Answer by  
                                                                                          lei (490)
                                                            
                          
                          
                                                          I've read in a magazine that it's lifespan is determined by the amount of steps it has had. SO for most running shoes, I think its about 5000 steps after which, the shoe cannot give as much suppor as it had when it were newer. It wears out, then it's time to replace to keep your foot in good health.