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 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 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 Flat Arch inside Flattening of the two-arch construction inside the foot 99 • Person with a high arch usually 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 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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103 • During running, the foot needs to be cushioned from damaging impact forces, guided and stabilised in the complex movement as the body’s load is transferred from the heel to the ball of the foot, while still returning most of the runner’s input energy in the form of a rebounding energy when the sole is compressed (this is called energy return ’). • In a normal run, an athlete takes about 300-400 steps per km. At each step, the impact force on his/her heel is 2-3 times the body weight. When selecting shoe materials, they need to possess good resilience against these repeated loads in addition to the above criteria. Sport Shoe Design Requirements: How to select sport shoes? 104
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This note was uploaded on 12/01/2010 for the course CHEM yscn0027 taught by Professor Drtong during the Spring '10 term at HKU.

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

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