Start lying on your left side with your legs extended and feet stacked, resting your head on your bent left arm. Rest your right palm gently on the floor just in front of your ribs.
Engaging your core, bend the top knee toward the ceiling and pull the toes in toward the bottom knee. Then kick the right leg up to the ceiling.
Reverse the motion, bending the knee, and then sliding the right foot back to the bottom foot. Try not to let your hips tip forward or backward during the movement. That's one rep.