Once you have mastered the modified version, move on to the full rolling plank by keeping both knees up the entire time. As you roll to the right, the left arm sweeps up and the left leg stacks on top ...

YOU PROBABLY THINK you know how to do a plank. The ab training staple is relatively simple, after all—boiled down to the basics, all you need to do is get down on the ground and hold in place.