Asymmetry in Twists

By Bernie Clark, March 9, 2022

Twisting is an asymmetric movement in that you do one side and then the other side.

How much you can twist in each direction may not be equal and rarely is for most people. One reason you can twist further to one side than the other may be due to scoliosis, which can be caused by the vertebrae being rotated, but another reason may be related to the angle of the facet joints along your spine. Or in other words, the reason may be due to the shape of your bones. The superior and inferior facets at the posterior side of the vertebrae, as shown in figure 2, have specific orientations. The superior facet of the lower vertebra comes into opposition with the inferior facet of the higher vertebra. The orientation of these pieces of the bones when they come into contact is one factor that determines how much movement is available to the vertebrae. In the lumbar spine, the facets are aligned almost vertically, with the superior facets facing inward/medially and the inferior facets facing outward/laterally. This alignment greatly restricts twisting motions in the lumbar spine. In the thoracic spine, the orientations are more front to back, rather than side to side, which facilitates twisting but limits flexion and extension movements.

FIGURE 2 A lumbar vertebra: (a) superior view; (b) lateral view. Notice that the size and orientation of the vertebral facets (in blue) are not symmetric. The facet on the right is more open than the one on the left, which means this person would be able to twist a little more to the right than to the left at this joint.

Unsurprisingly, the facets are not symmetric: the left thoracic facets often have orientations different from the right thoracic facets, but such asymmetries are less common in the lumbar facets.^[1] Right thoracic facets are oriented more vertically and point more anteriorly than left facets. This asymmetry means the restriction in movement that the facets introduce will not be the same when twisting to the left and to the right. You may find that you can twist easily to the right but not as easily or as far to the left. This may be due to muscular imbalance, fascial tightness or tension in other soft tissues, which may be changeable over time, or it might be due to the orientations of your facets, which will not change. These asymmetries are not signs of spine degeneration! They are normal.

In general, there is no correlation between the orientations of the articulating facets and age, gender or ethnic background. Barring pathologies or injuries, the orientations of your facets will not change as you grow older. Asymmetric variations in the orientation of the facets are called tropisms. When they do occur in the lumbar, they usually arise in L4/ L5 and L5/S1.^[2]

The medial/lateral orientations of the lumbar facets restrict twists and side flexions; the posterior/anterior orientations of the thoracic facets can restrict flexion/extension. As always, there is considerable variation among people, so not everyone’s facets correspond to the above generalization. Table 1 summarizes facet orientations by lumbar vertebrae, along with their standard deviations. The large standard deviations mean many people have lumbar facets that face medially/laterally; these people will have very restricted rotation in the lumbar spine. However, there are also a lot of other people whose lumbar facets face more front/back, and they will have more room to twist the lumbar spine. The lower the lumbar vertebra, the more the facets tend to face front/back; L5’s inferior facets face significantly anteriorly, matching the posterior orientation of the sacrum’s S1 superior facet. This helps to prevent the lumbar spine from sliding forward, but this is also why more twisting is available at L5/S1 than anywhere else in the lumbar segment.

TABLE 1 Angle of lumbar facets with one standard deviation. (Zero° would mean purely laterally/medially; 90° would mean purely anteriorly/posteriorly.) ^[3]

The point of the above discussion is to emphasize that your spine is not symmetric: your facets may be oriented in such a way that you can twist more to your left than your right, or vice versa. This can show up in many twisted postures, as illustrated in figure 3. In (a), a reclining twist (Jatharaparivartanasana), you may be able to lower one arm closer to the floor than when doing the pose on the other side, or you may be able to lower one leg closer to the floor than when doing the other side. In a seated twist (Ardhamatsyendrasana), (b) you may be able to turn and look further behind you to one side than the other side, or (c) to bind your arms on one side but not the other. These asymmetric differences in range of motion may be due solely to the orientation of your vertebral facets. However, the ability to twist and bind on one side but not the other may be due to a combination of factors. Notice in (c) that when twisting to the right side, the thigh is not very adducted. It is almost in line with the right hip. But when twisting to the left side, the thigh is adducted quite a bit, which makes it possible to wrap the arm around the leg and clasp hands. On this second side, the ability to twist and bind may be due more to the range of motion at the hip sockets and the shoulders than to the twisting ability of the spine. Or it may be due to a little of all these factors. Finally, notice the student in (d) can deeply twist in Revolved Side Angle Pose (Parivrttatrikonasana) to one side but not the other.

FIGURE 3 Twisting is not always symmetrical: notice the differences on the two sides of these poses. (a) Reclining Twist (Jatharaparivartanasana); (b) Seated Twist (Ardhamatsyendrasana); (c) Binding in a Seated Twist; (d) Revolved Side Angle Pose (Parivrttatrikonasana).

It is impossible to be exhaustive and list all the ways that spinal asymmetry can manifest in yoga postures, but so far, the focus has been on asymmetric twists. It is also possible for the vertebral facets to allow less or more lateral flexion of the spine. This means that you may notice you can side-bend more to one side than the other. As shown in figure 4, this may show up in standing side bends like a standing Half Moon Pose (Ardhachandrasana) or a Seated Side Bend (Parsvasukhasana).

FIGURE 4 Lateral flexion is not always symmetrical: notice the differences on the two sides of these poses. (a) Standing Half Moon Pose (Ardhachandrasana)—bending to the right is much deeper than to the left; (b) Seated Side Bend (Parsvasukhasana)— bending to the right allows this student to bring her elbow to the floor, but she cannot do that on her left side.

WHAT STOPS ME?

If any of the asymmetries in twisting postures are due to the shape of the vertebrae, yoga is not going to change this, and there is no way to lengthen the soft tissues and remove the asymmetry if it is caused by the shape of your bones. How can you tell if your asymmetries are due to the bones? If you feel stopped by compression on both sides of a pose, but you have different ranges of motion on each side, then your asymmetry is due to your bones and not your soft tissues. Compression between the facets of the vertebrae is challenging to sense, but if you can feel it, it will be a sense of stuckness deep in the midline of the body. You will sense that you just cannot move any further there. If tension in the soft tissues is limiting you, you may feel this as resistance around the ribs. Tension can be felt in the sides of the ribcage, along the back of the ribcage, or in the abdominal muscles.

Side flexion of the spine may be stopped by compression of the vertebrae, or it may arise due to the lowest ribs compressing against the top of the pelvis. Some people have very high ilia (the side of the pelvis) and even an extra rib or two. For these people, the distance from the bottom of the ribcage to the top of the pelvis is very short and they may quickly reach compression when they side-bend. You can check whether this is occurring by noticing any sensation in your waist in the direction you are bending toward. That is compression. Tension would be a tugging sensation on the opposite side of your waist and torso. Once again, if tension is limiting your range of twisting, over time you may be able to improve your range of motion. But if compression is stopping you, then you have reached your ultimate limit.

This article is excerpted from Your Upper Body, Your Yoga by Bernie Clark.

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[1] See Y. Masharawi et al., “Facet Orientation in the thoracolumbar Spine: Three-Dimensional Anatomic and Biomechanical Analysis,” Spine 29.16 (2004): 1755–63. 


[2] See R. Shane Tubbs, Mohammadali M. Shoja, and Marios Loukas (eds.), Bergman’s Comprehensive Encyclopedia of Hu man Anatomic Variation (London: Wiley-Blackwell, 2016), 35. 


[3] See Masharawi et al., “Facet Orientation.”