Jackknife Sit Up
Lying flat with arms overhead, you raise your straight legs and upper body at the same time and reach your hands toward your toes, folding into a V before lowering.
- Primary muscles
- Abs, Lower abs
- Secondary
- Obliques
- Difficulty
- Intermediate
- Logged as
- Reps
Loads from YouTube only when you press play. The video is by an independent creator.
Why do it
The jackknife works your upper and lower abs in the same rep, since both ends of your body move toward each other. It's a step up from crunches and reverse crunches, and it suits people who can already hold a hollow position without their back lifting. The lowering is where most of the control comes in: let it drop and your back arches off the floor. If the full version is too much, bend your knees or lift one leg at a time.
How to do it
Lie flat on your back with your legs straight and your arms stretched out overhead.
Lift your legs and upper body at the same time, reaching your hands toward your toes.
Fold into a V shape at the top and hold it briefly.
Lower everything back down slowly without letting your lower back arch off the floor. Bend your knees or lift one leg at a time if the full version pulls your back up.
Common mistakes
Arching your back on the way down
Dropping your arms and legs fast pulls your lower back off the floor. Lower slowly and keep your back pressed down until everything touches.
Swinging your arms to get up
Throwing your arms forward to build momentum skips the ab work. Lift with your abs and let your arms follow.
Moving legs and torso out of sync
If your legs rise first and your torso lags, you end up with half a crunch and half a leg raise. Start both together so they meet in the middle.
Sets, reps and progression
How many sets you do and how close to failure you take them depend on your goal and your week, not on the exercise. These guides cover it:
Alternatives that train the same thing
Same movement, a different angle or piece of equipment.
