Sirsasana stimulates the Sahasrara chakra, the energy center located at the crown of the head where our highest conciousness resides. Physically, Sirsasana revitalizes the body and mind, and is attributed with all manner of healing powers, not least of which its power to reverse the effects of gravity and slow the aging process. While the body is inverted, drainage of the lymph system is increased and it is generally taught in yoga circles that the brain and heart are provided with an abundance of fresh blood. However, Leslie Kaminoff, author of Yoga Anatomy, puts this notion of increased blood supply to the brain to rest by asserting that "the body has very robust mechanisms that control the amount of blood delivered to any given region -- irrespective of the orientation to gravity." But Kaminoff is still pro-headstand, assuring us that "inversions do offer a very beneficial opportunity for increased venous return from the lower body... not to mention the benefits derived from inverting the action of the diaphragm." The weight of the abdominal organs on the diaphragm encourages deeper, more complete exhalations, thus releasing more carbon dioxide from the lungs and thus encouraging fuller inhalations.
If you think you'd like to practice Sirsasana, there's a quick test you can do to find out if you're ready. Come to your hands and knees, then lower your forearms to the mat, palms flat, fingers pointing straight ahead. Now step your feet together behind you, elevating the knees in a forearm plank position. Keeping forearms on the floor, walk the feet forward so the hips lift and then stretch your heels down toward the floor. Press the shoulders away from the ears. This is Dolphin pose. If you can comfortably let your head hang here with your neck completely relaxed and lift out of the shoulders enough that the crown of your head does not touch the floor, you may be ready to try Sirsasana.
Never kick the legs up when entering Sirsasana. At first, practice with a wall behind you. Lift up into the pose by bending the knees and only if this is comfortable, slowly raise both legs together. Even if you're just learning, try not to allow the heels to rest against the wall. Use the wall as a safety net, but keep finding your balance. After some time and practice, one may enter Sirsasana with straight legs, but always move slowly with control. Draw the elbows in and keep the jaw, throat, and shoulders relaxed. If you feel any discomfort in the head or neck, come out of the pose immediately.
Sirsasana has been an ongoing project of mine over the past year. Much of my experience teaching myself to be comfortable in this posture has been chronicled here. I spent many weeks practicing my headstands at the wall before venturing out to the middle of the room. Iyengar, in his wisdom, changed the way I approach headstands. When first practicing the posture, I became frustrated that I couldn't seem to remain still, my body always swaying and rocking, however subtly, but then I read that "in Sirsasana the balance alone is not important. One has to wait from moment to moment and find out the subtle adjustments (Iyengar, Light on Yoga)." I learned to soften into the pose, to watch and wait, and be comfortable in having to make adjustments. Inversions have not come naturally to me, but with patience and practice, Sirsasana is now an essential and enjoyable part of my daily routine.