The pose known in Sanskrit as purvottanasana is called The Anti-Chaturanga Dandasana in English. The name literally means, "the upside down staff" as Chaturanga Dandasana is the staff pose and this is the opposite of it. Basically what this 'asana' is, is when you lie down on your back and lift your body up with your arms with your fingers facing towards your feet.
From your Chest to your feet should be a flat plane and your feet should lie pointed on the the floor. You then push the muscles in your shoulders up, extend your spine and drop your head back. Make sure your buttocks are tight and you are engaging your Mula Bandah. Another thing to watch for is staying in good body alignment. You should hold this for about five breaths.Now if you can't do this full posture, then there are a couple of
modifications that lead up to it.The first is a simple chair dip in which you put your hands on a chair and your feet about 3 feet in front of you and dip down as if you are sitting in an invisible chair lower then the one your hands are on.The next modification for Purvottanasana is an extension of the chair dip in which you start in the dip and thrust your hips up to do a Purvottanasana with your arms on the chair.
As the Chaturanga Dandasana works your: pectoralis major, pectoralis minor, the anterior deltoids, rectus abdominis, obliquus abdominis, iliopsoas, and your rectus femoris, the Purvottanasana streches these muscles. Purvottanasana also works your rhomboid muscles, your posterior deltoid muscles, your erector spinae and your gluteus maximus and hamstring muscles, all the muscles that Chaturanga Dandasana streches. This is why these poses are so complementary to each other. With all these muscles being stretched and used, doing the Chaturanga Dandasana and the Purvottanasana together really makes you feel wonderful as if you have expanded and worked your entire body.
When in this 'asana' I feel relaxed and although it is hard to hold, it is much easier on your body then the Chaturanga. Even when straining to hold this posture perfectly there is a sense of relaxation to it. Keeping your body in alignment is tough on your arms and your bandah as is keeping your feet extended.
Some Sites that were useful to me:
http://www.yogajournal.com/practice/2051#
http://www.yogajournal.com/images/old/Purvottdip_thumb.jpg
http://www.yogajournal.com/images/old/Purvottchair_thumb.jpg
http://studioyoga6.com/images/PURVATASANA.116201042_std_1_.jpg
http://www.yogabasics.com/asana/postures/inclinedplane.html
