Video: The plank is a great exercise for your core, but holding it like a statue is only one of many ways to work those muscles. This video shows a plank-based exercise you probably haven't seen before -- and it's great for your obliques.
Your obliques are the muscles on the sides of your torso, and you use them when you twist your body. Imagine sitting in a chair and turning to talk to the person behind you -- your obliques power that move. If you're in a plank position, twisting your hips to the side gives those muscles some extra work, and gives you a break from the monotony of holding a plank position.
Give this move a try, and you'll find it's tough but fun. Check out the video for a demo and explanation.
Hip Dip Plank Exercise for Obliques, Core Strength [Refinery29]