Running with worn out or old running shoes means you're inviting a host of potential injuries, any one of which can adversely affect your performance. Each time your foot hits the ground while running, it generates a force up to three times your body weight per square inch. When your shoes are worn they are less able to efficiently absorb and dissipate that impact. That sets up a chain reaction of force reverberating through muscles, bones and tendons. The shock of each impact winds its way up through your foot to your ankle, your knee and your hips then back again, causing trauma and creating a variety of injuries.
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Running with knee pain — the blanket term for which is runner's knee — is the most common form of running injury. The most common cause of runner's knee is running in shoes that don't protect you enough, or shoes that are worn out. This happens because running in worn shoes throws off your biomechanics. If you over- or underpronate (the amount a foot turns to absorb impact while running) and your shoes corrected for that, once they became worn they will stop fixing this issue and cause an improper torque that leads to runner's knee.
Swelling of the two tendons along your shin linking your knee to your foot is a painful condition called shin splints. One of the most common causes of this injury is running in old shoes that lack adequate shock absorption, or in shoes that are unevenly worn and lack stability. Icing the shin, taking aspirin or ibuprofen and stretching will help relieve the pain. Replacing your worn-out shoes will help eliminate the cause of the injury, keep it from growing into a chronic condition and prevent a relapse.
Irritating the length of fascia known as the iliotibial band, which goes from the outside of the hip to the knee, hurts. When aggravated, the IT band swells. Once swollen, it only gets more aggravated with increased use, such as when you run. The most common culprit that aggravates the IT band in the first place is running on uneven surfaces; this includes wearing old, unevenly worn shoes. Ice, stretching and rest will help alleviate the pain caused by a swollen IT band. Slipping your feet into new running shoes will help keep the pain from returning.
When to Replace Your Shoes
Replacing your running shoes can help you avoid injuries, if you know when to do it; generally, you should replace your shoes after running in them for a maximum of 500 miles. Turn your shoes over every now and then and look to see if the sole is lined, or if cracks are forming. That's a good indication your shoes need replacing. Also, as you should with all aspects of your running, listen to your body. If little aches and pains get bigger, or if new twinges show up, think about replacing your shoes. If your shoes are past their prime, they're not helping you stay in yours.