Patent Application
20070033834
The present invention relates in general to an improved shoe insole and more particularly to an insole providing improved cushioning and support to the foot of a wearer.
The human foot is a very complex biological mechanism. While walking the load on the foot at heel strike is typically about one and a half times a person's body weight. When running or carrying extra weight, such as a backpack, loads on the foot may exceed three times the body weight. The many bones, muscles, ligaments, and tendons of the foot function to absorb and dissipate the forces of impact, carry the weight of the body and other loads, and provide forces for propulsion. Properly designed shoe insoles can assist the foot in performing these functions and protect the foot from injury.
Insoles may be custom made to address the specific needs of an individual. They may be made based on casts of the end user's foot or may be made of a thermoplastic material that is molded to the contours of the end user's foot. However, it is not practical to make such insoles for the general public. Like most custom made items, custom insoles tend to be expensive because of the low volume and extensive time needed to make and fit them properly.
To be practical for distribution to the general public, an insole must be able to provide benefit to the user without requiring individualized adjustment and fitting. A first type of insole commonly available over-the-counter emphasizes cushioning the foot so as to maximize shock absorption. For typical individuals cushioning insoles perform adequately while engaged in light to moderate activities such as walking or running. That is, a cushioning may insole provides sufficient cushioning and support for such activities. However, for more strenuous or technically challenging activities, such as carrying a heavy backpack or traversing difficult terrain, a typical cushioning insole may not be adequate. Under such conditions, a cushioning insole by itself would not provide enough support and control, and may tend to bottom out during use.
Another type of over-the-counter insole emphasizes control. Typically, such insoles are made to be relatively stiff and rigid so as to control the bending and twisting of the foot by limiting foot motion. The rigid structure is good at controlling motion, but is not very forgiving. As a result, when motion of the foot reaches a limit imposed by the rigid structure, the load on the foot tends to change abruptly and may increase the load on the structures of the foot. Because biological tissues such as tendons and ligaments are sensitive to the rate at which they are loaded, the abrupt change in load may cause injury or damage.
In view of the foregoing, it would be desirable to provide an over-the-counter insole that provides both cushioning and control.
It would also be desirable to provide an insole that provides both cushioning and control and is practical for use by the general public.
In view of the foregoing, it is therefore an object of the present invention to provide an over-the-counter insole that provides both cushioning and control.
It is also an object of the present invention to provide an insole that provides both cushioning and control and is practical for use by the general public.
The above, and other objects and advantages of the present are provided by an insole that provides both motion control and cushioning. The insole includes a system of interacting components that cooperate to achieve a desired combination of foot cushioning and motion control. The components include a foam core, a semi-rigid stability cradle, and a number of elastomeric pods and pads. The characteristics of the components, their size and shape, and their position are selected to provide a desired blend of cushioning and control, and more specifically to achieve a desired biomechanical function.
In accordance with principles of the present invention, a cushioning core or base is combined with a relatively stiff stability cradle and a number of elastomeric pods to form an insole that provides cushioning, stability, and control. By altering the size, shape, and material properties of the pods insoles may be designed to address issues of over/under pronation, over/under supination, and other problems related to foot motion.
In a preferred embodiment of the present invention, the components of an insole are permanently affixed to each other to create an insole designed for an intended type or category of activity. Many insole designs may then be made available to address a broad range of different activities. In an alternative embodiment of the invention, an insole may comprise a kit including a number of interchangable pods having different characteristics. Using such a kit, an end user may selectivley change the pods to customize the insole to accommodate a specific activity.
The above, and other objects and advantages of the present invention will be understood upon consideration of the following detailed description taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:
FIGS. 4 to 7 are, respectively, dorsal (top), plantar (bottom), lateral (outside), and rear views of the insole of
In reference to FIGS. 1 to 11, an insole constructed in accordance with the principles of the present invention is disclosed. As shown in the exploded view of
As shown in
Base 22 has a raised edge 40 that wraps around the heel and extends partially along the sides of the foot such that the insole conforms to the natural shape of the foot. As seen in
Base 22 is partially disposed within stability cradle 24, which provides some rigidity to insole 20. Prefereably, stability cradle 24 is made of a material having sufficient rigidity to control foot motion. For example, stability cradle 24 may be made of polypropylene having a durometer of Shore A 90.
Stability cradle 24 generally extends under the from the calcaneus through the midtarsal joints of the foot. However, the forward medial portion is shaped to accommodate downward motion of the 1st metatarsal during toe off, as is described below. Indentations 58 around the heel and along the lateral side of stability cradle 24 help improve the fit of insole 20 into a shoe and minimize movement between insole 20 and the shoe.
As shown in FIGS. 6 to 10, stability cradle 24 includes walls that wrap up the sides and rear of base 22 to provide support for the foot. Preferably, stability cradle 24 is approximately 3 mm thick and the walls taper from approximately 2 mm to about 0.5 mm. The sides of stability cradle 24 are preferably higher on the medial side of the foot because of the higher loading. For example, medial side 48 of stability cradle 24 extends upward under the medial longitudinal arch. Slots 50 improve flexibility along the medial side of stability cradle 24 without sacrificing longitudinal arch support. Preferably, base 22 is molded so that portions 52 and 54 of the foam material project into slots 50 and holes 56 so that it is approximately flush with the outer surface of stability cradle 24, so as to mechanically lock stability cradle 24 and base 22 together. Advantageously, the foam is also able to bulge through slots 42 when base 22 is compressed, e.g., while walking to provide additional cushioning to the arch.
Pods 26 to 30 are affixed to the bottom of base 22 through corresponding openings 60 to 64 in stability cradle 24. Forefoot pod 32 and valgus pad 34 are affixed to the bottom of base 22 forward of stability cradle 24, and top sheet 36 is affixed to the top surface of base 22. As will be discussed below, the size, shape, and placement of these pods and pads are based on the location of various anatomical landmarks of the foot and the biomechanics of foot motion.
Foot contact with the ground is generally divided into three phases: heel strike, midfoot support, and toe off. During heel strike, the heel of the foot impacts the ground with significant force. To cushion the impact, lateral heel pod 26 is positioned along the rear and lateral side of the calcaneus (heel bone) and projects below stability cradle 24. Preferably, lateral heel pod 26 is made of a material having suitable cushioning properties. For example, lateral heel pod 26 may comprise approximately 6 mm of a polyurethane material with a durometer of about Shore C 40-60. More preferably, the characteristics of lateral heel pod 26 are selected based on an intended type of activity. For example, a polyurethane having a durometer of about Shore C 45-50 would be appropriate for lateral heel pod 26 in an insole designed for activities such as day hiking; whereas a polyurethane having a durometer of about Shore C 50-55 would be more appropriate in an insole designed for activities such as backpacking.
Following the initial impact of the heel with the ground, the foot twists, or pronates, bringing the medial side of the heel into contact with the ground. The foot is sensitive to the amount of pronation as well as the rate at which the pronation occurs. Pronation is natural, and some degree of pronation is desirable because it serves to absorb the stesses and forces on the foot during walking or running. However, an excessive amount or rate of pronation may result in injury.
Stability cradle 24 provides firm support along the medial portion of the foot to help control the amount of pronation. Medial heel pod 28 helps to control the rate of pronation by forming medial heel pod 28 out of a material having different characteristics than lateral heel pod 26. For example, to reduce a pronation rate, medial heel pod 28 may be made from a firmer material than lateral heel pod 26. A firmer or stiffer material does not compress as much or as fast as a softer material under the same load. Thus, a medial heel pod made from a firmer material would compress less than a lateral heel pod made of a softer material. As a result, medial heel pod 28 tends to resist or counteract pronation and thereby help to reduce the degree and rate of pronation. Conversely, making medial heel pod 28 from a softer material than lateral heel pod 26 would tend to increase the amount and rate of pronation.
Prefereably, the firmness of the material used in medial heel pod 28 is selected based on the firmness of lateral heel pod 26 and on the type of indended activity. For example, the firmness of lateral heel pod 26 and medial heel pod 28 may differ by about 20-30% for an insole to be used during light to moderate activities. More specifically, lateral and medial heel pods having durometer values of approximatly Shore C 45-50 and about Shore C 60, respectively, would be suitable for an insole designed to be used during light hiking.
Carrying a heavy backpack significantly increases the load on the foot and the rate of pronation during and following heel strike. Accordingly, medial heel pod 28 may be made significantly firmer in an insole designed for use while backpacking. As an example, a difference in firmness of about 20-40% may be more appropriate for such activities. More specifically, lateral and medial heel pods having durometer values of approximatly Shore C 50-55 and about Shore C 65-70, respectively, would be suitable for an insole designed to be used during backpacking.
Midfoot pad 30 provides cushioning and control to the lateral side of the foot during the midstance portion of a step. Typically, midfoot pod 30 is formed of a material having the same properties, e.g., firmness, as lateral heel pod 26. However, a material having different characteristics may also be used.
At the beginning of the propulsion or toe-off phase of a step, the heel begins to lift from the ground and weight shifts to the ball of the foot. Forefoot pod 32 is located under this part of the foot. Preferably, forefoot pod 32 is formed of a relatively resilient material so that energy put into compressing pod 32 is returned to help propel the foot at toe-off. For example, forefoot pod 32 may comprise a layer of an EVA material approximately 6.5 mm thick with a durometer of about 25-45 Shore C, and more particularly about 30-40 Shore C. Preferably, forefoot pod 32 includes diagonal grooves 66 as shown in
During toe off, the first metatarsal naturally flexes downward. Preventing this natural downward flex of the first metatarsal causes the the arch of the foot to flatten and the foot to over pronate, increasing stress on the ankles and knees. To accommodate the downward flex, medial portion 62 of forefoot pod 32 extends rearward into corresponding concave portion 64 of stability cradle 24. The shape of the stability cradle and forefoot pod permit the first metatarsal to flex more naturally and thereby encourage loading of the great toe during toe off.
Valgus pad 34 is positioned under the toes on the lateral side of the foot. Prefereably valgus pad 34 is firmer than base 22 to further encourage loading of the great toe during toe off. For example, valgus pad 34 may comprise a 1.5 mm layer of EVA having a durometer of about Shore C 70.
In a preferred embodiment, base 22 is covered with top sheet 36, which is preferably a non-woven fabric layer with a low coefficient of friction so as to minimize the possibility of blisters. In a preferred embodiment, the fabric is treated with an antibacterial agent, which in combination with a moisture barrier reduces odor causing bacteria and fungus. A series of air ports 66 extend through top sheet 36, base 22 and forefoot pod 32 to permit air circulation above and below insole 20.
In a first prefered embodiment of the present invention, the various components of an insole constructed according to the principles of the present invention are permanently affixed to base 22 using an appropriate means such as an adhesive. In an alternative embodiment of the present invention, at least some of the components, and the pods in particular, are affixed to base 22 in a way that they can be changed or replaced. For example, pods 26-32 may be attached to base 22 using hook and loop fasteners, a temporary adhesive, or other removable means of attachment. By providing an insole kit including interchangable components an end user may adapt the insole to their specific needs or to a specific end use. For example, an end user that is susceptible to over pronation or that will be hiking with a particularly heavy backpack may select a medial heel pod that is somewhat firmer than a typical user.
While the present invention has been described in relation to preferred embodiments, the detailed description is not limiting of the invention and other modifications will be obvious to one skilled in the art. For example, the illustrative embodiment of the invention disclosed above are premissed on a need to control over pronation. Thus, the illustrative embodiment have a medial heel pod that is firmer than the lateral heel pod. However, under pronation may be addressed by using a softer medial heel pod. Similarly, over or under supination during toe off may be addressed by changing the characteristics of any of base 22, forefoot pod 32, and valgus pad 34.
The present invention has been disclosed in the context of providing an over-the-counter insole that may be made available for distribution to the general public. However, the same principles may be used by a podiatrist or other medical professional to design or create an insole to address the needs of a specific patient.
Thus, an improved insole has been disclosed. It will be readily apparent that the illustrative embodiment of an insole thus disclosed may be useful in cushioning the foot and controlling pronation during activities such as hiking, backpacking, and the like. However, one will understand that the components of the insole system may be modified to accommodate other activities or to control other kinds of foot motion. Thus, the description provided herein, including the presentation of specific thicknesses, materials, and properties of the insole components, is provided for purposes of illustration only and not of limitation, and that the invention is limited only be the appended claims.
