Brad's Iyengar Yoga Notebook
Setu Bandha Sarvangasana
Setu Bandha Sarvangasana is a useful asana to follow Ustrasana or Sirsasana because it lengthens the back of your neck in the same way that Sarvangasana does after Sirsasana.
There are two primary versions of this asana with several variations of each.
In the first version, your shin bones are kept perpendicular to the floor.   Since the classical Setu Bandha Sarvangasana is done with the legs straight out, this version is given a separate name, Catus Padasana (pronounced "Chatoosh Padasana").   In one variation of Catus Padasana, you take your arms underneath your arching body in order to clasp your hands together with your arms straight along the floor (as is done in Halasana II).   In another variation, you grasp your ankles with your hands or place your palms underneath your heels.   In all versions of Catus Padasana, it is essential to keep your shin bones perpendicular to the floor.   If you allow your knees to go past your ankles, you will place strain on your knees.
For Catus Padasana, grasping your ankles and pulling will give you added traction to get more height in the pose and bring your sternum more toward your chin.   If you desire the added traction of taking your ankles, you should use a strap to hold your ankles unless you are sure you can keep your shin bones perpendicular to the floor while holding onto your ankles with your hands.   This is difficult for most people.   Grasping your ankles with your hands requires deepening the arch in your torso.
In the second version of this pose, the classical Setu Bandha Sarvangasana, you hold your hands on your back as in Salamba Sarvangasana and walk your feet away from your torso to the point of straightening your legs completely, keeping the soles of your feet on the floor and your ankles and knees together.   The best way to enter this asana is to drop back directly from Sarvangasana without changing the position of your hands on your back, since your hands will already be low down on your back in Sarvangasana to support a high arch in your torso in Setu Bandha.   This hand position low on your back is easier to establish in Sarvangasana than trying to achieve it by coming up from the floor into Setu Bandha Sarvangasana.
One good way to begin to practice dropping back is to take your Sarvangasana set-up to the wall, just far enough away that you can drop your feet back to the wall.   Go up into Sarvangasana and take your feet (one foot at a time) to the wall and then press your heels into the wall and press your spine away from the wall.   Walk your feet down a little on the wall and repeat the heel and spine action.   Keep walking them down the wall and repeating into you get as low you can and then walk back up into Sarvangasana.   Then pull your setup away from the wall a bit further and practice dropping into Setu Bandha one foot at a time and then both feet together to the wall.   Then finally practice dropping back from Sarvangasana to the floor.   Remember as you are slowly dropping back to lift your tailbone and keep it lifting as your legs go down.
In trying to learn to drop back to the floor into this pose from Sarvangasana, it helps to practice it one leg at a time, taking your other leg in front of you as a counter-balance.   Learn to drop onto your toes at first.   Keep your hands tucked as far down your back as possible.   The more flexibility you have in your spine, the less your back muscles will have to work to drop into the pose.   Your feet should touch down lightly like a feather.   Practice first dropping your feet onto a bolster or other support before going all the way to the floor.   When you are able to drop your legs into Setu Bandha Sarvangasana, then practice taking them back up into Sarvangasana as smoothly as possible.
Actions of the legs and feet
When practicing Catus Padasana, it is easier at first to keep your knees separated about hip width, although in the classical version you bring your legs together.   Starting with your feet up on bricks is a good way to increase your pelvic mobility.   If you are doing the pose without blankets, move back on your mat to have your head off the mat (as in Sarvangasana) so as not to catch your hair when you lengthen your neck in the pose.
In Catus Padasana, you must keep your shin bones vertical.   It is helpful sometimes to move your knees forward over the middle of your feet to help elongate your "bridge" (spine), but then return your knees to align over your ankles while keeping that length in your spine.   Raise up on your toes at first to gain height and then ground your heels while trying not to lose any height in the pose.   To get more lift in the pose, you can raise your heels, establish more lift, walk your feet in toward your head a little, and reground your heels, just as you do in Urdhva Dhanurasana.   But when you do this, the lift must come in your spine -- your shin bones remain perpendicular to the floor when you reground your heels.
Lengthen your thighs out from your pelvis toward your knees.   Your thighs will have a tendency to roll outward.   Draw your inner thighs toward the floor to keep the front of your thighs straight upward and to prevent your knees from splaying outward to the sides with the tightening of your buttocks.   Draw the skin of the backs of your thighs and hamstring muscles toward your buttocks.
Spread your toes and ground your feet evenly.   Keep your feet parallel, not turning outward.   Do not let your ankles roll outward.   You may need to press down more through the inner sides of your feet including your inner heels to achieve this evenness.
In the classical version of the pose, walk your feet away from your head so your legs straighten as much as possible.   Stretch your legs.   Draw your buttocks toward your heels.
Actions of the torso, hips, and pelvis
In all versions of this asana, tighten your buttocks somewhat and lift your hips as strongly toward the ceiling as possible.   In the upward pushing backbends like this pose and Urdhva Dhanurasana, there is tone in the buttocks but they are not hard or gripping.   The backbending power comes from the lifting of your upper hamstrings.   Press your tailbone up toward the ceiling using your hamstring muscles.   Work your hamstrings more than your buttocks.   Raise your tailbone as high as possible.   Lift your side ribs and back ribs toward the ceiling.   Broaden your upper chest and move your chest towards your chin.   Move your chin away from your sternum and move your sternum toward your chin.
Draw your frontal hip bones ("hip points" or anterior superior iliac crests) toward your abdomen and tuck your sacrum and buttocks underneath toward your legs so there is a circular action or rolling under of your pelvis.   Do this while keeping your quadriceps stretching away from your pelvis.   Draw your hamstrings toward your buttocks.   Try to create more and more space in the front of your groins.   These actions apply to almost all backbends.
Lift upward again toward the ceiling with your back ribs maximally.   Repeat this action over and over as you remain in the pose.
In the classical version of the pose, press your feet into the floor and lift with your feet and hamstrings to keep your weight off your wrists as much as possible.   If you feel too much strain in your wrists, you should continue to practice Catus Padasana.
Actions of the hands, arms, and shoulders
As in Sarvangasana, roll your shoulders under deeply in all versions of this asana.   Roll your trapezius muscles down toward your kidneys.   Move your rear armpits toward your front armpits strongly, just as in Sarvangasana, to help move your sternum toward your chin.   This is especially important in Catus Padasana and is also a basic principle for many other backbends.   This is just another way of saying circularize your armpit chest as in Tadasana.   Press your shoulder blades into your back to help bring your sternum more toward vertical.
In the classical version of the pose, try to keep your elbows from splaying out to the sides, just as you do in Sarvangasana.   Press your elbows down onto the floor to lift your chest strongly.   Lengthen your upper arms out toward your elbows and turn your upper arms inside outward.   Try to take your hands down your back as much as possible.   If you use a belt around your upper arms in Sarvangasana and drop back into Setu Bandha Sarvangasana, you can keep the belt on to help prevent your elbows from splaying outward as long as you have enough flexibility in your spine to achieve a high arch in Setu Bandha.