There are many postures in yoga and what I’m going to discuss today about the lumbar spine carries over into mainly the standing postures, which have the highest carryover of function into our daily activities.
The spine has 4 physiologic or anatomical curves and if standing with optimal posture we would be standing in what is called a neutral spine. When viewing the body from the side in optimal posture and focusing on the posterior aspect (backside) of the body you would see that the cervical curve is concave; thoracic curve is convex; lumbar curve is concave; and the sacral curve is convex.
These curves reciprocate and balance one another, providing added strength for the vertebral (spinal) column to withstand compressive loads. The lumbar curve is there because of the curve of the sacrum and without getting to technical the shape of the lumbosacral disc is wedge –shaped and so is L5.
The remainder of the lumbar lordosis (curve) is completed simply by inclination of the vertebrae above L5. The structural liability of the lumbar stems from the angle of the sacrum but the body has built in back-up systems for stabilization. Although the lumbar vertebrae can be encouraged to form a straight column this is not the shape that should be taken on by the lumbar spine in an upright posture.
By being curved the lumbar spine is protected to a substantial extent from compressive forces and shocks that are absorbed by ligaments and muscles. In a straight spine, the compressive force would be transmitted through the vertebral bodies and discs, here the only mechanism to protect the lumbar vertebrae would be the shock absorbing capacity of the discs, this increases wear and tear, and the only prize for unnecessary wear and tear is pain and early degenerative changes. Degeneration suspends function.
In many yoga classes and books there are many cues or descriptions for aligning the spine. Some of the most common cues are lengthening, straighten and to a degree the word neutral, unfortunately this has been interpreted as taking out the curves that are inherent to the spine, especially in the standing postures. I say this because of my experiences in many yoga classes as the student.
The pose Utkatasana or known by other names such as Thuderbolt, Fierce or Chair Pose, this pose you either stand with feet hips width apart or together; the knees bend and hips drop as if you were going to sit; once there, the cue tucking of the tail is given and this creates a straight or flat lumbar spine; remember by taking out the curve and straightening the lumbar spine the compressive forces have now been diverted into the vertebrae and discs; by giving the cue ‘ imagine you are sitting in a chair’, the body makes the attempt to restore lumbar curve by extending the hips, but yet the student is told to maintain the straight or flat spine, making this posture uncomfortable and painful on the lower back. It also tightens the very muscle that is chronically tight on people---the hamstring---by tucking the tail, this moves the pelvis into a posterior pelvic tilt, to achieve this one of the muscles that must be contracted is the upper hamstring.
This is a strength pose and strengthens the very muscles you use that mimic the posture such as sitting on a chair or on the toilet if done properly. The anatomical curves for the neutral spine range must be determined for each individual, based on the available range of motion, taking into consideration a pain free range.
When trying to work with a neutral spine its best to work in between the extreme ranges of an excessive lumbar curve (Donald Duck posture) and a straight, flat low back (Pink Panther posture).
Bogduk, Nikolai : Clinical Anatomy of the Lumbar Spine & Sacrum
Saunders, H. Duane: Evaluation, Treatment and Prevention of Musculoskeletal Disorders
Core Power 200 hour Certification Manual