Abstract
Background
The lumbar spine may experience significant shear forces during occupational tasks
due to the force of gravity acting on the upper body when bending the trunk forward,
or when performing tasks involving pushing or pulling. Shear force limits of 1000 N and 500 N have been recommended by previous authors for maximum permissible limit and action
limit, respectively.
Methods
The present paper reviews literature in terms of shear tolerance (ultimate shear stress
and fatigue life in shear stress) of the lumbar spine and develops recommended limits
based on results of studies examining shear loading of human motion segments. Weibull
analysis was used to assess fatigue failure data to estimate distributions of failure
at different percentages of ultimate shear stress.
Findings
Based on Weibull analysis of fatigue failure data from the best available data, a
1000 N shear limit would appear acceptable for occasional exposure to shear loading (≤100 loadings/day); however, a 700 N limit would appear appropriate for repetitive shear loading (100–1000 loadings/day)
for most workers.
Interpretation
Results of the current analysis support the 1000 N limit for shear stress, but for a rather limited number of cycles (<100 per day). Due to the logarithmic nature of the fatigue failure curve, a 700 N shear limit would appear to be acceptable for frequent shear loadings (100–1000
per day). This value is slightly higher than the action limit of 500 N previously recommended.
Keywords
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Article info
Publication history
Published online: September 10, 2012
Accepted:
August 24,
2012
Received:
June 13,
2012
Identification
Copyright
© 2012 Elsevier Ltd. Published by Elsevier Inc. All rights reserved.
