I did the cardio only premix of
CardioFit a few days ago because I'd done weights the day before and needed to give my muscles a break. The boxing and hi low chapters alternate, so there is just a little down time, but not long enough to bring down your heart rate. I had a nice, little sweat going. The next day, while doing a JS fusion workout, I realized my obliques were sore from Kelly's workout.
I'm still doing Power Splits twice a week and it hasn't gotten any easier.