Heel--shoe interactions and the durability of EVA foam running-shoe midsoles

Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UK.
Journal of Biomechanics (Impact Factor: 2.75). 10/2004; 37(9):1379-86. DOI: 10.1016/j.jbiomech.2003.12.022
Source: PubMed


A finite element analysis (FEA) was made of the stress distribution in the heelpad and a running shoe midsole, using heelpad properties deduced from published force-deflection data, and measured foam properties. The heelpad has a lower initial shear modulus than the foam (100 vs. 1050 kPa), but a higher bulk modulus. The heelpad is more non-linear, with a higher Ogden strain energy function exponent than the foam (30 vs. 4). Measurements of plantar pressure distribution in running shoes confirmed the FEA. The peak plantar pressure increased on average by 100% after 500 km run. Scanning electron microscopy shows that structural damage (wrinkling of faces and some holes) occurred in the foam after 750 km run. Fatigue of the foam reduces heelstrike cushioning, and is a possible cause of running injuries.

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    • "Ethylene-Vinyl Acetate foam (EVA) finds application in midsoles used for running shoes. Verdejo et al [2] performed experimental tests and numerical simulations to measure the pressure distribution at the heelpad-midsole interface. The midsole was composed of EVA foam which reduced the peak impact force of the heelpad through shock absorption. "
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