FIELD OF THE INVENTION
The present invention relates to a midsole, according to Claim 1, for a sports shoe, and a sports shoe comprising such a midsole. The midsole comprises a flexible body element, which extends essentially over the entire length of the sole of the foot, a flexible heel element located under the body element, which extends from under the heel bone (calcaneus) at least partly into the area of the cuboid bone (os cuboideum), and a plate-like stiffener element located at least partly between the body element and the heel element.
PRIOR ART
It is natural for human beings to move on bare feet. However, in sport, the mechanical strain acting on the feet makes it practically essential to use sports shoes. Shoes, however, always change the operation, i.e. the bio-mechanics, of the foot and the leg, in turn affecting the efficiency, i.e. the so-called ?economy?, of running, and, when running a great deal, also the paths of movement and physical condition of the sportsperson's feet in the long term.
The product development of running shoes, which started in the 1970s, has largely concentrated on creating various types of attenuation and support systems. Development has been particularly directed at attenuation systems for softening impacts in the area of the heel, i.e. so-called heel-attenuation. At least part of the reason for this has been the increase in stress injuries in the area of the foot and the entire kinetic chain. In development, the basic assumption has been that increased running requires a shoe that will protect the heel area in the heel-impact stage. In the case of support systems, the main object of development has been to prevent over-pronation of the foot structures, i.e. excessive inwards torsion of the foot, during the support stage, or, on the other hand, to prevent over-supination, excessive outwards torsion. A drawback with such solutions is that they do not use effectively the natural attenuation system of the foot and substantially alter the path of movement of the foot during a stride. In the worst case, the choice of shoe forces the runner into completely the wrong kind of stride, which can result in long-term detriments and even increased stress injuries.
One known solution comprising over-pronation or over-supination support and heel attenuation is disclosed in US patent application publication 2004/0154188. The solution is based on a stiffener element, which prevents pronation and supination and is shaped, together with the other parts of the sole, in such a way that a heel-attenuation ?pillar? remains in the area of the heel. U.S. Pat. No. 6,502,330 discloses another, slightly different, stiffener element improving lateral stability.
Another solution, which is in many ways similar, is known from U.S. Pat. No. 4,757,620. It discloses a sole construction for a sports shoe, which comprises a suspension and support structure located between the outer sole and the midsole. This suspension and support structure comprises a flexible toe part extending from the toe to essentially the area of the ball of the foot and a flexible body piece arranged above the heel part, thinning like a wedge from the rear edge of the shoe towards the toe of the shoe and extending at least over the area of the heel, which body piece is substantially stiffer and harder than the said heel part and toe part. Such a sole construction effectively receives the impact acting on the runner's heel, in the stage when the foot makes contact with the ground. In the foot's rolling stage, the sole construction supports the plantar arch, thus reducing the strains acting on the foot. In the propulsion stage, unnecessary slipping of the shoe is avoided.
In recent years, footwear solutions have also been presented, which seek to guide the stride in a more natural direction. Such a solution is disclosed in, for example, FI patent 117541, which represents the prior art closest to the present invention. In the sole construction presented in it, there is a midsole, in which there is a flexible body element, which extends over the entire length of the shoe, a flexible heel-attenuation element, which extends to the area of the heel, and a heel element fitted between them, which extends from the area of the heel to the area of the ball of the foot. The heel element is of a less flexible material than the body and heel-attenuation elements that delimit it above and below.
It is possible to say roughly that, when running barefoot, the loading on the sole of the foot is distributed evenly between the heel and the area of the ball of the foot. However, it has been observed that the heightened heel part typically contained in a heel-attenuated shoe, i.e. its heel, alters the loading of the sole of the foot in such a way that the heel has about 40 percent and the ball of the foot area 60 percent of the loading. This unequal loading emphasizes the importance of the correct action of the sole of the foot and especially of the ball-of-the-foot area. In known sole solutions for shoes, however, practically no attention has been paid to this, perhaps still generally unrecognized, factor.
In addition, a drawback of several known sole solutions is that the sense of the attitude of the foot is weak. As a result, the muscle functioning of the foot too cannot be optimal. In an optimal situation, the muscles of the foot act like an elastic spring and support operation of the natural arch structures of the sole of the foot. This can be achieved, however, only if a good tactile sense of the running surface, and in turn of the attitude of the foot, is retained. In several studies, the development of a sense of attitude, i.e. co-ordination, has been observed to reduce the number of injuries to the sole of the foot and the legs.
In terms of the action of the sole of the foot and the leg, shoes that are excessively attenuated and supported thus cause several important problems, for instance a weakened sense of attitude, a passivation of the small muscles of the foot, and a shortening of the aponeurosis plantaris. The latter can in turn lead to unequal loading of the foot, resulting in a shortening of the Achilles tendon. Over a long period of time, such a change can even become permanent. This is because the latest studies have shown that the frequent use of shoes that are too supportive may passivize the important support structures of the foot.
Therefore, there exists a need for new types of model of sports shoes.
SUMMARY OF THE INVENTION
The intention is particularly to create a new type of sole construction, which will eliminate at least some of the aforementioned and drawbacks and which will thus have a significant effect on stride. The invention is particularly intended to create a sole construction, with the aid of which the stride can be made more economic and natural. Further, the invention's purpose is to prevent stress injuries from arising.
The basic idea of the present invention is, instead of designing powerful heel attenuation and support systems, to design the sole of the shoe in such a way that the stride is guided from the heel-impact stage through the middle-support stage of the stride to the ball-of-the-foot propulsion stage according to the natural path of movement of the foot, equalizing the strain on the foot.
This is achieved by means of a sole-construction solution, which generally comprises a flexible body element, which extends essentially over the entire length of the sole of the foot, a flexible heel element located under the body element, which extends from under the heel bone at least partly into the area of the cuboid bone, as well as a plate-like stiffener element located at least partly between the body element and the heel element.
According to the first aspect of the invention, the stiffener element extends from the area of the heel forwards farther on the lateral side of the sole of the foot than on the medial side of the sole of the foot. This feature has been observed to have a significant effect guiding the movement towards the natural pressure centre-line of the foot, especially in the middle stage of the stride.
According to a preferred embodiment, the stiffener element extends on the lateral side at least over the level of the mid-tarsal joint, and on the medial side to at most the level of the mid-tarsal joint. This ensures a sufficient asymmetry and thus a guiding effect.
According to one embodiment, the front part of the stiffener element comprises one, and preferably two forwards-facing protrusions/prongs, of which the lateral-side protrusion/prong extends into the area of the first phalange of the small toe (metatarsal V). Such a protrusion/prong arranged on the side further ensures the desired effect.
According to one embodiment, the stiffener element consists of a material, the bending stiffness of which in the lateral direction is greater than in the longitudinal direction. The stiffener element preferably comprises carbon-fibre, or consists entirely of carbon-fibre, in which there are oriented fibres.
According to one embodiment, the rear part of the stiffener element comprises an opening following the shape of the calcaneus, which permits the activation of the calcaneus in the correct manner in the initial stage of the stride.
According to the second aspect of the invention, the heel element comprises a longitudinal groove delimiting its lateral parts and rear part, which is directed forwards from the area of the calcaneus essentially to the lateral side of the sole of the foot from the centre-line of the sole of the foot. By means of this feature, the movement is guided more laterally compared to the path determined by a traditional running shoe, and thus towards the natural pressure centre-line of the foot, at each moment in time.
According to one embodiment, the groove is further delimited by the upper part of the heel element, i.e. in other words it is a downwards-opening recess in the heel element. This permits the heel element to be connected to the constructions above it better and more tightly. According to one embodiment, the groove is open in the direction under the shoe, at least as far as the outer sole.
According to one embodiment, the heel element is formed from at least two parts, which are attached, or can be attached on top of each other, and longitudinally in the longitudinal direction of the sole of the foot, and which together form the said groove. The parts can be manufactured from materials with different flexibilities. The rearmost of the said two parts is preferably of a more flexible material than the foremost.
According to one embodiment, the rear part of the heel element comprises part of a groove penetrating it in the thickness direction and the front part comprises part of a groove in its under-surface, in which case when joined the said groove forms a foremost part on top of and in front of the rearmost part. By means of this solution, it is possible to improve the foot's sense of attitude together with its natural movement.
According to one embodiment, the body element comprises in its under-surface and/or the heel element in its upper surface a recess, the shape of which corresponds precisely to the shape of the stiffener element and the heel element is arranged to fit precisely into the said recess. In this way, a tight sole-totality is created.
According to a third aspect of the invention, the sole comprises a flexible element, which is of a more flexible material than the body element, essentially delimited to the area of the distal ends of the big toe and indirectly also of its adjacent toe (metatarsals I and II). This ensures in the final stage of the stride a more even propulsion take-off from the entire area of the ball of the foot and gives good support to the primary propulsion point.
According to one embodiment, a recess for the said flexible element is arranged in the body element, essentially at the location of the metatarsophalangeal joint of the big toe.
The aspects described above and depicted later in greater detail each separately have a positive effect on achieving the desired economical and natural running stride and each aspect by itself can act as a basis for a new patent application and a distributed patent application. Further, a better effect can be obtained with the aid of a sole that comprises two or all of the aspects described above. The solution that is the subject of the present application is defined more precisely in the independent Claims.
The invention also relates to a sports shoe, which comprises an inner sole coming into contact with the foot or sock, an outer sole coming into contact with the running surface, and a midsole according to one or several of the aspects or embodiments described above and fitted between the inner sole and the outer sole.
Considerable advantages are achieved with the aid of the aspects of the invention. In particular, the sole construction disclosed makes greater allowance than known running-shoe solutions for the natural manner in which human beings run and exploits the foot's own built-in attenuation system. In particular, the running shoe according to the invention and described in greater detail below conforms as precisely as possible to the natural operating model of the foot and leg, retains the foot's attitude sense, and activates the small muscles of the foot to act like a spring, i.e. to store and release the kinetic energy arising in active muscle work.
The most important task of a running shoe is to permit each runner's own individual movement model during running loading, so that the power output through the support surface formed by the shoe is transmitted to the running surface in the most natural manner possible. The totality formed by a running shoe should support and conform to the runner's own natural biomechanics in the various stages of the running stride. These objectives are achieved by means of the present solution.
The influences on the invention are, among others, the following observations:
The toes have an important balancing function in shoe solutions. Also when a person moves barefoot, in the so-called central-support stage of walking and running (the weight of the body is supported on one foot/leg) the toes grip the base lightly. The toes stabilize particularly the action of the foot, but at the same time also of the whole leg. As a result of this, toes that act effectively guide the propulsion to be directed forwards, thus improving the power output of the propulsion.
Human beings have a shock-absorbing mechanism as ?standard equipment?. When walking in shoes, the heel generally impacts the surface first, after which the entire foot follows by rolling. There is thus a powerful impact on the calcaneus. When moving barefoot, the foot descends on the surface in a nearly horizontal position. As a result, the impact strain acting on the calcaneus is reduced, because the harder impact is received by the front-middle part of the foot which has a larger surface area and more flexible construction, instead of the passive calcaneus, which has a smaller surface area. When the front-middle part of the foot strikes the surface first, the muscles affecting the operation of the foot are already activated, i.e. it is justified to say that the impact is received by the body's automatically operating active shock-absorbing mechanism. Further, after the contact of the front-middle part, the heel descends lightly towards the surface, when both the stretching reflex of the Achilles tendon and the operation of the calf muscles are optimized, and as a result of this operation, powerful forward-moving propulsion arises.
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