How to do: Jackknife Sit-Up

Step-by-step instructions

1. 1Lie flat on the floor (or exercise mat) on your back with your arms extended straight back behind your head and your legs extended also. This will be your starting position.
2. 2As you exhale, bend at the waist while simultaneously raising your legs and arms to meet in a jackknife position. Tip: The legs should be extended and lifted at approximately a 35-45 degree angle from the floor and the arms should be extended and parallel to your legs. The upper torso should be off the floor.
3. 3While inhaling, lower your arms and legs back to the starting position.
4. 4Repeat for the recommended amount of repetitions.

Photos & base instructions from the open-source Free Exercise DB (public domain).