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Developing common metrics of mechanical exposures across aetiological studies of low back pain in working populations for use in meta-analysis
  1. L E Griffith1,
  2. R P Wells2,
  3. H S Shannon1,3,
  4. S D Walter1,
  5. D C Cole3,4,
  6. S Hogg-Johnson3,
  7. on behalf of the Meta-Analysis of Pain in the Lower Back and Work Exposures (MAPLE) Collaborative Group
  1. 1
    Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Canada
  2. 2
    Department of Kinesiology, University of Waterloo, Waterloo, Canada
  3. 3
    Institute for Work and Health, Toronto, Canada
  4. 4
    Department of Public Health Sciences, University of Toronto, Toronto, Canada
  1. L Griffith, Program in Occupational Health and Environmental Medicine, McMaster University, HSC 3H57, Hamilton, Ontario, Canada L8N 3A5; griffith{at}


Objectives: One of the challenges of conducting meta-analyses on the relationship between workplace mechanical exposures and low back pain is that mechanical exposures are reported in a wide variety of ways. We aimed to develop common metrics to apply in the translation of literature-based workplace mechanical exposures for use in meta-analyses, and to test the metrics’ measurement properties.

Methods: We developed a set of 7-point scales to capture the intensity of important aspects of mechanical exposures that may be related to the development of low back pain in workers. The scales represented three dimensions of mechanical exposures at work: (1) trunk posture, (2) weight lifted or force exerted and (3) spinal loading, and estimated both peak and cumulative loads. Measurement properties of the scales were tested through a survey of experts in biomechanics and ergonomics who were asked to rate literature-based workplace exposure definitions using the scales and provide estimates of their confidence in their ratings.

Results: For each dimension the ratings for peak loads tended to be higher than the cumulative load ratings. The inter-rater reliability for the scales ranged from 0.3 to 0.5; we would need to average the ratings of at least four expert raters to have an acceptable level of reliability (>0.7). Inter-expert reliability was positively related to the experts’ level of confidence in their ratings. In most cases the ranking of intensity ratings from the experts matched the ranking of exposure intensity from the original articles.

Conclusions: This study provides insight into estimating the intensity of literature-based mechanical exposure metrics using a common set of scales which can be applied across epidemiologic studies. These metrics may be useful to quantify the relationship between workplace mechanical exposure and low back pain in a systematic review and meta-analysis.

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  • Funding: This study was funded by the Canadian Institutes for Health Research (FRN-67042 and ICH-63069, part of the Interdisciplinary Capacity Enhancement (ICE) Teams Grant Program) with support from the Centre of Research Expertise for the Prevention of Musculoskeletal Disorders (CRE-MSD).

  • Competing interests: None declared.

  • iOffice workers were non-executive office workers. About 40% of them performed clerical work with routine office tasks; others were professionals.

  • iiMachine operators comprised earthmover operators and longshoremen specialised in motorised stevedoring. Machine operators are exposed to low-frequency whole-body vibration and to static load due to prolonged sitting in a constrained posture and the handling of steering apparatus. Their work occasionally includes materials handling and maintenance of machines. The machine used most commonly by longshoremen is a forklift truck. Earthmover operators use heavier machinery, such as excavators, bulldozers, wheel-loaders, etc, in preparing the ground for buildings and in road construction.