Pieter Coenen, MOVE Research Institute Amsterdam, Faculty of Human Movement Sciences, VU University Amsterdam, Amsterdam, The Netherlands, and others reported in the Journal of Occupational Rehabilitation that work-based cumulative low back load is not only a significant risk factor for low back pain but it is actually more consistently associated with low back pain than some previously reported risk factors.
Coenen et al commented that although physical factors, such as twisting and bending, have been recognised as risk factors for low back pain, recent reviews have suggested that the evidence for the relationship between physical factors and low back pain is not that convincing. The authors commented: “Generally, data on exposure-response relationships are scarce and incomplete. It can be argued that the relationships of these physical exposures with low back pain might be less reliable than relationship of low back load dose (ie, the effect that physical exposure has in the human body) with low back pain, since different exposures (eg, lifting and bending) affect the same dose.” They added that studies have suggested that cumulative loads acting on the spine may contribute to low back pain, but these studies only used retrospective data. Coenen et al wrote: “The aim of this present study therefore was to investigate the association of cumulative low back load with low back pain in a large prospective study.”
Using data from SMASH (Studies on musculoskeletal disorders, absenteeism and health), which assessed risk factors for musculoskeletal disorders among a cohort of Dutch workers, the authors identified 1,745 eligible participants. At baseline, participants completed a questionnaire and individual physical loads were assessed at their workplaces (via video observations and force measurements). During the three years of follow-up, the incidence of low back pain was assessed annually through a self-administered questionnaire. Complete data (physical load, occurrence of low back pain, and cofounding variables) was only available for 1,086 participants. Of these, 416 (38%) reported low back pain at baseline and 537 (49%) reported low back pain during follow-up.
After adjustment for confounding variables, cumulative low back load was found to have a significant relationship with low back pain in participants with the highest cumulative low back load compared with participants with lowest cumulative low back load (odds ratio 2.06). Furthermore, of individual exposure factors, only repeatedly lifting a heavy load was found to be a significant additional risk factor for low back pain after adjusting for confounders. Coenen et al reported: “Lifting >15 times ≥25kg in an eight-hour day compared to no lifts of ≥25kg was a significant risk factor (odds ratio 2.03), while percentage of the working time in a flexed position and number of lifts in an eight-hour day did not significantly predict low-back pain.” According to the authors when the risk associated with cumulative low back load was adjusted for each individual exposure factor, participants with the highest cumulative low back load continued to have a significant risk of low back pain compared with participants with the lowest cumulative low back pain.
The authors stated that a significant risk of low back pain was only observed in participants with the highest levels of cumulative low back load (2MNm and above) and, as an example, that a person would need to lift a moderate weight 50 times during a working week for them to have a high cumulative low back load (and thus be at risk of low back pain). They noted: “Ergonomic interventions should therefore be targeted mainly to workers who encounter these levels of cumulative low back load, which can emerge from awkward postures and/or high exposure tasks at work.”
Concluding, Coenen et al commented: “Cumulative low back load has a more consistent association with low back pain than the risk factors time in a flexed position and number of lifts in a working day. This finding supports our hypothesis that a low back load dose measure provides a stronger relationship with low back pain than exposures of low back load since several exposures (eg, lifting and bending) are incorporated in the dose.”
Study author Jaap van Dieen, MOVE Research Institute Amsterdam, Faculty of Human Movement Sciences, VU University Amsterdam, Amsterdam, The Netherlands, told Spinal News International: “Our findings imply that interventions aimed at reducing the duration and frequency of exposure to high back loads, such as job rotation, can contribute to prevention of low-back pain in addition to reducing load levels.”