How to do it: Sit up straight with your knees bent, feet hip-width apart on the floor, knees over ankles. Hinge back at waist, placing your hands on the ground below your shoulders, fingers facing out (as shown). Lift your hips (like in a bridge) to raise your body, and then bend your elbows to point directly back as the body dips toward the ground. Push into your heels, and straighten both your arms to come back up; punch your right arm across chest, rotating your torso to the left. Return hand to ground, then immediately dip and twist to the opposite side. Alternate continuously for one minute.
Make it easier: Instead of twisting and punching, alternate lifting your hands off the ground.