Jackknife Sit-Up

A full-body crunch performed lying on the floor, lifting both legs and torso simultaneously to touch hands to feet.

How to do it

1. Lie face-up on the floor with arms extended overhead and legs extended straight.
2. Simultaneously lift the torso and the straight legs off the floor.
3. Reach the hands up toward the feet as the feet rise — meet above the hips.
4. Lower the torso and legs back to the floor under control.
5. Repeat for the recommended number of repetitions.

Tips

• 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.

Muscles

Primary: Abs

Secondary: Hip flexors, Obliques