Sitting Ergonomics And The Impact on Low Back Pain

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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 be discussed 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), and discuss different preventive strategies and interventions to reduce low back pain caused by sitting.

Ergonomics

Sitting posture

Often referred to as "human factors", ergonomics is the science of applying physical and psychological principles within an environment to increase both productivity and well-being[1]. 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 the human anatomy, physiology, and biomechanical factors influencing movement patterns and posture. This area of ergonomics is therefore of significant interest to physiotherapists and one in which we regularly address due to having a rich, in-depth understanding and knowledge of these factors.

Statistics in Britain

Research by Dul and Neuman (2009)[2] stated that ergonomics are important because they improve workplace performance. Ergonomics are an important consideration both when working from home and it the workplace.

In 2019 the Health and Safety Executive[3] completed a health and safety at work report for Great Britain. Within this report MSK disorders reported in 2018 and 2019 are displayed. 40% of all MSK disorders reported were related to the back. While this does not break down into specific types of back problems it is clear there is a link between work-related ergonomics and back pain. Explanations suggested for the high incidence rate were awkward or tiring body 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, in and around the five vertebrae (numbered L1-L5) [4]. 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 [5].

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 [6]. 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[7]

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

Anatomy Description
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[8]

The main ligaments of the lumbar spine include:

Ligament Description
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.
Interspinous ligaments This connects consecutive spinous processes together within the spine. It mainly limits the flexion of the spine.
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.
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
Superficial muscles of the back

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[9].

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.

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[10]. Further studies have found that sitting in a flexed position also reduces the activity of abdominal muscles which play a key role in stabilising the back [11].

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[12].

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[13]. 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[13]. 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[14]. 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.[15]

Sitting and low back pain

Occupational low back pain is one of the most prevalent types of back pain. Multiple factors can be responsible (e.g. heavy lifting and poor manual handling) putting multiple professions at risk, however, for the purpose of our Physiopedia page we have focused on those working in a sedentary role.

The main causes for this sitting induced back pain have been identified as:

  • Sustained sitting
  • Increased activation of the spinal muscles due to specific sitting postures
  • Lack of variation of movement

As a result of the high prevalence of this occupational back pain extensive government guidance exists for both employers and employees to follow:

Government advice for UK employers: https://www.hse.gov.uk/msd/backpain/index.htm

Government advice for UK employees: https://www.hseni.gov.uk/articles/back-pain-advice-employers

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[16].

The NHS also suggests these changes when explaining how to sit correctly [17]. This highlights that it is not just our physical posture that helps us to sit correctly but also our surroundings.

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[18]. One paper recommends moving every 20 minutes in order to reduce the likelihood of lower back pain caused by sitting[19].

A further study found that sitting for more than half a workday and sitting in an “awkward posture” significantly increased the likelihood of LBP [20]. 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 [21].

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 and Rehabilitation of Sitting Induced Low Back Pain

As with most incidences of low back pain there are multiple approaches that physiotherapists can take in order to help manage symptoms and prevent reoccurrence. The four main areas explored in the literature for the management of low back pain induced by sitting are as follows: Education around postural awareness, discouraging long sedentary periods, prescribing exercises to improve postural control and recommending equipment that will support a neutral spine.

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[22].

Further to this, one study found that improvements in postural awareness were longitudinally associated with reduced pain in patients with spinal pain[23] 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 [24].

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)[25] 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)[26] investigated the effectiveness of dynamic sitting via a systematic review. They concluded that although the evidence regarding this topic was of high quality, there were 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)[27] 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)[28] 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.

Postural rehabilitation

Exercise
Exercise two
one
Alternate hands and legs.jpg

Postural rehabilitation describes performing exercises that are specifically focussed on increasing core strength and body alignment in order to improve postural control[29]. Prescribing strength and flexibility exercises particularly, allows for better control of the lumbar region during both slow-voluntary and fast-reflexive movements; thus reducing the likelihood of low back pain.

Several different methods of postural rehabilitation have been devised, each putting greater emphasis on a different element of postural control e.g. proprioception, balance and core muscle strength. However, all have the ultimate aim of preventing and managing low back pain.

The most widely researched and recommended approaches are Pilates and the McKenzie method. The focus of Pilates is to encourage postural control through engagement in isometric contraction of the deep core and pelvic floor muscles; it also puts a strong emphasis on breathing control during movement. The McKenzie method takes a slightly different approach, focussing on correcting posture, usually through the restoration of lumbar lordosis. Below are links to the corresponding Physiopedia pages, providing further detail on the specific content of these two approaches:

Pilates: https://www.physio-pedia.com/Pilates

McKenzie method: https://www.physio-pedia.com/Mckenzie_Method

In 2019, Paolucci et al[30] conducted a literature review that investigated and compared the effectiveness of these two techniques, alongside three other methods of postural rehabilitation. The review concluded that each approach had sufficient evidence to support its efficacy in reducing back pain and disability, and improving quality of life; for Pilates and the McKenzie method particularly, the corresponding exercises were found to be more effective than alternative pharmacological and instrumental treatments. Though the review did not focus of sitting induced back pain specifically, the principles of the postural rehabilitation techniques included are applicable to our population of interest.

Use of equipment for prevention and management

With back pain being such a common issue the market has been flooded with equipment to try and alleviate back pain or relieve the symptoms. The equipment ranges from exercise balls and back braces to standing desks which are appearing in offices more and more. Research has been carried out on all the equipment to varying degrees. For example there is minimal research on sitting exercise balls rather then chairs and back braces specifically for low back pain rather than post-operative, however, they are used frequently due to them being cheap and easily accessible. 

Exercise Ball

One of the most common tools in rehabilitation and exercise is the exercise ball. Their popularity has risen in recent times as they are cheap and easily accessible, claiming not just to combat back pain but also to aid concentration whilst working. Research on its effects on back pain is limited, but generally does not show favourable results.

One of the first studies was conducted by Kingma and Dieën (2008)[31], who investigated static vs. dynamic posture. This was done by comparing females working at computers on an office chair to those on an exercise ball, and measuring muscle activity in the spinal muscles. Sitting on a ball led to 33% more trunk motion and 66% more variation in lumbar muscle activation – however, it also led to more spinal shrinkage. They concluded that whilst the advantages may slightly outweigh the disadvantages, overall, the real term benefits of sitting on an exercise ball were negligible. 

In addition to this, Elliot et al. (2016)[32] conducted a study comparing sitting on a ball for 90 minutes per day instead of a chair, to investigate the effects on lower back pain and core muscle endurance. Their results were not statistically significant, and they concluded exercise balls have little-to-no benefit for lower back pain, but did somewhat improve core endurance in the sagittal plane. 

Back Support Seat Attachment

A variety of seat attachments exist, for chairs in the office, at home and in the car, which claim to reduce lower back pain. However, the literature is mixed on the effect they have.

One of the earlier studies specifically targeted so-called ‘ergonomic chairs’, which have built-in lumbar support with the intent to improve posture and alleviate back pain, conducted by van Niekerk et al. (2012)[33]. Some subjects reported a reduction in back pain after the intervention, however the study reported that they used poor randomization procedures and lacked concealed allocation. This would suggest the chairs were possibly only useful for specific members of the population, and/or the existence of the placebo effect. They further stated being unable to make any strong recommendations due to the amount, level and quality of evidence being insufficient.

Following on from this, Curran et at. (2014)[34] found that the addition of a backrest and seat pan actually increased lower back pain in individuals with extensor-related pain, and generally provided no reduction in lower back pain for the general population. This is also supported by Ortiz et al. (2020), who investigated back supports for prolonged car journeys, and found little benefit.  

Back Braces

Evidence surrounding back braces is conflicting and does not form a strong conclusion. For example, when combined with physical therapy and pain medication, some studies suggest increased mobility and pain scores with a back brace compared to without – whilst some studies highlight a concern that back bracing may lead to muscle atrophy (Dang, 2018)[35]. Overall, research is very limited, with methods and patient participation being of poor quality, and thus more research needs to conducted in this area.

Standing Desks

Standing desks for workplaces have grown in popularity in recent times, orbiting the idea that standing and moving are beneficial to reducing back pain. These range in quality, from around $150 to well over $1000, all with the same fundamental idea: to allow you to work in a standing posture when necessary, and being able to adjust back to normal desk height to allow for flexibility.

Claus et al. (2008)[36] conducted a systematic review that suggested standing desks only provided benefits to a specific subgroup of the population – those with degenerated inter vertebral disks. They stated that for a healthy individual, sitting was no worse than standing for the incidence of lower back pain.

However, following on from this, Pillastrini et al. (2010)[37] claimed that standing desks reduced both the severity and risk of lower back pain. In a longitudinal study conducted over 30 months, they studied 100 video display terminal workers, following up at 5, 12 and 30 months to question the effects. However, one issue with this study was that it was not solely focused on standing desks, but included other interventions over the course of the 30 months.

As such, overall, more research – and more specific research – would need to be conducted to evaluate the effects of this trend. Research would also have to study the differences in quality between cheaper and more expensive desks, to understand if there was then a difference in outcome.

COVID-19

With COVID-19 and the lockdown 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 workspace at home that is ergonomically correct. There is also other advice from the NHS on low back pain and sitting. You can refer to these if you are working from home and need help or suffer from low back pain.

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