Patent Publication Number: US-10321734-B2

Title: Article of footwear with heel extender

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to U.S. application Ser. No. 15/063,968, filed Mar. 8, 2016, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present teachings generally include an article of footwear. 
     BACKGROUND 
     Footwear typically includes a sole structure configured to be located under a wearer&#39;s foot to space the foot away from the ground or floor surface. Athletic footwear in particular sometimes utilizes polyurethane foam, rubber, or other resilient materials in the sole structure to provide cushioning. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration in medial side view of an article of footwear including a sole structure with a heel extender in accordance with the present teachings. 
         FIG. 2  is a schematic illustration in rear view of the article of footwear of  FIG. 1 . 
         FIG. 3  is a schematic exploded perspective view of a sole structure of the article of footwear of  FIG. 1 . 
         FIG. 4  is a schematic illustration in fragmentary lateral side view of the sole structure of  FIG. 3 . 
         FIG. 5  is a schematic cross-sectional illustration of the sole structure of  FIG. 5  taken at lines  5 - 5  in  FIG. 2  with the upper not shown. 
         FIG. 6  is a schematic illustration in fragmentary inverted view of the sole structure of  FIG. 3  with the heel extender positioned for movement against a vertical surface. 
         FIG. 7  is a schematic illustration in plan view of a heel extender of  FIG. 1 . 
         FIG. 8  is a schematic illustration in bottom view of the heel extender of  FIG. 1 . 
         FIG. 9  is a schematic cross-sectional illustration of the heel extender of  FIG. 8  taken at lines  9 - 9  in  FIG. 8 . 
         FIG. 10  is a schematic illustration in front view of the heel extender of  FIG. 1 . 
         FIG. 11  is a schematic illustration in medial side view of an article of footwear including a sole structure with a heel extender in accordance with an alternative aspect of the present teachings and with an upper shown in phantom. 
         FIG. 12  is a schematic illustration in lateral side view of the article of footwear of  FIG. 11  and with an upper shown partially in phantom 
         FIG. 13  is a schematic illustration in rear view of the article of footwear of  FIG. 11 . 
         FIG. 14  is a schematic perspective illustration of the heel extender of the article of footwear of  FIG. 11 . 
         FIG. 15  is a schematic cross-sectional and fragmentary illustration of the heel extender of  FIG. 14  taken at lines  15 - 15  in  FIG. 14 . 
         FIG. 16  is a schematic cross-sectional illustration of the article of footwear of  FIG. 12  taken at lines  16 - 16  in  FIG. 12 . 
         FIG. 17  is a schematic illustration in fragmentary perspective view of another embodiment of an article of footwear including a sole structure with a heel extender in accordance with an alternative aspect of the present teachings. 
     
    
    
     DESCRIPTION 
     Various embodiments of an article of footwear are provided that include a relatively hard, smooth heel extender protruding at a heel portion of the article of footwear. As discussed herein, the heel extender extends further and is harder than adjacent components of the article of footwear to contact and provide ease of movement of the heel portion across a surface during various activities. For example, the heel extender is configured to contact a vertical wall surface during inverted wall push-up exercises. Additionally, the heel extender acts as a retaining wall that limits deformation of the article of footwear, such as by limiting outward deformation of a midsole layer under heavy loading, such when worn during weightlifting. The article of footwear also includes a variety of other features making it suitable for use in different activities, including athletic activities, such as but not limited to running, rope climbing, and weightlifting. 
     More specifically, an article of footwear includes a sole structure that has a heel portion with a rear, a lateral side, and a medial side. The article of footwear includes a heel extender that has a rear segment disposed at the rear of the heel portion, a lateral arm disposed at the lateral side of the heel portion, and a medial arm disposed at the medial side of the heel portion. The heel extender has a protuberance that establishes a rearmost extent of the article of footwear. The sole structure has a first hardness and the protuberance has a second hardness greater than the first durometer hardness. Stated differently, the sole structure is relatively soft, and the protuberance is relatively hard. The hardness may be determined according to a variety of indentation hardness tests, including but not limited to a Shore D durometer test. The hardness is a material property of the sole structure and of the heel extender. Accordingly, the sole structure and the heel extender may be different materials, or could be the same material with different densities that provide the different hardness values. 
     The heel extender may have a variety of configurations, shapes, and positions on the article of footwear. For example, the protuberance may be any shape that establishes the rearmost extent and has the rear segment, lateral arm, and medial arm as described. The protuberance may have a beveled shape, which may include a single bevel (i.e., a single angled surface) or two bevels (i.e., bi-beveled with two angled surfaces, such as an upper bevel and a lower bevel). Alternatively, other non-limiting examples include a protuberance with a rounded shape, or a protuberance that includes a series of discrete protrusions establishing the rear segment, the medial arm, and the lateral arm. 
     In one embodiment, the lateral arm and the medial arm are contiguous with and extend from the rear segment. For example, the rear segment, the lateral arm, and the medial arm may be configured in a C-shape. 
     For example, in one embodiment, the sole structure includes a midsole layer exposed at the heel portion, and the heel extender includes a base disposed on an outer surface of the midsole layer, and a bevel that slopes from the protuberance to the base. Additionally, the outer surface of the midsole layer adjacent the bevel may slope in continuance from the bevel. The entire heel extender may be below an upper extent of the midsole layer. 
     In an embodiment, the heel extender has a base, and a beveled outer surface with at least one of an upper bevel that slopes from the protuberance to the base and a lower bevel that slopes from the protuberance to the base. In such an embodiment, the protuberance is between the upper bevel and the lower bevel. 
     The protuberance may include a continuous ridge that extends along each of the rear segment, the lateral arm, and the medial arm. For example, the continuous ridge may be between upper and lower bevels of the protuberance. The protuberance may be the furthest medial extent of the article of footwear at the medial arm, and the furthest lateral extent of the article of footwear at the lateral arm. 
     In various embodiments, the sole structure includes a midsole layer having features complementary to those of the heel extender. In an embodiment, the sole structure includes a midsole layer exposed at the heel portion. The heel extender is secured to the midsole layer. The midsole layer includes a first ridge at the lateral side extending along the midsole layer in alignment with the protuberance on the lateral arm. The midsole layer also includes a second ridge at the medial side extending along the midsole layer in alignment with the protuberance on the medial arm. 
     In an embodiment, the midsole layer has a convex outer surface, and the heel extender has a concave inner surface flush with and secured to the convex outer surface of the midsole layer. The inner surface of the heel extender may have a first concavity from the medial arm to the lateral arm and a second concavity from an upper extent of the rear segment to a lower extent of the rear segment. 
     In an embodiment, the midsole layer is exposed at the heel portion, and the sole structure further includes an outsole underlying the midsole layer. The rear segment of the heel extender is secured to the midsole layer, and the heel extender includes a flange that extends from the rear segment and is disposed between the midsole layer and the outsole. 
     Additionally, the midsole layer may have an outer surface with a recess, and the heel extender may be nested in the recess. For example, the concave inner surface and the flange of the heel extender may fit to the outer surface of the midsole layer in the recess. 
     The midsole layer may include a first ridge at the lateral side of the heel portion extending in alignment with the protuberance on the lateral arm, and a second ridge at the medial side of the heel portion extending in alignment with the protuberance on the medial arm. 
     In one embodiment, the heel extender ends at the medial and lateral arms. In another embodiment, the heel extender includes a medial wing portion and a lateral wing portion. The medial wing portion extends from the medial arm and is secured to a medial side of an upper operatively secured to the sole structure. The lateral wing portion extends from the lateral arm and is secured to a lateral side of the upper. The wing portions help to provide greater coverage of the heel extender at the medial and lateral sides of the heel portion, thus increasing the ability of the heel extender to act as a retaining wall and to provide the low drag feature of the heel extender over a broader range of positions of the article of footwear. 
     The heel extender may be a variety of different materials having different properties. For example, in one embodiment, the heel extender may have a hardness value from about 60 to about 70 on a Shore D durometer scale. The heel extender may be but is not limited to a material that is at least partially a thermoplastic polyurethane (TPU), a metal, such as aluminum, a nylon, a ceramic material, bamboo, or wood. Moreover, the protuberance can have a first average surface roughness, and the sole structure can have a second average surface roughness greater than the first average surface roughness. The smoothness (i.e., the lower surface roughness) of the protuberance may be achieved by polishing at least a portion of the protuberance. For example, the heel extender  28  may be a polished TPU, and the sole structure may be unpolished, less smooth materials such as polymeric foam and rubber materials 
     In one embodiment, an article of footwear comprises an upper, and a sole structure supporting the upper. The upper and the sole structure establish a heel portion of the article of footwear. The article of footwear includes a C-shaped heel extender that has a rear segment disposed at a rear of the heel portion, a lateral arm disposed at a lateral side of the heel portion, and a medial arm disposed at a medial side of the heel portion. The heel extender has a continuous ridge sufficiently protruding at the rear segment, at the lateral arm, and at the medial arm to establish an outermost periphery of the article of footwear along the continuous ridge. The heel extender has a hardness greater than a hardness of the sole structure, such as but not limited to on a Shore D durometer scale. The heel extender may have a base, a first bevel extending from the continuous ridge to the base, and a second bevel extending from the continuous ridge and to the base, with the continuous ridge between the first bevel and the second bevel. The sole structure may include a midsole layer that is exposed at the heel portion, and may further include an outsole. The heel extender may be secured to an outer surface of the midsole layer, and the outer surface of the midsole layer may slope in parallel with the upper bevel. Furthermore, an outer surface of the outsole may follow a slope of the lower bevel. For example, the outsole may have a bevel at the rear of the heel portion, and the bevel may be at the same angle as the lower bevel. 
     Referring to the drawings, wherein like reference numbers refer to like components throughout the several views,  FIG. 1  is a medial side view of an article of footwear  10  that includes a sole structure  12 . The sole structure  12  has an outsole  14 , an outer midsole layer  16 , also referred to as an external midsole, and an inner midsole layer  18  (shown in  FIG. 3 ), also referred to as a drop-in midsole. An upper  15  is secured directly or indirectly to the sole structure  12  generally above the sole structure  12 . The sole structure  12  has a heel portion  20  with a rear  22 , a lateral side  24 , and a medial side  26 . The sole structure  12  has a heel extender  28  secured to the heel portion  20  of the sole structure  12 . More specifically, the heel extender  28  is secured to an outer surface  30  of the outer midsole layer  16  such that the heel extender  28  is exposed on the heel portion  20 . 
     As best shown in  FIG. 1 , the sole structure  12  has a heel portion  20 , a midfoot portion  32 , and a forefoot portion  34 . The midfoot portion  32  is between the heel portion  20  and the forefoot portion  34 . The heel portion  20  generally includes portions of the sole structure  12  corresponding with rear portions of a human foot including the calcaneus bone and of a size corresponding with the article of footwear  10 . Forefoot portion  34  generally includes portions of the sole structure  12  corresponding with the toes and the joints connecting the metatarsals with the phalanges of the human foot of the size corresponding with the article of footwear  10 . Midfoot portion  32  generally includes portions of the sole structure  12  corresponding with an arch area of the human foot of the size corresponding with the article of footwear  10 . The portions  20 ,  32 ,  34  are intended to represent general areas of the sole structure  12  relative to one another to provide a frame of reference during the following discussion, and also apply to and are used to describe portions of the article of footwear  10  or of any component of the article of footwear  10 . 
     As used herein, a lateral side of the article of footwear  10  or of a component of the article of footwear  10 , such as a lateral side  24  of the sole structure  12 , is a side that corresponds with the side of the foot of the wearer of the article of footwear  10  that is generally further from the other foot of the wearer (i.e., the side closer to the fifth toe of the wearer). The fifth toe is commonly referred to as the little toe. A medial side of a component for an article of footwear, such as a medial side  26  of the article of footwear  10 , is the side that corresponds with an inside area of the foot of the wearer and is generally closer to the other foot of the wearer (i.e., the side closer to the hallux of the foot of the wearer). The hallux is commonly referred to as the big toe. A rear  38  of the heel portion  20  extends between the lateral side  24  and the medial side  26 , and a front  40  of the forefoot portion  34  extends between the lateral side  24  and the medial side  26 . 
     As best shown in  FIGS. 2 and 7 , the heel extender  28  includes a rear segment  42  disposed at the rear  22  of the heel portion  20 , a lateral arm  44  disposed at the lateral side  24  of the heel portion  20 , and a medial arm  46  disposed at the medial side  26  of the heel portion  20 . The heel extender  28  is a unitary, one-piece component. The medial arm  46  and the lateral arm  44  extend contiguously from the rear segment  42 . The heel extender  28  includes a protuberance  52  that establishes a rearmost extent  54  of the article of footwear  10 . In the embodiment shown, the protuberance  52  is also the furthest medial extent of the heel portion  20  at the medial arm  46 , and the furthest lateral extent of the heel portion  20  at the lateral arm  44 . This is best illustrated in the bottom view of  FIG. 8  in which the perimeter of the outsole  14  is indicated in phantom. 
     For purposes of illustration, a vertical plane P perpendicular to a longitudinal midline LM of the heel extender  28  and drawn at the exposed portion of the heel extender  28  can be used to denote the rear segment  42 , the lateral arm  44 , and the medial arm  46 . The plane P is indicated in  FIGS. 4 and 7  and intersects the outer edge of the protuberance  52  at a point P 1 . A line L 1  is drawn tangent to the protuberance  52  at the point P 1 . The plane P also intersects the outer edge of the protuberance  52  at a point P 2 . A line L 2  is drawn tangent to the protuberance at the point P 2 . The rear segment  42  can be defined as that portion of the heel extender  28  between a line L 3  perpendicular to the line L 1  at point P 1  and a line L 4  perpendicular to the line L 2  at point P 2 . The lateral arm  44  can be defined as that portion of the heel extender  28  between the line L 3  and a first end  56  of the heel extender  28 . The medial arm  46  can be defined as that portion of the heel extender  28  between the line L 4  and a second end  58  of the heel extender  28 . Generally, in the medial side view of  FIG. 1 , the medial arm  26  is the entire portion to the left of the plane P in  FIG. 1 . The lateral arm  44  is the entire portion of the heel extender  28  to the right of plane P in the lateral side view of  FIG. 4 . The heel extender  28  is generally C-shaped in plan view as indicated in  FIG. 7 , with a concave inner boundary  48  and a convex outer boundary  50  in plan view. 
     The outer periphery  49  of the outsole  14  is shown in phantom in  FIG. 8 . The protuberance  52  protrudes further than the outsole  14  in that it is the furthest medial extent along the entire medial arm  46 , is the furthest lateral extent of the sole structure  12  along the entire lateral arm  44 , and is the furthest rear extent (i.e. rearmost extent) along the entire rear segment  42  as shown in  FIG. 8 . Additionally, the protuberance  52  is also the furthest medial, lateral, and rear extent of the entire article of footwear  10 , including the upper  15 , along the entire medial arm  46 , lateral arm  44 , and rear segment  42 , respectively. 
     By establishing the rearmost extent, the furthest medial extent, and the furthest lateral extent of the article of footwear  10 , the protuberance  52  is configured to make contact with an adjacent surface, such as a relatively flat, planar surface, in lieu of the sole structure  12  or the upper  15  over a wide range of positions and angles of the article of footwear  10  relative to the adjacent surface. For example, as shown in  FIG. 6 , when the article of footwear  10  is inverted and moved vertically up and/or down (as indicated by the double-sided arrow  60 ), with the heel extender  28  resting against a wall  62 , such as when worn during an inverted wall pushup only the heel extender  28  will be in contact with the wall  62 . The heel extender  28  rather than the sole structure  12  or the upper  15  will contact the wall  62 . In the embodiment of  FIG. 6 , the range of angles is at least 90 degrees. 
     Similarly, the heel extender  28  can be positioned against another surface such as a floor for movements requiring sliding motion of the heel portion  20  along the floor or other surface without the sole structure  12  and upper  15  in contact with the floor. The heel extender  28  will be the only component of the article of footwear  10  against the floor or other surface. 
     The heel extender  28 , or at least the protuberance  52  of the heel extender  28  is harder than the components of the sole structure  12 . More specifically, the components of the sole structure  12  have no more than a first hardness and the protuberance  52  has a second hardness greater than the first hardness. The hardness is an indentation hardness and the value of the hardness may be measured on a Shore D durometer scale or by another hardness test or scale well known to those skilled in the art. For example, the second hardness may be a hardness value at least 44 points harder than the first hardness on a Shore D durometer scale. In the embodiment shown, the inner midsole layer  18  and the outer midsole layer  16  may be an ethylene vinyl acetate (EVA) foam. Alternatively, one or both of the midsole layers  16 ,  18  could be replaced by or used in conjunction with a sole layer that is a fluid-filled bladder element, that may be a polymeric, fluid-retaining material. For example, the bladder element may have thermoplastic polyurethane layers that alternate with one or more second layers, also referred to herein as barrier layers, gas barrier polymers, or gas barrier layers, that comprise a copolymer of ethylene and vinyl alcohol (EVOH) that is impermeable to the pressurized fluid contained therein as disclosed in U.S. Pat. No. 6,082,025 to Bonk et al., which is incorporated by reference in its entirety. The outsole  14  may be a thermoplastic rubber or other durable material. The material for the outsole  14  may be selected to provide a desirable combination of durability and flexibility. The heel extender  28 , including the protuberance  52 , may be at least partially a thermoplastic polyurethane, metal, nylon, bamboo, wood, or ceramic material. Additionally, the protuberance  52  may be polished, formed, or otherwise provided with a first average surface roughness, while the sole structure  12  has a second average surface roughness greater than the first average surface roughness. In other words, the protuberance  52  is smoother than the sole structure  12 . 
     The shape and hardness of the protuberance  52  helps to reduce the contact area of the heel extender  28  with the wall  62 . For example, the heel extender  28  is sufficiently hard that it will not significantly deform under an expected range of loads while the protuberance  52  is in contact with the wall  62  or other surface. The smoothness together with the hardness helps to provide a relatively low coefficient of friction of the heel extender  28  when the heel extender  28  is moved across a surface, such as the wall  62 . The heel extender  28  is harder and has a lower coefficient of friction than both the sole structure  12  and the upper  15 . Accordingly, by configuring the article of footwear  10  so that it can be positioned with the heel extender  28  as the only portion of the article of footwear  10  in contact with the surface upon which the article of footwear  10  is moving, the force required to move the article of footwear  10  across the wall  62  is lower than if the sole structure  12  (including the outsole  14  and the midsole layer  16 ) or the upper  15  are in contact with the wall  62 . 
     In one embodiment, the heel extender  28  is a thermoplastic polyurethane with a highly polished surface and a hardness of 66 on a Shore D durometer scale. In other embodiments, the hardness of the protuberance  52  may be from 60 to 70 on a Shore D durometer scale. 
     The hardness of the heel extender  28  relative to the midsole layer  16  also provides desired stiffness and rigidity of the heel portion  20  of the article of footwear  10  when loading creates forces in the rear, lateral, and medial directions. The heel extender  28  acts as a retaining wall that limits outward deformation of the midsole layer  16  under heavy loading, such as when worn during weightlifting. Because the heel extender  28  has a rear segment  42 , a lateral arm  44 , and a medial arm  46  as described, the heel extender  28  surrounds the heel portion  20  from the rear  22 , the lateral side  24 , and the medial side  26 , and is able to limit outward deformation of the midsole layer  16  in rearward, lateral, and medial directions. 
     A heel extender within the scope of the present teachings can have various shapes and configurations that provide a protuberance as described. For example, in the embodiment of  FIGS. 1-10 , the rear segment  42 , the lateral arm  44 , and the medial arm  46  are configured in a C-shape, having a concave inner boundary  48  and the convex outer boundary  50  with the lateral arm  44  and the medial arm  46  contiguous with and extending from the rear segment  42 . 
     In the embodiment of  FIGS. 1-10 , the heel extender  28  has a beveled outer surface  66  that forms the protuberance  52 . As best shown in  FIGS. 4 and 5 , the beveled surface  66  includes a first bevel  68 , arranged as and referred to as an upper bevel  68 , and a second bevel  70 , arranged as and referred to as a lower bevel  70 . The heel extender  28  has a base  72 , which is a portion of the heel extender  28  closest to and disposed on and secured to the sole structure  12 , and more specifically on the outer surface  30  of the midsole layer  16 . The protuberance  52  is spaced from the base  72 . More specifically, the protuberance  52  has a continuous ridge  74  at an apex of the protuberance  52  displaced from the base  72 . The apex is the portion of the protuberance  52  furthest displaced from base  72 , not necessarily the highest portion of the protuberance  52 . 
     The continuous ridge  74  extends along each of the rear segment  42 , the lateral arm  44 , and the medial arm  46 . The continuous ridge  74  is between the upper bevel  68  and the lower bevel  70 . When the outsole  14  is on a ground surface, the protuberance  52  and continuous ridge  74  are generally horizontally disposed with the lateral arm  44  and medial arm  46  generally at the same elevation from the outsole  14 . The continuous ridge  74  sufficiently protrudes at the rear segment  42 , at the lateral arm  44 , and at the medial arm  46  to establish an outermost periphery of the article of footwear  10  along the continuous ridge  74 . The outer boundary  50  is at the continuous ridge  74  and is the outermost periphery of the heel extender  28  as shown in  FIG. 8 . 
     The upper bevel  68  slopes from the protuberance  52  to the base  72 , and more specifically generally upward and forward from the ridge  74  of the protuberance  52  to the base  72  when the outsole  14  is in the position of  FIGS. 1, 4, and 5  (e.g., on a ground surface). The second bevel  70  also slopes from the protuberance  52  to the base  72 , but generally rearward and forward from the ridge  74  of the protuberance  52  to the base  72  when the outsole  14  is in the position of  FIGS. 1, 4, and 5 . 
     The beveled outer surface  66  of the protuberance  52  in the embodiment shown is bi-beveled (i.e., has two bevels  68 ,  70 ). In other embodiments, only one of the bevels may be provided. For example, if only the lower bevel  70  is provided, the rearward most extent  54  would still protrude further than the outsole  14  and the midsole layer  16 , and would still be the only component of the article of footwear  10  in contact with the wall  62  in  FIG. 6 . The heel extender  28  could have any other shape at the portion that is provided in lieu of the upper bevel  68  in such an embodiment. If only the upper bevel  68  is provided, the rearward most extent  54  would still protrude further than the outsole  14  and the midsole layer  16 , and the heel extender  28  would still be the only component of the article of footwear  10  in contact with the wall  62  in  FIG. 6 . The heel extender  28  could have any other shape at the portion that is provided in lieu of the lower bevel  70  in such an embodiment. In still other embodiments, a protuberance within the scope of the present teachings could have another shape without bevels, and instead could be a rounded ridge, a squared ridge, or a series of discrete protrusions arranged generally in the C-shape of the protuberance. 
     The outsole  14  may also have a bevel that ensures that the heel extender  28  alone contacts the wall  62  or other surface over a wide range of positions of the heel extender  28  relative to the wall  62 . As is apparent in  FIGS. 4-6 , the outsole  14  has a bevel  80  at the rear  22  of the heel portion  20 . In the embodiment shown, the bevel  80  extends to the medial and lateral sides  26 ,  24  of the outsole  14  as well. Optionally, as shown, the bevel  80  and the lower bevel  70  of the heel extender  28  extend at a common angle A 1  relative to a vertical axis, such as the vertical axis at the intersection of plane P and the longitudinal midline LM shown in  FIG. 7  (which can be represented by plane P in  FIG. 4 ) or the vertical axis VA in  FIG. 5 . 
     Optionally, the outsole  14  could instead be configured with a bevel that extends in direct alignment and continuance with the bevel  70 , as indicated by phantom line  81  in  FIG. 4 , representing an alternative bevel. In other words, the bevel at phantom line  81  would follow the slope of the lower bevel  70 . The bevel  80  (or  81 ) reduces the thickness of the outsole  14  at the rear extremity of the outsole  14 , such as from thickness T 1  to thickness T 2  in  FIG. 4 . This allows the article of footwear  10  to be tilted upward at a higher angle relative to the wall  62  in  FIG. 6  without the outsole  14  contacting the wall  62  than would be possible if the outsole  14  had the full thickness T 1  at the extreme rear of the outsole  14 . Because the bevel  80  (or  81 ) extends on the medial side  26  and the lateral side  24  of the heel portion  20  as well, the range of angles and positions of the article of footwear  10  relative to the wall  62  or other surface over which the outsole  14  will not interfere with the heel extender  28  being the only portion of the article of footwear  10  in contact with the surface is increased when the medial arm  46  or lateral arm  44  of the heel extender  28  is adjacent the wall  62  rather than the rear segment  42 . 
     The midsole layer  16  is also configured to ensure that the heel extender  28  alone contacts the wall  62  or other surface over a wide range of positions of the article of footwear  10  relative to the wall  62 . The outer surface  30  of the midsole layer  16  adjacent the upper bevel  68  is parallel with the upper bevel  68 , as best indicated by the side view of  FIG. 4  in which the portion  83  of the outer surface  30  is parallel with the upper bevel  68 . The outer surface  30  can be said to slope in parallel with the upper bevel  68  at the portion  83 . 
     The midsole layer  16  is also configured to minimize contact area with a surface such as the wall  62  should contact of the midsole layer  16  with the wall  62  occur forward of the heel extender  28 . As shown in  FIG. 4 , the midsole layer  16  has a first ridge  84  at the lateral side  24  extending along the midsole layer  16  and in alignment with the ridge  74  of the protuberance  52  on the lateral arm  44 . The midsole layer  16  also has a second ridge  86  at the medial side  26  extending along the midsole layer  16  in alignment with the ridge  74  of the protuberance  52  on the medial arm  46 . The ridges  84 ,  86  have upper and lower bevels generally disposed at the same angle relative to a vertical axis as the upper and lower bevels  68 ,  70 , respectively. Due to the ridges  84 ,  86 , the midsole layer  16  forward of the lateral arm  44  and the midsole layer  16  forward of the medial arm  46  continues the slope of the bevels  68 ,  70  and thereby slopes in continuance from the bevels,  68 ,  70 . 
     The midsole layer  16  and the heel extender  28  are cooperatively configured to fit to one another. As shown in  FIG. 7 , the heel extender  28  has an inner surface  88  at the base  72  with a first concavity from the medial arm  46  to the lateral arm  44  as indicated by the C-shape of the heel extender  28  and the concave inner boundary  48 . The inner surface  88  of the heel extender  28  also has a second concavity from an upper extent  90  of the rear segment  42  to a lower extent  92  of the rear segment  42 , as shown in  FIG. 9 . The second concavity continues to the flange  104  of the heel extender  28  discussed herein. 
     As shown in  FIG. 3 , the midsole layer  16  has a convex outer surface  30 . The concavity of the inner surface  88  of the heel extender  28  is configured to be flush with the convex outer surface  30  of the midsole layer  16 . In other words, the entire inner surface  88  is in contact with the concave outer surface  30  of the midsole layer  16 . The concave inner surface  88  can be secured to the convex outer surface  30  with adhesive or may be thermally bonded to the midsole layer  16 . In an embodiment in which the midsole layer  16  is a fluid-filled bladder element, the heel extender  28  may be thermally bonded to the fluid-filled bladder element. 
     Additionally, with reference to  FIG. 3 , the midsole layer  16  has a recess  94  at the outer surface  30 . The recess  94  is sized to match the shape of the outer extent of the heel extender  28 . This enables the heel extender  28  to be nested in the recess  94 . The upper extent  90  of the heel extender  28  fits in the recess  94  adjacent an upper extent  96  or upper edge of the recess  94 . The inner boundary  48  of the heel extender  28  fits in the recess  94  adjacent a lower extent  98  or lower edge of the recess  94 . As indicated in  FIG. 1 , the first end  56  of the heel extender  28  fits adjacent a medial extent  100  or medial edge of the recess  94 . As is apparent in  FIGS. 3 and 4 , the second end  58  of the heel extender  28  fits adjacent a lateral extent  102  or lateral edge of the recess  94 . When secured to the midsole layer  16 , the entire heel extender  28  is below the upper extent  95  of the midsole layer  16 . 
     As best shown in  FIG. 9 , the heel extender  28  includes a flange  104  that extends forward from the rear segment  42  and establishes the inner boundary  48 . When the heel extender  28  is secured to the outer surface  30  of the midsole layer  16 , the flange  104  is disposed between the midsole layer  16  and the outsole  14 . Stated differently, the flange  104  is sandwiched between the midsole layer  16  and the outsole  14  and is not visible in the assembled article of footwear  10  of  FIG. 1 . The flange  104  may be adhered and/or thermally bonded to the midsole layer  16  and the outsole  14 . Trapping the flange  104  between the outsole  14  and the midsole layer  16  in this manner helps to anchor and secure the heel extender  28  to the sole structure  12 . 
     The inner midsole layer  18  is not adhered or otherwise secured to any component of the article of footwear  10 , thereby preventing undesirable rigidity. The inner midsole layer  18  is not as hard as the outer midsole layer  16  to enhance cushioning for running or other activities, while at the same time the outer midsole layer  16  and the outsole  14  provide stability for activities such as weightlifting. Moreover, the outsole  14  includes medial and lateral arch portions  21 ,  23  shown in  FIGS. 1 and 3  that extend upward along and are secured to the medial side  26  of the upper  15  and to a lateral side  24  of the upper  15  to provide traction for activities such as rope climbing. 
       FIG. 3  shows that the outer midsole layer  16  extends only over the heel portion  20  and over some of the midfoot portion  32 . The inner midsole layer  18  is supported by the outer midsole layer  16  and the outsole  14  but is not fixed thereto. In other words, the inner midsole layer  18  is not adhered, sewn, bonded, welded, or otherwise secured to any other component of the article of footwear  10 . Instead, the inner midsole layer  18  simply rests on a strobel unit (not shown) within a cavity defined and bounded by the upper  15  and the strobel unit. The strobel unit is stitched to the upper  15  and is well understood by those skilled in the art. Alternatively, heat seaming, bonding, or other methods of securing the upper  15  to the strobel unit can be used. The strobel unit is also adhered or bonded directly to an upward-facing surface of the outer midsole layer  16  at the heel portion  20 , to a portion of the midfoot portion  32  not covered by the outer midsole layer  16 , and directly to an upward-facing surface of the outsole  14  at the forefoot portion  34 . The upper  15  can be comprised of multiple separate pieces and materials such as fabric, textiles, leather, plastics, etc. 
     As shown in  FIG. 9 , the inner midsole layer  18  is a full-length midsole layer, such that it extends over the heel portion  20 , the midfoot portion  32 , and the forefoot portion  34  when placed in the foot-receiving cavity within the upper  15 . The inner midsole layer  18  can thus be selectively inserted or removed from the cavity, and is referred to as a drop-in midsole. Because the inner midsole layer  18  is not secured to any component of the article of footwear  10 , it may exhibit some minimal relative movement with respect to the sole structure  12  under some load forces. This reduces rigidity, and produces a flexible feel during wear. However, the inner midsole layer  18  is supported by outer midsole layer  16  and the outsole  14 , and is relatively confined by the outer midsole layer  16  and the upper  15 . For example, as best shown in  FIGS. 4 and 5 , the outer midsole layer  16  is configured to surround a periphery of the inner midsole layer  18  at the heel portion  20 . As also discussed herein, the heel extender  28  provides additional peripheral support to the outer midsole layer  16  in the heel portion  20 . 
     The outer midsole layer  16  may be harder than the inner midsole layer  18 . For example, in one embodiment, the outer midsole layer  16  is seven points harder than the inner midsole layer  18  when hardness is measured on a Shore D durometer scale. Both the inner midsole layer  18  and the outer midsole layer  16  can be a polymeric foam, such as ethylene vinyl acetate (EVA) foam. The inner midsole layer  18  can be a lighter weight, less dense foam than the outer midsole layer  16 . The inner midsole layer  18  is configured with a substantially uniform hardness that provides appropriate cushioning and compliance under the heel of a wearer, while the surrounding outer midsole layer  16  is harder to provide lateral support, resiliency, and energy absorption at the heel region  36 . 
     Moreover, the outsole  14  includes medial and lateral arch portions  21 ,  23  shown in  FIGS. 1, 2, 3, and 6 . The medial arch portion  21  extends upward along and is secured to the medial side  26  of the footwear upper  15 . The lateral arch portion  23  extends upward along and is secured to the lateral side  24  of the upper  15 . The medial and lateral arch portions  21 ,  23  have a plurality of spaced protrusions  27  configured to provide traction for activities such as rope climbing. The protrusions  27  generally protrude further closer to the bottom portion of the outsole  14 , and are wider closer to the bottom portion. 
     The outsole  14  has a bottom portion that establishes a ground contact surface. The outsole  14  is not of a uniform hardness. The bottom portion may have a first portion with a first hardness and a second portion with a second hardness greater than the first hardness. The first portion extends over only some of the forefoot portion  34  and the second portion surrounds the first portion and extends over a remainder of the outsole  14 . The softer first portion increases traction in the forefoot portion. 
     Specifically,  FIG. 3  shows a boundary H that generally separates a first portion  17  of the outsole  14  from a second portion  19  of the outsole  14 . The first portion  17  extends over only some of the forefoot portion  34  and coincides generally with a pressure-bearing region under the ball of a wearer&#39;s foot. The second portion  19  includes the entire remainder of the outsole  14 . The first portion  17  has a hardness less than a hardness of the second portion  19  on a Shore D durometer scale. The softer first portion  17  has a greater coefficient of friction with respect to a ground surface than does the harder rubber of the second portion  19 . The first portion  17  is thus both more compliant and provides greater traction with respect to forces conveyed from the ball of a wearer&#39;s foot through the forefoot portion  34 , such as during lateral movement and/or climbing. 
       FIGS. 11-16  show another embodiment of an article of footwear  210  having many of the features of the article of footwear  10 . Identical reference numbers are used for components and features that are the same as those of the article of footwear  10 . The article of footwear  210  has a sole structure  212  that has a heel portion  20  with a rear (at a rear segment  242 ), a lateral side  24 , and a medial side  26 . The sole structure  212  includes an outsole  214  and a drop-in inner midsole layer  18 . The sole structure  212  has no outer midsole layer, and therefore no outer midsole layer is exposed at the heel portion  20  as in the sole structure  12 . Instead, the outsole  214  is the only portion of the sole structure  212  exposed at the heel portion  20 . 
     The article of footwear  210  includes a heel extender  228  that has a rear segment  242  disposed at the rear of the heel portion  20 , a lateral arm  244  disposed at the lateral side  24  of the heel portion  20 , and a medial arm  246  disposed at the medial side  26  of the heel portion  20 . The lateral arm  244  and the medial arm  246  are contiguous with and extend from the rear segment  242 . The rear segment  242 , the lateral arm  244 , and the medial arm  246  are configured generally in a C-shape as is most apparent in  FIG. 14 . 
     The heel extender  228  does not terminate at the medial arm  246  and the lateral arm  244  as does the heel extender  28 . Instead, the heel extender  228  includes a medial wing portion  231  and a lateral wing portion  233 . The medial wing portion  231  extends from the medial arm  246  and is secured to a medial side  26  of the upper  215  as best shown in  FIG. 13 . A lateral wing portion  233  extends from the lateral arm  244  and is secured to a lateral side  24  of the upper  215 . The wing portions  231 ,  233  provide lateral and medial support at the heel portion  20  in addition to the support and stability provided by the rear segment  242 , the medial arm  246  and the lateral arm  244 , such as during weightlifting. The wing portions  231 ,  233  have regions  235  that are more highly polished than the remainder of the heel extender  228 . The regions  235 , the wing portions  231 ,  233 , the rear segment  242 , the medial arm  246 , the lateral arm  244 , the protuberance  252 , and the flange  204  discussed herein are all integrally formed as part of the unitary, one-piece heel extender  228 . 
     The heel extender  228  is secured to both the upper  215  and the outsole  214 , at the rear  22  as best shown in  FIG. 16 . More specifically, an inner surface  288  of the heel extender  228  is secured to the upper  215 . The heel extender  228  includes a flange  204  best shown in  FIG. 15 . An outer surface  289  of the heel extender  228  at the flange  204  is secured to the outsole  214  such as with adhesive or by thermal bonding. The flange  204  is thus sandwiched between the outsole  214  and the upper  215  and is not exposed. 
     The heel extender  228  includes a protuberance  252  that establishes a rearmost extent  254  of the article of footwear  210 . In the embodiment shown, the protuberance  252  is also the furthest medial extent of the heel portion  20  at the medial arm  246 , and the furthest lateral extent of the heel portion  20  at the lateral arm  244 . By establishing the rearmost extent, the furthest medial extent, and the furthest lateral extent, the protuberance  252  is configured to make contact with an adjacent surface, such as a relatively flat, planar surface, in lieu of the sole structure  212  or the upper  215 , depending on the position and angle of the article of footwear  210  relative to the adjacent surface, as described with respect to the heel extender  28  of  FIG. 6 . 
     The heel extender  228  rather than the sole structure  212  or the upper  215  will contact the wall  62  of  FIG. 6 . The heel extender  228 , or at least the protuberance  252  of the heel extender  228  is harder than the outsole  214 . More specifically, the outsole  214  has no more than a first hardness and the protuberance  252  has a second hardness greater than the first hardness. The hardness values may be measured on a Shore D durometer scale or on another scale. For example, the second hardness may be at least 44 points harder than the first hardness on a Shore D durometer scale. The second hardness may be from about 60 to about 70 on a Shore D durometer scale. The outsole  214  may be a thermoplastic rubber or other durable material. The material for the outsole  214  may be selected to provide a desirable combination of durability and flexibility. The heel extender  228 , including the protuberance  252 , may be may be at least partially a thermoplastic polyurethane, metal, nylon, bamboo, wood, or ceramic material. Additionally, the protuberance  252  may be polished, formed, or otherwise provided with a first average surface roughness, while the outsole  214  has a second average surface roughness greater than the first average surface roughness. In other words, the protuberance  252  is smoother than the outsole  214 . The protuberance  252  is also smoother than and harder than the upper  215 . The hardness and smoothness of the protuberance  252  and of the entire heel extender  228  provide a reduced friction and low drag across surfaces such as the wall  62  or a floor in comparison to the sole structure  212  and the upper  215 . 
     As shown in  FIG. 15 , the heel extender  228  has a base  272 , and a beveled outer surface  266  with a first bevel, referred to as an upper bevel  268 , and a second bevel, referred to as a lower bevel  270 . The beveled outer surface  266  forms the protuberance  252 . The base  272  is a portion of the heel extender  228  closest to and disposed on and secured to the outer surface of the upper  215 . The protuberance  252  is spaced from the base  272 . The protuberance  252  includes a continuous ridge  274  that extends along each of the rear segment  242 , the lateral arm  244 , and the medial arm  246 . The continuous ridge  274  is between the upper bevel  268  and the lower bevel  270 . The continuous ridge  274  sufficiently protrudes at the rear segment  242 , at the lateral arm  244 , and at the medial arm  246  to establish an outermost periphery of the article of footwear  210  along the continuous ridge  274 . The rearmost extent  254  of the article of footwear  210  is at the continuous ridge  274 . 
     The upper bevel  268  slopes from the protuberance  252  to the base  272 , and more specifically generally upward and forward from the ridge  274  of the protuberance  252  to the base  272  when the outsole  214  is in the position of  FIGS. 11 and 12  (e.g., on a ground surface). The second bevel  270  also slopes from the protuberance  252  to the base  272 , but generally rearward and forward from the ridge  274  of the protuberance  252  to the base  272  when the outsole  214  is in the position of  FIGS. 11 and 12 . 
     The beveled outer surface  266  of the protuberance  252  in the embodiment shown is bi-beveled (i.e., has two bevels  268 ,  270 ). In other embodiments, only one of the bevels may be provided. For example, if only the lower bevel  270  is provided, the rearward most extent  254  would still protrude further than the outsole  214 , and would still be the only component of the article of footwear  210  in contact with the wall  62  in  FIG. 6 . The heel extender  228  could have any other shape at the portion that is provided in lieu of the upper bevel  268  in such an embodiment. If only the upper bevel  268  is provided, the rearward most extent  254  would still protrude further than the outsole  214 , and the heel extender  228  would still be the only component of the article of footwear  210  in contact with the wall  62  in  FIG. 6 . The heel extender  228  could have any other shape at the portion that is provided in lieu of the lower bevel  270  in such an embodiment. In still other embodiments, a protuberance within the scope of the present teachings could have another shape without bevels, and instead could be a rounded ridge, a squared ridge, or a series of discrete protrusions arranged generally in the C-shape of the protuberance. 
     The outsole  214  may also have a bevel that ensures that the heel extender  228  alone contacts the wall  62  or other surface over a wide range of positions of the heel extender  228  relative to the wall  62 . As is apparent in  FIGS. 11, 12, and 16 , the outsole  214  has a bevel  280  at the rear of the heel portion  20 . In the embodiment shown, the bevel  280  extends to the medial and lateral sides  26 ,  24  of the outsole  214  as well. Optionally, as shown, the bevel  280  and the lower bevel  270  of the heel extender  228  extend at a common angle A 2  relative to a vertical axis VA (shown in  FIG. 12  and  FIG. 15 ). 
     The bevel  280  reduces the thickness of the outsole  214  at the rear extremity of the outsole  214 , allowing the article of footwear  210  to be tilted upward at a higher angle relative to the wall  62  in  FIG. 6  without the outsole  214  contacting the wall  62  than would be possible if the outsole  214  had the full thickness at the extreme rear of the outsole  214 . Because the bevel  280  extends on the medial side  26  and the lateral side  24  of the heel portion  20  as well, the range of angles and positions of the article of footwear  210  relative to the wall  62  or other surface over which the outsole  214  will not interfere with the heel extender  228  being the only portion of the article of footwear  210  in contact with the surface is increased when the medial arm  246  or lateral arm  244  of the heel extender  228  is adjacent the wall  62  rather than the rear segment  242 . 
       FIG. 17  shows another embodiment of an article of footwear  310  having many of the features of the article of footwear  10 . Identical reference numbers are used for components and features that are the same as those of the article of footwear  10 . The article of footwear  310  has a sole structure  312  that has a heel portion  20  with a rear, a lateral side  24 , and a medial side  26 . The sole structure  312  includes an outsole  314  and the drop-in inner midsole layer  18  of  FIG. 3  (not shown in  FIG. 17 ). The sole structure  312  has an outer midsole layer  316  exposed at the heel portion  20  as in the sole structure  12 . An upper  315  is secured directly or indirectly to the sole structure  312  generally above the sole structure  312 . In the embodiment shown, the upper  315  includes a first portion  311 , that surrounds a foot and may be a knit material or other construction, and a heel plate  313  that is harder than the first portion  311  and generally supports the first portion  311  at the heel portion  20 . 
     The article of footwear  310  includes a heel extender  328  identical to the heel extender  28  except that a taper of the lateral arm  44  and the medial arm  46  is different so that first and second ends  356 ,  358  are shaped differently than the ends  56 ,  58  of the heel extender  28 . More specifically, the arms  44 ,  46  taper upward toward the ends  356 ,  358 , so that a portion  317  of the outer midsole layer  316  is disposed between the heel extender  328  and the outsole  344  under each of the arms  44 ,  46 . The heel extender  328  includes the rear segment  42 , the lateral arm  44  disposed at the lateral side  24  of the heel portion  20 , and the medial arm  46  disposed at the medial side  26  of the heel portion  20 , with the lateral arm  44  and the medial arm  46  contiguous with the rear segment  42 , and the heel extender  328  configured generally in a C-shape. The lateral arm  44  is shown with hidden lines in  FIG. 17 . 
     The heel extender  328  includes the protuberance  52  establishing the rearmost extent  54  of the article of footwear  310 , and the beveled outer surface  66  with the first bevel  68  and the second bevel  70  sloping from the protuberance  52  to a base (not indicated with a reference number in  FIG. 17 , but identical to base  72  of  FIG. 9 ). The continuous ridge  74  is at an apex of the protuberance  52  and extends along each of the rear segment  42 , the lateral arm  44 , and the medial arm  46 . The protuberance  52  also establishes the furthest medial extent of the article of footwear  310  at the medial arm  46  and the furthest lateral extent of the article of footwear  310  at the lateral arm  44 . Stated differently, the protuberance  52  extends rearward further than the components of the sole structure  312  and the components of the upper  315 , and extends further medially and laterally at the medial and lateral arms  46 ,  44 , respectively, than the upper  315  and the components of the sole structure  312 . 
     The heel extender  328  may be secured to the outer surface  330  of the midsole layer  316 , and may include a flange similar to flange  104  of  FIG. 15  positioned between the midsole layer  316  and the outsole  314 . The midsole layer  316  is molded to have an upper bevel  327  and a lower bevel  329  with a ridge  331  between the bevels  327  and  329 . The entire lower bevel  329 , upper bevel  327 , and ridge  331  are inward of the heel extender  328 . The heel extender  328  is of any of the same materials, hardnesses, and roughness as described with respect to the heel extender  28 . For example, the heel extender  328  may be highly polished, with a surface roughness less than that of the components of the sole structure  312 , and may have a hardness value (i.e., a second hardness) at least 44 points harder than a (first) hardness of the components of the sole structure  312  on a Shore D durometer scale. 
     The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the modes for carrying out the present teachings when taken in connection with the accompanying drawings. 
     “A,” “an,” “the,” “at least one,” and “one or more” are used interchangeably to indicate that at least one of the items is present. A plurality of such items may be present unless the context clearly indicates otherwise. All numerical values of parameters (e.g., of quantities or conditions) in this specification, unless otherwise indicated expressly or clearly in view of the context, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. In addition, a disclosure of a range is to be understood as specifically disclosing all values and further divided ranges within the range. All references referred to are incorporated herein in their entirety. 
     The terms “comprising,” “including,” and “having” are inclusive and therefore specify the presence of stated features, steps, operations, elements, or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, or components. Orders of steps, processes, and operations may be altered when possible, and additional or alternative steps may be employed. As used in this specification, the term “or” includes any one and all combinations of the associated listed items. The term “any of” is understood to include any possible combination of referenced items, including “any one of” the referenced items. The term “any of” is understood to include any possible combination of referenced claims of the appended claims, including “any one of” the referenced claims. 
     Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” “top,” “bottom,” etc., may be used descriptively relative to the figures, without representing limitations on the scope of the invention, as defined by the claims. 
     While several modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not as limiting.