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97• For a person with a normal arch, when walking, the outside partof the heel makes initial contact with the ground. The foot "rolls"inward about five percent, comes in complete contact with theground, and can support the body weight without any problem. • The rolling inof the foot optimally distributes the forces of impact.This movement is called "pronation”.At the end of the walk cycle, the person push off evenlyfrom the front of the foot. (Pronationis the inward rollof the foot and in particular the heel and arch which occurs naturally at the heel strike as a cushioningmechanism.)Sport Shoe DesignNormal Arch98• Person with flat feetusually over-pronate. The foot rolls inward more thanthe ideal five percent, which is called "over-pronation." • This means the foot and ankle have problems stabilizing the body, and shock isn't absorbed as efficiently. • At the end of the walk cycle, the front of the foot pushes off the ground using mainly the big toeand second toe, which then must do all the work. Sport Shoe DesignFlat ArchinsideFlattening of the two-arch construction inside the foot99• Person with a high archusuallyunderunder-pronate (supinate)(i.e.,there is less rolling in than for those with normal or flat feet). • Consequently, forces of impact are concentrated on a smaller areaof the foot (the outside part), and are not distributed as efficiently. • In the push-off phase, most of the work is done by the smaller toeson the outside of the foot. High ArchSport Shoe DesignoutsideRaising of the two-arch construction inside the foot100Sport Shoe Designinsideoutsideover-pronateunder-pronate(supinate)normalflathigh101A neutral (or normal) footprint A flat-arch footprintA high-arch footprint Sport Shoe DesignA comparison of footprints(right foot)•over-pronate(too much rolling in)•under-pronate(less rolling in)102Foot typeSport Shoe DesignUnder-pronationOver-pronationNormal pronation
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