Patent Publication Number: US-2021186143-A1

Title: Modular insert system for shoe soles

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to soles for articles of footwear, in particular footwear for correcting, supporting or accommodating the gait of the wearer. 
     BACKGROUND OF THE INVENTION 
     In addition to providing general support for the wearer&#39;s feet while walking or running, shoe soles can be manufactured such that the degree of support for the foot differs between different regions of the sole. Thus the material of the heel region, for example, which experiences the greatest impact forces, is often manufactured to provide greatest impact cushioning effect. The desired variation in support may be achieved for example by varying mechanical properties of the material of the sole, such as the shape, thickness, density, hardness and flexural characteristics. In this way, the sole may be manufactured so as to provide optimum support for the typical wearer&#39;s feet. Since gait characteristics vary significantly from person to person, footwear manufacturers design the soles of their products to cater for a broad range of gait types, based around a putative norm. Soles may also be configured to suit different types of use. For example, soles may be configured for sprinting, long-distance running, playing particular sports such as golf or tennis or cross-country skiing, or for casual wear. Running shoes require different sole configurations for different distances, and for different types of terrain. 
     The wearer is therefore obliged either to settle for a sole which will cover a wide range of uses, but will not be well configured for any of those uses, or he may purchase different footwear for different uses; different shoes for road-running and for cross-country running, for example, or different shoes for different distances. 
     Specialist soles are also available which are configured to accommodate or correct particular types of gait, such as over-pronation or supination. Shoes are also available with soles which are customised to a particular combination of gait-type, or sport, or use. It is possible to have soles customised for a particular person, or even for a particular foot. However, bespoke soles are expensive, and the present invention is concerned primarily with soles for footwear which can be manufactured and distributed in significant numbers as a commercial retail product. 
     PRIOR ART 
     It has been suggested to provide a certain customizability of the support provided to a wearer&#39;s foot by means of an orthotic insole, laid on top of the integral sole of a shoe. 
     Such insoles may incorporate regions of different support, which are arranged to suit the particular use or gait-type. The hardness of the regions may be customised by exchanging portions of the orthotic, for example. Such a customisable orthotic is known from EP2383952, in which a shaped piece of the orthotic can be exchanged for a similarly-shaped piece having a different hardness. The orthotic described in this document thus provides a limited customizability of the support which is provided by the insole. 
     WO2016092353, from the same inventors as the present invention, describes a sole customising system in which hard inserts are located in cavities in the midsole. The application does not address the problem of ensuring constant and accurate sensory-motoric stimulus (see below), but nevertheless proposes an arrangement which could potentially offer a solution in that the inserts can be inserted into the cavities from the top, so that the cavity bottoms are closed by the outsole. 
     EP1352579 describes a midsole comprising regions of different hardnesses, so that the midsole can be customised for a particular wearer. The assembled portions of the midsole may be formed into a continuous moulding, in which case the customised sole is no longer customisable. Alternatively, the assembled portions can remain as discrete components of the sole, in which case the mechanical integrity of the sole as a whole is greatly reduced. 
     DE20320091 describes an adaptable insert which affords a limited customizability of the support provided at a particular region of the sole. The insert is introduced from the medial side of the sole (ie left-hand side of a right shoe or right-hand side of a left shoe) or the lateral side of the sole (ie right-hand side of a right shoe or left-hand side of a left shoe), and is held in place using a clip. The insert also includes vertical hexagonal-shaped holes into which can be inserted hexagonal pegs of a particular hardness. In this way, the effective hardness of the insert can be varied by inserting pegs which are harder than the material of the insert, which gives the wearer some control over the degree of support provided at that particular region of the sole when the insert is located in position. The midsole is provided with a wide horizontal cavity, open to one side, into which the insert can be pushed. The presence of a wide cavity reduces the overall mechanical integrity of the sole, even with the insert in place, and provides a path for water and dirt to enter the sole, and to work their way deep within the sole. The presence of the midsole material above and below the cavity means that the effectiveness of the lateral insert is reduced, in that the amount of vertical support it provides is reduced, and the total amount of vertical support provided may the sole in the region of the insert can be less accurately defined. Over time, the material of the midsole above and below the cavity, and the material of the insert element surrounding the pegs, will lose elasticity and resilience due to the repeated compression during the gait cycle. Such insert elements are typically positioned in regions of the sole where greater support is required, which means that the repeated compression, and the consequent crushing of the insert material and the midsole material above and below the insert, will be particularly susceptible to degradation, and thereby shorten the wearable life of the shoe. 
     It is also important for gait-correcting insert elements to retain a constant proprioceptive effect and to remain secured in the sole. If an insert works loose, or becomes plastically compressed, or if it is contaminated by ingress of dirt or water, the customised proprioceptive pressure effect of the insert will be altered. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention described in this application seeks to overcome at least some of the above and other disadvantages inherent in the prior art. In particular, the invention aims to provide a customisable article of footwear according to claim  1 , a method according to claim  23  and a method according to claim  25 . Further variants are defined in the dependent claims. 
     A support customising system is described below for the sole of a shoe or other article of footwear. The sole comprises a relatively soft, resilient midsole and (optionally) a harder outsole. Insert elements of various hardnesses are provided for inserting into vertical cavities in the midsole. By customising the hardnesses of different inserts in different vertical cavities, a precisely-tunable pronation control effect on the wearer&#39;s gait can be effected. First-order, second-order and third-order pronation control effects are described. 
    
    
     
       The invention and its advantages will further be explained in the following detailed description, together with illustrations of example embodiments and implementations given in the accompanying drawings. Note that the drawings are intended merely as illustrations of embodiments of the invention, and are not to be construed as limiting the scope of the invention. Where the same reference numerals are used in different drawings, these reference numerals are intended to refer to the same or corresponding features. However, the use of different reference numerals should not in itself be taken as an indication of any particular difference between the referenced features. In this description the terms hardness and durometer are used interchangeably, and numerical hardness values refer to the Shore A hardness scale. 
         FIG. 1 a    shows in side view a schematic cross-section of an example shoe employing a support-customising system of proprioception-enhancing inserts. 
         FIG. 1 b    shows in isometric view an example of support adjustment inserts for use in the support customising system of  FIG. 1   a.    
         FIG. 2  shows a schematic plan view, viewed from below, of a first example sole employing a support customising system. 
         FIGS. 3 to 8  show cross-sectional schematic views of various example geometries of proprioception-enhancing inserts. 
         FIGS. 9 to 11  show cross-sectional views of various example arrangements of proprioception-enhancing inserts in a sole. 
         FIGS. 12 and 13  show transverse cross-sectional views of two example arrangements of proprioception-enhancing inserts. 
         FIG. 14  shows a longitudinal cross-sectional view of an example arrangement of proprioception-enhancing inserts. 
         FIG. 15  shows a transverse cross-sectional view of an example of an insert-retention arrangement. 
         FIGS. 16 to 24  show cross-sectional views of example geometries of proprioception-enhancing inserts. 
         FIGS. 25 to 27  show cross-sectional views of example sealing and retention arrangements of proprioception-enhancing inserts. 
         FIGS. 28 to 30  show cross-sectional views of example cavities with linings. 
         FIGS. 31 to 33  show the cavities of  FIGS. 28 to 30  with examples of inserts. 
         FIG. 34  shows a cross-sectional view of a (sperical or cylindrical) cavity and insert having a circular cross-section. 
         FIGS. 35 and 36  show cross-sectional and plan views of an example of a lined cavity with a retaining protrusion. 
         FIG. 37  shows a cross-sectional view of an insert having a broaded distal end for aiding retention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An example of a support customising system is illustrated in  FIGS. 1 a  and 1 b   .  FIG. 1 a    depicts a schematic cross-section of a shoe with a sole  1  comprising an outsole  4 , aFF midsole  3 , bonded to the outsole  4 , and a liner or insole  6  laid on the upper surface  7  of the midsole  3 . The midsole  3  may be made of a resilient material, for example an elastomer such as ethyl vinyl acetate (EVA) or other suitable material. The outsole  4  may for example be constructed from a hard, resilient elastomeric material such as rubber/polyurethane, and may have a hardness which is greater than that of the midsole  3 , at least at the ground-facing surface of the outsole  4 . Alternatively, the midsole  3  and outsole  4  may comprise the same or similar materials, or may be contiguous, homogenous regions of the same moulded shape. The liner or insole  6  may be of relatively thin and/or softer material and serves to provide a comfortable surface for the sole of the wearer&#39;s foot. The liner or insole  6  may be removed to expose the upper surface  7  of the midsole  3 . 
     The example sole  1  illustrated in  FIG. 1 a    is provided with a plurality (six are shown) of vertical cavities  2 , each of which opens out through the outsole  4  and extends up towards the upper surface  7  of the midsole  3  along a vertical axis  8 . The midsole  3 , apart from the holes (cavities  2 ) which are formed in it, may be constructed of continuous material, in order to ensure the mechanical integrity of the sole as a whole. The vertical direction is understood in this text to be the vertical direction when the shoe is standing flat on level ground. The vertical axis  8  is thus substantially orthogonal to the general plane  9  of the sole  1 , which is taken to be generally parallel to the upper, foot-facing surface  7  of the midsole  3  and/or to the lower surface of the outsole  4 , at least in the heel and/or midfoot regions  13 ,  14  of the sole  1 . The sole  1  illustrated in  FIG. 1 a    has parallel upper and lower surfaces for clarity. In practice, the heel area of the sole may be thicker than the forefoot area (‘positive drop’), or vice versa (‘negative drop’), and/or the mid-foot zone may be thicker than both the heel and forefoot regions, for example. 
     The terms lower and upper used in this description are also defined in terms of the vertical axis  8 . Note that the term vertical is used in this text to denote a general rather than a precise orientation of the vertical cavities  2 , and includes orientations which differ by up to 15 degrees, or alternatively even up to 40 degrees from the vertical axis  8  shown in  FIG. 1   a.    
     While only six cavities/inserts are shown in particular cross-section of  FIG. 1 a   , all in the heel and mid-foot parts of the sole, it should be understood that the sole may also comprise similar cavities/inserts in forward regions of the sole. 
       FIG. 1 b    shows a set of inserts or plugs  5 , also referred to in this description as support adjustment inserts or proprioception-enhancing inserts, which are designed for insertion into the cavities  2  in the midsole  3 . In the example shown in  FIGS. 1 a  and 1 b   , the inserts  5  may be inserted into the cavities  2  through openings in the outsole  4 . Inserting the inserts from below has the advantage that the insertion openings are more readily accessible than if they are inserted from above. However, as discussed below, inserting the inserts through the outsole  4  renders the inserts liable to damage by over-compression (for example if the wearer steps on a stone) or by incursion of dirt or water. 
     The inserts  5  may also be made of an elastomeric material, for example, and they may have different hardnesses from the midsole  3  and/or from one another. Some of the inserts  5  may have substantially the same hardness as the material of the midsole  3 , in order to provide a null support adjustment at a particular cavity  2 . It is also possible to provide inserts  5  with lower hardnesses than the midsole  3 ; this may for example be useful for providing a negative support adjustment in a particular region of the sole  1  by reducing the average hardness of the region by inserting one or more inserts  5  which are softer than the material of the surrounding midsole  3 . 
     The hardnesses of the inserts  5  may be selected from a set of predetermined hardnesses. For example, a pair of shoes having soles such as that illustrated in  FIG. 1 a    may be purchased with a set of inserts  5  similar to those shown in  FIG. 1 b   , with multiple alternative inserts of different hardnesses available for insertion into each cavity, and with each insert having one of a predetermined selection of hardnesses. There may be more inserts  5  in the set than there are cavities  2  in the sole  1 . The midsole  3  may have a hardness in the range 30 to 70 Shore, or 45 to 60 Shore, for example, and the supplied set of inserts  5  may include some inserts having a hardness of 50 Shore, some of 60 Shore, some of 70 Shore, some of 80, 90 or even 100 Shore, for example. Different inserts  5  of different hardnesses may then be fitted into the cavities  2  provided, so as to achieve the desired local support hardness at each cavity location and collectively in each region of the sole  1  provided with cavities  2 . If the midsole has a first durometer, then the set of inserts from which inserts can be selected for insertion into the cavities may include inserts, each of which may have one of a predetermined plurality of durometers. The plurality of durometers may include durometers which differ from each other by between 5 and 20 Shore, including a durometer which is greater than the first durometer by between 5 and 40 Shore. As will be discussed below, the plurality of durometers may include a durometer which is the same as the first durometer and/or one or more durometers which are less than the first durometer. The first durometer of the midsole  3  may be constant for all regions of the midsole  3 , or it may vary between regions of the midsole  3 . In the latter case, the first durometer may either be taken to be an average durometer of the midsole  3  or a local durometer of a particular region of the midsole  3 . 
     When the wearer puts weight on the sole, for example while walking, the inserts  5  which are harder than the surrounding midsole material serve to transfer a force from between the ground and the wearer&#39;s foot which is greater than that transferred by the surrounding midsole material. Each of these harder inserts thereby provides increased support for the wearer&#39;s foot at the location in the sole at which it is inserted. Because the inserts  5  each have one of a predetermined set of hardnesses, at least in the vertical direction, and because they extend along substantially the whole vertical depth  11  of the sole  1 , or at least substantially the whole depth  11  of the midsole  3 , the net vertical hardness of the sole  1  at the location of each cavity  2  is determined exclusively, or in a great majority, by the hardness of the particular insert  5 . The hardness of the outsole  4 , if it is different from the hardness of the insert  5 , may also contribute an effect to the net vertical hardness of the sole  1  at that location, but the contribution may be small, particularly if the outsole  4  is thin and/or the hardness difference between the outsole  4  and the insert  5  is small. Similarly, the contribution of the insole  6  or any minor part of the midsole which extends above or below the insert  5  when the insert  5  is inserted, will also have only a small effect on the net vertical hardness of the sole  1  at the particular cavity. The term net vertical hardness is used here to indicate a measure of the compressibility and resilience of the sole in an approximately vertical direction (ie as measured along the vertical axis  8 ). The net vertical hardness at a particular location may be represented or measured for example using the 25% compressive strength measurement at the location. This measure may be used, for example, where the inserts are 50% or less than the thickness of the sole at the location. 
     For example, the 25% compressive strength (the pressure required to compress the sole thickness by 25%) of the sole at the location of a cavity containing an insert. An insert may be considered to have a proprioceptive effect if the durometer of the insert is such that the 25% compressive strength of the sole at its location is at least 50% greater than the 25% compressive strength of the surrounding sole adjacent to the insert/cavity. The presence or absence of a proprioceptive insert may be determined using a test as follows: 
     The pointwise compressive strength of the sole at a particular location can be measured by vertically compressing the sole between a small upper plate, having a predetermined area of for example between 2 and 4 cm2, placed directly over the region of the sole being measured, and a larger lower plate, placed directly beneath the region of the sole being measured and beneath the lower surface of the lower surface of the sole (ie the lower surface of the insert and the outsole if present). The plates may be moved together so as to compress the sole vertically to a compression of 25% of the thickness of the sole (reduce the distance between upper and lower plates by 25%). The pressure which must be applied to the upper plate to achieve the 25% compression can be taken as a measure of the compressive strength of the sole at that location. 
     If the 25% compressive strength of the sole with the insert is at least 50% greater than the 25% compressive strength of the adjacent sole material alone, then a significant proprioceptive effect is said to be present. 
     Where an insert occupies at least half the thickness of the sole at a particular location, the propioceptive effect may be considered to be present when the durometer of the insert is at least 5 Shore A greater, or optionally 10 Shore A greater, than the durometer of the surrounding midsole. 
     The vertical cavities  2  and the inserts  5  shown in the example of  FIGS. 1 a  and 1 b    have substantially parallel vertical side-walls. The cavities  2  may thus have a horizontal cross-section which is substantially constant along their length  11 , for example, or they may have a tapering cross-section, any other shape which allows them to be fitted into the cavities  2  and/or subsequently removed for exchange. The horizontal cross-section of the cavities  2  and inserts  5  may be of any regular shape, such as circular, oval, ovoid, hexagonal, triangular, square or rectangular, or it may have an irregular shape. The inserts  5  and cavities  2  are advantageously dimensioned such that it is possible to fit two or more cavities/inserts into a particular gait control region of the sole  1 , as will be discussed below. In this respect the cavities and inserts  5  may be formed with a horizontal cross-section which has a largest transverse dimension of between 5 mm and 50 mm across, for example, or preferably between 10 mm and 30 mm. 
     Because the inserts  5  are oriented substantially vertically in the midsole  3 , and because they have relatively small lateral dimensions, multiple inserts  5  and cavities  2  can be located in a particular region of the sole  1  in order to adjust the net vertical hardness of sole with a fine resolution. Thus, a pronation control zone in the forefoot area  12  of the sole  1  may incorporate multiple (eg three to ten inserts), for example, each with a hardness suitable for the pronation control requirement of the wearer. The hardnesses of the three to ten inserts  5  may be the same, or they may be graded. For example, the hardnesses of the inserts may be increased from the rear-most insert  5  to the foremost insert  5 . 
     The discussion above has related primarily to the inserts  5  and cavities  2  of a single shoe. In a pair of shoes, the inserts  5  and cavities  2  may similarly be made so that the same inserts  5  can be used in the cavities  2  of either shoe. The support customising system may be arranged such that, multiple pairs of shoes can share the same set of support adjustment inserts  5 . 
     The use of multiple, interchangeable inserts  5  having different hardnesses means that the support provided by the sole  1  can be finely tuned to the needs of the wearer. The support may be differently tuned between the left shoe and right shoe, between different regions  12 ,  13 ,  14  of one sole  1 , or even within the same region of the sole  1 . 
       FIG. 2  shows a plan view of a shoe sole  1  similar to the sole  1  shown in  FIG. 1 a   , and shows in more detail how the support adjustment inserts  5  can be arranged in the midsole  3  to achieve a customised support, for example as an aid to gait correction for the wearer. 
       FIG. 2  shows the midsole  3  of a left shoe, viewed from below, but it will be understood that the following description applies equally to a corresponding right shoe, although the arrangement of inserts  5  may be different between the left and right shoes. 
     In the example configuration of  FIG. 2 , the sole  1  comprises a heel region  19 , a heel medial region  21 , a heel lateral region  22 , a forefoot lateral region  23 , a metatarsal region  24  and a forefoot medial region  25 . These regions are merely examples—other regions may be chosen. If there are multiple inserts  5  in each region, as shown, the support offered by the region as a whole can be adjusted precisely by including individual inserts having different durometers—either to give an overall average hardness which is equivalent to an intermediate durometer value between the available values of the available inserts, or to give a graded support across the region. 
     Left and right feet naturally have slightly different pronation styles, due to the natural asymmetry in the person&#39;s posture and due to neurological effects which gives rise to asymmetries in gross motor control, reflected in the person&#39;s posture and gait. However, the characteristics of the landing portion  19  of the heel region should preferably be the same for left and right shoes. 
     Because the inserts  5  of a particular region, or of multiple regions of the sole, may have the same cross-sectional shape, the inserts  5  may be made interchangeable between all cavities  2  of a particular region or between all cavities  2  of the sole. In this case many different configurations of the support offered by the sole can be achieved with a relatively modest number of inserts  5 . 
     Each insert  5  may be formed as a single contiguous piece of material, or it may be formed from two or more constituent pieces. It may be solid, for example to assure its rigidity, or it may be hollow, for example to cut down on shoe weight and material costs. It may be open at one or both ends, and it may have openings in its side wall(s). 
     Also illustrated in  FIG. 2  is an ideal gait line  20 , also known as the stability axis or “S-line”, which indicates approximately how the wearer&#39;s foot should pronate during its heel-to-toe contact (gait cycle) with the ground. The example regions  19 ,  21 ,  22 ,  23 ,  24  are identified only approximately, and are used to illustrate how inserts  5  in the various regions can be used for controlling the wearer&#39;s gait. 
     The multiple cavities  2  may advantageously have the same size and shape, as illustrated in  FIG. 2 . The inserts  5  of a particular set, even if they have different hardnesses, may also have the same size and shape, so that multiple inserts  5  of different hardnesses can be interchangeably fitted into each cavity  2 , and so that a particular insert  5  can be fitted into multiple cavities  2 . The hind-most heel part  19  of the midsole  3  in  FIG. 2  is shown without any inserts  5  in this example. There may be instances when it may be useful to be able to adjust the hardness of this hind-most region  19 , but the illustrated example is designed to show how the support adjustment inserts  5  can be used for pronation/supination control, and the hindmost region  19  of the midsole  3  serves primarily to cushion and control the landing impact of the heel on the ground and the initial forward motion of the foot. 
     Medial and lateral control regions  21  and  22  can be used to control the amount of pronation during the initial phase of the gait cycle (ie following initial heel impact). By judicious choice of the hardnesses of the inserts  5   1  of the medial region  21  and the hardnesses of the inserts  5   1  and  5   2  of the medial  21  and lateral  22  control regions, it is possible to influence the degree of pronation of the foot around the stability “S-line”  20 . Furthermore, the use of inserts  5  of graded hardnesses in a particular region permits a second-order control, in which not only the amount of pronation can be controlled, but also the rate of change of pronation with respect to the forward motion of the foot during the sole&#39;s contact with the ground when walking or running. Taking the six medial control inserts  5   1  illustrated in  FIG. 2  as an example, a first-order pronation control can be obtained by selecting the hardness of the three inserts  5   2  relative to the hardness of midsole  3  and/or of the medial control inserts  5   1 . Harder lateral inserts  5   2  will encourage greater pronation, softer lateral inserts  5   2  will promote pronation less. However, by varying the difference between the durometers of the lateral inserts  5   2 , it is possible to achieve a second-order control effect. If the hardness difference between inserts along the heel to toe direction is large, for example (ie the rear-most lateral insert  5   2  is much harder than the forward-most lateral insert  5   2 , then the rate of pronation with respect to the foot&#39;s forward motion is greater. This means that the pronation occurs during a shorter time, when considered as proportion of the total contact time with the ground. On the other hand, if the hardness of the inserts  5   2  varies little along the heel to toe direction, then the pronation-enhancing effect with respect to the foot&#39;s forward motion will be less. If the foremost lateral insert  5   2  is harder than the rear-most insert  5   2 , then this will act to reduce the rate of pronation. 
     The lateral and medial inserts  5   1  and  5   2  can further be used to achieve a third-order control effect, in that inserts can be selected to vary the rate of pronation. If the lateral control region  22  is provided with more cavities and inserts  5   2 , (say five inserts in a line running parallel to the heel-toe axis, for example), then the hardnesses of the five lateral inserts  5   2  can be chosen so as to vary the rate pronation along the heel-to axis. Thus, by being able to select the hardnesses of the lateral inserts  5   2  it is possible not only to vary the amount of pronation (first-order effect), but also to vary the rate at which pronation occurs (second order effect) and the axial variation in the rate of pronation (third-order effect). 
     By using many cavities/inserts, it is possible to vary the pronation/supination control with a fine resolution, and in many different ways. For example, it is possible to take set the hardness of the inserts  5  to take account of individual bones or bone groups in the foot. Excessive calcaneal/talar tilt can be compensated for, for example, while minimising the effect on the metatarsal or forefoot regions. 
     The control effects described above in relation to the interchangeable inserts  5   2  of the lateral region  22  also apply to the other illustrated regions in  FIG. 2 ; the medial control region  21  with its multiple medial control inserts  5   1 , and the forefoot control regions  23  and  25 , with their forefoot control inserts  5   3  and  5   5 . A single mid-foot control insert  5   4  is illustrated in midfoot control region  24 , which may be included in the midfoot/metatarsal region to discourage the wearer&#39;s arch from sinking. The sole  1  may comprise such a single midfoot insert  24  on its own or in combination with one or more other inserts, as shown in  FIG. 2 , for example. 
     As a consequence of such finely-adjustable and adaptable gait control, it is possible to improve the wearer&#39;s gait and straighten the wearer&#39;s axial skeleton, which not only has beneficial effects for the wearer, but also promotes even wear on the outsoles  4  and therefore extends the life of the shoes. 
     Furthermore, if the individual inserts are replaceable, then the soles can be “tuned” for different uses, or for different wearers, or as the shoes age, or as the wearer&#39;s gait changes. 
     The following examples illustrate the insert hardnesses which could be chosen for different gait control purposes. The examples are based on a sole configuration similar to that shown in  FIG. 2 , and the hardnesses given are relative to an example midsole material of hardness 50 Shore. Where different inserts hardnesses are listed for a particular region, these are listed on the order from rear-most to foremost). 
     Example 1: For Correcting a Slight Supination 
     Lateral control region  22 : 50 Shore, 60 Shore, 60 Shore 
     Medial control region  21 : all 50 Shore or less 
     Forefoot lateral control region  23 : all 60 Shore 
     Example 2: For Correcting a Delayed Overpronation 
     Lateral control region  22 : all 50 Shore (no correction) 
     Medial control region  21 : 50, 60, 70, 80, 80, 60 Shore 
     Forefoot lateral control region  23 : all 60 Shore 
     Example 3: For Correcting Severe General Overpronation 
     Lateral control region  22 : 50, 50, 60 Shore 
     Medial control region  21 : 70, 80, 90, 80, 70, 60 Shore 
     Forefoot lateral control region  23 : all 60 Shore 
     Example 4: For Correcting Early, Slight Overpronation 
     Lateral control region  22 : 50, 50, 60 Shore 
     Medial control region  21 : 70, 60, 50, 50, 50, 50 Shore 
     Forefoot lateral control region  23 : 70, 60, 50, 50, 50 Shore 
     Example 5: For Correcting Delayed, Slight Overpronation 
     Lateral control region  22 : all 50 Shore (no correction) 
     Medial control region  21 : 50, 50, 60, 60, 70, 70 Shore 
     Forefoot lateral control region  23 : all 50 Shore (no correction) 
     The sole of  FIG. 2  also shows how a stiffening plate  10  may optionally be included to maintain longitudinal and torsional stiffness of the part of the sole under the arch of the wearer&#39;s foot. The presence of such a plate can improve the stability of the wearer&#39;s foot with respect to the ground surface, and may increase the life of the shoe sole. The plate  10  is also visible in  FIGS. 12 to 14 . 
       FIGS. 3 to 8  illustrate various example arrangements for the cavities  2  and inserts  5 , as mentioned above. In  FIG. 3 , the cavity  2  comprises an opening in the upper surface  7  of the midsole  3 , and is closed at its lower end by outsole  4 . In  FIG. 4 , the cavity  2  is shown with an opening above and below.  FIGS. 5 to 8  show arrangements in which the cavity  2  is closed at its upper end by a minority portion (eg 10%-20%) of the thickness of the material of the midsole  3 . The inserts  5  may be secured in the cavities  2  by any suitable means. If an insert is intended to remain in its cavity permanently, then it may be glued or bonded or welded in place in the cavity  2 . The insert  5  may even be supplied as a liquid which can be introduced into the cavity  2  and which then sets with a predetermined hardness.  FIGS. 5 and 6  show the cavity with and without the insert  5  inserted. The insert of this example comprises a body portion  5 , which may have a hardness selected to give the desired proprioceptive stimulus pressure to the foot at that location, and an outsole portion  5 ′, which may comprise a similar material to that of the outsole  4 . Alternatively, the insert may be of a single heterogenous piece of material. 
     The lower portion  5 ′ (eg the outsole portion) of the insert  5  may advantageously be wider than the body portion which fits into the cavity  2 . This has the following advantages which help to maintain a constant proprioceptive stimulus pressure provided by the insert  5  at the location. Firstly, the broader outer part  5 ′ abuts the lower surface  15  of the midsole element  3 . This prevents the insert from being over-compressed and receding into the cavity. It also distributes the load on the insert more evenly, thereby ensuring a constant proprioceptive stimulus effect from the insert as a whole on the wearer&#39;s foot at that location. Secondly, the broader outer part  5 ′ covers the region where the sidewall of the insert body is in contact with the sidewall of the cavity. If sand, grit, dust or water is allowed to penetrate this region, which may happen in the arrangement of  FIGS. 5 and 6 , for example, the accumulated matter may cause a hardening effect which will alter the proprioceptive pressure at the location and/or erode the material of the midsole  3  or the insert  5 , such that the insert may work loose and drop out. 
       FIG. 8  shows an example variant in which the insert  5  extends downward beyond the outsole  4 , thereby increasing the proprioceptive pressure effect at the location. This is made possible, with a reduced risk of the insert being pushed up into the cavity, by the shoulder which abuts the lower surface  15  of the midsole  3  as described above. 
       FIGS. 9 to 11  show variants in which an optional plate  16  is included over all or some of the inserts  5  in order to delocalise the pressure which occurs between the foot and the individual inserts  5 . The plate  16  may be hard enough and flexible enough to distribute the pressure without influencing the proprioceptive or sensory-motoric effect of graded or varied hardnesses of the inserts. The plate  16  may optionally cover the whole foot-contact area of the sole or even the whole area of the sole. The plate  16  may optionally be recessed into the upper surface  7  of the midsole  3  as shown. The inserts  5  of  FIG. 9  are shown flush with the lower surface of the outsole  4 . The inserts  5  of  FIG. 10  extend slightly (1 mm to 5 mm) proud of the lower surface of the outsole  4 , and the inserts  5  of  FIG. 11  are profiled and extend further, thereby further increasing the localised proprioceptive stimulus pressure at the location. 
       FIGS. 12 to 14  show variants in which the cavities and inserts are angled slightly from the vertical, in a transverse direction as in  FIG. 13  and/or in a longitudinal direction as in  FIG. 14 . The vertical axes  8 ,  8   1 ,  8   2 ,  8 ′ of one or more cavities may be angled slightly outwardly or inwardly in order to enhance the effect of the choice of insert hardness. The cavities of the forefoot region may be angled forwards from the vertical in order to increase an acceleration effect at the end of the gait ground contact cycle, thereby enhancing a rolling or rocking in the gait of the wearer. With this configuration it is thus possible to perform a pronation control as discussed above, in addition to enhancing a rolling gait of the wearer. The tilt angles mentioned here are preferably less than 30 degrees, or more preferably less than 15 degrees. 
       FIG. 15  shows an example of an insert retention arrangement. The inserts may be retained in the midsole  3  by gluing, bonding, welding, or by form-fit, compression fit or other mechanical fitting. Advantageously, the inserts may be glued in position using an adhesive which allows the insert to be released (for example by application of heat) and replaced. Alternatively, or in addition to the gluing, bonding etc, a retention element such as a peg or pin  17  may be inserted, for example transversely, as shown in  FIG. 15 , to secure the insert  5  in position so that it cannot fall out or work its way out of its cavity  2 . 
     Inserts  5  may be made so that they can be inserted into the midsole  3  by hand, for example.  FIGS. 16 to 27  show various configurations in which the lower (outsole) part  5 ′ of the insert extends laterally outward of the insert body  5 . The outsole  4  is provided with an opening shaped and dimensioned to accommodate the corresponding lower part  5 ′ of the insert. 
       FIG. 16  shows a simple insert geometry in which the lower part  5 ′ is flush with the upper and lower surfaces of the outsole  4 . 
       FIG. 17  shows an arrangement in which the upper surface of the lower part  5 ′ is flush with the upper surface of the outsole  4 , and the lower surface of the lower part  5 ′ extends proud of the lower surface of the outsole  4 . As with any of the arrangements described, the lower surface of the lower part  5 ′ of the insert may be provided with a texture or tread for improved grip. 
       FIG. 18  shows an arrangement in which the shoulder formed by the upper surface of the lower part  5 ′ abuts a corresponding shoulder formed in the sidewall of the opening in the outsole  4 . In this example, the lower part  5 ′ also extends proud of the outsole  4 . 
       FIG. 19  shows an arrangement in which the lower part  5 ′ abuts the outer surface of the outsole  4 . 
       FIG. 20  shows how the side surfaces of the lower part  5 ′ of the insert may have other profile shapes such as the angled surface shown. 
       FIG. 21  shows an arrangement in which the lower part  5 ′ of the insert has two shoulders; a first, upper one which may be similar to the abutment arrangement of  FIG. 16 or 17 , for example, and a second, lower shoulder similar to the abutment arrangement of  FIG. 19 . Two or more shoulders may be advantageous in that they provide more protection against dirt or water ingress. They also provide more surface area for bonding the inserts lower part  5 ′ to the outsole  4  and/or the midsole  3 . 
       FIG. 22  shows how the upper part of the insert body  5  may be provided with a cavity  12  which may help to retain the insert in the cavity by vacuum suction. When vertical pressure is exerted on the insert, compressing it slightly, air may be expelled from the cavity  12 . When the pressure is release, the surfaces around the cavity may be drawn together by the resulting pressure differential so as to create a gas-tight seal which prevents air from re-entering the cavity  12 . The cavity  12  may be deeper than illustrated. The hardness of the insert material may be increased so as to maintain the propriocepive (sensory motoric) stimulus effect with the reduced volume of solid insert material. 
       FIG. 23  shows a two-shoulder arrangement similar to that of  FIG. 21 , in which the lower should is adapted to accommodate bending movement of the outsole  4  by being sufficiently elastic and/or sufficiently well bonded to the outsole  4  that the lower should forms a reliable permanent seal against the ingress of dirt or water. 
       FIG. 24  shows how the insert may be shaped to be retained in the cavity by mechanical fitting. In the example shown, the middle part of the insert body may be slightly wider than the opening through which the insert is inserted, thereby preventing the insert from falling out or riding out of the cavity. 
     The inserts  5  may be provided with a positive-fit engagements, which may engage with corresponding recesses in the cavity wall, for example. The protrusions may alternatively be arranged in the cavity and the recesses on the insert.  FIGS. 24 to 27  show illustrate various further examples of how the inserts may be retained in the cavities by such positive fit or other mechanical interference. Such retention arrangements may be used alone or in combination. 
       FIG. 25  shows an example in which the insert is retained in the cavity by one or more latch-rings or laching or stepped protrusions  26 ,  27  in the body and/or outsole part of the insert  5 . 
       FIG. 26  shows an example in which the insert and cavity engage by means of a thread  28 , whereby the insert can be screwed into the cavity. A slot  29  or other engagement profile may be provided for ease of turning the insert. 
       FIG. 27  shows how a form fit insert retention may be implemented by angled or tapered surfaces  30 . In this case it may be advantageous to provide a special tool configured to compress the lower part  5 ′ of the insert during insertion, so that it will pass more easily through opening of the outsole  4 . 
     The inserts may extend up to 5 mm or more proud of the lower surface  15  of the outsole  4 , for example, thereby enhancing a sensomotoric (proprioceptive) loading-response of the wearer, in which the foot alters its orientation and movement in response to localised pressure from the inserts and thereby influences the gait of the wearer. 
     In the above examples, the inserts  5  have been shown inserted from below into cavities  2  which extend vertically to a point below the upper surface  7  of the midsole  3 . The inserts and cavities may alternatively be configured to extend right to the upper surface  7  of the midsole  3  or even to protrude above the upper surface  7  so as to create a further enhanced proprioception (sensory-motoric) stimulus in the sole of the wearer&#39;s foot. 
     The cavities  2  may be provided with a protective liner  18  as shown in  FIGS. 28 to 33 . The linings  18  of the cavities may be formed as separate pieces and pressed or bonded into the cavities in the midsole  3 . Advantageously, the linings  18  may be formed (for example moulded) as part of the outsole  4 , for example such that the outsole  4  and linings  18  form a contiguous waterproof barrier to prevent water from contacting the midsole material, which may be partially absorbant. The cavities formed by the linings may be provided with stepped shoulders, as shown in  FIGS. 29, 30, 32 and 33 , for receiving the broader outsole part  5 ′ of the insert inserted into the lining. 
     The cavities and inserts are shown vertically oriented in  FIGS. 28 to 33 , however, they may be oriented at up to 15°, or up to 30°, from the vertical, for example to provide priorioceptive stimulus along the direction of local maximum force transfer to the wearer&#39;s foot. 
     The inserts are shown as straight-sided cylinders, but they may be waisted or bulged so as to enhance their retention in the cavity. 
       FIG. 34  shows a variant in which the insert  5  has a substantially round cross-section (eg spherical or cylindrical). The elastomeric outsole  4  and lining  18  may be configured to be elastic that the cavity can be opened wide enough to push the round insert in, and tight enough to retain the round insert once inserted. 
       FIGS. 35 and 36  show how a retaining lug or protrusion  17  can be formed (advantageously contiguous with the material of the outsole  4  and lining  18 . The outsole can be made sufficiently elastic that the cavity opening can be widened enough to push in the insert (which may or may not have an indent corresponding to the lug  17 ), such that, when the cavity is allowed to close again, the insert is retained in position by the additional lateral compression of the lug  17  on the insert body  5  in the cavity  2 . Cavities in the forefoot and ball regions may advantageously be provided with one or more such lugs, as these regions are susceptible to the greatest flexing during walking or running. In particular, the lug may advantageously be located on the forwarded side wall of the cavity, so as to retain the insert against flexing from the forefoot region. One or more lugs may optionally be provided on the rearward wall, and/or on one or both lateral or medial side walls of a cavity. 
     As shown in  FIG. 37 , a widened part  19  may be formed at a distal end of the insert  5 , and may act as a similar retaining function be exerting lateral force on the side walls of the cavity  2  into which is it inserted. The distal widened part  19  may advantageously be made harder than the body of the insert  5 , to provide additional ‘bite’ into the side wall. If the insert is made of an elastomeric foam material, the widening may be achieved by pressing a hot plate against the end surface of the insert, or by cutting the insert from an extruded length of the material using a hot wire or blade. This process has the advantage that it also seals the open cellular end surface against eg water absorption.