We all have heard the recommendation to change shoes around 300-500 miles of use, but why? Where does this recommendation come from? When running, forces more than 2.5 times your body weight are applied up the leg and through the musculoskeletal system. Footwear has been designed to assist in absorbing these highmagnitude forces in order to improve performance and reduce injury risk. The cushioning in shoes can absorb shock and reduce how fast the force of landing acts on the body.