Association between sitting and occupational Lower Back Pain
From: European Spine Journal. 2007 February; 16(2): 283–298.
Lower back pain has been identified as one of the most costly disorders among the worldwide working population. Sitting has been associated with risk of developing lower back pain. The purpose of this literature review is to assemble and describe evidence of research on the association between sitting and the presence of lower back pain. The systematic literature review was restricted to those occupations that require sitting for more than half of working time and where workers have physical co-exposure factors such as whole body vibration and/or awkward postures. Twenty-five studies were carefully selected and critically reviewed, and a model was developed to describe the relationships between these factors. Sitting alone was not associated with the risk of developing lower back pain. However, when the co-exposure factors of whole body vibration and awkward postures were added to the analysis, the risk of lower back pain increased fourfold. The occupational group that showed the strongest association with lower back pain was Helicopter Pilots.
For all studied occupations, the odds ratio increased when whole body vibration and/or awkward postures were analyzed as co-exposure factors. whole body vibration while sitting was also independently associated with non-specific lower back pain and sciatica. Vibration dose, as well as vibration magnitude and duration of exposure, were associated with lower back pain in all occupations. Exposure duration was associated with lower back pain to a greater extent than vibration magnitude. However, for the presence of sciatica, this difference was not found. Awkward posture was also independently associated with the presence of lower back pain and/or sciatica. The risk effect of prolonged sitting increased significantly when the factors of whole body vibration and awkward postures were combined. Sitting by itself does not increase the risk of lower back pain. However, sitting for more than half a workday, in combination with whole body vibration and/or awkward postures, does increase the likelihood of having lower back pain and/or sciatica, and it is the combination of those risk factors, which leads to the greatest increase in lower back pain.
Lower back pain is an important public health problem in all industrialized countries. It remains the leading cause of disability in persons younger than 45 years old and comprises approximately 40% of all compensation claims in the United States. More than one-quarter of the working population is affected by lower back pain each year, with a lifetime prevalence of 60–80% and a large percentage of lower back pain claims for long durations (more than 90 workdays lost.
Approximately one-third of American workers are in jobs that contribute to an increased risk of developing back disorders, although the causes of lumbar disorders are complex and difficult to identify. This situation is similar in Great Britain, where the average estimated year-prevalence derived from British population surveys is 38%.
Because of the potential economic and social benefits to be gained from reducing the magnitude of lower back pain in industry, many investigations have focused their attention on the factors that lead to injury, particularly on those activities and events associated with the onset of symptoms. The major thrust of research about lower back pain has been to identify occupational risk factors associated with its presence and occurrence.
With the rapid development of modern technology, sitting has now become the most common posture in today’s workplace. Reinecke et al. reports that three-quarters of all workers in industrialized countries have sedentary jobs that require sitting for long periods. For many activities, however, sitting can be a less straining posture than standing. Both postures are commonly used, and have advantages and disadvantages depending on the task to be performed. In this review, sitting is discussed in the context of Western standards. Sitting is described as an erect posture in which the head and trunk are vertical, the lower legs are bent at about 90° at the hips and knees, and the feet are firmly placed on the floor. The concept of sitting is very different in non-Western societies. In India and Southeast Asia, for example, it is still common to see workers sitting cross-legged on the ground, squatting (knees bent severely, the thighs close to the trunk, and weight concentrated on the heels), or kneeling. Although common, these variations of sitting are not discussed in this review.
The existence of the relationship between workplace factors and the occurrence of lower back pain has long been recognized. Among the occupational exposures identified, sitting is commonly cited as a risk factor in the literature, in addition to heavy physical work, heavy or frequent lifting, non-neutral postures (i.e., trunk rotation, forward bending), pushing and pulling, and exposure to whole body vibration (whole body vibration) (i.e., motor vehicle driving).
Laboratory studies have focused on biomechanical hypotheses to explain the association between sitting and lower back pain. The literature on this subject is extensive, but the evidence is somewhat contradictory. It has been shown that intradiscal pressure is increased in the sitting posture. In a more recent investigation, Wilke et al. reevaluated the intradiscal pressure in sitting and found that, in fact, it can be lower in sitting than in erect standing. Another hypothesis is that prolonged static sitting postures may have a negative effect on the nutrition of the intervertebral disc. Thus, a constantly changing position may promote the flow of fluid (nutrition) to the disc.
The purpose of this paper is to review the more recent literature that examines the association between sitting and the report of lower back pain among working populations. This review also intends to identify if there is an interaction between occupational lower back pain/sciatica and sitting in combination with whole body vibration and/or awkward postures. The importance of this association cannot be underestimated. Understanding the risk factors for lower back pain and sciatica can lead to prevention programs that have the potential to mitigate the high prevalence rates of occupational lower back pain. Although other factors (i.e., physiological and psychosocial) may also be important, they are not the focus of this paper.
For this review, sitting is defined as a sustained upright trunk posture with limited possibilities to change posture or position. lower back pain is represented here by reported or examined ache, pain, stiffness, or discomfort in the lumbar spine. Sciatic pain is considered a reported or examined radiating pain extending below the knee in one or both legs. Workers in occupations who performed tasks while sitting may also be exposed to whole body vibration and/or awkward posture, and these exposures are independently analyzed in the literature. Awkward posture represents a non-neutral trunk posture (i.e., bending forward and/or twisting of the trunk). Postural load and unfavorable posture are terms used in the literature that refer to awkward posture. whole body vibration is present when the body receives continuous vibration transmitted from the seat over a period of time.
This systematic review seeks to examine the association between the presence and/or occurrence of lower back pain and sciatica among occupational groups in which the seated posture is the major physical requirement for the work. The following questions were considered: (1) Is there evidence in the recent epidemiological literature for an association between occupational groups exposed to sitting and reported lower back pain?, (2) Is there evidence in the recent epidemiological literature of an association between exposure to whole body vibration while sitting and reported lower back pain?, (3) Is there evidence in the recent epidemiological literature for an association between awkward posture while sitting and reported lower back pain?, and (4) Is there evidence in the recent epidemiological literature for an association between the combined effect (both whole body vibration and awkward posture) while sitting and reported lower back pain?
The prevalence rates of lower back pain have been affecting the economy of industrialized countries in many ways. The prevalence rate of reported lower back pain in those occupations that require the worker to sit for the majority of a working day is significantly higher than the prevalence rate of the general population. Physical factors, psychosocial factors, and individual characteristics contributed to these findings, but only the physical factors will be discussed here.
Sitting
Sitting has been a complex topic for researchers of lower back pain. For many years, the sitting position has been identified as one of the major risk factors for developing lower back pain. Nachemson and Elfström found that body position affects the magnitude of the loads on the lumbar spine, and that the magnitude of the loads increases markedly when sitting is compared with upright standing and well-supported reclining. This finding created much controversy, and while some subsequent lab studies supported this finding, others have found different results. For instance, the conclusions of Wilke et al. reevaluate the assumption that there is an increased presence of higher intradiscal pressure while sitting as opposed to erect standing. In fact, Rohlmann et al. reports that intradiscal pressure is up to 10% less when standing. Some studies have reported odds ratio’s as low as 0.7 for occupations in which the major physical requirement is sitting, indicating that people in these occupations may actually have a lower risk of lower back pain than in other occupations. However, although the rate of lower back pain among occupations requiring extended periods of sitting may not be as high as the rate of lower back pain among more strenuous occupations, Lee et al. reported that this group had the highest hospitalization rate for lower back pain, indicating that when low back injuries occur among persons in these occupations, these injuries tend to be more severe. Hence, the risk of prolonged sitting in the workplace should not be overlooked.
A definitive experimental conclusion about the effect of sitting on lower back pain has yet to be confirmed. However, the majority of the literature reviewed for this paper has shown that sitting by itself does not imply a markedly increased association with the presence and/or occurrence of reported or examined lower back pain. In fact, a considerably stronger association was found only when the occupational groups studied were exposed to whole body vibration and/or awkward postures while sitting. It is still unknown if other confounders as psychosocial factors may affect the strength of the association between sitting alone and lower back pain.
Sitting and exposure to whole body vibration
One of the major co-exposure factors for all the occupations analyzed was whole body vibration. There is a clear indication of an increased risk of reported lower back pain and/or sciatica in occupations with exposure to whole body vibration while sitting, mostly in professional driving occupations. Many authors have carefully reviewed the risk effect expressed as increased associations from exposure to whole body vibration and lower back pain, and have concluded that there is indeed an association between whole body vibration and lower back pain. However, there is limited evidence regarding a dose–response relationship. There are many confounding factors that interfere with the relationship between lower back pain and whole body vibration exposure. A worker’s age, duration of exposure, history of lower back pain, previous exposure, and even posture while being exposed to whole body vibration seems to affect that relationship. Chen et al. found that daily increments of the vibration dose by each m2/s4-hour resulted in an increase in the odds ratio of lower back pain by 3.7 even after controlling for age and professional seniority, which is almost analogous to duration of exposure.
Even though the number of studies that use control and exposure groups to analyze the association between lower back pain and whole body vibration is limited, there is strong evidence of a major association between whole body vibration while sitting and lower back pain/sciatica. For instance, occupational groups such as helicopter pilots have shown a very high odds ratio for a vibration-dose exposure greater than 800 m2 h/s4 after adjusting for awkward postures. Only one study did not find an association between sitting plus whole body vibration and lower back pain; however, the low response rate in that study compromised its quality. Therefore, this does not affect the conclusion that there is a strong relationship between sitting plus whole body vibration and lower back pain.
In addition to dose, the magnitude and duration of exposure have also been found to be important exposure factors for the presence of occupational lower back pain and sciatica. The articles reviewed showed that the duration of the exposure had a slightly stronger association with the presence of lower back pain than did magnitude of vibration. This finding suggests a cumulative effect. As the duration of exposure increases, the risk of lower back pain increases. Bovenzi and Betta found that prolonged tractor driving and exposure to whole body vibration were the factors most associated with chronic lower back pain and sick leave. They suggested an excessive accumulated vibration dose effect as the main reason, which is in agreement with the Boshuizen findings. However, in the case of sciatica the pattern is not the same. The duration of the exposure was constantly related to sciatica to a lesser extent than vibration magnitude for all the occupations. The reasons for such results are not clear. Moreover, it is important to understand that in both cases either duration or magnitude were positively associated with the presence of reported lower back pain or sciatica symptoms. It is also important to take into account that the recommended ISO standards did not reveal any preventive health effect. Even with following ISO recommendations, the levels of vibration magnitude to which most drivers are exposed seems to be higher than the recommended maximum level of exposure, especially when exposed for long periods of time. Many authors argue that these recommendations should be reviewed.
Sitting and awkward posture
It has been postulated that sustained awkward seating posture (lordosed or kyphosed, overly arched, or slouched) can result in higher intradiscal pressure and may be injurious to spinal postural health. Therefore, awkward postures while sitting have been described as possible risk factors for the presence of lower back pain. Many experimental studies have demonstrated that postural changes affect spinal loads. Keyserling et al. used a computer-aided system to investigate trunk posture during work by measuring the time spent in neutral and non-neutral postures. Their results suggested that by controlling non-neutral trunk posture, the risk of developing back pain on industrial jobs can be reduced. Non-industrial occupations such as professional drivers, dentists, and helicopter pilots are also potentially exposed to awkward postures. However, only four epidemiological studies showed the associated risk of being exposed to awkward postures and having lower back pain and/or sciatica. The results of these studies confirms that in the case of bus drivers, tractor drivers, road washing vehicle drivers, and helicopter pilots, the risk of having lower back pain increases due to awkward posture while driving. The Road Washing Vehicle drivers have the highest odds ratio of all the occupations It may be important to note that these drivers are exposed to trunk flexion, bending, and twisting, whereas the other occupational groups are exposed to only one of these factors. Hence, flexion, bending, and twisting may be more detrimental than only flexion. The question to be asked in this case is if the observed adverse effects of driving in these studies should be attributed to the exposure to awkward posture alone or to a combination of prolonged sitting, twisting, and bending postures, once sitting per se was not investigated.
A proposed model
The literature reviewed has indicated an increased risk of lower back pain and sciatica for individuals in those occupations that require prolonged sitting (defined as sitting for more than half of a working day). However, the risk increases after combining factors such as whole body vibration and awkward postures. In fact, for all the occupations studied, these co-exposure factors were the variables that led to a significantly increased risk. The fact of being seated for an extended period does not significantly demonstrate an impressive risk of having lower back pain and/or sciatica. Bovenzi and Betta compared a group of agricultural tractor drivers with a group of office workers. Both groups were exposed to static load due to prolonged sitting. However, only the tractor drivers group was exposed to the combined factors of whole body vibration and awkward posture. They found that tractor drivers were 2.39 times more likely to report lower back pain than office workers. The association was similar when they looked at whole body vibration while sitting (adjusted for awkward posture). The association increased when postural load was analyzed adjusting for vibration dose.
A model was constructed based on whole body vibration and awkward postures. The model aims to describe how the risk effect of prolonged sitting increases significantly as other co-exposure factors (in this case whole body vibration and awkward postures) play a role. As such, just the fact of sitting probably does not present a risk until the worker is exposed to a certain level of whole body vibration and/or an awkward posture. When these co-exposure factors are combined, the risk for reporting lower back pain and/or sciatica increases. Bovenzi and Betta tried to demonstrate this finding after analyzing the combined effect of postural load and total vibration dose. They found that the combination of vibration dose and postural load increases the risk of reporting lower back pain. In fact, there was a linear trend of increasing prevalence of lower back pain as the combined effect increases, perhaps demonstrating a dose–response relationship.
It could be argued that this model has many limitations due to the fact that lower back pain is multi-factorial in its origin. Through this literature review, some physical (mechanical) factors (whole body vibration, awkward posture, and a combination of both) were identified that are associated with the occupations performed while sitting. However studies have shown that there are other risk factors for lower back pain to which workers are exposed during the time period when they are sitting or not sitting, such as manual material handling or lifting activities, or psychosocial factors.
Summary
No previous research has been reported that investigated the sitting posture with respect to lower back pain and sciatica in a manner similar to this literature review, so no direct comparisons can be made. However, it could be argued that the conclusions of this paper, as well as of this model, have some limitations due to the fact that lower back pain is multi-factorial in its origin. Through this literature review, an association was made between some work-related factors while sitting (whole body vibration, awkward posture, and the combination of both) and reported lower back pain and sciatica. A quantitative determination of how much exposure to these risk factors (whole body vibration and awkward posture) would alter the risk of occupational-related lower back pain was not conducted (dose–response relationship). Just being seated on the job is not a risk factor; sitting becomes risky when combined with other risk factors. There is a lack of research on how much the risk increases for all populations. Other individual or psychosocial risk factors that have been found to be predictive of lower back pain were not studied in this literature review. Thus, no conclusions can be made about the interactions between these factors while sitting and the presence of lower back pain/sciatica.
More epidemiological studies are needed to provide clear evidence of the association between sitting and occupational lower back pain. However, our review suggests the following conclusions:
- Sitting by itself does not show an increased association with the presence of reported lower back pain.
- Sitting in combination with other co-exposures such as whole body vibration and awkward posture does increase the association with the presence of lower back pain.
- Sitting in combination with whole body vibration and awkward posture seems to have the strongest association with the presence of lower back pain. However, this conclusion is based on only one study whose results have not since been replicated. Hence more studies are needed to confirm this hypothesis.
- Occupational groups exposed to whole body vibration while sitting are at an increased risk of having lower back pain. Also, the influence of the duration of the exposure seems more important than the magnitude of the exposure, suggesting a cumulative effect.
- Although awkward posture while sitting has not been as well investigated as whole body vibration, the results of the preliminary research reveal a strong association with the presence of lower back pain. Thus, occupational groups exposed to awkward postures while sitting have an increased risk of having lower back pain. However, further research is needed on this topic due to the lack of valid and reliable instruments for its measurement.
- The interaction of factors such as sitting, whole body vibration, and awkward posture should also be carefully analyzed in terms not only of their association with lower back pain, but also of their dose–response.
- Awkward posture and whole body vibration have been previously associated with lower back pain, even without sitting. Further research should be conducted to probe if sitting adds to the risk of lower back pain.
