This exercise is called the Hover Hold, which consists of resting your upper body on your elbows and forearms and holding your body as straight as possible. Holding this position will work your lower back and core. The Beginner level will show that you can rest the lower part of your body on your knees, but eventually you can move to the Advanced version where you will be using your feet instead. For the Freak of Nature version, a weighted vest will do excellent.