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  • Arianne Gosselin

The Biomechanics of Leg Crossing



When helping patients understand what osteopathy is, I frequently tell them that my job is to look for motion restrictions and asymmetries in the body. Of these two variables, asymmetry is one that many people don’t even pay attention to. To illustrate this point, just think about your own posture when you sit on the couch watching your favorite show. When doing this, are you thinking about how symmetrical your body is? The answer is most likely no. Many people will sit with one leg tucked under them, one arm resting on a pillow, or with both feet up on a coffee table, ankles crossed, lower back sinking into the comfort of the couch. Sound familiar?


When sitting in this asymmetrical way, some muscles will be stretched, others will be slackened, and the tension in certain ligaments will change based on the position of your joints. If this position is then held for a long time, the body will adopt this new position as "normal". However, we know that this new position is actually abnormal, and as a result, you start running into health issues.


So how do we avoid this? Let’s start with one of the key offenders: leg crossing. When sitting with one leg crossed over the other, it creates an asymmetry in the pelvis. In a study performed by Snijders et al., it was proposed that certain muscles will experience alterations in activity and length as a result of this position. They found that “cross-legged sitting resulted in a relative elongation of the piriformis muscle of 11.7% compared to normal sitting and even 21.4% compared to standing” (Snijders et al., 2006). The aforementioned piriformis muscle is very important in the stability of your sacroiliac joint. Thus, it appears as though sitting cross-legged can be correlated to the de-stabilization of this important joint. As this joint begins losing its healthy range of motion and becomes stuck in an abnormal position, it can create unwanted health concerns throughout the whole body.


Another similar study looked not only at the length of the muscles but also at the position of the spine in a few cross-legged variations. They found that “cross-legged sitting postures showed significantly greater kyphotic curves in the lumbar and the thoracic spines and pelvic posterior tilting” (Ahn et al., 2013). Simply put, the lumbar spine (lower back) was curving in a direction that is opposite to its natural direction, and the curvature in the thoracic spine (mid-back) was being exaggerated. Neither one of these things is great for the nerves that are exiting the spine, which is why abnormal positions of the spine and restricted spinal motion lead to a wide range of symptoms.


Based on all this information, it seems like a good idea to avoid the cross-legged position in order to maintain healthy body functions. The problem is that this position has become a habit for many people. And not just that, for some people, sitting without their legs crossed is uncomfortable! This is because, as previously mentioned, the length and tone of the muscles have changed. This means that the legs must be crossed in order for the sacroiliac joints to feel stable. This is where osteopathy comes in. By combining your voluntary change in postural habits with osteopathic treatments, it is possible to re-set the resting length of your muscles and re-establish motion and symmetry in your body. The result? Less pain, better function, and a whole lot of relief.


References:


Snijders, C. J., Hermans, P. F., & Kleinrensink, G. J. (2006). Functional aspects of cross-legged sitting with special attention to piriformis muscles and sacroiliac joints. Clinical Biomechanics,21(2), 116-121. doi:10.1016/j.clinbiomech.2005.09.002


Ahn, S., Kim, S., Kang, S., Jeon, H., & Kim, Y. (2013). Asymmetrical change in the pelvis and the spine during cross-legged sitting postures. Journal of Mechanical Science and Technology,27(11), 3427-3432. doi:10.1007/s12206-013-0865-5

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