Most people think to change their sneakers when they look old and beat up and the tread is starting to wear down. By the time these signs of wear and tear are apparent, you are well passed the time you should have retired them.
The issue is the midsole, which lies between the rubber bottom of your sneaker and where your foot sits. The midsole provides the majority of the cushioning for your shoe, and is therefore vital to the protection of your joints from the impact of your exercise.
The midsole wears out way before the other parts of the shoe do. So I tell all of my clients that no matter how new the rest of the sneaker looks, replace them after 6 months.
You don’t have to throw them out. You can certainly wear them around the house or to go shopping or whatever, just not for your cardio.
If you have knee, hip or back issues, changing your sneakers consistently can be a simple way to reduce your pain and discomfort.