according to one embodiment of the present invention , an article of footwear comprises a stability element , which is arranged beneath the foot of the wearer . this can be achieved by integrating the stability element in accordance with the present invention into the outsole of the article of footwear , or sandwiching it between the outsole and the midsole , or between the midsole and the insole . if the stability element is arranged within the outsole , it may differ in color from the surrounding material of the sole , so that the special form ( which is an indication for which sport the corresponding article is intended , as described more fully below ) of the stability element can easily be recognized from the outside . according to another embodiment , the outsole itself consists essentially of the stability element . in this case , an optional midsole and an optional insole can be applied to the upper side of the stability element to provide comfort and damping to the wearer of the article . the above described different possible arrangements of the stability element do not significantly influence the functional properties of the article comprising the stability element in accordance with the present invention , therefore , reference is made in the following ( and in the figures ) only to an article of footwear in general . before the design and the functional characteristics of the stability element in accordance with the present invention are described in detail , reference is made to the skeleton of a human foot 90 shown in fig1 to facilitate the understanding of the inventive principles with respect to the particular parts of the foot that are selectively supported . in fig1 reference numeral 92 depicts the metatarsals of a left human foot 90 , and reference numeral 95 depicts the phalanges ( toes ). essentially , both the metatarsals 92 and the phalanges 95 form the forefoot part of the foot . the metatarsal - phalangeal joints 93 are located between metatarsals 92 and phalanges 95 . the phalanges 95 include a plurality of interphalangeal joints 96 . during a walking or running cycle , the metatarsal - phalangeal joints 93 and the interphalangeal joints 96 allow the foot to flex and push - off from the ground . altogether , there are five metatarsals 92 referred to as the first , second , third , fourth and fifth metatarsals , 92 - 1 to 92 - 5 , moving from the medial side 99 of the foot to the lateral side 98 . similarly , there are five phalanges , 95 - 1 to 95 - 5 . finally , the heel bone 91 is depicted . for a stability element in accordance with the present invention , it is important for the sake of pronation or supination control to appropriately support the phalanges and the metatarsals . in the case of pronation control , metatarsal 92 - 1 and / or metatarsal 92 - 2 is supported , preferably with phalange 95 - 1 and / or 95 - 2 . in the case of supination control , metatarsal 92 - 5 and / or metatarsal 92 - 4 is supported , preferably with phalange 95 - 5 and / or 95 - 4 . the necessary support is provided by a stability element in accordance with the present invention , however , since supination is rarely a problem , and for the sake of conciseness in the following description , only pronation control stability elements are discussed . the present invention is , however , not restricted to this field . complementary shaped stability elements supporting the respective metatarsals and phalanges for supination control are also covered by the present inventive concept . one embodiment of a stability element for an article of footwear 1 for a right foot , in accordance with the present invention , is shown in fig2 . the stability element 10 comprises an oblong shape with a rearfoot area 12 and a forefoot area 13 . the stability element 10 extends from the rearfoot portion 2 of the article of footwear 1 into the forefoot portion 3 . as may be derived from fig2 the forefoot area 13 is designed and located within the shoe such that the first and / or second metatarsal of the wearer &# 39 ; s foot rests on the stability element , with any necessary additional sole layers therebetween , and are effectively supported . according to a particular embodiment of the invention , the stability element also supports the first and / or second phalange . between areas 12 and 13 , the stability element 10 comprises an area 11 with reduced lateral dimensions which allows twisting of the forefoot area 13 of the stability element 10 ( and thereby of the footwear ) relative to the rearfoot area 12 . the resistance and twisting of the stability element 10 in the area 11 defines the rotational flexibility of the footwear . a defined rotational flexibility can also be achieved by a more elastic material in area 11 . the above described stability element has several important advantages over the prior art . first , since the stability element 10 extends almost over the complete longitudinal extension of the article of footwear 1 , the longitudinal arch of the foot is effectively supported over its total length . many injuries which may occur if the arch is overstressed are avoided . second , support at the forefoot area of an article of footwear , which is the part subjected to the greatest load during running or walking , is significantly improved . in the embodiments of the invention shown in fig2 to 4 , the forefoot area 13 of the stability element 10 extends substantially along the medial side of the article of footwear to compensate for excessive pronation , as discussed above . and last , any twisting movement of the forefoot portion 3 of an article of footwear 1 with respect to the rearfoot portion 2 can be controlled in a preselected manner by the shape and the selection of the material of the stability element 10 in area 11 . to determine the material properties of the stability element in the forefoot area 13 which are well suited to reduce pronation , the foot contacts of running athletes were filmed from behind with a high speed camera taking 200 images per second . these recordings were analyzed to determine the maximum pronation angle of the foot with respect to the material properties of the stability element in the forefoot area . the pronation angle or rearfoot angle is defined as the angle α between a vertical line through the foot and the plane of the ground ( see fig1 b ). in a normal position of the foot , this angle is 90 °. all measured angles were therefore referenced to this value so that a positive value corresponds to a rearfoot angle of more than 90 °, i . e ., pronation , and a negative angle corresponds to a rearfoot angle of less than 90 °, i . e ., supination . as a result of this study ( see fig1 a ), it was found that a stability element 10 with a bending strength in the longitudinal direction , i . e ., parallel to the fiber direction ( the fibers being aligned with a longitudinal axis of the shoe ), between 350 n / mm 2 and 600 n / mm 2 ( measured according to din 53452 ), and a bending strength in the lateral direction , i . e ., perpendicular to the fiber direction , between 50 n / mm 2 and 200 n / mm 2 successfully reduced the maximum pronation angle of the foot . in particular , bending strengths between approximately 450 n / mm 2 and 500 n / mm 2 and between approximately 90 n / mm 2 and 160 n / mm 2 yielded the best results . whereas athletes wearing footwear without a stability element ( see sample a in fig1 a ) showed a pronation angle of 1 . 6 degrees , the pronation was considerably reduced (− 0 . 9 and − 0 . 6 degrees , see samples b and c in fig1 a , the error bars indicate statistical errors of the measurements ) with athletes wearing footwear equipped with stability elements having the above described material properties . according to a second aspect of the present invention , the stability element 10 preferably comprises in the forefoot area 13 an elastic forefoot plate which stores energy by elastic deformation during the landing of the foot and releases the energy essentially without any loss during the push - off of the foot from the ground to facilitate and support the course of motion . although , it would in principle be possible to integrate this forefoot plate into the shoe independent of a stability element , for cost and production it may be advantageous and preferred to combine these two parts . in the described embodiments , the forefoot plate can therefore be invisibly integrated into the forefoot area 13 of the stability element 10 ( and therefore not shown in the figures ). according to an alternative embodiment the stability element 10 itself consists of an elastic material to achieve the described energy storing function . in the following , the forefoot plate or the stability element is further described with respect to its elasticity , which is the necessary precondition for the substantially loss - free storing and release of the energy from the deformation of the plate . for noticeable support of an athlete during running , in particular during sprints , the forefoot plate should have a stiffness which is both great enough to facilitate the push - off of the foot with the energy that has been stored during the landing , and not so stiff as to undesirably hinder the natural course of motion . studies with athletes have shown that a stiffness in the range of approximately 50 n / mm to 100 n / mm is best suited to meet these requirements . the stiffness was measured with an astm 790 test installation as shown in fig7 and described in the following . to this end , a 250 mm long and 50 mm wide sample plate 200 of the material to be tested is symmetrically positioned on two 80 mm distant support points 310 . subsequently , the sample plate is deformed with the vertical force which acts upon the sample plate in the center ( vertical arrow in fig7 ). in this way , the deformation of the sample plate depending on the force can be measured with a dynamometer . fig8 shows results of measurements of sample plates with varying stiffnesses . the stiffness is the gradient of the curve in the linear range , i . e ., the range of small deformations . for application as a forefoot plate , a stiffness between approximately 50 n / mm ( sample plate f ) and approximately 100 n / mm ( sample plate e ) is preferred . another important criteria for a forefoot plate is elasticity , i . e ., whether the force necessary for the deformation can be regained when the plate springs - back into its original shape . fig9 to 12 show hysteresis loops of different sample plates , each with a stiffness between approximately 50 n / mm and 100 n / mm . to measure these loops , the force was measured by cyclically deforming and releasing the sample plates in the above described test installation ( fig7 ), where the time for one cycle was 200 milliseconds . the difference between the upper and lower line , i . e ., the area enclosed by the two lines , is representative of the loss of elastic energy during the deformation of the sample plates . it follows from the curves in fig9 to 11 that the energy loss in the planar shaped sample plates of the above mentioned stiffness is between 4 . 6 % and 6 %, i . e ., a major part of the energy is regained during the spring - back into the original shape . fig1 shows a hysteresis loop for a sample plate that was not planar shaped . the significantly greater energy loss of this plate , 18 . 3 %, is shown in fig1 . the forefoot plate according to the invention is , therefore , preferably planar . with respect to the shape of the stability element 10 , additional support elements 15 can be arranged at the side in the forefoot area 13 as well as at the rearfoot area 12 , which extend essentially laterally with respect to the longitudinal axis of the foot , as shown in fig2 and 3 . the support elements 15 extend the supporting effect of the stability element 10 into the lateral and medial side parts of the article of footwear 1 to enhance protection of the lateral arch of the foot against excessive strain . the extension of the side elements 15 depends on the shape of the article of footwear . fig3 shows an embodiment for a narrower article of footwear , where the supporting elements 15 are correspondingly shorter . in a further embodiment of a stability element , as shown in fig4 the stability element 10 comprises two parts , 20 and 30 , which form a v - like shape . part 30 supports the medial part and part 20 the lateral part of the longitudinal arch of the foot . the connection of the two parts , 20 and 30 , in rearfoot area 12 of stability element 10 allows , ( in contrast to a “ normal ” continuous sole ) for twisting around area 11 , and relative movement of the two parts , 20 and 30 , with respect to each other . in the embodiments of stability elements shown in fig5 and 6 , the medial part 30 of the stability element 10 comprises notches 31 and holes 32 to increase the flexibility of the stability element in the forefoot portion 3 in the lateral direction . the embodiment shown in fig5 is optimized for sports where the foot is not subjected to extreme lateral stress ; for example , track - and - field athletics , jogging , etc . support of the lateral half of the foot is , therefore , only necessary in the midfoot area so part 20 is designed correspondingly shorter then part 30 . in the embodiment shown in fig6 the lateral part 20 , as well as the medial part 30 , extends into the forefoot portion 3 of the article of footwear . this embodiment , in particular , is used in sports with many changes of direction and many sideways steps ; for example , tennis , basketball , etc . the elongated part 20 in this case serves to support the lateral side of the forefoot against the high strain resulting from these movements . in the embodiment shown in fig5 and fig6 additional side elements 40 are provided to increase the stability of the connection between the stability element 10 and the surrounding material of the article of footwear in the area 11 by sideways and upwardly encompassing the article of footwear . in the embodiments shown , side elements 40 are provided on the medial side of the article of footwear , an arrangement on the lateral side is also possible and in particular useful for further reinforcement of the lateral side in the above mentioned sports like tennis , basketball , etc . as material for the stability element and the integrated forefoot plate , preferably a composite material of carbon fibers embedded into a matrix of resin is used . other suitable materials include glass fibers or para - aramid fibers , such as the kevlar ® brand sold by dupont . these materials combine good elasticity values with low weight . also , steel or other elastic metal alloys could be used in particular for the forefoot plate . suitable plastic materials include thermoplastic polyether block amides , such as the pebax ® brand sold by elf atochem , and thermoplastic polyester elastomers , such as the hytrel ® brand sold by dupont . plastic materials have advantages with respect to production by injection molding , however , the necessary elastic properties can only be obtained through additional reinforcement with fibers . other suitable materials will be apparent to those of skill in the art . having described embodiments of the invention , it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and the scope of the invention . the described embodiments are to be considered in all respects only as illustrative and not restrictive . therefore , it is intended that the scope of the present invention be only limited by the following claims .
an article of footwear including a sole with a stability element constructed of a material and configured for controlling , in a preselected manner , the rotation of the forefoot portion of the article of footwear around the longitudinal axis with respect to the rearfoot portion .