BACKGROUND A shoe comprises an upper part and an inner sole that is attached to the upper part.

The upper part and the inner sole together form a cavity for a foot. An outer sole is arranged on the external surface of the inner sole. During the performance of a number of sports, there is a need for the performer to move rapidly and securely with shoes that give a firm foothold without the risk of slipping. A second requirement is normally that the wearer of the shoe must be able to maintain the orientation of the feet on the underlying surface. Shoes, and in particular sports shoes, are therefore provided with an outer sole with studs or a coarse pattern in order increase friction against the underlying surface and in this way provide a better foothold for the wearer.

Shoes can thus be provided with studs or other means of increasing friction that provide a secure grip on the underlying surface. Problems arise when a person wearing shoes that provide a firm grip against the underlying surface at the same time needs to be able to rotate the body and the feet in order to, for example, regain balance or to compensate for an abnormal rotation. When a person accidentally rotates the body while wearing shoes that do not allow the foot to be rotated against the underlying surface, rotational forces accumulate in joints and in the skeleton. Thus the leg, and in particular the knee and/or ankle, is exposed to the rotation, with joint injuries and fractures as a consequence. These injuries are often serious and take a long time to treat.

Document WO 97/13422 describes a sole for footwear. The aim of the sole is to reduce the risk for injuries when the wearer rotates or twists the foot during sporting activities and/or to assist rotational movements of the foot. The sole has one or several recesses, where each recess has a turntable mounted in it. The turntable can rotate to a limited degree in either direction from an initial resting position. It is an aspect of the design of the sole to prevent dirt from entering between the sole and the turntable. Furthermore, the document reveals an

embodiment in which the turntable returns to its initial position when the load is removed. A further embodiment specifies soft fins that are deformed during rotation of the sole.

Document US 5 392 537 describes footwear with a sole arranged with a turntable. The aim of the arrangement is to reduce the number of knee and foot injuries of performers of various sports by making possible or assisting a rotation of the foot/shoe even in the presence of a firm grip between the sole and the underlying surface.

One or several turntables are arranged in the outer sole of the shoe, in order to make turning of the foot/shoe possible. The turntables are arranged in the forward or rearward part of the sole or they are spread across the complete sole. If the shoe has studs, these are preferably located on the turntables. The turntables function such that they are rotated when the wearer wants to turn the foot and this is made impossible by the friction between the shoe and the underlying surface. In this way, rotation of the shoe relative to the underlying surface is made easier. The rotation would lead to injuries of the foot and knee of the wearer if the turntables were not present.

It is a present trend that sports clubs enter into expensive contracts with skilled performers. One requirement that has been expressed is that the players should be able to participate in planned matches during complete seasons. This, on the whole, produces the requirement that the players do not suffer injury. The most common injuries to the legs are joint injuries and fractures of the ankle and knee, with the problems that follow from these.

During production and use of shoes of the type specified above, a need therefore arises for a shoe that protects the foot/leg of the wearer from torsional forces by being sensitive to and reacting to the rotation and wobbling of the foot and in this way to the need of the upper part and the inner sole to be able to move relative to the outer sole.

The shoes in the documents specified above are not able to satisfy these requirements.

SUMMARY OF THE INVENTION A shoe comprises an upper part, which forms a cavity for a foot. Further, a shoe comprises an outer sole, which makes contact with the underlying surface on which the wearer of the shoe is walking. The outer sole can consist one or several sole elements.

Alternatively, the outer sole is built up from several layers, each of which consists of one or several sole elements.

The aim of the present invention is to arrange an outer sole in the form of one or several sole elements on a shoe defined as specified above. The outer sole is so attached that it permits in all situations rotation and wobbling of the foot and the upper part relative to the outer sole when friction between the outer sole and the underlying surface reaches a critical level at which the risk for an injury arises. The description"wobbling"concerns a sideways movement of the foot, which most often leads to an injurious angle for the foot. The aim of the invention is also to eliminate the accumulation of forces in joints and the skeleton of a person who rotates the body.

The solution according to the invention is characterised by the shoe specified in claim 1 comprising an upper part, an outer sole, and means for removably attaching the outer sole to the upper part and a sole attached to the upper part. The said means is arranged to instantaneously release during wearing of the shoe the outer sole from the upper part at a predetermined threshold value, selected in order to avoid injury to the wearer of the shoe, of a force acting between the upper part and the outer sole, which force arises through the pressure of the foot against the inner surface of the shoe and an engagement force between the outer sole and an underlying surface.

When the wearer of the shoe rotates the body, rotation and/or wobbling forces propagate through the body, via the leg to the foot and onwards to the shoe. When the forces, which have reached the foot and been transferred to the shoe, reach a predetermined threshold value, the outer sole is released instantaneously from the upper part according to the independent claim concerning the method. The wearer's foot, placed into the cavity formed by the upper part of the shoe, is released from the outer sole and can thus be moved completely independently of the underlying surface while at the same time the outer sole remains/is attached to the underlying surface.

It is part of the innovative concept to arrange pressure-sensitive devices in the upper part of the shoe, which record the pressure that the foot transfers to the shoe, particularly when rotating and/or wobbling. The pressure recorded provides a measure of the rotation and wobbling forces and, in this way, of the load on the wearer's foot. A second aim of the invention is to design the shoe with a data processor, for example, a computer chip, that calculates the total load that acts on the foot in the form of rotation and wobbling forces. The calculation is based on the recordings of a number of pressure-sensitive devices, where the devices are strategically placed preferably in the upper part of the shoe. In one embodiment of the invention, the pressure-sensitive device is designed as a tape or as a network.

The possibility of specifying a critical value of the calculated total load in the form of rotation and/or wobbling based on a number of selected recordings is also part of the innovative concept. Furthermore, it is part of the innovative concept that the outer sole is removably attached to the upper part in a number of different ways, all with the common property that they can be arranged to release/free the outer sole at a certain calculated load as described above. The calculation is based on signals from pressure-sensitive devices, where the signals are equivalent to the pressure that the wearer's foot achieves on the devices. The strategically placed pressure-sensitive devices are principally built into and distributed across the upper part of the shoe, particularly along the medial side and lateral side against which the foot presses during rotation and/or wobbling. This ensures that one or several sole elements are released from the sole of the shoe if and when the force between the upper part and the outer sole reaches a critical value that has been previously determined by trials. This critical value is selected and placed at a level corresponding to an acceptable level when considering the risk for injury. The critical value of the load varies between different points and regions of the shoe and in this way provides a measure of the load to which different parts of the foot can be exposed without being injured.

According to one advantageous embodiment of the invention, the outer sole is provided with one or several magnets. Electromagnets and a current source are built into the upper part of the shoe. When the foot rotates and/or wobbles in the shoe and thus applies pressure onto the pressure-sensitive devices, the value of the total load at certain points of the foot is calculated. These points can lie very close together and in this way cover entire areas of the foot. When the calculated value at one point or at several points reaches a predetermined critical value, the current to the electromagnets is broken and the outer sole is instantaneously released. It is also part of the innovative concept to release the outer sole through inverting the polarity of the magnets in the upper part.

It is also part of the innovative concept that the magnets are constructed from a coated plastic material with a magnetic active surface. In one advantageous embodiment of the invention, the magnetic surface is constructed with protuberances in order to increase the contact area between the magnets without increasing the size of the upper part/outer sole.

According to another advantageous embodiment of the invention, it is a mechanical attachment, for example in the form of a magnetic lock with balls, that is released when the current ceases.

In another advantageous embodiment of the invention, the outer sole is attached to the upper part with a glue that releases instantaneously when a certain critical loading, defined as specified above, acts in the glue layer. Alternatively, the glue may be dissolved by chemical means, where the solvent is stored in spaces that break at a previously selected critical loading. According to another advantageous embodiment of the invention, the outer sole is attached to the upper part with a laminate that is similar to double-adhesive tape, where the material in one layer of the layers of the laminate instantaneously breaks.

It is part of the innovative concept that the outer sole is released from the upper part with the aid of an explosive force that is activated at a certain critical load defined as specified above.

It is part of the innovative concept that the outer sole comprises several sole elements, which are attached at the upper part according to two or more of the embodiments specified above.

The innovative concept includes shoes that are used for football, American football, rugby and baseball. It is also part of the innovative concept that a certain pressure from the foot is to be accepted without the outer sole being released, for example, that it should be possible for a football player to kick a ball. The innovative concept also includes the description"shoe"comprising normal shoes, boots, sandals, and other footwear provided with a sole.

This description is not to be seen as a limitation of the invention but only as a guide to full understanding of the invention. Adaptation to footwear with other active parts incorporated and the replacement of parts and items that are obvious for one skilled in the arts can, naturally, be made within the innovative concept.

DESCRIPTION OF DRAWINGS The invention will be explained in more detail through the description of an embodiment with reference to the attached drawings, where Fig. 1 shows a shoe according to the present invention equipped with magnets, Fig. 2 shows an alternative embodiment of the invention, where the shoe is equipped with a double-adhesive laminate,

Fig. 3 shows the shoe according to Figure 2 where the laminate has been replaced by a glue layer, Fig. 4 shows a glue layer provided with balls containing solvent mixed into it, where the glue layer has been applied to an outer sole, Fig. 5 shows an outer sole that consists of three sole elements, Fig. 6 shows a layer with protuberances with a magnetic surface that has been applied to an outer sole.

DESCRIPTION OF EMBODIMENTS A shoe (see Fig. 1) comprises an upper part 2 with a sole 3. The upper part 2 forms a cavity 4 for the wearer's foot (not shown). The sole 3 comprises an inner surface 3a and an outer surface 3b. The inner surface 3a faces in towards the cavity 4 and the foot. The outer surface 3b faces outwards towards an outer sole 6 and the underlying surface, on which the wearer of the shoe walks. The outer sole 6 has a upper surface and a lower surface. The upper surface faces and makes contact with the outer surface 3b of the sole 3 on assembly. The lower surface faces and makes contact with the underlying surface when the shoe is in use.

Pressure sensors 7a and 7b are built into the upper part 2 and are distributed principally along the medial side 7a and the lateral side 7b of the foot/shoe. Electromagnets 8 are built into the upper part 2, preferably in the sole 3, and lie at the level of the outer surface 3b of the sole. The outer sole 6 contains built-in magnets 9, which lie at the level of the upper surface of the outer sole. A programmable unit or a data processor (not shown) is built into the upper part 2 and is electrically connected to the pressure sensors 7. A current source, normally in the form of a battery (not shown), is arranged in the upper part 2 in order to power the electromagnets 8 and the programmable unit.

The shoe functions as follows. The wearer of the shoe rotates and/or wobbles the foot, whereby it presses against certain pressure sensors 7, which send a signal corresponding to the level of pressure to the programmable unit. The unit, which contains a computer program, records the values that correspond to the signals. The program combines the values from the pressure sensors that belong together from the point of view of the loading as described above. For example, a combination of signals from the pressure sensors on the medial side at the toe and from the lateral side at the heel gives a measure of the load, defined as specified above, that acts on the foot. Calculation models are stored in the program for different

combinations of signals, together with equivalent preselected critical values of the load, defined as specified above, for each combination. The critical values are selected such there is no risk for injury. The critical values can be adjusted and vary from person to person.

The shoe functions such that if a rotation and/or wobbling of the foot gives a calculated loading of a critical magnitude, defined as specified above, a signal to break the current passes from the programmable unit to the current source. The magnetic field around the electromagnets 8 disappears and thus the outer sole 6 is instantaneously released.

Alternatively, a signal passes from the programmable unit to invert the polarity of the electromagnets and thus the outer sole 6 is instantaneously repelled. The shoe in Fig. 1 is provided with studs 12, which increase the grip/friction of the outer sole against the underlying surface.

A shoe is shown in Figure 2 with an upper part 2 comprising a sole 3 and an outer sole 6. A layer 13 in the shape of the sole, consisting of a laminate, with two sticky surfaces 13a and 13b is arranged between the sole 3 and the outer sole 6. The layer 13 is applied by the sticky surface 13a being attached to the outer surface 3b of the shoe and the sticky surface 13b being attached to the upper surface 6a of the outer sole. The layer 13 is manufactured from a laminate with such material properties that it instantaneously breaks/cracks at a certain critical load, determined through trials, and defined as specified above.

A shoe is shown in Figure 3 with a sole 3 and an outer sole 6. The outer sole 6 is glued onto the sole 3 with a glue layer 14. The glue in the layer 14 has the property of instantaneously breaking at a certain critical load, determined through trials, and defined as specified above. An alternative is shown in Figure 4 in which the glue layer 14 is instantaneously dissolved in a chemical manner. A solvent is mixed into the glue layer in the form of small balls/bubbles that contain the solvent, which balls/bubbles break at a certain critical load, determined through trials, and defined as specified above. The solvent will, in this way, come into contact with the glue and dissolve it.

Figure 5 shows an alternative design of the outer sole 6 in which it is divided into several sole elements 6a, each of which is provided with at least one magnet 9.

Figure 6 shows an alternative design of the outer sole 6 in which the magnets have been replaced by a layer 16 of coated plastic material with a magnetic active surface. The layer is designed with protuberances 17 in order to increase the area of contact between the sole 3 and the outer sole 6.