1. Field of the Invention
This invention pertains to footwear in general, and in particular, to a heel spring and foot stabilizing device for an athletic shoe.
2. Description of the Related Art
For most, the act of walking or running involves the use of the entire foot, and starts with heel strike, followed by a rolling onto the mid-foot, and then finally by a propelling off of the forefoot and toes. Before heel strike, the foot is in a supinated position, i.e., oriented at an upward angle relative to the ground and twisted outwardly. At heel strike, the involved ankle, knee and hip all flex to cushion and absorb the shock of the impact, and the foot rolls and turns inward in a process called pronation.
During this sequence, it is desirable to absorb as much of the foot strike shock energy as possible, consistent with landing stability, to avoid chronic or traumatic injury to the runner. Where possible, and again, consistent with good running stability, it is also desirable to store the shock energy absorbed and return it to the foot during the propelling-off portion of the stride, for energy-efficiency reasons. It is also desirable to limit any tendency of the foot to over-supinate or to over-pronate during contact of the foot with the ground for both medical and running stability reasons.
It is known in the shoe art to incorporate spring devices in the soles of shoes, and particularly the heels of the shoes, to store shock energy imparted by foot strike during running and to return at least a portion of that energy to the wearer's foot during foot lift. It is likewise known to provide transverse and longitudinal stiffening elements within the sole of a shoe to overcome the effect of over-supination or over-pronation of the wearer's foot during running.
For example, in U.S. Pat. Nos. 4,486,964 and 4,506,460, M. F. Rudy describes various types of plastic and heat-treated steel "spring moderators" whose primary purpose is said to be to distribute foot strike forces more evenly and quickly to underlying, gas-filled sole members. A horseshoe-shaped heel component of these moderators is said to act like a Bellville spring in cooperation with the foot to store and return energy during running, and in one version, is also said to provide vertical stabilization of the ankle.
In U.S. Pat. Nos. 2,357,281 and 2,394,281, V. P. Williams discloses a shock resisting built-up heel assembly for dress shoes which incorporates a steel spring.
In U.S. Pat. No. 4,709,489, K. F. Welter describes a spring device for a shoe heel which comprises a steel plate supported at its lateral ends by a U-shaped, non-compressible support member. In addition to providing a heel-spring effect, the support member is also said to provide lateral stabilization of the heel.
In U.S. Pat. No. 4,881,329, K. J. Crowley discloses yet another form of energy storing heel spring which is said to be moldable from high tensile materials such as graphite and/or glass fibers and resin.
Finally, the Etonic company of Brockton, Mass., advertises a "Stability System" which includes various configurations of a "DRP Plus Plate" made of a composite of graphite, acrylic and fiberglass, and which is disposed in various locations within the soles of its shoes to compensate for over-pronation and/or over-supination problems of individual wearers.
This application discloses a novel device for encapsulation within the midsole of an athletic shoe which combines the advantages of a heel spring for absorbing, storing and returning to the wearer's foot the shock energy experienced during running, and a stabilizer plate which, during the same activity, aids in the prevention of over-supination and over-pronation of the foot. Because of the methods and material of its manufacture, the device is simple and inexpensive to manufacture and very light in weight.