Filed to:athletic shoes Photo: PAstudio, Shutterstock You’ve probably heard that you should replace your running shoes when the cushioning wears down, which tends to be after 300 to 500 miles (500-800km) according to most manufacturers. But it turns out there’s another problem with old shoes, even if you haven’t been running in them. The cushioning in running shoes isn’t made to last, even when those shoes are sitting on the shelf. Fleet Feet, a running shoe store, notes that the rubber and foam that form the shoes’ cushioning break down with age, and the foam can even splinter apart. Other components of the shoe, like the stitching on the upper, may break down over time, as well.