Running in old or worn-out shoes is a common cause of running injuries. Your running shoes lose shock absorption, cushioning and stability over time. Continuing to run in worn-out running shoes increases the stress and impact on your legs and joints, which can lead to
overuse injuries. The easiest thing you can do to prevent those types of injuries is replace your running shoes when they're worn-out and have lost their cushioning.
So how do you know when shoes need to be retired? Don't use the treads of your running shoes to determine whether you should replace your shoes. The midsole, which provides the cushioning and stability, usually breaks down before the bottom shows major signs of wear. If you've been feeling muscle fatigue,
shin splints, or some pain in your joints -- especially your knees -- you may be wearing running shoes that no longer have adequate cushioning.
A good rule of thumb is to replace your running shoes every 300 to 400 miles, depending on your running style, body weight, and the surface on which you run. Smaller runners can get new running shoes at the upper end of the recommendation, while heavier runners should consider replacement shoes closer to the 300 mile mark. If you run on rough roads, you'll need to replace your running shoes sooner than if you primarily run on a treadmill. Keep in mind that you're also wearing down your shoes when you're wearing them for things other than running, even just walking around in them.