Lie on the floor with your knees pulled into your chest and your hands behind your head. Lift your shoulder blades off the ground and pull your abs toward your spine, pressing your low back into the mat.
Straighten your left leg out while turning your upper body to the right, bringing your left elbow toward your right knee. Make sure your ribcage is moving and not just your elbows.
Repeat this action on the other side to complete one rep.