A shock absorbent shoe includes an outsole having a toe, a heel, and a cavity in the heel. An elastomeric shock absorbing plug is disposed within the heel cavity and includes a planar lower surface and an upper surface. The upper surface of the plug includes a raised central portion, an outer boundary,...http://www.google.es/patents/US6050001?utm_source=gb-gplus-sharePatente US6050001 - Shoe having layered shock absorbing zones
