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Title:
VARIABLE FRICTION SHOE
Document Type and Number:
WIPO Patent Application WO/2020/206428
Kind Code:
A1
Abstract:
A variable friction shoe includes a midsole and an outsole. The outsole includes at least a first high-friction surface and at least a first low-friction surface, wherein the first low-friction surface remains prominent if vertical ground reaction forces (GRFs) are low and wherein the high-friction surface is prominent in response to increasing GRFs.

Inventors:
SUSKO TYLER (US)
HAWKES ELLIOT (US)
SLOAN ERINN (US)
DEVLIN MATTHEW RYAN (US)
Application Number:
PCT/US2020/026881
Publication Date:
October 08, 2020
Filing Date:
April 06, 2020
Export Citation:
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Assignee:
UNIV CALIFORNIA (US)
International Classes:
A43B13/22; A43B13/00; A43B13/04; A43B13/18
Foreign References:
US9439474B22016-09-13
US20120260535A12012-10-18
US20120233885A12012-09-20
US20120144695A12012-06-14
US8844170B22014-09-30
Attorney, Agent or Firm:
COLLINS, Michael et al. (US)
Download PDF:
Claims:
CLAIMS:

1. A variable friction shoe comprising:

a midsole; and

an outsole having at least a first high-friction surface and at least a first low- friction surface, wherein the first low-friction surface is prominent if vertical ground reaction forces (GRFs) are low and wherein the high- friction surface is prominent in response to increasing GRFs.

2. The variable friction shoe of claim 1, further including:

a compressible layer located vertically adjacent to the first low-friction surface, wherein the compressible layer compresses in response to increasing GRFs.

3. The variable friction shoe of claim 2, wherein the at least a first low-friction surface includes a plurality of low-friction surfaces, wherein each of the plurality of low- friction surfaces are associated with one of a plurality of compressible layers.

4. The variable friction shoe of claim 3, wherein the plurality of low-friction surfaces and the plurality of compressible layers have a cylindrical geometry.

5. The variable friction shoe of claim 2, wherein the compressible layer is located in the midsole.

6. The variable friction shoe of claim 1, wherein the first low-friction surface is located in a forward portion of the outsole.

7. The variable friction shoe of claim 6, wherein the at least a first low-friction surface is a continuous horse-shoe shape having first and second legs extending around an outside of the outsole.

8. The variable friction shoe of claim 7, wherein the high-friction surface is located between the first and second legs of the horseshoe shaped low-friction surface.

9. The variable friction shoe of claim 6, wherein the at least a first low-friction surface includes a first low-friction surface and at least a second low-frictions surface.

10. The variable friction shoe of claim 9, wherein the first low-friction surface is located opposite the second low-friction surface.

11. The variable friction shoe of claim 10, wherein the first low-friction surface is located on an inner portion of the outsole and the second low-friction surface is located on an outer portion of the outsole.

12. The variable friction shoe of claim 1, wherein the at least a first high-friction surface includes a first high-friction surface and a second high-friction surface.

13. The variable friction shoe of claim 12, wherein the at least a first high-friction surface is located forward of the second high-friction surface.

14. The variable friction shoe of claim 1, wherein the at least a first high-friction surface includes a plurality of high-friction surfaces.

15. The variable friction shoe of claim 14, further including a plurality of non- compressible layers, each non-compressible layer associated with one of the plurality of high-friction surfaces.

16. A variable friction shoe comprising:

a midsole; and an outsole having at least a first high-friction surface and at least a first low- friction surface, wherein the first low-friction surface is prominent during a swing phase of a gait and wherein the high-friction surface contacts the ground during a stance phase of the gait.

17. The variable friction shoe of claim 16, further including a second low-frictions surface, wherein the first low-friction surface is located opposite the second low-friction surface.

18. The variable friction shoe of claim 17, wherein the first low-friction surface is located on an inner portion of the outsole and the second low-friction surface is located on an outer portion of the outsole.

19. The variable friction shoe of claim 16, wherein the first low-friction surface is a horse-shoe shape extending around a front portion of the variable friction shoe.

20. The variable friction shoe of claim 19, wherein the high friction surface is located at least in an area interior of the horse-shoe shape of the first low-friction surface.

Description:
VARIABLE FRICTION SHOE

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims benefit of US Provisional Application No. 62/829,254, filed on April 4, 2019, titled“VARIABLE FRICTION SHOE” and which application is incorporated herein by reference. A claim of priority is made.

BACKGROUND

[0002] The present invention is related to footwear, and in particular to footwear designed to aid those suffering from a condition that makes it difficult to clear the floor during swing such as foot drop.

[0003] Foot Drop is a mobility disorder that limits ankle dorsiflexion, complicating the swing phase of gait and balance. It is a common result of a neurological injury or disease such as stroke, cerebral palsy, peripheral nerve disease, brain tumor or multiple sclerosis.

[0004] While symptoms of stroke, multiple sclerosis, brain tumors, peripheral nerve disease and cerebral palsy vary from patient to patient, a subset of patients in each group will experience foot drop, characterized by the inability to dorsiflex, or lift the toes toward the shin, due to impaired control of the tibialis anterior and/or the triceps surae. It inhibits the rhythmic swing phase of gait, increases the probability of foot scuff and falls, and forces conscious monitoring of one's gait, typically manifesting into abnormal gait patterns.

[0005] Assistive technology refers to devices meant to aid a person in desirable tasks. For walking, available devices include functional electrical stimulation (FES) applied to the tibialis anterior muscle or a static ankle-foot orthosis (AFO). Rehabilitation technology refers to devices meant to restore healthy movement via use of the technology. Robotic rehabilitation devices are beginning to target populations with foot drop. For example, researchers at Massachusetts Institute of Technology (MIT) developed the MIT-Skywalker which allows free motion during the swing phase of gait, temporarily restoring rhythmicity originally lost due to inability to clear the floor. The Skywalker and other robotic rehabilitation devices, while promising, have three areas for improvement: cost, complexity and portability. Rehabilitation is most effective with repetition. A device that a patient could own or at least use regularly outside of clinical visits would allow for a higher volume of rehabilitation training. Currently, there is not a rehabilitative solution that is cost effective and practical for every day independent use.

SUMMARY

[0006] According to some aspects, a variable friction shoe includes a midsole and an outsole. The outsole includes at least a first high-friction surface and at least a first low- friction surface, wherein the first low-friction surface remains prominent if vertical ground reaction forces (GRFs) are low and wherein the high-friction surface is prominent in response to increasing GRFs.

DESCRIPTION OF THE DRAWINGS

[0007] Figures 1a and 1b are side and orthogonal views, respectively, of a variable friction shoe according to some embodiments.

[0008] Figures 2a and 2b are side and orthogonal views, respectively, of a variable friction view according to some embodiments.

[0009] Figures 3a and 3b are cross-sectional views of the variable friction sole in an unloaded state and a loaded state, respectively, according to some embodiments.

[0010] Figures 4a-4c are graphs illustrating performance of the variable friction shoe as compared with a typical show according to some embodiments.

[0011] Figure 5a is a bottom view of a variable friction shoe according to some embodiments; Figure 5b and 5c are side views of the variable friction shoe in an uncompressed state and a compressed state, respectively, according to some embodiments.

[0012] Figure 6 is an exploded view of a variable friction shoe according to some embodiments.

[0013] Figure 7a is a bottom view of a variable friction shoe according to some embodiments; Figure 7b and 7c are side views of the variable friction shoe in an uncompressed state and a compressed state, respectively, according to some embodiments. [0014] Figure 8a is a botom view of a variable friction shoe according to some embodiments; Figure 8b and 8c are side views of the variable friction shoe in an uncompressed state and a compressed state, respectively, according to some embodiments

DETAILED DESCRIPTION

[0015] According to some aspects, a variable friction shoe is disclosed herein that provides variable levels of friction with the ground during various gait stages. For purposes of this discussion, the gait is divided into the swing phase and the stance phase. During the swing phase the variable friction shoe presents a low-friction surface that protrudes or extends from the outsole of the shoe. During the stance phase of the gait the variable friction shoe presents a high-friction surface at the outsole of the shoe to prevent slipping with respect to the ground. In some embodiments, the outsole of the variable friction shoe includes a botom surface configured to provide contact between the shoe and the ground, wherein the botom surface is a high-friction surface. For example, the bottom surface may utilize materials and geometries such as tracks to provide a high- friction surface. The outsole further includes one or more columns or islands that retain a compressible material and a low-friction material. During the swing portion of the gait, when vertical ground reaction forces (GRFs) are low , the compressible material is in an uncompressed state allowing the low-friction material to protrude from the high-friction surface of the outsole. During the stance stage of the gait, when vertical GRFs are high, the compressible material is in a compressed state that causes the low-friction material to recede within the high-friction surface of the outsole such that a high-friction surface is put into contact with the ground

[0016] Figures 1a and 1b are side and orthogonal views, respectively, of variable friction shoes according to some embodiments. Variable friction shoe 100 includes a top portion 101, a midsole 102, a high-friction surface 108, a low-friction surface 106, and a compressible material 104. In the embodiment shown in Figure 1a, a plurality of cylindrical pairs of compressible material 104 and low-friction material 106 are shown in an exploded view to illustrate the components utilized. In the embodiment shown in Figure lb, the plurality of cylindrical pairs of compressible material 108' and low-friction material 106' are shown installed within the high-friction surface 108' of the midsole 102'. In some embodiments, the islands or patches of compressible material 104 and low-friction material 106 are distributed evenly along the bottom of the variable friction shoe 100. In other embodiments the islands or patches of compressible material 104 and low-friction material 106 are placed at locations most likely to come into contact with the ground during the swing phase of the gait. For example, in one embodiment the columns of compressible material 104 and low-friction material 106 are located primarily at the front of the shoe 100 where the shoe is likely to scuff against the ground during the swing phase of gait.

[0017] In some embodiments, the compressible material 104 is comprised of a soft elastic foam and the low-friction material 106 is comprised of polytetrafluoroethylene (PTFE). In other embodiments, other materials may be utilized that provide the desired characteristic of compressibility in the compressible material 104 in response to the force exerted during the stance stage and low-friction in the low-friction material to allow the shoe to scuff the ground during the swing stage. In particular, the materials are selected such that the low- friction material 106 remains proud during the swing stage when the vertical GRFs are relatively low, and wherein the low-friction material 106 is compressed by the higher vertical GRFs provided during the stance stage of the gait to allow the high-friction surface 108 to come into contact with the ground (i.e., such that the low-friction material 106 is no longer proud or protruding from the high-friction surface 108).

[0018] Figures 2a and 2b illustrates side and orthogonal views, respectively, of a variable friction shoe 200 and 200' according to another embodiment of the present invention. The variable friction shoe 200 (as well as 200') once again includes a top portion 201, an outsole 202, a high-friction material 210 and a plurality of islands or patches that include a hollow, cylindrical bushings 204, a compressible material 206 and a low-friction material 208. In the embodiment shown in Figure 2a, the hollow, cylindrical bushings 204, compressible material 206 and low-friction material 208 are shown in an exploded view that illustrates the relative locations of each. In the embodiment shown in Figure 2b, the hollow, cylindrical bushings 204' are shown in a cut-away view that illustrates the location of compressible materials 206' and low-friction material 208' within the hollow, cylindrical bushings 204'. The embodiment shown in Figure 2b also illustrates the relative location of the cylindrical bushings 204', compressible material 206' and low-friction material 208' within the outsole 202' and high-friction surface 210'.

[0019] In some embodiments the compressible material 206 and the low-friction material 208 are housed within the hollow, cylindrical bushing 204. In the embodiment shown in Figures 2a and 2b, the low-friction material 208 is comprised of delrin, the compressive material is comprised of soft, elastic foam, and the hollow cylindrical linear bushings 204 are plastic. In other embodiments, other types of materials may be utilized. Once again, materials are selected such that the low-friction material 208 remains proud during the swing stage when the vertical GRFs are relatively low, and wherein the low-friction material 208 is compressed by the higher vertical GRFs provided during the stance stage of the gait to allow the high-friction surface 210 to come into contact with the ground (i.e., such that the low-friction material 208 is no longer proud or protruding from the high- friction surface 210).

[0020] Figures 3a and 3b are cross-sectional views that illustrate the variable friction shoe in an uncompressed state (presumably during the swing stage of the gait) and in a compressed state (presumably during the stance stage of the gait), respectively. Shown in Figures 3a and 3b is a compressible material 302, a low-friction material 304, and a high stiffness, high-friction material 306. As shown in Figure 3a, during the swing state the vertical GRFs are relatively low, allowing the compressible material 302 to remain largely uncompressed. As a result, the low-friction material 304 protrudes beyond the high- friction surface or high-friction materials 306. During the swing stage of the gait, a person suffering from foot drop may inadvertently allow the shoe to come into contact with the ground during the swing stage. In the event this happens, the low-friction material 304 will come into contact with the ground and allow the shoe to slide over ground rather than catch. As the wearer enters the stance stage of the gait the vertical GRFs increase as the wearer transitions weight to the foot. The increase in vertical GRFs causes the compressible material 302 to compress, which allows the low-friction material 304 to recede such that the high-friction material 306 comes into contact with the ground. In some embodiments, the high-friction material 306 has a stiffness substantially greater than the compressible material 302. In some embodiments, the high-stiffness material 306 is also the high-friction material. In some embodiments, the high- stiffness material 306 is separate from the high-friction material (not labeled) that comes into contact with the ground during the stance stage of the gait. In this embodiment, the high-friction material would be located on the bottom exterior surface of the high- stiffness material 306.

[0021] Figures 4a-4c are graphs illustrating patient improvement according to various quantifiable aspects utilizing various embodiments of the present invention. In particular, Figure 4a illustrates percent change in walking speed utilizing various versions of the variable friction shoe; Figure 4b illustrates percent change in maximum over ground speed reached utilizing various versions of the variable friction shoe; and Figure 4c illustrates percent change in hip angle utilizing various versions of the variable friction shoe. Results shown in Figures 4a-4c illustrate tests of first and second models of the variable friction shoe, the first variable friction shoe labeled 400 and the second variable friction shoe labeled 402. The first variable friction shoe utilizes patches having soft elastic foam with a thin layer of low-friction material (for example as shown in Figures 1a-1b). The second variable friction shoe utilizes patches having a delrin peg attached to a soft elastic foam, wherein the delrin pegs are cylindrical with rounded edges and are supported by hollow cylindrical linear bushings.

[0022] As shown in Figure 4a, for most participants both the first and second versions of the variable friction shoe provided an improved comfortable walking speed over fixed friction shoes (e.g., normal tennis shoes or sneakers), with the second variable friction shoe showing slightly improved performance as compared with the first variable friction shoe.

[0023] Similarly as shown in Figure 4b, for most participants both the first and second versions of the variable friction shoe provided an improved maximum over ground speed over fixed friction shoes (e.g., controlled running sneakers with the same geometry as the variable friction shoes), with the second variable friction shoe showing improved performance as compared with the first variable friction shoe. [0024] Figure 4c illustrates that the hip angle of the participants decreased for most participants utilizing both the first and second versions of the variable friction shoe. In order to advance gait, some impaired individuals adopt a circumduction gate. For these individuals, greater frontal plane hip angles represent greater compensation and thus higher levels of physical exertion. While both versions of the shoe improved hip angles, the second version provided slightly better performance by decreasing frontal plane hip angles.

[0025] Referring now to Figures 5a-5c, a variable friction shoe 500 is illustrated according to some embodiments. In particular, Figure 5a is a bottom view of the variable friction shoe 500, Figure 5b is a side view of the variable friction shoe 500 in an uncompressed state (presumably during the swing stage of the gait) and Figure 5c is a side view of the shoe 500 in a compressed state (presumably during the stance stage of the gait).

[0026] In the embodiment shown in Figure 5a, variable friction shoe 500 includes a midsole 510 and an outsole 502, which in turn includes a low-friction surface 504 and a high-friction surface 506. The low-friction surface 504 extends in a horse-shoe shape around the front portion of the outsole 502. During the swing stage of the gait, the low- friction surface 504 is prominent (i.e., remains proud relative to the high-friction surface 506). In the case of a scuff, the low-friction surface 504 allows the shoe to slide across the ground. The low-friction surface 504 (or adjacent compressible material) is compressed by the higher vertical GRFs provided during the stance stage of the gait to allow the high-friction surface 506 to become prominent (i.e., such that the low-friction surface 508 is no longer proud or protruding from the high-friction surface 506). In the embodiment shown in Figure 5a the high-friction surface 506 is located in the center portion of the shoe, in the region between the horseshoe- shape of the low-friction surface 504. In other embodiments, the location of high-friction surface 506 and low-friction surface 504 relative to one another may be modified. For example, a modified arrangement is shown in Figure 6, Figure 7a, and Figure 8a. In each however, the principle of operation remains the same. The low-friction surface 504 remains prominent during the swing portion of the gait when GRFs are relatively low and wherein the low-friction surface 504 recedes in response to increasing GRFs, resulting in the high-friction surface 506 of the outsole 502 coming into contact with the ground during the stance stage of the gait.

[0027] Figure 5b is a side view of the variable friction shoe 500 in an uncompressed state and Figure 5c is a side view of the variable friction shoe 500 in a compressed state. In response to little or no ground reaction force (GRF) - typical during the swing stage of the gait - the low-friction surface 504 is prominent (i.e., proud relative to the high-friction surface 506). As a result, the shoe is allowed to slide along the ground via the low-friction surface 504 without catching during the swing stage of the gait. As increasing GRFs are applied to the variable friction shoe 500 (in response to a transition to the stance stage of the gait) a compressible material (not visible) located vertically adjacent to the low-friction surface 504 is compressed as shown in Figure 5c. As a result, the high-friction surface 506 becomes prominent and therefore contacts the ground, thereby preventing the shoe from slipping across the surface contacted.

[0028] For some applications, a benefit of the low-friction surface 504 being continuous or nearly continuous is that there are fewer sharp transitions between the low-friction surface 504 and the high-friction surface 506. In some embodiments, another benefit is the size of the low-friction surface 504 relative to the high-friction surface 506 prevents the low-friction surface 504 and/or high-friction surface 506 from getting caught in cracks during either stage of the gait. In some embodiments, the low-friction surface 504 is continuous. In other embodiments, the low-friction surface 504 is not continuous. For example, low-friction surface 504 may include a first low-friction surface and a second low-friction surface. For example, the embodiment shown in Figure 6 illustrates the low- friction surface separated into first and second low-friction surfaces.

[0029] Figure 6 is an exploded view of a variable friction shoe 600 that illustrates the plurality of layers utilized according to some embodiments. For the sake of simplicity, the top portion of the shoe is not shown in this view. In some embodiments, outsole 602 is the topmost layer and extends along the entire length of the variable friction shoe 600. In some embodiments, outsole 602 includes at least a first recess configured to receive at least a first compressible layer 604a. In the embodiment shown in Figure 6, outsole 602 includes a first recess and a second recess located towards the front of the shoe, on opposite sides from one another. In other embodiments, first recess and second recess may be connected to one another, forming a single recess for example in a horseshoe shape positioned along the front of the shoe (for example, as shown in Figure 5a in a horseshoe shape). In some embodiments, a compressible material 604a, 604b is located in the first and second recess respectively. In some embodiments, the compressible material 604a, 604b is more compressible than the outsole 602, such that the compressible material 604a, 604b compresses (more than outsole 602) in response to GRFs.

[0030] Adjacent to the outsole 602 and compressible layer 604a, 604b is an intermediate layer 606 that includes low-friction surface 608 (in this example, first and second low- friction surfaces 608a, 608b). In some embodiments, low-friction surfaces 608a, 608b are coextensive with compressible material 604a 604b and the associated recesses. In other embodiments, low-friction surfaces 608a, 608b are slightly smaller in surface area than the corresponding compressible layers 604a, 604b. In some embodiments, intermediate layer 606 extends only along a front portion of the variable friction shoe 600. In some embodiments, low-friction surfaces 608a, 608b include a height or thickness (relative to bottom layer 610) that ensures low-friction surface 608a, 608b is protrudes beyond the bottom layer 610 in an uncompressed state. In some embodiments, low-friction surfaces 608a and 608b are made of the same material as intermediate layer 606. In some embodiments, low-friction surfaces 608a and 608b and intermediate layer 606 are integral. In other embodiments, low-friction surfaces 608a and 608b are made from different materials, wherein only low-friction surface 608a and 608b are comprised or present a low- friction surface.

[0031] The bottom layer 610 is positioned adjacent to the intermediate layer, wherein the intermediate layer is located between the bottom layer 610 and the outsole 602. In some embodiments the bottom layer 610 is defined by a width that allows the bottom layer 610 to be positioned between the low-friction surface 608a and 608b. In some embodiments, the length of bottom layer 610 extends along the entire length of the outsole 602. In other embodiments, bottom layer 610 may extend along a portion of the outsole 602 (for example as shown in Figure 6). A high-friction surface 612 is located on the bottom surface of the bottom layer 610.

[0032] As described above, during the swing stage of the gait, when no GRF are applied to the variable friction shoe 600, the low-friction surfaces 608a and 608b remain prominent or proud relative to the high- friction surface 612. Incidental contact with the ground during this stage (e.g., scuffing) results in the low-friction surface 608a and/or 608b coming into contact with the ground, the low-friction surface allowing the shoe to slide along the ground and not catch. In response to increasing GRFs as the user transitions to the stance stage of the gait, the compressible layer 604a, 604b is compressed, resulting low-friction surface 608a receding from the position of prominence relative to the high-friction surface 612. As a result of the compression of the compressible layer 604a and 604b, high-friction surface 612 is brought into contact with the ground and provides the prevents the shoe from sliding along the ground/surface.

[0033] In the embodiment shown in Figure 6, the compressible layer 604a and 604b and low-friction surface 608a and 608b are located on the outer and inner portion of the front portion of the shoe. In other embodiments, the location of these layers and surfaces may be modified depending on the application. For example, in some embodiments the compressible layer 604a and 604b and low-friction surface 608a and 608b may be continuous in the form of a horseshoe as shown, for example, in Figure 5a-5c. In other embodiments - such as those described with respect to Figures 7a, 7b and 8a, 8b - other geometries may be utilized.

[0034] With respect to Figure 7a-7c, a variable friction shoe 700 is provided with a different geometry of low-friction surfaces 704 and high-friction surfaces 702. In particular, Figure 7a is a bottom view of the outsole 701 of the variable friction shoe 700 and Figures 7b and 7c are side views during an uncompressed and compressed state, respectively. In contrast with the embodiment shown in Figures la and lb, the embodiment provided in Figures 7a-7c utilizes a plurality of islands of high-friction surfaces 702 separated from one another by a low-friction surface 704. As shown in Figures 7b and 7c, the low-friction surface 704 remains prominent relative to the plurality of islands of high- friction surfaces 702 when GRFs are low (i.e., during the swing stage of the gait) as shown in Figure 7b. Compressible material (not shown) located between the low-friction surface 704 and the midsole is compressed in response to increasing GRFs. Conversely, non- compressible material (relative to the compressible material associated with the low- friction surface 704) is located vertically adjacent to each of the plurality of high-friction surfaces 702. In response to increasing vertical GRFs, the compressible material vertically adjacent to the low-friction surface 704 compresses wherein the non-compressible material vertically adjacent to the plurality of high-friction surfaces 702 does not compress. As a result, the plurality of high-friction surfaces 702 transition to a position prominent or at least co-extensive relative to the low-friction surface 704 as shown in Figure 7c. In response to the increased force and compression the position of the low-friction surface 704 is modified relative to the plurality of high-friction surfaces 702 such that the low- friction surface 704 is no longer proud or protruding from the plurality of high-friction surfaces 702 during the stance stage of the gait. As shown in Figure 7c, the high-friction surface 702 does not necessarily have to be prominent or proud relative to the low-friction surface 704, but positioned such that high-friction surface 702 is able to contact the ground

[0035] With respect to Figures Sa-8c, a variable friction shoe 800 is provided with a different geometry of low-friction surfaces 802 and high-friction surfaces 804a, 804b. In particular. Figure 8a is a bottom view of the outsole 801 of the variable friction shoe 800 and Figures 8b and 8c are side views during an uncompressed and compressed state, respectively. In contrast with the embodiment shown in Figures la and lb, the embodiments provided in Figures 8a-8c utilizes a first high-friction surface or region 804a and a second high-friction surface or region 804b separated by a low-friction surface or layer 802. As shown in Figures 8b and 8c, the low-friction surface 802 remains prominent relative to the first and second high-friction surfaces or regions 804a, 804b when GRFs are low (i.e., during the swing stage of the gait) as shown in Figure 8b. Compressible material (not show) located vertically adjacent to the low-friction surface 802 is compressed in response to increasing GRFs during the stance stage of the gait. Conversely, non- compressible material (relative to the compressible material) located vertically adjacent to the first and second high-friction surfaces 804a and 804b does not compress. As a result of the increased force and compression the position of the low-friction surface 802 is modified relative to the plurality of high-friction surfaces 804a and 804b such that the low- friction surface 802 is no longer proud or protruding from the plurality of high-friction surfaces 804a and 804b during the stance stage of the gait. As shown in Figure 8c, the high-friction surfaces 804a and 804b do not necessarily have to be prominent or proud relative to the low-friction surface 802, but positioned such that one or both of the high- friction surfaces 804a and 804b are able to contact the ground

[0036] While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.