  are arranged corresponds to the ground contact regions illustrated in  FIGS. 2A and 2B , which is the region where the wearer firstly contact the ground and executes a step movement in a state that the entire weight is loaded on the athletic prosthetic leg  1 . Consequently, to maintain balance of the entire body even if the wearer places his entire weight on the athletic prosthetic leg  1 , it is vital that the region fully grips the road surface S. Accordingly, by arranging the width direction land portion  10  with an excellent edge effect in the width direction W and the width direction land portions  11 ,  14  which are similar to the width direction land portion  10 , an excellent edge function is applied to this region and a gripping force to the road surface S is fully secured, which provides a high anti-slip property to the region. 
     Additionally, the width direction land portion  11  has a larger width than the width direction land portion  10 . As illustrated in  FIG. 2B , in a state of stepping immediately after the ground contact, the ground contact region is changed to the side of the curved portion  3  from a region which firstly contacts the ground, that is, to the opposite side from a direction that the wearer advances. Here, movement of an upper body in which the wearer tries to move forward and a direction of the change of the ground contact region are temporarily opposite, and this is a stage in which a high propulsive force is needed for the kick-out movement at the latter half of the ground contact form as illustrated in  FIGS. 2C to 2D . By arranging the width direction land portion  11  having a larger width than the width direction land portion  10  at the side of the curved portion  3  from the width direction land portion  10  to make a land portion ratio higher, rigidity of this arrangement region is increased, and a high propulsive force is achieved such that the step movement is smoothly continued to the kick-out movement. 
     Further, at the side of the toe T of the width direction land portion  14 , the width direction land portions  12  are sequentially arranged. A region where the width direction land portions  12  are arranged is the region which contacts the ground when the kick-out movement of the athletic prosthetic leg  1  is started as illustrated in  FIG. 2C . Each width direction land portion  12  is the land portion extending to be wavy-shaped in the same manner as the width direction land portion  10 , and wherein, especially, a land portion width which is a width in a direction of a normal line of the wavy line is varied. In other words, it is wavy-shaped in which the land portion width in a ½ wavelength of a wave (from a ridge to a valley or from a valley to a ridge of the wave) is repeatedly wide and narrow. More specifically, as illustrated in  FIG. 8 , each width direction land portion  12  is wavy-shaped such that, in a ½ wavelength of one wavelength λ 3  of a wave, that is, in a land portion width w 1  from a valley V 2  to an adjacent ridge M 2  of a wavy line P 2  and a land portion width w 2  from the ridge M 2  to an adjacent valley V 2 , such a relation is repeated that the land portion width w 1  is relatively wide, while the land portion width w 2  is relatively narrow. Also, in a ½ wavelength of one wavelength λ 4  of the wave, that is, in a land portion width w 2  from a ridge M 2  to an adjacent valley V 2  of the wavy line P 2  and a land portion width w 1  from the valley V 2  to an adjacent ridge M 2 , such a relation is repeated that the w 1  is relatively wide, while the w 2  is relatively narrow. By allowing the land portion width w 1  at one side to be wider compared to the land portion width w 2  at the other side, land portion rigidity can be improved, and wear resistance performance can be improved. In other words, by allowing the land portion width w 2  at the other side to be narrower compared to the one side, slipperiness due to widening of the land portion width can be avoided. Considering comprehensively the above, by appropriately setting the land portion widths w 1  and w 2 , both the drainage performance and the wear resistance performance can be achieved at a high dimension. From such a viewpoint, a ratio w 1 /w 2  of the land portion widths w 1  and w 2  is preferably 2.0 to 15. More preferably, the land portion widths w 1  and w 2  satisfy the following numerical range.
     2.0 mm&lt;w 1 &lt;4.0 mm   0.3 mm&lt;w 2 &lt;1.0 mm   

     Here, in this embodiment, such a mutual arrangement is preferable that an arrangement phase of the line-symmetric sipe pair  130  is synchronized with a phase of waves of the width direction land portions  10 ,  11 ,  12  and  14 . As illustrated in  FIG. 9A , a plurality of line-symmetric sipe pairs  130 , five pairs are illustrated here, are arranged along the width direction W to make an array of the sipe pairs, which has an arrangement along a triangular wave made by connecting, in the width direction W, intersection points of lines virtually extended from both ends of each of the sipes  13 A and  13 B constituting the array along the shape of each sipe. These intersection points are referred to as a ridge m 1  and a valley v 1  of the triangular wave. As illustrated in  FIG. 9A , a position of the ridge m 1  in the width direction W of the triangular wave followed by the array of the plurality of line-symmetric sipe pairs  130  corresponds to a position of the ridge M 1  of the wavy-shaped width direction land portion  10 , and moreover, a position of the valley v 1  in the width direction W corresponds to a position of the valley V 1  of the wavy-shaped width direction land portion  10 . Additionally, in this embodiment, such a mutual arrangement is presented that the waves of the width direction land portion  10  have the same phase as in the waves in the width direction land portions  11 ,  12  and  14 , and an arrangement phase of the line-symmetric sipe pairs  130  is synchronized with the phase of the waves of the width direction land portions  10 ,  11 ,  12  and  14 . 
     With this configuration, equalization of rigidity distribution at the sole bottom surface  50   s  can be achieved. In other words, an aspect that the sipes  13 A and  13 B constituting the line-symmetric sipe pair  130  are convex toward the side of the toe T or the side of the curved portion  3  corresponds to an aspect of convex portions of the wavy-shaped width direction land portions  10 ,  11 ,  12  and  14 , which prevents deterioration of the rigidity in the sole bottom surface  50   s . As illustrated in  FIG. 9B , in a case where a phase of the triangular wave followed by the array of the line-symmetric sipe pairs  130  is different from a phase of the width direction land portions  10 ,  11 ,  12  and  14 , a deformation occurs at a portion where a position of the valley v 1  in which the line-symmetric sipe pair  130  is convex corresponds to a position of the ridge M 1  of the waves of the width direction land portion  10  in the width direction W, so that the rigidity of the sole bottom surface  50   s  may be deteriorated. Consequently, as illustrated in  FIG. 9A , by allowing the arrangement phase of the line-symmetric sipe pair  130  to correspond to the phase of the wavy line P 1  of the waves of the width direction land portion  10 , no deformation occurs, which achieves equalization of the rigidity distribution at the bottom surface  50   s.    
     Additionally, the array of the line-symmetric sipe pairs  130  is preferably arranged with even intervals in the width direction W and on a straight line. In other words, as illustrated in  FIG. 3 , in the array of the line-symmetric sipe pairs  130 , a minimum width and a maximum width of a gap between adjacent line-symmetric sipe pairs  130  are uniform, and in the leg portion front-rear direction Y, each end portion at the side of the toe T of the sipes  13 A and  13 B constituting each sipe pair  130  is arranged on a straight line G 1  along the width direction W, while each end portion at the side of the curved portion  3  is arranged on a straight line G 2  along the width direction W. With this arrangement, equalization of rigidity distribution at the portion Q can be achieved. 
     Additionally, while the line-symmetric sipe pair  130  refers to the above-described line-symmetric sipe pair constituted by two sipes in this embodiment, in other embodiments, one sipe pair may be constituted by three or more sipes. When one sipe pair is constituted by three or more sipes, one sipe pair is preferably radially arranged.  FIG. 10A  is a case where one sipe pair is constituted by three sipes, in which sipes  13 Fa,  13 Fh,  13 Fc are paired and radially arranged. Also,  FIG. 10B  is a case where one sipe pair is constituted by four sipes, in which sipes  13 Ga,  13 Gb,  13 Gc and  13 Gd are paired and radially arranged. Further,  FIG. 10C  is a case where one sipe pair is constituted by five sipes, in which sipes  13 Ha,  13 Hb,  13 Hc,  13 Hd and  13 He are paired and radially arranged. 
     REFERENCE SIGNS LIST 
       1  athletic prosthetic leg 
       2  leg portion 
       2   a  straight portion 
       2   b ,  2   c  curved portion 
       3  curved portion 
       4  ground contact portion 
       4   s  ground contact region 
       5  sole 
       5   s ,  50   s  sole bottom surface 
       10 ,  11 ,  12 ,  14  land portion 
       10   b  toe side protruding portion 
       10   c  curved portion side protruding portion 
       13 A,  13 B,  13 C,  13 D,  13 E sipe 
       13 Fa,  13 Fb,  13 Fc sipe 
       13 Ga,  13 Gb,  13 Gc,  13 Gd sipe 
       13 Ha,  13 Hb,  13 Hc,  13 Hd,  13 He sipe 
       130  line-symmetric sipe pair 
     M 1 , M 2 , m 1  ridge 
     V 1 , V 2 , v 1  valley