The elastically deformable base of an article of footwear has a substantially plane lower surface which is formed with a deep recess below the heel, with an elongated shallow recess below the outer portion of the instep, with a two-part recess below the ball and with a two-part recess below the toes...http://www.google.es/patents/US4697361?utm_source=gb-gplus-sharePatente US4697361 - Base for an article of footwear
