The jackknife can be done by lying flat on your back with your arms extended overhead and your feet raised slightly above the floor. The jackknife is completed by slowly bringing your straight arms toward your hips and lifting your upper torso off the floor.

1. Sit on the ground with your hands placed slightly behind you for support.
2. Extend your legs out in front of you, keeping them off the ground.
3. Pull your knees towards your chest.
4. Extend your legs back out to the starting position.