Jackknife Sit-up tutorial
The jackknife sit-up is a compound exercise for the abs and hip flexors in which arms and legs rise together. It suits intermediate lifters and improves core control.
How to perform
- Lie on your back with your arms extended overhead and your legs straight.
- Brace your abs and press your lower back into the floor.
- Raise your arms and legs together so they meet over your body.
- Lift the legs to about 35 to 45 degrees from the floor.
- Pause briefly.
- Lower arms and legs slowly without letting the back arch.
Breathing: Exhale as you rise and inhale as you lower.
Key tips
- Bend your knees slightly if the movement is too hard.
- Take your time on the lowering phase.
- Lift with your abs, not momentum.
Common mistakes
- Arching the lower back as the legs lower.
- Using momentum to come up.
- Throwing the arms forward.
Safety: If you have back pain or cannot keep your lower back down, raise your legs higher or choose an easier exercise.
Abs and corePrimary muscle
Body weightEquipment
IntermediateLevel
HomeLocation
Assisting muscles
Suggested sets and reps
Beginner3 sets × 8–12 reps
Muscle mass4 sets × 6–12 reps
Strength5 sets × 3–6 reps
Fat burning3 sets × 12–15 reps, short rest
Pick a weight where the last 1 to 2 reps are hard but done with correct form.
Get a complete workout program
Do this exercise within a personalized program based on your goal and level.
Get a free program
