Just to help a bit, I've added a HIIT session once a week usually, and found good results with jump roping. Works up a great sweat and all, but really only fatigues the calves. I do it for a little longer then I would sprints (i figure sprints are MUCH more demanding). Also seems to be sparking a bit of calf growth, which is always good. lolLike other have said, though, keep cardio to a minimum. I only did it to spark a little more fat loss.