Shoe construction

Abstract: A walking shoe (10) has a sole with a heel portion (24) and forefoot portion (22) each of which has an integral resilient flexible compression protrusion (42,28) having maximum extension at the rear edge of the protrusion, curving upwardly forwardly therefrom, and bounded by a groove (44,30) that extends along both side edges and across the rear vertically offset edge of the protrusion, the groove increasing in depth toward the rear of the protrusion. The rear of at least the forefoot protrusion is undercut. The upper surface of the sole has at least one transverse cavity (56,60) just forwardly of the rear edge of the protrusion.

Description: This invention relates to walking shoes and particularly to walking shoes and shoe sole exhibiting superior shock attenuating characteristics and more efficient toeoff. Walking shoes of various styles and constructions have been made over the decades, but in recent years the increased interest in energetic walking for cardiovascular health has stimulated efforts to improve walking shoe comfort and action. These two factors of comfort and shoe action have a significant effect on the attitude and willingness of walkers to continue in this beneficial activity. These two different factors do not normally arise from the same construction. An object of this invention is to provide a walking shoe which effects excellent comfort as well as improved propulsive action. This object is achieved by the present invention which represents an improvement in prior art walking shoe soles of the construction comprising a resilient, flexible, compressible material and having a forefoot portion and a heel portion. According to the present invention, a walking shoe sole comprises a resilient, flexible, compressible material and has a forefoot portion and a heel portion, the heel portion having a peripheral region in the form of a marginal ledge and having an integral compression protrusion extending downwardly beneath the level of the marginal ledge, the maximum extension of the compression protrusion being at the rear of the protrusion and the protrusion sloping upwardly and forwardly from the rear of the protrusion, and a groove which bounds the protrusion at least at the side edges and rear edge of the protrusion, the groove extending up into the sole above the level of the marginal edge. The features of the invention can with benefit also be applied to the forefoot portion with most benefit being achieved by applying them to both such portions. The invention also extends to walking shoes comprising shoe soles according to the invention and a shoe upper connected thereto. Force platform measurements of the biomechanical actions of walking show that employment of the invention produces improved shock attenuation and greater toeoff efficiency. Consequently, the walking shoes are more comfortable and effect improved action. It may be mentioned that in EP-A1-0407862 there is described a sports sole particularly for use in indoor sports which is provided with a peripheral bead of circular or approximately circular cross section and which is connected to the remainder of the sole over a small part of its periphery and is separated, in the region of the ground engaging surface of the sole, from the remainder of the sole by a groove. The purpose of this bead on this sports sole is to accommodate lateral forces which are of significance in indoor sports but are of much lesser significance for a walking sole. The structure and function of the bead described in EP-A1-0407862 are quite different from the structure and function of the sole of the present invention. In a preferred construction of shoe sole in accordance with the invention, the shoe sole is formed of a resilient rubber type material having a general sole level defined by a peripheral marginal ledge portion, having a uniquely curved, offset and isolated, integral compression protrusion on the heel portion of the sole and a similarly curved, offset and isolated, integral compression protrusion on the forefoot. The maximum downward extension of the forefoot protrusion is behind the metatarsal heads, the protrusion curving forwardly upwardly from a vertically offset rear edge toward the level of the sole. The compression protrusions are each bounded by a deep groove to isolate and allow the vertical movement therebetween. The rear edge of at least the forefoot protrusion has a rear overhang, i.e., is undercut at the rear edge. The heel protrusion, like the sole protrusion, has the maximum downward protrusion at the rear edge, curving upwardly forwardly from the vertically offset rear edge toward the front of said heel. Upon impact the maximum protrusion portion of the heel is compressed into the sole, absorbing shock impact. With forward movement of the foot through the gait cycle, the compressed rear portion of the protrusion on the heel reverts back to its original position to propel the rear of the foot forwardly and upwardly, while the rear portion of the forefoot protrusion is compressed into the sole. Further advancement of the foot through the gait cycle causes the rear portion of the forefoot protrusion to revert, i.e., re-extend, which, combined with the rolling action over the curved protrusion, causes rapid toeoff of the foot. The result is efficient toeoff, as has been illustrated from vertical ground reaction force plots taken of persons wearing the novel shoe and walking across a force platform. The invention may be carried into practice in various ways but one walking shoe sole constructed in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a side elevational view of the lateral side, i.e., outside, of the sole which forms part of a right shoe, the shoe upper being shown in phantom lines; Fig. 2 is a bottom view of the sole shown in Fig. 1; Fig. 3 is a rear elevational view of the shoe sole in Figs. 1 and 2; Fig. 4 is a front elevational view of the shoe sole; Fig. 5 is a cross sectional view taken on plane V-V of Fig. 2; Fig. 6 is a top plan view of the sole, Fig. 7 is a force plot of a stocking-bearing foot of a person walking across a force platform; Fig. 8 is a force plot of the person wearing the shoe shown in Figures 1 to 6 and walking across the force platform; Fig. 9 is a diagrammatic cross sectional view of the sole taken transversely across the heel portion at plane IX-IX; Fig. 10 is a diagrammatic cross sectional view of the sole in Fig. 9 but distorted under compressive load; Fig. 11 is a fragmentary diagrammatic cross sectional view of the rear portion of the forefoot protrusion and adjacent undercut groove showing the overhang; and Fig. 12 is a fragmentary diagrammatic view comparable to Fig. 11 but distorted under compressive load. Referring now specifically to the preferred embodiment illustrated in the drawings, the walking shoe 10 there disclosed includes an upper subassembly 12 as of conventional type and a sole subassembly 14. This sole comprises a resilient, flexible, compressible, polymeric material, preferably low density, microcellular, i.e., foam type polyether polyurethane, having a durable skin. Such a material has been found to exhibit effective compressive action with excellent rebound. Alternative materials would include other polymers such as expanded polyesters commonly used for shoe soles, foam rubber compounds and the like. The sole includes an upper surface 16, a periphery 18, and a lower sole level 20. The sole has a forefoot portion 22 and a heel portion 24. The forefoot portion 22 includes a peripheral marginal ledge 26 and an integral compression protrusion 28 extending downwardly beneath the level of the marginal ledge 26. The maximum extension of this protrusion 28 is at the rear thereof, causing a vertical offset relative to the plane of ledge 26, the protrusion 28 curving upwardly forwardly from the rear to blend to the plane of marginal ledge 26 at the toe. At this area, the protrusion extends down below the level of the ledge 26 about 4.75mm (3/16 inch). The curvature of protrusion 28 upwardly forwardly thus forms a gently curved sloping surface. Extending around protrusion 28, isolating it from marginal ledge 26, is a deep groove 30 which includes a transverse groove portion 30′ along the rear edge of the protrusion 28. The groove 30 is progressively deeper from the toe area along the side edges toward the rear of the protrusion 28, and is deepest across the rear edge of protrusion 28 on the forefoot 22. The groove 30 preferably starts at a depth of about 1.58 mm (1/16 inch) at the toe and deepens to about 4.75mm (3/16 inch) above the ledge 26 at the sides adjacent the rear edge of the protrusion. Groove portion 30′ undercuts the rear edge of protrusion 28 (Fig. 5) such that the rear portion of the protrusion 28 overhangs the groove to form a lip 28′ (Fig. 5). This offset rear edge lip 28' is to the rear of the metatarsal heads for proper action of the shoe, and at an angle substantially parallel to the metatarsal break M of the foot, i.e., a line between the second and fifth metatarsal heads. This angle is about 60° to the centre line of the shoe. The bottom surface of the sole curves into groove portion 30′ (see Fig. 5). Groove 30 extends upwardly into the sole above the level of ledge 26. This groove 30 effectively isolates the vertical action of protrusion 28 from peripheral ledge 26, in a manner to be described more fully hereinafter. The bottom surface of protrusion 28 preferably has a series of shallow, generally transverse slots 34 and a decorative arcuate recess 36. The heel portion 24 of the shoe 10 also has a peripheral marginal ledge 40 extending around a protrusion 42. A groove 44 extends around both sides and the rear of protrusion 42. Groove 44 extends upwardly into the sole above the level of the marginal ledge 40. Groove 44 is progressively deeper from the front of the heel portion 24 (about 1.58mm - 1/16 inch) rearwardly to the deepest portion around the rear of the heel (about 4.75mm - 3/16 inch). The maximum extension of the heel protrusion 42, preferably about 4.75mm (3/16 inch), is at the very rear thereof, forming a vertical offset, sloping from there in an upwardly forwardly curving fashion to the level of marginal ledge 40. Groove 44 thus substantially isolates the vertical action of protrusion 42 from the marginal ledge 40, as more fully explained hereinafter. The bottom surface of protrusion 42 preferably has a plurality of transverse shallow slots 46 and an arcuate fanciful recess 48 extending out to the lateral side of the protrusion for traction. The upper surface of sole subassembly 14 preferably has at least one, and here shown to be four, transverse cavities 50 just forwardly of the maximum extension of the forefoot protrusion 28. Also in the top surface of the sole, just forwardly of the maximum extension of the heel protrusion 42, is at least one, here shown to be two, transverse cavities 56. These cavities provide space for furthering the vertical compressive activity of the polymeric sole upwardly in a manner to be more fully described hereinafter. The lower surfaces of protrusions 28 and 42 are preferably in substantially the same horizontal plane at the deepest, i.e., maximum rear, extension of these protrusions 28,42. The upper surface of the heel portion 24 of the sole subassembly 14 is preferably at a higher elevation than the forefoot portion 22. The reaction forces, as analyzed on a force platform in a biomechanics evaluation laboratory at a state university, have shown that the structure has excellent shock attenuation and toeoff efficiency. Referring to the force plots in Figs. 7 and 8, a comparison is shown between the walker with stocking feet (Fig. 7) and with the described shoe (Fig. 8) for illustration purposes. The horizontal axis is time in milliseconds in these figures, while the vertical axis is in percentage of body weight. The longer curve portrays the vertical ground reaction force, the somewhat sinusoidal curve portrays the braking and propulsive force, and the smallest curve represents the lateral to medial force, all three curves being superimposed on each other. In Fig. 7, the initial sharp impact force experienced by the heel shows as a spike at the left end of the vertical force curve. The absence of this initial force spike at foot contact (see Fig. 8) using the described structure indicates that the force is advantageously dissipated over a greater period of time. Secondly, the described shoe evidences a highly efficient toeoff indicated by the level of the toeoff curve (the second peak of the vertical force curve) being as low as that for stocking feet, rather than being considerably higher as might be anticipated, meaning that less force is required during the propulsion phase of the gait. This reduces stress and muscle fatigue. These are highly desirable traits of a shoe since fatigue and injury are often attributed to the high rates of load initially applied, and the effort required for toeoff when wearing shoes. The described design indicates synergistic function with the natural biomechanism of the foot in attenuating ground reaction forces associated with impact and effecting toeoff efficiency by reducing the amount of force necessary to propel the body forward. The full technical explanation of the action of the shoe sole may not be known. It is believed that the following may be at least a partial explanation of the action. The attenuation of shock is believed aided by the fact that the initial impact of the heel region is at the maximum extension of the heel protrusion 42, causing this protrusion to be compressed up into the sole, with groove 44 there being the deepest, allowing this protrusion to move vertically substantially independently of the marginal ledge 40, and also to distort and accommodate the shifting protrusion. Referring to Figs. 9-12, Fig. 9 illustrates the sole cross section at the rear of the heel protrusion 42, prior to ground engagement. Upon impact (Fig. 10) protrusion 42 is forced upwardly with the cellular polymer being compressed, groove 44 being distorted, some of the protrusion 42 shifting into recesses 56, and even the marginal ledge 40 sometimes being slightly distorted under compression. The vertically offset rear edge of protrusion 42 tends to distort rearwardly-upwardly, approaching or reaching the level of ledge 40. The foot then rocks forwardly on the upwardly, forwardly curving protrusion. As weight is removed from the rear portion of protrusion 42, it resiliently reverts to its original extended position by reason of its inherent memory, returning energy to the walker. Further movement of the foot in the next stage of the gait causes the rear downwardly extending protrusion of the forefoot protrusion 28 to engage the surface and, as weight is shifted, the maximum extension rear lip portion 28′ of protrusion 28 (Fig. 11) is compressed up into the undercut (Fig. 12) and also into the sole in the same manner as illustrated by Figs. 9 and 10. Groove 30 allows this to occur substantially independent of the surrounding marginal ledge 26. Further movement of the body weight onto the metatarsal heads and then onto the great toe results in the foot gently rocking forwardly on the upwardly, forwardly sloping curvilinear portion of protrusion 28, with the rear compressed portion of the protrusion resiliently returning to its original position to thereby restore energy to the walker as toeoff from the great toe occurs. There may be other physical actions and biomechanics occurring which are not fully understood. It is conceivable that certain minor deviations of the construction illustrated as the preferred embodiment of the invention could be made to accommodate particular types of situations or personal biomechanics. Hence, the invention is not intended to be limited specifically to the illustrative embodiment set forth.

Claims: A walking shoe sole comprising a resilient, flexible, compressible material and having a forefoot portion (22) and a heel portion (24), the heel portion having a peripheral region (18) in the form of a marginal ledge (40) and having an integral compression protrusion (42) extending downwardly beneath the level of the marginal ledge, the maximum extension of the compression protrusion being at the rear of the protrusion and the protrusion sloping upwardly and forwardly from the rear of the protrusion, and a groove (44) which bounds the protrusion at least at the side edges and rear edge of the protrusion, the groove extending up into the sole above the level of the marginal ledge (40). A walking shoe sole according to claim 1 in which the forefoot portion (22) has a peripheral marginal ledge (26) and an integral compression protrusion (28) extending downwardly beneath the level of the marginal ledge, the maximum extension of the compression protrusion of the forefoot portion is at the rear of the said protrusion, the said protrusion curves upwardly forwardly from the said rear, and a groove (30) bounds and isolates the said forefoot protrusion, the groove (30) extending up into the sole above the level of the forefoot marginal ledge (26). A sole according to claim 2 wherein each compression protrusion (28,42) has side edges and a rear edge, the rear edge of the heel protrusion having a vertical offset, and the heel groove extending along the side edges and the rear edge of the heel protrusion (42). A sole according to claim 3 wherein the rear of the protrusion in the forefoot portion has an undercut. A walking shoe sole according to claim 3 or claim 4 wherein each groove (44,30) is progressively deeper along the side edges toward the rear of the corresponding protrusion (28,42) and is deepest at the rear of said protrusion. A walking shoe sole according to any of claims 2 to 5 wherein the rear edge of the forefoot portion protrusion is to the rear of the position of a wearer's metatarsal heads and at an angle generally parallel to the metatarsal break line. A walking shoe sole according to any of claims 1 to 6 wherein the upper surface (16) of the sole has at least one transverse cavity (34) just forwardly of the rear of the forefoot portion. A walking shoe sole according to any of claims 1 to 7 wherein the upper surface (16) of the sole has at least one transverse cavity (46) just forwardly of the rear of the heel portion (24). A walking shoe comprising a sole according to any of claims 1 to 8 and a shoe upper (12) connected thereto.

Inventors: BLISSETT MALCOLM G, FERDERICKSEN RAYMOND M, BLISSETT, MALCOLM G., FERDERICKSEN, RAYMOND M.
Applicants: WOLVERINE WORLD WIDE INC, WOLVERINE WORLD WIDE, INC.
Application year: 1991
Main classification: A43B13
IPC codes: A43B13