Jackknife sit-up

Follow these steps to increase your core strength. Floor or rug burns are the worst, so grab a mat to cushion your spine before you begin.

Lengthen your body on your mat. Lie flat on your back and neutralize your low back (avoid a rounded or an arched spine).
Extend your legs out long and reach your arms above your head.
Hover your arms and legs a few inches off the mat (still press your tailbone into the mat).
Take a deep breath, and on your exhale lift your head and pull your arms and legs up into a V-shape (lift roughly 30-45 degrees away from the mat).
On your lift, keep your legs straight and your arms parallel to your thighs.
Lower back down to your starting position.
Repeat these steps for 10 to 12 reps and 2 to 3 sets.

How to Make Jackknife Sit-Ups Easier

We understand that this exercise is hard. Build up to the burn with these simple variations that will still cause your muscles to quake.

Try doing single leg jackknife sit-ups, alternating lifting one leg at a time.
Work through jackknife sit-ups with bent elbows and knees, rather than straight arms and legs.