How posture affects disc pressure
Let’s first take a look at the science behind sitting and then discuss how to do it properly. Nachemson and Elfstrom (1970) studied what happens to the intervertebral discs (IVDs) during different seating positions. The pressure that occurs within your IVDs when you sit (especially between the 3rd and 4th lumbar vertebrae) is at its least when the spine and hips are at 100 and 110 degrees. Sitting with your hips at 80 or 90 degrees results in IVD pressure increasing upwards of nearly 200%. The diagram below demonstrates IVD pressure when sitting in various positions according to the study done by Nachemson and Elfstrom.
Another study by Andersson et al (1974) found similar findings when they assessed how the spine is affected when sitting in a chair, at a desk, in a wheelchair and in a car. They also concluded that the highest level of pressure occurred in the flexed or forward sitting posture with the hips at 80 degrees and the lowest when the hips are at 100 degrees.
Not only is the low back significantly affected during poor sitting postures, but also the neck and upper spine as well. A study by Dvorak et al (1991) found that sitting in a flexed position increased cervical disc pressure and muscle activation, however, they noted that the most important effects were that of tension on the cervical spinal cord, brain stem and nerve roots. Several other authors also noted the physical effects that occur from poor long-term sitting posture such as a forward head carriage, increased upper cervical curvature, decreased lower cervical curvature, increased upper thoracic kyphosis (hyperkyphosis), shoulder dysfunction and elevation of the first and second ribs (Lafferty-Braun and Amundson, 1989; Ayub, Glasheen-Wray and Kraus, 1984; Saunders and Saunders, 1993; Darnell, 1983).
This image demonstrates common mistakes when sitting at a desk. Not only is the sitting position not adequate but the screen is also too low.
How do I fix my posture while sitting?
It’s important to note that the back angle is not the most efficient way to address your sitting posture – the key is in the angle of your hips relevant to your spine. For example, if you had your back-rest set at 110 degrees (image 1) then you are essentially leaning back away from your desk and this will make you stretch your arms and head out further to reach the desk and screen. It also does not support your spinal curvatures well and will lead to spinal strain. It is therefore recommended that the backrest be set at 90 degrees and sit on a seat wedge. This will allow the hips to sit at 100 degrees and therefore accomplish the same effect without the need to lean or stretch forward and allow your spine to sit upright with minimum effort. Your spinal curvatures will also be in a neutral position.
The image below demonstrates the correct desk posture. The backrest is at 90 degrees and the hips are at 100 degrees. The chair is as close to the desk as it can be so your arms are not stretched out to reach the keyboard and mouse and the screen is at eye level. Feet are flat on the floor (no angled footrests)
Poor sitting posture at work is not the only time your spine is at risk; sitting at home on the sofa can also lead to long-term spinal problems if it is too deep, too low or too soft.
From left to right: the first image demonstrates the worst type of sitting posture, which most commonly occurs when sitting on your sofa (190% IVD pressure), which will lead to chronic repetitive spinal injury, neck and shoulder dysfunction. The second image demonstrates better sitting posture, but still not perfect (140% IVD pressure), this will lead to stress and discomfort in the low back, neck and shoulders. The third and fourth image demonstrates perfect sitting posture (normal disc pressure – 110%).
Poor sitting posture is one of the hardest bad habits to break and many people tell me that they love to sit on their sofa as it’s so comfortable or that they always find themselves slouching. With a little effort and dedication, you can improve your spinal health, reduce the risk of injury and long-term spinal problems and still be comfortable by addressing a simple daily habit.
- Sitting with a 90 degree backrest and your hips at 100 degrees is the optimal sitting position and will allow your spine to sit upright with minimal effort
- Sitting flexed or bent over your desk increases the risk of long-term spinal health problems
- Sitting with the back rest at 90 degrees and your hips at 90 degrees is not ideal and can still lead to spinal problems.
- Sitting on a sofa creates enormous pressure in your low back (nearly 200%) and will also lead to neck and shoulder problems
A seat wedge is a very simple remedy for most poor sitting postures
The Wider Dangers of Sitting Excessively
Many of us spend a lot of time sitting during an average day. We spend most of the day at our desks. In the car, while we drive to work or run errands. On the sofa with our iPads, books, or remotes. Because of this kind of sedentary lifestyle, some of the top health experts have said that sitting is the new smoking. This means that the risks of spending too much time sitting is having serious effects on our overall health.
What does the research say about sitting too much?
Researchers have found that sitting for long periods of time makes you more likely to get serious diseases like cancer, heart disease, and type 2 diabetes. With more and more studies being done on this topic every day. Even if you work out a lot, sitting too much is bad for your health. Unless you have a job that keeps you moving, you probably spend most of your time sitting down when you’re not exercising. And that would make you an “active couch potato,” a term coined by an Australian researcher to describe people who work out but spend most of their day sitting down. A 12-year study of more than 17,000 Canadians found that, no matter how much they worked out, the more time people spent sitting, the shorter lives people lived.
Our Top Tips for Reducing Your Sitting Time
We have given you tips on how to sit with better posture; however, here are our tips to be more active in general and reduce your time sitting.
- Taking Phone Calls – Using a headset to take calls and walk around the house or the block while talking on the phone.
- Take a break from the screen – Get up and move around during commercials if you must watch TV. Get up from your desk every so often and do something other than stare at a screen; for example, get a drink of water, stroll around the block, or chat with a co-worker. A phone reminder or a post-it note at eye level can help if you have trouble remembering to take breaks.
- Stand instead of sitting when possible – Standing adjustable desks are becoming increasingly popular, and it’s for a good reason. Standing has been shown to reduce tiredness and boost productivity.
- Mind where you park – A great way to sit less is to park further away from anywhere you are going. A little willpower to do this simple thing can make a big difference to your step count while reducing your overall sitting time.
- Go the long route – Any time you are walking to a meeting, going shopping, or visiting friends. Go the long route, talk the time to walk a little further any chance you can get.
- Walk after each meal – Creating a simple habit, like a five or ten-minute walk after each meal, can also dramatically reduce the time you spend sedentary.
We hope you have found this article informative. If you are looking for any advice or help with chiropractic adjustment please book an appointment.
- Dvorak, J., Panjabi, M.M., Novotny, J.E. and Antinnes. J.A. (1991). In vivo flexion/extension of the normal cervical spine. Journal of Orthopaedic Research, 9, 828-834.
- Lafferty-Braun, B. and Amundson, L.R. (1989). Quantitative assessment of head and shoulder posture. Archive of Physical Medicine and Rehabilitation, 70, 322-329
- Ayub, E., Glasheen-Wray, M. and Kraus, S. (1984). Head posture: a case study of the effects of the rest position of the mandible. Journal of Orthopaedic and Sports Physical therapy, 8, 179-183
- Darnell, M. W. (1983). A proposed chronology of events for forward head posture. Journal of Cranio-mandibular Practice, 1, 49-54
Saunders, H.D. and Saunders, R. (1993). Evaluation, treatment and prevention of musculoskeletal disorders, Vol 1, Educational Opportunities, Minnesota.
- Nachemson, A. and Elfstrom, G. (1970). Intravital dynamic pressure measurements in lumbar discs. A study of common movements, manoeuvres and exercises. Scandinavian Journal of Rehabilitation Medicine, 1, 1-40.
- Colinda C. J. M. Simons, Laura A. E. Hughes, Manon van Engeland, R. Alexandra Goldbohm, Piet A. van den Brandt, Matty P. Weijenberg (2013), Physical Activity, Occupational Sitting Time, and Colorectal Cancer Risk in the Netherlands Cohort Study, American Journal of Epidemiology, Volume 177, Issue 6, 15 March 2013, Pages 514–530, https://doi.org/10.1093/aje/kws280
- Dempsey, P.C., Owen, N., Yates, T.E. (2016) Sitting Less and Moving More: Improved Glycaemic Control for Type 2 Diabetes Prevention and Management. Curr Diab Rep 16, 114. https://doi.org/10.1007/s11892-016-0797-4
- Katzmarzyk PT, Church TS, Craig CL, Bouchard C (2009) Sitting time and mortality from all causes, cardiovascular disease, and cancer. Med Sci Sports Exerc. May;41(5):998-1005. doi: 10.1249/MSS.0b013e3181930355. PMID: 19346988.