Footwear, footwear inserts and socks for reducing contact forces
Footwear, footwear inserts and socks that include a cavity adapted to receive a portion of an individual's heel foot to reduce contact forces. The cavity can be adapted to contain a liquid, a solid or two layers of material in which the stiffness of the layers differ.
The present invention generally relates to footwear, footwear inserts and socks for reducing contact forces on an individual's body.
Many physical activities involve repeated impacts between an individual's feet and the ground surface. For example, during a five kilometer run an individual's body experiences approximately 3,000 impacts with the ground. These impacts generate forces on the body commonly known as peak forces within the first ten to thirty milliseconds of a foot coming into contact with the ground surface. A force-time wave (also known as an impact shock wave) is generated each time an individual's foot makes impact with the ground surface. Unfortunately, immediately after an impact shock wave is created it does not remain contained within the individual's foot but rather traverses through the knee and hip joints toward the individual's brain.
A shock wave can be characterized by its amplitude or peak force (A) and duration (T) with both of these parameters depending upon several factors such as the speed at which the individual is running, the nature of the ground surface upon which the individual is running (for example, soft versus hard), the anatomy of the foot, and the runner's running style. Moreover, these parameters depend upon whether the individual is wearing footwear, footwear inserts and/or socks as well as the material and design of the footwear, footwear inserts and/or socks. Of the two parameters, A and T, if A (the force amplitude) is of a sufficient magnitude, then it can cause both short and long term detrimental effects on an individual's body. For example, it can cause one or more of the following: (i) damage to the soft tissue structures within the knee and hip joints, (ii) low back pain by enhancing forces on the lumbar spine, and (iii) stress fractures when the body is burdened with excessive physical exercise over a very short period. Measurements have shown that the shock wave amplitude A during casual running can exceed ten to twenty times the runner's bodyweight. Moreover, these high forces, which are a result of the downward momentum (or velocity) of an individual's body that is brought to virtually zero immediately after an individual's foot contacts the ground, are dynamic in nature and last for only ten to thirty milliseconds. This is analogous to the situation in which a fast-moving baseball caught by a catcher produces a force several times in magnitude the baseball's weight. Thus, footwear, footwear inserts and socks that minimize the amplitude (A) of a shock wave could help minimize detrimental impact-related effects on an individual's body.
For day-to-day activities such as normal walking and stair climbing the forces within the knee and hip joints can easily reach five times the force of an individual's bodyweight. This somewhat counterintuitive result occurs because an individual's joint counterbalances the tensile action of the muscles acting on the joint by undergoing compression itself so as to satisfy force equilibrium conditions. Since on an average an individual walks about five kilometers a day this translates into approximately 1.2×106 heel strikes with the ground surface for each foot per year. The long-term effects of the impact pulses generated with each heel strike on the soft tissue structures of the knee and hip joints has been well established. The cumulative effect of the impact pulses is to cause joint arthritis. The time to develop this condition depends upon the type and frequency of the physical activity such as walking, running or playing sports.
The amplitude A is roughly the velocity V at which the foot strikes the ground (considering only its vertical component) divided by the time it takes the ground to bring the downward velocity of the body and hence its momentum to zero (known as the ground interaction time T). Since the speed at which a person's feet strike the ground is usually set by the runner and therefore “non-negotiable” one way to reduce A is to increase T. This can be accomplished by running on grassy and softer surfaces, or equivalently, by avoiding runs on hard pavements. Another way to increase T, which has been widely exploited heretofore by the footwear industry, is to provide an easily deformable thick rubber sole at the heel portion of the shoe. During each heel strike, the rubber sole makes contact with the ground first and then it compresses continuously under the action of the downward moving heel while providing an increasingly upward resisting pressure to the heel of the foot. This resisting pressure acts to reduce the downward velocity of the heel and acts during the entire time that the sole material is being compressed. Once the sole material underneath the heel has been fully compressed while the heel does feel the impact from the ground below the magnitude of this impact is now significantly reduced as the heel strikes the ground with a much lower velocity due to the upwardly directed pressure from the deforming sole. Viewed alternatively, the time taken by the sole material to compress increases the overall time T for bringing the heel velocity to zero. This strategy to reduce impact force amplitude by increasing T is identical to that employed by a baseball catcher while catching a fast pitch. By moving his catching hand in the same direction as the arriving baseball, the impact on his hand is considerably decreased. This is because this action of moving the catching hand increases the time T over which the velocity of the arriving baseball is brought to zero.
When applied to footwear, there are practical limitations to decreasing the force amplitude A by arbitrarily increasing the time T for example by providing a very soft sole material in the heel section of the shoe. This is because if the material is too soft (e.g., a soft foam), it will simply deform without providing the necessary resisting pressure to slow down the downward (towards the ground) velocity of the striking heel. Therefore, the heel will essentially suffer the same impact with or without the sole material. Moreover, at another extreme the material underneath the heel cannot be too hard either as higher stiffness tends to increase A. Various manufacturers and designers have focused on different structural and material strategies to provide the optimal stiffness (not too soft and not too hard as discussed above) in the heel section of the shoe for reducing A. Some of these strategies include use of novel polymers with optimal levels of stiffness, incorporation of air pockets within the heel section of the sole material, and the addition of plastic protrusions or patterns of small structural units in the form of beams and columns in the heel section of the shoe's sole. In the latter strategy, the amplitude of the shock wave A is reduced by increasing the time T for arresting the upper body momentum through deflection and bending of the beam and column network. There have also been suggestions to design soles using active materials whose stiffness can be changed depending upon the ground stiffness, much like the dynamic suspension system used in many modern cars. Regardless of the sophistication of the material or the mechanical technology used, the fact remains that each one of the prior art focuses on providing some form of padding material directly between the striking heel and the ground surface.
As can be seen, there is a need for footwear, footwear inserts and socks that can lower impact forces inside the knee and hip joints. In addition, there is a need for footwear, footwear inserts and socks that can lower the shock wave amplitude inside the knee and hip joints. Also, there is a need for footwear, footwear inserts and socks that manage and mitigate the physical effects on an individual's body caused by ground impact forces.
SUMMARY OF THE INVENTIONIn one embodiment of the present invention, footwear for mitigating impact forces on an individual's heel bone includes an outsole unit having an outsole upper side and an insole unit having a insole lower side secured to the outsole upper side and an insole upper side including a cavity wherein the cavity is adapted to receive the heel bone portion (including the soft-tissue that covers the heel bone) of an individual's foot.
In another embodiment a footwear insert for mitigating impact forces on an individual's heel bone includes an insole unit adapted to be inserted into footwear including a cavity wherein the cavity is adapted to receive the heel bone portion of an individual's foot.
In yet another embodiment a sock for mitigating impact forces on an individual's heel bone includes a cavity adapted to receive the heel bone portion of an individual's foot.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The intellectual framework for the claimed invention in this application is based on a study in which knee forces were measured in professional and casual runners. This study is discussed to provide the scientific basis for the claimed invention. This study researched the impact shock waves (both A and T) experienced by various runners. In this study, instead of directly measuring A, the acceleration-time wave was measured, which is exactly proportional to the impact shock wave and characterized by an amplitude B and the same time T as that of the impact shock wave. The impact shock wave's amplitude A can be obtained by multiplying the acceleration wave amplitude B by the mass of the runner. Use of acceleration pulses in the study therefore allowed comparing shock wave amplitudes for runners with different weights (masses). Accordingly, the amplitude of the impact shock wave A is measured in units of lb-f or Newton, while B is measured in units of acceleration, ft/s2 or m/s2. Moreover, sometimes the amplitude B is conveniently expressed in units of g, which is the acceleration due to gravity. When B is set to equal 1 g, this results in a shock wave amplitude A equal to one times the runner's bodyweight, which is essentially the force experienced by the body when the runner is essentially standing. Accordingly, 5 g will produce shock wave amplitude A that is 5 times the runner's bodyweight. The value of B when expressed in terms of g thus provides a very convenient way to compare intensities of forces in terms of runner's bodyweight. For this reason B is also referred to as the “G-Force,” in the biomechanics community.
Since impact shock is known to vary systematically with running speed and surface gradient (Clarke, T. E., Cooper, L. B., Clark, D. E., & Hamill, C. L., 1985, “The effect of increased running speed upon peak shank deceleration during ground contact.” In D. Winter, R. Normal, R. Wells, K. Hayes, & A. Patla (Eds.), Biomechanics, IX-B, pp. 101-105, Champaign, Ill.: Human Kinetics and Hamill, C. L., Clarke, T. E., Frederick, E. C., Goodyear, L. J., & Howley, E. T., 1984, “Effects of grade running on kinematics and impact force.” Medicine and Science in Sports and Exercise, 16, 185), changing the speed and gradient of a motorized treadmill provides a convenient means of manipulating the levels of impact shock in a laboratory environment. In the research, each subject walked and ran on a motorized treadmill (Precor956) at 1.3 m·s−1 (3 mph; average walking speed), 2.8 m·s−1 (6.3 mph), 3.3 m·s−1 (7.4 mph), 4.2 m·s−1 (9.4 mph) and 5.0 m·s−1 (11.2 mph). Subjects were allowed to rest between trials. The use of treadmill allowed maintaining a proper control over walking and running speeds across different runners.
Subjects were selected from a pool of volunteers to participate in these experiments. The selection was based on running experience in which professional athletes were chosen which run a minimum 50 km and casual runners were chosen which run at least one time a month. Moreover, all runners were chosen with the same shoe size (U.S. size 11). However, the weights and heights of the runners were however allowed to vary in the study. This control, as discussed below, allowed for a better understanding of the mechanism of dramatically reducing shock waves reduction in professional athletes compared with casual runners.
Regarding the instrumentation of the research, skin-mounted accelerometers have been used before to measure the shock waves transmitted into the body during running. Following this approach, axial accelerations of the lower right leg were recorded in various runners by means of a piezo-resistive accelerometer (PCB Model 3701D1FB20G) attached to the skin onto the anterior-medial (front and center) portion of the tibia (shin bone) just distal (just below the knee level) to the knee joint. The sensitive axis of the accelerometer was aligned with the long axis of the bone. This site was selected because the soft tissue overlying the bone is relatively thin at this point and this minimizes the signals resulting from the muscle action, which in turn was of little interest to this study. To facilitate the attachment, the accelerometer was bonded inside a wooden mounting block. The block was held in position by a Velcro strap and tightened to the comfort level of the runner. Such tightening has also been shown to reduce the influence of soft tissue on the accelerometer signal. While the accelerometer itself has a mass of 77.8 g and a nominal resonant frequency superior to 900 Hz, the mass of the encased accelerometer was 83 g with its natural frequency inclusive of its attachment is between 60 Hz and 90 Hz. While the dominant component in the acquired acceleration signal relates to the impact shock wave, it also includes components corresponding to muscular action and noise resulting from the compliant attachment of the accelerometer to the body. Spectral analysis was used to distinguish and separate the impact shock wave data from these unwanted signals. Outputs from the accelerometer were sampled using an oscilloscope (Tektronics, MSO4000 Series) and processed using a computer using software (Wavestar for Oscilloscopes). Each sample taken contained at least 3 correct peaks of acceleration before it was considered for analysis.
The results indicate that professional long distance runners take the impact on their forefoot by maintaining smaller steps and pushing higher while a casual runner runs with longer strides that results in taking the impact on his or her heels. At 7.4 mph running speed, peak accelerations in the range of 4 g to 5 g (which corresponds to a dynamic force 4 to 5 times the body weight) were recorded in causal runners just below their knees while they ranged between 2 g and 3 g for a professional athlete. Both sets of runners wore the same-size shoes from the same top of the line brand. The reduction in G force in a professional athlete substantially cuts down the impact on his knee and hip joints. However, this reduced G-force comes at the expense of highly straining his Achilles' tendon that undergoes substantial tension to reduce the forefoot impact force. Moreover, over a long distance run the professional runner can in fact fatigue his Achilles' tendon. Interestingly, the results have indicated that use of shoes that are well padded towards the heel (that is, with thicker soles) can destroy professional athlete's years of hard work by increasing his or her G-force to the same level as experienced by a casual runner. That is, when the same professional athlete was given a high performance shoe that had a fairly thick sole in the heel region of his shoes his G-force was significantly higher compared with when he or she ran bare feet or with shoes with very thin heels. A thicker sole automatically results in a heel strike with the ground surface first even for a professional athlete. This happens naturally because of the thick-soled geometry of the shoe. This hypothesis is supported by the data shown in Table 1 of
Based on the above discussion, one can conclude that whenever a person's heel strikes the ground first during running it generates substantially higher force amplitudes compared to when the impact is taken first by the forefoot. When the heel portion of the shoe strikes the ground first, the reaction force from the ground is almost immediately directed in line with the axis of the shinbone. The shock wave thus created is launched immediately into the shaft of the shinbone towards the knee joint and the only attenuation (reduction in the shock wave amplitude) it receives is caused by the soft tissue structure that is directly covering the heel bone. In addition to the direction, the entire force is generated over a very small area of the heel bone, which results in a very large contact pressure (force divided by contact area). The large contact pressure very quickly compresses both the natural tissue overlaying the heel bone and the sole material of the shoe that is directly underneath the heel area. This then leads to a much shorter time T and an increase in the shockwave amplitude A, as discussed above.
In considering the situation for a professional athlete running bare foot that results in a minimum value of the shock wave or acceleration pulse amplitude, the impact generates a shock wave however it is directed to an area forward of the ankle joint. The generated shock wave travels to the ankle first, and then turns almost 90 degrees into the shaft of the shinbone to proceed towards the knee joint. It is well known in the field of shock wave physics field that there is a significant dissipation in the amplitude of the shock wave when it turns by a significant angle, as here, by almost 90 degrees into the shaft of the shinbone. This natural turning of the shockwave results in shock wave attenuation not present in ordinary runners where the wave is generated directly in line with the shaft of the shinbone. Even more important than this effect is a second effect resulting from foot rotation about the ankle joint that occurs immediately after impact. The foot essentially acts like a rotational spring and increases the time T over which the upper body momentum is brought to zero upon foot impact. Any increase in T, as discussed above, will bring down the amplitude of the shock wave A. The same foot rotation mechanism also works for “flat footed runners,” such as marathoners, who do not experience forefoot impact that would significantly fatigue their Achilles tendons. Moreover, the area of contact upon the impact is much larger in the forefoot-impacted region because there are no protrusions of any kind underneath the forefoot in contrast to the downwardly protruding apex of the heel bone in the heel region. This effect is even larger for flat footed runners. A large area reduces the impact pressure (force per unit area) and thus it takes more time to compress the material of the sole. The synergistic effect of all these mechanisms leads to this dramatic decrease in the impact shock wave amplitude in a professional athlete compared with that experienced by a casual runner. One can also see why this beneficial effect disappears as soon as the professional athlete runs with shoes with a thicker sole in the heel region that results in the impact point and hence the center of pressure essentially moving towards the heel region. Indeed, the results have shown that one of the professional athletes running at 7.4 mph, 9.4 mph and 11.2 mph experienced G forces of 4.6 g, 4.5 g and 4.5 g, respectively, which compares well with the corresponding figures of 4.5 g, 5.0 g, and 5.5 g recorded for a casual runner at the same speeds. The same professional athlete recorded 3.6 g, 3.4 g and 3.8 g, respectively, at the above speeds, when using a shoe which had a very thin sole in its heel region and therefore the athlete was still able to strike his forefoot first without the geometry of the shoe forcing him to land on his heels first. One can therefore conclude that a professional athlete should avoid wearing thick heel shoes during running.
The claimed invention in this application are a result of the natural query as to which design for shoes, shoe inserts and socks could be created for a casual runner that will yield the reduced G-forces forces obtained by a professional runner achieve through years of training! The claimed invention as well as actual force measurements using the claimed invention are discussed next.
DETAILED DESCRIPTION OF THE INVENTIONThe following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Referring now to the figures,
The following is a list of different types of footwear according to individual embodiments of the present invention, which is not meant to be exhaustive: athletic shoes, tennis shoes, cleats, climbing shoes, hiking shoes, skating shoes, cycling shoes, skateboarding shoes, golf shoes, snow shoes, wrestling shoes, ski boots, work shoes, dress shoes, boots, sandals, flip flops, mules, pumps, high heels, slingbacks, esparilles, clogs, platform shoes, mocassins, loafers, boat shoes, slippers, dance shoes, bowling shoes, childrens' shoes and corrective shoes.
While insole unit 15 can include any type of material, preferably it is made of a cushioning material that includes a synthetic foam such as polyurethane, polyolefin, or the like according to one embodiment of the present invention. Insole unit 15 can function alone according to one embodiment of the present invention or in combination with other functional units in an article of footwear 10 according to one embodiment of the present invention.
In one embodiment of the claimed invention a cavity is incorporated directly in the construction of the footwear or sock itself where a partial cavity will be placed in the heel area of insole of the footwear or sock. Even though the invention has been demonstrated with a specific cavity or cutout diameter and depth, they can all be varied to any size depending upon the weight and foot anatomy of the user. The design could also be introduced in a customized manner in which an individual's foot anatomy could be scanned to produce a shoe that maximizes the scientific effect of the claimed invention. Moreover, the cavity could be designed to be adjustable in one embodiment of the claimed invention.
In one embodiment of the claimed invention a cavity is incorporated directly in the construction of the footwear, footwear insole or sock itself in which a partial or full cavity is placed in the heel area of insole of the footwear, footwear insole or sock. In one embodiment of the claimed invention the aforesaid cavity is filled partially or completely with a substance such as a polymer that is much softer (or has a much lower stiffness coefficient value) compared with the material that is used to make the shoe's insole or its outer sole. During the initial stages of the heel strike, this idea works identically to the first one where the support to the heel bone is provided annularly by the stiffer material present at the edges of the soft polymer-filled cavity and the forefoot. However, as the heel drives further into the cavity by compressing the soft polymer, the soft polymer starts to support the heel bone as well as its own stiffness increases upon compression caused by the downward-moving heel. This extends the time T over which the support to the heel bone is provided which in turn reduces the force amplitude A. Experiments were done with this design for casual runners and the results showed that the level of low G-forces recorded earlier using an unfilled cavity were essentially reproduced, and in some cases, even superior results were obtained as shown in Table 2 of
In another embodiment of the claimed invention, the cavity is filled with a number of widely available cooling gels, medicated pads or even aromatic gels for those suffering from foul foot odor. This may particularly prove attractive to patients suffering from diabetics and other foot diseases.
In one embodiment of the claimed invention there is a cutout or a cavity in the heel region of the shoe's insole directly underneath where the apex of the heel bone and its soft tissue covering (or the protruding portion of the heel bone) contacts the shoe's insole during normal walking and running. In principle the diameter of the cutout should be slightly larger than the footprint of the heel bone (without the soft tissue) on the shoe's insole. The depth of the cutout is such that before the apex of the heel bone gets to the bottom of the cavity and the ground reaction starts to build up directly underneath it, the area of the heel immediately surrounding the heel bone apex contacts the areas of the insole, at and immediately, adjoining the edges of the cavity. This latter contact occurs as the apex of the heel bone is stilling moving (downwards) unsupported inside the cavity. The pressure from the ground reaction builds up immediately on the annular portions of the heel, around the apex of the heel bone, since those areas come into contact with the edges of the cavity first. This resisting pressure substantially decelerates the apex of the heel bone that is still moving downwards towards the ground but has not yet contacted the bottom of the cavity. Interesting during this time while the heel bone is still moving downward without experiencing any direct upward resistance from the ground, the forefoot region of the foot impacts the ground through the sole. At this point both the annular area around the apex of the heel bone and certain areas of the forefoot start to compress the portions of the sole directly beneath them. All this happens while the apex of the heel bone has not contacted the ground yet. The resisting pressure at these areas results in further reduction of the speed by which the apex of the heel bone is approaching the ground. Finally, at some point, the apex of the heel bone contacts the bottom of the cavity and this immediately results in additional resistance from the ground because of the compression of the sole that is now directly underneath the apex of the heel bone. This resisting pressure is added onto the already operating resisting pressure that continues to act over the forefoot and annular area of the heel surrounding the apex of the heel bone. The combined effect of this is that the center of reaction-pressure on the heel is now shifted away from the heel bone apex towards the front of the foot. As discussed above, this immediately brings into action the beneficial effects of foot rotation about the ankle joint, additional shock wave attenuation due to wave bending at the ankle joint, and an increase in T caused by a reduction in the contact foot pressure. From the viewpoint of impact shock wave management, this effectively converts a casual runner who is a heel striker to a forefoot professional runner or even a flat foot marathon runner. This fact was established by measuring the impact shock wave amplitude A just below the knee level in both casual as well as professional runners all of whom wore the same size and brand-named shoes in which a cavity slightly larger than the apex of the heel bone was provided in the heel region of the shoes' insoles. The depth of the cavity varied between 5 mm and 10 mm over the heel area, with the smallest depth towards the forefoot. Experiments were also done using a thicker insole in which the depth of the cavity varied between 10 mm and 20 mm over the span of the heel region. Results for casual runners showed that the shock wave amplitude could be reduced by 20% by using shoes in which holes or cavity were provided in the heel region of the insoles. Results for one of the professional runners showed that the use of the claimed invention reduced the G force from 1.5 g to 1.1 g at 7.4 mph, from 2.5 g to 2.2 g at 9.4 mph and 3.5 g to 3 g at 11.2 mph. These represent reductions in the G-force ranging from 12% to 25%, using the claimed invention. The reduced levels of G force is even better than values of 1.0 g, 2.5 g and 3.5 g that were recorded during bare feet running, which typically resulted in the lowest levels of G force for the professional athlete. This essentially means that a professional athlete can better his impact management by using the claimed invention. What is even more exciting is that this reduction in the G-force level comes while also reducing the tension on his Achilles tendon. This happens because the annular area of the athlete's heel around the apex of the heel bone is fully supported and this takes off the reactionary tension from his Achilles tendon. This means that a professional runner when using the technology disclosed in this patent may be doubly benefited, thereby minimizing the impacts on his knees while reducing the fatigue on his Achilles tendon. This can turn out to be the difference between winning and loosing in a very competitive race. The exact depth of the cavity that will maximize the beneficial effects of the invention will depend upon the weight and foot anatomy of the runner and the specific material used for making the insole.
In one embodiment of the claimed invention a removable footwear insert includes a cavity in the heel area of the footwear insert, which it was found through testing to reduce the impact force between 20% and 44%. Motivated by this embodiment, tests were made of shoe inserts widely marketed in world commerce today and compared them with ones similar to the embodiment shown in
Measurements were also made of the G-forces during normal walking and since a large population goes to work in formal dress shoes, experiments were extended to include these types of shoes as well. All measurements were made at walking speed of 3 mph. Results for one of the female subjects showed that the G-force was 0.7 g when using no footwear inserts, 0.5 g when using a regular brand-named shoe insert, and only 0.3 g when using the same footwear insert but with a hole provided in its heel area. The G-forces for other subjects did not show any variation as the natural padding of the athletic footwear provided the G-force decrement. Results using formal leather footwear showed benefits to all users. For one of the subjects, the G-forces were 1 g when using no footwear insert, 0.95 g when using a standard footwear insert, and 0.8 g when using the footwear insert as shown in
The following is a list of different types of socks according to individual embodiments of the present invention, which is not meant to be exhaustive: athletic socks, hiking socks, ski socks, anklet socks, dress socks, medical socks and hosiery.
Even though embodiments of the claimed invention have been shown with a specific diameter and cavity depth (or substance-filled areas), they can all be varied to any size depending upon chosen criteria such as the weight and foot anatomy of the user. The claimed design could be introduced in a customized manner in which an individual's foot anatomy could be scanned to produce footwear or footwear inserts that maximize impact management. Along the same idea, prefabricated footwear or footwear inserts that are size-dependent and age-dependent could be dispensed for example at the office of a Podiatrist, Orthopedist, Pediatrician, Chiropractor, etc., as the need may be determined.
Use of some of the particular embodiments of the claimed invention cuts down the impact force amplitudes experience during normal walking or running anywhere from 20% to 30% over the heel technology utilized in the most expensive top brand shoes being marketed today.
According to certain specific embodiments of the claimed invention, shoe footwear, footwear inserts and/or socks including a cavity are used for high heeled footwear. Prior research has shown that a person wearing high heeled footwear experiences not one but two shock waves. The two shock waves occur almost next to each other in time. This is because the heel impacts the ground first and it is immediately followed by the impact on the toe-region of the high heeled footwear. Both impacts result in shock wave amplitudes that are similar to those discussed earlier in this application. Because of this, a person wearing high heeled footwear is essentially doubling the number of shock waves that impacts his or her body compared to when the person walks the same distance using standard footwear. The basic invention that is discussed in this application can be used to reduce the two shock waves peaks to only one and therefore significantly improve the detrimental effects on the body of the wearer. For this purpose, a cavity in the heel section of the high heeled footwear is provided and/or in the footwear inserts or socks. The cavity is contoured so as to take the shape of the arch of the foot, meaning that the area in the heel section will be indented deeper compared to the inclined section of the high heeled footwear where the forefoot makes the contact. The depth and contour of the cavity can be customized for each individual, if needed. As the pointed portion of the heel strikes the ground the heel of the wearer will be still moving downwards in the cavity so no reaction force or the impact shock wave will be generated. When the wearer's heel will strike the bottom of the cavity, the forefoot region will also strike the inclined portion of the high heel shoes. The depth of the cavity is so designed that the wearer's forefoot and heel will make contact with their respective supporting portions of the insole in the footwear, footwear insert or sock almost about the same time. It is not necessary to make the two contacts occur at exactly the same time but they must be close enough. This will not only lead to one shock wave impact but its magnitude will also diminish significantly as it will bring into effect all the beneficial effects of forefoot walking as already discussed earlier in this application.
In addition to the shock wave management, there are added benefits of specific embodiments of the claimed invention. For example, the cavity in the footwear, footwear inserts and/or socks can also provide stability to the foot with respect to pronation and suplination for individuals engaged in sports such as tennis, squash, basketball and the like where frequent and sudden movements are made by an athlete. Pronation refers to an inward roll of the foot during normal motion and occurs as the outer edge of the heal strikes the ground and the foot rolls inward and flattens out. When excessive pronation occurs the foot arch flattens out and stretches the muscles, tendons and ligaments underneath the foot to cause injury. Suplination is the opposite of pronation and refers to the outward roll of the foot during normal motion and occurs during the toe push off portion of the gait. Excessive suplination (outward rolling) places a large strain on the muscles and tendons that stabilize the ankle, and can lead to the ankle rolling completely over, resulting in an ankle sprain or total ligament rupture.
To fully appreciate the benefits of the claimed invention over prior art and to motivate the general population to embrace the claimed technology, a detailed discussion on its effect on increasing the life of bone cartilage and consequently delaying the onset of osteoarthritis in the joints is provided below. Specifically, the question that is answered below is how significant medically is the effect of reducing the G-forces by 10% to 30% as realized by the claimed invention over the presently available footwear, footwear insert and sock technology.
The soft tissue structures comprising the joints undergo tribological wear and tear upon repeated interactions with the acceleration pulses. With time, depending upon an individual's level of physical activity, these joints become arthritic, a condition where the soft tissue padding (also called the cartilages on the articulating bones within the joint is mostly worn out such that during, weight-bearing gait phase, a direct contact between the ends of the articulating bones ensues. The loads produced by repeated impacts have also been linked to degenerative joint diseases and athletic overuse injuries including stress fractures (Milgrom et al., “A Prospective Study of the Effects of a Shock-absorbing Orthodic Device on the Incidence of Stress Fractures in Military Recruits”, Foot and Ankle, 1985, Vol. 6, pages 101-104), shin splints (Detmer, “Chronic Shin Splints Classification and Management of Medical Tibial Stress Syndrome”, Sports Medicine, 1986, Vol. 3, pages 436-446), cartilage breakdown, and low back pain (Voloshin & Wosk, “An in vivo study of low back pain and shock absorption in human locomotor system”, Journal of Biomechanics, 1982, vol. 5, pages 267-272). Interestingly, some studies have also suggested that repeated impacts increase the rate of red blood cell breakdown and contribute to the depressed iron status of many distance runners (Falsetti, Burke, Feld, Frederick, & Ratering, “Hermatological variations after endurance running with hard and soft-holded running shoes,” Physician and Sports Medicine, 1983, vol. 11(8), pages 118-127; Miller, Pate, & Burgess, “Foot impact force and intravascular hemolysis during distance running,” International J. Sports Medicine, 1988, vol. 9, pages 56-60). Even though the exact mechanisms of these injuries are still under investigation, there is no question that any effort to minimize the amplitude A of the shock wave can not only avoid short-term overload injuries but also significantly prolong the onset of degenerative diseases such as arthritis. How the amplitude A affects the latter has been researched by Weightman (“Tensile Fatigue of Human Cartilage”, J. Biomechanics, 1976, vol. 9(4), pages 193-200) who performed cyclic fatigue experiments in-vitro (tested outside the body) on cartilage specimens extracted from human cadavers of different ages. The extracted cartilages were loaded into a tension machine by straining the specimen from a zero stress (or Force) to a peak stress S (proportional to amplitude A, discussed here) and then the specimen was unloaded slowly to zero stress. This constituted one loading cycle. The machine was programmed to load the specimen with a large number of continuous cycles, each with an amplitude S. The number of loading cycles N that caused failure (fracture, damage, etc) of the cartilage was recorded. Their data is represented by the following empirical equation:
S=23−0.41a−1.83 log10N, (1)
where S is the failure stress measured in units of MN/m2, a is the age of individual in years, and N is the number of cycles to failure, each with a maximum amplitude S. In the context of discussion here, the amplitude A of the shock wave is directly proportional to the stress S and each heel strike with the ground constitutes one cycle of loading. An average person makes approximately 106 heel strikes per year on each foot. This is based on about 3 miles of impact running each day that could arise from simple running, climbing stairs, or spot running such as while performing aerobic exercises in a gym. The value of S at the joints during normal walking has been estimated between 1.5 and 3 MN/m2, which will correspond to A values of about 0.4 to 0.6 G. Magnitudes of both S and A increase during running, with the specific value depending upon the speed of the run. Since S and A are proportional, the factor by which S will increase will be roughly the same amount as the increase in the G-force (or A) measured in our experiments during running. This factor is about 3 to 5 times higher as seen in Table 2 of
So the natural question to ask is how much increase in the cartilage life (which directly controls osteoarthritis) one can expect if the impact force level is reduced by 20% to 30% as accomplished by the claimed invention? If this is significant, it could make the value of the claimed invention quite significant. In the following, calculations are made for different running speeds. For each running speed, the beneficial effect for runners of different age group is also determined. First consider a running speed of 6.3 mph. This corresponds to a value of S equal to about 7 MN/m.2 Based on equation (1), at this level of S, the cartilage life is about 38 years, 17.4 yrs, 3 years, and 0.9 year for population with 30 years, 40 years, 50 years and 60 years of age, respectively, assuming an individual makes 106 foot-impacts each year, which as discussed above will correspond to an individual walking (stair climbing) or running (including spot running during aerobic exercising) about 2.6 miles/day. Now let us calculate the increased life of the cartilage for various age groups, if S or A is decreased by 20%, as possible with the claimed invention. For a 30-year-old person who runs at the 106 foot-impacts per year level, a 20% reduction in A (and hence in S) will result in an astonishing 5 times (500%) increase in the number of cycles to failure for a 30 yr old population. This will roughly correspond to 60 years of increased cartilage life. Similar calculations yield, on an average, an enhancement of 17.4 years for 40 yr old, and 4.9 years for 50 yr old population. Thus, any technology that can reduce the stress S or impact amplitude A by 20% could be really significant for population with age exceeding 40 years of age. A 30% decrease in S will further enhance the life of the cartilage. For 50 years olds, this could add 13.4 years, while for 60 years olds this will increase the cartilage life by 3.8 years. All the above estimations are for level of stress in the joints that will probably be caused in a population that is involved with moderate exercising. The same set of calculations can also be done for lower level of physical activity, say one that places the stress in the joint to about 6 MN/m.2 A 10% decrease will enhance the cartilage life by 14.3 years; 4 years, and 1 year for the 40 years, 50 years, and 60 years old population. A 30% decrease will enhance it by 110 years, 31 years, and 8.8 years, respectively. It appears that if one is able to reduce S or G-force by 30% it can almost avoid osteoarthritis in a healthy population with age 40 years and higher. It certainly will provide significant relief to population that already suffers from arthritis. Any technology that can reduce the peak shock wave amplitudes should benefit the current elderly population and future population of baby boomers.
So far in this application novel designs have been discussed to reduce the G-forces that are subjected on a runner's body. There are situations in many sports such as basketball and racquet sports (tennis, squash, etc.) where the athlete is required to make quick and abrupt changes to his body, which inadvertently places very large pressures on discrete portions of the shoe's outer sole 12 and inner sole 15 about which the body is being pivoted. Under such increased pressure, the said sole areas compress more that other sole areas, the result of which is not only to provide a decreased support from the shoe but also to increase the ground contact time for the body, which in turn can slow down the athlete's movements. This can be important for professional players. Excessive displacement of the sole also makes the athlete prone to the injuries especially when such pivoting actions are quick with the body being aggressively jostled about the pivot point.
Because of the above reasons, it is desirable to have a sole material (both for outer sole 12 and inner sole 15 for shoes and removable soles 65 and 75) that would respond to the high pressure from the body by actively increasing its own stiffness. This way the sole will provide increased resistance to areas of the athlete foot about which the athlete is pivoting. This will also result in a smaller sole displacement and consequently lowering the ground contact time for the body during the pivoting action. Sophisticated electronic sensors and actuator-based shoe soles have been designed that essentially work like the car suspension systems. These are very expensive and therefore not accessible to general population. Additionally the effectiveness of these active systems is limited by how densely these sensors and actuators can be placed throughout the shoe's sole.
An alternate idea, claimed here, is to accomplish the above goals using a passive system without using the sophisticated sensors and actuators. In one embodiment of the claimed invention the sole material comprises a two-phase substance designed to change its stiffness when subjected to higher pressures by undergoing transformation in its internal material structure. In other words in this embodiment as the pressure is increased that area of the sole material will undergo transformation in its material structure to increase its stiffness while the rest of the sole will naturally deform. In other specific embodiments of the claimed invention the sole material 12 or 15 or 65 or 75 comprises a rubber matrix and/or filler having a phase transformation property such that the substance 40 can be reversibly transformed to a crystal structure under increased pressure to thereby have a higher stiffness than compared with its natural crystal state. Examples of fillers, which are not meant to be exhaustive, include active materials such as ninitol. In another embodiment of the claimed invention, the sole material comprises a single-phase material that is capable of undergoing a phase transformation allowing for enhanced stiffness with the displacement of this substance remaining essentially constant under increasing pressure. In one embodiment of the claimed invention, the sole material has a negative Poisson's ratio such that when the sole is compressed by the pressure from the foot the sole material contracts in its plane perpendicular to the direction of the applied foot pressure. The above embodiment can be utilized for example in walking shoes for heavier persons, for whom the sole displacements are excessive, resulting in uncomfortable walking experience and increased wear rates of the sole.
The basic underlying concept leading to the above embodiments can also be extended to other product lines. For example, it could be utilized in mats that can be used by individuals engaged in aerobic exercises that require jogging or stepping on the same spot. For these applications, mats can be provided with cavities on their outer surface.
Additional modifications and improvements of the present invention may also be apparent to those of ordinary skill in the art. Thus, the particular combination of parts described and illustrated herein is intended to represent only certain embodiments of the present invention, and is not intended to serve as limitations of alternative devices within the spirit and scope of the invention.
Claims
1. Footwear for reducing contact forces, comprising:
- an outsole unit having an outsole upper side; and
- an insole unit having an insole lower side secured to the outsole upper side and an insole upper side comprising a cavity wherein the cavity is adapted to receive a portion of an individual's heel.
2. The footwear of claim 1 wherein the insole unit and outsole unit are configured as a unitary structure.
3. The footwear of claim 1, wherein the cavity is configured to contain a liquid.
4. The footwear of claim 3, wherein the liquid is configured to support a portion of an individual's heel.
5. The footwear of claim 1, wherein the cavity is configured to contain a solid.
6. The footwear of claim 5, wherein the solid is configured to support a portion of an individual's heel.
7. The footwear of claim 1, wherein the cavity contains a first layer and a second layer wherein the first layer is disposed above the second layer and the stiffness of the first layer and the second layer differ.
8. The footwear of claim 1, wherein the cavity contains means for supporting a portion of an individual's heel.
9. A footwear insert for reducing contact forces, comprising:
- an insole unit adapted to be inserted into footwear wherein the insole comprises a cavity adapted to receive an individual's heel.
10. The footwear insert of claim 9, wherein the cavity is configured to contain a liquid.
11. The footwear insert of claim 9, wherein the liquid is configured to support a portion of an individual's heel.
12. The footwear insert of claim 9, wherein the cavity is configured to contain a solid.
13. The footwear insert of claim 12, wherein the solid is configured to support a portion of an individual's heel.
14. The footwear insert of claim 9, wherein the cavity contains a first layer and a second layer wherein the first layer is disposed above the second layer and the stiffness of the first layer and the second layer differ.
15. The footwear insert of claim 9, wherein the cavity contains means for supporting a portion of an individual's heel.
16. A sock for reducing contact forces, comprising an insole unit wherein the insole unit comprises a cavity adapted to receive an individual's heel.
17. The sock of claim 16, wherein the cavity is configured to contain a liquid.
18. The sock of claim 16, wherein the cavity is configured to contain a solid.
19. The sock of claim 16, wherein the cavity contains a first layer and a second layer wherein the first layer is disposed above the second layer and the stiffness of the first layer and the second layer differ.
20. The sock of claim 19, wherein the32cavity contains means for supporting a portion of an individual's heel.
Type: Application
Filed: Oct 16, 2008
Publication Date: Apr 22, 2010
Inventors: Honey Gupta (Sherman Oaks, CA), Edouard Coyon (Le Tignet)
Application Number: 12/288,080
International Classification: A43B 13/20 (20060101); A43B 13/12 (20060101); A43B 21/28 (20060101); A43B 13/38 (20060101); A43B 17/00 (20060101);
