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Exercise guide
Jackknife Sit-Up
A full-body crunch performed from a floor-hover position, lifting both legs and torso simultaneously to touch hands to feet.
What this exercise works
- Muscles
- rectus abdominis · hip flexors · obliques
- Goals
- hypertrophy · endurance
- Equipment
- No equipment
- Category
- Strength
- Difficulty
- intermediate
Demonstration
Step 1
Step 2
How to perform the movement
- Lie face-up on the floor with arms extended overhead and legs extended straight.
- Simultaneously lift the torso and the straight legs off the floor.
- Reach the hands up toward the feet as the feet rise — meet above the hips.
- Lower the torso and legs back to the floor under control.
- Repeat for the recommended number of repetitions.
Technique cues and common mistakes
- Arms and legs move at the same speed — avoid a kick-first cheat.
- If the lower back arches on the return, slow down and don't fully touch the floor.