Academic journal article Human Factors

Continuous Assessment of Back Stress (CABS): A New Method to Quantify Low-Back Stress in Jobs with Variable Biomechanical Demands

Academic journal article Human Factors

Continuous Assessment of Back Stress (CABS): A New Method to Quantify Low-Back Stress in Jobs with Variable Biomechanical Demands

Article excerpt

Jobs with a high degree of variability in manual materials handling requirements expose limitations in current low-back injury risk assessment tools and emphasize the need for a probabilistic representation of the biomechanical stress in order to quantify both acute and cumulative trauma risk. We developed a hybrid assessment methodology that employs established assessment tools and then represents their evaluations in a way that emphasizes the distributions of biomechanical stress. Construction work activities in the home building industry were evaluated because of the high degree of variability in the manual material handling requirements. Each task was evaluated using the Revised NIOSH Lifting Equation, The University of Michigan Three-Dimensional Static Strength Prediction Program [TM], and the Ohio State University Lumbar Motion Monitor Model. The output from each model was presented as time-weighted histograms of low-back stress, and the assessments were compared. The results showed considerable differe nces in what were considered high-risk activities, indicating that these 3 assessment tools consider the risk of low-back injury from different perspectives. The time-weighted distribution aspect of this methodology also contributed vital information toward the identification of high-risk activities. These results illustrate the necessity for more advanced low-back injury risk assessment techniques for jobs with highly variable manual materials handling requirements.

INTRODUCTION

Over the last three decades, several low-back injury risk assessment tools have been developed to provide ergonomics practitioners with the ability to evaluate the relative risk posed by manual materials handling (MMH) tasks. The Work Practices Guide for Manual Lifting (NIOSH, 1981) and the Revised NIOSH Lifting Equation (Waters, Putz-Anderson, & Garg, 1994; Waters, Putz-Anderson, Garg, & Fine, 1993) are two well-established methods developed by the National Institute for Occupational Safety and Health (NIOSH). The lumbar motion monitor risk assessment model (Marras et al., 1993) and the Three-Dimensional Static Strength Prediction Program [TM] (3DSSPP) were developed by researchers at Ohio State University and the University of Michigan, respectively. Based on our current understanding of the etiology of occupation-related low-back disorders, it is clear that each of these assessment tools addresses an important facet of the low-back injury risk paradigm but that none of these models individually is able to identify all high-risk activities. This perspective is supported by the recent research of Lavender, Oleske, Nicholson, Andersson, and Hahn (1999), which showed poor correlation among the estimates of low-back disorder risk that were produced by these three tools when assessing a variety of MMH tasks. The goal of the current study was to incorporate the strengths of each of these existing assessment tools into one hybrid assessment methodology. To build the foundation for this hybrid model, we will present an overview of each of these constituent models along with our perceptions of each model's strengths and limitations.

NIOSH Model

The NIOSH models (NIOSH, 1981; Waters et al., 1993) utilize static workplace configuration information to develop estimates of weights that can be safely lifted by a majority of the working population. The workplace variables considered in the Revised NIOSH Lifting Equation (Waters et al., 1993) are vertical position of load, horizontal distance between the load and the spine, frequency of lifting, vertical travel distance of the load, asymmetric posture of torso, and coupling quality between the lifter and the object being lifted. These measures are then combined in a multiplicative model to arrive at an appropriate weight (called the recommended weight limit, or RWL) that can be lifted safely by a majority of the working population. The ratio of the actual weight being lifted to this RWL is a value called the lifting index (LI). …

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