Components of a running shoe

Soft or firm midsole?

Shoes have several components. The component that controls and gives the foot support is called the midsole. This is the part of the shoe sandwiched between the part that touches the ground, called the outsole, and the part of the shoe in which the sock liner rests, called the insole.

The midsole serves as the external shock absorption system, which can protect your body from the potentially harmful effects of repeated loading from running.

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Different brands of running shoes have different kinds of midsoles. A midsole can be made from polyurethane foam, air units, gel units and ethyl vinyl acetate (EVA).

A midsole made primarily of EVA generally is light and compressible. Midsoles made of polyurethane are denser, heavier and more durable than those made of EVA.

Each material has unique properties and can react differently in various climates. For instance, polyurethane and air units were found to remain firmer in hot temperatures than EVA and gel units, and so they give more support to your foot when you’re running in hot weather.

The stiffer and firmer the midsole, the more control the shoe will give your foot. You can use your thumbnail to push on the midsole to determine the firmness along the inside of shoe.

The type of midsole that is right for you depends on the mechanics of your foot throughout the running cycle. Pronation of the foot occurs after the foot hits the ground. Pronation is our bodies’ ability to absorb ground reaction forces. It is a natural movement of the foot that occurs differently in each person. A runner who over-pronates usually has a low arch. A runner who under-pronates, or supinates, usually has a higher foot arch.

Generally, if you have high arches, you should run in cushion-type shoes, which have a softer midsole. High-arch runners are prone to bony type injuries like stress fractures due to higher loading rates from inadequate foot pronation. Cushioned shoes allow the foot to pronate, or turn, so your body can absorb the shock of your feet hitting the ground.

If you have low arches, you should run in stability or motion-control type shoes with firmer midsoles that control the amount of pronation. Low-arch runners generally are prone to overuse soft tissue injuries like tendinopathy due to excessive foot pronation.

No two feet are alike. Generalizations about arch height can be made, but they are not hard and fast rules. For example, a runner can have a low arch but need a cushion shoe.

Several variables contribute to pronation of our feet and may affect the type of shoe needed.  For instance, weakness of the hip muscles can cause more foot pronation.

If you’re a runner, it’s best to seek an evaluation from a physical therapist in a sport-specific rehabilitation program to determine the variables that contribute to your foot type and guide you in selection of a good shoe. A physical therapist will help you understand your body, and address the variables that can help keep you injury-free.

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