NIOSH Lifting Equation Research Articles

Panel Discussion In Honor of Dr Tom Waters The NIOSH Lifting Equation - Part I

The NIOSH Lifting Equation, specifically the 1991 Revised Lifting Equation or RLE (Waters et al., 1993) is used worldwide by occupational ergonomists, industrial engineers and safety specialists to assess and (re)design manual lifting tasks and industrial systems that involve either single or repetitive lifting. Since the initial publication of the RLE, there have been a number of published studies on its usability, effectiveness and validation. The purpose of this panel discussion will be to critically review these RLE-related studies and examine implications of applying the RLE in various occupational settings and working populations. The first of four presentations will summarize recent epidemiological studies that have quantified exposure-response relationships between the RLE and incidence of low-back pain-related care and medication use issues, and discuss the RLE implications for job surveillance, intervention, and design approaches. The second presentation discusses practical relevance of the RLE and issues surrounding its sensitivity and specificity in correctly identifying hazardous lifting tasks. The third presentation will critically examine the conservativeness of the recommended weight limit derived from RLE by comparing the output of the RLE with the output from the specific biomechanical, psychophysical and physiological criteria utilized in its initial development of the lifting equation. Although application of the RLE has exponentially grown since its inception, the final presentation explores its feasibility in applying it to a non-US work force. The primary audience for this session will be occupational ergonomists who utilize the NIOSH equation for job assessment and (re)design, although the discussion should be of interest to researchers as well. The overall goal of this Part 1 symposium is to provide RLE users with some practical suggestions and recommendations.

Panel Discussion In Honor of Dr Tom Waters The NIOSH Lifting Equation - Part II

With the introduction of the NIOSH Lifting Equation, specifically after the publication of the Revised Lifting Equation (RLE) (Waters et al., 1993), occupational health and safety professionals across the world have successfully utilized the RLE to evaluate the risks associated with lifting and lowering tasks in the workplace. Although the RLE takes into consideration of various job task variables to determine recommended weight limits for a variety of task combinations, a number of articles and peer reviewed publications have appeared with a notion of either extending or modifying the RLE to address manual handling situations that the original equation was not able to assess comprehensively. The purpose of this panel discussion will be to provide an overview to ergonomics practitioners and researchers of these extensions and beyond, thus exploiting the full potential of this lifting equation. The first presentation will discuss the Variable Lift Index (VLI) for highly variable manual lifting tasks, whereas the second presentation describes the Sequential Lift Index (SLI) in assessing a sequence of lifting tasks that workers perform while they rotate to different tasks over a workday. In addition to the inherent variability in lifting tasks assumed by the RLE, we often encounter materials handling scenarios associated with one-handed lifting, team lifting, lifting of people (e.g., patient handling), lifting while seated or kneeling, lifting on improper frictional surfaces, lifting unstable loads, or lifting for more than 8 hours. To this effect, the third presentation examines the wider application of the RLE by adding new multipliers to the equation. Extending further on quantifying typical lifting task-related variables and associated risk on the lower back, the final presentation explores the fatigue failure process experienced by the lumbar spine when performing multiple and varied lifting tasks. This innovative approach is nascent in ergonomics literature, especially in ergonomics risk assessment, and has great potential in injury prevention at the workplace.

The Cumulative Lifting Index (CULI) for the Revised NIOSH Lifting Equation: Quantifying Risk for Workers With Job Rotation.

The objectives were to: (a) develop a continuous frequency multiplier (FM) for the Revised NIOSH Lifting Equation (RNLE) as a function of lifting frequency and duration of a lifting task, and (b) describe the Cumulative Lifting Index (CULI), a methodology for estimating physical exposure to workers with job rotation. The existing FM for the RNLE (FME) does not differentiate between task duration >2 hr and <8 hr, which makes quantifying physical exposure to workers with job rotation difficult and presents challenges to job designers. Using the existing FMs for 1, 2, and 8 hr of task durations, we developed a continuous FM (FMP) that extends to 12 hr per day. We simulated 157,500 jobs consisting of two tasks each and, using different combinations of Frequency Independent Lifting Index, lifting frequency and duration of lifting. Biomechanical stresses were estimated using the CULI, time-weighted average (TWA), and peak exposure. The median difference between FME and FMP was ±1% (range: 0%-15%). Compared to CULI, TWA underestimated risk of low-back pain (LBP) for 18% to 30% of jobs, and peak exposure for an assumed 8-hr work shift overestimated risk of LBP for 20% to 25% of jobs. Peak task exposure showed 90% agreement with CULI but ignored one of two tasks. The CULI partially addressed the underestimation of physical exposure using the TWA approach and overestimation of exposure using the peak-exposure approach. The proposed FM and CULI may provide more accurate physical exposure estimates, and therefore estimated risk of LBP, for workers with job rotation.

The NIOSH Lifting Equation for Manual Lifting and Its Applications

The literature on the problems caused by frequent lifting and lowering tasks has grown rapidly in the past few decades. This paper focuses on presenting literature on the NIOSH Lifting Equation, which is used for calculating injure-free lifting capabilities for workers who perform two-handed manual lifting tasks and using the study as a basis for applying it to a manufacturing company Technocrats India, Nagpur. The papers acquired for the study focus on the importance of the equation to reduce the effect of Low Back Pain (LBP) associated with various lifting operations. The result of the study is a systematic research and compilation of various aspects of the equation and its applications at construction sites and industrial organizations and its use at a manufacturing company where the manufacturing process comprises the machining of the Cylinder Body part and Valve body part. The equation will be used for these to know the effect of the work on workers. The final assessment of the study is that for successful outcomes for reduction in Work related Musculoskeletal Disorders (WMSDs) and LBP, the equation should be thoroughly considered for manual lifting practices.

A toolkit for the analysis of biomechanical overload and prevention of WMSDs: Criteria, procedures and tool selection in a step-by-step approach

BackgroundWhen studying work related musculoskeletal disorders (WMSDs), various factors (mechanical, organizational, psychophysical, individual) and their interrelationships have been considered to be important in general models for epidemiologic surveys and risk assessment and management. Hence the need for a “holistic” approach towards MSD prevention. On the other hand, considering the widespread presence of these factors and of WMSDs in many work places located in both developed and developing countries, there is a strong demand from OSH agencies and operators for “simple” risk assessment and management tools that can also be used by non-experts. ObjectivesThis paper is one of the main contributions towards a WHO/IEA project for developing a “Toolkit for WMSD prevention” by the TC on MSD of the IEA. The paper focuses on selecting tools at different levels for hazard identification, risk estimation and management. The proposals were primarily developed in this context but they also derive from other converging issues such as the ISO TR 12295 – published in 2014. Methods and criteriaProposals are based on two essential criteria: 1) adoption of a step-by-step approach starting with basic tools and moving to more complex tools only when necessary; 2) factoring in complexity and the presence of multiple influencing factors at every step (although with different degrees of in-depth analysis). ResultsThe proposals include: Step one: identification of preliminary occupational hazards and priority setting via “key-enter” questions (at this step, all potential hazards affecting WMSDs should be considered). Step two: identification of risk factors for WMSDs, consisting of a “quick assessment” and substantially aimed at identifying three possible conditions: acceptable/no consequences; critical/redesign urgently needed; more detailed analysis required. Step three: recognized tools for estimating risk (of WMSDs) are used depending on the outcomes of step two. Examples of such tools include “adaptations” of the Revised NIOSH Lifting Equation, Liberty Mutual Psychophysical Tables, OCRA Checklist, etc. These tools should adequately cover most of the influencing factors. Relevance to industryThe use of a step-by-step approach and validated risk estimation tools, in accordance with international standards, makes it possible to tackle the challenge of simplifying complexity in the assessment of biomechanical overload conditions and in the prevention of WMSDs in enterprises of all sizes, small businesses, agriculture, and in developing countries.

Ergonomic Assessment for Manual Materials Handling of Livestock Feed by Elderly Farmers in Korea

Objective: The purpose of the study is to evaluate appropriate weight for aged farmers in manually handling livestock feed in bags using ergonomic methods.BR Background: In the livestock industry in South Korea, despite the trend of aging of labor manpower, heavy items are still manually handled in many farms. In particular, among stockbreeding works, the handling of feed in bags weighing 25~30kg is reported as a cause of frequent injuries and musculoskeletal system diseases. However, studies on the standard for recommended weight allowed considering the physical characteristics of aged farmers older than 60 years with greatly decreased physical strength and muscle strength are insufficient.BR Method: To evaluate appropriate weight for handling of heavy livestock feed in bags, physical techniques for measuring recognized levels of physical work loads, the NLE (NIOSH lifting equation) a method that is an observation type technique, and an ergonomic modeling technique to predict compressive force imposed on L5/S1 were used. Subjects who participated in the experiment were organized into two groups of males/females with mean age exceeding 60 years, and lifting tasks were evaluated for nine weight levels.BR Results: Based on the results of psychophysical measurement, females showed a tendency of more drastic increases compared to males when weight was over 19kg. The results of estimation of regression models for the weight, 18.0 kg (r²=0.97) and 15.3kg (r²=0.97) were evaluated as stable load for males and females, respectively. In addition, both the observation type evaluation and ergonomic model evaluation showed stable loads in a range of 15~18kg.BR Conclusion: Given the results of the study, the weight of the feed in bags currently distributed to farms can become a cause of not only overexertion but also farm work related disasters such as musculoskeletal disorders and safety accidents. Providing livestock feed in bags weighing not more than 19kg for aged farmers is judged desirable, and managerial improvement for this matter is considered necessary. BR Application: The results of the present study can be utilized as useful data for institutional improvement of the weight of livestock feed in bags.

Revised NIOSH Lifting Equation May generate spine loads exceeding recommended limits

The 1991 NIOSH Lifting Equation (NLE) is widely used to assess the risk of injury to spine by providing estimates of the recommended weight limit (RWL) in hands. The present study uses the predictive equations developed based on a detailed trunk musculoskeletal biomechanical model to verify whether the RWL generates L5-S1 loads within the limits (e.g., 3400 N for compression recommended by NIOSH and 1000 N for shear recommended in some studies). Fifty lifting activities are simulated here to evaluate the RWL by the NLE and the L5-S1 loads by the predictive equations. In lifting activities involving moderate to large forward trunk flexion, the estimated RWL generates L5-S1 spine loads exceeding the recommended limits. The NIOSH vertical multiplier is the likely cause of this inadequacy; a revised multiplier accounting for the trunk flexion angle is hence needed. The use of a fixed 3400 N compression limit is also questioned. Relevance to industryErgonomist and occupational health practitioners are advised to use the NLE along with the predictive equations of the spine loads proposed in this study when evaluating the risk of injury to the spine in lifting activities particularly those involving moderate to large trunk flexion.

Dynamic Footwear Fit Model Similar to NIOSH Lifting Equation

Improper footwear design causes injuries and illnesses, and hence it is important to understand not only the foot but also the footwear. In order to reduce injuries and illnesses, the foot and footwear have to match in such a way to avoid high pressure points and friction due to movements. As far as footwear fit is concerned, literature review has indicated that static footwear fit has mostly been studied, even though dynamic pressure, friction, and foot movement beyond the normal range of motion will cause different type of injuries and illnesses when compared to static fit. Therefore, this paper proposes a theoretical model for dynamic fit. The dynamic footwear fit model is developed similar to the NIOSH lifting equation. The dynamic fit is related to static fit and several multipliers related to footwear design, material properties, and time factor. More research is being carried out to set the parameter values of the theoretical model. The importance of this model is useful for quantification of dynamic footwear fit as it is more related to the actual situation. Better footwear fit, both static and dynamic, will generally improve foot health.

Association between lifting and use of medication for low back pain: results from the Backworks Prospective Cohort Study.

To evaluate relationships between lifting and lowering of loads and risk of low back pain resulting in medication use (M-LBP). At baseline, worker demographics, psychosocial factors, hobbies, LBP history, and lifting and lowering (quantified using the Revised NIOSH Lifting Equation) were assessed. A cohort of 258 incident-eligible workers was followed up for 4.5 years to determine new M-LBP cases and changes in lifting/lowering requirements. Proportional hazards regression with time-varying covariates was used to model associations. Factors predicting M-LBP included peak lifting index (PLI) and composite lifting index (PCLI), LBP history, anxiety, and housework. In adjusted models, PLI and PCLI showed exposure-response relationships with peak hazard ratios of 3.8 and 4.3, respectively (P ≤ 0.02). Lifting of loads is associated with increased risk of M-LBP. The PLI and PCLI are useful metrics for estimating the risk of M-LBP from lifting.

0319 Biomechanical Comparison of Lumbar Risk Assessment in Manual Material Handling Work

ObjectivesIn this study, lifting index (LI) by NIOSH lifting equation (NLE) and biomechanical load by lumbar motion monitor (LMM) were determined to assess low-back disorder (LBD) risk associated with manual...

A Review of the NIOSH Lifting Equation and Ergonomics Analysis

The revised NIOSH Lifting Equation developed in 1991 is an ergonomic intervention assessment tool that used to calculate the recommended weight limit (RWL) for lifting tasks and to identify the hazardous lifting tasks. But this equation application is limited to those conditions for which it was designed and the different populations have different anthropometric distributions. This research will propose a solution to determine the effect of different manual lifting tasks on biomechanical, physiological and psychophysical limitation and develop the new automatic system tool to calculate the ideal RWL for Malaysian people for the working tasks perform. This new system tool which design according to the criteria of Malaysian people can increase the safe working environment for the workers.

소방대원의 중량물작업에 대한 인간공학적 분석

본 연구에서는 소방대원이 수행하는 업무 중 중량물을 다루어야 하는 작업에 대한 분류 및 정량적 분석(NLE, 3DSSPP)을 수행하여 향후 소방대원의 중량물 관련 작업에 대한 위험도를 예측하고, 관련 위험도를 감소시키기 위한 기초 자료를 도출하고자 하였다. 도출된 위험도 등급은 위험도 점수가 3점부터 9점까지 총 7단계로 구성되었다. 가장 위험도가 높은 1등급은 나타나지 않았으며 인명구조 작업이 두 번째로 높은 2등급에 속하는 것으로 나타났다. 3등급은 파괴기구 활용, 환자 들어올리기작업 등으로 나타났다. 본 연구 결과들은 소방대원의 허리 부상을 포함하는 근골격계 질환 예방을 위한 작업방법 및 장비의 개선, 교육 프로그램의 개발에 기본 토대가 될 수 있다고 판단되며, 소방대원들의 근골격계 질환에 대한 지속적인 예방을 위해서는 본 연구의 골격을 토대로 한 추후 심층적인 조사와 연구가 시급하다고 사료된다. Modern fire fighting jobs have been expanded to include areas of rescue, emergency medical service as well as conventional fire suppression, so that load for fire fighting jobs has been increased. Specifically, musculoskeletal disorders (MSDs) such as low back injury have been considered as one of major industrial hazards in heavy manual material handling during fire fighting jobs. This study tried to evaluate risk levels and to prepare background for reducing risk levels associated with heavy manual material handling during fire fighting jobs. This study applied two major tools in evaluating heavy manual material handling jobs which were NLE (NIOSH Lifting Equation) and 3DSSPP (3D Static Strength Prediction Program). A risk index in terms of heavy manual material handling during fire fighting jobs was identified. This index consisted of seven risk levels ranged from nine points (the first level) to three points (the seventh level). There was no job associated with the first level (the highest risk level) of index. There was only one job (life saving job) belonging to the second level (the second highest risk level) of index. The third level had jobs such as usage of destruction equipment and lifting patient. A total of basic eighteen jobs was categorized into six different levels (2nd-7th levels) of index. The outcome of the study could provide a good basis for conducting job intervention, preparing good equipment and developing good education program in order to prevent and reduce MSDs including low back injury of fire fighting jobs.

The NIOSH Lifting Equation and Low-Back Pain, Part 2

The aim of this study was to investigate the relationship between the revised NIOSH lifting equation (RNLE) and risk of seeking care for low-back pain (SC-LBP). The RNLE is commonly used to quantify low-back physical stressors from lifting/lowering of loads in workplaces. There is no prospective study on relationship between RNLE and SC-LBP. A cohort of 258 incident-eligible workers from 30 diverse facilities was followed for up to 4.5 years. Job physical exposures were individually measured. Worker demographics, medical history, psychosocial factors, hobbies, and current low-back pain were obtained at baseline. The cohort was followed monthly to ascertain SC-LBP and quarterly to determine changes in physical exposure. Associations between SC-LBP and both the peak lifting index (PLI) and peak composite lifting index (PCLI) were tested in multivariate models using proportional hazards regression. SC-LBP lifetime prevalence at baseline was 31.9%, and there were 24 incident cases during follow-up. Factors predicting SC-LBP included job physical exposure (PLI and PCLI), history of low-back pain, age, female gender, and lower body mass index. In adjusted models, risk (hazard ratio [HR]) increased per unit increase in PLI and PCLI (p = .03 and .02, and maximum HR = 23.0 and 21.9, respectively). Whereas PCLI suggested a continuous increase in risk with an increase in PCLI, the PLI showed elevated, though somewhat reduced, risk at higher exposures (HR = 14.9 at PLI = 6). Job physical stressors are associated with increased risk of SC-LBP. Data suggest that both the PLI and PCLI are useful metrics for estimating exposure to job physical stressors.

The NIOSH Lifting Equation and Low-Back Pain, Part 1

The aim of this study was to evaluate relationships between the revised NIOSH lifting equation (RNLE) and risk of low-back pain (LBP). The RNLE is commonly used to quantify job physical stressors to the low back from lifting and/or lowering of loads. There is no prospective study on the relationship between RNLE and LBP that includes accounting for relevant covariates. A cohort of 258 incident-eligible workers from 30 diverse facilities was followed for up to 4.5 years. Job physical exposures were individually measured. Worker demographics, medical history, psychosocial factors, hobbies, and current LBP were obtained at baseline. The cohort was followed monthly to ascertain development of LBP and quarterly to determine changes in job physical exposure. The relationship between LBP and peak lifting index (PLI) and peak composite lifting index (PCLI) were tested in multivariate models using proportional hazards regression. Point and lifetime prevalences of LBP at baseline were 7.1% and 75.1%, respectively. During follow-up, there were 123 incident LBP cases. Factors predicting development of LBP included job physical exposure (PLI and PCLI), history of LBP, psychosocial factors, and housework. In adjusted models, risk (hazard ratio [HR]) increased per-unit increase in PLI and PCLI (p = .05 and .02; maximum HR = 4.3 and 4.2, respectively). PLI suggested a continuous increase in risk with an increase in PLI, whereas the PCLI showed elevated, but somewhat reduced, risk at higher exposures. Job physical stressors are associated with increased risk of LBP. Data suggest that the PLI and PCLI are useful metrics for estimating exposure to job physical stressors.

Can the Revised NIOSH Lifting Equation Predict Low Back Pain Incidence in a ‘90-day-pain-free-cohort’?

LBP is a major public health concern with enormous human and economic burden. The validity of the Revised NIOSH Lifting Equation (RNLE), a widely used job assessment tool, has not been studied previously in individuals with past LBP. The primary aim of this research was to study the relationship between RNLE measures and incident LBP episode risk after a 90-day pain free period using a prospective study design. One hundred and thirty industrial workers were identified as eligible to become an incident case for LBP. Univariate relationships between RNLE measures and incidence of LBP episode were studied using the Cox proportional hazards model. Significant associations between RNLE measures and incident LBP risk were found. It is concluded that the RNLE is predictive of incident LBP episode risk in individuals with past pain.

Índice de levantamento da equação do NIOSH e lombalgia

Este estudo tem por objetivo avaliar a relação entre o Índice de Levantamento obtido mediante a aplicação da Equação de Levantamento do NIOSH e a incidência de lombalgia entre quarenta e oito trabalhadores envolvidos nas tarefas de levantamento manual de cargas. Aplicou-se a equação em onze tarefas e realizou-se entrevista com os trabalhadores. As condições mais desfavoráveis apresentavam-se no destino do levantamento. As variáveis da tarefa que mais contribuíram para os valores inadequados do Índice de Levantamento foram: a distância horizontal, a frequência de levantamentos e a distância vertical; além do peso elevado da carga. A incidência de lombalgia nos últimos doze meses foi de 19%, enquanto que a incidência da lombalgia relacionada ao trabalho, no mesmo período, foi de 10%. Em 72,7% das tarefas avaliadas o Índice de Levantamento Composto foi superior a três, sendo consideradas como de alto risco ergonômico.

Efficacy of the Revised NIOSH Lifting Equation to Predict Risk of Low Back Pain Due to Manual Lifting

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. 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. 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. It is clear that as the LI increases, the risk of LBP increases. Longitudinal studies are needed.

Validation of Revised NIOSH Lifting Equation and 3D SSP Model to Predict Risk of Work-Related Low Back Pain

This study is based upon data collected for a large scale, multi-site prospective cohort study of work-related low back pain (WLBP). The aim of this study was to validate the Revised NIOSH Lifting Equation (RNLE) and the 3D Static Strength Prediction Model (3D SSPM) to predict the risk of WLBP. Complete baseline and follow up data on job physical exposure and WLBP status were available on 258 workers free of WLBP at baseline. Relationships between job physical factors and incident cases of WLBP were analyzed using the Cox proportional hazards model. There was evidence of association between load moment and the Lifting Index calculated from the RNLE and incidence of WLBP, and no evidence of association with estimated compressive force on L5/S1 disc and percent capable population. It is concluded that the RNLE is predictive of future risk of WLBP.

Ergonomics Case Study: Revised NIOSH Lifting Equation Instruction Issues for Students

This case study investigated the effectiveness of formal instruction of the Revised NIOSH Lifting Equation for university students who may use the equation in their future work. Their successes and challenges were examined through a class exercise and two exams, all of which followed the classroom instruction in applying the Lifting Equation. Results showed students (1) had difficulty determining relevant values for task variables from reading a job description, and (2) generally were able to calculate the Recommended Weight Limit (RWL) and Lifting Index (LI) when task variables were such that the associated multipliers were less than or equal to 1. However, when the multiplier was calculated to be greater than 1, students had difficulty interpreting the result. The task variable and multiplier (consistently the greatest challenge) were the asymmetry task variable, A, and the asymmetric multiplier, AM. Results indicate that the layout of the Job Analysis Worksheet for Step 1 may make it easy to make arithmetic errors when calculating multipliers. It is recommended that the worksheet be redesigned to help individuals decrease the probability of making an arithmetic error when calculating the task variables, multipliers, RWL, and LI. It is also recommended that the redesigned worksheet be tested to determine whether fewer arithmetic errors are made and if the worksheet is less confusing for an inexperienced user to use.

A psychophysical evaluation of NIOSH Lifting Equation in a Chinese young male population: a pilot study

To determine the maximum acceptable weight of lift (MAWL) in a Chinese young male population, and examine whether the revised weight limit recommended by the US. National Institute for Occupational Safety and Health can be used for Chinese workers. Eleven young male college students participated in the experiment. The psychophysical approach was used to determine the MAWL with the different frequencies of lift, the heart rate and the self-evaluation. The weight was lifted from the floor to the work-table (760 mm). The results were compared with the recommended weight limit (RWL) and the MAWL by Snook. The MAWL of young male was 34.1 kg while the MAWL with frequency of 1, 4 and 8/min was 17.4, 14.7 and 12.2 kg respectively. The overall MAWL were lower than RWL of NIOSH and the results of Snook. The NIOSH 1991 equation such as load constant and frequency multiple should be revised when the NIOSH limits is used in Chinese population.