Step 1: Lie on the back with the legs extended. Keep the shoulder blades off of the floor.
Step 2: Bring one knees in so leg is at 90 degree angle. Hold for 1 count. Bring the opposite elbow up to meet the up knee.
Step 3: Push out through heels to starting position in controlled manner while simultaneously repeating the motion with the other leg.
Tips: Keep the legs parallel to the floor the entire time. Don't let them flail up and down (core is all about controlling the movement). Keep the lower back flat against the ground by not letting up on the core and keeping the shoulder blades lifted from the surface.
Link™ to Exterior: Attached to external anchor
Stance: Lying on back. Legs fully extended