Is Sitting Really The New Smoking?
It’s a bit of a bold statement but it did get your attention. So… is sitting really killing us?
There is no doubt that sitting has become routine in today’s society. On average Australian’s sit for almost 10 hours a day!(1). We know that prolonged sitting and a sedentary life style will increase your risk of many health conditions, particularly cardiovascular and metabolic diseases, not to mention the bio-mechanical strain it places onto your musculoskeletal structures. So, it’s no secret that sitting is a significant risk factor for developing low back pain which is the number one global health burden and implies a tremendous economic strain world-wide.
When we sit our spine is forced into a flexed position and the pelvis tilts posteriorly (backwards) resulting in a loss of that natural lumbar curve (lordosis). This places significantly higher forces on the passive elements of the low back including the ligaments, joint capsules and the fibres of the posterior intervertebral disc. The majority of this pressure is localised to the L5/S1 and L4/L5 spinal segments respectively (2), coincidentally these happen to be the most common locations for a lumbar disc herniation. Sitting for a little as 20 minutes has been shown to increase ligament laxity and delay our protective muscle reflexes that support the segments of the spine during movement, potentially leading to injury generating scenario’s (2).
Creep is the term used for this gradual change in tissue properties. Passive structures, when placed under a constant load will slowly deform. For example, when sitting in a flexed posture, your upper body (head, arms and trunk) is the load, which is constantly applied to the lower back. The posterior elements of the spine (ligaments, joint capsules and muscles) are going to stretch and lengthen to relieve the tension place on the anterior parts of the spine (abdomen, vertebrae and discs) and therefore it will take longer to activate mechanoreceptors as we approach end range of motion. This delay in activation results in abnormal motor control segmentally in the spine, where we are more likely to move through the mid range of healthy joint motion and perform activities towards physiological end range, placing higher stress on tissues and leaving us venerable to injury. This is especially true in prolonged exposure to sitting, where it takes a much longer time for the lengthened tissue structures to return to normal. Just imagine this poorly controlled or “lazy” support system suddenly being placed under high demand such as going to the gym or doing some sort of extreme physical activity (or perhaps just everyday activities), can you see how this can increase your chances of injuring yourself?
There are two common reasons why we may be sitting for long periods that are generally beyond our control.
Work – Sitting at work in the office is becoming more and more common. We have to work, so what do we do?
Travel – Particularly in the car, travelling for prolonged periods sometimes cannot be avoided and often we go from sitting in the car to sitting down at work!
Subsequently, both these activities and their parameters have attracted a lot of research around how they are causing harm, and what to do to minimise it.
Office chairs have been shown to put you into approximately 70% of your maximum spinal flexion range of motion (2). Most car seats are designed for the 50th percentile male (3) and therefore totally inappropriate for the rest of the population and provide little or no support for the lumbar spine. In addition, it has been shown that a fixed lumbar support that does not match its owner can contribute to pain generation and discomfort (4) – in other words they can make the problem worse!
Lumbar supports and seating aids have been developed for both the office chairs and car seats that aim to promote a better sitting posture. Some aim to make you sit upright, such as a tilted seat pan or a wedge to sit on, where a forward tilt of the pelvis and an active upright torso aims to recover the lumbar lordosis. Replacing the regular office chair with dynamic office chair or a stability ball was another solution thought to keep the spine in a more active and supported posture. However, studies have actually found that these methods can result in increased soreness due to increased muscle activity and fatigue (2). Similarly, studies done on using a stability ball again resulted in an increased level of low back pain, plus no significant difference was seen in muscle activity, spinal loads and overall spinal posture when compared to sitting in an office chair! (5).
There are passive lumbar supports that place direct pressure to the lumbar spine allowing for increased extension locally, attempting to relax the musculature of the back while maintaining a lumbar lordosis. (De Carvello et al 2015) looked at spine posture and discomfort in prolonged simulated driving and found that when participants were given the choice to select the amount of lumbar support they thought would be comfortable for a long car drive, all participants selected at least some amount of support, however, even though participants were comfortable in the short term, pain was still not avoided in the long term when driving up to two hours (6). In other words, lumbar supports and correctly fitted chairs can be good for pain in the short term, but have little or no benefit for prolonged sitting.
Essentially, chair features are fairly limited as they only influence posture locally at the point of contact and no one feature was found to be superior to another. In the end, as long as you are still sitting, the spine is still in flexion and therefore the stresses and strain associated with flexion will still be exerted onto the tissues!
So, what about standing? Surely that’s the answer! This concept has certainly gained a lot of traction in recent years. But not so fast…. Just as a sitting posture places a flexion force through the spine, standing places the spine into extension. Studies are finding standing induced low back pain can commonly develop from as little as 15min to 45mins of static standing (7). What’s more, low back pain associated with static standing without previous injury is a predictor for the development of chronic low back pain (7).
Standing at work can definitely help reduce sedentary times, which translates to less reported upper back and neck pain plus there is evidence that suggest an overall increase in job productivity. However, without the proper training and advice in the transition to a sit-to-stand work station, problems are arising. There is evidence to suggest an increase in discomfort of the upper extremities especially of the wrist is common due to the different bio-mechanical loads at a computer station when changing from sitting to standing (it’s not simply a matter of standing up!). Also, 50% of people reported that their lower back pain persisted, with only temporary relief from sitting and immediately returned when standing again. So it seems that simply shifting from prolonged sitting position to a prolonged static standing position is not the answer either.
To sum it all up, there is no perfect sitting posture and there is no one simple solution. The take home message however is to avoid any static posture for long periods of time, and try to reduce overall sedentary behaviours. If you have to sit, be sure to move often, and the same goes for standing! Once again movement is the key! If you’re in the car, being able to adjust and move the supports can help, or better yet stopping and taking a break and actually getting out of the car is vital for preserving overall health of the seated individual.
Take home points and recommendations:
We are designed to move! It is important to reduce overall sedentary times.
Perform low level physical activity at work.
Any sitting posture is going to put strain on the spinal structures and can potentially cause pain.
Take regular rest breaks to encourage movement and try not to sit in the same posture for longer than 20 mins.
Change postures before you feel pain. Workers who changed position more often, even if the total sedentary time was the same had better health outcomes.
Static standing places the spine into extension and can therefore also cause pain in susceptible individuals.
For an 8-hour work day, a 1:1 ratio of sitting for 4 hours to standing/walking/other activities for the other 4 hours can be recommended.
If you get low back pain standing, start with more sitting time and slowly build to longer time standing. Start with 20 minute standing, then sit for 40 minutes and repeat throughout the day.
When transitioning from a standard work station to a sit-stand desk it is essential to have the proper training and education for compliance and to achieve a reduction in discomfort. In work places where appropriate training had not been carried out, there was no difference in health outcomes compared with sitting!
An adjustable monitor is necessary when moving between sitting to standing as the ergonomics of a computer work station will change when moving between the two postures.
It may be beneficial to participate in a stabilisation-based exercise program targeting trunk and hip strength, plus seeking manual therapy for low back pain as appropriate. An evidence based chiropractor would be a good starting point if you don’t already have a good provider.
References:
Active working C.I.C (2018) Australians sit almost 10 hours a day (on average) [online] Available at: http://www.getaustraliaactive.org.au [accessed 20 May 2018].
Diana De Carvalho, Diane Grondin & Jack Callaghan (2017) The impact of office chair features on lumbar lordosis, intervertebral joint and sacral tilt angles: a radiographic assessment, Erganomics, 60:10, 139-1404.
Kolich, M (2003) Automobile seat comfort: Occupant preferences vs. anthropometric accommodation, Applied Erganomics, 51, 193-207.
Reed, M and Schneider, L (1996) Lumbar support in auto seats: Conclusions from a study of preferred driving posture (SAE Technichnical Paper 960478). Warrendale, PA: SAE International.
Michael Holmes, Diana De Carvalho, Thomas Karakolis and Jack Callaghan (2015) Evaluating Abdominal and Lower-Back Muscle Activity While Performing Core Exercises on a Stability Ball and a Dynamic Office Chair, Human Factors, 57:7, 1149-1161.
Diana E. De Carvalho and Jack Callaghan (2015) Spine Posture and Discomfort During Prolonged Simulated Driving with Self-Selected Lumbar Support Prominence, Human Factors, 57:6, 976-987.
Jack Callaghan, Diana De Carvalho, Kaitlin Gallagher, Thomas Karakolis and Erika Nelson-Wong (2015) Is Standing the Solution to Sedentary Office Work? Ergonomics in Design, 20-24.
