Application issues and theoretical concerns regarding the 1991 NIOSH equation asymmetry multiplier

The lifting equation developed by the National Institute for Occupational S afety and Health in 1981 was revised in 1991. One goal of the revision was to accommodate non-sagittal lifting tasks, since sagittal lifting tasks are an exception rather than the rule in many industrial settings. This goal o f expanding the equation to non-sagittal tasks was accomplished by adding a n asymmetry multiplier to the lifting equation. This paper examines the rat ionale behind the development of the asymmetry multiplier and provides an a lternative perspective by reviewing additional literature. The usability of the asymmetry multiplier in industry is discussed with particular emphasis on the applications manual for the 1991 NIOSH equation. The concept of ope rational definitions required to be able to use the equation as intended is presented. Data from three different sources illustrate the problems and v ariability associated with measuring asymmetry, as required by the NIOSH eq uation, in industrial settings. Finally, recommendations for further resear ch and potential modifications to the asymmetry multiplier are presented. Relevance to industry The discussion of measuring asymmetry in industry has particular relevance to industrial settings where the NIOSH equation is applied and asymmetry mu st be measured. (C) 1999 Elsevier B.V. All rights reserved.