GB2114869A - Dynamic support system for athletic shoes - Google Patents

Abstract

An athletic running shoe having a polymeric foamed midsole 33 has a stiffening formation 37 formed separately of the midsole and located above the midsole or, as shown, between two layers of the midsole to stiffen the midsole along a pre- selected region. <IMAGE>

Description

SPECIFICATION Dynamic support system for athletic shoes The present invention relates to athletic shoes and is particularly concerned with running or jogging shoes of the type having a closed cell polymeric foamed midsole.

Present day sliplasted and boardlasted running and jogging shoes, as well as other types of athletic shoes, are customarily manufactured with a laminate bottom construction having a closed cell polymeric foam midsole overlying and adhered to a flexible outsole. Sliplasted athletic running shoes mainly differ from boardlasted athletic shoes in that they have no insole board and instead have a closed fabric bottom to extend completely around the foot like a slipper. In the boardlasted athletic running shoes, the upper has an open bottom which is closed by an insole board overlying the midsole, The foamed midsole is used in both types of shoes because of its lightness and shock absorbing properties to cushion the wearer's foot against impacts during running.

Sliplasted athletic shoes are generally preferred over boardlasted athletic shoes because they usually are more comfortable than boardlasted athletic shoes. Due to the absence of an insole board, however, sliplasted athletic shoes are usually less stable than boardlasted athletic shoes because during running concentrated stresses are developed in the foamed midsole which stresses non-uniformly degrade the foamed midsole to an objectionable extent. The foamed midsole therefore loses much of its effectiveness as a shock absorber because of the non-uniform degradation.

Degradation of the foamed midsole arises from continual stresses which are developed by the repeated and cyclic deformation and relaxation of the midsole during the course of running. The degradation may take the form of a permanent compressive deformation or compression set, as it is called, of the midsole. It may also occur without compression set where there is a breakdown or loss of the closed cells in the foamed midsole.

Midsole degradation is frequently localized due to concentrated force patterns which arise from a runner's particular running style. For example, localized midsole degradation may occur at the rear outside border of the shoe in the region of the back of the heel. Midsole degradation also occurs throughout the impact absorbing region of the midsole as a result of the compressive forces which cause the midsole to expand laterally outwardly of the shoe.

Localized midsole degradation along either the medial inside or lateral outside shoe edges is particularly troublesome because it tends to cause the shoe to lose its stability by tilting as the runner's foot strikes the ground. To compensate for the instability, the runner may adjust his running style which, in turn, could lead to foot or ankle injuries. Furthermore, the problem of midsoie degradation is compounded by the fact that it frequently occurs before the outsole loses its service life.

The foamed midsole in a boardlasted athletic running shoe will also degrade as a result of usage, but the degradatiion is not as non-uniform as the midsole degradation in a sliplasted athletic shoe because the insole board of the boardlasted athletic shoe disperses the forces acting on the midsole to some extent as long as the insole board itself does not degrade.

Although an insole board does disperse the forces acting on the foamed midsole to some extent, we have found that if the insole board is made stiff enough to adequately spread the forces over the foamed midsole, the shoe becomes too hard, causing appreciable discomfort to the wearer. On the other hand, low strength insole boards which meet the wearer's comfort requirements are likely to degrade, thus giving rise to excessive non-uniform midsole degradation even in boardlasted shoes.

With the foregoing in mind, the general aim and purpose of this invention is to provide a novel structure for improving the stability of the athletic shoe, reducing midsole degradation, and enhancing the anatomical support for the wearer's foot, all without making the shoe uncomfortably hard and without using any parts which reduce the foot-receiving volume of the upper. A more specific aim and purpose of this invention is to provide a novel structure for substantially reducing the non-uniform midsole degradation of a slipiasted athletic shoe without resorting to an insole board and without otherwise impairing the comfort properties of a sliplasted athletic shoe.

This is generally accomplished by engaging the foamed midsole with a special formation at a region lying below the midsole's upper surface to stiffen a selected midsole surface area. In the illustrated embodiment, the special formation takes the form of a thin, stiff, substantially nonstretchable layer or stiffening board, as it may be called, which lies between and is adhered to two midsole layers at a level lying between the upper and lower surfaces of the midsole. The stiffening board is required to be sufficiently stiff to effectively disperse the forces acting on the shoe throughout the region covered by the board to thereby provide for a more uniform distribution of the forces acting on the shoe.

Because the stiffening board of this invention is effective in stiffening the foamed midsole support underneath the foot, its geometrical shape is particularly important. In the illustrated embodiment, the shape of the stiffening board is such that it underlies the wearer's entire rear-foot or heel region and extends forwardly approximately to the first, second and third metatarsal heads to underlie the inside arch, but not the outside arch of the wearer's midfoot.

Because of the selected region covered by the stiffening board, the board does not interfere with the required flexure of the shoe. It therefore may be made as stiff as possible but not so stiff that it becomes brittle.

By dispersing the forces acting on the midsole, the stiffening board of this invention significantly reduces deleterious, non-uniform midsole degradation and substantially lengthens the useful life of the shoe. The adherence of the stiffening board to the opposing midsole layers by itself has the effect of restraining the outward lateral expansion of the midsole due to compressive forces, thereby reducing midsole degradation due to such outward expansion. The degradation resulting from outward expansion of the midsole takes the form of cell wall failures which are caused by shear forces acting on the midsole material.

By locating the stiffening board of this invention at a level intermediate to the upper and lower surfaces of the midsole and by utilizing a boardless insole (i.e. a sliplasted construction without an insole board), the foot support system is advantageously lowered. The foamed midsole layer underlying the stiffening board is used solely for absorbing forces resulting from the impact of the foot on the ground. The midsole layer overlying the stiffening board also acts as a shock absorber and additionally cushions the wearer's foot so that the shoe does not feel hard due to the presence of the stiffening board. Furthermore, the foamed midsole layer overlying the stiffening board in the region of the wearer's rearfoot is of sufficient thickness to closely conform to the shape of the wearer's heel, thereby enhancing the comfort qualities of the shoe.

By stiffening the foamed midsole in the manner described above, the extent of penetration of the runner's foot into the midsole is advantageously reduced by selectively increasing the stiffness of the midsoie material. By extending the stiffening board to a region where it underlies the inside or medial arch-supporting region of the midsole, the stiffening board and foamed midsole also advantageously acts as a comfortable dynamic arch support. This aspect of the present invention eliminates the need for arch cookies or other conventional arch supporting inserts which disadvantageously reduce the foot-receiving volume of the shoe upper.

The midsole stiffening formation of this invention may advantageously be manufactured separately from the shoe as a customized product for use by podiatrists and orthopedists in modifying existing running shoes to compensate for leg and foot asymmetries or other problems.

Heretofore, various shoe inserts, such as heel cushions, arch supports and other so-called orthotic devices, have been used for this purpose.

They all have the common disadvantage of causing some discomfort because they take up foot-receiving space in the shoe upper.

In contrast to these prior shoe inserts, the stiffening formation of this invention lies in the midsole, and not in the upper so that the full volume of the upper remains available for comfortably covering the wearer's foot.

With the foregoing in mind, a further object of this invention is to provide an athletic shoe with a novel midsole construction having a stiffening formation lying between the upper and lower surfaces of the foamed midsole for stiffening the foamed midsole along a selected surface area under the foot.

Still a further object of this invention is to provide an athletic shoe with a novel midsole construction wherein a special formation engages the foamed midsole body to reduce or retard deleterious, non-uniform degradation of the foamed midsole.

Yet another object of this invention is to provide an athletic shoe with a novel midsole having a dynamic arch support.

Another object of this invention is to provide an athletic shoe with a novel, economical midsole construction which is easy to manufacture and which achieves the objects mentioned above.

Still another object of this invention is to provide a novel, customized formation for modifying existing athletic shoes for the purpose of accommodating a wearer's particular anatomy or asymmetries.

Yet another object of this invention resides in a novel method of utilizing the customized, shoemodifying formation mentioned above to compensate for different body weights and/or different leg lengths.

The invention may be put into practice in various ways and a number of specific embodiments will be described by way of example to illustrate the invention with reference to the accompanying drawings in which: Figure 1 is a perspective view of an athletic running shoe in accordance with the present invention for a left foot; Figure 2 is a longitudinal section of the athletic running shoe shown in Figure 1; Figure 3 is a horizontal section taken substantially along the line 3-3 of Figure 2 and showing the configuration of the stiffening formation according to a first embodiment of the present invention; Figure 4 is a transverse section taken substantially along the line 4-4 of Figure 2; Figure 5 is a further transverse section taken substantially along the line 5-5 of Figure 2; ; Figure 6 is a transverse section similar to Figure 4 but showing a variation which is applicable for runners who pronate excessively; and Figure 7 is another transverse section similar to Figure 4 but showing a further variation which is applicable to runners who supinate excessively.

In this specification, the term "rearfoot" is used to identify the heel portion of the foot containing the heel bone, the term "midfoot" is used to identify the intermediate portion of the foot lying adjacent to the rearfoot and containing the five bones which are connected together to form the beginning of the arches in the foot, and the term "forefoot" is used to identify the foot portion lying adjacent to the midfoot and containing the metatarsals.

Although the midsole stiffening formation of this invention is incorporated into a sliplasted athletic running shoe in the illustrated embodiment, it will be appreciated that the principles of the present invention are also applicable to athletic shoes having an insole board where the insole board is made sufficiently flexible so that it does not impair the functions of the special stiffening formation of the present invention Referring to Figures 1 and 2, an athletic running shoe incorporating the present invention comprises a flexible, sliplasted upper 10, a bottom 12 underlying the upper 10 and a soft, pliable sliplasted insole 13 (see Figure 2). The upper 10 has a closed fabric bottom 1 5 so that it extends completely around the foot in the customary manner. The insole 13 is received in the upper 10 and overlies the fabric bottom 1 5.

The upper 10 may be of any suitable, conventional construction and is shown to comprise a toe portion or toe box 14, a vamp portion 16, a heel portion 18, foxing 20 wrapped around the back of the heel portion, a throat 22 extending along the vamp portion 1 6 for the lacing which is indicated at 24, a padded tongue 26 extending along the throat 22, and a padded collar 28 extending around the shoe's footreceiving opening.

The shoe bottom 12 is a laminated construction having a flexible, ground-engaging outsole 32 and a shock-absorbing midsole 33 overlying and bonded to the outsole 32. The outsole 32 may be of any suitable construction and may be fabricated from synthetic or natural rubber material. The ground-engaging surface of the outsole 32 is preferably formed with a suitable tread pattern 36. The midsole 33 is substantially coextensive with the outsole 32. The upper 10 is bonded or otherwise suitably secured to the midsole 33 along its fabric bottom 1 5.

The midsole 33 is formed from any suitable closed cell polymeric foam shock absorbing material. For example, the midsole 33 may be formed from a blend of ethylene vinyl acetate and polyethylene and then cross-linked with a peroxide during moulding. The foam material is preferably lightweight having a density on the order of 0.2 grams per cubic centimetre or somewhat less.

The midsole 33 is thickest at its rearfoot or heel portion 39 where it underlies the wearer's heel or rearfoot. in the illustrated embodiment, the midsole's heel portion 39 is of substantially uniform thickness The midsole 33 tapers forwardly at an intermediate region lying forwardly of the heel portion 39 to form a wedge as shown in Figure 1 and 2. The wedge may be formed separately of midsole 33 and it may overlie or underlie the midsole.

In the illustrated embodiment, the midsole stiffening formation of this invention is in the form of a thin, stiff, planar, flat-sided layer 37 or stiffening board, as it may also be called. The stiffening board 37 is formed separately of the foamed midsole 33 and is incorporated into the midsole in a manner to be described in detail later on.

In the illustrated embodiment, the insole 13 comprises a soft, flexible, flat cushion liner 38 for the wearer's sock. The liner 38 overlies the fabric bottom 1 5 of the upper 10 and may be formed from any suitable pliable material such as a foam material or terrycloth. The insole 13 is characterized by the fact that it does not have an insole board.

As shown in Figures 1 to 5, the stiffening board 37 is received in a slit 42 which is formed in the midsole 33 between the upper and lower surfaces of the midsole to partially divide the midsole 33 into upper and lower layers 44 and 46, respectively. The stiffening board 37 is glued or otherwise suitably adhered to the bottom surrasa of the upper midsole layer 44 and to the upper surface of the lower midscle layer 46. Any suitable adhesive may be used for adhering the stiffening board 37 to the midsole layers 44 and 46.

Preferabiy, the adhesive is applied over the entire interface between the stiffening board 37 and the midsole layer 44 and also over the entire interface between the stiffening board 37 and the lower midsole layer 46.

The slit 42 extends parallel to or at least generally parallel to the outsote 32 when the shoe bottom is in its straight, unflexed condition.

With the possible exception of the midsole's rearmost heel region which may be tapered as shown in Figure 2, the lower midsole layer 46 in this embodiment is provided with a substantially uniform thickness throughout the length and width of the slit 42. The rearfoot section of the upper midsole layer 44 underlying the wearer's rearfoot or heel in this embodiment also ha a substantially uniform thickness, though it tends to get thinner in the midfoot region sooner than does the lower midsole layer.

The slit 42 is formed in the midsole 33 at a level lying about midway between or slightly below the upper and lower surfaces of the midsole's ,-earfoot section. The level of the slit 42, in any case, is required to be low enough to provide the upper midsole layer 46 with a thickness that is sufficient to keep the wearer s foot from bottoming on the stiffening board 37 during the maximum expected impact on the midsole. The thickness and other dimensions of the midsole 33 may be customary, suitable values presently used in the shoe industry to manufacture running shoes.

At a region centrally underlying the wearer's rearfoot or heel, the overall thickness of midsole 33 may, for example, be about 3/4 inches (1.9 cms) and the height of slit 42 above the lower surface of the midsole may be about 5/16 inches (0.8 cms).

As shown in Figures 1 to 3, the configuration or outline of the slit 42 conforms to that of the stiffening board 37 to snugly and fully receive the stiffening board. The slit 42 extends throughout the rearfoot or heel portion of midsole 33 so that it opens completely around the midsole's rearfoot portion at the back and also at both sides. From the rearfoot portion of the midsole 33, the slit 42 opens out through the inside or medial border of the shoe and extends forwardly along to approximately the first metatarsal head so as to underlie the wearer's inside arch. The slit also opens out through the outside border of the shoe and extends forward along to approximately below the front edge of the ankle opening (see Figures 1 and 3).

It will be appreciated that the stiffening board 37 may be assembled with the midsole 33 in any suitable manner. For example, after the slit 42 is formed in the midsole and an adhesive is applied to both sides of the stiffening board 37, the stiffening board may be fully inserted into the slit 42. The midsole layers 44 and 46 and stiffening board 37 may then be pressed together to firmly adhere the stiffening board to the midsole layers 44 and 46.

The stiffening board 37 may be formed from any suitable, durable substantially non-stretchable material. For example, it may be a stiff composite material sheet formed from polyester resin and woven or chopped fibreglass in which the amount of fibreglass present is equal to approximately 25 percent by volume of the sheet.

The stiffening board's minimum flexural or bending modulus required for an adequate dispersion or spreading of the forces acting on midsole 33 is dependent on the thickness of the stiffening board. The thickness of the stiffening board 37 should normally be at least approximately 0.05 inches (0.13 cms) and preferably is approximately 0.06 inches (about 1/16 inch) (0.15 cms). For a stiffening board thickness of 0.06 inches (0.15 cms), the bending or flexural modulus is desirably required to be at least 1,000,000 psi and is more preferably about 2,000,000 psi.

As shown in Figure 3, the stiffening board 37 extends throughout the rearfoot region of the shoe bottom to the outer edge of the heel and from one side of the midsole to the other. From the rear of the midsole 33, the stiffening board 37 extends forwardly along the shoe's medial or inside border to the location 50 which is proximal to the wearer's first metatarsal head. From here, the edge or perimeter of the stiffening board 37 arcs posteriorly and laterally along a line 51 which is proximal to the wearer's second and third metatarsal heads.The edge of the stiffening board then turns to take a direct longitudinaily extending line 52 posteriorly to a region underlying the wearer's cuboid where it arcs out at 53 to extend laterally to the lateral or outer border of the shoe bottom along a line 54 lying approximately normal to the shoe's longitudinal axis at the forward end of the midsole's rearfoot or heel section 39.

By the foregoing construction, it is clear that the stiffening board 37 underlies the wearer's entire rearfoot and extends forwardly to underlie the wearer's inside arch along the medial border, but not the wearer's outside arch or the forefoot region extending forwardly of the wearer's first, second and third metatarsal heads. Because of the selected area covered by the stiffening board 37, the board does not interfere with the required fiexure of the running shoe. It therefore may be made as stiff as desired without making it brittle.

The stiffening board 37 is preferably feathered or skived to a taper along its curved, forward edge (see lines 51-54) as indicated at 56 in Figure 3 to keep the wearer from sensing or feeling an abrupt change in stiffness due to the stiffening board edge as he presses down on the shoe bottom. Additionally, the rear lateral or outside corner 58 (see Figure 3) may also be similarly skived to avoid the development of stress concentrations at the most common first heel of strike region and also to eliminate or significantly reduce accelerated, deleterious sole wear due to the presence of the stiffening board 37.

The lower midsole layer 46 functions solely as a shock absorber for absorbing the forces resulting from the impact of the runner's foot on the ground. The upper midsole layer 44 also acts as a shock absorber for absorbing such forces and additionally cushions the wearer's foot so that the shoe does not feel hard due to the presence of the stiffening board 37. Furthermore, the thickness of the upper midsole layer 44 in the region of the wearer's rearfoot or heel is sufficient to allow it to closely conform or mould itself to the shape of the wearer's heel to provide additional comfort for the wearer.

By stiffening the midsole 33 in the manner described above, the extent of penetration of the runner's foot into the upper midsole layer 44 overlying the stiffening board 37 is advantageously and significantly reduced as compared with a conventional shoe not having the stiffening formation of the present invention. The stiffening effect encountered at initial deformation or penetration of the wearer's foot into the upper midsole layer 44 is approximately doubled by the presence of the stiffening board 37 in the midsole 33, with the result that energy is absorbed at about twice the rate of a conventional shoe.

Although the maximum force will be increased over a new conventional shoe, it nevertheless will stiil be acceptably low. In addition, conventional shoes are known to frequently lose about half of their energy absorbing properties due to continuous use as, for example, while running a marathon distance.

Reducing the extent of rearfoot penetration into the midsole 33 has the advantageous effect of enabling the runner to have greater control over his rearfoot motion, thus improving rearfoot stability without any significant tradeoff of the shock absorbing properties of the midsole 33.

By extending the stiffening board 37 to a region where it underlies the runner's inside or medial arch, the composite of the midsole 33 and the stiffening board 37 underlying the inside arch establishes a comfortable arch support for the wearer which is dynamic in the sense that it is felt only with the application of substantial forces. This eliminates the need for arch cookies or other conventional arch-supporting inserts which are placed in the shoe upper and which disadvantageously reduce the foot-receive volume of the shoe upper.

The stiffening board 37 acts to reduce midsole degradation in two ways. First, it is sufficiently stiff to effectively disperse or spread out the forces acting on the midsole 33 throughout the area or region of the stiffening board to thereby provide for a more uniform distribution of the forces acting on the midsole 33 in the region of the stiffening board. The stiffening board 37 thus eliminates or substantially reduces large, concentrated force patterns resulting from a runner's particular running style and consequently reduces nonuniform degradation of the midsole 33.

Second, the stiffening board 37 has the effect of restraining outward lateral expansion of the midsole 33 under the influence of compressive forces because of its adherence to the midsole layers 44 and 46 and because of its substantially non-stretchable properties, it being relatively nonstretchable relative to the foam midsole. The tensile properties of the midsole foam cell walls lying contiguous to the adhesive surfaces will therefore act to restrain the outward expansion under the influence of the compressive forces.

While some outward midsole expansion will occur because of these compressive forces, the extent of the outward expansion in each of the midsole layers 44 and 46 will nevertheless be substantially less than the expansion that would take place without the stiffening formation of the present invention. Midsole degradation resulting from such outward expansion is therefore correspondingly reduced with the present invention.

With the foregoing construction, it is important to observe that the stiffening board 37 has the effect of significantly improving the stability of a new running shoe in which no midsole degradation has occurred. In this regard, the stiffening board 37 has the effect of dispersing offcentered or unbalanced forces created by a particular running style. Such dispersement produces a restoring force which opposes an unbalanced or off-centered landing of the foot where, for example, the runner lands on the ground along the outside or lateral border of the shoe instead of landing flat. Furthermore, the stiffening board 37 provides an improved foot support during running by employing the midsole layer 44 as a cushion which comfortably conforms to the configuration of the wearer's heel while running and by further establishing a dynamic arch support for the runner's inside or medial arch.In addition to the foregoing, the stiffening board 37 significantly reduces non-uniform midsole degradation to substantially improve the stability of the running shoe over the long term and to substantially lengthen the problem-free life of the shoe as compared to the same shoe not having the stiffening board.

Because the outward expansion of the midsole is restrained just by the non-stretchable or tensile properties of the stiffening board 37 and by the adherence of the stiffening board to the midsole layers 44 and 46, such outward midsole expansion may be reduced by using a flexible, substantially non-stretchable layer or formation in place of the stiffening board 37 and by adhering such a non-stretchable flexible formation or layer to the midsole layers 44 and 46.

Instead of being moulded in one piece and thereafter slit to accommodate the stiffening board 37, the midsole 33 may be manufactured with two separately formed foamed layers, and these layers may have different densities. Because of the stiffening formation of this invention, different foam materials not previously thought to be suitable for midsoles may be used in the manufacture of the running shoe.

The stiffening board 37 is not required to lie horizontally as shown in Figures 1 to 5. Instead, it may be tilted or rotated in one direction or the other about a longitudinal axis as shown in Figures 6 and 7.

In Figure 6, the stiffening board 37 is tilted in a direction to locate its side edge at the lateral or outside shoe bottom border at a level that is lower than its side edge at the medial or inside shoe bottom border to compensate for the forces which are created by runners who pronate excessively. In Figure 7, stiffening board 37 is tilted in the opposite direction such that the side edge of the stiffening board at the medial or inside shoe bottom border is at a level lower than the opposite stiffening board side edge at the lateral or outside shoe bottom border to compensate for the forces created by runners who supinate excessively.

The midsole stiffening formation of this invention is not required to be flat or planar as is the case with the stiffening board 37. The stiffening board 37 may therefore be replaced with differently shaped stiffening formations. For example, the stiffening formation may have a curved or contoured configuration, and it may also be moulded. Furthermore, various factors associated with the stiffening formation of the present invention may be suitably varied depending upon the circumstances. For example, such factors as the thickness of the stiffening formation, the stiffness of the formation, the geometrical extent or area covered by the stiffening formation, and the placement height of the formation may all be varied to accommodate different running styles, leg and foot asymmetries and body weights.

It also will be appreciated that the stiffening formation of this invention avoids difficult and costly attempts to vary the support pattern of the running shoe by introducing different elastomeric materials into the midsole foam.

Furthermore, the midsole stiffening formation of this invention may advantageously be manufactured separately from the running shoe as a customized product for use by pediatrists and orthopedists for modifying existing or fully constructed shoes after they are manufactured to compensate for leg and foot asymmetries or other problems and to thereby customize the shoe to the individual. For example, the midsole stiffening formation of this invention may be used to compensate for different leg lengths with the added advantage of not requiring the insertion of any parts of components into the shoe upper itself.

The method of using the stiffening formation in this manner mainly comprises the steps of first slitting the foamed midsole of an existing athletic shoe or otherwise forming a cavity in the midsole for receiving the stiffening formation, and thereafter inserting the specially formed stiffening formation into the slit or cavity and adhering the stiffening formation to the midsole.

It will be appreciated that the parts of the athletic running shoe for the right foot are the mirror image of the previously described parts of the shoe for the left foot.

Claims (20)

1. An athletic shoe for running and other sports involving running, having an upper and a bottom, the said upper overlying and being attached to a part of the said bottom, the said bottom comprising a flexible outsole and a flexible shockabsorbing midsole overlying and secured to the said outsole, the said midsole being formed from a foamed polymeric material, formation means formed separately of the said midsole and engaging the said midsole over a pre-selected region or surface area underlying the wearer's foot and located intermediate to the upper and lower surfaces of the said midsole for stiffening the said midsole over the said pre-selected region.

2. An athletic shoe for running and other sports involving running, having an upper and a bottom, the said upper overlying and being attached to a part of the said bottom, the said bottom comprising a flexible outsole and a flexible shockabsorbing midsole overlying and secured to the said outsole, the said midsole being formed from a foamed polymeric material, formation means formed separately of the said midsole and engaging the said midsole over a pre-selected region or surface area located exteriorly of the said upper for reducing non-uniform degradation of the midsole due to stresses developed in the midsole by the wearer during the course of running.

3. An athletic shoe as claimed in Claim 1 or Claim 2 in which the said formation means underlies at least the wearer's heel, but not the entirety of the wearer's foot, to stiffen the said midsole at least in the region underlying the wearer's heel.

4. An athletic shoe as claimed in Claim 1,2 or 3 in which the said formation means extends forwardly from the region underlying the wearer's heel to a location underlying the wearer's medial arch to provide support for the wearer's medial arch.

5. An athletic shoe as claimed in Claim 1, 2, 3 or 4 in which the said formation means spans only the portion of the said midsole lying rearwardly of a perimeter which extends inwardly from the medial border of the said bottom along a curved path which is proximal to the wearer's first, second and third metatarsal heads, which then curves to extend posteriorly to a section of the midsole underlying the wearer's cuboid, and which is curved along the said section to extend laterally to the lateral border of the said bottom such that the said midsole is stiffened by said formation means along the entire region lying rearwardly of the said perimeter.

6. An athletic shoe as claimed in Claim 1, 2, 3 or 4 in which the said formation means spans the entire portion of the said midsole underlying the wearer's heel and extends forwardly from said portion to underlie the wearer's medial arch but not the wearer's lateral arch or the region of the wearer's foot lying forwardly of his first, second and third metatarsal heads.

7. An athletic shoe as claimed in any one of Claims 1 to 6 in which the said upper is of the sliplasted type having a bottom adhered to the said midsole, and wherein an insole overlies the said bottom within the said upper and is formed only from one or more soft, flexible materials.

8. An athletic shoe as claimed in any one of Claims 1 to 7 in which the said formation means comprises a stiffening layer lying between and adhered to upper and lower layers of the said midsole.

9. An athletic shoe as claimed in any one of Claims 1 to 7 comprising an insole, the said midsole being at least partially divided into upper and lower layers, the said formation means comprising a stiffening layer lying between and adhered to the said layers, the said upper layer underlying at least the wearer's heel to cushion the heel and the said insole being sufficiently pliable to enable the said upper layer to compress under the load of the wearer's heel to conform to the configuration of the wearer's heel as the wearer's foot strikes the ground during running.

1 0. An athletic shoe as claimed in any one of Claims 1 to 9 in which the said formation means comprises a one-piece, substantially nonstretchable board lying between and adhered to upper and lower layers of the said. midsole, the said board being sufficiently stiff to disperse the forces created by the impact of the wearer's foot on the ground while running and acting on the said midsole in the region of the said board to provide for a more uniform distribution of the forces acting on the said region.

11. An athletic shoe as claimed in any one of Claims 1 to 7 in which the said midsole is at least partially divided into upper and lower layers, and in which the said formation means comprises a stiffening board lying between and engaging the said layers, the said board being at least approximately parallel to the said outsole when the outsole is in its straight, unflexed condition, wherein certain forces created by the impact of the wearer's foot on the ground while running act on the said midsole in the region of the said board, and wherein the said board is sufficiently stiff to disperse the said forces more uniformly throughout the said region, and wherein the said board is substantially non-stretchable and is adhered to the said upper and lower layers to resist lateral expansion of the midsole under the influence of the said forces.

12. An athletic shoe as claimed in Claim 1 substantially as specifically described herein with reference to Figures 1 to 5 or Figures 1 to 3, 5 and 6 or Figures 1 to 3, 5 and 7 of the accompanying drawings.

13. A method of modifying an existing athletic running shoe having a polymeric foamed midsole, comprising the steps of cutting the midsole to provide a formation-receiving space lying between the upper and lower surfaces of the midsgle, inserting a stiff formation of pre-selected configuration into the said space to stiffen the midsole over a pre-selected region or surface area, and adhering the formation to the midsole.

14. A method as claimed in Claim 13 substantially as specifically described herein with reference to the accompanying drawings.

1 5. An athletic shoe whenever modified by a method as claimed in Claim 13 or Claim 14.

1 6. A shoe having a polymeric foamed midsole and a thin relatively stretch resistant or stiff formation located within the said midsole and extending over substantially the whole of the heel region thereof and extending forward therefrom to a region not extending beyond the first metatarsal head on the inside edge of the shoe and not extending beyond the cuboid on the outside edge of the shoe.

1 7. A stiffening formation for use in a shoe as claimed in the preceding claims comprising a stiffening board which relative to the foam midsole with which it is to be used is thin and stiff or non-stretchable and which is dimensioned and shaped to extend over substantially the whole of the heel region thereof and to extend forward therefrom to a region not extending beyond the first metatarsal head on the inside edge and not extending beyond the cuboid on the outside edge.

18. A stiffening formation as claimed in Claim 17 in which the front edge of the board is skived.

1 9. A stiffening formation as claimed in Claim 17 or 18 in which the outside corner of the heel is skived.

20. A stiffening formation as claimed in Claim 1 7 substantially as specifically described herein with reference to Figures 1, 2, 3 and 5 of the accompanying drawings.