Laying on your back with legs pointed straight toward the ceiling, lower legs up/down while keeping your core engaged. Try not to arch your back.
Beginning (my grandma on the left) – Alternate dropping legs down one at a time with bent knees, place hands under bum for more support.
Intermediate (my mom in the middle) – Bend knees slightly while dropping legs down and up, place hands under bum for more support.
Advanced (me on the right) – Keep legs straight when dropping legs up and down, place hands on the ground to the side.