Alternate Leg Raises

Take a deep breath and exhale slowly through your mouth. Now bring one knee up towards the shoulder, then return the foot to the mat, sliding the leg all the way out. When the leg is all the way out, slide it back to the starting position. Now bring the other knee up towards the shoulder, return the foot to the mat, and slide the leg all the way out. When the leg is all the way out, slide it back to the starting position. Do this exercise twice more, alternating each leg.

This exercise is designed to release tension and relax the muscles in the middle and lower back. The important thing to keep in mind about this exercise is not to bring the knee too far back. You'll know your're bringing it too far back if you lift your buttock from the mat.
If you lift your buttock, you will produce tension, and you want to release tension with the exercise. Just bring the knee up to where it stops naturally without raising the buttock.