Exercise guide
Band Jackknife Sit-Up
- Intermediate
- Compound
- Rep-based
- Waist
The Band Jackknife Sit-Up on a bench is a potent core exercise that uses elastic resistance to overload the rectus abdominis and hip flexors through a full range of motion. The elevated position on the bench allows for deeper leg extension, increasing the leverage and tension on the lower abs.
Reviewed by the Crucible Fit team · Updated June 2026
Muscles worked
Setup
- Anchor a resistance band to a low point behind the head-end of a flat bench.
- Sit on the end of the bench, facing away from the anchor point, and grasp the band handles or ends with both hands behind your head.
- Lean back slightly and extend your legs straight out in front of you, hovering them off the floor.
- Grip the edges of the bench with your hands if you prefer to anchor the band to your feet, otherwise keep hands behind the head to resist the torso crunch.
How to do it
- Exhale and simultaneously pull your knees toward your chest while crunching your torso forward to meet them in a 'folding' motion.
- Squeeze your abdominals hard at the peak of the contraction, ensuring the band is at maximum tension.
- Inhale as you slowly extend your legs back out and lean your torso back to the starting position.
- Maintain a controlled tempo, taking 2 seconds to extend and 1 second to crunch, never letting your feet touch the floor.
Form checklist
- Keep your lower back slightly rounded during the crunch to maximize abdominal engagement.
- Ensure the movement of the upper body and lower body is synchronized.
- Avoid pulling with your neck; keep your chin tucked and use your abs to move the weight of the band.
- Keep your legs squeezed together throughout the entire set to engage the adductors.
Pro tips
- Focus on bringing your ribcage toward your pelvis rather than just moving your arms and legs.
- To increase hip flexor and lower ab recruitment, keep your toes pointed away from you (plantarflexion) throughout the movement.
Make it harder
- Perform the exercise with straight legs (Band V-Up) to increase the lever length and difficulty.
- Add a 3-second isometric hold at the peak of the contraction where the band tension is highest.
Frequently asked
- What muscles does the band jackknife sit-up work?
- The band jackknife sit-up primarily targets the abs and obliques, and also works the erector spinae as secondary muscles.
- What equipment do you need for the band jackknife sit-up?
- The band jackknife sit-up uses resistance band.
- Is the band jackknife sit-up good for beginners?
- The band jackknife sit-up is rated intermediate. Build a base with simpler variations first, then progress to it with light load and strict form.