Patent Publication Number: US-6668470-B2

Title: Shoe sole with rounded inner and outer side surfaces

Description:
CONTINUATION DATA 
     This application is a continuation of U.S. application Ser. No. 09/522,174, filed Mar. 9, 2000, now U.S. Pat. No. 6,314,662, which is a continuation of U.S. application Ser. No. 08/477,640, filed Jun. 7, 1995, now pending, which is a continuation of U.S. application Ser. No. 08/162,962, filed Dec. 8, 1993, now U.S. Pat. No. 5,544,429, which is a continuation of U.S. application Ser. No. 07/930,469, filed Aug. 20, 1992, now U.S. Pat. No. 5,317,819, which is a continuation of U.S. application Ser. No. 07/239,667, filed Sep. 2, 1988, now abandoned. 
    
    
     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, and has a constant thickness in frontal plane cross sections, 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 an understanding of the reasons for such problems, and proposing a novel solution to the problems, 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. The entire weight of the body, multiplied by a factor of approximately three at running peak, is concentrated at the sole edge. Since an unnatural lever arm and a force moment are created under such conditions, the foot and ankle are destabilized. When the destabilization is extreme, beyond a certain point of rotation about the pivot point of the shoe sole edge, ankle strain occurs. In contrast, the unshod foot is always in stable equilibrium without a comparable lever arm or force moment. 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. 
     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 shoe designs. 
     It is another objective of this invention to provide a running shoe which overcomes the problems of the prior art. 
     It is another objective of this invention to provide a shoe wherein the outer extent of the flat portion of the sole of the shoe includes all of the support structures of the foot but which extends no further than the outer edge of the flat portion of the foot sole so that the transverse or horizontal plane outline of the top of the flat portion of the shoe sole coincides as nearly as possible with the load-bearing portion of the foot sole. 
     It is another objective of the invention to provide a shoe having a sole which includes a side contoured like the natural form of the side or edge of the human foot and conforming to it. 
     It is another objective of this invention to provide a novel shoe structure in which the contoured sole includes a shoe sole thickness that is precisely constant in frontal plane cross sections, and therefore biomechanically neutral, even if the shoe sole is tilted to either side, or forward or backward. 
     It is another objective of this invention to provide a shoe having a sole fully contoured like and conforming to the natural form of the non-load-bearing human foot and deforming under load by flattening just as the foot does. 
     It is still another objective of this invention to provide a new stable shoe design wherein the heel lift or wedge increases in the sagittal plane the thickness of the shoe sole or toe taper decrease therewith so that the sides of the shoe sole which naturally conform to the sides of the foot also increase or decrease by exactly the same amount, so that the thickness of the shoe sole in a frontal planar cross section is always constant. 
    
    
     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 prior art running shoe to which the improvement of the present invention is applicable; 
     FIG. 2 is a frontal plane cross section showing a shoe sole of uniform thickness that conforms to the natural shape of the human foot, the novel shoe design according to the invention; 
     FIGS. 3A-3D show a load-bearing flat component of a shoe sole and naturally contoured stability side component, as well as a preferred horizontal periphery of the flat load-bearing portion of the shoe sole when using the sole of the invention; 
     FIGS. 4A and 4B are diagrammatic sketches showing the novel contoured side sole design according to the invention with variable heel lift; 
     FIG. 5 is a side view of the novel stable contoured shoe according to the invention showing the contoured side design; 
     FIG. 6D is a top view of the shoe sole shown in FIG. 5, wherein FIG. 6A is a cross-sectional view of the forefoot portion taken along lines  6 A of FIG. 5 or  6 D; FIG. 6B is a view taken along lines  6 B of FIGS. 5 and 6D; and FIG. 6C is a cross-sectional view taken along the heel along lines  6 C in FIGS. 5 and 6D; 
     FIGS. 7A-7E show a plurality of side sagittal plane cross-sectional views showing examples of conventional sole thickness variations to which the invention can be applied; 
     FIGS. 8A-8C show 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; 
     FIGS. 9A-9C show the contoured sole design according to the invention when applied to various tread and cleat patterns; 
     FIG. 10 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. 11 shows a fully contoured shoe sole design that follows the natural contour of the bottom of the foot as well as the sides. 
     FIGS. 12 and 13 show a rear diagrammatic view of a human heel, as relating to a conventional shoe sole (FIG. 12) and to the sole of the invention (FIG.  13 ); 
     FIGS. 14A-14F show the naturally contoured sides design extended to the other natural contours underneath the load-bearing foot such as the main longitudinal arch; 
     FIGS. 15A-15E illustrate the fully contoured shoe sole design extended to the bottom of the entire non-load-bearing foot; and 
     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 line perpendicular to a line tangent to a sole surface; and 
     FIG. 18 shows an embodiment wherein the contour of the sole according to the invention is approximated by a plurality of line segments. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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 portion  21  and a sole  22 . Typically, such a sole includes a truncated outwardly flared construction, wherein the lower portion of the sole heel is significantly wider than the upper portion 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. Pat. 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 20 mm. The rounded portion lies along approximately the rear-half of the length of the outer side of the mid-sole 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. Pat. No. 4,557,059 to Misevich, 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. 
     FIG. 2 shows in a frontal plane cross section at the heel (center of ankle joint) the general concept of the applicant&#39;s design: a shoe sole  28  that conforms to the natural shape of the human foot  27  and that has a constant thickness (s) in frontal plane cross sections. The surface  29  of the bottom and sides of the foot  27  should correspond exactly to the upper surface  30  of the shoe sole  28 . The shoe sole thickness is defined as the shortest distance (s) between any point on the upper surface  30  of the shoe sole  28  and the lower surface  31  by definition, the surfaces  30  and  31  are consequently parallel. In effect, the applicant&#39;s general concept is a shoe sole  28  that wraps around and conforms to the natural contours of the foot  27  as if the shoe sole  28  were made of a theoretical single flat sheet of shoe sole material of uniform thickness, wrapped around the foot with no distortion or deformation of that sheet as it is bent to the foot&#39;s contours. To overcome real world deformation problems associated with such bending or wrapping around contours, actual construction of the shoe sole contours of uniform thickness will preferably involve the use of multiple sheet lamination or injection molding techniques. 
     FIGS. 3A,  3 B, and  3 C illustrate in frontal plane cross section a significant element of the applicant&#39;s shoe design in its use of naturally contoured stabilizing sides  28   a  at the outer edge of a shoe sole  28   b  illustrated generally at the reference numeral  28 . It is thus a main feature of the applicant&#39;s invention to eliminate the unnatural sharp bottom edge, especially of flared shoes, in favor of a naturally contoured shoe sole outside  31  as shown in FIG.  2 . The side or inner edge  30   a  of the shoe sole stability side  28   a  is contoured like the natural form on the side or edge of the human foot, as is the outside or outer edge  31   a  of the shoe sole stability side  28   a  to follow a theoretically ideal stability plane. According to the invention, the thickness (s) of the shoe sole  28  is maintained exactly constant, even if the shoe sole is tilted to either side, or forward or backward. Thus, the naturally contoured stabilizing sides  28   a , according to the applicant&#39;s invention, are defined as the same as the thickness  33  of the shoe sole  28  so that, in cross section, the shoe sole comprises a stable shoe sole  28  having at its outer edge naturally contoured stabilizing sides  28   a  with a surface  31   a  representing a portion of a theoretically ideal stability plane and described by naturally contoured sides equal to the thickness (s) of the sole  28 . The top of the shoe sole  30   b  coincides with the shoe wearer&#39;s load-bearing footprint, since in the case shown the shape of the foot is assumed to be load-bearing and therefore flat along the bottom. A top edge  32  of the naturally contoured stability side  28   a  can be located at any point along the contoured side  29  of the foot, while the inner edge  33  of the naturally contoured side  28   a  coincides with the perpendicular sides  34  of the load-bearing shoe sole  28   b . In practice, the shoe sole  28  is preferably integrally formed from the portions  28   b  and  28   a . Thus, the theoretically ideal stability plane includes the contours  31   a  merging into the lower surface  31   b  of the sole  28 . Preferably, the peripheral extent  36  of the load-bearing portion of the sole  28   b  of the shoe includes all of the support structures of the foot but extends no further than the outer edge of the foot sole  37  as defined by a load-bearing footprint, as shown in FIG. 3D, which is a top view of the upper shoe sole surface  30   b . FIG. 3D thus illustrates a foot outline at numeral  37  and a recommended sole outline  36  relative thereto. Thus, a horizontal plane outline of the top of the load-bearing portion of the shoe sole, therefore exclusive of contoured stability sides, should, preferably, coincide as nearly as practicable with the load-bearing portion of the foot sole with which it comes into contact. Such a horizontal outline, as best seen in FIGS. 3D and 6D, should remain uniform throughout the entire thickness of the shoe sole eliminating negative or positive sole flare so that the sides are exactly perpendicular to the horizontal plane as shown in FIG.  3 B. Preferably, the density of the shoe sole material is uniform. 
     Another significant feature of the applicant&#39;s invention is illustrated diagrammatically in FIGS. 4A and 4B. Preferably, as the heel lift or wedge  38  of thickness (s 1 ) increases the total thickness (s+s 1 ) of the combined midsole and outersole  39  of thickness (s) in an aft direction of the shoe, the naturally contoured sides  28   a  increase in thickness exactly the same amount according to the principles discussed in connection with FIGS. 3A-3D. Thus, according to the applicant&#39;s design, the thickness of the inner edge  33  of the naturally contoured side is always equal to the constant thickness (s) of the load-bearing shoe sole  28   b  in the frontal cross-sectional plane. 
     As shown in FIG. 4B, for a shoe that follows a more conventional horizontal plane outline, the sole can be improved significantly according to the applicant&#39;s invention by the addition of a naturally contoured side  28   a  which correspondingly varies with the thickness of the shoe sole and changes in the frontal plane according to the shoe heel lift  38 . Thus, as illustrated in FIG. 4B, the thickness of the naturally contoured side  28   a  in the heel section is equal to the thickness (s+s 1 ) of the shoe sole  28  which is thicker than the shoe sole  39  thickness (s) shown in FIG. 5A by an amount equivalent to the heel lift  38  thickness (s 1 ). In the generalized case, the thickness (s) of the contoured side is thus always equal to the thickness (s) of the shoe sole. 
     FIG. 5 illustrates a side cross-sectional view of a shoe to which the invention has been applied and is also shown in a top plane view in FIG.  6 . Thus, FIGS. 6A,  6 B and  6 C represent frontal plane cross-sections taken along the forefoot, at the base of the fifth metatarsal, and at the heel, thus illustrating that the shoe sole thickness is constant at each frontal plane cross-section, even though that thickness varies from front to back, due to the heel lift  38  as shown in FIG. 5, and that the thickness of the naturally contoured sides is equal to the shoe sole thickness in each FIGS. 6A-6C cross section. 
     Moreover, in FIG. 6D, a horizontal plane overview of the left foot, it can be seen that the contour of the sole follows the preferred principle in matching, as nearly as practical, the load-bearing sole print shown in FIG.  3 D. 
     FIGS. 7A-7E show typical conventional sagittal plane shoe sole thickness variations, such as heel lifts or wedges  38 , or toe taper  38   a , or full sole taper  38   b , in 
     FIGS. 7A-7E and how the naturally contoured sides  28   a  equal and therefore vary with those varying thicknesses as discussed in connection with FIGS. 4A and 4B. 
     FIGS. 8A-8D illustrate an embodiment of the invention which utilizes varying portions of the theoretically ideal stability plane  51  in the naturally contoured sides  28   a  in order to reduce the weight and bulk of the sole, while accepting a sacrifice in some stability of the shoe. Thus, FIG. 8A illustrates the preferred embodiment as described above in connection with FIGS. 4A and 4B wherein the outer edge  31   a  of the naturally contoured sides  28   a  follows a theoretically ideal stability plane  51 . As in FIGS.  2  and  3 A- 3 D, the contoured surfaces  31   a , and the lower surface of the sole  31   b  lie along the theoretically ideal stability plane  51 . The theoretically ideal stability plane  51  is defined as the plane of the surface of the bottom of the shoe sole  31 , wherein the shoe sole conforms to the shape of the wearer&#39;s foot sole, particularly the sides, and has a constant thickness in frontal plane cross sections. As shown in FIG. 8B, an engineering trade off results in an abbreviation within the theoretically ideal stability plane  51  by forming a naturally contoured side surface  53   a  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  28   a  defined by the constant thickness lying along the surface  31   a  is coplanar with the theoretically ideal stability plane  51 . FIGS. 8C and 8D show similar embodiments wherein each engineering trade-off shown results in progressively smaller portions of contoured side  28   a , which lies along the theoretically ideal stability plane  51 . The portion of the surface  31   a  merges into the upper side surface  53   a  of the naturally contoured side. 
     The embodiment of FIGS. 8A-8D 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 10° times for each single time it rolls out to 40°. For a basketball shoe, shown in FIG. 8B, 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. 8D is possible. A typical running/jogging shoe is shown in FIG.  8 C. The range of possible variations is limitless, but includes at least the maximum of 90 degrees in inversion and eversion, as shown in FIG.  8 A. 
     FIGS. 9A-9C show the theoretically ideal stability plane  51  in defining embodiments of the shoe sole having differing tread or cleat patterns. Thus, FIGS. 9A-9C illustrate that the invention is applicable to shoe soles having conventional bottom treads. Accordingly, FIG. 9A is similar to FIG. 8B further including a tread portion  60 , while FIG. 9B is also similar to FIG. 8B 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. 9C is similar to FIG. 8C 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. 10 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. 11 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. 11 would deform by flattening to look essentially like FIG.  10 . Seen in this light, the naturally contoured side design in FIG. 10 is a more conventional, conservative design that is a special case of the more general fully contoured design in FIG. 11, which is the closest to the natural form of the foot, but the least conventional. The amount of deformation flattening used in the FIG. 10 design, which obviously varies under different loads, is not an essential element of the applicant&#39;s invention. 
     FIGS. 10 and 11 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. 11 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&#39;s foot surface  29 , to which the theoretically ideal stability plane  51  is by definition parallel. 
     For the special case shown in FIG. 10, 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&#39;s foot; and, third, by the frontal plane cross section width of the individual&#39;s load-bearing footprint  30 b, which is defined as the upper surface of the shoe sole that is in physical contact with and supports the human foot sole, as shown in FIGS. 3A-3D. 
     The theoretically ideal stability plane for the special case is composed conceptually of two parts. Shown in FIGS.  10  and  3 A- 3 D the first part is a line segment  31   b  of equal length and parallel to  30   b  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  28   b . The second part is the naturally contoured stability side outer edge  31   a  located at each side of the first part, line segment  31   b . Each point on the contoured side outer edge  31   a  is located at a distance which is exactly shoe sole thickness (s) from the closest point on the contoured side inner edge  30   a ; consequently, the inner and outer contoured edges  31 A and  30 A are by definition parallel. 
     In summary, the theoretically ideal stability plane is the essence of this invention because it is used to determine a geometrically precise bottom contour of the shoe sole based on a top contour that conforms to the contour of the foot. This invention specifically claims the exactly determined geometric relationship just described. It can be stated unequivocally that any shoe sole contour, even of similar contour, that exceeds the theoretically ideal stability plane will restrict natural foot motion, while any less than that plane will degrade natural stability, in direct proportion to the amount of the deviation. 
     FIG. 12 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. 12, 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  70  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 flat like the ground, rather than contoured like the foot. 
     In contrast, the new design, as illustrated in FIG. 13, 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 modern 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. 
     FIGS. 14A-14D 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 of sole  30  shown in FIGS. 3A-3D. 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). 
     More particularly, FIGS. 14C and 14D disclose a shoe sole  28  having a sole inner surface  30  adjacent the location of an intended wearer&#39;s foot  27  inside the shoe including at least a first concavely rounded portion  43 , as viewed in a frontal plane. The concavity being determined relative to the location of an intended wearer&#39;s foot  27  inside the shoe, during an upright, unloaded shoe condition. The shoe sole  28  further includes a lateral or medial sidemost section  45  defined by that part of the side of the shoe sole  28  located outside of a straight line  55  extending vertically from a sidemost extent  46  of the sole inner surface  30 , as viewed in the frontal plane during a shoe upright, unloaded condition. A sole outer surface  31  extends from the sole inner surface  30  and defines the outer boundary of the sidemost section  45  of the side of the shoe sole  28 , as viewed in the frontal plane. The shoe sole  28  further including a second concavely rounded portion  44  forming at least the outer sole surface  31  of the sidemost section  45 , the concavity being determined relative to the location of an intended wearer&#39;s foot  27  inside the shoe, as viewed in the frontal plane during a shoe upright, unloaded condition. The second concavely rounded portion  44  extending through a sidemost extent  47  of the sole outer surface  31  of the sole sidemost section  45 , as viewed in the frontal plane during an upright, unloaded condition. Further, the second concavely rounded portion  44  extends to a height above a horizontal line  48  through the lowermost point of the sole inner surface  30 , as viewed in the frontal plane in the heel area  51  during an upright, unloaded shoe condition. FIG. 14C illustrates the above aspects of the shoe sole  28  at the shoe midtarsal area  52  located between the forefoot area  50  and the heel area  49 . 
     FIGS. 15A-15D show, in frontal plane cross sections, the fully contoured shoe sole design extended to the bottom of the entire non-load-bearing foot. FIG. 15E shows a sagittal plane cross section. The shoe sole contours underneath the foot are the same as FIGS. 14A-14E except that there are no flattened areas corresponding to the flattened areas of the load-bearing foot. The exclusively rounded contours of the shoe sole follow those of the unloaded foot. A heel lift  38 , the same as that of FIGS. 14A-14D, is incorporated in this embodiment, but is not shown in FIGS. 15A-15D. 
     FIG. 16 shows the horizontal plane top view of the left foot corresponding to the fully contoured design described in FIGS. 14A-14E, 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 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 . The medial (inside) and lateral (outside) sides supporting the base of the calcaneus are shown in FIG. 15 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. 15 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 nonessential 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 upper surface of shoe sole  30  shown in FIGS. 3A-3D. A horizontal plane bottom view (not shown) of FIG. 15 would be the exact reciprocal or converse of FIG. 15 (i.e. peaks and valleys contours would be exactly reversed). 
     FIG. 17 illustrates the method of measuring sole thickness in accordance with the present invention. The sole thickness is defined as the distance between a first point on the inner surface  30  of the sole  28  and a second point on the outer surface  31  of the sole  28 , the second point being located along a straight line perpendicular to a straight line tangent to the inner surface  30  of the sole  28  at the first point, as viewed in a shoe sole frontal plane when the shoe sole is upright and in an unloaded condition. 
     The theoretically ideal stability can also be approximated by a plurality of line segments  110 , such as tangents, chords, or other lines, as shown in FIG.  18 . Both the upper surface of the shoe sole  28 , which coincides with the side of the foot  30   a , and the bottom surface  31   a  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.  18 . 
     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.