Relationships between static load acceptability, ratings of perceived exertion, and biomechanical demands

Several guidelines for manual material handling have been derived using psychophysical methods. Despite ease of use and interpretation, such guidelines have received limited verification and can be criticized for their dependence on subjective measures. In this study, 10 participants reported both maximum acceptable loads and subjective ratings. This was done statically, and in postures that isolated the elbow, shoulder, or lower torso joint demands. Two major conclusions were reached from examination of the relationships among maximum acceptable loads, ratings of perceived exertion, and relative joint demands (external/strength moment). First, relative joint demands appeared to be used in determining acceptable limits, but this use differed both within and between individuals. Second, linear relationships were found between relative joint demands and perceived exertion, though again inconsistencies were found among individuals. Relevance to industry: Toward the end of providing a stronger theoretical/objective basis for psychophysical methods, the present results, along with existing evidence, provide only mixed support. Guidelines for material handling based on psychophysical methods, while of clear value, should be interpreted with some caution until future evidence indicates the source upon which acceptable limits are obtained by experimental participants. © 2005 Elsevier B.V. All rights reserved.