Running Shoe Basics
Running is an almost perfect activity. It’s great exercise: one of the best ways to lose weight and boost endorphins. It’s easy to get started and doesn’t cost a lot of money. However, it can be a high-impact activity. When a runner’s heel strikes the ground the body may absorb 3.5 to 5 times its own weight; the shock can travel up the leg, causing injury. Luckily, running shoe companies are well aware of the dangers and potential for injury. They are constantly inventing new materials and using the most up-to-date technologies to improve each shoe’s cushioning and support.
Running Shoe Midsole
Most of a running shoe’s cushioning is in the midsole. The midsole is between the outsole (the black rubber part that touches the ground) and the upper (the leather or mesh part of the shoe that covers your foot). Most midsoles are soft, usually white, foam-like material, designed to give your foot a cushioned ride. Most traditional midsoles use two different materials to create cushioning for your foot: ethylene vinyl acetate (EVA) and polyurethane.
Midsole Cushioning Materials
EVA is an excellent cushioning material. It is relatively lightweight, flexible and quick to rebound from a compressed state. EVA is foam filled with tiny air bubbles. Each time pressure is applied to the EVA it compresses, forcing some of the gas in the bubbles out. When the pressure is removed, the EVA rebounds to its normal state and pulls gas back in; however, each time it is compressed the EVA will rebound a little bit less. Over time, this results in permanent compression and less rebound which ultimately means less cushioning for your foot. Once the EVA has become permanently compressed, it is probably time to replace your running shoes.
Polyurethane foam is heavier and denser than EVA; therefore, it makes the entire running shoe heavier. It works basically the same way as EVA; however, polyurethane takes longer to become permanently compressed than EVA so the shoes generally last longer.
Most of today’s running shoe midsoles combine both polyurethane and EVA, making them lightweight and longer lasting. In addition, nearly all of today’s running shoes also incorporate other proprietary cushioning technologies such as gel, springs and air pads. Cushioning is big business and companies spend millions of dollars developing this technology.
While cushioning is an important part of running shoes, it is not the only factor to consider. Your foot structure plays an integral role in selecting an appropriate shoe.Foot types are divided into three general categories:
- normal (medium arch, medium pronation)
- flat (low or no arch, severe overpronation)
- high (high arch, no pronation, may supinate)
If you’re not sure what type of foot you have, you can perform the “Wet Test”—a simple home test. Step in a shallow tray of water and then step on a brown paper bag. You should be able to tell what type of foot you have based on the outline your foot leaves behind.
Pronation is an inward rolling motion of the foot that happens after the foot’s impact with the ground. Pronation is actually a natural motion that serves to cushion the foot’s impact with the ground. The only time pronation becomes negative is when the foot begins to overpronate, creating a danger of many injuries including overuse injuries. Supination is the exact opposite of pronation. Supination is an outward rolling motion of the foot after impact with the ground. Unlike pronation, supination does not help cushion the foot and is often associated with high, rigid arches putting supinating runners at risk for injuries. Luckily, actual supination is pretty uncommon so most runners don’t have to worry about it.