To do this exercise you will need a mat and a soft ball. Start by lying on your side with the soft ball underneath your hip. Lengthen both legs long beneath you. Inhale into the back of your ribcage as you rotate your top leg outward at the hip socket and then exhale as you bend the knee and begin sliding the foot up the leg. Inhale again as you straighten the leg into the air and then exhale as you flex your foot and reach your top heel to your bottom heel. Repeat 8-10 times.
Things to think about
As you straighten the leg into the air most likely it will not line directly with the pelvis. To keep the pelvis stacked most people have external rotation that is slightly less than 180 degrees. Be sure that you are being true to your rotation.
You can always progress this exercise by suspending yourself on your elbow, and work hard to maintain an elongated spine with ease and flow in the leg movement.