You can do calves, abs, and cardio this day if you have too much bodyfat. Or, you can do what I do and use it to focus on a lagging bodypart. I often choose to work back a second time, along with biceps, calves, and abs, and forego the cardio since my metabolism is high. If your legs are lagging, hit them again on this day. Whatever bodyparts you work a second time, I recommend doing completely different exercises (and possibly different training method) than for what you did the first workout of the week. Here's MY typical Friday workout.