Over the years, I've heard varing numbers for the useful life of a running sneaker. Ranging from 300-400 miles, 400-600 miles, 350-550 miles, etc. What is that magic number? The number depends on a lot of different factors. How often do you run? Where do you run? Treadmill or outside? How much do you weigh? Geesh....enough with the questions. I personally feel the best way to tell when you need new sneakers is by just listening to your body. Are you beginning to feel joint pain, have shin splints or achy knees? These are all signs that your sneaker is beginning to breakdown and is not as supportive as it once was. When that happens, it's time to get out there and do what a girl does best...Buy some new shoes. Not replacing your sneakers is the leading cause of running injuries. I also believe in rotating my sneakers. When the end is coming near on a pair of sneakers, I slowly start rotating my new pair into my running schedule. You should never wear a new pair of sneakers for a long run until they are broken in. At least that is the rule I follow or its Blister City for this Little Miss Runner.