I learned this lumbar stretch from my teacher Susi Hately Aldous during one of the Therapeutic Yoga Trainings I have taken from her. I'm a bit of a hyper-extender so I was surprised that this pose would be good for me. What it does is lengthen your lumbar vs. kink it - which is a typical move for me in any kind of backbending posture. Here's how it works:
Step 1. Get yourself a felted pad or a firm blanket or even a big towel (like a beach towel) and make a roll that is about a handful for you. Sit on the tail of the blanket if you have extra.
Step 2. Lay down over the roll, supporting yourself on your elbows to ease your body down.
Step 3. As you lay down, lift your seat up so you are in a tiny bridge pose. Adjust your roll so it is at your waist - not your sacrum). You know if it is in the right place if it is centered behind your bellybutton.
Step 4. Now start to lower your seat towards the floor, arching your spine over the roll. When you settle your seat your back should feel like "Ahhhh" not "Ow, ow, ow." You should not look over arched. Your belly is not raised by the roll under your back. If you are not comfortable, lift your seat (into little bridge again) and make your roll smaller until your back is happy. Conversely, if you feel nothing, you will need to lift your seat into little bridge and make your roll a little bigger.
Step 5. Lay here for 5-10 minutes or until you are feeling done.
Enjoy!