Posture in Health and Disease

Posture in health and disease is a huge topic of discussion and very important for everyone to understand (in my opinion). Your posture, the shape and function of your spine is more than just about back pain, it has an impact on your health and quality of life. Poor posture or abnormal posture adaptations fall into a category of injury known as Cumulative Injury Disorder¹. The cumulative injury cycle as defined by Hammer and Leahy (1999) results from repetitive injury, constant pressure or constant tension type mechanisms.

Hammer and Leahy (1999) discuss this injury with a proportional model:

Where I = Insult to the tissue, N = number of repetitions, F = force or tension of each repetition as a percentage of maximum muscle strength, A = amplitude of each repetition and R = relaxation time between each repetition. In the example of posture; the Force loads are constant or unchanging, therefore F high. As the Force is constant, the Number of repetitions is near zero as are the Amplitude and Relaxation, because constant means the is no relaxation between the repetitions. This results in Insult or injury to the tissues being high with gradual effect over time.

In the absence of external loads and forces (e.g. picking up or holding objects with any mass), the single largest contributor to loading the structures of the lower back is increased spinal muscle activity². In other words, carrying a bag on your back or an object in front of you (e.g. boxes), increases both muscle activity in your low back (muscle contraction) and increases the pressure on the structures of the lower back (e.g. the vertebrae and discs). The same process of increased muscle activity occurs when the spine moves and adapts to different body postures. As we discussed in our blog “Your Spine: The Basics” the spine is nothing more than a lever system that requires balance and symmetry. As you apply a load to say, the right side of the spine for example, the body will contract the muscles on the left side to counter that load, keeping you standing upright. The spine is the lever in middle that these opposing loads are applied to, allowing you to remain upright and balanced. Think of it like a balanced see saw with two arms and a fulcrum in the middle. However, because the spine is a biological see saw, applying loads to the spine that may be repetitive or sustained, over time can cause injury and tissue damage.

It has been shown that sustained, increased compressive loads to the spinal discs triggers the release of substances called matrix metalloproteinases³. These substances cause a breakdown of the disc tissue, they are catabolic in their function. Different substances in the body can be anabolic, meaning they build things up, or catabolic, meaning they break things down. Lets now throw into the mix someone who smokes, which as discussed in our previous blog on smoking and spinal health, which accelerates disc degeneration, disc disease and leading to back pain.

These facts, coupled with physiological laws such as Wolf’s Law of bone remodelling⁴, Davis’s Law of soft tissue remodelling, neuroplasticity (brain remodelling) and hysteresis (viscoelastic creep), suddenly poor posture becomes a mechanism that changes the tissues of the brain, muscles, discs, ligaments, tendons and eventually our bones.

Prolonged Poor Posture and Tension on the Spinal Cord and Nerves

It has been known since 1966 when Alf Breig, a neurosurgeon and researcher published books and articles into the movements, biomechanics and functions of the spinal cord during different postures⁵. When looking up, the spine goes into backwards bending (extension), during this motion, the back (posterior) aspects of the spinal cord become short and relaxed, while the front portion elongates due to tension⁵. The opposite happens during flexion. This process is known as Poisson’s effect, defined as the increase or decrease in cross-sectional area of something by changing its length with no change in its volume⁶. In other words, by putting tension through the spinal cord, like a rubber band, stretching it increases its length making it thinner, but the amount or volume of rubber remains the same. This tension placed on the spinal cord has been described as a mechanism for reduced blood flow (ischemia) to the spinal cord, leading to neurological damage^5,6.

In relation to posture in health and disease, being in a stooped or flexed position for a prolonged period of time, for example, when working at a desk, leaning forwards to see the screen. You may do this for a few hours a day. You spend a few hours a day sitting in this posture, 5 days a week, for 48 weeks the year, for a number of years, now the cumulative injury disorder hypothesis starts to make sense. Whilst it is true, the statement of “your best posture is your next posture”, this only applies when we aren’t dealing with someone who has spend many years with altered or poor posture. This statement certainly doesn’t apply when we are discussing patients with neurological disorders such as Parkinson’s disease where a stooped posture is considered part of the disease process^7,8. Whilst this may be seen as an extreme example by some readers of this blog, it leads me to simple say that these patients do exist and ignoring their posture may be detrimental to the patient with Parkinsons’ for the reasons discussed above. It also nicely leads to asking therapists the question, at what point does abnormal posture become pathological or worthwhile addressing? Is it before or after the onset of symptoms? Ignoring symptoms for a moment, is it worth addressing before the discs start to break down, as this process may well be asymptomatic, a nonpainful process. Is it not therefore, worth addressing before this occurs? I will leave you to answer these questions, I know where I stand on the subject, and I am entitled to my opinion in light of the facts discussed above. This blog post references only a small faction of the science and research going back as far the mid 1960’s.

In summary, when discussing posture in health and disease, all aspects of what poor posture is and can be is important. Some patients may have poor posture as a result of a health condition,  such as Parkinson’s. Others may go on to suffer long-term mechanical/spinal changes as a result of poor posture over time. Sustained poor posture in any direction (forwards, backwards or side to side) falls into the category of cumulative injury disorder, because it leads to the break down of the intervertebral discs and impaired function of the spinal cord and nerve roots. Whilst short-term poor posture may not have much of an impact on your overall health, these issues need to be addressed on an individual, case by case basis. I am not for a moment suggesting that all patients need to be treated identically with their posture being addressed regardless of their health status. Healthcare needs a common-sense approach, applying evidence and medicine on an individual basis for what that person needs for their health. To ignore these points addressed above may be at the detriment of the person sitting in front of you. For more information on this topic, here is a video of Dr Deed Harrison going through in detail research on the topic. Warning, he gets very excited and passionate in this video lol.

References:

1. Hammar WI, Leahy MP. Active Release Techniques: Logical Soft Tissue Treatment. In: Functional Soft Tissue Examination and Treatment by Manual Methods. 2nd ed. Gaithburg: Aspen Publishers Inc; 1999:549-562.
2. Harrison DE, Colloca CJ, Harrison DD, Janik TJ, Haas JW, Keller TS. Anterior thoracic posture increases thoracolumbar disc loading. Eur Spine J. 2005;14(3):234-242. doi:10.1007/s00586-004-0734-0
3. Hsieh AH, Lotz JC. Prolonged spinal loading induces matrix metalloproteinase-2 activation in intervertebral discs. Spine (Phila Pa 1976). 2003;28(16):1781-1788. doi:10.1097/01.BRS.0000083282.82244.F3
4. Ahn AC, Grodzinsky AJ. Relevance of collagen piezoelectricity to “Wolff’s Law”: A critical review. Med Eng Phys. 2009;31(7):733-741. doi:10.1016/j.medengphy.2009.02.006
5. Breig A, Turnbull I, Hassler O. Effects of mechanical stresses on the spinal cord in cervical spondylosis. A study on fresh cadaver material. J Neurosurg. 1966;25(1):45-56. doi:10.3171/jns.1966.25.1.0045
6. Panjabi M, White A. Biomechanics of nonacute cervical spinal cord trauma. Spine (Phila Pa 1976). 1988;13(7):838-842. http://www.ncbi.nlm.nih.gov/pubmed/3057648. Accessed July 26, 2019.
7. Doherty KM, van de Warrenburg BP, Peralta MC, et al. Postural deformities in Parkinson’s disease. Lancet Neurol. 2011;10(6):538-549. doi:10.1016/S1474-4422(11)70067-9
8. Anderson JM, Oakley PA, Harrison DE. Improving posture to reduce the symptoms of Parkinson’s: a CBP<sup>®</sup> case report with a 21 month follow-up. J Phys Ther Sci. 2019;31(2):153-158. doi:10.1589/jpts.31.153