The basic plank is a great exercise for building your core, which can help prevent back injuries and is great for overall stability and posture. It’s not the most exciting move in the world, but there are many variations that can add to the challenge and get other muscles in on the act. One of these is the X plank. Not familiar with it? Neither was I until my editor set me the challenge of doing it every day for a week. Once again, I just couldn’t thank her enough.