I'm running in an old pair of Mizuno trail shoes (Wave Elixir 4 X10 if you need to know) from yonks ago (in my 2008 fitter days). I bought them from a professional store after some gait analysis. Problem is, they don't seem to be supporting my ankles/knees as much as before (or am I older???). According to Nike+ they've done about 500kms, a mixture of road and trails, but all road on C25K.
Would I expect more than that? Do I need new shoes?