The Confusion About Curves
Updated: Jan 20, 2021
The hope of every yoga practitioner is for their asana practice to enhance wellness and vitality while making their time on the mat therapeutic and injury preventative. Yoga can provide these objectives so long as postures are constructed according to the body’s natural design and function. The closer practice adheres to alignment and body mechanics - based upon anatomy - the more powerful yoga’s effectiveness and less the likelihood of injury.
The specifics of spinal mechanics are generally not explored in yoga trainings and are usually misapplied in practice. All too often, the actual instructions teachers give to their classes run contrary to its function.
Understanding how the curves of the spine function is fundamental to all asana. In this blog, we will review side-bending and back-bending postures. Skillful engagement of the spinal curves determines whether our yoga practices take the role of healer or slayer.
Two primary avoidances: Spinal compression and Muscular imbalance
Excessive deepening of a curve causes both. Let’s first look at the general design of a spinal curve. A curve has two sides. The hollow side of a curve is referred to as the concavity. The rounded side of the curve is called the convexity. When a curve is more concave, it compresses and its mobility is restricted. When a curve is more convex, it becomes more unstable but gains in its mobility.
First avoidance: Spinal compression
Spinal compression can occur on the concave side of the cervical and lumbar curves. This is where the spinal discs and nerve roots are vulnerable. The cervical and lumbar curves are naturally convex toward the anterior and concave toward the posterior, which is referred to as lordosis. If the curve becomes overly deep, or hyper-lordotic, the discs wedge and spinal joints (facets) tighten and constrict the opening for the spinal nerve roots. Significant disc and nerve injury can occur with either sudden extension, like a whiplash, or if posture is chronically poor and hyper-lordotic.
Avoid bending and compressing sharply into the concavity. Instead, lengthen the concave side of the spine, from the “hip to the pit”.
The idea of lengthening the concavity can seem counterintuitive or confusing. Most students have learned to specifically lengthen the musculature of the convex side, yet mechanically, the correct action in the posture is the opposite.
Second avoidance: Muscular imbalance
Balanced muscle tension and tone is an important aspect of posture, especially in the supportive para-spinal muscles. Yoga embodies the principle of Samasthiti, the “quality” where tension, tone, and energy between opposing regions of the body are in balance. Samasthiti does not imply that the actual muscle mass, strength, flexibility, or range of motion are physically equal - but instead, the functional relationships are in balance; one muscle group does not unnaturally overpower its opposing muscle group. This is similar to balancing the line tension along the various sides of a mast or pole. In body mechanics, this is the principle of co-activation, a valuable tool utilized in yoga therapy.
Many yogis are familiar with the term Samasthiti used as an alternative name for Tadasana, the Mountain pose, where it describes the principle of steady and even standing. However, it is useful to embrace Samasthiti’s expanded definition as the “quality” of equal tension in every aspect of every posture.
Perhaps the best way to understand muscle mechanics and balanced tension in spinal curves is to review the actions of muscles in the presence of scoliosis, a lateral curvature in the spine. Ideally, the spine remains aligned on the body’s vertical central axis without any lateral curvature. Should the spine shift laterally off its axis, the stresses of gravity and heel strike cause many compensations.
When the spine shifts off its axis, curvatures can form. Muscle strength and even its mass becomes asymmetric. On the concave side of the curvature, muscles shorten because they have less distance to travel. When muscles shorten, they become stronger and more efficient. This is seen with aging; to compensate for loss of mass, muscles shorten to increase their efficiency. Muscles along the convexity are forced to lengthen to accommodate for the additional distance they must travel. This reduces their efficiency and causes them to weaken. Scoliosis can become a debilitating condition. From a yoga therapy perspective, there are methods to address this muscular imbalance. Avoid bending and compressing the concave side of the spine is perhaps the primary concern. A specific therapy to employ are one-legged balance poses. They strengthen the muscles along the convexity. It is best to perform balance poses only on the convex side of the spine when there is significant scoliosis or at least to repeat balancing on the convex side a second time.
Lengthen the side being bent toward and contract the muscles on the outer, convex side of the spine to enable controlled, graceful, and safe bending.
These principles also apply to all spines, not only those with scoliosis These procedures do not reduce flexibility but instead, enables postures to deepen with less chance of injury. The type of contraction engaged on of the convex side of the spine is called eccentric contraction.
Side Bending Postures
In poses such as Triangle, Trikonasana, and Extended Side-Angle, Parsvakonasana, the side being bent toward tends to form a concavity. The instructions and actual intention of many teachers is to lengthen and stretch the muscles along the convexity, or the “top” of the pose. From the point of view of the intention of the posture’s outer appearance, this would seem appropriate. However, the mechanics of the spine are opposite. Instead, lengthen the “lower” side body, where the spine is forming a concavity. Lengthen from the hip to a deepened armpit. To balance the action, contract the muscles of the convexity, supporting and letting the side bend gracefully as the posture deepens. This enlists the quality of Samasthiti and maintains balanced tension between the two opposing sides of the spine.
When muscles feel tight, the most common, go-to idea is to stretch them. However, the sensation of tightness may instead be coming from torn and weakened muscles. In fact, when muscles are simply tight, they less often produce pain since they are not being challenged. Their opposing muscles or ones local to them generally have to work harder and are more at risk in becoming traumatized and producing pain sensations.
Anterior-Posterior spinal curves
The same principles used in movement of the spine laterally equally apply to the curves that align anterior and posterior from the central axis. These are the curves normally formed during early child development.
Chronically poor postures and excessively deep arching in “back-bends” can cause compression and muscular imbalance in the same fashion as with lateral curves. In the lumbar and cervical spines, extension is already built into their natural design. Taking them into hyper-extension is undesirable but commonly practiced, thereby increasing compression into the discs and nerve roots. Discs easily budge or rupture and nerves become inflamed, all causing pain and dysfunction and unnecessary wear and tear.
In hip extension postures, such as Natarajasana, the Dancer's Pose, the lumbar spine is often forced to extend, not the hip. The hip only has approximately 10° range of motion in extension when the knee is bent, Since the lumbar spine is already in extension with its natural lordosis, it is easily and often exploited. This causes spinal compression and is a common way to injure the lower back. For those familiar with yogic philosophy, this is an example of Asteya; stealing and exploiting the flexibility of the lumbar spine for the sake of the posture.
Stabilizing the spine using Bandhas
The most effective method to prevent compression and hyper-extension in the lumbar spine is to engage the actions of Mula Bandha, Uddiyana Bandha, and Manipura chakra. This is accomplished by gliding the tailbone forward (Mula Bandha), gliding the xiphoid or tip of the breastbone posterior (Uddiyana Bandha), and drawing the navel inward (Manipura Chakra). This procedure stabilizes the lumbar spine and prevents hyper-extension. It enables “back-bends” to initiate from the thoracic spine and not exploit the naturally-extended lumbar and cervical curves. Back-bends are best performed as chest openers, which engage extension of the thoracic spine. This approach does not restrict back-bend postures but instead, takes them deeper and more safely - deeper by using the untapped flexibility hidden thoracic extension and more safely by avoiding compression of the lumbar spine. This is an example of the quality of equal tension, or Samasthiti.
It is important to establish a lumbar curve that is egg-shaped before engaging the bandhas. This is easiest to accomplish by tilting the pelvis forward. The egg-shaped curve is the most efficient position for the lumbar spine and the lower torso muscles are in ideal balance. Ideally the lumbar spine maintains this curve configuration - in all postures and at all times. The egg is never crushed nor increased to three or four.
An egg-shaped curve is the most efficient position for the lumbar spine.
Muscularly, the muscles of the posterior lower back, the abdominals, and the centrally-located Psoas group all contract with Samasthiti. These actions occur when the bandhas are engaged. When all three muscles are in balance, you will know you have arrived when the lumbar spine forming into an egg-shaped curve. The good news is that all these actions are linked together and take place at the same time.
Before engaging the bandhas and balancing the musculature, is important to always glide the thighs posterior, which naturally occurs when the pelvis is tilted forward. Do not allow them to pop forward when the bandhas are engaged. This topic is a more involved than presented here and available in the book in full detail but these cues alone will help with lower back stabilization in "back-bends".
The Cervical spine
The cervical spine also has a posterior concavity. To begin movement, draw the neck posterior from the hyoid bone posterior, approximately at the center of the cervical spine; then lift its outer horns up slightly to behind the ears. This action de-compresses the spine and increases its mobility. All ranges of motion initiate with this action. In cases of a straight spine that can occur from a Whiplash injury, the best approach is to only lift the base of the skull gently superior, not from the hyoid bone.
The thoracic spine, the least mobile spinal region, should be the first place to engage, either in a back-bend or any posture that involves the whole body. The cervical spine, as is the lumbar spine, already in a natural extended “back-bend” concavity. These two regions begin their movement after the thoracic spine initiates the posture; given the chance to utilize its flexibility before the more flexible regions dominate. When the cervical spine extends posterior, the anterior muscles on the front of the neck contract (eccentric contraction), controlling and limiting the degree of cervical hyper-extension as the head extends back.
“Back-bends” initiate from the thoracic spine; then followed by controlled lumbar and cervical extension.
The Thoracic curve
Unlike the cervical and lumbar curves, the thoracic spine has a convexity rounded toward the posterior, which is termed kyphosis. Its concavity is anterior. This creates the necessary space or cavity for the heart and lungs and is the remnant of the fetal "C" shaped curve. The muscles of the anterior shoulders and chest are shorter than the muscles of the upper back, in part due to the thoracic concavity. As a result, the anterior musculature is approximately 30% stronger than the opposing upper back muscles. This natural imbalance, along with a first-world lifestyle that is anterior body-based, makes the emphatic case to both strengthen the upper back muscles and maximize its flexibility.
To activate thoracic extension, which enables flexibility, the chest opens by pressing the heart forward and lengthening the collar bones wide. The shoulder blades remain on the back body, gliding toward the spine with the bottom tips of the shoulder blades pressing forward.
Because the arms attach to the shoulders, they are structures of the back body, which may be a new thought for some of us. When moving the arms, first and as much as possible, engage the muscles of the upper back since the chest muscles will quickly overpower the upper back's weaker muscles Another detail, although beyond this discussion is that arm engagement and shoulder mechanics follow the course of the Latissimus dorsi muscle from its origin to insertion.
Like a compressed spring, there is potential energy stored on the concave side of all spinal curves and increases as it compresses. Yoga teachers often refer to back-bend postures as emotionally releasing. When curves de-compress, such as when the thoracic spine is lengthened and extended, kinetic energy is liberated. Yogis will sometimes experience an accompanying energetic or emotional release.
Moving the spine according to its design and mechanics will ensure a safe and liberating practice. In time, these concepts, whether new or not, will become instinctive. Hopefully, the excitement of applying precise alignment and seeing its quick results of greater flexibility and freedom of movement will encourage additional alignment exploration throughout the body.
*An additional note on Scoliosis: Scoliosis causes compensations in the positioning of the hips, shoulders, and head and neck. Scoliosis can also skew the focal distances of the eyes, causing additional head tilt to compensate. To note, not only can scoliosis cause these compensations but the imbalances themselves are often what causes scoliosis itself.