Start seated on the ground. Place your hands about an inch behind your back with your fingers facing forward. Your feet should be on the ground.
Lift both feet up off of the ground and extend both legs as you simultaneously lower your upper body. Be sure to get full extension at your hips and legs.
With control, bring your legs back to your chest without touching the ground with your feet (this is your tuck) and return to the starting position. This counts as one rep.