If you're up for another (ab) challenge, you'll like this workout even more. We've upped the time factor by a minute and zeroed in on a particular part of your core: your lower abs. "Make sure to keep your back from over-arching in these positions, so you get max activation in your lower abs" . Yep, that means no cheating. these exercises are tagged onto a session, however, to really max out your core muscles you want to be taking things slow and focusing on form.