More Effects of Slouched Posture: Muscle Imbalances, Spinal Stresses, and Into Old Age

Slouched posture "caves" in the chest and restricts breathing. Taking a deep breath stretches the opposing front chest muscles that may have shortened and tightened, and helps bring back the shoulders and straightens the mid back.

Sometime slouched posture with forward head leads to the tendency of the entire body to lean forward of the center of gravity—as the head goes, so does the body. The pelvis rotates backward, almost as if trying to pull the trunk erect, and in the process pulls back on and flattens the lumbar spine. Hip flexors (front thigh and hip muscles) elongate and weaken, and hip extensors (gluts, and hamstrings at back of thigh) shorten and tighten. With loss of the normal lumbar lordotic curve ( "Flat– back Syndrome") the body tends to lean forward when sitting, walking or standing. As with forward neck/head, the added weight of the out–of–balance upper body requires more force applied by the back extensors to keep the upper body from falling forward—causing them to be in a constant state of tightness. The muscles that bend the back forward—not back muscles at all but front (anterior) abdominals—have little to do and become weakened. See Fix the Posture

Slouched Sitting Posture: Many of us spend more time sitting than standing. Some of us work leaning forward, our heads craned toward the computer screen. Some of us curve our backs into a big "C" so that we sit on our lower backs, pelvis rotated back, which rounds the lower back into kephosis, reversing the normal lordotic curve.
For the sake of keeping the neck and head erect, neutral sitting posture in a chair with lumbar support is best. Interestingly, Dr. Bashir et al did a study using a positional MRI machine to image the spinal discs of subjects in three sitting postures:
1. Hunched forward (kyphotic lower back)
2. Upright at a back–thigh 90 degree angle with knees bent and feet flat on the floor,
3. Upright at a 135 degrees back–thigh angle (pelvis boosted up with a wedge–shaped bolster) and feet flat on the floor (tilts pelvis forward increasing lumbar lordosis).
    The authors found that intervertebral discs showed less compression with increasing lumbar lordosis. "Slouched posture" showed the most disc compression. The 135 degree "position was shown to cause the least 'strain' on the lumbar spine, most significantly when compared with an upright 90 degree sitting posture." (But how do you stay in the chair without sliding off? You'd have to be strapped in.) They do not make clear if the 90 degree sitting position was with a lumbar support, which helps maintain the lumbar lordotic curve effectively as long as one sits back in the chair against the lumbar support.

The Aging Disc: Even a lifetime of balanced posture and moving in posturally healthy ways will result in normal wear and tear of the spine over time. The shock absorbers of the spine, the intervertebral discs, lose water content, going from 90% down to 65% water, which causes loss of disc height. Body weight becomes increasingly borne by the more delicate rear vertebral facet joints, which over-stresses them and leads to new bone growth (bone-spurs, arthritic changes) in the body's attempt to thicken and stabilize them. Acceleration of this spinal aging process may occur from an acute injury as in a car accident or from the many small stresses of poor posture. Chronic hyperextension (hyperlordosis) or hyperflexion (round backed), eventually accelerate arthritic degeneration of the spine. "Repeated eccentric* (Force in a direction the spine is not designed to accept) and torsional (twisting) loading and recurrent microtrauma result in tears in the annular fibers" (tough outer layer of the disc) and lead to the gel-like nucleus losing water content faster. See emedicine article: Low Back Pain and Sciatica

(Roef, 1960. A Study of the Mechanics of Spinal Injuries), Mechanical stress tests done on spinal sections from human cadavers, both young and old.
— The disc of normal height and fluid content is very resistant to compression. The nucleus does not alter in shape or position on compression or flexion. The annulus bulges very little. On increasing compression the vertebral body breaks before the disc does.
— If the nucleus pulposus has lost fluid pressure, as in the aged spine, there is abnormal mobility between vertebral bodies. On gentle compression or flexion the annulus protrudes on the concave side—not on the convex side as is commonly thought.
— Disc prolapse consists mainly of the outer layer (annulus); and occurs only if the nucleus pulposus has lower fluid pressure and the annulus is lax and protrudes easily.
— In the normal disc, hyperextension or hyperflexion do not easily cause rupture of spinal ligaments but rotation forces can easily cause ligament rupture and dislocation.
— A combination of rotation and compression can produce almost every kind of spinal injury.

Effect of Faulty Lower Back Posture on Vertebra:
— If the pelvis tilts forward, the low back is brought into excessive extension or hyper-lordosis, which shifts more of upper body weight onto the relatively delicate rear vertebral joints making them prone to damage. Also the excessive curve crowds the rear vertebral joints, and the spaces (foramina) through which nerve roots travel become narrowed (see middle picture of illustration below); nerve impingement is risked if pre-existing disc degeneration has caused loss of disc height, bone spurring and stenosis (narrowing) of foramina through which nerve roots leave the spine. The large central canal containing the Cauda Equina (or spinal cord in thoracic and cervical spine) may also be narrowed.


Illustration 4. Effect of Extension and Flexion of Lumbar Spine on Vertebral Anatomy

Effect of Extension and Flexion on Intervertebral Discs: If the pelvis tilts backward, bringing the lumbar spine flat, weight is borne more by the discs—a good thing up to a point—but as the forward curve (flexion, see right picture of illus. 4 above) increases, such as when bending forward, slouched sitting, or any sit-up type exercises, all the weight of the upper body is borne on the discs, increasing their internal pressure up to two-fold (during sit-ups). The worst maneuver for increasing intradiscal pressure and also increasing the risk of a disc tear or herniation, is to lift weight with a curved forward/flexed spine. Direct measurements of intradiscal pressure showed 2.75 times the pressure compared to standing in neutral posture. And the heavier the weight, the greater the load on the disc. See "The Lumbar Spine: An Orthopaedic Challenge" by Alf L. Nachemson. (However, bending forward enlarges the nerve root foramina, which is the reason patients with severe nerve root compression may get relief walking or sitting with their backs rounded in flexion.)

Slouched Posture into Old Age: With time and arthritic degeneration, spinal flexibility is lost and all the varieties of poor posture result in fixed spinal changes—essentially permanent deformities.
— A fixed, excessive kyphotic thoracic curve can't be changed without serious surgery. The resulting forward head and neck can only be minimally improved by standing as erect as possible and maintaining optimal lumbar lordosis. But even a little improvement is better than slouching, which over time causes progression of the curvature.
— Forward head posture causes the head's weight to press unevenly on the cervical spine. Uneven pressure hastens disc degeneration as one side of the containment structure wears out (cracking, thinning, allowing moisture loss) more than the other. The bulge worsens, eventually desiccating and hardening. See link to Dr. Bookspan's article.
— Straightening of the cervical lordotic curve also becomes permanent with time; see below: "Loss of normal lordotic curve in the cervical spine." (In my case, because of arthritic degeneration, my cervical spine has minimal flexibility. I can barely bend my neck to the sides*, and the lordotic curve is almost nonexistent. Thankfully my upper back is still flexible. I can reduce the kyphosis so that my neck is in a more stable position over my shoulders.) *Now in 2013, I have discovered that part of my cervical inflexibility was due to weakness of supporting muscle and not entirely to arthritis. Weak muscles that must support a critical structure such as the neck need to be tight to compensate for weakness. And as those muscles strengthen, they relax. Thus as my neck muscles were able to strengthen due to improved posture, my neck has become more flexible, though not as flexible as I'd like, but much better than even a year ago.
— In the lower back also, loss of the normal lumbar lordotic curve can become permanent. (I had believed my lumbar lordotic curve was lost to arthritic degeneration, which in an MRI looked almost as bad as my cervical spine, but then discovered that my pelvis was "locked" in a back-tilted position due to tightness of back hip extensors (hamstrings). Doing a "dead lift hamstring stretch" during chores helped me regain a somewhat normal lumbar curve. Definitely there's lack of flexibilty as I can't "overextend" my lower back, but that's not necessary for balanced posture.)
If lower back surgery is ever considered, preservation and/or return of the normal lordotic curve should be insured. Back surgeries often fail without this step. See Flat Back Syndrome — Dr. Justin Paquette Interview.
— Same goes for cervical spine surgery. Outcomes are much better with preservation and/or return of the normal cervical lordotic curve.

Loss of normal lordotic curve in the cervical spine seems to be common in neck pain sufferers—I have it. (see my MRI) Several factors may be involved: 1–neck extensors too weak from injury or overuse atrophy to both pull the head back and bend the neck into extension (lordosis), 2–laxity of spinal ligaments because of injury, or shrinkage of disc height (Degenerative Disc Disease), 3–wedging of vertebral bodies from congenital causes, compression fracture or low bone density.
Long term forward head posture aggravates all the preceding, and "the (off-balance) weight of the head can cause progression of the curvature." (See "A Patient's Guide to Cervical Kyphosis" from U. Maryland Spine Program.) Without a cervical lordotic curve the only alternative to reducing pain from stressed back neck extensors is to maintain a posture where the neck is as straight as possible, which entails reducing thoracic kyphosis and maintaining a normal lumbar lordotic curve.


Continue to How Slouched Posture Causes Neck Pain





                                                     


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