Begin by lying on your back with your arms extended above your chest. Raise your shoulders and legs off the floor, holding this position.
Lift your left leg up, then perform a crunch, reaching your fingers toward your left foot.
Lower the torso without letting your shoulders touch the ground and scissor your legs so the right leg is in the air and the left leg is hovering above the floor. Perform a crunch.
Continue alternating legs for 30 seconds, followed by a 15-second rest.