Jack knife is one of the classical Pilates mat exercises included in Joseph Pilates’ book “Return to Life Through Contrology.” It builds on skills learned in the roll over; you should be able to do roll over before attempting jack knife. To do it well, you must use your Pilates powerhouse and your sense of the midline.
In addition to strengthening the abdominals, jack knife provides a stretch for the back and shoulders. It requires spinal articulation (carefully rolling the spine up and down), which improves flexibility and posture—essential for the health of your back. Pilates also recommended rolling exercises like this one to improve circulation and even sleep.
Start on your back with your arms along your sides, palms down. Lightly press the backs of your arms to the mat and open your chest. Your ribs stay down. Imprint your spine on the mat as you extend your legs, feet toward the ceiling.
- Inhale to bring the legs into roll over position. Use a deepening scoop of your abdominal muscles and some help from the press of your arms to bring your legs over your head, parallel to the floor. Your back is curved so that the weight is on your shoulders and not on your neck.
- Exhale to sweep the legs up. Keep your chest open and the backs of your arms pressing down as you lift your legs up so that you are as close as you can get to perpendicular to the floor. You are on your shoulders, not your neck, getting help from the press of your shoulders and arms on the mat. This is a strong powerhouse move requiring hip extension with upper body flexion. Think “up, up, up” and shoot up through the midline of your body.
- Inhale to bring your legs back to parallel to the floor. Do not go all the way to the floor.
- Exhale to roll down with straight legs, vertebra by vertebra, until you are back to the start position.
- Repeat the exercise 2 more times.
It is easy to get caught up in the neck and shoulder area. Keep your neck and chest released toward the floor and your shoulders away from your ears. Your weight should always, always be on your shoulders and not on your neck, and your power should always come from your core (not momentum).
Modifications and Variations
Use caution as you perform this exercise, since it is very challenging.
Need a Modification?
Use your hands to help lift your hips up as you begin the jack knife. Another modification is to raise the legs only 45 degrees from the roll over position, instead of 90 degrees (step 2).
Up for a Challenge?
If you are very flexible, you can take the feet to the floor behind your head in step 1 as you prepare to lift the legs up into perpendicular.
These instructions give a basic breath pattern—an inhale or exhale for each part of the exercise with the exhale on the most exertion. For a variation, you can try going over and up into the jack knife on one inhale. Then exhale to legs over. Hold to inhale. Roll down. Then exhale when you are down.
Safety and Precautions
If you have shoulder, back, or neck problems, you should skip jack knife. It it also not recommended in the second and third trimester of pregnancy.