Abstract
Vertebral joint fatigue life non-linearly decreases with increasing anterior shear force magnitude. Therefore, equal treatment of independent shear force exposures will underestimate low-back injury potential. This investigation developed mathematical functions for deriving appropriate weighting factors (WFs) to be applied in occupational cumulative shear force estimates. Porcine vertebral joints were repetitively loaded in shear to 20%, 40%, 60% or 80% of their calculated shear failure tolerance for 21,600 cycles or until bone failure was detected. Two WF functions were derived from mathematical relationships between sub-maximal shear force magnitude and sustained cumulative shear force to failure. These functions explained 98.2% and 88.6% of the variance in sustained cumulative shear force. Accelerated injury potential represented by WFs greater than unity was assigned to shear forces above 35.6% and 695 N. These weighting approaches will enhance sensitivity in future evaluations between exposure and lost-time/injury for detecting relationships between cumulative shear loading and low-back injury.
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