The effectiveness of a chair intervention in the workplace to reduce musculoskeletal symptoms. A systematic review

Prolonged sitting at sub-optimal workstations is associated with musculoskeletal dysfunction[1‐5]. The musculoskeletal dysfunction presents as pain or muscle tension of the cervical, shoulder, and lumbar regions. A range of modifiable and non-modifiable risk factors are associated with the musculoskeletal symptoms. Non-modifiable risk factors are genetic predisposition, structural spinal deformities or disorders and female gender. The modifiable factors include body alignment (posture), nature and duration of the tasks and job demands as well as physical features of the work[5, 6]. Commitment from supervisors and employees is essential to modify these risk factors; so is capital investment to improve the ergonomic design of workstations in an attempt to reduce the occurrence of musculoskeletal symptoms.

Workstation modifications frequently address the work surface and chair[5, 7‐10]. Since the chair has a direct influence on body alignment (posture), individuals suffering from musculoskeletal symptoms related to prolonged sitting are often advised to alter the chair of their workstations[5, 7‐10]. Changing the chair is also the most pragmatic action because altering the work surface may be limited by physical space constraints and an adjustable work surface is not always economically viable. Therefore modifying the workstation’s chair is often the most feasible initial step to ascertain whether the design of the workstation is associated with the musculoskeletal symptoms.

In the selection of a chair, adjustability of the seat height and the seat pan depth in correlation with the anthropometrics of the user should be taken into consideration[11, 12]. A mismatch in the dimensions of the chair impairs the ability of the postural muscles to support the body and could also lead to abnormal strain of the neuromuscular system, consequently causing pain[5, 13, 14]. Chairs which can prevent these effects can thus be beneficial in the prevention of spinal pain. A chair meeting the ergonomic requirements is thus postulated to reduce the occurrence of musculoskeletal symptoms.

Musculoskeletal dysfunction in the workplace is typically classified as repetitive strain disorders, which account for about one third of the related injuries leading to absenteeism[15]. The loss of productivity amounts to about $3.3 billion per annum in Washington State, USA[10]. Within the constraints of the current economic climate, employers demand evidence for the benefits attributed to an investment to alter workstations. Therefore, the aim of this study is to appraise the evidence base for the effectiveness of a chair intervention in the workplace to reduce musculoskeletal symptoms.

We found five studies of moderate quality that offer some support for the use of chair interventions to improve musculo-skeletal pain or discomfort in workers who sit for prolonged periods. However there was a high degree of clinical heterogeneity meaning that more specific conclusions cannot be drawn. Because of the high occurrence of musculoskeletal problems among office workers, changes to their chairs are often recommended. The shortage of evidence involving office workers (only one study) is thus of concern, considering the investment in ergonomic chairs by corporations and companies. There is also a lack of evidence to assess the effect of chairs on children and adolescents in preventing or reducing musculoskeletal symptoms. Further research into this population with growing keyboard time is required - reinforced by the increasing trend of musculoskeletal symptoms among youths[21‐23].

The findings of this review indicate a consistent trend of support for the role of a chair intervention to reduce the severity, intensity and frequency of musculoskeletal pain among workers who are required to sit for prolonged periods. However because the studies reported different body areas it is not possible to be more specific about which kinds of musculoskeletal pain benefit the most. The most common parameter introduced in the chair intervention/s was to have an adjustable feature such as seat and back height. Electromyographic (EMG) studies have reported that a chair which is height adjustable and has adjustable backrest and armrests can reduce the muscle activity of the neck, shoulder and back, and also decreases the inter-vertebral disc pressure[24‐26]. Therefore there is some support that adjustability of the chair can be directly associated with the function of the musculoskeletal system. The second most common feature reported as a chair intervention, was that the participants received training in the use of their chair (how to adjust appropriately). This is intuitive and it is now valuable to have studies which support this as an essential feature of ergonomic interventions.

Other features of the interventions varied such as curved pan versus flat seating – two studies[17, 19]compared these with some suggestion that curved pan seating may be better in reducing upper body pain whilst flat seating may be superior for lower body pain. The authors postulated that the curved, 2-part seat pan supports the forward leaning posture by allowing a more open thigh-torso angle. These findings need confirmation in further studies. Saddle seating also seemed to have differential effects on back versus lower limb comfort – again this requires further careful investigation before recommendations can be made[18].

The study by Gadge[18] was the only eligible publication which included productivity as an outcome. The study sample was very small and the types of outcomes – i.e. typing speed and errors – were not relevant to all seated workers. It is an assumption that ergonomic intervention correlates with productivity[9, 27]. However, this review found no supporting evidence for positive gains in productivity and this factor should be incorporated as an outcome in future research. No studies reported on cost aspects of the intervention.

Although all five studies conducted follow-up assessments of the symptoms, the longest follow-up period was only a year[4]. This indicates a gap in showing whether the effectiveness of a chair intervention has long-term benefits, particularly with respect to musculoskeletal symptoms, as well as the recurrence of symptoms and the consequent cost of care. Chronicity in work-related musculoskeletal pain is multifactorial, with risk profiles relating to psychosocial factors dominating the literature[28]. We believe future studies, addressing long-term effects, need to be designed to take these factors into account.

The findings of this review indicate a consistent trend of support for the role of a chair intervention to improve musculoskeletal symptoms among workers who are required to sit for prolonged periods. The small number of studies and moderate risk of bias impacts on the interpretation and strength of the evidence. We can make cautious recommendations pertaining to the effect of a chair intervention – in particular that adjustable chairs with appropriate training hold the most promise. We have identified gaps in showing whether the effectiveness of a chair intervention has long-term benefit, particularly with respect to musculoskeletal symptoms as well as the recurrence of symptoms and the consequent cost of care.