Inserts and heel specifications of shoes
As runners pound their feet onto the ground there is a movement that the foot goes through which is called pronation which is when the foot rolls inward, comes into contact with the ground, and distributes the forces of impact. It’s important as it absorbs some of the shock. However there are two problems that can occur such as overpronation and underpronation. The runner then pushes off evenly with the front of their foot.
Overpronation is when the foot rolls inward but too much. The shock isn’t absorbed as efficiently and most of the work of pushing off is done with the runner’s big toe and second toe.
Underpronation or supination is when the foot does not roll inward enough. The impact forces are distributed mostly to the outside part of the foot and most of the work of pushing off is done by the runner’s smaller toes.
It’s because overpronation and underpronation that torque is put on the ankle and knee joint which may cause injury to the runner.
People that overpronate should wear shoes with straight or semicurved lasts. A medial arch support on a somewhat harder midsole may reduce pronation. A rounder heel usually reduces pronation as well.
People that underpronate should wear shoes with curved lasts to allow pronation. Lightweight trainers are often best, as they allow more foot motion. Also, check for flexibility on the medial (inner) side of the shoe.