A great way to guarantee injury is to continue running on a worn out pair of running shoes. Old shoes lack necessary shock absorption and do not provide sufficient stability for your foot when you land. This can not only lead to foot injuries, such as plantar fasciitis, but also injuries of the lower leg (achilles, shin, etc.) and hip problems.
Pronators are especially at risk because an unstable running show will lead to injuries quickly, especially IT-Band problems. Therefore, it is very important that runners only train in shoes that have some life left in them.
The general rule of thumb is that running shoes are good for about 500 miles. However, this can vary depending on the type of shoe and your running gait. A good tip is to keep track of the exact date that you begin using a running shoe. That way, if you are running in the same shoes six months after they were purchased, and you averaged around 30 miles a week for those six months, it’s a good bet that you need new shoes.
Another tip is to watch for “compression lines” in the sole of the shoes. Once a shoe has a lot of these crease lines, it’s a good sign that it will not absorb impact anymore.
Perhaps the most obvious test for determining whether your running shoes are too old is to listen to your body. If you start to feel nagging aches and pains on runs, and you have owned your shoes for a few months, it is probably a good idea to spring for a new pair. By the way, make sure that you try to jog around the store a little before purchasing shoes to test them out. They should feel great out of the box and you should not have to break them in.