Feet swell during the course of the day due to increased blood flow to the feet from walking and running. When running, this process of swelling increases. It is important to buy a shoe that is slightly too large and too wide so that the feet have room to swell without causing blisters or cramping. In order to find the correct shoe size, go shopping later in the day after your feet have swollen, then choose a roomy shoe. By doing this, injuries decrease and the runner is able to enhance performance by evading discomfort.

Feet tend towards one of three arch types: normal, low, or high. Most shoes are designed for normal arches. However, low arches tend to cause feel to roll inward, causing strain from overuse that can either injure or slow down a runner. High arches tend to roll feet outward, causing ankle injuries when not properly supported. To determine arch type, dip your foot in paint or water and step on a piece of paper. A normal arch will have about a 1 inch thick print between toes and heel, while a low arch will be wider and a high arch will be thinner. For high and low arches, choose a shoe that provides more ankle support and has soles designed to fit your feet.

Gait is how you land after taking a step. Overpronated gaits force landings on the outside of the heel first, while underpronated gaits cause landing on the inside of the heel. Overpronators are more likely to lose balance and fall, causing serious ankle and leg injuries; a shoe with stabilizing soles and ankle support will help decrease the likelihood of injuries. An underpronator, as well as someone with a normal gait, needs cushioning to decrease shock. A thicker sole can also help to reduce injuries, keeping a runner running longer.