Modular Insert System for Shoe Soles

Abstract

A support customising system is described for a sole 1 of a shoe. The sole 1 comprises a relatively soft, resilient midsole 3 and an a harder outsole 4. Hard insert elements 5 are provided for inserting into vertical cavities 2 in the midsole 3. By varying the hardnesses of different inserts 5 in different vertical cavities, a precisely-tunable pronation control effect on the wearer's gait can be effected. First-order, second-order and third-order pronation control effects are described.

Claims

1. Pronation control customising system for an article of footwear, the system comprising: a sole comprising a midsole of a first material having a first durometer, the midsole having an upper, foot-facing surface and a lower, ground-facing surface, a plurality of vertical cavities in a first region of the midsole, each vertical cavity extending along a vertical axis substantially orthogonally to the upper surface, between the lower and the upper surfaces of the midsole, and a plurality of support adjustment elements, for each being substantially wholly inserted into one of the vertical cavities so as to adjust a vertical support hardness of the sole at the location of said each vertical cavity; wherein each vertical cavity comprises a insertion opening in the upper surface and/or in the lower surface for receiving one of the support adjustment elements, and wherein the plurality of support adjustment elements comprises a first support adjustment element having a second durometer and a second support adjustment element having a third durometer, different from the second durometer, wherein at least one of the second and third durometers is greater than the first durometer, wherein the cavities and support adjustment elements are each configured such that the net vertical hardness of the sole at the location of each cavity is determined in a great majority by the hardness of the particular insert in the cavity, and wherein the cavities and support adjustment elements are arranged for pronation control such that a first plurality of the vertical cavities is arranged in a first pronation control region of the sole, and a second plurality of the vertical cavities is arranged in a second pronation control region of the sole, the first and second pronation control regions being on medial and lateral sides, respectively, of the ideal gait line of the sole.

2. System according to claim 1, wherein each of the first and second support adjustment elements, when inserted into a first one of the vertical cavities, and the plurality of vertical cavities have substantially the same cross-section as the first vertical cavity in a horizontal plane parallel to the upper and or lower surface, such that the first and second support adjustment elements are interchangeably insertable into the first vertical cavity through the insertion opening of the first vertical cavity.

3. System according to claim 1, wherein the first support adjustment element, the second support adjustment element and a first one of the plurality of vertical cavities have substantially the same vertical length along the vertical axis.

4. System according to claim 1, wherein the first and second support adjustment elements and the plurality of vertical cavities each has a substantially constant cross-section along at least a majority of its vertical length.

5. System according to claim 1, wherein: the first and second support adjustment elements each comprises a first protrusion arranged on a lateral outer wall of said first or second support adjustment element; and/or the first vertical cavity comprises a second protrusion arranged on a lateral inner wall of the first vertical cavity; wherein the first and/or second protrusions are configured to provide a positive-fit or friction grip between the lateral outer wall of said first or second support adjustment element and the inner wall of the first vertical cavity, for resisting a movement of said first or second support adjustment element in the first vertical cavity along the vertical axis in a withdrawal direction of the first and/or second support adjustment elements from the first vertical cavity.

6. System according to claim 5, wherein the first and/or second protrusion is formed as a screw thread.

7. System according to claim 1, wherein one or more of the support adjustment elements (5) comprises engagement purchase means formed at an end of said each support adjustment element, wherein: the engagement purchase means is configured for providing a pulling purchase for withdrawing the support adjustment element from within one of the vertical cavities along the vertical axis of the vertical cavity, and/or the engagement purchase means is configured for providing rotational driving purchase for driving a rotation of the support adjustment element about the vertical axis of the vertical cavity when the support adjustment element is inserted into the vertical cavity or when the support adjustment element is being withdrawn from the vertical cavity.

8. System according to claim 1, wherein the first and/or second support adjustment elements comprise a sensory-motoric stimulus protrusion configured to protrude proud of the upper surface when said first and/or second support adjustment element is fully inserted in one of the vertical cavities, the proudness of the sensory-motoric stimulus protrusion being configured to provide a sensory-motoric load-response stimulus to a wearer's foot at the location of the said first or second support adjustment element.

9. System according to claim 1, wherein each support adjustment element, when fully inserted into a corresponding one of the vertical cavities, extends along substantially the whole vertical depth of the midsole.

10. System according to claim 9, wherein the first and second pluralities of vertical cavities and the plurality of support adjustment elements have substantially the same cross-section, such that the first plurality of support adjustment elements can be fittedly inserted into the vertical cavities of the first and second pluralities.

11. System according to claim 1, in which the second durometer is at least 5 Shore greater than the first durometer.

12. System according to claim 1, in which the third durometer is at least 5 Shore greater than the second durometer.

13. System according to claim 1, in which the second durometer is less than or equal to the first durometer.

14. System according to claim 1, in which the sole comprises an outsole, below the lower surface of the midsole, the outsole having a fourth durometer greater than the first durometer.

15. System according to claim 14, wherein at least one of the vertical cavities is closed at its lower end by the outsole.

16. System according to claim 14, wherein at least one of the vertical cavities comprises a lower insertion opening, extending through the outsole, for receiving one of the support adjustment elements.

17. An article of footwear comprising the sole of claim 1.

18. The plurality of support adjustment elements of claim 1.

19. A method of using the system of claim 1, the footwear of claim 17 or the support adjustment elements of claim 18 to customise the pronation control provided to a wearer's foot by the sole, the method comprising the steps of: determining a pronation control requirement of the wearer's foot, based on the pronation control requirement, selecting said first and second support adjustment elements from said plurality of support adjustment elements, based on the pronation control requirement, selecting said first vertical cavity, wherein the first vertical cavity is located in a third gait control region for adjusting the pronation control provided by the sole to the wearer's foot for meeting the pronation control requirement, inserting one of the first and second support adjustment elements into said first vertical cavity.

20. Method according to claim 19, further comprising the step of inserting the other of the first and second support adjustment elements into a second vertical cavity in said third gait control region or in a fourth gait control region, different from the third gait control region.

Description

BRIEF DESCRIPTION OF DRAWINGS

Description of Drawings

[0011] FIG. 1a shows in side view a schematic cross-section of an example shoe employing the support customising system of the invention.

[0012] FIG. 1b shows in isometric view an example of support adjustment inserts for use in the support customising system of the invention.

[0013] FIG. 2 shows a schematic plan view of a first example sole employing a support customising system of the invention.

[0014] FIG. 3 shows a schematic plan view of a second example sole employing the support customising system of the invention.

[0015] FIGS. 4a, 4b and 4c show side elevation views of example vertical cavities arrangements in a sole for a support customising system according to the invention.

[0016] FIG. 5 shows in side view cross-section an example of a vertical cavity arrangement in a sole for a support customising system according to the invention.

[0017] FIG. 6 shows in rear view cross-sections of example vertical cavity arrangements in the heel region of a sole for a support customising system according to the invention.

[0018] FIG. 7 shows in rear view cross-sections of example vertical cavity arrangements in the forefoot region of a sole for a support customising system according to the invention.

[0019] FIG. 8 shows in side view cross-section a further example of a vertical cavity arrangement in a sole for a support customising system according to the invention.

[0020] FIGS. 9 and 9b show in side-view cross-sections a first example of an insert-retention arrangement for retaining a support adjustment insert in a vertical cavity in a support customising system according to the invention.

[0021] FIGS. 10a and 10b show in side-view cross-sections a second example of an insert-retention arrangement for retaining a support adjustment insert in a vertical cavity in a support customising system according to the invention.

[0022] FIGS. 11a and 11b show in isometric view examples of pulling purchase and rotational driving means of support adjustment inserts for use in a support customising system according to the invention.

[0023] FIGS. 12a and 12b show in isometric view examples of variants of support adjustment inserts having upper protruding portions for use in a support customising system according to the invention.

[0024] FIG. 13 shows in rear-view cross-section an example arrangement of the support adjustments inserts of FIGS. 13 and 14 in a sole for a support customising system according to the invention.

[0025] FIGS. 14a and 14b show in side view cross section an example of a compound insert for use in a support customising system according to the invention.

DISCLOSURE OF INVENTION

Detailed Description of the Invention

[0026] An example of a support customising system according to the invention is illustrated in FIGS. 1a and 1b. FIG. 1a depicts a schematic cross-section of a shoe with a sole 1 comprising an outsole 4, a 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 material such as rubber or 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. 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's foot. The liner or insole 6 may be removed to expose the upper surface 7 of the midsole 3.

[0027] The example sole 1 illustrated in FIG. 1a is provided with a plurality (six are shown) of vertical cavities 5, each of which extends from the lower surface 15 of the midsole (ie the upper surface of the outsole 4 in this example) up to the upper surface 7 of the midsole 3 along a vertical axis 8. The midsole 3, apart from the holes (cavities 5) 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, ground-facing surface 15 of the midsole 3, at least in the heel and/or midfoot regions 13, 14 of the sole 1. 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 30 degrees from the vertical axis 8 shown in FIG. 1a.

[0028] FIG. 1b shows a set of inserts or plugs 5, also referred to in this description as support adjustment inserts, which are designed for insertion into the cavities 2 in the midsole 3. In the example shown in FIGS. 1a and 1b, the inserts 5 may be inserted into the cavities 2 by first removing or raising the insole 6, and then pushing an insert 5 into each cavity 2 through insertion openings 10 in the upper surface 7 of the midsole. It is alternatively possible to configure the sole 1 such that the inserts 5 are inserted from below, through openings in the outsole 4. This has the advantage that the insertion openings 10 are more readily accessible. An alternative possibility is to provide insertion openings 10 in both the outsole 4 and the upper surface 7 of the midsole 3, as discussed below.

[0029] 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.

[0030] 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. 1a may be purchased with a set of inserts 5 similar to those shown in FIG. 1b, 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.

[0031] 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'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'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).

[0032] The vertical cavities 2 and the inserts 5 shown in the example of FIGS. 1a and 1b 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 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 30 mm across, for example.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] FIG. 2 shows a plan view of a shoe sole 1 similar to the sole 1 shown in FIG. 1a, 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 right shoe, viewed from above, but it will be understood that the following description applies equally to a corresponding left shoe, although the arrangement of inserts 5 may be different between the left and right shoes.

[0037] 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 region 23 and a metatarsal region 24. 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.

[0038] Left and right feet naturally have slightly different pronation styles, due to the natural asymmetry in the person's posture and due to neurological effects which gives rise to asymmetries in gross motor control, reflected in the person's posture and gait.

[0039] 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.

[0040] 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).

[0041] 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'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's gait.

[0042] 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 hind-most 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.

[0043] 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.sub.1 of the medial region 21 and the hardnesses of the inserts 5.sub.1 and 5.sub.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's contact with the ground when walking or running. Taking the six medial control inserts 5.sub.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.sub.2 relative to the hardness of midsole 3 and/or of the medial control inserts 5.sub.1. Harder lateral inserts 5.sub.2 will encourage greater pronation, softer lateral inserts 5.sub.2 will promote pronation less. However, by varying the difference between the durometers of the lateral inserts 5.sub.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.sub.2 is much harder than the forward-most lateral insert 5.sub.2, then the rate of pronation with respect to the foot'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.sub.2 varies little along the heel to toe direction, then the pronation-enhancing effect with respect to the foot's forward motion will be less. If the foremost lateral insert 5.sub.2 is harder than the rear-most insert 5.sub.2, then this will act to reduce the rate of pronation.

[0044] The lateral and medial inserts 5.sub.1 and 5.sub.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.sub.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.sub.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.sub.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).

[0045] 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/talal tilt can be compensated for, for example, while minimising the effect on the metatarsal or forefoot regions.

[0046] The control effects described above in relation to the interchangeable inserts 5.sub.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.sub.1, and the forefoot control region 23, with its forefoot control inserts 5.sub.3. A single mid-foot control insert 5.sub.4 is illustrated in midfoot control region 24, which may be included in the midfoot/metatarsal region to discourage the wearer'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.

[0047] As a consequence of such finely-adjustable and adaptable gait control, it is possible to improve the wearer's gait and straighten the wearer'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.

[0048] 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's gait changes.

[0049] 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 fore-most).

Example 1: For Correcting a Slight Supination

[0050] Lateral control region 22: 50 Shore, 60 Shore, 60 Shore

[0051] Medial control region 21: all 50 Shore or less

[0052] Forefoot lateral control region 23: all 60 Shore

Example 2: For Correcting a Delayed Overpronation

[0053] Lateral control region 22: all 50 Shore (no correction)

[0054] Medial control region 21: 50, 60, 70, 80, 80, 60 Shore

[0055] Forefoot lateral control region 23: all 60 Shore

Example 3: For Correcting Severe General Overpronation

[0056] Lateral control region 22: 50, 50, 60 Shore

[0057] Medial control region 21: 70, 80, 90, 80, 70, 60 Shore

[0058] Forefoot lateral control region 23: all 60 Shore

Example 4: For Correcting Early, Slight Overpronation

[0059] Lateral control region 22: 50, 50, 60 Shore

[0060] Medial control region 21: 70, 60, 50, 50, 50, 50 Shore

[0061] Forefoot lateral control region 23: 70, 60, 50, 50, 50 Shore

Example 5: For Correcting Delayed, Slight Overpronation

[0062] Lateral control region 22: all 50 Shore (no correction)

[0063] Medial control region 21: 50, 50, 60, 60, 70, 70 Shore

[0064] Forefoot lateral control region 23: all 50 Shore (no correction)

[0065] A second example sole layout is shown in FIG. 3. In this case, multiple inserts 5.sub.5 are provided in the midfoot region 13, in a midfoot pronation control region 25. Such an arrangement can be used on its own or in addition to inserts in other regions 19, 21, 22 and/or 23 to influence the pronation from the lateral side to the medial side. Increasing the hardnesses of inserts 5.sub.5 from lateral to medial, for example, would help to slow the pronation rate in the midfoot area, while the pronation rate can be enhanced by decreasing the hardnesses of the inserts 5.sub.5 from the lateral towards the medial side. In the configuration of FIG. 3, inserts of two sizes are shown. In such a configuration the shoes could therefore be provided with two sets of inserts 5.sub.1/5.sub.2 and 5.sub.3/5.sub.5, each set having inserts of multiple hardnesses.

[0066] FIGS. 4a to 4c illustrate example arrangements for the openings 10 of the cavities 2, as mentioned above in relation to FIG. 1. In FIG. 4a, the cavity 2 comprises an opening 10 in the upper surface 7 of the midsole 3, and is closed at its lower end by outsole 4. In FIG. 4b, the cavity 2 is shown with an opening 10 in the outsole 4, and closed at its upper end by a small portion (eg less than 10% of the vertical thickness) of the material of the midsole 3. FIG. 4c shows a third variant, wherein the cavity 2 has an upper opening through the upper surface 7 of the midsole and a lower opening through the outsole 4, such that the inserts 5 can be inserted or replaced via either end of the cavity 2. Thus in the variants shown in FIGS. 4b and 4c, the vertical cavity 2 extends through the lower surface 15 of the midsole 3 to the lower surface 15′ of the outsole 4.

[0067] 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.

[0068] FIG. 5 shows a variant of the system of the invention in which a 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 6 may be hard enough and flexible enough to distribute the pressure without influencing the effect of graded or varied hardnesses of the inserts. The plate 16 may optionally be recessed into the upper surface 7 of the midsole 3 as shown in FIG. 5.

[0069] FIG. 6 shows three variants of cavities 2 which are angled slightly from the vertical, in this case in a transverse direction. The vertical axes 8.sub.1, 8.sub.2 of one or more cavities 2 may be angled slightly outwardly or inwardly in order to enhance the effect of the choice of insert hardness. Similarly, the cavities 2 of the forefoot region may be angled slightly from the vertical as shown in FIG. 7.

[0070] The cavities 2 may also be angled in a longitudinal direction, as shown in FIG. 8. In the illustrated example, six inserts 5 are shown having vertical axes 8′ which are set at different angles α to the axis 8 orthogonal to the principal plane of the sole. In this example, the rearmost inserts are angled rearward and the foremost inserts are angled forward, 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.

[0071] Inserts 5 may be made so that they can be pushed into the midsole 3 by hand, for example. FIG. 9a shows how the outer wall of the insert 5 may be provided with a positive-fit engagements means, in this case protrusions 25, which may engage with corresponding recesses 25′ in the cavity wall, as shown in FIG. 9b. The protrusions 25 may alternatively be arranged in the cavity 2 and the recesses 25′ on the insert 5. Alternatively, the protrusions 25 on the insert 5 wall may simply grip on the wall of the cavity 2 (insert 5) without the need for preformed recesses 25′ in the cavity wall.

[0072] FIGS. 10a and 10b show an alternative arrangement for securing the inserts in the cavities, in which the insert 5 is provided with a thread 26 on its outer wall. The inner wall of the cavity 2 may be provided with a corresponding thread 26′.

[0073] In order to insert and/or remove the inserts 5 into or out of the cavities 2, the inserts 5 may be provided with pulling engagement means for withdrawing the insert by pulling, or rotational driving engagement means for screwing the insert 5 into or unscrewing the insert out of the cavity 2. Two example arrangements are illustrated in FIGS. 11a and 11b. FIG. 11a shows how an end of an insert 5 can be provided with a recessed or otherwise shaped grip 27 for providing a purchase when pulling the insert 5 out of its cavity 2. FIG. 11b illustrates a slotted recess 28 for engagement with a screwdriver or similar tool so that the threaded insert 5 can be screwed in or out of a cavity 2.

[0074] FIGS. 12a and 12b illustrate two examples of how an end of an insert 5 can be shaped so as to provide an enhanced gait-control effect when located in a cavity 2. The insert 5 shown in FIG. 12a has a rounded raised portion 29 which extends beyond that length 11 of the insert 5 which will be accommodated by the cavity 2. The raised portion 29 can provide an enhanced gait control effect if one or more such inserts 5 fitted in the sole 1 extend above the upper surface 7 of the midsole 3. The protrusion(s) may extend up to 5 mm or even up to 10 mm above the surface 7 of the midsole 3, for example. Such protrusions 29 are felt by the wearer's foot and engender an effect known as sensomotoric loading-response, in which the foot alters its orientation and movement in response to localised pressure from the protrusions 29, and thereby influences the gait of the wearer.

[0075] FIG. 12b shows an insert 5 having an angled upper surface 30, which may be used for example to reinforce a direction of pronation, as in the example shown in FIG. 13, which shows a rear-view cross-section of a midsole 3 with medial and lateral inserts 5. The medial insert 5 has a domed protrusion 29 for loading-response as described with reference to FIG. 12a, and the lateral insert 5 has an angled upper surface 30 for enhanced pronation control. Such different types of protruding inserts may be used separately or together, depending on the desired effect.

[0076] If an insert is made from two or more insert sub-pieces, then the individual sub-pieces may each form a portion of the cross-section of the insert, for example, each extending over the vertical length 11 of the insert 5, or they may each form a portion of the vertical length 11 of the insert, such that the insert 5 is formed from two or more insert sections arranged along the vertical axis. An example of such an insert 5 is shown in FIGS. 14a and 14b, and may comprise insert sections of different vertical lengths and/or different hardnesses. Insert sections 5′, 5″, 5′″ of different hardnesses and/or vertical lengths may be combined in one insert in order to provide the insert 5 with a particular required overall vertical hardness. Inserts and insert sections may be colour coded or otherwise marked in order to indicate their hardness, their vertical length, and/or the region(s) of the sole for which they are intended. Different regions of the sole may be provided with inserts 5 of different cross-sectional shapes or dimensions, in which case different sets of inserts 5 or insert sections 5′, 5″, 5′″ may be required for different regions of the sole 1. Alternatively, the vertical cavities 2 and the inserts 5 or insert sections 5′, 5″, 5′″ may be sized and shaped such that each insert 5 fits each vertical cavity 2.

[0077] The compound insert 5 of FIGS. 14a and 14b may thus comprise multiple pieces 5′, 5″, 5′″, which may be glued, bonded, screwed, clipped, or welded together, for example, or may be inserted and secured in the cavity 2 separately. The pieces 5′, 5″, 5′″ may have different heights and/or different hardnesses, so that a compound insert may be assembly whose height and net vertical hardness height can be finely tuned by selecting appropriate pieces 5′, 5″, 5′″.