Step by step instructions
Start seated with hands behind body, elbows bent, fingertips facing hips. Shift weight back into arms and extend legs as straight as possible to ceiling, squeezing inner thighs together. Draw abs in tight to spine.
Slowly lower legs to the left, shifting weight onto left hip, lifting right cheek off the floor. Stop legs just before they touch the floor. Using abdominal muscles, lift legs back up to the center, and then repeat to the opposite side (imagine drawing a triangle with legs each time). That's one rep.