The Nature Boy said:it's simple really. If you run before your actual workout there is no way your intensity and strength levels will be the same. In order to build muscle, you need to tear it down with intense excercise. 30 minutes of running prior to working out will crush your glycogen levels, leaving you with a less intense workout. Plus true cardio fat burning benefits occur when glycogen levels are low or non-existant. Doing intense workouts deplete your glycogen levels, so you'd want to do workout first before doing cardio.
hope this makes sense. I'm sure the morning crew will explain it better than I have.
thx for the explanation on that nature boy, though what about in the morning it is said do cardio on empty stomach b/c you have no gluycogen so you will use fat as energy. then contradicting it says run before you lift, b/c otherwise you will use your glycogen up when running and you will use muscle as energy. i dont get it?