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Last updated March 2, 2026
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abs
Jackknife Sit Up
Simultaneously raise your torso and legs to touch your toes at the top, forming a V-shape.
Quick facts
- Difficulty
- Moderate
- Mechanic
- Compound
- Force
- Pull
- Type
- Strength
- Injury Risk
- Low
- Hypertrophy
- Medium
- Calorie Burn
- Low-Medium
Muscle focus
Primary and secondary muscle groups targeted by this movement.
Primary
abship flexors
Secondary
deep abs / coreside abs / obliques
Equipment & setup
What you need and how to position yourself before starting.
Equipment
body weight
Movement pattern
Bilateral
Posture
Lying
Tracking parameters
reps
Step-by-step instructions
Follow these cues to master proper technique and stay safe through every rep.
- Step 1Setup
- Lie face up on a mat with legs straight and arms extended overhead.
- Keep your lower back pressed into the floor.
- Step 2Starting Position
- Arms are behind your head, legs are flat on the ground.
- Engage your core before initiating the movement.
- Step 3Execution
- Simultaneously raise your upper body and legs off the ground.
- Reach your hands toward your toes, forming a V-shape.
- Keep your legs as straight as possible throughout.
- Pause briefly at the top with your abs contracted.
- Lower both your torso and legs back to the floor under control.
- Avoid using momentum to swing up.