How do sports shoes help our feet push us forward?

A runner’s shoe presses against the ground. It might look as if the foot only pushes down, but it also pushes backward during part of a step. The ground pushes forward on the shoe, helping the runner move.

That grip comes from friction. Friction resists the shoe sliding against the ground. The sole can stay in place for a short moment while the body moves over it. A shoe does not have to scrape backward to receive a forward push.

The sole’s material and the ground both matter. Rubber can bend against small bumps and grip a surface. On grass, studs can press into the ground. A shoe made for one surface may work poorly on another.

Water, mud, or loose dust can change the contact and make a foot slip. When the shoe cannot grip enough, the push no longer works as intended. A running step is a little partnership: the foot pushes on the ground, and the ground helps move the person.