We all understand that running shoes have a limited lifespan. Most people, however, continue to wear them well after their useful life has ended. In my office, I most commonly will have people tell me that their shoes are several years old BUT (insert excuse here...). Some of my favorites, it fits my feet perfectly (meaning it's broken down), the heel is worn out just how I like it (meaning it has a hole inside the shoe), new shoes just bother me (meaning that I've worn these for so long, the support is too different at this point), and my favorite: They still look new.

Yes, they still look new. When all you do is run on the treadmill, use the elliptical, and some stationary bike, and your shoes never see the light of day, of course they look new. What's problematic is the part you don't see.

The support and function of a running shoe has little or nothing to do with the overall appearance of the upper part of the shoe or even the sole. It's the midsole, the portion of the sole that is largely invisible from the outside, that has the most function and limits the useful lifetime of a shoe. With every stride, the midsole compresses and, with time, loses the majority of its support. I estimate the useful lifetime of a running shoe for runners to be approximately 350 miles. This amount may be slightly shorter for heavier runners and slightly longer for lighter ones. For those who really don't run regularly, or partcipate in other sports and activities that can't me measured by mileage, your shoes should be replaced every 4-6 months, depending on the frequency and level of the activity.

So start keeping track of the life of your shoes. Dedicate a pair of shoes (or more) exclusively for exercise to get the most out of its useful life. You can record your mileage in your running journal, or even in pen on the side of the shoe. To help you remember how old a shoe is, write the date on the tongue or the outsole.

Whenever you are involved in serious exercise, minor injuries are inevitable. You must do everything in your power to minimize them. Just wearing the proper shoes is one simple way to help you along.