There are no gold standard cut points (threshold values that mark the boundary which when exceeded increases the probability of injury) for low back exertion identified by ergonomic evaluation tools/methods, according to a literature review performed by Vieira and Kumar. The authors conclude that the cut points of reviewed assessment procedures are markedly different and compromised by assumptions made in establishing each of the proposed values.
Over 90 references were cited in this literature review. For an article/method to be analyzed, it needed to define back force exertion cut points, present a cut point classification system, use quantitative measures, report results objectively and support conclusions with more than just expert opinion.
Studies were grouped by method of cut point identification – weight and distance of the load from the body, percentage of maximum voluntary contraction used, acceptable loads based in worker opinion, weight and number of repetitions, intra-abdominal pressure, spinal compression forces and compound index.
Given the high incidence and catastrophic effects of low back injury (to both the individual and the workplace), cut points for task-required low back exertion are valuable. Vieira and Kumar suggest that a quality low back exertion tool would:
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utilize quantitative measurements
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measure the magnitude of low back exertion
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define cut points based on epidemiological studies involving various levels of low back exertion
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consider both peak load and cumulative back force exertion
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involve different duration exposures relative to back force exertion
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provide cut points for a normative population realizing values will be different for select populations such as older or pregnant workers
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involve muscle cross-sectional area to define normalized strength as opposed to absolute strength
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be based on isolated (i.e., force generated by low back concentric contraction prior to injury) and combined (muscle strength, tensile capacity of ligament, limits of compression force on disc prior to failure) back tissue capabilities
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apply to for lifting, pushing, pulling and carrying tasks
The authors note that current understanding requires more research for the development of a measuring tool having these capabilities.
Article Title: Cut-points to prevent low back injury due to force exertion at work
Publication: Work 27: 75-87, 2006
Authors: E R Vieira and S Kumar
This article originally appeared in The Ergonomics Report™ on 2006-11-08.