A shoe heel insert, especially suitable for athletic shoe applications, providing for superior shock absorption and energy return characteristics to the wearer, as well as a high degree of stability. The unit which is referred to as the SPRING-AIR SYSTEM, will consist of a substantially heel shaped...http://www.google.co.uk/patents/US5743028?utm_source=gb-gplus-sharePatent US5743028 - Spring-air shock absorbtion and energy return device for shoes
