In a normal walking gait, there is a clear sequence in which various parts of each foot contact a surface, and in which the weight imposed on each foot is transferred. The heel of a foot is first to contact the surface (the heel strike). The metatarsal region of the sole of the foot then rotates downwardly and comes into contact with the surface, as the walker's weight is transferred forwards. The heel is then raised, and the weight on the foot is imposed entirely on the metatarsal region and the toes. The second foot is by now in contact with the surface, bearing much of the walker's weight, and the first foot is rotated further until its toes push off from the surface (the toe-off). The first foot is then swung forward, for its next heel strike, while the second foot is going through a similar sequence. The maximum impact on the foot occurs during the heel strike. There is a secondary impact on the metatarsal region, which also undergoes significant flexion during the foot movements described. It is therefore advantageous for a shoe or other item of footwear (henceforth, for simplicity, referred to as a shoe) to be designed to dissipate the shock of the heel strike and the metatarsal contact, and to distribute the pressure exerted on particular parts of the foot, such as the heel and the metatarsal region (especially the ball of the foot). This both reduces the prospect of injury to the foot and increases the comfort of the shoe.

A large number of designs for soles for shoes have been designed to such ends, incorporating pouches or the like, filled with air or other gases, and disposed beneath a wearer's heel and metatarsal region. In many cases, the pouch beneath the heel and the pouch beneath the metatarsal region are linked, allowing air, etc, to flow from one region to the other as each is brought into contact with a surface.

However, it has been found necessary to introduce many complicating features into such designs, in an attempt to provide the necessary degree of shock dissipation and cushioning.

For example, US Patent No. 4446634 discloses a shoe with two such pouches and two conduits connecting them. One conduit allows air to flow only from heel to sole, the other only in the reverse direction. Each conduit has a manually adjustable valve to regulate the airflow out of, and hence the springiness of, each pouch. UK Patent Application No.

2114425 discloses a system of non-return valves and an intermediate air reservoir to control the transfer of air from a heel pouch to one beneath a wearer's metatarsal region. PCT Patent Application No. WO 01/78539 describes a shoe sole containing a plurality of pouches and a control system, comprising valves, pressure sensors and even a central processing unit, to regulate the airflow between the pouches.

There are a large number of other, similar, air-pouch systems in the prior art, but their common feature appears to be an increasing degree of complexity, and a correspondingly increased difficulty of manufacture. Even so, none of them appear to be totally satisfactory.

One particular problem of an air-filled pouch is that it can collapse completely under load, and will then provide no further cushioning to the foot. The sole will then require further elaborate cushioning elements.

There is clearly a need for a more effective, efficient and convenient means of dissipating the shock of the heel strike and the metatarsal contact, and for improving pressure distribution across the foot.

It is hence an object of the present invention to provide a sole for a shoe, as herein defined, which cushions the foot of a wearer, dissipating the shock of impact of the foot on a surface and distributing the pressure of the wearer's weight about the foot, while obviating the above problems of complexity and the performance limitations of systems employing gas-filled bladders. It is also an object of the present invention to provide a cushioning element capable of use in such a sole, and to provide a shoe incorporating such a sole.

According to a first aspect of the present invention, there is provided a sole for a shoe, as herein defined, comprising a cushioning element of open-cell foamed plastics material extending substantially the length of the shoe from a heel zone disposable beneath a heel of a wearer's foot to a metatarsal zone disposable beneath a metatarsal region of said foot and including a connecting zone therebetween, and a compression means adjacent the heel zone and adapted to compress the heel zone when a heel portion of the sole is brought into contact with a surface.

Preferably, the compression means is a compression member extending upwardly from an outsole component of the sole.

Advantageously, the compression member is configured to contact a majority of a lower, in use, surface of said heel zone of the cushioning element.

Preferably, the cushioning element comprises an open-cell elastomer foam, advantageously an open-cell polyurethane foam, optionally a super-blown polyurethane foam.

The elastomer foam may have an uncompressed density of between 0.2 and 0.4 g. cm~3.

The metatarsal zone may extend to underlie at least parts of the toe regions of the foot and/or the arch of the foot.

The cushioning element may be generally planar and of generally even thickness, optionally slightly thinner along a median heel-toe zone.

The metatarsal zone, and optionally the connecting zone, of the cushioning element may be provided with a plurality of thickened zones, each adapted to underlie a region of the foot, such as the ball of the foot and the lateral edge of the foot, on which relatively high pressures are imposed during a step. Said thickened zones may be linked by a plurality of raised ribs, optionally extending from the connecting zone towards a toe end of the metatarsal zone.

The metatarsal zone may further be provided with a plurality of shallow grooves, aligned transversely to said heel-toe direction.

The cushioning element may be encapsulated by a continuous membrane impermeable to air or other gases.

Said membrane may comprise a flexible thermoplastics material, such as a polyester film, or may be a continuous surface layer of the plastics material comprising the cushioning element.

The sole may comprise an outsole element and a tread element or elements, mounted to a lower surface thereof, to contact the ground or other surface to be walked upon.

The outside element and the tread element (s) may each comprise a thermoplastic elastomeric material, such as a rubber.

The tread element or elements preferably are of greater hardness than the outsole element.

The tread element or elements may have a hardness, measured on the Shore A scale, of between 40 and 75, optionally approximately 55. The outsole element may have a hardness, measured on the Shore A scale, between 35 and 70, optionally approximately 50.

The compression member may be of the same material as the outsole element, and may be moulded integrally therewith.

The compression member may have a core zone of greater compressibility than a remainder thereof.

Said core zone may be hollow.

Alternatively, said core zone may comprise a foamed or blown zone.

The outsole element may comprise an array of locating members, configured to maintain the cushioning element in position.

Some or all of said locating members may extend supportingly beneath parts of the cushioning element, such as the heel zone thereof.

The sole may be provided with at least one translucent panel, extending through the tread element (s) and the outsole element thereof.

One such translucent panel may be disposed to underlie at least part of the compression means and the heel zone of the cushioning element.

One such translucent panel may alternatively or additionally underlie at least part of the metatarsal zone of the cushioning element.

A further such translucent panel may underlie at least a part of the connecting zone of the cushioning element.

The translucent panel or panels may advantageously have a hardness close to that of the tread element.

According to a second aspect of the present invention, there is provided a cushioning element of foamed plastics material as described above.

According to a third aspect of the present invention, there is provided a shoe, as herein defined, comprising a sole as described above.

Preferably, said shoe further comprises an insole element, mounted to the outsole element so as to overlie the cushioning element, and an upper element.

An embodiment of the present invention will now be more particularly described, by way of example and with reference to the accompanying drawings, in which: Figure 1 is a plan view from above of a sole for a shoe embodying the invention; Figure 2 is a schematic cross-sectional view of the sole of Figure 1, taken along the line II-II of Figure 1; Figure 3 is a plan view from above of a cushioning element, viewed separately from the sole of Figure 1; Figure 3A is a cross-section of the cushioning element of Figure 3, taken along the line A-A; Figure 3B is a cross-section of the cushioning element of Figure 3, taken along the line B-B; Figure 3C is a cross-section of the cushioning element of Figure 3, taken along the line C-C; and Figure 4 is a plan view from below of a sole embodying the invention.

Referring now to the drawings, and to Figures 1 and 2 in particular, a sole unit for a shoe comprises an outsole unit 1 and a tread 2. The outsole unit 1 and the tread 2 each comprise a thermoplastic rubber, the tread 2 having a Shore A hardness of approximately 55 and the outsole unit 1 a Shore A hardness of approximately 50.

The sole unit further comprises a cushioning insert 3 of open-cell superblown polyurethane foam, with an uncompressed density of approximately 0.3g. cm~3 The insert 3 comprises a heel zone 4 and a metatarsal zone 6, linked by a connecting zone 5.

The outsole unit 1 is provided with a plurality of struts 7 extending inwardly from a rim thereof, which contact a periphery of the insert 3 to maintain it in position. The struts 7 adjacent the heel zone 4 are provided with extensions 8 which underlie and help to support the heel zone 4 of the insert 3. (Not shown in Figure 2 for clarity).

The sole unit has a substantially hollow heel section 9. A striker pod 10 extends upwardly from an internal surface of the outsole unit 1 and the heel zone 4 of the insert 3 rests on an upper surface of the striker pod 10. The striker pod 10 is integrally moulded with the outsole unit 1, and has a foamed core 11, rendering it more compressible than the remainder of the outsole unit 1.

In one embodiment (not shown), the striker pod has a recess in its upper surface to accommodate a locating thickening of the insert 3.

The outsole unit 1 is provided with a rebate 12 to receive an insole unit (not shown for clarity) which completely encloses an upper surface of the insert 3. Details of the sole unit associated with its attachment to the remainder of a shoe, for example to the upper of the shoe, are conventional and are omitted from these Figures.

As is shown in greater detail in Figures 3,3A, 3B and 3C, the insert 3 is generally flat, with a plurality of thickened zones 12 raised slightly above the surface of the metatarsal zone 6.

The elliptical zones 12 are connected by a set of branching ribs 13, which stem from a trunk 14 disposed along the connecting zone 5. The zones 12 and the ribs 13 typically stand about 0. 5-l. Omm proud of the surface of the insert. The metatarsal zone 6 of the insert 3 is also provided with a series of parallel transverse grooves 15, about 0. 5-l. Omm deep, and further grooves 16 surround each zone 12 and rib 13. The thickened zones 12, ribs 13, trunk 14 and grooves 15,16 are present on both upper and lower surfaces of the insert 3.

The zones 12 provide additional cushioning beneath parts of the foot which come under particular pressure or required particular support, such as the ball of the foot, the lateral edge of the foot and the front part of the arch of the foot. The ribs 13 provided added strength to the metatarsal zone 6, and to a certain extent channel an increased airflow to the thickened zones 12. The transverse grooves 15 increase the flexibility of the metatarsal zone 6 of the insert 3.

The metatarsal zone 6 and the heel zone 4 each have a slightly thinner medial zone (17,18 respectively).

In use, the tread 2 of the heel section 9 of the sole unit strikes the surface first. The heel zone 4 of the insert is compressed between the wearer's weight transmitted from above and the striker pod 10, and the pressure of the heel strike is dissipated into the metatarsal zone 6. The internal structure of the open-cell foam is such that the heel zone 4 does not collapse and the shock dissipation provided is thus appreciably superior to current systems. The impact of the heel strike on the wearer's heel is thus much less intense.

The dissipation of pressure caused by the compression of the heel zone 4 will, in the main, cause a small increase in pressure within the metatarsal zone 6, just prior to the impact of the corresponding part of the sole on the surface. This provides added cushioning to reduce the shock of this secondary impact, and due to the increased foam thickness beneath parts of the foot on which most weight falls, these parts benefit from increased cushioning, helping to distribute pressure across the foot.

As the heel section 9 is raised and the metatarsal zone 6 receives the full weight exerted through the foot, a reverse, but less intense, dissipation of energy occurs and the insert 3 as a whole is able to return to its uncompressed state by the time that the next heel strike occurs. In the sole unit shown from below in Figure 4, three translucent panels 19,20, 21 are provided in the tread of the sole. These extend through the tread 2 and the outsole unit 1.

Each panel is of a hardness similar to that of the tread 2 and the outsole unit 1.

The sole unit described, and shoes containing it, thus provide an improved degree of shock dissipation and pressure dispersion, compared to soles known hitherto. The sole unit shown is significantly more comfortable than current sole units at each stage of its contact with the surface walked upon. Shoes incorporating such a sole are hence more comfortable to wear, and help to obviate injury or strain to the wearer's feet.