During my recent workshops I noticed that there is still a lot of confusion about the importance of nutating the sacroiliac joints in various forms of back-bending (but also in forward bending). Here is a modified passage from my 2009 text Ashtanga Yoga The Intermediate Series that sheds light on sacrum nutation during Kapotasana. This is something that any natural backbender will do automatically but even if you do not belong to this group, the actions can be induced by understanding and learning. This will improve your backbend significantly. This passage is shortened as the original has over 5500 words.
Inhaling jump forward to a kneeling position with your torso upright and your hands on your hips. Keep your feet and knees roughly hip width apart. You can place your feet slightly closer together than your knees to make it easier to ‘walk’ around the outside of your feet with your hands in phase 2. To place the feet together and the knees apart in Kapotasana, however, is not recommended as it will externally rotate the femurs (thigh bones). Externally rotated femurs in turn will tend to ‘jam’ the sacrum into a counter-nutated position.
If your chest is not yet completely open (for most of us it won’t be at this point of practice), lift your chest by pressing your hands onto your hips. Lift your heart as high as possible and grow as tall as you can. Imagine the entire front of your torso being sucked up to the sky, while the posterior aspect of your trunk flows down to the earth. If necessary you may initially take several extra breaths to achieve this effect.
As your backbend deepens, steer away from just folding your pelvis backwards and jutting the pubic bone forward. This method is an easy way out, as it will carry the stretch only into the softest part of your spine but not into those areas where you are stiff and inflexible. One axiom of physical yoga however is to support where we are weak and open the areas where we are tight and closed. If you use the method of jutting the pubic bone forward you will not only stop the heart from opening but also you will put undue pressure onto your low back and sacroiliac joints.
Drop now the pubic bone downwards and towards the coccyx by engaging Mula Bandha. Rather than folding the pelvis backwards, lift the front of the whole pelvis together with the entire front of the torso up to the ceiling. Check that you are not clenching your buttocks to avoid externally rotating your thigh bones. Clenching the buttocks means the gluteus maximus and piriformis muscles are fully engaged. The gluteus maximus along with the hamstrings performs hip extension (that action necessary for back bends). When the knees are bent the hamstrings are already shortened and thereby less powerful. The gluteus max is needed to initiate the action of hip extension as we raise our pelvis upwards with our knees bent. The lower fibres of the gluteus maximus muscle also perform external (lateral) rotation of the femur, as does the piriformis muscle. This rotation will put more pressure on your sacroiliac joints because it squeezes the ischii (sit bones) together, and prevent nutation (forward bowing) of the sacrum, another necessary motion for harmonious back bending. It is thereby necessary to not excessively clench the buttocks whilst in a back bend position. Of course like all other actions in yoga also this action can be taken too far. The glutei need to maintain a certain core tension that cannot be too low either.
To prevent the clenching of the lower fibres of the gluteus maximus and of the piriformis it is suggested to gently internally rotate the femurs during all back bending postures. This action will prevent over-activation of the lower fibres of the glut max, piriformis, and other deep external rotator muscles in the buttocks, enabling the low back to lengthen, and sacroiliac joints to move freely.
There is another action, which has a similar effect. It is the squeezing of the thighs together by engaging of the adductors in back bends. Placing a block between the knees or at least imagining one to be there may bring about this effect. This action is, however, recommend only for those whose low backs or sacrums are very unstable and who have tried internal (medial) rotation of the femurs with no success. The disadvantage of squeezing the knees together in back bending is that the action may be performed to such an extent that it will tighten your adductors. For this reason inward rotation of the femurs is to be preferred and only then to be replaced with squeezing the knees together when it has failed to achieve its objective.
Engage now your psoas and draw the upper, frontal rim of the sacrum, called the promontory, into nutation. Increase your nutation by strongly engaging Uddiyana Bandha, thus drawing your anterior superior iliac spines towards each other. Complementary, spread your sit bones, meaning draw the ischii apart from each other. If you previously used to squeeze your knees together or squeezed an imagined or real block between your thighs, you will need to leave this technique behind now as it will also draw the ischii together and the ASIS’s apart and thus prevent nutation of the sacrum. Replace therefore squeezing of the thighs together with internally rotating the thighbones.
These three movements, nutation of the sacrum, drawing towards each other of the ASIS’s and the spreading of the sit bones are really only one movement surfacing in three different ways. It is helpful, however, to consciously do them all three consecutively.
Exhaling, extend your arms over your head, and arch backwards, keeping your arms straight and hands shoulder-width apart. Let the back bend start from the uppermost thoracic vertebrae. Imagine that you arch back over a bar extending across your back behind your shoulderblades rather than behind your low back. This will help you to distribute as much backbend as possible from your low back where you are soft and unprotected to your thorax where you are armoured and need to open. Observe the weight distribution in your legs. Notice that with the weight distributed forward towards the knees, the stretch is taken further up the spine. As the weight is taken back towards the feet the stretch occurs lower down towards the low back. Use this to accentuate the stretch in areas of tightness. Draw your shoulder blades down the back and as you arch backwards lift your heart up to the ceiling to increase back arch. Strongly use your abdominal muscles to keep space between the spinous processes of the lumbar vertebrae to create more length in the spine for further back arching. Use both the abdominal muscles and the lifting of the heart up to the ceiling to lengthen through your low back.
As your head and arms travel backwards, let the pelvis draw forward. Let this movement however come from the front of the pelvic bone rather than from the pubic bone for the reasons already mentioned. Use the drawing forward of the anterior superior iliac spines of the ileum, rather than the pubic bone, to stretch the quads.
As your pelvis draws forward and your hands come closer to the floor, continue to lift your heart to the ceiling, creating more space beneath you. Continue to draw the anterior aspect of all vertebrae apart from each other, drawing the spine as long as possible. Ideally of course you would perform all of this on one exhalation. If this is not possible take as much time as necessary to study the movement closely and to experience and feel all aspects of the movement. Needless to say there is an entire universe in this movement. If you quickly hurry through it, you will not awaken your spine properly. Depending on your muscle tone it might be necessary to hang in the posture with straight arms parallel to the floor pointing to the backend of the mat for several breaths until you have isolated all individual functions and awakened your chest. Take that time.
Once your hands touch the floor walk your hands in a little towards your feet. Now attempt to extend the arms to further open the chest and armpits. Now return your elbows towards the floor and walk your hand in to reach your feet. If you find that challenging, try walking in one hand a little way in and then the other, repeating until you reach your limit. Rather than lifting your entire hand off the floor, creep along the mat with your fingers, like a caterpillar would move: place your fingertips firmly on the floor, lift the heels of your hands off, flex your hand, and place the heel of your hand down close to your fingers; then lift the fingertips off, extend your hand and place the fingertips down closer to your toes. This way you will never loose traction on the floor. If you are slipping and don’t get in closer, the fabric of your mat may not be suitable. If necessary, use a fabric that provides more traction.
Once you reach your feet, don’t make the mistake of walking up your soles. Instead, walk with your hands around the outside of your feet. If this is too difficult, place your feet slightly closer together. Once you reach the limit of your flexibility walk your hands inwards to get hold of your feet, heels or even ankles.
While you breath deeply make use of the following mechanism. Even when you stand upright inhaling will gently extend (back arch) your thoracic spine, while exhaling will lightly extend your lumbar spine. Unless your spine is frozen breathing will always result in a gentle resonance frequency going up and down your spine, which is a sign of spinal health.
Use this mechanism by exaggerating the back arch in your upper back during inhalation and of your low back during exhalation. You will see that using this method creatively over time, will get you much deeper into your back bend. Stay in Kapotasana A for five breaths and gaze towards your nose.
Inhale and, letting go of your feet. If you need to, walk your hands out slightly but the further you get away from your feet the less deep the now ensuing Kapotasana B will become. Place your hands firmly on the floor, shoulder-width apart, fingers pointing towards you knees and now straighten your arms. Look towards your nose and hold Kapotasana B for 5 breaths. Kapotasana B is a more advanced and more intense version of A. However this is dependent on the fact that you don’t walk your hands out too much. There is even more emphasis here on opening the chest than in the A-version.
Inhaling, engage your quads and come up on your knees again. Coming out of the backbend reverse the movement that got you into it. Start from the pelvis and let the movement travel in a wavelike motion up the spine, lifting the head last.
If you find it difficult to come up that way, bend your arms slightly and inhaling, push off the floor to come up with momentum. Keep your arms straight and over your head as you push your pelvic bone (again not the pubic bone) forward, during the upward movement to maintain your backbend as you come up.
At the end of the inhalation, place your hands on your hips.
Exhaling place the hands down on the floor on either side of your knees. Don’t place your hands too far forward as this will mean that you will use your legs too much in the subsequent jump-up.
Inhaling lift up into an arm balance with your feet way off the ground and your arms straight. Hold this phase for the duration of the inhalation. This is again important to counteract the backbend. From here jump back and transit through your regular vinyasa.