The spine serves to provide support as part of our skeleton and also carries the spinal cord which is part of the Central Nervous System. What is remarkable is the range of motion that it is capable of; bending forward and backward (in the sagittal plane), side to side (laterally) and twisting. Together with neck muscles, it also supports a massive 4lbs of head weight.
The diagram to the left shows the spinal column and the pelvis (left side removed). The pelvis (meaning Basin in Latin) comprises the sacrum, coccyx and the two hip bones.
The first thing you might notice is how curved the spine is. It’s far from being like ‘stack of children’s toy bricks’. This curve is achieved by each vertebra being a bit wedge shaped. In between the vertebra are tyre shaped discs (intervertebral discs) which absorb shock loads and allow movement. These are surrounded by a muscle that gives movement and support.
Most meditators move at least a bit when meditating. This maybe to change posture to improve alertness or releasing previously hidden tensions. I have noticed that there is sometimes a point in my meditation where, as I become more concentrated, my body starts sitting up straighter, more aligned; the body following the mind.
Ideally we are looking for a posture that helps us stay relaxed and alert. This suggests that there should be no muscular strain, that the body should be in a position of natural poise. In sitting, this starts from the base of the posture, the pelvis. In texts on meditation posture and dancing this is often described as having the pelvis ‘level’ so that water would not tip over the edge of the basin. One way to check this is to put your fingers under your butt between your seat (bench, cushion or chair) and feel where the sitz bones (the lowest part of the pelvis) are. When they are pointing downwards the pelvis will be level.
In an original study (“Sagittal plane alignment of the spine and gravity
A radiological and clinical evaluation” by Jean LEGAYE, Ginette DUVAL-BEAUPÈRE Acta Orthop. the authors refers to an “optimal economic balance” being indicated by “no muscular electric activity observed in the posterior [or anterior] spinal muscles”
The projection of this gravity centre is 36.2 mm (S.D. 20.6) behind the line connecting the centers of the femoral heads. This expresses an optimal economic balance : under such conditions, no muscular electric activity is observed in the posterior spinal muscles. On the contrary, if anterior tilt of the trunk occurs and the projection of the gravity centre becomes more anterior, muscular activity in the posterior musculature is detected.
It is this “optimal economic balance” that we are looking for in our meditation posture.
What happens when we are not in balance?
When in balance, each inter-vertebral disc has little or no correcting forces being applied to it. When the force of the centre of gravity of our body does not pass near the spinal cord the muscles have to work harder to stop slumping or falling back. See the diagram from the the same study.
The Bio-mechanics of Meditation Posture
While testing a prototype for a new meditation chair that has the same benefits of the Kindseat Meditation bench but taller, I became interested in the dynamics of what is happening when we sit. As an engineer I am interested in the forces and stresses that are at work in a mechanism. This article explores some of what happens as we change our sitting posture.
“Sagittal plane alignment of the spine and gravity A radiological and clinical evaluation” by Jean LEGAYE, Ginette DUVAL-BEAUPÈRE Acta OrthopBelg., 2005, 71, 213-220)
Psoas muscle and lumbar spine stability: a concept uniting existing controversies. Critical review and hypothesis http://www.ncbi.nlm.nih.gov/pubmed/11189930