Patent Publication Number: US-9894958-B2

Title: Flexible article of footwear and related method of manufacture

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to footwear and, more particularly, to footwear that promotes the natural movement of the wearer&#39;s foot and conformity to the ground. 
     Conventional footwear typically includes two primary elements: an upper and a sole construction. The upper at least partially covers the wearer&#39;s foot, and the sole construction provides support for the wearer&#39;s sole. The sole construction can include multiple layers and materials. For example, conventional sole constructions can include a molded foam midsole over a natural rubber outsole. The molded foam midsole can provide cushioning while the natural rubber outsole can provide traction and wear resistance. 
     Conventional sole constructions are primarily flexible in a single direction. In particular, many sole constructions are intended to flex in the upward direction, in which the ground engaging surface of the outsole is convex. Flexibility of this kind is typically achieved with modifications to the outsole. For example, it is known to introduce grooves in the outsole to promote the bending of the outsole in the upward direction. It is also known to separate the outsole into individual components that move away from each other as the outsole is bent in an upward direction. 
     The natural movement of the wearer&#39;s foot is not limited to flexure in the upward direction, however. In addition to upward flexure, or dorsi-flexion, the human foot naturally exhibits downward flexure, or plantar-flexion. Conventional sole constructions typically exhibit significant resistance to plantar-flexion, however. For example, many conventional sole constructions include an outsole or a midsole that resists plantar-flexion of the wearer&#39;s foot. By opposing the natural ability of the human foot to flex downwardly, many such sole constructions compromise stability and grip on all but even surfaces. 
     SUMMARY OF THE INVENTION 
     An improved article of footwear and a related method of manufacture are provided. The improved article of footwear includes a sole construction configured to promote the natural motion of the wearer&#39;s foot over a variety of surfaces and for a variety of activities. The sole construction includes enhanced flexibility in the forefoot region to accommodate planar-flexion and dorsi-flexion of the wearer&#39;s foot. The related method of manufacture provides the assembly of an article of footwear having these and other features, which can be suitable for athletic wear, outdoor wear and casual wear by adults, adolescents and small children. The related method of manufacture can be modified to meet the specific demands of the end-use application, thereby providing an article of footwear having the desired degree of cushioning and ground protection while also providing the desired degree of flexibility for the wearer. 
     In one embodiment, an article of footwear includes an insole element, a midsole, and an outsole. The insole element includes an opening or cutout, optionally including an elastic material spanning the opening or cutout. The opening or cutout extends over flex grooves in the midsole that can define anatomical pods beneath the wearer&#39;s forefoot and that promote upward and downward flexibility. The outsole includes a lower surface defining outsole flex grooves in general alignment with the midsole flex grooves. The midsole lower surface and the outsole upper surface define an interface about which the article of footwear can be flexed to accommodate planar-flexion and dorsi-flexion of the wearer&#39;s forefoot. 
     The midsole can include an upper surface defining a plurality of lateral flex grooves and a plurality of longitudinal flex grooves. The plurality of lateral flex grooves include a first lateral flex groove extending generally beneath a junction between the wearer&#39;s toe bones and metatarsal bones and a second lateral flex groove extending generally beneath the wearer&#39;s metatarsal bones. The plurality of longitudinal grooves intersect the plurality of lateral grooves in the forefoot region of the midsole. The midsole grooves, both longitudinal and lateral, can define a depth that is a percentage of the thickness of the midsole. For example, the midsole flex grooves optionally define a depth between about 25% and 95% of the thickness of the midsole, further optionally between about 70% and 90% of the thickness of the midsole. The midsole flex grooves can alternatively extend entirely through the thickness of the midsole. In other embodiments, the depth of the midsole flex grooves varies, such that the depth of one midsole flex groove is different from the depth of another of the midsole flex groove. 
     The outsole flex grooves can minor the midsole flex grooves, extending between adjacent tread elements of the outsole. The tread elements are optionally positioned below individual bones, joints and/or muscles and move independently of each other, and are interconnected with each other. For example, individual tread elements are positioned beneath the wearer&#39;s toe bones, beneath the wearer&#39;s metatarsal bones, beneath the wearer&#39;s tarsal bones, and/or beneath the wearer&#39;s calcaneus (heel) bone. The tread elements are optionally surrounded by a color dam, which acts as a separation element between the tread elements and the outsole flex grooves. The outsole flex grooves can define a depth that is a percentage of the thickness of the outsole (inclusive of the tread elements). The outsole flex grooves optionally define a depth between about 25% and 95% of the thickness of the outsole, further optionally between about 50% and 70% of the thickness of the outsole. The outsole flex grooves can alternatively extend entirely through the thickness of the outsole. 
     In another embodiment, a method of manufacturing an article of footwear is provided. The method generally includes lasting an upper with an insole element, forming a midsole including midsole grooves, forming an outsole including outsole grooves, joining the outsole to the midsole, joining the midsole to the insole element, removing an area of material from the forefoot region of the insole element, and positioning a footbed over the insole element. Joining the insole element to the upper can include sewing the insole element to the upper. In embodiments where the insole element is a Strobel board, the insole element can be joined to the upper along a butt seam. In embodiments where the insole element is a lasting board, the insole element can be joined to the upper with cement. Joining the midsole to the insole element can include gluing the midsole to all except the forefoot portion of the insole element. Removing the area of material can include directly or indirectly pulling a perforated segment from the remainder of the insole element. The perforated segment can additionally include a pull tab sewn, cemented or otherwise joined to the perforated portion to aid in the removal of the perforated segment. The remainder of the insole element can include a border around an opening in the forefoot region. 
     In these and other embodiments, the improved article of footwear can include a sole construction that promotes the natural movement of the foot and ground conformance. The sole construction is generally flexible longitudinally, laterally, and diagonally, accommodating plantar-flexion, dorsi-flexion, and twisting. The sole construction provides a balance of dynamic, multi-directional, barefoot-like movement and conformance with the ground and cushioning with improved surface area contact. The improved surface area contact can enhance stability, proprioception, traction and agility with effective ground protection for a variety of pursuits. Example pursuits include trail running, hiking, hunting, boating, and aquatic activities. Additional applications include footwear specifically adapted to promote walking for infants and small children. The related method of manufacture can be tailored to meet desired levels of flexibility and performance while providing the desired degree of support to the wearer&#39;s sole. 
     These and other advantages and features of the invention will be more fully understood and appreciated by reference to the description of the current embodiments and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevation view of an article of footwear in accordance with a current embodiment. 
         FIG. 2  is a plan view of a first insole element for the article of footwear of  FIG. 1 . 
         FIG. 3  is a plan view of a second insole element for the article of footwear of  FIG. 1 . 
         FIG. 4  is a plan view of a third insole element for the article of footwear of  FIG. 1  with non-stretch webbing. 
         FIG. 5  is a plan view of a first midsole for the article of footwear of  FIG. 1  including flex grooves and anatomical pods. 
         FIG. 6  is a plan view of the midsole of  FIG. 5  having a superimposed bone structure for the human foot. 
         FIG. 7  is a plan view of a second midsole for the article of footwear of  FIG. 1  including flex grooves and anatomical pods. 
         FIG. 8  is a plan view of a third midsole for the article of footwear of  FIG. 1  including flex grooves and anatomical pods. 
         FIG. 9  is a plan view of the underside of a midsole illustrating a protective film in the forefoot region of the midsole. 
         FIG. 10  is a plan view of the underside of a midsole illustrating a protective film in the forefoot, mid-foot, and rearfoot regions of the midsole. 
         FIG. 11  is a plan view of the upper surface of a midsole in accordance with a current embodiment. 
         FIG. 12  is a plan view of the lower surface of an outsole in accordance with the embodiment of  FIG. 11 . 
         FIG. 13  is a cross-sectional view of the midsole of  FIG. 11  and the outsole of  FIG. 12  taken along line  13 - 13  in  FIGS. 11-12 . 
         FIG. 14  is a second cross-sectional view of the midsole of  FIG. 11  and the outsole of  FIG. 12  taken along line  14 - 14  in  FIGS. 11-12 . 
         FIG. 15  is a third cross-sectional view of the midsole of  FIG. 11  and the outsole of  FIG. 12  taken along line  15 - 15  in  FIGS. 11-12 . 
         FIG. 16  is a plan view of an outsole in accordance with a current embodiment illustrating anatomical tread elements. 
         FIG. 17  is a flow-chart illustrating a method for manufacturing an article of footwear in accordance with an embodiment of the present invention. 
         FIG. 18  is a plan view of insole elements including perforations surrounding a removable forefoot portion. 
         FIG. 19  is a plan view of an insole element including webbing joined to the removable forefoot portion of the insole element. 
         FIG. 20  is a plan view of the underside of an insole element including non-stretch webbing extending across the forefoot region and joined to the upper. 
     
    
    
     DESCRIPTION OF THE CURRENT EMBODIMENTS 
     The current embodiments relate to an improved article of footwear and a related method of manufacture. In these embodiments, the improved article of footwear includes a flexible sole construction adapted to promote the natural motion of the wearer&#39;s foot and conformance with the ground, while providing ground protection and support for the wearer. The related method provides the manufacture of an article of footwear having a flexible sole construction for use across a range of activities. 
     I. Construction 
     Referring now to  FIG. 1 , an article of footwear in accordance with one embodiment is illustrated and generally designated  10 . The article of footwear  10  includes an upper  12  and a sole construction  14 . The upper  12  is formed from a variety of material elements that are joined together to cover at least a portion of the wearer&#39;s foot. The material elements can be selected based on the intended uses of the article of footwear  10 , and can include synthetic textiles, mesh textiles, polymers or leather, for example. The upper  12  is generally constructed to not impede the flexibility of the sole construction  14 , and can include stretchable or elastic material elements. For example, the material elements can include Lycra, Neoprene or Spandex. The upper  12  can include one or more closure elements  16 , including for example shoelaces or hook and loop fasteners. The upper  12  additionally includes an upper opening  18  for receiving the wearer&#39;s foot and a lower periphery  20  for attachment to the sole construction  14 . 
     The sole construction  14  is also illustrated in side-profile  FIG. 1 . The sole construction  14  is adapted to provide flexibility for a range of foot movements, including for example plantar-flexion and dorsi-flexion. The sole construction  14  includes an insole element  22  (not shown in  FIG. 1 ), a midsole  24  and an outsole  26 , but greater or fewer elements of the sole construction  14  can be included in other embodiments. For example, some embodiments can include only a midsole an outsole, while other embodiments can include only an insole element and an outsole. Still other embodiments can include a unit sole, in which the midsole and the outsole are combined into a single unitary element. The unit sole can include EVA foam with a cushioning top portion and a firmer, wear resistant bottom portion. Each of the insole element  22 , the midsole  24  and the outsole  26  can additionally include a forefoot region  28 , a mid-foot or arch region  30 , and a rearfoot region  32 . 
     An insole element  22  in accordance with one embodiment is illustrated in  FIG. 2 . The insole element  22  is generally non-stretchable and lightweight and joined to the upper  12  to provide a void for receipt of the wearer&#39;s foot. The insole element  22  includes enhanced flexibility in at least the forefoot region  28  in the illustrated embodiment, and can include increased flexibility in the mid-foot region  30  and rearfoot region  32  in other embodiments. The enhanced flexibility is optionally achieved with an interior opening  34  extending entirely through the thickness of the insole element  22 . The interior opening  34  generally overlies one or more flex grooves in the midsole  24  as discussed below. In addition, the interior opening  34  is enclosed by a peripheral lip  36 . The peripheral lip  36  is generally flat, includes a generally uniform width, and is joined to the upper  12 , optionally along a butt seam. The insole element  22  includes a Strobel board in the current embodiment, while in other embodiments the insole element  22  includes a lasting board. The insole element  22  can be non-woven, woven or fibrous, and can be formed of nylon, polyester, or polypropylene. Still other constructions for the insole element  22  are possible in other embodiments where desired. 
     The outline of the interior opening  34  generally mimics the shape of the forefoot region of the insole element  22 . In particular, the outline of the interior opening  34  generally includes a straight portion  38  adjacent the mid-foot region  30  of the insole element  22  and a curved portion  40  forward of the straight segment  38 . The curved portion  40  is spaced apart from the outer periphery  42  of the insole element  22  by 7 mm to 17 mm in the present embodiment, but can be spaced apart by other distances in other embodiments. For example, the spacing can be between 5 mm and 25 mm, further optionally between 10 mm and 15 mm. 
     The interior opening  34  can be modified as desired. As further optionally shown in  FIG. 3 , for example, a flexible, stretchable covering  44  can extend over the opening  34  in the insole element  22 . The flexible, stretchable covering  44  can include an elastic membrane that extends partially or completely over the opening  34  in the forefoot region  28  of the insole element  22 , being generally secured to the downward facing surface of the insole element  22 . The elastic membrane includes Lycra, Neoprene or Spandex in the illustrated embodiment, while in other embodiments other materials can be used as desired. The opening  34  can additionally include one or more web stiffeners. As shown in  FIG. 4 , two web stiffeners  46 ,  48  are arranged to extend across the opening  34 , thereby providing an added degree of dimensional stability to the flexible covering  44 . In the illustrated embodiment, the web stiffeners  46 ,  48  are formed separately from the insole element  22  and are glued, stitched or stapled thereto prior to the formation of the opening  34  in the insole element  22 . In other embodiments the web stiffeners  46 ,  48  are formed of the same material as the insole element  22 , and separate the opening  34  into sub-openings. In still other embodiments, the interior opening is replaced by one or more web stiffeners  46 ,  48  that are joined to the upper  12  and that span the forefoot region. As shown in  FIG. 20  for example, the web stiffeners  46 ,  48  are joined to the lower periphery of the upper  12 , optionally by means of a butt seam, on the upward facing surface of the insole element  22 . An optional flexible covering  44  can extend across the remainder of the open area in the forefoot region, and can be Lycra, Neoprene or Spandex as generally discussed above in connection with  FIGS. 3-4 . The web stiffeners  46 ,  48  are generally cut or removed once the article of footwear is assembled as discussed below to enhance flexibility of the finished construction. 
     A midsole  24  in accordance with one embodiment is illustrated in  FIG. 5 . The midsole  24  is positioned below the insole element  22 , and includes a lower surface  50 , an upper surface  52 , and a sidewall  54  extending therebetween. The upper surface  52  can include multiple midsole grooves  60 . The midsole grooves  60  are positioned to provide enhanced bending flexibility to the midsole, and in particular, bending flexibility in the downward (plantar-flexion) direction. The midsole grooves  60  generally underlie the insole opening  34 , providing enhanced flexibility in the forefoot region  28 . In addition, the midsole grooves  60  are contained within the midsole upper surface  52 . In other embodiments, the midsole grooves  60  are contained within the midsole lower surface  50 . In still other embodiments, both of the lower surface  50  and the upper surface  52  include midsole grooves  60 . In yet other embodiments, the midsole grooves  60  extend to the edge of the midsole  24  and define a break in the midsole sidewall  54 . 
     The midsole grooves  60  can assume a variety of configurations. In the illustrated embodiment of  FIG. 5 , the midsole grooves  60  include a depth that extends partially through the thickness of the midsole  24 , such that the midsole grooves  60  are not in communication with the outsole  26 . For example, the midsole  24  can include a local thickness of about 11 mm and the midsole grooves  60  can include a depth of about 9 mm, leaving a connecting portion of about 2 mm. These dimensions can vary in other embodiments as desired. In dimensionless terms, the midsole grooves  60  can define a depth between about 25% and 95% of the thickness of the midsole  24 , further optionally between about 70% and 90% of the thickness of the midsole  24 . In other embodiments the midsole grooves  60  include a depth that extends entirely through the thickness of the midsole  24 , such that the midsole grooves  60  are in communication with the outsole  26 . The midsole grooves  60  can include a width (gap) that is selected to provide the desired degree of flexibility for the sole construction. For example, the width can be 1 mm in embodiments where modest flexibility is desired, and 3 mm in embodiments where greater flexibility is desired. 
     Referring again to  FIG. 5 , the midsole grooves  60  include multiple lateral grooves and multiple longitudinal grooves. The lateral grooves include a first lateral groove  62  and a second lateral groove  64 . The first lateral groove  62  is positioned to extend generally beneath the wearer&#39;s toes and forefoot. The second lateral groove  64  is spaced apart from the first lateral groove  62  in the longitudinal (heel-to-toe) direction. As shown in  FIG. 6  for example, the second lateral groove  64  is positioned to extend generally beneath and between a junction between the wearer&#39;s phalanges (toe bones) and metatarsals. As also shown in  FIG. 6 , the first and second lateral grooves  62 ,  64  are arcuate in the present embodiment, but can be straight, angled or segmented in other embodiments. The longitudinal grooves  66  extend in the heel-to-toe direction, and intersect the first and second lateral grooves  62 ,  64 . The longitudinal grooves  66  are positioned generally beneath and between adjacent metatarsals/toes, and facilitate torsional and longitudinal bending of the midsole  24 . While shown as being located in the forefoot region of the midsole in the present embodiment, the midsole grooves  60  can extend into the mid-foot region  30  and/or the rearfoot region  32  of the midsole in other embodiments. 
     The midsole grooves  60  can define anatomical pods  68  that are shaped to generally correspond with one or more anatomical features of the human foot. As shown in  FIG. 5 , for example, each anatomical pod  68  is bordered on two, three or four sides by the midsole grooves  60 . A first row of anatomical pods  70  is bordered by the first lateral groove  62  and by the longitudinal grooves  66 . A second row of anatomical pods  72  is bordered by the first and second lateral grooves  62 ,  64  and by the longitudinal grooves  66 . A third row of anatomical pods  74  is bordered by the second lateral groove  64  and by the longitudinal grooves  66 . In addition, each anatomical pod  68  underlies one or more bones in the wearer&#39;s foot. The first and second rows of anatomical pods  70 ,  72  generally underlie the metatarsals, while the third row of anatomical pods  74  generally underlies the phalanges. The pods  68  can assume other anatomical or non-anatomical shapes or locations in other embodiments as desired. 
     The midsole grooves  60  can deform to accommodate movement of the wearer&#39;s foot. For example, the gap within each midsole groove  60  can widen or narrow depending on the curvature imposed on the midsole  24  and the predominate direction of the midsole groove  60 . If the midsole groove  60  is predominately laterally disposed (e.g., grooves  62  and  64 ), the midsole groove  60  can widen as the midsole  24  is flexed upwardly or narrow as the midsole  24  is flexed downwardly. If the midsole groove  60  is longitudinally disposed (e.g., grooves  66 ), the midsole groove  60  can widen as the midsole  24  assumes a longitudinally convex curvature and can narrow as the midsole  24  assumes a longitudinally concave curvature. The presence of the lateral midsole grooves  62 ,  64  therefore assist in promoting the natural movement of the human foot, and conformance to the ground, beyond that which is accommodated by conventional footwear constructions. 
     The midsole grooves  60  can assume a variety of alternative configurations. For example, the midsole grooves  60  can include a depth that extends entirely through the thickness of the midsole  24 , such that the midsole grooves  60  are in communication with the outsole  26 , enhancing the flexibility of the outsole  26 . In other words, the midsole grooves  60  define slots  76  that perforate the entire thickness of the midsole. As shown in  FIG. 7 , the slots  76  (the shaded portions of the grooves  60 ) can penetrate the second lateral groove  64  and the longitudinal grooves  66  at selective locations along the length of the longitudinal grooves  66 . As shown in  FIG. 8 , the slots  76  can penetrate the first and second lateral grooves  62 ,  64 , the outermost longitudinal grooves  66 , and the innermost longitudinal grooves  66  at selective locations along their length. An optional third lateral groove  78  extends forward of the second lateral groove  64 . Individual connectors  80  join adjacent anatomical pods  68  that would otherwise be disconnected from the remainder of the midsole  24 . The outsole  26  is generally viewable through the slots  76  (around the connectors  80 ) in these embodiments, optionally extending upwardly into the slots  76 . The connectors  80  can be severed or removed during the manufacture of the article of footwear, for example after joining the outsole  26  to the midsole  24 . The connectors  80  can also be suspended above the outsole  26 . That is, the midsole grooves  60  can define a relief in the upper surface of the midsole  24  and can define a matching relief in the lower surface of the midsole  24 . For example, the midsole  24  can have a thickness of 8 mm, an upper midsole groove having a 3 mm depth, and a lower midsole groove having a 3 mm depth, leaving a connector  80  having a thickness of 2 mm (in the vertical dimension) that is suspended above the outsole  26 . Different configurations can be utilized in other embodiments where desired. 
     The midsole  24  can include essentially any material suitable for providing foot support. For example, the midsole  24  can include ethylene-vinyl acetate, polyurethane, or thermoplastic elastomer. The midsole  24  can be compression molded in some embodiments, while in other embodiments the midsole  24  can be injection molded. Other manufacturing techniques can be used in other embodiments as desired. The midsole  24  can additionally include a protective film  82  (also referred to as a protective plate  82 ) that extends over the upper surface  52 , the lower surface  50 , or both the upper surface  52  and the lower surface  50  of the midsole  24 . As shown in  FIG. 9 , for example, a 1 mm protective film  82  extends over the lower surface  50  of the forefoot region  28  of the midsole  24 . As shown in  FIG. 10 , the protective film  82  extends over substantially the entire lower surface  50  of the midsole  24 . The protective film  52  optionally includes ethylene-vinyl acetate plastic, thermoplastic polyurethane, or Pebax® (polyether block amide, available from Arkema), which can provide enhanced strength to the midsole  24  without degrading the flexibility of the midsole  24 . The midsole  24  can additionally be formed of two or more materials having different material properties. For example, the midsole  24  can include a first material in a first one of the anatomical plurality pods  68  and a second material in a second one of the plurality of anatomical pods  68 . Further by example, the midsole  24  can include a first material in the forefoot region and a second material in the rearfoot or mid-foot region. 
     An outsole  26  in accordance with one embodiment is illustrated in  FIG. 12 . The outsole  26  includes a lower surface  84 , an upper surface  86 , and a sidewall  88  extending therebetween. The lower surface  84  additionally includes one or more tread elements  90  (shown in  FIGS. 12  as  92 ,  94 , and  96 ). The tread elements  90  optionally include a two-dimensional shape that corresponds to one or more anatomical features of the human foot. For example, the tread elements  90  can include a two-dimensional shape (in plan view) that corresponds to the following anatomical features: the phalanges, the metatarsal bones, the tarsal bones, the arch, and/or the calcaneus (heel) bone. As optionally shown in  FIGS. 12 and 16 , the tread elements  90  include a first row of five tread elements  92  beneath the wearer&#39;s toes, a second row of five tread elements  94  beneath the wearer&#39;s metatarsals, and a third row of five tread elements  96  beneath the wearer&#39;s metatarsals. Additional tread elements  98  can extend below the wearer&#39;s heel and arch. The tread elements  90  can assume other anatomical features or non-anatomical features in other embodiments as desired, and can be textured or smooth. 
     The outsole  26  can additionally include one or more outsole grooves  100 . The outsole grooves  100  generally include an upwardly recessed portion (relative to the lowermost extend of the tread elements  90 ) between adjacent tread elements  90 . In other embodiments the outsole grooves  100  include downwardly recessed grooves in the upper surface  86  of the outsole  26 . The outsole grooves  100  can be linear, curved, angled, segmented, circular, or polygonal. As shown in  FIG. 12 , the outsole grooves  100  are positioned between adjacent tread elements  90 , and are aligned with the midsole grooves  60  discussed above, including both longitudinal and lateral outsole grooves. Each outsole groove  100  includes a length, a width, and a depth. The depth can extend partially through the thickness of the outsole  26 , such that the outsole grooves  100  are not in communication with the midsole  24 . For example, the outsole  26  can include a thickness of approximately 6 mm (including the tread elements  90 ), and the outsole grooves  50  can define a depth of approximately 4 mm (leaving a 4 mm tread element and a 2 mm base layer). Still further by example, the outsole  26  can include a thickness of approximately 6 mm (including the tread elements), and the outsole grooves  50  can define a depth of approximately 3 mm (leaving a 3 mm tread element and a 3 mm base layer). In dimensionless terms, the outsole grooves  100  can define a depth between about 25% and 95% of the overall thickness of the outsole  26 , further optionally between about 50% and 70% of the overall thickness of the outsole  26 . In other embodiments, the outsole grooves  100  include a depth that extends entirely through to the outsole  26 , such that the outsole grooves are in communication with the midsole  24 . The outsole  26  can additionally include color dams  101 . As shown in  FIG. 12 , for example, the color dams  101  extend around the tread elements  90  and separate the tread elements  90  from the adjacent outsole grooves  100 . In other embodiments color dams  101  are not included, and the outsole grooves  100  abut the tread elements  90 . 
     The width of each outsole groove  100  can deform to accommodate movement of the wearer&#39;s foot. In particular, the width of each outsole groove  100  can widen or narrow based on the curvature imposed on the outsole  26  and based on the predominate direction of the outsole groove  100 . If the outsole groove  100  is laterally disposed on the lower surface of the outsole  26 , the width can widen/stretch as the outsole  26  is flexed upwardly and can narrow/compress as the outsole  26  is flexed downwardly. If the outsole groove  50  is longitudinally disposed on the lower surface of the outsole  26 , the width can widen/stretch as the outsole  26  assumes a longitudinally convex curvature and can narrow/compress as the outsole  26  assumes a longitudinally concave curvature. 
     The outsole  26  can include essentially any material suitable for providing a durable wear surface. For example, the outsole  26  can include natural or synthetic rubber. Also by example, the outsole  26  can include thermoplastic polyurethane, thermoplastic rubber or high density ethylene-vinyl acetate foam. The outsole  26  is a unitary component in the present embodiment, but can be formed of separately molded components in other embodiments. The outsole  26  can be compression molded in some embodiments, while in other embodiments the outsole can be injection molded. Other manufacturing techniques can be used in other embodiments as desired. The outsole  26  can additionally include a protective film  82  that extends over either or both of the upper surface  86  and the lower surface  84  of the outsole  26 . The protective film  82  can includes insert molded ethylene-vinyl acetate plastic, which can provide enhanced resistance to wear and ground protection without limiting the flexibility of the outsole  26 . 
     Various modifications of the outsole  26  are possible. For example, the midsole grooves  60  and the outsole grooves  100  can be offset with respect to each other. In addition, the lower surface  50  of the midsole  24  and the upper surface  86  of the outsole  26  can include interengaging portions that ensure the appropriate alignment of the midsole  24  with respect to the outsole  26 . For example, the outsole  26  can include a raised upper surface portion  102  overlying each outsole groove  100 , while the midsole  24  can include a recessed lower surface portion  104  underlying each midsole groove  60 . The protective film  82  can extend across the sole construction  14 , generally undulating between the midsole  24  and the outsole  26 . The tread elements  90  project downwardly from the lower surface  84  of the outsole  26  and adjacent to the outsole grooves  100  as discussed above in connection with  FIG. 12 . 
     As also shown in  FIGS. 13-15 , the article of footwear  10  can include a footbed  106 . The footbed  106  can include a molded foam element having a size and a shape adapted to support at least a portion of the wearer&#39;s foot. In addition, the footbed  106  can generally compliment the flexibility of the insole element  22 , the midsole  24 , and the outsole  26 , without restricting the same. In some embodiments the footbed  106  can generally surround the forefoot of the wearer, the arch of the wearer, and the heel of the wearer. In other embodiments the footbed  106  does not surround the forefoot of the wearer, and is generally limited to the rearfoot portion of the insole element  22 . The footbed  106  is removable in some embodiments, while in other embodiments the footbed  106  is bonded to the insole element  22 , the midsole  24 , or both the insole element  22  and the midsole  24 , while being generally free from attachment in the forefoot region. The footbed  102  can be formed of essentially any lightweight material, including for example foam latex, ethylene-vinyl acetate, thermoplastic elastomer, or polyurethane. The footbed  106  can additionally include flex grooves substantially as set forth above in connection with the midsole flex grooves  60  of  FIGS. 5-11 , and can include a protective film substantially as set forth above in connection with  FIGS. 9-10 . 
     II. Method of Manufacture 
     Referring now to  FIG. 17 , a flow chart illustrating a method for forming an article of footwear including a flexible sole construction is provided. In general terms, the method according to one embodiment includes: a) joining an insole element to an upper, the insole element having a removable portion; b) forming a midsole including a midsole groove in an upper surface thereof; c) forming an outsole including an outsole groove in a lower surface thereof; d) joining the outsole to the midsole; e) joining the midsole to the upper or the insole element; f) separating the removable portion from the insole element to define an opening in the insole element; and g) positioning a footbed over the insole element. 
     Joining an insole element to an upper is depicted as step  110  in  FIG. 17 . This step can include stitching, tacking, or gluing an insole element  22  to an upper  12 , optionally while the upper  12  is drawn over a last. For example, this step can include sewing an insole element  22  to an upper  12  along a butt seam, the butt seam extending around the entire periphery of the insole element  22 . When joined together, the insole element  22  and the upper  12  provide a void for receipt of the wearer&#39;s foot. The insole element  22  and the upper  12  can be formed according to any desired method and can include any desired material. For example, the insole element  22  can include a Strobel board or a lasting board, can be non-woven, woven or fibrous, and can be formed of nylon, polyester, or polypropylene. Also by example, the upper  12  can include multiple elements that are joined together, and can include synthetic textiles, mesh textiles, polymers or leather. 
     Forming a midsole including a midsole groove is depicted as step  112  in  FIG. 17 . This step generally includes molding a material into the shape of the midsole  24 , the material being pliable or flexible. Optional materials include ethylenevinyl acetate, polyurethane, or thermoplastic elastomer. Other materials can be used in other embodiments where desired. The midsole  24  can be formed by compression molding the midsole in a cavity having the desired exterior shape of the finished midsole or by injection molding the midsole in a cavity having the desired exterior shape of the finished midsole. The finished midsole can generally include a plurality of midsole grooves  60  on an upper surface thereof to improve the flexibility of the midsole. The plurality of midsole grooves  60  are substantially as set forth above in connection with  FIGS. 5-11 , and can include lateral grooves  62 ,  64  and longitudinal grooves  66 . The midsole grooves  60  define a depth less than the thickness of the midsole  24 , such that the midsole grooves  60  do not extend entirely through to the bottom of the midsole  24 . In other embodiments, however, and as shown in  FIGS. 7-8 , the midsole grooves  60  includes slots  76  extending entirely through to the bottom of the midsole  24 . While located in the forefoot region of the midsole in the present embodiment, the midsole grooves  60  can extend into the mid-foot region  30  and/or the rearfoot region  32  in other embodiments. 
     The step of forming the midsole  24  can additionally include forming a protective film  82  on the midsole  24 . The protective film  82  can extend over all or a portion of the lower surface  50  of the midsole  24  in some embodiments, and can extend over all or a portion of the upper surface  52  of the midsole  24  in other embodiments. For example, the protective film  82  can extend over a substantial portion of the forefoot region  28  as shown in  FIG. 9 , and can extend over the rearfoot, mid-foot and forefoot regions of the midsole  24  as shown in  FIG. 10 . The protective film  82  can include essentially any protective coating. In the present embodiment, the protective film  82  includes an insert molded ethylenevinyl acetate plastic, thermoplastic polyurethane, or Pebax® (polyether block amide, available from Arkema). The protective film  82  can include other materials in other embodiments where desired. 
     Forming an outsole including an outsole groove is depicted as step  114  in  FIG. 17 . This step generally includes molding a material into the shape of the outsole  26 , the material being wear resistant. Optional materials include natural or synthetic rubber, thermoplastic rubber, or high density ethylene-vinyl acetate. Other materials can be used in other embodiments where desired. The outsole  26  can be formed by compression molding the outsole  26  in a cavity having the desired exterior shape of the finished outsole or by injection molding the outsole  26  in a cavity having the desired exterior shape of the finished outsole. As discussed above in connection with  FIGS. 12-16 , the outsole  26  can include a plurality of outsole grooves  100  to improve the flexibility of the outsole  26 . For example, the plurality of outsole grooves  50  can extend around one or more tread elements  90 . In the illustrated embodiment, the outsole grooves  100  define a depth less than the thickness of the outsole  26 , such that the outsole grooves  100  do not extend entirely through to the top of the outsole  26 . In other embodiments, however, the outsole grooves  100  include slots extending entirely through to the top of the outsole  26 . The outsole grooves  100  are located in the forefoot region  28  in the illustrated embodiment, but can extend into the mid-foot region  30  and/or the rearfoot region  32  in other embodiments. In still other embodiments, additional outsole grooves  100  extend downwardly from the upper surface of the outsole  26  in the forefoot region  28 , mid-foot region  30  and/or rearfoot region  32 . As discussed above in connection with the midsole  24 , the outsole grooves  100  can be in vertical alignment with each other, such that a thin outsole connector is suspended between the outsole grooves  100 , thereby providing enhanced flexibility to the outsole  26 . 
     The step of forming the outsole  26  can additionally include forming a protective film  82  on the outsole  26 . The protective film  82  can extend over all or a portion of the upper surface  86  of the outsole  26  in some embodiments, and can extend over all or a portion of the lower surface  84  of the outsole  26  in other embodiments. The protective film  82  can include essentially any protective coating for the outsole  26 . In the present embodiment, the protective film  82  includes ethylenevinyl acetate plastic. The protective film  82  can include other materials in other embodiments where desired. 
     The step of joining the outsole to the midsole is depicted as step  116  in  FIG. 17 . This step generally includes applying adhesive or cement, or otherwise bonding the outsole upper surface  86  to the midsole lower surface  50 . For example, this step can include powder coating the midsole  24  or the outsole  26  before joining the midsole  24  to the outsole  26 . When bonded together, the midsole  24  and the outsole  26  form a flexible sole element that can flex upwardly for dorsi-flexion and that can flex downwardly for plantar-flexion. 
     The step of joining the midsole to the insole element or to the upper is depicted as step  118  in  FIG. 17 . This step generally includes applying adhesive or cement, or otherwise bonding the midsole upper surface  52  to the insole element  22  and/or the upper  12 . This step is optionally performed while the insole element  22  and the upper  12  are positioned over a last. The adhesive, cement or other bonding agent is optionally not applied to the portion of the midsole  24  underlying the opening in the insole element  22 . Instead, the adhesive, cement or other bonding agent is applied to the rearfoot portion, the arch portion, and the periphery of the forefoot portion of the midsole uppers surface  52 . 
     Separating a removable portion from the insole element is depicted as step  120  in  FIG. 17 . As shown in  FIG. 18 , the removable portion  108  is generally interiorly disposed, being spaced apart from the outer periphery of the insole element  22 . For example, the removable portion  108  can be surrounded by a peripheral lip  36 , which remains attached to the insole element  22 . The removable portion  108  is optionally formed by perforating the insole element  22  in advance of the step  110  above. The perforations can include 10 mm slots with 1.5 mm spacing in one embodiment, or 1 mm holes with 1.5 mm spacing in other embodiments. As shown in  FIG. 19 , the removable portion  108  can include a pull tab or webbing  110  which can be pulled for separating the removable portion  108  from the insole element  22 . The webbing  110  can be joined to the removable portion  108  by sewing, gluing, stapling, or otherwise attaching the webbing  110  to the removable portion  108 . The attachment between the webbing  110  and the removable portion  108  is generally stronger than the perforation between the removable portion  108  and the remainder of the insole element  22 . When the webbing  110  is pulled toward the heel, the removable portion  108  is separated from the remainder of the insole element  22  along the perforation line  112 , leaving the opening in the forefoot region of the insole element  22 . The webbing  110  is formed from the same material as the insole element  22  in the present embodiment, but can be formed from other materials in other embodiments. The webbing  110  and the removable portion  108  can then be discarded as scrap material or reused as webbing for subsequent insole elements. 
     Positioning a footbed over the insole elements is depicted as step  122  in  FIG. 17 . The footbed  106  can include a molded foam element having a size and a shape adapted to support at least a portion of a foot of the wearer of the article of footwear  10 . For example, in some embodiments the footbed  106  can generally surround the forefoot of the wearer, the arch of the wearer, and the heel of the wearer. The footbed  106  is a free-floating removable element in some embodiments, while in other embodiments the footbed  106  is bonded to the insole element  22 , the midsole  24 , or both the insole element  22  and the midsole  24 . The footbed  106  can be formed of essentially any lightweight material, including for example foam latex, ethylene-vinyl acetate, thermoplastic elastomer, or polyurethane. 
     The order and/or inclusion of the above steps can be modified in other embodiments where desired. For example, the step of separating the removable portion from the insole element (step  120 ) can occur before the step of joining the midsole to the insole element (step  118 ). Also by example, the step of positioning a footbed  106  in the article of footwear (step  122 ) can be omitted. Additional steps can also be included. For example, the above method steps can include placing additional cushioning elements in the sole construction, thereby providing additional cushioning to the wearer. 
     The finished article of footwear generally includes a midsole lower surface is directly or indirectly joined to the outsole upper surface to define a midsole-outsole interface. The interface is functionally a flexible spine about which the sole construction can be flexed. For example, the flexible spine can be flexed upwardly in the forefoot region for dorsi-flexion. Also by example, the flexible spine can be flexed downwardly in the forefoot region for plantar-flexion. The flexible spine can also flex in the rearfoot region of the sole construction and in the arch region of the sole construction. The flexible spine can also accommodate twisting about the longitudinal axis of the sole construction. For example, the forefoot region can twist with respect to the rearfoot region. The sole construction therefore provides flexibility and support, even where flexibility and support are competing objectives in conventional footwear constructions. 
     The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. For example, and without limitation, any individual element(s) of the described invention may be replaced by alternative elements that provide substantially similar functionality or otherwise provide adequate operation. This includes, for example, presently known alternative elements, such as those that might be currently known to one skilled in the art, and alternative elements that may be developed in the future, such as those that one skilled in the art might, upon development, recognize as an alternative. Directional terms, such as “vertical,” “horizontal,” “top,” “bottom,” “upper,” “lower,” “inner,” “inwardly,” “outer” and “outwardly,” are used to assist in describing the invention based on the orientation of the embodiments shown in the illustrations. The use of directional terms should not be interpreted to limit the invention to packages of any specific orientation(s). Further, the disclosed embodiments include a plurality of features that are described in concert and that might cooperatively provide a collection of benefits. The present invention is not limited to only those embodiments that include all of these features or that provide all of the stated benefits, except to the extent otherwise expressly set forth in the issued claims. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular. Any reference to claim elements as “at least one of X, Y and Z” is meant to include any one of X, Y or Z individually, and any combination of X, Y and Z, for example, X, Y, Z; X, Y; X, Z; and Y, Z.