Critical survey on the biomechanical criterion in the NIOSH method for the design and evaluation of manual lifting tasks

Abstract

In 1981, the National Institute for Occupational Safety and Health (NIOSH) published a comprehensive guide for the evaluation and design of manual lifting, based on epidemiological, physiological, psychophysical, and biomechanical knowledge. A revised version of the easy-to-use “NIOSH lifting equation” was provided in 1991 considering occasional new findings from literature. For assessing the load on the lumbar spine during lifting, a limit of 3.4 kN for lumbosacral disc compression was introduced. Regarding this biomechanical criterion, several inconsistancies and discrepancies are revealed when comparing the NIOSH substantiation approaches and the respective data of the literature sources: For example, essential results referred to by NIOSH or NIOSH-authorized presenters are not included in or cannot be reproduced from the cited sources. Furthermore, the epidemiological studies showing the relationships between low-back disorder incidence rates and lumbar mechanical exposures cannot be used for confirming the 3.4 kN value as an appropriate limit. It is concluded that the 3.4 kN criterion is substantiated neither epidemiologically nor biomechanically by the provided sources. More comprehensive data compilations, available in the meantime, may be regarded as a better background for the derivation of lumbar load limits in order to diminish the individual overexertion risk during manual materials handling.

Relevance to industry

NIOSH has provided a multi-disciplinarily justified lifting guide for evaluation and design of lifting tasks. A critical survey of the cited sources shows that the considered biomechanical criterion is only weakly substantiated.

Introduction

The Work Practices Guide for Manual Lifting provided by the National Institute for Occupational Safety and Health of USA (NIOSH, 1981) or the “Revised NIOSH Lifting Equation” (Putz-Anderson and Waters, 1991; Waters et al., 1993, Waters et al., 1994), respectively, is accepted as a valuable tool for the design and evaluation of manual lifting in ergonomics and occupational health. Many industries have found the Work Practices Guide to be very useful in identifying problems and reducing injuries. Moreover, the NIOSH method has gained considerable recognition in the drafting of European and international standards (CEN, 1996; ISO, 1995). Therefore, knowledge of the scientific basis, its reliability and comprehensiveness is of great interest and relevance. In this context, the aim of this paper is to scrutinize the biomechanical criterion considered in the NIOSH method, in particular, with respect to the material referred to in the cited sources. In addition, hints will be given toward a more comprehensive basis for the derivation of recommendations with regard to the lumbar load-bearing capacity. Consequently, the aim is not to question the NIOSH method with its undoubtedly helpful physiological and psychophysical components, but to give additional help in the evaluation of its biomechanical background.