Lisa Bell, Know Your Numbers

Running shoes need to be replaced -- not just when they're falling apart, but once they have about 400 miles on them.

Experts say that, depending on their shock-absorbing qualities and what kinds of activities you do, most shoes will typically wear out within 300 to 500 miles.

If you are a runner, that could be in as little as two months, but for the rest of us, doctors say replacing your sneakers at least once a year is the best way to keep your soles, your arches, your knees and even your back happy.