Shoe

Abstract: A shoe (1) is provided, in particular a sports shoe, comprising a stability element (10) to adjust in a controlled way the rotatability of the forefoot part (3) of the shoe around the longitudinal axis with respect to the rearfoot part (2), wherein the stability element comprises a base element extending from the rearfoot part (2) into the forefoot part (3).

Description: 1. Technical Field The invention relates to a shoe, in particular to a sports shoe with a stability element to control the rotatability of the forefoot area with respect to the rearfoot area of the shoe. 2. Background The processes in the human foot during walking or running are characterized by an enormous complexity. Between the first contact of the heel and the push-off with the toes a number of different movements take place in the whole foot. During these movements, a plurality of parts of the foot move or turn with respect to each other. It is the objective in the construction of "normal" shoes, in particular of sport shoes, to obstruct these natural movements (as they occur in barefoot running) as little as possible and to support the foot only where it is necessary (depending on the intended use of the shoe). In other words, it is attempted to simulate walking or running without shoes. In contrast thereto, it is an objective of orthopaedic shoes to correct malpositions or orthopedical deformities of the foot for example by reinforcing the material in certain parts of the sole to provide additional support for the foot. The present invention, however, does not relate to this aspect but relates only to the construction of shoes for "normal" feet, in particular "normal" sports shoes in the above meaning. In this context, it was already realized in the past that the classical outsole which extends over the whole area of the shoe does not meet the above mentioned requirements. In particular rotations of the forefoot area around the longitudinal axis of the foot with respect to the rearfoot area (referred to in physics as torsional movements) are at least considerably hindered by a homogeneously formed, continuous outsole or an arrangement of soles. To overcome these difficulties, stability elements were developed which connect with a controlled rotational flexibility separate parts of the sole, and which define by their form and their material the resistance of the sole against such twisting movements. One example for such known stability element is disclosed in the US-A-5 647 145. The shoe sole construction described in this prior art approach complements and augments the natural flexing actions of the muscles of the heel, metatarsals and toes of the foot. To meet this objective, the sole comprises a base of resiliently compressible material, a plurality of forward support pads supporting the toes, a plurality of rearward support lands supporting the metatarsals, a heel member supporting and protecting the heel of the wearer's foot, and a central heel fork which overlies and is applied to the heel member. At heel strike, the heel fork tend to help stabilize and hold or reduce the rearfoot from over-supination or over pronation by guiding and stabilizing the heel bone. A further embodiment of a known stability element is disclosed in the DE 42 28 248. In this document a ridge-like element is arranged between a heel part and a forefoot part, which serve as damping means during heel strike and push-off, respectively. Further, the US 4,766,679 refers to a stabilizing frame encompassing the heel and the lateral side of the foot, in order to improve the damping properties in the heel part of the shoe. Another embodiment of a known stability element (which is similar to the above described heel fork) is shown and discussed in conjunction with Fig. 14 of the present application. The stability element 10' shown there is shaped like a bar, a cross, or a V, and starts at the rearfoot area 2' of the sole and terminates in the midfoot area of the sole. Although these known stability elements are capable of providing through their rigidity some stability to the various parts of the foot, they have, however, the important disadvantage that they only insufficiently provide for a joint support of the longitudinal and lateral arch of the foot. Compared to an ordinary continuos sole molded to the contour of the foot, the stability is therefore considerably reduced. Furthermore, the arrangement of layers of foamed materials typically used in the prior art for the forefoot area 3' of the shoe is comparatively yielding so that due to the high pressure during running the sole yields on the medial or lateral side, and the foot rotates in response thereto by a few degrees to the inside or the outside, particularly if the wearer's foot anatomy tends to supports such rotational movements. These rotational movements are known in the art as pronation and supination, respectively, and lead to a premature fatigue of the joints of the foot and knee, and sometimes even to injuries. Additionally, a soft or yielding forefoot area of the sole leads to a loss of energy since the deformation of the shoe during the push-off phase of the step is not elastic and therefore the energy used for the preceding deformation of the sole can not be regained. The WO 91/09546 discloses a stability element for footwear, such as soccer boots or training shoes, comprising a stiffening means having a first and a second portion. The first portion stiffens the waist or shank of the sole to resist transverse flexure, whereas the second portion stiffens the fore-part of the sole and provides resilience, to cause or assist in returning the fore-part of the sole to its original shape, after it has been subjected, in use, to transverse flexure. The DE 298 10 357 U1 describes a torsion system for a cycling shoe comprising a stiff plate. The stiff plate has a rigid forefoot area, a rigid heel area, and a rotatable intermediate area connecting the rigid forefoot area with the rigid heel area. In view of the above mentioned prior art approaches, it is the problem of the present invention to provide a shoe which allows a controlled rotation of forefoot area with respect to the rearfoot area and supports at the same time in particular the forefoot part, to avoid excessive pronation or supination, and thereby a premature fatigue or injuries of the wearer of the shoe. 3. Summary of the invention The above mentioned problem is solved by a shoe, in particular a sports shoe, with a stability element in accordance with claim 1. According to a further preferred embodiment, in case of pronation control, the metatarsals one and two of the wearer's foot are supported, preferably together with the phalanges one and two. In case of supination control, the metatarsals five and preferably four are supported, even more preferred together with the phalanges five and four. Due to the extension of the base element from the rearfoot part into the forefoot part where the metatarsals and phalanges are located, the foot is supported over its effective longitudinal length, however, without affecting the flexibility of the shoe with respect to the twisting of the forefoot part relative to the rearfoot part. An excessive strain or even the breaking of the longitudinal arch of the foot under high stress, for example the landing after a leap, is thereby effectively avoided. The stability element supports at the same time in the forefoot area the front part of the foot. Film shootings with a high-speed film camera of running athletes during a pronation study have shown that a supported forefoot area of the shoe avoids effectively the turning of the foot to the medial side. The reason is that due to the material properties of the base element in the forefoot area the shoe does not yield on the medial side under higher pressure. Preferred materials for the forefoot part have a longitudinal bending strength in the range of 350 N/mm 2 to 600 N/mm 2 and a lateral bending strength of 50 N/mm 2 to 200 N/mm 2 (measured according to DIN 53452). According to a second aspect of the invention, the stability element preferably comprises in the forefoot area an elastical forefoot plate, or has elastic properties in this region. During the landing of the foot and the subsequent rolling of the toes the forefoot area is thus elastically bent. In the subsequent course of the movement, when the rearfoot part has already left the ground, the foot is stretched to push-off from the ground. At this moment the forefoot area of the base element springs elastically back into its original shape and supports thereby the pushing-off from the ground. In this way the energy invested for the elastical deformation of the shoe is regained and facilitates the continuation of the movement. The forefoot plate shows to this end preferably a stiffness in the range of 50 N/mm up to 100 N/mm (measured according to ASTM 790). According to a preferred embodiment, the base element of the stability element is divided and comprises two V-like connected front parts. This allows a precise adaptation to the different form of the medial and the lateral side of the longitudinal arch of the foot. Preferably, the base element also comprises support elements at the side. Thereby also the lateral arch of the foot is specifically supported by the stability element. The stability element comprises preferably additional side elements which extend starting from the base element upwards over the edge of the shoe. This embodiment is preferably in particular used in sports with a high lateral strain on the foot. For a light-weight shoe the above mentioned material properties are preferably obtained by a composite material of resin and carbon fibers. 4. Short Description Of The Drawing In the following detailed description of the invention, preferred embodiments of the present invention are described with reference to the drawing which shows: Fig.1: A human skeleton foot for explaining the principles of the present invention; Fig.2: A shoe according to a preferred embodiment; Fig.3: Another preferred embodiment of a narrower shoe; Fig.4: A shoe with a stability element with two V-like connected parts; Fig.5: Another preferred embodiment with three additional side elements; Fig.6: Another preferred embodiment where the medial and the lateral part of the stability element extend into the forefoot area; Fig.7: A test installation to determine the stiffness of the forefoot plate; Fig.8: Force-deformation characteristics to determine the stiffness of the forefoot plate; Fig.9: Hysteresis loop of the deformation of the sample plate E; Fig. 10: Hysteresis loop of the deformation of the sample plate F; Fig.11: Hysteresis loop of the deformation of a planar sample plate; Fig. 12: Hysteresis loop of a shaped sample plate; Fig. 13a: Results of the pronation measurements with different stability elements; Fig. 13b: A schematic drawing for explaining the pronation angle; and Fig. 14: A shoe with a V-shaped stability element according to the prior art. 5. Detailed Description Of The Preferred Embodiments According to a preferred embodiment of the present invention a shoe comprises a stability element, which is arranged beneath the foot of the wearer. This can either be achieved by integrating the stability element in accordance with the present invention into the outsole of the shoe, or sandwiching it between outsole and midsole, or between midsole and insole. If the stability element is arranged within the outsole, it may have a different color than the surrounding material of the sole, so that the special form (which is an indication for which sport the corresponding shoe is intended, see below) of the stability element can easily be recognized from the outside. According to another preferred embodiment, the outsole itself consists essentially of the stability element. In this case, an optional midsole and an optional insole might be applied to the upper side of the stability element to provide comfort and damping to the wearer of the shoe. Since the above described different possibilities to arrange the stability element in the shoe do not significantly influence the functional properties of the shoe comprising the stability element in accordance with the present invention, reference is made in the following (and in the Figures) only to a shoe in general. Before the design and the functional characteristics of the stability element in accordance with the present invention are described is detail, reference is made to the human skeleton foot 90 shown in Fig. 1, to facilitate the understanding of the inventive principles, according to which particular parts of the foot are selectively supported. In Fig.1, reference numeral 92 depicts the metatarsals of a left human foot 90, whereas the phalanges (toes) are referenced with reference numeral 95. Both, the metatarsals 92 and the phalanges 95 together basically form the forefoot part of the foot. Between metatarsals 92 and phalanges 95, the metatarsal-phalangeal joints 93 are provided. The phalanges 95 additionally 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 provided 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, five phalanges 95-1 to 95-5 are provided. Finally, the heel bone 91 is depicted. For the 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 case of pronation control, particularly metatarsal 92-1 and/or the metatarsal 92-2 is supported, preferably together with the phalanges 95-1 and/or 95-2. In case of supination control, particularly metatarsal 92-5 and/or metatarsal 92-4 is supported, preferably together with the phalanges 95-5 and/or 95-4. This is provided for by the stability element in accordance with the present invention. However, since supination is seldomly a problem, and for 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. Accordingly, the stability element in accordance with the present invention for a right shoe 1 shown in Fig. 2 comprises an oblong base element 10 with a rear part 12 and a front part 13. The base element 10 extends, starting from the rearfoot part 2 of the shoe 1, into the forefoot part 3. As may be derived from Fig.2, the front part 13 is designed and located within the shoe such that the first and/or second metatarsals of wearer's foot (not shown), which rests on the stability element with additional sole layers therebetween, as appropriate, are effectively supported. According to an even more preferred embodiment, the stability element even supports the first and/or second phalanges. Between these two parts 12 and 13 the base element 10 comprises preferably an area 11 with reduced lateral dimensions which allows twisting of the front part 13 of the base element 10 (and thereby of the shoe) relative to the rear part 12. The resistance against twisting of the base element 10 in the area 11 defines the rotational flexibility of the shoe. A defined rotational flexibility can also be achieved by a more elastic material in the area 11. The above described stability element has several important advantages over the prior art. Firstly, since the base element 10 extends almost over the complete longitudinal extension of the shoe 1, the longitudinal arch of the foot is over its total length effectively supported. Any injuries which may occur, if the arch is overstressed, are therefore avoided. Secondly, the support of the front part of the shoe, which is the part subjected to the greatest load during running or walking, is significantly improved. In the two preferred embodiments shown in the Figs. 2 to 4, the front part 13 of the base element 10 extends essentially on the medial side of the shoe (the dashed line 100 indicates the longitudinal centre line), to compensate for excessive pronation, as discussed above. Finally, any twisting movement of the front area 3 of the shoe 1 with respect to the rear area 2 is nevertheless possible, i.e. it can be controlled in a predetermined way by the shape and the selection of the material of the base element 10 in the area 11. To determine the material properties of the base element in the front part 13 which are best suited to avoid pronation, the foot contacts of running athletes were filmed from behind with a high speed camera taking 200 images per second. These recordings were analysed to determine the maximum pronation angle of the foot in dependence of 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 (cf. Fig. 13b). 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. a pronation, whereas a negative angle corresponds to a rearfoot angle of less than 90°, i.e. supination. As a result of this study (cf. Fig. 13a), it was found that a base element 10 with a preferred bending strength in 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 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 in fiber direction between 450 N/mm 2 and 500 N/mm 2 and between 90 N/mm 2 and 160 N/mm 2 yielded the best results. Whereas athletes with shoes without a stability element (cf. sample a in Fig. 13a) showed a pronation of 1.6 degrees, the pronation was considerably reduced (-0.9 and -0.6 degrees, samples b and c in Fig. 13a, the error bars indicate statistical errors of the measurements) with athletes wearing shoes equipped with stability elements having the above described material properties. According to a second aspect of the present invention, the base element 10 comprises in the front part 13 preferably an elastical forefoot plate which stores energy by elastical deformation during the rolling-off 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 independently of a stability element into the shoe, it is for cost and production reasons advantageous and preferred to combine these two parts. In the described embodiments the forefoot plate can therefore be invisibly integrated into the front part of 13 of the base element 10 (and therefore not shown in the Figures). According to an alternative embodiment the base element 10 itself consists of an elastical material to achieve the described energy storing function. In the following, the forefoot plate of the base element is further described with respect to its elasticity, which is the necessary precondition for the loss-free storing and release of the energy of the deformation of the plate. For a noticeable support of an athlete during running, in particular during sprints, the forefoot plate should have a stiffness which is on the one side great enough to facilitate the push-off of the foot with the energy which has been stored during the rolling-off, and which is on the other side not too stiff to undesirably hinder the natural course of motion. Studies with athletes have shown that stiffnesses in the range of 50 N/mm up to a 100 N/mm are best suited to meet these requirements. The stiffness was measured with the test installation ASTM 790 shown in Fig. 7 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 centre (vertical arrow in Fig. 7). In this way, the deformation of the sample plate depending on the force can be measured with a dynamometer. Fig. 8 shows results of measurements for sample plates with different stiffnesses. The stiffness is the gradient of the curve in the linear range, i.e. the range of small deformations. For the application as a forefoot plate stiffnesses between 50 N/mm (sample plate F) and 100 N/ mm (sample plate E) are particularly suitable. A further important criteria for the use as a forefoot plate is the elasticity, i.e. whether the force necessary for the deformation can be regained when the plate springs-back into its original shape. Figs. 9 to 12 show hysteresis loops of different sample plates with a stiffness between 50 N/mm and 100 N/mm. To measure these loops, the force was measured in a periodical deformation and springing-back with the above described test installation (Fig. 7), 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 for the loss of elastic energy during the deformation of the sample plates. It follows from the curves in the Figures 9 to 11 that the energy loss in the sample plates of the above mentioned stiffness is between 4.6% and 6%, i.e. the by far major part of the energy is regained during the spring-back into the original shape. Fig. 12 shows a hysteresis loop for a sample plate which was not exactly planar shaped for the adaptation to a shoe. The significant larger energy loss of 18.3 % of this plate is shown in Fig. 12. The forefoot plate according to the invention is therefore preferably planar. With respect to the shape of the base element 10, preferably additionally support elements 15 are arranged at the side in the front part 13 as well as at the rear part 12, which extend essentially laterally with respect to the longitudinal axis of the foot, as shown in Figures 2 and 3. These support elements 15 broaden the supporting effect of the base element 10 into the lateral and medial side parts of the shoe 1 to protect also specifically the lateral arch of the foot against excessive strain. The extension of the side elements 15 depends on the shape of the shoe. Fig. 3 shows an embodiment for a narrower shoe, where the supporting elements 15 are correspondingly shorter. Fig. 4 shows a further embodiment of a stability element for a right shoe. The base element 10 comprises in this embodiment two parts 20 and 30, which are V-like connected to each other. The part 30 supports again the medial part and the part 20 the lateral part of the longitudinal arch of the foot. The connection of the two parts 20 and 30 in the rear part 12 of the base element 10 allows (in contrast to a "normal" continuous sole) under a twisting around the area 11 a relative movement of the two parts 20 and 30 with respect to each other. In the embodiments of stability elements for a left shoe shown in the Figs. 5 and 6, the medial part 30 of the base element 10 comprises notches 31 and holes 32 to increase the flexibility of the stability element in the forefoot part 3 in the lateral direction. The embodiment shown in Fig. 4 is optimised for sports where the foot is not subjected to extreme lateral stress (for example track-and-field athletics, jogging). A support of the lateral half of the foot is therefore only in the midfoot area necessary so that the part 20 is correspondingly designed shorter as the part 30. In the embodiment shown in Fig. 5 the lateral part 20 extends as well as the medial part 30 into the forefoot part 3 of the shoe. This embodiment is in particularly used in sports with many changes of direction and many sideways steps (for example tennis, basketball etc.). The prolonged part 20 serves in this case to support the lateral side of the forefoot against the high strain resulting from these movements. In the embodiment shown in Fig. 5, as well as in the embodiment shown in Fig. 6, additional side elements 40 are provided which increase the stability of the connection between the base element 10 and the surrounding material of the shoe in the area 11 by sideways, upwardly encompassing the shoe. In the shown embodiments these side elements 40 are provided on the medial side of the shoe, 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, basket ball 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. Also Kevlar or glass fibers can be used. 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. Plastic materials as Pebax or Hytrel have advantages with respect to the production by injection molding, however, the necessary elastic properties can only be obtained with the additional reinforcement with fibers.

Claims: Shoe (1), in particular a sports shoe, with a stability element integrated into the outsole or sandwiched between outsole and midsole or midsole and insole to control the rotatability of the forefoot part (3) of the shoe (1) around the longitudinal axis relative to the rearfoot part (2), a. wherein the stability element comprises a base element (10) extending from the rearfoot part (2) into the forefoot part (3), b. wherein the base element extends in or along the medial (99) and/or the lateral side (98) of the forefoot part (3), and c. wherein the base element comprises an area (11) having reduced lateral dimensions and/or a more elastic material allowing a twisting of the forefoot part (3) relative to the rearfoot part (2), characterized in that d. the base element (10) comprises a front part (13) having a bending strength in longitudinal direction between 350 N / mm 2 and 600 N / mm 2 , and a bending strength in lateral direction between 50 N / mm 2 and 200 N / mm 2 . Shoe according to claim 1, wherein the base element (10) supports the metatarsals one (92-1) and/or two (92-2), and/or the phalanges one (95-1) and/or two (95-2) of the foot (90). Shoe according to claim 1 or 2, wherein the base element (10) supports the metatarsals five (92-5) and/or four (92-4), and/or the phalanges five (95-5) and/or four (95-4) of the foot (90). Shoe according to any of the claims 1 - 3, wherein the base element (10) comprises a front part (13) having a bending strength in longitudinal direction between 450 N/mm 2 and 500 N/mm 2 and a bending strength in lateral direction between 90 N/mm 2 and 160 N/mm 2 . Shoe according to anyone of the preceding claims, wherein the base element (10) comprises at least in the forefoot part (3) elastic properties storing energy during the rolling-off of the shoe (1) and releasing the energy essentially without any loss during the push-off of the foot from the ground. Shoe according to anyone of the preceding claims, wherein the base element (10) has at least in the forefoot part (3) a stiffness in the range of 50 N/mm up to 100 N/mm. Shoe according to anyone of the preceding claims, wherein the forefoot part (3) is substantially planar in shape. Shoe according to anyone of the preceding claims, where the base element (10) comprises two V-like connected parts (20, 30). Shoe according to anyone of the preceding claims, wherein the base element (10) extends on the medial (99) and on the lateral (98) side of the forefoot part (3). Shoe according to anyone of the preceding claims, wherein the base element (10) comprises additional support elements (15) on the side. Shoe according to one of the preceding claims, wherein the stability element comprises additional side elements (40) which extend from the base element (10) upwardly over the edge of the shoe (1). Shoe according to anyone of the preceding claims, wherein the stability element consists of a composite material reinforced by carbon fibers.

Inventors: GEBHARD JEFFREY E, KAELIN FRANZ XAVIER KARL, KRAEUTER CHARLES D, LUTHI SIMON, GEBHARD, JEFFREY E., KAELIN, FRANZ XAVIER KARL, KRAEUTER, CHARLES D., LUTHI, SIMON, Kälin, Franz Xavier Karl
Applicants: ADIDAS INT MARKETING BV, ADIDAS INTERNATIONAL MARKETING B.V.
Application year: 2000
Main classification: A43B13
IPC codes: A43B13, A43B7