EP0811330B1

EP0811330B1 - Shoe with naturally contoured sole

Info

Publication number: EP0811330B1
Application number: EP97250029A
Authority: EP
Inventors: Frampton E. Ellis Iii
Original assignee: Anatomic Research Inc
Current assignee: Anatomic Research Inc
Priority date: 1988-07-15
Filing date: 1989-07-14
Publication date: 2001-10-17
Anticipated expiration: 2009-07-14
Also published as: EP0983734B1; DE68929338D1; EP0424471B1; DE68929335D1; AU4060989A; ATE206884T1; HK1028939A1; JP2002101905A; JP3248151B2; EP0983734A1; WO1990000358A1; ATE207316T1; EP1038457B1; ATE209867T1; NZ229949A; DE68928347D1; EP1104658A1; EP1034714A2; KR900701188A; DE68929355D1

Abstract

A construction for a shoe (20), particularly an athletic shoe such as a running shoe, includes a sole (28) provided with at least one bulge having concavely rounded inner and outer surfaces (30, 31). The bulge may be located on a side of the shoe sole (28) at a location which substantially corresponds to the location of one of the essential structural support and propulsion elements of an intended wearer's foot when inside the shoe. The thickness of the bulge decreases gradually in at least one of an anterior or posterior direction to a lesser thickness, as viewed in a horizontal plane when the shoe sole (28) is in an upright, unloaded condition.

Description

Background of the Invention

This invention relates to a shoe, such as a street shoe, athletic shoe, and especially a running shoe with a contoured sole. More particularly, this invention relates to a novel contoured sole design for a running shoe which improves the inherent stability and efficient motion of the shod foot in extreme exercise. Still more particularly, this invention relates to a running shoe wherein the shoe sole conforms to the natural shape of the foot, particularly the sides, permitting the foot to react naturally with the ground as it would if the foot were bare, while continuing to protect and cushion the foot.
By way of introduction, barefoot populations universally have a very low incidence of running "overuse" injuries, despite very high activity levels. In contrast, such injuries are very common in shoe shod populations, even for activity levels well below "overuse". Thus, it is a continuing problem with a shod population to reduce or eliminate such injuries and to improve the cushioning and protection for the foot. It is primarily to an understanding of the reasons for such problems and to proposing a novel solution according to the invention to which this improved shoe is directed.
A wide variety of designs are available for running shoes which are intended to provide stability, but which lead to a constraint in the natural efficient motion of the foot and ankle. However, such designs which can accommodate free, flexible motion in contrast create a lack of control or stability. A popular existing shoe design incorporates an inverted, outwardly-flared shoe sole wherein the ground engaging surface is wider than the heel engaging portion. However, such shoes are unstable in extreme situations because the shoe sole, when inverted or on edge, immediately becomes supported only by the sharp bottom sole edge where the entire weight of the body, multiplied by a factor of approximately three at running peak, is concentrated. Since an unnatural lever arm and force moment are created under such conditions, the foot and ankle are destabilized and, in the extreme, beyond a certain point of rotation about the pivot point of the shoe sole edge, forcibly cause ankle strain. In contrast, the unshod foot is always in stable equilibrium without a comparable lever arm or force moment and, at its maximum range of inversion motion, about 20°, the base of support on the barefoot heel actually broadens substantially as the calcaneal tuberosity contacts the ground. This is in contrast to the conventionally available shoe sole bottom which maintains a sharp, unstable edge.
Existing running shoes interfere with natural foot and ankle biomechanics, disrupting natural stability and efficient natural motion. They do so by altering the natural position of the foot relative to the ground, during the load-bearing phase of running or walking. The foot in its natural, bare state is in direct contact with the ground, so its relative distance from the ground is obviously constant at zero. Even when the foot tilts naturally from side to side, either moderately when running or extremely when stumbling or tripping, the distance always remains constant at zero.
In contrast, existing shoes maintain a constant distance from the ground - the thickness of the shoe sole - only when they are perfectly flat on the ground. As soon as the shoe is tilted, the distance between foot and ground begins to change unnaturally, as the shoe sole pivots around the outside comer edge. With conventional athletic shoes, the distance most typically increases at first due to the flared sides and then decreases; many street shoes with relatively wide heel width follow that pattern, though some with narrower heels only decrease. All existing shoes continue to decrease the distance all the way down to zero, by tilting through 90 degrees, resulting in ankle sprains and breaks.
A corrected shoe sole design, however, avoids such unnatural interference by neutrally maintaining a constant distance between foot and ground, even when the shoe is tilted sideways, as if in effect the shoe sole were not there except to cushion and protect. Unlike existing shoes, the corrected shoe would move with the foot's natural sideways pronation and supination motion on the ground. To the problem of using a shoe sole to maintain a naturally constant distance during that sideways motion, there are two possible geometric solutions, depending upon whether just the lower horizontal plane of the shoe sole surface varies to achieve natural contour or both upper and lower surface planes vary.
In the two plane solution, the naturally contoured design, which will be described in Figures 1-23, both upper and lower surfaces or planes of the shoe sole vary to conform to the natural contour of the human foot. The two plane solution is the most fundamental concept and naturally most effective. It is the only pure geometric solution to the mathematical problem of maintaining constant distance between foot and ground, and the most optimal, in the same sense that round is only shape for a wheel and perfectly round is most optimal. On the other hand, it is the least similar to existing designs of the two possible solutions and requires computer aided design and injection molding manufacturing techniques.
U.S. Patent No. 4,305,212 discloses a unitary shoe sole S having a convexly rounded inner surface 20, relative to a section of the sole directly adjacent to the inner surface. The shoe sole S also includes rounded portions of the outer surface 21 as shown in Figs. 8-11. The sole S is integrally formed as one body from a flexible and resiliently depressible elastomer that is adapted to be distorted by force and to return to its original form at a predetermined rate. See col. 6, lines 17-29. Fig. 12, a cross-section at the heel area, shows the sole S provided with a circumferential rib B which establishes an instep cavity C which permits sole deformation to simulate running in the sand, a key feature of the invention of this patent as discussed with regard to Fig. 4 and at col. 8, lines 39-44.
It is thus an overall objective of this invention to provide a novel shoe design which approximates the barefoot. It has been discovered, by investigating the most extreme range of ankle motion to near the point of ankle sprain, that the abnormal motion of an inversion ankle sprain, which is a tilting to the outside or an outward rotation of the foot, is accurately simulated while stationary. With this observation, it can be seen that the extreme range stability of the conventionally shod foot is distinctly inferior to the barefoot and that the shoe itself creates a gross instability which would otherwise not exist.
Even more important, a normal barefoot running motion, which approximately includes a 7° inversion and a 7° eversion motion, does not occur with shod feet, where a 30° inversion and eversion is common. Such a normal barefoot motion is geometrically unattainable because the average running shoe heel is approximately 60% larger than the width of the human heel. As a result, the shoe heel and the human heel cannot pivot together in a natural manner; rather, the human heel has to pivot within the shoe but is resisted from doing so by the shoe heel counter, motion control devices, and the lacing and binding of the shoe upper, as well as various types of anatomical supports interior to the shoe.
Thus, it is an overall objective to provide an improved shoe design which is not based on the inherent contradiction present in current shoe designs which make the goals of stability and efficient natural motion incompatible and even mutually exclusive. It is another overall object of the invention to provide a new contour design which simulates the natural barefoot motion in running and thus avoids the inherent contradictions in current designs.
It is an objective of this invention to provide a new stable shoe design wherein the heel lift or wedge increases the thickness of the shoe sole in the sagittal plane or toe taper decreases the thickness of the shoe sole in the sagittal plane.
It is another objective of this invention to provide a shoe having a shoe sole having a naturally contoured design as described wherein the sides of the shoe sole are abbreviated to essential structural support and propulsion elements to provide flexibility and in which the density of the shoe sole may be increased to compensate for increased loading.
It is another objective of this invention to provide a shoe sole design which includes a plurality of freely articulating essential structural support elements in the sole of the shoe which are consistent with the sole of the foot and are free to move independently of each other to follow the motion of the freely articulating bone structures of the foot.
It is still another object of this invention to provide a shoe sole of the type described wherein the material of the sole is removed except beneath essential structural support elements of the foot.
It is another object of this invention to provide a shoe sole of the type described with treads having an outer or a base surface which follows the theoretically ideal stability plane.
The present invention achieves these objects by providing a shoe sole including a bottom sole, a midsole which is softer than the bottom sole, and a heel lift. The sole inner surface includes a portion that is convexly rounded relative to a section of the shoe sole located directly adjacent to the convexly rounded portion, and the sole outer surface includes an uppermost portion which extends to at least the height of the lowest point of the inner surface, both as viewed in a frontal plane cross-section when the shoe sole is in an upright, unloaded condition. The sole outer surface includes at least one concavely rounded portion which extends down a sole side to at least proximate a lowest point of the shoe sole side, the concavity being determined relative to an inner section of the sole located directly adjacent to the concavely rounded portion, also as viewed in a frontal plane cross-section when the shoe sole is in an upright, unloaded condition. The concavely rounded portion of the sole outer surface includes midsole thereby providing improved stability. The midsole part of the concavely rounded portion of the outer surface extends below a sidemost extent of the shoe sole side.
These and other objectives of the invention will become apparent from a detailed description of the invention which follows taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

In the drawings:
Fig. 1 is a perspective view of a typical running shoe known to the prior art to which the invention is applicable.
Fig. 2 shows, in Figs. 2A and 2B, the obstructed natural motion of the shoe heel in frontal planar cross section rotating inwardly or outwardly with the shoe sole having a flared bottom in a conventional prior art design such as in Fig. 1; and in Figs. 2C and 2D, the efficient motion of a narrow rectangular shoe sole design.
Fig. 3 is a drawn comparison between a conventional flared sole shoe of the prior art and the contoured shoe sole design according to the invention.
Fig. 4 shows, in Figs. 4A-4C, the extremely stable conditions for the novel shoe sole according to the invention in its neutral and extreme situations.
Fig. 5 is a side cross-sectional view of the naturally contoured sole side showing in Fig. 5A how the sole maintains a constant distance from the ground during rotation of the shoe edge; and showing in Fig. 5B how a conventional shoe sole side cannot maintain a constant distance from the ground.
Fig. 6 shows, in Figs. 6A-6E, a plurality of side sagittal plane cross-sectional views showing examples of conventional sole thickness variations to which the invention can be applied.
Fig. 7 shows, in Figs. 7A-7D, frontal plane cross-sectional views of the shoe sole according to the invention showing a theoretically ideal stability plane and truncations of the sole side contour to reduce shoe bulk.
Fig. 8 shows, in Figs. 8A-8C, the contoured sole design according to the invention when applied to various tread and cleat patterns.
Fig. 9 illustrates, in a rear view, an application of the sole according to the invention to a shoe to provide an aesthetically pleasing and functionally effective design.
Fig. 10 shows a fully contoured shoe sole design that follows the natural contour of the bottom of the foot as well as the sides.
Fig. 11 is a diagrammatic frontal plane cross-sectional view of static forces acting on the ankle joint and its position relative to the shoe sole according to the invention during normal and extreme inversion and eversion motion.
Fig. 12 is a diagrammatic frontal plane view of a plurality of moment curves of the center of gravity for various degrees of inversion for the shoe sole according to the invention, and contrasted to the motions shown in Fig. 2.
Fig. 13 shows, in Figs. 13A and 13B, a rear diagrammatic view of a human heel, as relating to a conventional shoe sole (Fig. 13A) and to the sole of the invention (Fig. 13B).
Fig. 14 shows the naturally contoured sides design extended to the other natural contours underneath the load-bearing foot such as the main longitudinal arch.
Fig. 15 illustrates the fully contoured shoe sole design extended to the bottom of the entire non-load-bearing foot.
Fig. 16 shows the fully contoured shoe sole design abbreviated along the sides to only essential structural support and propulsion elements.
Fig. 17 shows a method of establishing the theoretically ideal stability plane using a perpendicular to a tangent method.
Fig. 18 shows a circle radius method of establishing the theoretically ideal stability plane.
Fig. 19 illustrates an alternate embodiment of the invention wherein the sole structure deforms in use to follow a theoretically ideal stability plane according to the invention during deformation.
Fig. 20 shows an embodiment wherein the contour of the sole according to the invention is approximated by a plurality of line segments.
Fig. 21 shows a shoe sole design that allows for unobstructed natural eversion/inversion motion by providing torsional flexibility in the instep area of the shoe sole.
Fig. 22 shows several embodiments wherein the bottom sole includes most or all of the special contours of the new designs and retains a flat upper surface.
Fig. 23 shows, in Figs. 23A - 23C, an enhancement applied to the naturally contoured sides embodiment of the invention.

Detailed Description of the Preferred Embodiment

A perspective view of an athletic shoe, such as a typical running shoe, according to the prior art, is shown in Fig. 1 wherein a running shoe 20 includes an upper 21 and a sole 22. Typically, such a sole includes a truncated outwardly flared construction of the type best seen in Fig. 2 wherein the lower portion 22a of the sole heel is significantly wider than the upper portion 22b where the sole 22 joins the upper 21. A number of alternative sole designs are known to the art, including the design shown in U.S. Patent No. 4,449,306 to Cavanagh wherein an outer portion of the sole of the running shoe includes a rounded portion having a radius of curvature of about 20mm. The rounded portion lies along approximately the rear-half of the length of the outer side of the midsole and heel edge areas wherein the remaining border area is provided with a conventional flaring with the exception of a transition zone. The U.S. Patent to Misevich, No. 4,557,059, also shows an athletic shoe having a contoured sole bottom in the region of the first foot strike, in a shoe which otherwise uses an inverted flared sole.
In such prior art designs, and especially in athletic and in running shoes, the typical design attempts to achieve stability by flaring the heel as shown in Figs. 2A and 2B to a width of, for example, 3 to 3-1/2 inches on the lower portion 22a of the sole heel of the average male shoe size (10D). On the other hand, the width of the corresponding human heel foot print, housed in the upper 21, is only about 2.25 in. for the average foot. Therefore, a mismatch occurs in that the heel is locked by the design into a firm shoe heel counter which supports the human heel by holding it tightly and which may also be reinforced by motion control devices to stabilize the heel. Thus, for natural motion as is shown in Figs. 2A and 2B, the human heel would normally move in a normal range of motion of approximately 15°, but as shown in Figs. 2A and 2B the human heel cannot pivot except within the shoe and is resisted by the shoe. Thus, Fig. 2A illustrates the impossibility of pivoting about the center edge of the human heel as would be conventional for barefoot support about a point 23 defined by a line 23a perpendicular to the heel and intersecting the bottom edge of upper 21 at a point 24. The lever arm force moment of the flared sole is at a maximum at 0° and only slightly less at a normal 7° inversion or eversion and thus strongly resists such a natural motion as is illustrated in Figs. 2A and 2B. In Fig. 2A, the outer edge of the heel must compress to accommodate such motion. Fig. 2B illustrates that normal natural motion of the shoe is inefficient in that the center of gravity of the shoe, and the shod foot, is forced upwardly, as discussed later in connection with Fig. 12.
A narrow rectangular shoe sole design of heel width approximating human heel width is also known and is shown in Figs. 2C and 2D. It appears to be more efficient than the conventional flared sole shown in Figs. 2A and 2B. Since the shoe sole width is the same as human sole width, the shoe can pivot naturally with the normal 7° inversion/eversion motion of the running barefoot. In such a design, the lever arm length and the vertical motion of the center of gravity are approximately half that of the flared sole at a normal 7° inversion/eversion running motion. However, the narrow, human heel width rectangular shoe design is extremely unstable and therefore prone to ankle sprain, so that it has not been well received. Thus, neither of these wide or narrow designs is satisfactory.
The shoe sole thickness is defined as the shortest distance (s) between any point on the inner surface 30 of the shoe sole 28 and the outer surface 31 (Figs. 17 and 18 will discuss measurement methods more fully).
Fig. 3 thus contrasts in frontal plane cross section the conventional flared sole 22 shown in phantom outline and illustrated in Fig. 2 with the contoured shoe sole 28 according to the invention.
Fig. 4 is suitable for analyzing the shoe sole design according to the applicant's invention by contrasting the neutral situation shown in Fig. 4A with the extreme situations shown in Figs. 4B and 4C. Unlike the sharp sole edge of a conventional shoe as shown in Fig. 2, the effect of the applicant's invention having a naturally contoured side 28a is totally neutral allowing the shod foot to react naturally with the ground 43, in either an inversion or eversion mode. This occurs in part because of the unvarying thickness along the shoe sole edge which keeps the foot sole equidistant from the ground in a preferred case. Moreover, because the shape of the edge 31a of the shoe contoured side 28a is exactly like that of the edge of the foot, the shoe is enabled to react naturally with the ground in a manner as closely as possible simulating the foot. Thus, in the neutral position shown in Fig. 4, any point 40 on the surface of the shoe sole 30b closest to ground lies at a distance (s) from the ground surface 43. That distance (s) remains constant even for extreme situations as seen in Figs. 4B and 4C.
A main point of the applicant's invention, as is illustrated in Figs. 4B and 4C, is that the design shown is stable in an in extremis situation. The theoretically ideal plane of stability is where the stability plane is defined as sole thickness which is constant under all load-bearing points of the foot sole for any amount from 0° to 90° rotation of the sole to either side or front and back. In other words, as shown in Fig. 4, if the shoe is tilted from 0° to 90° to either side or from 0° to 90° forward or backward representing a 0° to 90° foot dorsiflexion or 0° to 90° plantarflexion, the foot will remain stable because the sole thickness (s) between the foot and the ground always remain constant because of the exactly contoured quadrant sides. By remaining a constant distance from the ground, the stable shoe allows the foot to react to the ground as if the foot were bare while allowing the foot to be protected and cushioned by the shoe. In its preferred embodiment, the new naturally contoured sides will effectively position and hold the foot onto the load-bearing foot print section of the shoe sole, reducing or eliminating the need for heel counters and other relatively rigid motion control devices.
Fig. 5A illustrates how the inner edge 30a of the naturally contoured sole side 28a is maintained at a constant distance (s) from the ground through various degrees of rotation of the edge 31a of the shoe sole such as is shown in Fig. 4. Figure 5B shows how a conventional shoe sole pivots around its lower edge 42, which is its center of rotation, instead of around the upper edge 41, which, as a result, is not maintained at constant distance (s) from the ground, as with the invention, but is lowered to .7(s) at 45° rotation and to zero at 90° rotation.
Fig. 6 shows typical conventional sagittal plane shoe sole thickness variations, such as heel lifts or wedges 38, or toe taper 38a, or full sole taper 38b, in Figs. 6A-6E and how the naturally contoured sides 28a equal and therefore vary with those varying thicknesses. As shown in Fig. 6A, heel lift 38 has a thickness (s¹) in the heel area to increase the sole thickness to (s + s¹). In the midtarsal area, heel lift 38 has a decreased thickness (s²).
Fig. 7 illustrates an embodiment of the invention which utilizes varying portions of the theoretically ideal stability plane 51 in the naturally contoured sides 28a in order to reduce the weight and bulk of the sole, while accepting a sacrifice in some stability of the shoe. Thus, Fig. 7A illustrates the preferred embodiment wherein the outer edge 31a of the naturally contoured sides 28a follows a theoretically ideal stability plane 51. The outer edge 31 a and the outer surface of the sole 31b lie along the theoretically ideal stability plane 51. The theoretically ideal stability plane 51 is defined as the plane of the outer surface 31 of the shoe sole 28, wherein the shoe sole conforms to the natural shape of the foot, particularly the sides, and has a constant thickness in frontal plane cross sections. As shown in Fig. 7B, an engineering trade-off results in an abbreviation within the theoretically ideal stability plane 51 by forming a naturally contoured upper side surface 53a approximating the natural contour of the foot (or more geometrically regular, which is less preferred) at an angle relative to the upper plane of the shoe sole 28 so that only a smaller portion of the contoured side 28a defined by the constant thickness lying along the surface 31a is coplanar with the theoretically ideal stability plane 51. Figs. 7C and 7D show similar embodiments wherein each engineering trade-off shown results in progressively smaller portions of contoured side 28a, which lies along the theoretically ideal stability plane 51. The portion of the surface 31a merges into the upper side surface 53a of the naturally contoured side.
The embodiment of Fig. 7 may be desirable for portions of the shoe sole which are less frequently used so that the additional part of the side is used less frequently. For example, a shoe may typically roll out laterally, in an inversion mode, to about 20° on the order of 100 times for each single time it rolls out to 40°. For a basketball shoe, shown in Fig. 7B, the extra stability is needed. Yet, the added shoe weight to cover that infrequently experienced range of motion is about equivalent to covering the frequently encountered range. Since, in a racing shoe this weight might not be desirable, an engineering trade-off of the type shown in Fig. 7D is possible. A typical running/jogging shoe is shown in Fig. 7C. The range of possible variations is limitless.
Fig. 8 shows the theoretically ideal stability plane 51 in defining embodiments of the shoe sole having differing tread or cleat patterns. Thus, Fig. 8 illustrates that the invention is applicable to shoe soles having conventional bottom treads. Accordingly, Fig. 8A is similar to Fig. 7B further including a tread portion 60, while Fig. 8B is also similar to Fig. 7B wherein the sole includes a cleated portion 61. The surface 63 to which the cleat bases are affixed should preferably be on the same plane and parallel the theoretically ideal stability plane 51, since in soft ground that surface rather than the cleats become load-bearing. The embodiment in Fig. 8C is similar to Fig. 7C showing still an alternative tread construction 62. In each case, the load-bearing outer surface of the tread or cleat pattern 60-62 lies along the theoretically ideal stability plane 51.
Fig. 9 shows, in a rear cross sectional view, the application of the invention to a shoe to produce an aesthetically pleasing and functionally effective design. Thus, a practical design of a shoe incorporating the invention is feasible, even when applied to shoes incorporating heel lifts 38 and a combined midsole and outersole 39. Thus, use of a sole surface and sole outer contour which track the theoretically ideal stability plane does not detract from the commercial appeal of shoes incorporating the invention.
Fig. 10 shows a fully contoured shoe sole design that follows the natural contour of all of the foot, the bottom as well as the sides. The fully contoured shoe sole assumes that the resulting slightly rounded bottom when unloaded will deform under load and flatten just as the human foot bottom is slightly rounded unloaded but flattens under load; therefore, shoe sole material must be of such composition as to allow the natural deformation following that of the foot. The design applies particularly to the heel, but to the rest of the shoe sole as well. By providing the closest match to the natural shape of the foot, the fully contoured design allows the foot to function as naturally as possible. Under load, Fig. 10 would deform by flattening to look essentially like Fig. 9. Seen in this light, the naturally contoured side design in Fig. 9 is a more conventional, conservative design that is a special case of the more general fully contoured design in Fig. 10, which is the closest to the natural form of the foot, but the least conventional. The amount of deformation flattening used in the Fig. 9 design, which obviously varies under different loads, is not an essential element of the applicant's invention.
Figs. 9 and 10 both show in frontal plane cross section the essential concept underlying this invention, the theoretically ideal stability plane, which is also theoretically ideal for efficient natural motion of all kinds, including running, jogging or walking. Fig. 10 shows the most general case of the invention, the fully contoured design, which conforms to the natural shape of the unloaded foot. For any given individual, the theoretically ideal stability plane 51 is determined, first, by the desired shoe sole thickness (s) in a frontal plane cross section, and, second, by the natural shape of the individual's foot surface 29.
For the special case shown in Fig. 9, the theoretically ideal stability plane for any particular individual (or size average of individuals) is determined, first, by the given frontal plane cross section shoe sole thickness (s); second, by the natural shape of the individual's foot; and, third, by the frontal plane cross section width of the individual's load-bearing footprint, which is defined as the upper surface of the shoe sole that is in physical contact with and supports the human foot sole.
The theoretically ideal stability plane for the special case is composed conceptually of two parts. Shown in Fig. 9, the first part is a line segment 31b of equal length and parallel to 30b at a constant distance (s) equal to shoe sole thickness. This corresponds to a conventional shoe sole directly underneath the human foot, and also corresponds to the flattened portion of the bottom of the load-bearing foot sole 28b. The second part is the naturally contoured stability side outer edge 31a located at each side of the first part, line segment 31b. Each point on the contoured side outer edge 31a is located at a distance which is exactly shoe sole thickness (s) from the closest point on the contoured side inner edge 30a.
Fig. 11 illustrates in a curve 70 the range of side to side inversion/eversion motion of the ankle center of gravity 71 from the shoe according to the invention shown in frontal plane cross section at the ankle. Thus, in a static case where the center of gravity 71 lies at approximately the mid-point of the sole, and assuming that the shoe inverts or everts from 0° to 20° to 40°, as shown in progressions 16A, 16B and 16C, the locus of points of motion for the center of gravity 71 thus defines the curve 70 wherein the center of gravity 71 maintains a steady level motion with no vertical component through 40° of inversion or eversion. For the embodiment shown, the shoe sole stability equilibrium point is at 28° (at point 74) and in no case is there a pivoting edge to define a rotation point as in the case of Fig. 2. The inherently superior side to side stability of the design provides pronation control (or eversion), as well as lateral (or inversion) control. In marked contrast to conventional shoe sole designs, the applicant's shoe design creates virtually no abnormal torque to resist natural inversion/eversion motion or to destabilize the ankle joint.
Fig. 12 thus compares the range of motion of the center of gravity for the invention, as shown in curve 70, in comparison to curve 80 for the conventional wide heel flare and a curve 82 for a narrow rectangle the width of a human heel. Since the shoe stability limit is 28° in the inverted mode, the shoe sole is stable at the 20° approximate barefoot inversion limit. That factor, and the broad base of support rather than the sharp bottom edge of the prior art, make the contour design stable even in the most extreme case as shown in progressions 16A-16C and permit the inherent stability of the barefoot to dominate without interference, unlike existing designs, by providing constant, unvarying shoe sole thickness in frontal plane cross sections. The stability superiority of the contoured side design is thus clear when observing how much flatter its center of gravity curve 70 is than in existing popular wide flare design 80. The curve 70 demonstrates that the contoured side design has significantly more efficient natural 7° inversion/eversion motion than the narrow rectangle design 82 the width of a human heel, and very much more efficient than the conventional wide flare design 80; at the same time, the contoured side design is more stable in extremis than either conventional design because of the absence of destabilizing torque.
Fig. 13A illustrates, in a pictorial fashion, a comparison of a cross section at the ankle joint of a conventional shoe with a cross section of a shoe according to the invention when engaging a heel. As seen in Fig. 13A, when the heel of the foot 27 of the wearer engages an upper surface of the shoe sole 22, the shape of the foot heel and the shoe sole is such that the conventional shoe sole 22 conforms to the contour of the ground 43 and not to the contour of the sides of the foot 27. As a result, the conventional shoe sole 22 cannot follow the natural 7° inversion/eversion motion of the foot, and that normal motion is resisted by the shoe upper 21, especially when strongly reinforced by firm heel counters and motion control devices. This interference with natural motion represents the fundamental misconception of the currently available designs. That misconception on which existing shoe designs are based is that, while shoe uppers are considered as a part of the foot and conform to the shape of the foot, the shoe sole is functionally conceived of as a part of the ground and is therefore shaped like the ground, rather than the foot.
In contrast, the new design, as illustrated in Fig. 13B, illustrates a correct conception of the shoe sole 28 as a part of the foot and an extension of the foot, with shoe sole sides contoured exactly like those of the foot, and with the frontal plane thickness of the shoe sole between the foot and the ground always the same and therefore completely neutral to the natural motion of the foot. With the correct basic conception, as described in connection with this invention, the shoe can move naturally with the foot, instead of restraining it, so both natural stability and natural efficient motion coexist in the same shoe, with no inherent contradiction in design goals.
Thus, the contoured shoe design of the invention brings together in one shoe design the cushioning and protection typical of modem shoes, with the freedom from injury and functional efficiency, meaning speed, and/or endurance, typical of barefoot stability and natural freedom of motion. Significant speed and endurance improvements are anticipated, based on both improved efficiency and on the ability of a user to train harder without injury.
These figures also illustrate that the shoe heel cannot pivot plus or minus 7 degrees with the prior art shoe of Fig. 13A. In contrast, the shoe heel in the embodiment of Fig. 13B pivots with the natural motion of the foot heel.
Figs. 14A-D illustrate, in frontal plane cross sections, the naturally contoured sides design extended to the other natural contours underneath the load-bearing foot, such as the main longitudinal arch, the metatarsal (or forefoot) arch, and the ridge between the heads of the metatarsals (forefoot) and the heads of the distal phalanges (toes). As shown, the shoe sole thickness remains constant as the contour of the shoe sole follows that of the sides and bottom of the load-bearing foot. Fig. 14E shows a sagittal plane cross section of the shoe sole conforming to the contour of the bottom of the load-bearing foot, with thickness varying according to the heel lift 38. Fig. 14F shows a horizontal plane top view of the left foot that shows the areas 85 of the shoe sole that correspond to the flattened portions of the foot sole that are in contact with the ground when load-bearing. Contour lines 86 and 87 show approximately the relative height of the shoe sole contours above the flattened load-bearing areas 85 but within roughly the peripheral extent 35 of the upper surface 30 of sole 28. A horizontal plane bottom view (not shown) of Fig. 14F would be the exact reciprocal or converse of Fig. 14F (i.e. peaks and valleys contours would be exactly reversed).
Figs. 15A-D show, in frontal plane cross sections, the fully contoured shoe sole design extended to the bottom of the entire non-load-bearing foot 27. Fig. 15C shows that in the midtarsal area, the sole 28 may include a concavely rounded outer surface portion on only one of the lateral and medial sole sides which does not extend to the middle portion of the sole 28. Fig. 15E shows a sagittal plane cross section. The shoe sole contours underneath the foot 27 are the same as Figs. 14A-E except that there are no flattened areas 85 corresponding to the flattened areas of the load-bearing foot 27. The exclusively rounded contours of the shoe sole follow those of the unloaded foot 27. A heel lift 38, the same as that of Fig. 14, is incorporated in this embodiment, but is not shown in Fig. 15.
Fig. 16 shows the horizontal plane top view of the left foot corresponding to the fully contoured design described in Figs. 15A-E, but abbreviated along the sides to only essential structural support and propulsion elements. Shoe sole material density can be increased in the unabbreviated essential elements to compensate for increased pressure loading there. The essential structural support elements are the base and lateral tuberosity of the calcaneus 95, the heads of the first and fifth metatarsals 96, and the base of the fifth metatarsal 97. They must be supported both underneath and to the outside for stability. The essential propulsion element is the head of first distal phalange 98. As shown in Figs. 15-16, the sole 28 can include concavely rounded portions 95a, 95b, 95c and 95d at the base and lateral tuberosity of the calcaneus 95, concavely rounded portions 96c, 96d, 96e and 96g at the heads of the first and fifth metatarsals 96, and concavely rounded portions 98, 98a at the head of the first distal phalange 98. As shown in Fig. 15, the sole 28 can include an indentation 96h in the middle portion of the forefoot area as well as an indentation 96f in the forefoot area. Fig. 16 also shows that the thickness of the sole (28) at the concavely rounded portions 95b, 95c, 96d, 96e and 98 decreases gradually, as viewed in a horizontal plane, to form areas of lesser sole thickness 95e, 95f, 96a, 96b, 97a and 98a. As seen in Fig. 16, the concavely rounded portions of the shoe sole 28 may extend to the front 44 and the rear 45 of the shoe sole 28.
As shown in Fig. 15E, shoe sole 28 may also include concavely rounded portions, as viewed in a sagittal plane cross-section and one concavely rounded portion may extend through a lowermost heel area 28". Also, the thickness of shoe sole 28 may remain constant from the lowermost heel area 28" to a rearmost heel extent 34 and then decrease gradually and continuously at an upper rear heel portion 46, all as viewed in a sagittal plane cross-section.
The medial (inside) and lateral (outside) sides supporting the base of the calcaneus are shown in Fig. 16 oriented roughly along either side of the horizontal plane subtalar ankle joint axis, but can be located also more conventionally along the longitudinal axis of the shoe sole. Fig. 16 shows that the naturally contoured stability sides need not be used except in the identified essential areas. Weight savings and flexibility improvements can be made by omitting the non-essential stability sides. Contour lines 86 through 89 show approximately the relative height of the shoe sole contours within roughly the peripheral extent 35 of the undeformed inner surface 30 of shoe sole 28. A horizontal plane bottom view (not shown) of Fig. 16 would be the exact reciprocal or converse of Fig. 16 (i.e. peaks and valleys contours would be exactly reversed).
Fig. 17 shows a method of measuring shoe sole thickness to be used to construct the theoretically ideal stability plane of the naturally contoured side design. The constant shoe sole thickness of this design is measured at any point p1, p2 on the contoured sides along a line that, first, is perpendicular to a line tangent to that point on the surface of the naturally contoured side of the foot sole and, second, that passes through the same foot sole surface point.
Fig. 18 illustrates another approach to constructing the theoretically ideal stability plane, and one that is easier to use, the circle radius method. By that method, the pivot point (circle center) of a compass is placed at the beginning of the foot sole's natural side contour (frontal plane cross section) and roughly a 90° arc (or much less, if estimated accurately) of a circle of radius equal to (s) or shoe sole thickness is drawn describing the area farthest away from the foot sole contour. That process is repeated all along the foot sole's natural side contour at very small intervals (the smaller, the more accurate). When all the circle sections are drawn, the outer edge farthest from the foot sole contour (again, frontal plane cross section) is established at a distance of "s" and that outer edge coincides with the theoretically ideal stability plane. Both this method and that described in Fig. 17 would be used for both manual and CAD/CAM design applications.
The shoe sole according to the invention can be made by approximating the contours, as indicated in Figs. 19A and 19B. Fig. 19A shows a frontal plane cross section of a design wherein the sole material in areas 107 is so relatively soft that it deforms easily to the contour of shoe sole 28 of the proposed invention. In the proposed approximation as seen in Fig. 19B, the heel cross section includes a sole upper surface 101 and a bottom sole edge surface 102 following when deformed an inset theoretically ideal stability plane 51. The sole edge surface 102 terminates in a laterally extending portion 103 joined to the heel of the sole 28. The laterally-extending portion 103 is made from a flexible material and structured to cause its lower surface 102 to terminate during deformation to parallel the inset theoretically ideal stability plane 51. Sole material in specific areas 107 is extremely soft to allow sufficient deformation. Thus, in a dynamic case, the outer edge contour assumes approximately the theoretically ideal stability shape described above as a result of the deformation of the portion 103. The top surface 101 similarly deforms to approximately parallel the natural contour of the foot as described by surfaces 30a and 30b.
It is presently contemplated that the controlled or programmed deformation can be provided by either of two techniques. In one, the shoe sole sides, at especially the midsole, can be cut in a tapered fashion or grooved so that the bottom sole bends inwardly under pressure to the correct contour. The second uses an easily deformable material 107 in a tapered manner on the sides to deform under pressure to the correct contour. While such techniques produce stability and natural motion results which are a significant improvement over conventional designs, they are inherently inferior to contours produced by simple geometric shaping. First, the actual deformation must be produced by pressure which is unnatural and does not occur with a bare foot and second, only approximations are possible by deformation, even with sophisticated design and manufacturing techniques, given an individual's particular running gait or body weight. Thus, the deformation process is limited to a minor effort to correct the contours from surfaces approximating the ideal curve in the first instance.
The theoretically ideal stability plane can also be approximated by a plurality of line segments 110, such as tangents, chords, or other lines, as shown in Fig. 20. Both the upper surface of the shoe sole 28, which coincides with the side of the foot 30a, and the bottom surface 31a of the naturally contoured side can be approximated. While a single flat plane 110 approximation may correct many of the biomechanical problems occurring with existing designs, because it can provide a gross approximation of the both natural contour of the foot and the theoretically ideal stability plane 51, the single plane approximation is presently not preferred, since it is the least optimal. By increasing the number of flat planar surfaces formed, the curve more closely approximates the ideal exact design contours, as previously described. Single and double plane approximations are shown as line segments in the cross section illustrated in Fig. 20.
Fig. 21 shows a shoe sole design that allows for unobstructed natural inversion/eversion motion of the calcaneus by providing maximum shoe sole flexibility particularly between the base of the calcaneus 125 (heel) and the metatarsal heads 126 (forefoot) along an axis 120. An unnatural torsion occurs about that axis if flexibility is insufficient so that a conventional shoe sole interferes with the inversion/eversion motion by restraining it. The object of the design is to allow the relatively more mobile (in eversion and inversion) calcaneus to articulate freely and independently from the relatively more fixed forefoot, instead of the fixed or fused structure or lack of stable structure between the two in conventional designs. In a sense, freely articulating joints are created in the shoe sole that parallel those of the foot. The design is to remove nearly all of the shoe sole material between the heel and the forefoot, except under one of the previously described essential structural support elements, the base of the fifth metatarsal 97. An optional support for the main longitudinal arch 121 may also be retained for runners with substantial foot pronation, although would not be necessary for many runners. The forefoot can be subdivided (not shown) into its component essential structural support and propulsion elements, the individual heads of the metatarsal and the heads of the distal phalanges, so that each major articulating joint set of the foot is paralleled by a freely articulating shoe sole support propulsion element, an anthropomorphic design; various aggregations of the subdivisions are also possible. An added benefit of the design is to provide better flexibility along axis 122 for the forefoot during the toe-off propulsive phase of the running stride, even in the absence of any other embodiments of the applicant's invention; that is, the benefit exists for conventional shoe sole designs.
Fig. 21A shows in sagittal plane cross section a specific design maximizing flexibility, with large non-essential sections removed for flexibility and connected by only a top layer (horizontal plane) of non-stretching fabric 123 like Dacron polyester or Kevlar. Fig. 21B shows another specific design with a thin top sole layer 124 instead of fabric and a different structure for the flexibility sections: a design variation that provides greater structural support, but less flexibility, though still much more than conventional designs. Not shown is a simple, minimalist approach, which is comprised of single frontal plane slits in the shoe sole material (all layers or part): the first midway between the base of the calcaneus and the base of the fifth metatarsal, and the second midway between that base and the metatarsal heads. Fig. 21C shows a bottom view (horizontal plane) of the inversion/eversion flexibility design.
It is presently contemplated that the controlled or programmed deformation can be provided by either of two techniques. In one, the shoe sole sides, at especially the midsole, can be cut in a tapered fashion or grooved so that the bottom sole bends inwardly under pressure to the correct contour. The second uses an easily deformable material in a tapered manner on the sides to deform under pressure to the correct contour. While such techniques produce stability and natural motion results which are a significant improvement over conventional designs, they are inherently inferior to contours produced by simple geometric shaping. First, the actual deformation must be produced by pressure which is unnatural and does not occur with a bare foot and second, only approximations are possible by deformation, even with sophisticated design and manufacturing techniques, given an individual's particular running gait or body weight. Thus, the deformation process is limited to a minor effort to correct the contours from surfaces approximating the ideal curve in the first instance.
Fig. 22 shows a non-optimal but interim or low cost approach to shoe sole construction, whereby the midsole and heel lift 127 are produced conventionally, or nearly so (at least leaving the midsole bottom surface flat, though the sides can be contoured), while the bottom or outer sole 128 includes most or all of the special contours 25 of the new design which, as shown in Fig. 22A, extend to a lowest point (28') of a lowermost side section of the outer surface 31. Not only would that completely or mostly limit the special contours 25 to the bottom sole 128, which would be molded specially, it would also ease assembly, since two flat surfaces of the bottom of the midsole 127 and the top of the bottom sole 128 could be mated together with less difficulty than two contoured surfaces, as would be the case otherwise. The advantage of this approach is seen in the naturally contoured design example illustrated in Fig. 22A, which shows some contours on the relatively softer midsole sides which extend to and through the sidemost extent 28a' of the sole side and form an uppermost portion 53a' of upper side surface 53a, which are subject to less wear but benefit from greater traction for stability and ease of deformation, while the relatively harder contoured bottom sole 128 provides good wear for the load-bearing areas. As shown in Fig. 22A, the uppermost section 54 of midsole 127 extends to and above the height of a lowest point 30' of the same sole side to an uppermost extent 54' of midsole 127. The contours on the sides form a concavely rounded portion of the outer surface 31, the concavity being relative to an inner section of the sole 28 directly adjacent to the concavely rounded portion, and a convexly rounded portion of inner surface 30, the convexity being determined relative to a section of the sole 28 directly adjacent to the convexly rounded portion of the inner surface 30. The portion of sole 28 bounded by the convexly rounded inner surface portion and the concavely rounded outer surface portion is concavely rounded relative to an intended wearer's foot location inside the shoe, all as shown in Fig. 22A.
Also shown in Fig. 22A is that the shoe sole 28 includes a sidemost lateral section 58 located outside a vertical line 59 at the sidemost extent 30" of the lateral side of the inner surface 30 of the shoe sole 28, and a sidemost medial section 48 located outside a vertical line 49 of the sidemost extent 30" of the medial side of the inner surface 30 of the shoe sole 28. The midsole 127 extends into the sidemost lateral and medial sections 58, 48, as shown.
Fig. 22B shows in a quadrant side design the concept applied to conventional street shoe heels, which are usually separated from the forefoot by a hollow instep area under the main longitudinal arch. Fig. 22C shows in frontal plane cross section the concept applied to the quadrant sided or single plane design and indicating in Fig. 22D in the shaded area 129 of the bottom sole 128 that portion which should be honeycombed (axis on the horizontal plane) to reduce the density of the relatively hard outer sole 128 to that of the midsole material to provide for relatively uniform shoe density. Fig. 22E shows in bottom view the outline 36 of a bottom sole 128 made from flat material which can be conformed topologically to a contoured midsole of either the one or two plane designs by limiting the side areas to be mated to the essential support areas discussed in Fig. 16; by that method, the contoured midsole and flat bottom sole surfaces can be made to join satisfactorily by coinciding closely, which would be topologically impossible if all of the side areas were retained on the bottom sole 128.
Figs. 23A-23C, frontal plane cross sections, illustrate the inner shoe sole stability sides enhancement. The enhancement positions and stabilizes the foot relative to the shoe sole 28, and maintains the constant shoe sole thickness (s) of the naturally contoured sides 28a design, as shown in Figs. 23B and 23C; Fig. 23A shows a conventional design. The inner shoe sole stability sides 131 conform to the natural contour of the foot sides 29, which determine the theoretically ideal stability plane 51 for the shoe sole thickness (s).
Thus, it will clearly be understood by those skilled in the art that the foregoing description has been made in terms of the preferred embodiment and various changes and modifications may be made without departing from the scope of the present invention which is to be defined by the appended claims.

Claims

A shoe sole (28) for a shoe, including:

a bottom sole (128);

a midsole (127) which is softer than the bottom sole (128);

a heel lift (127);

an inner surface (30) including at least one portion that is convexly rounded relative to a section of the shoe sole (28) located directly adjacent to the convexly rounded portion of the inner surface (30), as viewed in a frontal plane cross-section, when the shoe sole (28) is in an upright, unloaded condition;

an outer surface (31) having an uppermost portion (53a') which extends to at least the height of the lowest point (30') of the inner surface (30), as viewed in a frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition; characterized in that:

the outer surface (31) includes at least one concavely rounded portion which extends down at least one side of the shoe sole (28) to at least proximate a lowest point (28') of the shoe sole side, the concavity of the concavely rounded portion of the outer surface (31) is determined relative to an inner section of the shoe sole (28) located directly adjacent to the concavely rounded portion of the outer surface (31), as viewed in a frontal plane cross-section, when the shoe sole (28) is in an upright, unloaded condition; and

wherein the concavely rounded portion of the outer surface (31) of the side of the shoe sole (28) includes a part formed by midsole (127), and the midsole part of the concavely rounded portion of the outer surface (31) extends below a sidemost extent (28a') of the shoe sole side so that the rounded portion of the shoe sole side deforms to flatten easily under a wearer's body weight load during sideways motion of the shoe sole (28), thereby providing improved lateral stability,.
A shoe sole (28) as claimed in claim 1, wherein the at least one concavely rounded portion of the outer surface (31) is located at one or more locations on the shoe sole (28) proximate to the locations of one or more of the following parts of an intended wearer's foot when inside the shoe: the base of the calcaneus (95), the lateral tuberosity of the calcaneus (95), the base of the fifth metatarsal (97), the head of the fifth metatarsal (96), the head of the first metatarsal (96), and the head of the first distal phalange (98).
The shoe sole (28) of any one of claims 1-2, wherein:
the concavely rounded portion of the outer surface (31) extends up at least one shoe sole side to a location on the shoe sole side proximate to a sidemost extent (28a') of the shoe sole side, as viewed in a frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition.
The shoe sole (28) of any one of claims 1-2, wherein:
the concavely rounded portion of the outer surface (31) extends up at least one shoe sole side through a sidemost extent (28a') of the shoe sole side, as viewed in a frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition.
The shoe sole (28) of any one of claims 1-4, wherein:
at least a lowermost part of the concavely rounded portion of the outer surface (31) is formed by bottom sole (128).
The shoe sole (28) of any one of claims 1-5, wherein:
at least a part of a bottom surface of the midsole (127) and at least a part of a top surface of the bottom sole (128) are substantially flat, as viewed in the frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition.
The shoe sole (28) of any one of claims 1-6, wherein:
the concavely rounded midsole part of the outer surface (31) is located at least at a location on the shoe sole (28) proximate to the location of the base of the calcaneus (95) of an intended wearer's foot when inside the shoe.
The shoe sole (28) of any one of claims 1-7, wherein:
the concavely rounded midsole part of the outer surface (31) is located at least at a location on the shoe sole (28) proximate to the location of the lateral tuberosity of the calcaneus (95) of an intended wearer's foot when inside the shoe.
The shoe sole (28) of any one of claims 1-8, wherein:
the concavely rounded midsole part of the outer surface (31) is located at least at a location on the shoe sole (28) proximate to the location of the base of the fifth metatarsal (97) of an intended wearer's foot when inside the shoe.
The shoe sole (28) of any one of claims 1-9, wherein:
the concavely rounded midsole part of the outer surface (31) is located at least at a location on the shoe sole (28) proximate to the location of the head of the fifth metatarsal (96) of an intended wearer's foot when inside the shoe.
The shoe sole (28) of any one of claims 1-10, wherein:
the concavely rounded midsole part of the outer surface (31) is located at least at a location on the shoe sole (28) proximate to the location of the head of the first metatarsal (96) of an intended wearer's foot when inside the shoe.
The shoe sole (28) of any one of claims 1-11, wherein:
the concavely rounded midsole part of the outer surface (31) is located at least at a location on the shoe sole (28) proximate to the location of the head of the first distal phalange (98) of an intended wearer's foot when inside the shoe.
The shoe sole (28) of any one of claims 1-12, wherein the shoe sole (28) includes at least two concavely rounded portions of the outer surface (31) each including midsole (127) and which are located on opposing sides of the shoe sole (28), as viewed in a frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition.
The shoe sole (28) of any one of claims 1-6 and claim 13 when dependent from any one of claims 1-6, wherein the frontal plane cross-section is located in the heel area.
The shoe sole (28) of any one of claims 1-14, wherein the thickness of the shoe sole (28) decreases gradually from a sole thickness at least at one of the concavely rounded portions of the outer surface (31) of the shoe sole (28) to a lesser sole thickness on the side of the concavely rounded portion of the outer surface (31), as viewed in a horizontal plane, to thereby provide torsional flexibility and weight savings to the shoe sole (28).
A shoe sole (28) as claimed in claim 15 wherein the thickness of the shoe sole (28) decreases gradually on both sides of the concavely rounded portion of the outer surface (31), as viewed in a horizontal plane.
The shoe sole (28) of any one of claims 1-16, wherein:
the upper surface of a side portion of the bottom sole (128) is substantially flat, as viewed in a frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition.
The shoe sole (28) of any one of claims 1-17, including a combined midsole and lift (127), and wherein the thickness of the midsole and lift (127) of a portion of the shoe sole (28) having a concavely rounded outer surface (31), as measured in a first frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition, is greater than the thickness of the midsole and lift (127) of a different sole portion which does not have a concavely rounded outer surface, as measured in a second frontal plane cross-section, when the shoe sole (28) is in an upright, unloaded condition.
The shoe sole (28) as claimed in claim 18, wherein the thickness of the midsole and lift (127) is defined as the distance between any point on a top surface of the combined midsole and lift (127) and the closest point on a bottom surface of the combined midsole and lift (127), as viewed in a frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition.
The shoe sole (28) of any one of claims 18-19, wherein the lift is a heel lift.
The shoe sole (28) of any one of claims 1-20, wherein the at least one concavely rounded portion of the outer surface (31) is also concavely rounded relative to an inner section of the shoe sole (28) located directly adjacent to the concavely rounded portion of the outer surface (31), as viewed in a horizontal plane when the shoe sole (28) is in an upright, unloaded condition.
The shoe sole (28) of any one of claims 1-21, wherein the portion of the shoe sole (28) with a concavely rounded outer surface (31) has a thickness which decreases gradually through successive, adjacent frontal plane cross-sections to thereby increase the torsional flexibility of the shoe sole (28), when the shoe sole (28) is in an upright, unloaded condition.
The shoe sole (28) of any one of claims 1-22, wherein the uppermost portion (53a') of the at least one concavely rounded portion of the outer surface (31) forms an arc of more than 90°, as viewed in a frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition.
The shoe sole (28) of any one of claims 1-23, wherein the portion of the shoe sole (28) which has a concavely rounded outer surface (31) further includes an area of increased material density to form a structural support or propulsion element for the foot (27) of an intended wearer.
The shoe sole (28) of any one of claims 1-24, wherein the midsole part of the concavely rounded portion of the outer surface (31) includes an upper part (53a') of the outer surface (31), as viewed in a frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition.
The shoe sole (28) of any one of claims 1-25, wherein the concavely rounded portion of the outer surface (31) is located only on a side portion of the shoe sole (28), as viewed in a frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition.
A shoe sole (28) as claimed in any one of claims 1-26, wherein at least part of the concavely rounded portion of the outer surface (31) of the shoe sole (28) is formed by a plurality of substantially straight line segments which, taken together, approximate a concavely rounded surface portion, as viewed in a frontal plane cross-section when the shoe sole (28) is in an upright, unloaded condition.
A shoe sole (28) as claimed in any one of claims 1-27, wherein a heel area of the shoe sole (28) has a thickness that is greater than the thickness of the shoe sole (28) in a forefoot area.
A shoe sole (28) as claimed in any one of claims 1-28, including a tread pattern (60, 62) on at least part of the outer surface (31) of the shoe sole (28).