To do this exercise you will need a mat and a soft ball. Start by lying on your side with your knees bent and your heels lined up with your sitz bones. Your bottom hip will be on the soft ball. Inhale into the back of your ribs and then exhale as you externally rotate at the hip to lift the knee while squeezing the legs together. Inhale to release and then exhale angain. Repeat 8-10 times.
Things to think about
Keep the pelvis stacked in this exercise. To isolate the rotation, it is important that the top hip does not fall backwards. It is sometimes helpful to place a hand on the top hip to make sure that it is staying still.
As always with the soft ball try suspending the sine in the air on the elbow. This will provide an environment that requires good connection between the ribs and the pelvis.