Spinal exploration: a yoga myth and healthy discs

A while ago I mentioned attending a Judith Lasater workshop on the sacroiliac joint. I promised to tell you some of the interesting things I learned at the workshop, and now I’d like to do that. I’ve followed up what I learned in the workshop with additional research about the spine, to share with you how yoga can help you can nourish your spine and prevent back pain.

Judith’s focus was on the natural curves of the spine. When each of the curves is allowed to be in natural alignment, the spine becomes a very stable structure that supports our bowling-ball head and what’s known as the axial load—the downward weight of the body when we are vertical (sitting or standing). It might seem counter-intuitive, but it is the balance of the curves that creates the stability. The diagram to the left shows a side view of the curves of the spine. The person is facing to the right.

There are five sections or groupings of vertebrae in the spine, with the curves reversing direction from one section to the next, from anterior (frontwards at the neck) to posterior (upper back) to anterior (lower back) to posterior (butt), and finally anterior and posterior again in the sacrum and coccyx. The five vertebrae in the sacrum fuse together between the ages of 16-18 and 25-26. This fusing is one of the factors that causes us to lose flexibility with age. Also notice how the natural curve of the spine situates the sacrum at almost a 45-degree angle from vertical. The 3 to 5 coccygeal vertebrae form the coccyx, which usually fuses into a single bone, but not always. As you can see in the diagram, the coccyx forms an extension of the curve of the sacrum and it tilts backwards. The coccyx is commonly known as the tailbone.

Tailbone tucked, or let the lordosis sway?

Any of you who have been in a yoga class, whatever the style, have probably been told to keep your tailbone tucked in mountain pose. I know I’ve heard it a hundred times, and learned to instruct students to do this in multiple teacher training courses. But what does tucking the tailbone do to the natural curve of the spine? Tucking the tailbone means drawing the coccyx forward, which causes the lower back to flatten, and then causes flattening up the whole length of the spine. This movement totally abolishes the natural curve of the spine, messing with the stability and the load-bearing capability that the spine has with the natural curves.

Judith encourages her students to experiment with not tucking the tailbone. In fact, to fully allow the natural curve of the spine, you might need to slightly exaggerate the curve in your lower back, especially if you have worked for years to flatten the curve. It seems like a very radical idea, because most of us have been so indoctrinated to tuck the tailbone. Judith demonstrated on three different students how the natural curve of the spine means our butts and chest are sticking out. Too sexy for this party! Many of the students had been told they had lordosis (an exaggerated curve in the lower back) and that they needed to straighten it. The pain these women have suffered as a result is shocking. Some of us postulated that the reason we are taught to keep our tailbones tucked is to keep women down! My mom and sister didn’t agree with this theory when I shared it with them. Hmm, bummer.

Another theory occurred to me when Judith demonstrated on the single man in the class that his hip bones were much higher than a woman’s, and his pelvis was a rectangular shape rather than curved like a woman’s hips. I think most of the lineage of yoga teachers in India, dating back thousands of years, were men. Krishnamacharya, born in 1888 and teacher to many of the teachers who brought yoga to the west, including Indra Devi (often called the First Lady of Yoga), B. K. S. Iyengar, T. K. V. Desikachar, Gerard Blitz, and Jean Klein, traced his lineage of male yoga teachers back to the ninth century. That’s centuries of practicing and perfecting on the male body. Perhaps the instruction to tuck the tailbone makes sense for the male body in a way that doesn’t hold true for the female one with its radically different pelvic anatomy.

I would love to hear from any of you out there, male and female alike, about your thoughts on this. Personally, I have been experimenting with the non-tailbone-tucked, natural spinal curve in mountain pose and all the other poses that move from this standing position. I must say I have experienced less pain in my sacroiliac joint—the pain that motivated me to attend Judith’s workshop in the first place. So I think there might be something enlightening and world-view shattering (on a smallish scale) about this idea of letting the spine be in its natural curve. I invite those of you with a regular yoga practice to try it for yourselves and see what you think. I also introduced this idea in a class I taught recently for the Society for Technical Communication. I will explore this further in another posting.

The discs between the vertebrae

Another fact that Judith mentioned about the spine was that the discs between the vertebrae are avascular. This means they don’t receive a direct blood supply to bring them the vital water needed for hydration, food in the form of glucose, building material in the form of amino acids, and oxygen. I was curious about this, and decided to do a bit of research to find out how the discs do receive their nourishment.

I found what I was looking for at Chirogeek.com. The discs are situated between the vertebrae, and are composed of a high percentage of water in a closed hydraulic system that is able to withstand a great deal of pressure. A well-hydrated disc is even stronger than the vertebrae themselves. Interestingly, the compression on the discs when we are standing causes us to shrink in height. The height of the disc increases as much as 20% overnight when we are lying down and the discs have the opportunity to re-hydrate.

The discs contain sponge-like molecules that hold 500 times their weight in water! The health of the cells within the discs affects their capacity for holding this water, which is what gives the discs a very high hydrostatic pressure and therefore their incredible strength to support the axial load of being upright. From the time we begin to spend most of our time upright, at about age two, until about age 10, there is a diminishment in the nutrient-providing capillary beds that supply the discs and take away the waste products of cell activity. It seems that the pressure of standing causes this diminishment. Therefore, after the age of 10, the supply of nutrients to the discs occurs through diffusion from tiny capillary beds in the subchondral bone above the end-plates of the vertebrae, and through diffusion from capillaries in the outer layers of the anulus, or outer edge, of the discs.

This diagram from Chirogeek.com illustrates the process of diffusion. The pink balls are nutrients. The mauve plates are the subchondral bones containing capillary beds. As shown here, the capillaries don’t go directly into the disc from the top and bottom after the age of 10, though there are still some capillaries that enter the outer edges of the disc.

It seems a miracle that this diffusion can occur. The better hydrated the discs, the more easily that nutrients can diffuse into them. It is easier to travel through water than through dense matter. And this is where yoga can help to improve nutrition to the discs. The movements of yoga in flexing, extending, and twisting the spine cause gentle pressure on the discs. Imagine squeezing a sponge and then putting it in a bowl of water. When you release the squeeze, the sponge soaks up the water. This is what happens to the discs when they are gently squeezed and released through the movements of yoga. The release creates a bit of a vacuum, into which water-bearing nutrients can flow. Obviously, staying well hydrated is important too.

It is often said that a flexible spine is a healthy spine, and a healthy spine is what keeps us young. With the understanding of the physiology of the discs, it is easy to see how doing yoga, drinking enough water, and getting enough sleep (which gives the discs time to re-hydrate in a non-weight-bearing position) all contribute to keeping us healthy and pain-free. Dried out discs don’t receive as much nourishment. This can lead to chronic lower back pain and possible disc degeneration—conditions that often occur as we age.

I am grateful to Judith Lasater for pointing me in the direction of better understanding why yoga is so beneficial for a healthy spine.

As a common-sense caution, yoga might not be appropriate if you already have a problem with your spine or discs. Seek professional advice if this is the case for you, before beginning to add yoga to your life.

P.S. If you’d like to read about the sacroiliac joint and how to prevent pain there, here is an excellent article by Judith Lasater.