Item of footwear

1. An item of footwear for increasing leg-muscle and/or lower-abdominal-/back-muscle tone comprising:

a securing means for securing the item of footwear to a foot of a user; and

a sole comprising at least an upper layer, for engaging the foot of the user in use or a further layer, and a lower layer, for engaging the ground in use,

wherein:

the upper layer comprises a separately formed arch region, a separately formed frontal/toe region and a separately formed heel region, said arch region being formed of a first material having a hardness of substantially 25 to 35 on the Asker C scale, said frontal/toe region being formed of a second material having a hardness of substantially 40 to 50 on the Asker C scale, and said heel region being formed of a third material having a hardness of substantially 40 to 60 on the Asker C scale, said arch region being connected between said frontal/toe region and said heel region; the thickness of the sole tapers from the heel region to the frontal/toe region;

the sole being a ground-engaging surface from the frontal/toe region to the heel region;

the heel region has a greater thickness than the frontal/toe region; and

the sole being arranged such that application of the user's weight, when stepping on the sole in a progression from the heel region to the toe region, causes at least one of medio-lateral instability or anterior-posterior instability in at least one portion of the upper layer, which requires balance correction by the user.

2. An item of footwear as claimed in claim 1 , wherein the frontal/toe region, the arch region and the heel region are formed as a unitary sole.

3. An item of footwear as claimed in claim 1 wherein the sole is anatomically shaped.

4. An item of footwear as claimed in claim 1 , wherein the regions of the sole are provided internally, within the sole.

5. An item of footwear as claimed in claim 1 , wherein the second material and the third material are composed of different materials.

6. An item of footwear as claimed in claim 1 , wherein the arch region, the frontal/toe region and the heel region are arranged in a layered configuration.

7. An item of footwear as claimed in claim 1 , wherein:

an interface between the arch region and the frontal/toe region is substantially vertical; and

an interface between the arch region and the heel region is substantially vertical.

8. An item of footwear as claimed in claim 6 , wherein:

a first tapered portion of the arch region overlaps with a tapered portion of the frontal/toe region to form a substantially horizontally-oriented interface between the arch region and the frontal/toe region;

a tapered portion of the heel region overlaps with a second tapered portion of the arch region to form a horizontally-oriented interface between the arch region and the heel region; and

wherein the first tapered portion of the arch region is shorter than the second tapered portion of the arch region.

9. An item of footwear as claimed in claim 7 , wherein both the interface between the arch region and the frontal/toe region and the interface between the arch region and the heel region include irregularly shaped joining edges.

10. An item of footwear as claimed in claim 1 , wherein the second material and the third material have different hardnesses.

11. An item of footwear as claimed in claim 1 , wherein the hardness of the second material is substantially 45.

12. An item of footwear as claimed in claim 1 , wherein the hardness of the first material is substantially 31.

13. An item of footwear as claimed in claim 1 , wherein the hardness of the third material is substantially 54.

14. An item of footwear as claimed in claim 1 , wherein the upper layer comprises an upper-sole and a mid-sole, and wherein the mid-sole comprises the first material, second material and third material.

15. An item of footwear as claimed in claim 14 , wherein the upper-sole is integral with the mid-sole.

16. An item of footwear as claimed in claim 1 , wherein:

adjoining edges of the arch region and the frontal/toe region are irregularly-shaped to provide overlap of the first material and the second material; and

adjoining edges of the arch region and the heel region are irregularly-shaped to provide overlap of the first material and the third material.

17. An item of footwear as claimed in claim 1 , wherein the sole comprises an elastomer material, a silicone material, a natural rubber material, a synthetic rubber material, or a polyurethane material.

18. An item of footwear as claimed in claim 1 , wherein the sole comprises EVA (ethylene vinyl acetate).

19. An item of footwear as claimed in claim 1 , wherein the item of footwear is an item of open footwear.

20. An item of footwear as claimed in claim 19 , wherein the item of open footwear is a flip-flop or a sandal.

21. An item of footwear for increasing leg-muscle and/or lower-abdominal-/back-muscle tone comprising:

a securing means for securing the item of footwear to a foot of a user; and

a sole comprising a separately formed arch region, a separately formed frontal/toe region and a separately formed heel region, said arch region being formed of a first material having a hardness of substantially 25 to 35 on the Asker C scale, said frontal/toe region being formed of a second material having a hardness of substantially 40 to 50 on the Asker C scale, and said heel region being formed of a third material having a hardness of substantially 40 to 60 on the Asker C scale, said arch region being connected between said frontal/toe region and said heel region;

the sole being a ground-engaging surface from the frontal/toe region to the heel region;

the sole being arranged such that application of the user's weight, when stepping on the sole in a progression from the heel region to the toe region, causes instability in at least one portion of the sole, which requires balance correction by the user,

wherein the thickness of the sole tapers from the heel region to the frontal/toe region and the heel region has a greater thickness than the frontal/toe region, the sole comprises an upper surface, for receiving a foot of a user or an upper layer of sole, and a lower surface, for contacting the ground or a lower layer of sole, the upper surface and the lower surface being closer together at the frontal/toe region than they are at the heel region.

22. An item of footwear for increasing leg-muscle and/or lower-abdominal-/back-muscle tone comprising:

a securing means for securing the item of footwear to a foot of a user; and

a sole comprising an arch region formed of a first material, a frontal/toe region formed of a second material and a heel region formed of a third material, said arch region being connected between said frontal/toe region and said heel region such that application of the user's weight, when stepping on the sole in a progression from the heel region to the toe region, causes instability in at least one portion of the sole, which requires balance correction by the user, the sole being a ground-engaging surface from the frontal/toe region to the heel region,

wherein the thickness of the sole tapers from the heel region to the frontal/toe region and the heel region has a greater thickness than the frontal/toe region;

wherein the first material has a hardness of substantially 25 to 35 on the Asker C scale, the second material has a hardness of substantially 40 to 50 on the Asker C scale and the third material has a hardness of substantially 40 to 60 on the Asker C scale; and

wherein the third material has a relatively higher compressive resistance or density than the second material.

23. An item of footwear as claimed in claim 22 , wherein upper and lower faces of the sole taper from the heel region to the frontal/toe region.

24. An item of footwear as claimed in claim 22 , wherein at least upper and lower lateral edges of the sole taper from the heel region to the frontal/toe region.