Relationships between the NIOSH (1991) Lifting Index, Compressive and Shear Forces on the Lumbosacral Joint, and Low Back Injury Incidence Rate Based on Industrial Field Study

Abstract

The main objective of this study was to investigate relationships between the values of NIOSH (1991) Lifting Index calculated for as set of industrial manual handling tasks, the corresponding (estimated) compressive and shear forces on the lumbosacral joint (L5/S1), and the back injury incidence rates based on analysis of the epidemiological field data. A strong positive correlation was observed between the estimated compressive forces on L5/S1 and the lifting index (LI) values, and between the incidence rates (IR) of low back injury and the LI index. Two sets of regression models describing the relationships between the lifting index (LI) and the compressive forces on the L5/S1 were developed. It was shown that the LI=1.0 corresponds to about 1.8 kN and 2.4 N of compression on the L5/S1, for the destination and origin of the lift, respectively. For the lumbar compressive strength values (with safety factor of one standard deviation) of 4.1 kN for males (40 years of age), proposed by Jager and Luttman (1992), the corresponding values of the lifting index are as follows: LI=4.1 (for the lift destination) and 6.4 (for the lift origin). Implications of results for prevention of back injury due to manual lifting were discussed.