Sitting Ergonomics And The Impact on Low Back Pain

Introduction

We all, at some point in our lives, will sit for a long period of time. Whether that is at a desk at work, eating dinner at the table, or sitting to watch a film. Many theories have been produced about how our posture should be during this time. From sitting up straight with no support to using specialised equipment to keep our backs in a correct and safe position. Below will discuss what the evidence says to keep our backs healthy. This page will also aim to cover ergonomics and the basic anatomy of the lower back. The prevalence of low back pain within the work environment (based on UK stats). Discuss different preventive strategies and interventions to reduce low back pain caused by sitting.

Ergonomics

Often referred to as "human factors", ergonomics is the science of applying physical and psychological principles within an environment to increase both one's productivity and well-being. The study of ergonomics can be divided into three main areas of research:

1. Physical ergonomics
2. Cognitive ergonomics
3. Organisational ergonomics

Physical ergonomics places a greater emphasis on human anatomy, physiology, and biomechanical factors influencing one's movement patterns and posture. This area of ergonomics is therefore of significant interest to physiotherapists and one in which they regularly address due to having a rich, in-depth understanding and knowledge of these factors.

Statistics in Britain

Research by Dul and Neuman, (2009) stated that ergonomics are important because they improve workplace performance. Ergonomics are an important consideration both when working from home and it the workplace.

Health and Safety Executive, (2019) complete a Health and safety at work Summary statistics for Great Britain 2019. Within this report the MSK disorders (2018/2019) are displayed and 40% of all MSK disorders are related to the back, while this does not break down I to specifics of the lower back it is clear there is an issue around wor- related ergonomics and the back. it suggests that the high occurrence is due to awkward or tiring positions, keyboard work (desk sitting), repetitive actions, and poor manual handling.

The Lower Back

Clinically relevant anatomy

The lumbar spine - This is where most back pain occurs and it has 5 vertebrae (numbered L1-L5) (Low Back Pain, 2020). In between each vertebra, there is an intervertebral disc. This is known as the intervertebral disc joint. There are also two (left and right) facet joints between each vertebra. L5 is also attached to the sacrum. The sacrum then attaches to the pelvis, creating the sacroiliac joint. (Drake, Vogl and Mitchell, 2005)

The vertebra

The lumbar vertebra

Each vertebra consists of many features, including a vertebral body, a spinous process, the spinal canal for the spinal cord, and transverse processes. There are several distinct features of the typical lumbar vertebra. These include:

• Large vertebral body
• Short and thick spinous process
• Relatively vertical facet joint
• A mammillary process on the posterior aspect of the superior articular process
• L5 has the largest body and transverse process of all vertebra

Structural function

The main function of the lumbar spine is to bear the weight of the body. It absorbs the stresses of lifting and carrying objects as well as general movement (Hines, 2018). Below discusses the structural function of the spine:

• The spine holds an increasing amount of weight as you move down into the lumbar region, for this reason, the lumbar vertebra has the larger bodies in the spine.
• Due to the relative size of the spinous process and body, the lumbar spine has the largest degree of extension.
• The lumbar spine allows flexion, extension, and lateral flexion but not rotation and this is due to the orientation of the facet joints
• The mammillary processes provide an attachment point for many lower back muscles.

The intervertebral Disc

Between each vertebra, there is an intervertebral disc. The intervertebral disc is made out of the nucleus pulposus, annulus fibrosis, and the cartilage endplates.

Nucleus pulposus - This is a highly hydrophilic substance that is located in the centre of the intervertebral disc. It acts as a shock absorber as it allows for the distribution of pressure in all directions.

Annulus fibrosis - This contains multiple fibrocartilaginous bands. It surrounds the nucleus pulposus and its main function is to protect the nucleus pulposus.

Cartilage endplates - This is found on the superior and inferior ends of the disc and represents the anatomic limit of the disc. Its main functions include protecting the contents of the disc and providing a source of nutrition to the disc (Twomey and Taylor, 1994).

Ligaments

The main ligaments of the lumbar spine include:

Anterior longitudinal ligament - This is a thick band of tissue that runs along the anterior surfaces of the vertebral bodies. It protects against hyperextension of the spine.

Posterior longitudinal ligament - This is thinner than its anterior counterpart and runs along the anterior wall of the vertebral canal. It is involved in preventing disc prolapse.

Ligamentum flavum - This runs between each consecutive laminae and is extremely elastic. Its function is to help maintain an upright posture and to resume this position after flexion. It also prevents buckling of the ligament during extension.

Interspinous ligaments - This connects consecutive spinous processes together within the spine. It mainly limits the flexion of the spine.

Supraspinous ligament - Connects the ends of each spinous process together. Helps to prevent hyperflexion

Iliolumbar ligaments - This consists of two parts, an anterior and posterior part. It plays a huge role in the stability and restricts both side flexion and rotational movement at the lumbosacral junction

Muscles of the trunk

There are multiple muscle groups that support the spine. Each plays an important role in stabilising the trunk and allowing movement into flexion, extension and rotation (Waxenbaum et al 2020).

Muscles that attach into the lumbar vertebrae:

• Erector spinae
• Interspinales
• Intertransversarii
• Latissimus dorsi
• Rotatores
• Serratus posterior inferior

The lumbar spine is also supported by the muscles of the abdomen and pelvic floor.

Flexors - external oblique, internal oblique, psoas major, psoas minor and rectus abdominis

Extensors - erector spinae, Latissimus dorsi

Lateral rotators - internal obliques, external obliques, and quadratus lumborum

Rotators - external obliques and internal obliques

Effect of sitting on anatomy

There are many studies that look into how sitting affects our spine, some of these even look into how we change physiologically.

One study found that when flexing the spine, to flatten the lumbar spine, improves the transport of metabolites in the intervertebral discs, reduces the stresses on the facet joints and gives the spine a high compressive strength. This suggests very positive effects of flexing the spine, however this study did also report negative effects including increasing stress on the annulus fibrosis and increasing the hydrostatic pressure in the nucleus pulposus. It is also important to consider that this paper is from 1985 and does not discuss who participated in the studies and therefore this may not be generalisable to the population as a whole (Adams and Hutton, 1985). Further studies have found that sitting in a flexed position also reduces the activity of abdominal muscles which play a key role in stabilizing the back (Wong et al., 2019).

Finally a recent study found that when a person sat for prolonged periods of time (for 4 hours), there was a significant reduction to the height of L4-5 intervertebral disc, however, the sample size had a female predominance and studies have found that males and females do respond to static lumbar flexion differently and therefore this may not be generalisable to the population as a whole (Billy, Lemieux and Chow, 2014).

Low Back Pain

Low back pain can be defined as pain originating in the low back region that may or may not radiate down into the legs. This pain can further be categorised by sensation such as dull or sharp pain as well as duration:

• Acute ( <6 weeks )
• Sub-acute ( 6-12 weeks )
• Chronic ( >12 weeks )

Low back pain is an extremely common disorder with a mean point prevalence rate of 18.1%. Furthermore, 38.1% of these individual's will suffer from low back pain for up to a year. This presents a vast array of knock on effects with the most notable being that on the UK economy. It is estimated that low back pain costs £1623 million annually via direct healthcare-related costs and indirectly £10668 million through avenues such informal care and loss of productivity. This is partly due to 15.5% of all employed low back pain suffers requiring absence from work at some point and for varying sustained periods.

What is a good sitting posture?

From research it seems that protecting our lower back when sitting is multifactorial. These factors are, the environment, time and posture and all influence lower back pain when we sit.

One study found that adapting our environment is important for low back pain. This includes making sure our eyes are inline with monitors, our devices such as keyboards are close and our chairs are a good height (Al-Otaibi, 2015).

The NHS also suggest these changes when explaining how to sit correctly (NHS, 2019). This highlights that it is not just our physical posture that helps us to sit correctly but also our surrounding.

The length of time we sit may also have an impact on lower back pain. Recent evidence has proven that sitting time is positively associated with LBP intensity. This study looked at 201 blue-collar workers and the length of time they sat in both their day job and leisure time and found that those who sat for longer throughout the day had a higher prevalence of low back pain. However, this study used a cross-sectional study design and therefore a causal relationship cannot be made. (Gupta et al., 2015). One paper recommends moving every 20 minutes in order to reduce the likelihood of lower back pain caused by sitting (Wong et al., 2019).

A further study found that sitting for more than half a work day and sitting in an “awkward posture” significantly increased the likelihood of LBP. (Lis et al, 2006). This shows that posture does impact back pain, but usually when maintained for a long period. A study found that people who sat in a flexed, more relaxed position for long periods of time did experience more back pain than those who did not. (Womersley and May, 2006)

Due to all of this evidence, it is important for us as physiotherapists to consider all of these factors when helping someone with sitting induced LBP. It could be argued that there is no one answer to “what is good sitting posture” and that as long as we keep moving, make sure our environment is adequate and keep a natural posture, we can say that we are maintaining a good sitting posture.

Prevention of low back pain due to sitting posture

Ergonomic education

A study was conducted on physiotherapists to see what they believed the best posture was. That same study was also conducted on people experiencing and not experiencing LBP. They found again, that there was no consensus on what good posture looked like and this really adds to the importance of educating both physiotherapists and our patients.

(O'Sullivan et al., 2013)

Further to this, one study found that improvements in postural awareness were longitudinally associated with reduced pain in patients with spinal pain (Cramer et al., 2018) and this really highlights the importance of educating our patients. However, it is important to consider that this study, again used mostly female participants and therefore these results are not generalisable, it also uses uncontrolled longitudinal data and therefore we can not make any causal inferences.

Finally, one study educated office workers about ergonomics and found a significant change in perception of health and reported less pain and discomfort at work when sitting (Bohr, 2000)

Movement for prevention and rehabilitation of sitting related low back pain

Various interventions are used across the spectrum of occupational settings in an attempt to both minimise the risk of low back pain arising but also reduce the impact of sitting on those with already existent low back pain. However, the utility and effectiveness of these interventions is somewhat mixed within the literature. The main source of evidence regarding these interventions comes in the form of a Cochrane systematic review by Parry et al. (2019) who, after exploring research surrounding the use of such interventions as sit-stand workstations, treadmill workstations and activity trackers, found the effectiveness of these interventions in reducing both the intensity and presence of low back pain for sitting based individuals at work was poor. Another movement based intervention not included within the Cochrane systematic review involves the use of "dynamic sitting" which involves the used of both active and passive implements to encourage regular movement of the trunk and lower extremities in a seated position. O'Sullivan et al. (2012) investigated the effectiveness of dynamic sitting via a systematic review. They concluded that although the evidence regarding this topic was of high quality, there was inconsistent results to support and recommend the use of said intervention.

The primary movement-based intervention that the literature appears to moderately support is the implementation of movement breaks throughout the day for those individuals who are in a seated position for prolonged periods of time such as office workers. Waongenngarm, Areerak and Janwantanakul (2018) carried out a systematic review evaluating "movement schedules" with work durations ranging from 5 minutes to 2 hours and breaks lasting 20 seconds to 30 minutes. They found low-quality evidence supporting both a reduction in pain and discomfort for those carrying out movement breaks which also included simple changes in postural position with detriment on productivity. This is further supported by a later study by Sheahan, Diesbourg and Fischer (2016) who also found that even short, regular breaks of standing from a seated position reduced both the regularly and intensity of acute low back pain within a office worker population.

Use of equipment for prevention and management

Back Braces

There is little evidence for back braces to be worn when sitting to prevent low back pain and more research needs to be done in to this area.

Rehabilitation of low back pain caused by sitting

Exercises for low back pain caused by sitting and the rehabilitation of this

COVID-19

With COVID-19 and the lock down people have been forced to stay at home and work from home as much as possible if they are non-essential. this could lead to poor ergonomics and lack of movement leading to an increase in low back pain.

There is advice on the Gov.co.uk website which if you are struggling might be helpful to read.

- the document Protect Home Workers is PDF with information and a video showing how to set up a temporary work space at home that is ergonomically correct.

there is also other advice from the NHS on low back pain and sitting.