Old, worn-out running shoes are one of the most common reasons for running injuries. 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.

After about 300 to 400 miles of use, running shoes should be replaced, depending on 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.

Try to mark your calendar when you buy a new pair of shoes so you know when to replace them. If you use a training log, record new shoe purchases on that. Or try writing the purchase date on the inside of each shoe's tongue.

If you want to make your pair of running shoes last longer, buy a second pair of running shoes about halfway through the life of your original pair. Your shoes will last longer when you allow them to decompress and dry out between workouts. Also, having a fresh pair of shoes as a reference will help you notice when your old ones are ready to be replaced.