chem_note4 - Normal Arch Sport Shoe Design Flat Arch...

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97 • For a person with a normal arch , when walking, the outside part of the heel makes initial contact with the ground. The foot "rolls" inward about five percent , comes in complete contact with the ground, and can support the body weight without any problem. • The rolling in of the foot optimally distributes the forces of impact . This movement is called "pronation”. At the end of the walk cycle, the person push off evenly from the front of the foot. ( Pronation is the inward roll of the foot and in particular the heel and arch which occurs naturally at the heel strike as a cushioning mechanism.) Sport Shoe Design Normal Arch 98 • Person with flat feet usually over -pronate . The foot rolls inward more than the 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 toe and second toe , which then must do all the work. Sport Shoe Design Flat Arch inside Flattening of the two-arch construction inside the foot 99 • Person with a high arch usually under under -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 area of 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 toes on the outside of the foot. High Arch Sport Shoe Design outside Raising of the two-arch construction inside the foot 100 Sport Shoe Design inside outside over-pronate under-pronate (supinate) normal flat high 101 A neutral (or normal) footprint A flat-arch footprint A high-arch footprint Sport Shoe Design A comparison of footprints (right foot) over-pronate (too much rolling in) under-pronate (less rolling in) 102 Foot type Sport Shoe Design Under-pronation Over-pronation Normal pronation
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