If you've never really run or jogged before and then go and start doing loads of it on concrete you should be careful, grass is a lot easier to run on as it gives a bit when your foot lands, when I started running properly one of my friends who runs at competition level showed me various ways of minimizing damage to knees.
Im sure Google can help find all the technical gumf.
Tom
Im sure Google can help find all the technical gumf.
Tom