How to Do Jackknife Sit-Up: Muscles Worked & Proper Form

Muscles Worked in Jackknife Sit-Ups

Primary muscles worked:

• Abs
• Hip Flexors

Secondary muscles worked:

• Obliques

How to Do Jackknife Sit-Ups

1. Lie on your back with your arms extended overhead and legs straight.
2. Engage your core and lift both your legs and upper body off the floor simultaneously, as if trying to reach your toes with your hands.
3. Continue lifting until your body forms a “V,” aiming for your hands and feet to meet.
4. Briefly pause at the top, then lower in a controlled manner without letting your feet or arms touch the floor.
5. Repeat for reps.

Commentary

The jackknife sit-up is an effective exercise for building core strength by engaging both the abs and obliques. It also activates the hip flexors and improves body control and stability by keeping arms and legs straight during the movement, challenging both your strength and balance.