Comparing the revised NIOSH lifting equation to the psychophysical,biomechanical and physiological criteria used in its development

The purpose of this study was to perform a systematic and comprehensive comparison between the recommended weights of lift (RWL) from the revised NIOSH lifting equation, and the specific biomechanical, psychophysical and physiological criteria that were stated to be used in the equation's development. A composite acceptable load (CAL) table was developed for the 216 conditions presented in the female lifting table of Snook and Ciriello (1991). Each CAL value was calculated to correspond to the most conservative load of the three design criteria. The RWLs caused lumbar compression forces close to the biomechanical limit of 3400 N for lifts below knuckle height, but resulted in compression forces that are much lower at higher lifting heights. At moderate lifting frequencies, the average RWL would be acceptable to more than 95% of female workers according to the psychophysical criterion. At the highest frequencies, the RWL was found to be an average of 63% of the CAL values based on the integration of the psychophysical and physiological criteria. It is recommended that ergonomists acknowledge the very conservative nature of the revised NIOSH lifting equation when using it to evaluate occupational lifting tasks.