Unlike the old days, sneakers of today are made with the dynamic function of the foot in mind. Modern running shoes are made with synthetic foam midsoles usually Polyurethane (PU) and Ethylene vinyl acetate (EVA) that improve shock absorption. The outsoles are made from synthetic rubber that resists abrasion and improves traction. The uppers are usually made of mesh material that maximizes ventilation. So what key points must we consider when selecting the correct pair of running shoes?
The midsole of the shoe is what provides shock absorption. Since most runners first contact with the outside of the heel, the midsoles are usually dual density with the outside made of a softer material than the inside. Aside from absorbing shock this also acts to reduce pronation, which is when your foot turns in. The thickness of the midsole is also important. Although it would seem logical that a thicker insole would absorb more shock, excessive midsole cushioning has actually been shown to increase injury by impairing balance and reducing the foots ability to sense it’s environment. About 10 millimeters of midsole cushioning seems to be ideal by minimizing weight while at the same time maximizing energy return.
Finally, when selecting running shoes, the foot type needs to be considered. A flatter foot type usually requires a running shoe with motion control. These shoes have dual density midsoles and made with a straight last to better adapt to the shape of a pronated foot. A person with a higher arch would usually benefit from a softer midsole and a curved last. Flexibility of the midsole can usually be tested by grasping the forefoot with one hand and the heel with the other. The softer midsole shoe will bend and twist easily while the stiffer midsole will resist bending and twisting. Although a stiffer midsole is ideal for the flat foot, an excessively stiff midsole can be quite uncomfortable and difficult to get used to.
The flatfoot poses a challenge to most health care providers, as this foot type is able to absorb the least amount of shock. When shock is not absorbed properly it tends to be transmitted up the lower extremity chain to the knee and lower back. Flatfooted barefoot runners pose the greatest risk, which will be the subject of a future post in the coming weeks.
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