RUNNING SHOES

Abstract: A pair of running shoes (20) each of which has a midsole (36) which, at least in the heel region, is made of two layers (40, 42) with complementary tapers across the width of the sole to provide a horizontal upper surface (46) when the lower surface (48) is horizontal. The two layers are of different durometers, the tapers and durometers being so selected that the ratio of the thickness of higher durometer to lower durometer material is greatest adjacent the inner or varus side (26) of the sole. This construction lessens abnormal pronation of the foot as the arch flattens during running and increases contact surface area, thus distributing impact shock more evenly.

Description: RUNNING SHOES This invention relates to running shoes. Various athletic shoes particularly suited for running are commercially available. Such shoes commonly include an upper and what can be called a "neutral plane" sole, that is a sole which is of uniform thickness between the inner (varus) side of the shoe and the outer (valgus) side of the shoe. Such soles, although usually comprising an outsole and a midsole, are commonly formed of uniform density between the varus and valgus sides. The human anatomy is such that when a person runs, or walks for that matter, the rear valgus portion of the heel of each foot makes initial contact during each step. The ground contacting foot then rolls inward, a process called pronation, whereupon the person's body weight is brought from the outside edge of the foot inward toward the centre of the arch. The foot then rolls outwardly and toes off toward the great toe to complete a step. It is widely recognized that the vast majority of runners exhibit improper pronation when running in prior art shoes like those described above. Many people initially land on the outside of the heel of the ground contacting foot, with the foot rolling inward with improper biomechanical action and remaining rolled inward. Such improper action is referred to as overpronation. In addition, it has been shown that when running, three to four times the gravitational force is applied to the outside edge of the foot, and in particular to the heel area, than occurs when walking. The high force concentrated at the heel area, coupled with the tendency of most runners to roll their feet inward forcefully during running results in increased shock to the foot and increased heel wear of the shoe being worn. In US-A-4,180,924 there is described a running shoe featuring a sole having a wedged portion canted upward in a transverse direction from the outer side of the shoe to the inner side of the shoe so that during running a substantial portion of the sole makes contact with the ground during each step. Although this type of construction remedies many of the drawbacks associated with a conventionally designed running shoe, the physical canting of the sole may not be desired by some runners, e.g., slow runners. In US-A-4,364188 there is described a running shoe having a neutral plane sole including portions at the heel on the varus side which are of higher density (durometer) than the remaining portion of the sole in the interest of "rearfoot stability". It is a general object of the invention to provide running shoes which overcome the disadvantages inherent in the prior art running shoes and, in particular, to provide a pair of neutral plane running shoes, each of which has means for lessening the abnormal pronation of the foot as the arch flattens during running. These objects are attained by the present invention according to which each of a pair of running shoes comprising an upper and a sole running the length of the shoe from the heel to the toe, the sole comprising an outsole and a midsole, is characterised in that the midsole includes a first member and a second member, each member varying in thickness across the width thereof, said first member being disposed about said second member so that the combined thickness of said members is constant across the width of said sole, the said members being formed of materials having different durometers from one another so that the ratio of the thickness of the higher durometer material relative to the thickness of the lower durometer material is greatest immediately adjacent the inner side of the sole and is lowest immediately adjacent the outer side of the sole. The construction of the sole according to the invention lessens abnormal pronation. In addition, the shoes may.be constructed so that impact shock is distributed evenly during running; at the same time the shoes employ a transversely level or "neutral plane" sole. Moreover, the construction of sole permits greater contact surface area than conventional shoes, thereby distributing impact shock more evenly during running, yet providing medialongitudinal arch support for decreasing abnormal pronation, while allowing for the natural pronation of the foot. The invention may be carried into practice in various waysbut two pairs of running shoes embodying the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of the right shoe of the first pair of running shoes; Figure 2 is an enlarged sectional view taken along line 2-2 of Figure 1; and Figure 3 is an enlarged sectional view of the right shoe of the second pair of running shoes taken along a line located at a position corresponding to the line 3-3 of Figure 1. Figure 1 shows a running shoe 20 designed to be used by the competitive runner or recreational jogger alike. The shoe basically comprises a conventional upper 22 and a sole unit 24. The upper 22 has an inner or varus side 26 and an outer or valgus side 28. The sole unit 24 runs the entire length of the shoe from the heel 30 to the toe 32 between the varus and valgus sides 26 and 28, respectively. In referring to Figure 2 it can be seen that the sole unit 24 comprises an outsole 34 and a midsole 36. The outsole is of conventional construction and includes plural gripping elements or cleats 38. The midsole is formed as a composite structure and, as will be described in detail hereinafter, is arranged to provide the over-pronation lessening characteristics exhibited by running shoes constructed in accordance with US-A-4,180,924 in a neutral plane sole. To that end the midsole 36 includes two layers, namely top layer 40 and bottom layer 42. The layers extend for a substantial length of the sole between the heel and to a point adjacent the front of the arch. Each layer is formed of a resilient material like that used in midsoles of conventional running shoes, except that the hardness or durometer of each layer is different from that of the other. In the embodiment of the midsole shown in Figure 2 the upper layer is of higher durometer material than the lower layer. For example, depending upon the type of shoe, the upper layer can have a durometer within the range of 45+ 10%, Shore A, while the lower layer has a durometer within the range of 35+ 10%, Shore A. The layers of the midsole 36 are preferably made of ethyl vinyl acetate (EVA) but, alternatively, may be made of polyurethane or any number of other materials used in running shoes. The thickness of each layer varies across the width of the sole, i.e., between the varus and valgus sides, but with the combined thickness of both layers being constant across said width. This feature ensures that the sole is of the "neutral plane type. The layers 40 and 42 are constructed so that the layer having the thicker portion contiguous with the varus side is of the higher durometer material. Accordingly, the hardness of the midsole contiguous with the varus side of the sole is higher than that of the valgus side. With such a construction, during the pronation phase of each running step the varus side of the shoe does not compress-as readily as the valgus side. Therefore, the abnormal tendency toward over pronation is obviated or at least minimized. In the embodiment of Figures 1 and 2, the top layer 40, which is formed of higher density material tapers linearly in thickness from the varus side to the valgus side, with the ratio of the higher density material to the lower density material being approximately 3 to 1 adjacent the varus side and approxi- mately 1 to 3 adjacent the valgus side.. Conversely the lower layer 42, which is formed of the lower density material, tapers linearly in thickness from the valgus side to the varus side. The degree of taper of both layers is.the same. The layers are adhesively secured along their interface 44. The top surface 46 of the top layer 40 and the bottom surface 48 of the bottom layer are disposed horizontally so that the combined overall thickness of two layers of the midsole 36 in a transverse direction across the width of the sole is constant. As is conventional, the midsole 36 is thicker under the heel of the upper and tapers downward longitudinally under the arch toward the forefoot area, to provide the necessary heel lift or elevation for comfortable, safe running. The total thickness of the midsole 36 is between 15 mm and 25 mm at its thickest portion, with the exact thickness depending on several factors, such as the type of running intended (e.g., racing, recreational jogging, etc.) and the personal preference of the wearer. From Figure 1, it will be seen that at least on the varus side, the bottom layer 42 of lower durometer tapers longitudinally to a thickness of zero adjacent the arch of the wearer's foot and from there forward the midsole consists only of the upper layer 40 of higher durometer. In an alternative construction, however, the bottom and top layers both extend the full length of the sole but in the region forward of the wearer's arch they are both of constant thickness across the width of the sole. Thus, in either construction, the ratio of the thickness of the lower durometer material to the higher durometer material varies from the outer side of the shoe to the inner side of the shoe over the portion of the sole region extending the full length of the heel to a point adjacent the arch of the wearer's foot, said ratio being constant over the remaining portion of the sole. It will be understood that the left shoe of the pair is of corresponding construction but appropriately 'handed' so that the higher density material is again thicker at the varus side and the lower density material is thicker at the valgus side. In the second pair of shoes embodying the invention, the general construction is the same as that described with reference to Figures 1 and 2 but, as is shown in Figure 3, the higher density and lower density materials, forming the two layers of the midsole, are transposed. Accordingly in this embodiment the top layer 40 is formed of the lower density material and tapers from the valgus side to the varus side, while the bottom layer 42 is formed of the higher density material and tapers from the varus side to the valgus side. It must be pointed out at this juncture that the two layers 40 and 42 need not taper linearly across the width of the sole, as shown in Figures 2 and 3, nor need they be of corresponding thicknesses tapering in opposite directions, so long as the ratio of the thickness of the higher durometer material relative to the lower durometer material is greatest adjacent the varus side, e.g., the layer of higher density has its thicker side at the varus side of the sole, and the top surface of the top layer is substantially horizontal in the transverse direction when the outsole is flat on a horizontal running surface. Moreover, the two layers need not be formed as separate units which are secured together.

Claims: CLAIMS 1. A pair of running shoes (20), each of said shoes comprising an upper (22) and a sole (24) running the length of the shoe from the heel (30) to the toe (32), the sole comprising an outsole (34) and a midsole (36), characterised in that the midsole includes a first member (40) and a second member (42), each member varying in thickness across the width thereof, said first member being disposed about said second member so that the combined thickness of said members is constant across the width of said sole, the said members being formed of materials having different durometers from one another, so that the ratio of the thickness of the higher durometer material relative to the thickness of the lower durometer material is greatest immediately adjacent the inner side (26) of the sole and is lowest immediately adjacent the outer side (28) of the sole. 2. A pair of running shoes as claimed in Claim 1 in which the ratio of the thickness of the lower durometer material to the higher durometer material varies from the outer side (28) of the shoe to the inner side (26) of the shoe over the portion of the sole region extending the full length of the heel to a point adjacent the arch of the wearer's foot, said ratio being constant over the remaining portion of the sole. 3. A pair of running shoes as claimed in Claim 1 or Claim 2 in which the ratio of relative thicknesses of the two materials varies linearly across the width of the sole. 4. A pair of running shoes as claimed in Claim 1 or Claim 2 or Claim 3 in which the midsole is constructed such that the higher durometer material is on top of the lower durometer material. 5. A pair of running shoes as claimed in Claim 1 or Claim 2 or Claim 3 in which the midsole is constructed so that the lower durometer material is on top of the higher durometer material. 6. A pair of running shoes as claimed in any of Claims 1 to 5 in which said higher durometer material is 45+ 10%, Shore A, and said lower durometer material is 35+ 10%, Shore A, durometer. 7. A pair of running shoes as claimed in any of Claims 1 to 6 in which the thickness of the midsole is greater in the heel portion than in the toe portion.

Inventors: CHESKIN, MELVYN PETER
Applicants: WOLVERINE WORLD WIDE, INC.
Application year: 1983
Main classification: A43B13
IPC codes: A43B13, A43B5