Use of NIOSH equation inputs to calculate lumbosacral compression forces

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Abstract
The purpose of the current paper was to develop regression-based models that use NIOSH lifting equation H and V values to accurately calculate L5/S1 compression forces during symmetrical load-bearing tasks. Results from a linked-segment, biomechanical model were used as the criterion. Twenty-two subjects (11 males, 11 females) performed movements through a wide range of postures in the sagittal plane. Each model was developed with the data from 16 subjects (n = 1704 postures) and validated with 6 subjects (n = 750 postures). Five loads were iterated from 0 to 28 kg (females) or 36 kg (males) or until the strength demand at one joint exceeded the 98th percentile value predicted for that gender. Both models required the input of the NIOSH H and V values, subject body mass, load mass and trunk angle. MODEL1 used regression equations to calculate the moment arm from the load, and the upper body centre of mass, to the L5/S1 joint. These lengths were subsequently used in a biomechanical model to calculate the joint compression force (R 2 = 0.989, RMS error = 147 N). MODEL2 predicted compression force directly with one equation using the same inputs as MODEL1. (R 2 = 0 983, RMS error = 183 N, both models n = 6467). The results were slightly improved for both models when applied to the validation subject data (n = 2303). Regression models were also developed to estimate the maximum and minimum expected trunk angles for all possible H and V combinations so that ‘worst case’ scenarios could be evaluated for given load positions.

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