There are countless miracles happening in our physical bodies every moment of our existence. One that continues to intrigue me is the symphony of cranial motion that happens with our every breath! This motion is synchronised with another gentle movement at our sacrum as it rocks between the two pelvic halves or ilia. Cranial-sacral motion is constant and rhythmical as it circulates the vital fluid that our brain produces – cerebrospinal fluid or CSF. CSF nourishes and protects our nervous system, transports important hormones from the pituitary gland and maintains central nervous system homeostasis.
Although the motion at the sacrum when we breathe happens involuntarily as a micro-movement, we can also exaggerate this movement in our posture. This specialised movement pattern is termed nutation and counter-nutation. Nutation comes from the Latin word nutare, which means to nod, analogous to nodding the head. Although there are different theories on the exact axis and movement of the sacrum, the classic theory of Farabeuf is that in nutation the sacral promontory (the upper most part of the sacrum where it joins the spine) ‘nods’ or drops forward (anterior) and down (inferior), while the coccyx or tailbone moves posterior and superior (see figure 1). Counter-nutation is simply the opposite movement.
Posturally, nutation and counter-nutation of the sacrum spontaneously happen as our body adapts to its natural demands and surroundings. Living on a steep mountain I notice how naturally the position of my sacrum, pelvis and spine shift to change my centre of gravity. When ascending the steep slopes my sacrum moves forward into nutation, my pelvis also tips forward and my spine arches towards the ground. Descending the mountain, the opposite happens: my sacrum tilts back into counter-nutation, my pelvis shifts back and my whole spine curves backward pulling me in closer towards the slope. These same sacral movements participate in the physiology of labour and childbirth. The sacrum counter-nutates to increase the dimensions of the pelvic inlet encouraging the descent of the baby’s head into the pelvis and then tilts forward into nutation to increase the aperture of the pelvic outlet, facilitating delivery of the newborn.
Sacral Versus Pelvic Movement
It is important to understand that movement of the sacrum and movement of the whole pelvis are different phenomena. Sacral movement happens in relation to the pelvis or ilia. When the sacrum moves anterior into nutation, relatively, the ilia move posterior. This means that the entire pelvis can be flexed forward, as in a forward bend, and the sacrum can be either nutated or counter-nutated in this position. The same applies when the pelvis is extended back as in a back bend. Try this: make a fist with one hand. This hand will represent our sacrum. Cup the palm of your opposite hand up against the thumb side of your fist. This hand represents one ilium (see figure 2).
As you move your fist forward into nutation, feel how it rotates in relation to the hand it articulates with. Relative to the sacral fist, the ilium hand moves posterior. This coordinated movement between the sacrum and ilia happens naturally and is not something that we can manipulate. If the sacrum is not able to float and move freely between the two ilia, normal sacroiliac movement cannot happen. This leads to dysfunction and a whole cascade of compensatory adaptations.
More important than sacral nutation itself is the effect this movement has on the spine, the pelvis and the limbs. When the sacrum tips forward into nutation the lumbar lordosis (natural curve in the low back) is increased and the entire spine unravels and lengthens. Additionally, the rib cage lifts and opens. In Yoga, nutation of the sacrum may seem paradoxical in that it can be applied to both forward and back bending. It is this elongation of the spine that is complimentary to both groups of postures. Sacral nutation enables us to freely lengthen our spine and open our chest and heart energy centre or chakra.
Conversely, when we counter-nutate the sacrum by tipping its base posteriorly and tucking the coccyx under, the low back or lumbar curve flattens and the chest compresses as the rib cage is anchored down. Counter-nutation has a stabilising effect on the entire axial column. It is helpful in most of the yoga standing postures, arm-balances, inversions and leg-behind-head postures. Counter-nutation of the sacrum in back bends makes it difficult to arch the lumbar spine and open the heart area. This method is sometimes taught to beginners to yoga to protect the low back as it greatly inhibits extension of the lumbar spine. However, extension of the spine will then be forced into the lower lumbar vertebrae, especially where the lumbar spine meets the sacrum (L5/S1).
Let’s look what happens at the pelvis during nutation and counter-nutation. The sacroiliac (SI) joints are not parallel to each other but lie at a 45-degree angle. This means that as the sacrum nods forward into nutation, the wings of the ilia move towards each other (medially) in the front of the pelvis. Correspondingly, the ischial tuberosities or sit bones move apart (see figure 3). In fact, this is one of the easiest ways to access the movement of sacral nutation. The common instruction given in yoga classes to initiate sacral nutation is to broaden or “flare the sit bones”. In counter-nutation the opposite happens, the sit bones draw toward each other and the iliac wings flare open in the front of the pelvis.
Key to Straight Feet in Back Bends
What has not yet been described in texts on Yoga Anatomy is what happens to our lower limbs during sacral nutation and counter-nutation. As our thighbones or femur are connected to the pelvis at the hip joint (acetabulofemoral joint), this movement of the pelvis during sacral nutation translates into medial or internal rotation of the legs. In this way sacral nutation is not only a liberating technique to arching backward, it is also the key to keeping your feet straight in backbends! Contrary to this, if the sacrum is counter-nutated in a back bend the thighs will tend to externally rotate as the iliac wings move towards the back of the body (see figure 3). This translates into turning the feet out in back bends.
This kinematic chain or reciprocal movement pattern in the spine, the pelvis and the legs are best assessed from an all-fours position. From all-fours, without tipping the pelvis forward or backward, try broadening the sit bones. Notice the natural exaggerated curve that happens in the low back. This corresponds to the psoas muscle pulling the sacrum forward into nutation. The psoas attaches to all the lumbar vertebrae and transverses the SI joint as it reaches down through the pelvis to attach at the lesser trochanter at the proximal end of the femur. Feel how your chest freely opens and lifts. And now feel the internal rotation that happens in your legs without any concentrated effort or muscle engagement. This is how nutation of the sacrum enables us to keep the feet straight in back bends.
In my last article, ‘Glute Max for Maximum Extension’, I described the importance of using the gluteus maximus muscle when performing backbends. Back bending is a complex movement pattern. Written ‘asana workshops’ are often limited by the burden of the copious amount of text needed to describe a posture and are thereby often incomplete. If sacral nutation is not adopted as a preparation for backbends, the posterior pelvic tilt generated by the engagement of glute max will often find students counter-nutating their sacrum. This is the reason that students sometimes report that relaxation of their glute max relieves discomfort in backbends. Not engaging glute max in backbends, however, leaves the fulcrum of the backward arch in the lumbar spine instead of at the hip joint. This brings me back to my walking uphill analogy: it is my gluteus maximus muscle that powerfully propels me up the slopes! To not use glute max in back bends can cause excessive wear and tear on the already inherently mobile joints of the lumbar spine.
Sacral Nutation in Back Bends
So let’s look at accessing sacral nutation in backbends. Because of the reciprocal movement cascade between the sacrum, pelvis and femur we can access sacral nutation via any of these different movements. For most people, it is difficult to isolate movement of the sacrum itself. An easier way to access sacral nutation in back bends, is to already put a back bend in your spine by arching the lumbar spine and lifting and opening the heart area. This setup will transform ease into strenuous back bends such as Purvottanasana. Now activate the posterior fascial chain by engaging the hamstring and glute max muscles.
An alternative to accessing sacral nutation is to spread or widen your sit bones. If your feet are grounded you can also induce this movement at the sit bones, via the long lever of your legs, with the action of drawing the feet apart without actually moving them. This action is termed abduction and engages the tensor fascia latae muscle, which also internally or medially rotates the legs. Some teachers will also instruct students to draw their legs together in the opposite action of adduction whilst drawing the upper thighs back toward the coccyx. This action has a similar effect by engaging the other medial rotator muscles of the hip joint, the anterior portion of adductor magnus and the gracilis. In this way sacral nutation is accessed by actively internally rotating the legs.
Sacral Nutation in Other Postures
Let’s look at the effects of sacral nutation in other postures. The easiest postures to access sacral nutation are the wide-legged forward bends, e.g., Prasarita Padottanasana. With the legs abducted (apart) the sit bones freely broaden as the sacrum tips forward into nutation. You have probably noticed that the feet will often excessively inwardly rotate in this posture. This is a result of the natural reciprocal internal rotation of the legs as the sacrum nutates and the pelvic halves move medially. In contrast, in standing postures like Trikonasana and Parshvakonasana where the sacrum is counter-nutated, this sacral positioning compliments the external rotation of the legs needed here to open the hip joints. This same movement pattern occurs in leg-behind-head postures.
The Brakes of Sacral Motion
Why is it easy for some to access sacral movement and more difficult for others? Movement at the sacroiliac joints is small (5 to 10 degrees) and varies between individuals and circumstances. The sacrum is suspended between the ilia by strong articular ligaments. It is these ligaments that stabilise the SI joints and determine how much sacral movement is possible (see figures 4a and 4b). The very strong interosseous or axial ligament acts as the fulcrum for sacral nutation whilst the other numerous sacral ligaments act as brakes. Generally speaking, sacral movement will be easier in flexible females (eg, during labour!) and more difficult in stiff males. Additionally, females may notice an increase in flexibility around menstruation and ovulation as the spike of hormones at these times increase the pliability of their ligaments. For this reason excessive nutation in counter indicated in those with hypermobility and in pre and postnatal women. These students will often get relief of their SI joint, sacrum or low back discomfort by either externally rotating their legs or drawing the sit bones together, leading to a more stabilised counter-nutated sacrum.
If you’ve read my previous articles: ‘What’s Functional in Yoga’ and ‘Glute Max for Maximum Extension’ you will know that how I perform and teach Yoga is very much based on the body’s natural movement patterns. Ultimately, if you wish to practice yoga for the rest of your life, what you do and how you move must be in harmony with the way Nature has designed us. It cannot come from our head, our ideas or concepts or even our most well intended ideals.
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Muscle images taken from visible body 3D Muscle Premium, www.visiblebody.com