Thomas R. Waters

Revised NIOSH equation for the design and evaluation of manual lifting tasks

In 1985, the National Institute for Occupational Safety and Health (NIOSH) convened an ad hoc committee of experts who reviewed the current literature on lifting, recommend criteria for defining lifting capacity, and in 1991 developed a revised lifting equation. Subsequently, NIOSH developed the documentation for the equation and played a prominent role in recommending methods for interpreting the results of the equation. The 1991 equation reflects new findings and provides methods for evaluating asymmetrical lifting tasks, lifts of objects with less than optimal hand-container couplings, and also provides guidelines for a larger range of work durations and lifting frequencies than the 1981 equation. This paper provides the basis for selecting the three criteria (biomechanical, physiological, and psychophysical) that were used to define the 1991 equation, and describes the derivation of the individual components (Putz-Anderson and Waters 1991). The paper also describes the lifting index (LI), an index of relative physical stress, that can be used to identify hazardous lifting tasks. Although the 1991 equation has not been fully validated, the recommended weight limits derived from the revised equation are consistent with or lower than those generally reported in the literature. NIOSH believes that the revised 1991 lifting equation is more likely than the 1981 equation to protect most workers.

Niosh Research Efforts to Prevent Musculoskeletal Disorders in the Healthcare Industry

Healthcare workers, including orthopaedic nurses, face a number of risk factors in the workplace for musculoskeletal disorders such as back and shoulder injuries. These disorders are associated with excessive back and shoulder loading due to manual patient handling, applying excessive forces during pushing and/or pulling of objects, required use of awkward postures during patient care, and working long hours and shiftwork. No healthcare workers are immune from injury because workers in all clinical areas are exposed to occupational risk factors, including hospitals, nursing homes, emergency services, critical care, operating rooms, orthopaedic units, and home healthcare environments. This article includes a summary of the scientific efforts of the researchers and their partners at the National Institute for Occupational Safety and Health (NIOSH) in evaluating and developing the best practice recommendations for reducing risk of these disorders for exposed workers. The studies conducted by NIOSH researchers and their partners approach the problem from a variety of perspectives, ranging from comprehensive epidemiological studies examining the effectiveness of implementation of a safe patient handling and movement program to laboratory studies evaluating the biomechanical stress associated with using patient handling equipment, and education training programs for use in schools of nursing to educate new workers about safe work practices. Results of these studies have provided scientific evidence that significant occupational risks for musculoskeletal disorders exist and that effective interventions are available to reduce the risk for these workers.

Evaluation of the revised NIOSH lifting equation. A cross-sectional epidemiologic study.

STUDY DESIGN A cross-sectional study of the 1-year prevalence of low back pain was conducted in workers employed in manual lifting jobs. OBJECTIVES To provide epidemiologic data to determine the correlation between the prevalence of low back pain and exposure to manual lifting stressors, measured with the lifting index component of the revised lifting equation from the National Institute for Occupational Safety and Health (NIOSH). SUMMARY OF BACKGROUND DATA The NIOSH lifting equation has been proposed as a practical, yet valid tool for assessing the risks of low back pain caused by manual lifting. To date, however, there have been few studies in which the effectiveness of the equation to identify jobs with elevated rates of low back pain has been evaluated. METHODS Fifty jobs from four industrial sites were evaluated with the NIOSH lifting equation. A symptom and occupational history questionnaire was administered to 204 people employed in lifting jobs and 80 people employed in nonlifting jobs. Regression analysis was used to determine whether there was a correlation between the lifting index and reported low back pain. RESULTS As the lifting index increased from 1.0 to 3.0, the odds of low back pain increased, with a peak and statistically significant odds ratio occurring in the 2 < lifting index < or = 3 category (odds ratio = 2.45). For jobs with a lifting index higher than 3.0, however, the odds ratio was lower (odds ratio = 1.45). CONCLUSIONS Although low back pain is a common disorder, the lifting index appears be a useful indicator for determining the risk of low back pain caused by manual lifting.

National occupational research agenda (NORA) future directions in occupational musculoskeletal disorder health research.

Musculoskeletal disorders are among the most costly health care problems facing society today. The scientific literature has indicated that psychosocial factors, individual factors, workplace physical requirements, and workplace organizational factors have been associated with risk. Since musculoskeletal risk is multi-dimensional, the magnitude of risk attributable to various factors can be of importance to scientists and policy makers in designing countermeasures to reduce injury incidence. Traditionally, the disciplines of biomechanics, physiology, and psychophysics have dominated the body of knowledge that has defined exposure limitations to work. However, recent research has explored the association of psychosocial and work organization factors with musculoskeletal problems. Advances have been made to better quantify the levels of occupational exposure by improved exposure metrics, quantification of three-dimensional loads experienced by certain joints (e.g. the spine), identification of tissue tolerance limits and tissue response to mechanical stresses, and the impact of psychosocial stresses. However, efforts to quantitatively link epidemiological, biomechanical loading, soft tissue tolerance, and psychosocial studies should be pursued to establish a better understanding of the pathways of injury and resultant preventive strategies. Although we are beginning to understand how the major risk factors influence the load-tolerance relationship of human tissue, how these risk factors interact is virtually unexplored. Since the impact of the interactions may be far greater than that of any individual factor, the impact of the interactions between risk factors must be delineated so that work-related risk can be better quantified. Efforts to quantitatively link epidemiological, biomechanical loading, soft tissue tolerance, and psychosocial studies should be pursued to establish a better understanding of the pathways of injury and resultant preventive strategies.

A Cross-Sectional Study of Risk Factors for Musculoskeletal Symptoms in the Workplace Using Data From the General Social Survey (GSS)

Objective: Assessments of potential risk factors for musculoskeletal disorders (MSDs) from large, national study populations using personal interviews are critical to our understanding of exposure-response relationships. To address this need, we analyzed two outcome measures—self-reported back pain and upper extremity pain—from the quality of work life (QWL) module of the General Social Survey (GSS). We investigated several individual, psychosocial, and physical factors for their relationship to these outcome measures. Methods: The study population included US adults, noninstitutionalized, English-speaking, aged 18 years or older, and employed at least part time (≥20 hr/wk). Final sample size was 1484 workers. Results: Variables of physical exposure significantly increased the risk of both low back pain and upper extremity pain. Multiple injuries and some psychosocial factors were associated with MSDs, and there was an additive effect on risk of MSDs with exposure to both physical exposure and work stress. Conclusions: A relationship between physical loads and musculoskeletal disorders was indicated by the results, which will enable creating a database for tracking reports of MSDs in the US working population.

Accuracy of measurements for the revised NIOSH lifting equation

Twenty-seven non-ergonomists who participated in a one-day training session on the use of the NIOSH lifting equation (NLE) were subsequently tested on a simulated lifting task eight weeks later to determine their accuracy in measuring the variables. Analysis of the results indicate that (1) inter-observer variability was small, especially for the most important factor (i.e. horizontal distance); (2) individuals can be trained to make measurements with sufficient accuracy to provide consistent recommended weight limit and lifting index values; and (3) measurement of the coupling and asymmetric variables were the least accurate.

The impact of operating heavy equipment vehicles on lower back disorders

Literature reviews examining the relationship between heavy equipment vehicle (HEV) operation and the development of musculoskeletal disorders have generally been qualitative in nature and have not employed an evidence-based assessment procedure. This research determines the extent to which whole-body vibration/shock and working postures are associated with lower back and neck disorders among HEV operators, while accounting for individual (i.e. age, gender, prior history of back or neck disorders) and occupational (i.e. material handling, climatic conditions, psychosocial factors) confounders. Published articles were obtained from a search of electronic databases and from bibliographies in the identified articles. A critical appraisal of these articles was conducted using an epidemiological appraisal instrument (Genaidy et al. 2007). The meta-analysis was conducted using statistical techniques employing fixed-effect and random-effect models. Eighteen articles reporting observational studies satisfied the inclusion criteria adopted for this research. The methodological qualities of the published studies ranged from marginal to average. The meta-relative risk was found to be 2.21, indicating that operators exposed to driving HEVs are at more than twice the risk of developing lower back pain in comparison to those not exposed to driving HEVs. Therefore, it seems possible that there is a causal relationship between working as a HEV operator and development of lower back disorders. Prospective cohort studies are urgently needed to confirm the outcomes of this evidence-based methodology (based in part on the meta-analysis) and the biological plausibility should be further explored. The reported findings point to a need for improved ergonomic design of HEVs.

Evidence of Health Risks Associated with Prolonged Standing at Work and Intervention Effectiveness

Purpose: Prolonged standing at work has been shown to be associated with a number of potentially serious health outcomes, such as lower back and leg pain, cardiovascular problems, fatigue, discomfort, and pregnancy‐related health outcomes. Recent studies have been conducted examining the relationship between these health outcomes and the amount of time spent standing while on the job. The purpose of this article was to provide a review of the health risks and interventions for workers and employers that are involved in occupations requiring prolonged standing. A brief review of recommendations by governmental and professional organizations for hours of prolonged standing is also included. Findings: Based on our review of the literature, there seems to be ample evidence showing that prolonged standing at work leads to adverse health outcomes. Review of the literature also supports the conclusion that certain interventions are effective in reducing the hazards associated with prolonged standing. Suggested interventions include the use of floor mats, sit‐stand workstations/chairs, shoes, shoe inserts and hosiery or stockings. Studies could be improved by using more precise definitions of prolonged standing (e.g., duration, movement restrictions, and type of work), better measurement of the health outcomes, and more rigorous study protocols. Conclusion and Clinical Relevance: Use of interventions and following suggested guidelines on hours of standing from governmental and professional organizations should reduce the health risks from prolonged standing.

Methods for Assessing the Physical Demands of Manual Lifting: A Review and Case Study from Warehousing

Assessment of the physical demands of potentially hazardous manual material handling (MMH) activities is fundamental to the prevention of disabilities from occupationally related low back pain, a problem costing the nation billions of dollars annually. Although there is a variety of ergonomic assessment methods available for assessing MMH activities, there is a lack of practical information to assist users in choosing the most appropriate assessment methods of a particular job. This article reviews currently available assessment methods and presents case study results of a physically demanding repetitive manual lifting job in two grocery warehouses. The case study will provide a framework for a comparison of the methods and a discussion of relevant application issues designed to assist users in selecting appropriate methods for assessing MMH jobs. Based on the results of the study, it is concluded that all of the ergonomic methods were in agreement that the job of grocery selector has a high level of risk for low back pain. Differences between the methods were noted, however, that should be considered when choosing a specific method for a specific application.

Efficacy of the Revised NIOSH Lifting Equation to Predict Risk of Low Back Pain Due to Manual Lifting Expanded Cross-Sectional Analysis

Objective: To evaluate whether the Revised NIOSH Lifting Equation (RNLE) is a valid tool for assessing risk of low back pain (LBP) due to manual lifting by using combined data from two cross-sectional studies of 1-year prevalence. Methods: Results from a symptom and occupational history questionnaire and RNLE analysis for 677 subjects employed in 125 manual lifting jobs at nine industrial sites were combined from two studies. Results: The odds of LBP increased as the lifting index (LI) increased from 1.0 to 3.0. A statistically significant odds ratio (OR) was found for both the 1 < LI ⩽ 2 (OR = 1.81) and the 2 < LI ⩽ 3 categories (OR = 2.26). For jobs with an LI value greater than 3.0, however, the OR remained nonsignificant. The 2 < LI ⩽ 3 group remained statistically significant after adjusting for age, gender, body mass index, and psychosocial factors. Conclusions: It is clear that as the LI increases, the risk of LBP increases. Longitudinal studies are needed.