i'm about to start stage 2 in the new rules of lifting for women book, and it involves "high intensity interval training", which has you doing some sort of cardio (running or stationary bike or whatever) for 15 minutes, with 1 minute intervals and 2 minute rest periods. my question is, should i be doing this at the end or the beginning of my workout? or even in the middle somewhere? in the book it doesn't specify... they sort of tack it on to the end of workout B (which actually looks way harder than workout A). they don't say exactly when to do it though. also, i was thinking about doing it after both workouts A and B, because it doesn't specify whether or not you should do this either. any reason why i shouldn't do it both days?