Begin by lying on your side. Bring your right elbow directly under your right shoulder. Engage your core, press your right elbow into the floor, and rise into a side elbow plank.
Stack your heels or modify by staggering your feet so your left foot is just in front of your right.
Reach your left arm up toward the ceiling, which will help you lift your waist.
Hold for 40 seconds, and repeat the plank on the opposite side.