How to do the Jackknife Sit-up
Jackknife Sit-up is a beginner single-joint isolation pushing exercise targeting the Abs in the Waist region. Performed using bodyweight, it falls under the strength category. Secondary muscles engaged include Hip Flexors.
Jackknife Sit-up demonstration · © GymiaFit
Jackknife Sit-up at a glance
- Primary muscles
- Abs
- Secondary muscles
- Hip Flexors
- Equipment
- Body Weight
- Level
- Beginner
- Type
- Isolation (single-joint)
- Force
- Push
Jackknife Sit-up step by step
- 1Lie flat on your back with your legs extended and your arms overhead.
- 2Engage your core and lift your legs and upper body simultaneously, reaching your hands towards your toes.
- 3Pause for a moment at the top, then slowly lower your legs and upper body back down to the starting position.
- 4Repeat for the desired number of repetitions.
Jackknife Sit-up — questions
What muscles does the Jackknife Sit-up work?
The Jackknife Sit-up primarily targets the Abs. It also recruits the Hip Flexors as secondary movers.
What equipment do I need for the Jackknife Sit-up?
None — the Jackknife Sit-up uses your bodyweight only, so it works at home with nothing but floor space.
Is the Jackknife Sit-up suitable for beginners?
Yes. It is classed as a beginner movement: the pattern is simple enough to learn in a session and easy to scale by adjusting range of motion or load.
What can I do instead of the Jackknife Sit-up?
3/4 Sit-up, 45° Side Bend, Air Bike train the same muscles and make good substitutes when the equipment is taken or the movement does not suit you.
Log it, don't guess it.
The GymiaFit app has the Jackknife Sit-up demo, form cues and set logging built in — plus a muscle map that shows what you have actually trained this week. Free on iOS and Android.