Repetitive Lifting Task Research Articles

Productivity Improvement for Optimum Utilization of a Worker's Capabilities in Repetitive Lifting Tasks

In spite of a high degree of mechanization and automation found in industries, it has been observed that repetitive manual lifting jobs involving the handling of loads varying from a few hundred grams to as much as about fifty kilograms continue to be undertaken manually by industrial workers. One of the major and most inescapable of all tasks on an industrial shop floor is frequent manual material handling. A large number of industrial workers suffer from various types of cumulative trauma disorders (CTDs) due to ill designed manual lifting jobs and processes. A physically stressful and sustained manual lifting job needs to be viewed ergonomically in the light of workers' capabilities and after-effects of such jobs on the workers in the long run. In this paper, an attempt has been made to identify important factors that have a bearing on the capabilities of an industrial worker involved in such repetitive manual lifting jobs. This paper focuses on the ergonomics aspects of the manual lifting with particular reference to physical capabilities and limitations of a worker. Critical factors such as age, weight, height, oxygen up take, heart rate (HR), pulse rate (PR), electromyographic measurements (EMG), loads (weight of the material), distance of the load from the operator, posture, frequency of lifts, etc. have been considered. Aspects such as operational process sequence or the exact nature of the load to be lifted is situation specific in an industry. Some of the industries that may benefit from this work are tire manufacturing, railroad, automobile, chemical, ceramic, brick and pottery, glass, cement, steel and iron, building and construction, and defense related industries. An integrative ergonomic approach for evaluating a worker's capabilities for the job requirements has been developed. It is important to consider all approaches such as physiological, biomechanical, psychophysical, psychological and biochemical to optimize the worker's capabilities in such types of physically demanding jobs. In order to optimally utilize a worker's physical capabilities in such tasks an integrative systematic approach is recommended so that a worker's physical capabilities are correctly matched and production is optimized benefiting both the worker and the organization.

Ventilation Challenge in Lifting with and without a Belt

The hypotheses tested in this research are: (1) does the frequency and the volume of ventilation increases when lifting with a belt; (2) does the frequency and the volume of ventilation increases more when wearing a belt with a larger tension. The result of this study indicated a significant increase in breath-by-breath respiration (difference between the post-lifting and the pre-lifting ventilation) while wearing the belt during low workload and repetitive lifting task. There are also evidence showed that the mechanism responsible for modulating the breath was different when lifting with and without the belt.

Repetitive lifting tasks fatigue the back muscles and increase the bending moment acting on the lumbar spine

During manual handling, the back muscles protect the spine from excessive flexion, but in doing so impose a high compressive force on it. Epidemiological links between back pain and repetitive lifting suggest that fatigued muscles may adversely affect the balance between bending and compression. Fifteen volunteers lifted and lowered a 10 kg weight from floor to waist height 100 times. Throughout this task, the bending moment acting on the osteoligamentous lumbar spine was estimated from continuous measurements of lumbar flexion, obtained using the 3-Space Isotrak. Spinal compression was estimated from the electromyographic (EMG) activity of the erector spinae muscles, recorded from skin-surface electrodes at the levels of T10 and L3. EMG signals were calibrated against force when subjects pulled up on a load cell, and correction factors were applied to account for changes in muscle length and contraction velocity. Fatigue in the erector spinae muscles was quantified by comparing the frequency content of their EMG signal during static contractions performed before, and immediately after, the 100 lifts. Results showed that peak lumbar flexion increased during the 100 lifts from 83.3±14.8% to 90.4±14.3%, resulting in a 36% increase in estimated peak bending moment acting on the lumbar spine ( P=0.008). Peak spinal compression fell by 11% ( p=0.007). The median frequency of the EMG signal at L3 decreased by 5.5% following the 100 lifts ( p=0.042) confirming that the erector spinae were fatigued, but measures of fatigue showed no significant correlation with increased bending. We conclude that repetitive lifting induces measurable fatigue in the erector spinae muscles, and substantially increases the bending moment acting on the lumbar spine.

THE EFFECTS OF RESISTANCE TRAINING ON A HIGH INTENSITY MANUAL MATERIALS HANDLING TASK IN WOMEN

1806 Manual materials handling tasks in the workplace place high demands on strength and endurance. It is recognized that men possess advantages (i.e. because of greater size and strength) over women during such tasks, but the potential of training interventions for the improvement of women's occupational performance is largely unexplored. We evaluated the effects of two resistance training programs: (1) upper body training (UBT) and (2) total body training (TBT) on a repetitive box lifting task (RBLT) and a 1 repetition maximum (1RM) boxlift (BL). The RBLT consisted of the maximum # of boxes lifted from the floor to a height of 1.32 m within a 10 min period (subjects moved between two boxes 2.4 m apart between lifts). 37 women (24±4 yrs, 166±6 cm, 64±9 kg) underwent either UBT (n=17) or TBT (n=20) and trained 3 x/wk for 6 months (3 sets/exercise, reps were periodized from 8 to 12; rest periods varied between 45-90 secs). A 20-30 min aerobic component concluded each workout. Testing occurred pre (T1), mid-way (T2) and post (T3) training. An ANOVA with repeated measures indicated significant (p≤0.05) training effects for both the RBLT and 1RM BL (T1<T2<T3), but no group or interaction effects. Results (mean±SD) were: 1RM BL (TBG: T1=30±5, T2=35±5, T3=38±4; T1 to T2%Δ=≈17%, T1 to T3%Δ=≈27%; UBG: T1=31±6, T2=35±7, T3=38±6, T1 to T2%Δ=≈13%, T1 to T3%Δ=≈23%); RBLT (TBG: T1=89±24, T2=109±18, T3=118±16, T1 to T2%Δ=≈22%, T1 to T3%Δ=≈33%; UBG: T1=86±24, T2=108±26, T3=118±20, T1 to T2%Δ=≈26%, T1 to T3%Δ=≈37%). These data indicate that(1) adaptations in the upper body appear to account for a greater proportion than the lower body for the performance changes and (2) women can continue to exhibit performance improvements beyond 3 month of training.

Lifting technique and abdominal belt usage: a biomechanical, physiological and subjective investigation

Some 10 male subjects carried out a repetitive lifting task for 15 min under four conditions on separate days. Subjects used either a squat lifting or a stoop lifting technique with or without an abdominal belt on each day. Measurements of spinal shrinkage, heart rate, perceived exertion and regional body pain were made under each condition. Although there was a significant difference in spinal shrinkage under all lifting conditions compared with shrinkage during 15 min of quiet standing (4.36 ± 2.24 vs. 1.13 ± 1.18 mm), there were no significant differences in shrinkage between the conditions. The subjects' heart rates were higher during the squat lift than the stoop lift (123 vs. 97 beats/min; p < 0.001). While the squat lift was perceived to be the safest lift by 90% of the subjects, 60% regarded this lift as the least preferred method (with or without the belt). Although all 10 subjects perceived the safest lifting method to involve the use of the belt, 50% rated the belt as their least preferred lifting condition. The findings cast doubt on the efficacy and acceptability of both abdominal belts and the practice of training workers in ‘safe’ lifting techniques and indicate that individual characteristics and preferences need to be considered when attempting to improve the safety of manual handling operations in industry.

Changes in trunk dynamics and spine loading during repeated trunk exertions.

Trunk and hip kinematic and spinal loading changes were documented as experienced subjects performed a set of standard free-dynamic lifting tasks at various intervals throughout a 5-hour repetitive manual materials handling session. To document how spine loading changes as a function of repetitive lifting during an extended period of lifting cycles. Many studies have evaluated spine loading as a function of a specific lifting task, but no studies could be found in the literature that evaluated how spine loading may change with repeated exposure to a lifting task. Ten experienced material handlers were recruited. Each was required to transfer 11 pallets of 23 kg boxes at a rate of 125 lifts per hour. Before and after unloading each pallet, subjects were asked to perform a set of five standard free-dynamic lifting tasks. Electromyographic activities of 10 trunk muscles were recorded along with kinematic and kinetic data. An electromyography-assisted model was used to evaluate spine loading during the standard lifting tasks. Subjects significantly changed their motion patterns throughout the lifting session. Trunk range of motion, velocity, and acceleration decreased in the sagittal plane, whereas these same measures increased for the hip. Trunk moment also decreased by 7% during the standard lifts. These changes were accompanied by a redistribution of muscle recruitment patterns, resulting in a decrease in spine compression and an increase in anterior/posterior shear. This study has shown that spine loading patterns do indeed change with repetition, suggesting that one needs to monitor these changes throughout repetitive lifting tasks if low back disorder risk is to be minimized.

The effect of fatigue on multijoint kinematics and load sharing during a repetitive lifting test.

A repetitive lifting test in the sagittal plane was performed with a submaximal load at a maximal lifting rate to understand the effects of fatigue on kinematic and kinetic measures of performance. To quantify the effect of fatigue during a highly repetitive lifting task, in terms of lifting force transmitted to the load, joint motion patterns, and internal joint load sharing. Industrial surveillance and epidemiologic data suggest that repetitive lifting is a risk factor for low back pain. Previous studies examining the effect of fatigue have either been constrained to isolated trunk movement, or have not explored the internal load distribution and potential alteration in the loading patterns. Sixteen healthy male subjects performed repetitive lifting in the sagittal plane with a load equal to 25% of their maximal lifting capacity, at a maximal lifting rate. Changes in lifting performance were determined from the power transferred to the box, joint kinematics, and joint kinetics. Data from three cycles at the start and end of the exercise were tested for the effect of fatigue using repeated-measures analysis of variance. Fatigue was documented by a reduction in average lifting force and hip and spine torque generation, whereas internal joint load sharing was relatively unchanged. The fatigue was associated with decreased knee and hip motion, and increased lumbar flexion. Decreased postural stability also was evident. The significant decrease in postural stability and force generation capability because of the repetitive lifting task indicated a higher risk of injury in the presence of unexpected perturbation. Multijoint coordinated lifting tasks provide a more realistic protocol to study neuromuscular fatigue.

Evaluation of the probability of spinal damage caused by sustained cyclic compression loading.

A sensitivity analysis of two alternative models predicting damage to vertebral motion segments (VMS) in cyclic compression was performed to evaluate the relative probability of damage occurring when peak compression force, loading frequency, or duration in a lifting task is changed. The first model is based on the assumption that fatigue failure is the mechanism underlying damage to the VMS in cyclic compression. The second model is based on the assumption that the VMS damage in cyclic compression is determined by the viscoelastic deformation of the segment and that the instant of failure can be predicted on the basis of the energy stored in this process. With both models, we estimated the percentage of the population likely to incur a VMS injury when performing a repetitive lifting task with peak compression forces ranging from 1500 to 4100 N, frequencies from 2 to 12 min-1, and durations between 30 and 120 min. The results indicate a dominant influence of the peak compression force on this outcome over the domain studied. This conclusion holds qualitatively for both models, suggesting that for a comparative analysis they can be considered interchangeable. However, a considerable quantitative difference in the absolute outcomes of the two models was found, which stresses the importance of further study on the validity of these models.

An investigation of respiration while wearing back belts

The research was conducted to evaluate the frequency of respiration during a repetitive lifting task when abdominal compression occurs from wearing a back belt. Three back belts were evaluated in this study: a nylon back belt, an inflatable back belt and an elastic vest. Analysis of the data revealed that the frequency of respiration increased while wearing the back belts at rest and while performing a repetitive lifting task. A statistically significant increase in the frequency of respiration was found while wearing the nylon back belt during the lifting task.

The effect of eumenorrheic menstrual cycle phase on physiological responses to a repeated lifting task.

Cyclic variations in physiological and endocrinological baselines are known to be consistent with the eumenorrheic (healthy) menstrual cycle. The aim of this study was to examine the interaction of these variations with the physiological responses to repeated lifting. Sixteen females visited the laboratory in each of five phases of their menstrual cycle. During each visit, subjects performed a repetitive lifting task, lifting a weighted box, from knee to shoulder height, at six repetitions per minute for 10 min. Oxygen consumption, minute ventilation, heart rate (HR), and perceived exertion were monitored throughout the task. The variation in physiological and subjective responses to lifting with menstrual cycle phase did not reach statistical significance (p > .05). However, the HR response to lifting was elevated by approximately 10 beats x min-1 in the postovulatory phases of the cycle (effect size > 0.61). Although the impact of the menstrual cycle upon lifting performance is minimal, alterations in HR must be taken into account in determining new international standards for manual handling.

An ergonomic evaluation of three classes of material handling device (MHD)

The proliferation of material handling devices (MHDs) such as articulated arms and hoists is a direct result of the staggering increases in workers compensation claims attributed to repetitive lifting. In reducing the occurrence of repetitive lifting through MHD use, however, manufacturers have opened a Pandora's Box of other issues, ranging from the asymmetric nature of torso exertions common in MHD use to various job design and motor control issues. This study evaluates the effects of some critical job design parameters such as handled load and movement distance on the movement performance of three major classes of MHD. Ten young healthy male and female subjects used three different types of common MHDs with loads of 10 and 30 kg over distances of 0.6 and 1.8 m. Peak hand forces ranged from 50–80 N for the articulated arm and hoist with overhead rail MHDs, but reached 200 N with a fixed pivot hoist MHD. As a percent of each subjects' strength, peak hand forces generally tended to remain between 30 and 50%, except for the fixed pivot hoist when moving 30 kg over a 1.8 m distance. These conditions exceeded the strengths of 80% of the subjects. Peak velocities ranged from 0.8 to 1.2 m/s with the articulated arm and hoist when moving on an overhead rail, and from 0.8 to 1.6 m/s with the fixed pivot hoist. Subjects showed the fastest movement with the fixed pivot hoist, except with heavy loads. A distinct tradeoff between movement performance and biomechanical safety was discovered. In most cases, the MHD which showed the fastest movement also required the highest stresses. In general, implementation strategies should involve selection of the fastest MHD which does not exceed accepted limits of biomechanical stress. However more sophisticated limits for dynamic back stress must be developed and must reflect the various populations in the workforce. Relevance to industry The proliferation of MHDs in industry to replace repetitive lifting tasks has created a new source of potential musculoskeletal problems. This paper evaluates the comparative movement performance and ergonomic stresses of the three major classes of MHD in an effort to provide industry with some guidance for MHD implementation.

Methods and limitations of assessing functional work capacity objectively

This paper examined the methods and issues of assessing objectively the functional capacity of workers. The primary emphasis was on aerobic capacity (VO2max ) and repetitive lifting. While the direct measurement of expired gases during exhausting exercise is the most valid method of assessing the VO2max of workers, it is rarely done outside research or medical settings. The methods more commonly used are: maximal exercise tests; submaximal exercise tests; and non-exercise tests. Maximal tests are accurate, but require medical monitoring when testing workers at medical risk. Submaximal tests are less accurate, but are safer and faster than a maximal test. Submaximal tests use heart rate response to submaximal power output to estimate VO2max ; thus, any factor that alters heart rate response reduces the accuracy of the test. Non-exercise tests are as accurate as sub maximal tests, but require a self-report rating. The physiological criteria used to help define the recommended repetitive lift loads of the revised NIOSH equation included baseline aerobic capacity and energy expenditure values. While the goal is to reduce the risk of injury, the baseline aerobic capacity (≈ 25 ml/kg/min) and energy expenditure levels are so low (≤3.5 METs) that they may have an adverse effect on public health. Normative VO2max data on industrial cohorts suggest that 44% of male and 79% of female industrial workers are at a health risk of low aerobic fitness. Data are presented that suggests that repetitive lifting tasks are more of a function of strength and fat-free weight than aerobic capacity. While aerobic capacity, strength, and fat-free weight are objective methods to assess functional capacity, worker motivation and reaction to chronic pain can affect test results.

Rapid Communication Effects of posture, weight and frequency on trunk muscular activity and fatigue during repetitive lifting tasks

We examined the effects of posture, weight and frequency on trunk muscular activity and fatigue during repetitive dynamic lifting. Electromyographic (EMG) signals from eight primary trunk muscles were collected during 120 min for four different task conditions. The patterns of muscle recruitment and the levels of relative activation were analysed using the normalized EMG data. Median power frequency (MPF) shift patterns were analysed to examine muscular fatigue. The muscles in the dorsal part of the trunk were activated at the symmetric posture, while the muscles on the contralateral side to the workload were more strongly activated at the asymmetric posture. Decreasing trends of MPFs were found in some active muscles, and they were more pronounced for the asymmetric posture than for the symmetric posture. It was also seen that the muscles became fatigued faster for the light load-high frequency task than for the heavy load-low frequency task.

Biomechanical risk factors for occupationally related low back disorders.

A continuing challenge for ergonomists has been to determine quantitatively the types of trunk motion and how much trunk motion contributes to the risk of occupationally-related low back disorder (LBD). It has been difficult to include this motion information in workplace assessments since the speed at which trunk motion becomes dangerous has not been determined. An in vivo study was performed to assess the contribution of three-dimensional dynamic trunk motions to the risk of LBD during occupational lifting in industry. Over 400 industrial lifting jobs were studied in 48 varied industries. The medical records in these industries were examined so that specific jobs historically categorized as either low, medium, or high risk for occupationally-related LBD could be identified. A tri-axial electrogoniometer was worn by workers and documented the three-dimensional angular position, velocity, and acceleration characteristics of the lumbar spine while workers worked at these low, medium, or high risk jobs. Workplace and individual characteristics were also documented for each of the repetitive lifting tasks. A multiple logistic regression model indicated that a combination of five trunk motion and workplace factors predicted well both medium risk and high risk occupational-related LBD. These factors included lifting frequency, load moment, trunk lateral velocity, trunk twisting velocity, and trunk sagittal angle. Increases in the magnitude of these factors significantly increased the risk of LBD. The analyses have enabled us to determine the LBD risk associated with combined changes in the magnitudes of the five factors. The results indicate that by suitably varying these five factors observed during the lift collectively, the odds of high risk group membership may decrease by over ten times. These results were related to the biomechanical, ergonomic, and epidemiologic literature. The five trunk motion and workplace factors could be used as quantitative, objective measures to redesign the workplace so that the risk of occupationally-related LBD is minimized.

The Effects of Task Conditions on Trunk Muscular Fatigue during Dynamic Lifting

To investigate the effects of MMH task conditions on the activity and fatigue of the trunk musculature, EMG signals from eight major trunk muscles were analyzed during 120 minutes of repetitive dynamic lifting tasks. Two independent task variables were the work strategy of weight and lifting frequency combination and the body posture. The dependent variables were the amplitude of EMG signals and the amount of median power frequency (MPF) decrease over time for the eight trunk muscles. The results of the study indicated that the recruitment and the level of force exertions of the trunk muscles during manual lifting tasks are a function of the direction and the weight of the external load. The different activities of the muscles due to given task conditions also influence the fatiguing process of the individual muscle. The muscles in the dorsal part of trunk were activated during the symmetric task conditions, while the muscles on the contralateral side to the workload were more strongly activated during the asymmetric task conditions. The decreasing trends of MPF were found in some activated muscles, and they were more pronounced for the asymmetric posture than for the symmetric posture. It was also seen that the muscles became fatigued faster for light load-high frequency conditions than for heavy load-low frequency conditions.

Modelling the Additivity of Perceived Exertion in Symmetric, Mid-Sagittal Lifting

Psychophysical approaches to quantifying perceived effort have been used to evaluate the physical demand of many industrial work activities. An experiment was conducted to examine the relationship between ratings of whole-body perceived exertion and differentiated, regional ratings of exertion. The Borg, CR-10 scale was used by 16 subjects performing a simulated repetitive lifting task. Ratings of perceived exertion were obtained for the arms, legs, torso, and central (cardiorespiratory) effort sensations as well as a rating of overall, whole-body exertion. A multiple linear regression analysis was used to predict the whole-body rating of exertion from the differentiated ratings in lifting tasks using both a squat and stoop posture. In the stoop posture condition the coefficient of determination between whole-body perceived exertion and the model including arm, torso, and central ratings was R2=0.81. In the squat posture condition, the final regression model predicting whole-body exertion contained only the rating from the legs (R2 = 0.62). Differentiated ratings explained the majority of the variance in whole-body perceived exertion for squat and stoop lifting tasks.

A novel approach to preemployment worker fitness evaluations in a material-handling industry.

Effectiveness of a pre-employment worker fitness evaluation in a sample of grocery warehouse order selectors was studied retrospectively. Implementation of the program began in March 1990 and as of September 10, 1993, 1100 prospective employees have been tested. Identification of prospective employees with the necessary job specific physical requirements was conducted with a standardized test protocol based on job analysis and normative data. Follow-up injury rates and costs for this department were supplied by the company for statistical analysis. To establish normative data for minimum standards of job performance, a control group of current, uninjured and experienced order selectors was evaluated in respect to job requirements and isokinetic variables. In the control group, 17 variables were identified including one each from two 5-minute repetitive lifting tasks with weighted crates and 15 isokinetic trunk function and lifting variables. Prospective employees were required to successfully complete at least 15 variables for hire as an order selector. The t-test for significance of difference between two proportions was used to compare injury rates in 1989 to those reported in 1990, 1991, 1992, and 1993. Statistically significant differences were found between the unimplemented comparison year of 1989 and the 4 years post-implementation. Preliminary data suggests that a worker fitness evaluation using the above methodology may be an effective method of reducing injuries and subsequent costs.

Kinematic and kinetic changes in cycling during an exhausting steady-rate ride

A personal lift assist device (PLAD) was designed with passive elastic elements that act with a similar line of action to the spine muscles and reduce the extension moment experienced during lifting activities. The purpose of this paper was to evaluate the device's ability to reduce fatigue during a repetitive lifting task. Women (n = 12) lifted a box load representing 20% maximal extensor strength repetitively (12 lift/lowers per minute) for 45 min while electromyography (EMG) was recorded from the lumbar and thoracic erector spinae, and cardiovascular measures were monitored. Subjects were also tested on strength and endurance tests prior to, and after lifting. The increase in EMG RMS amplitude from the start until the end of the lifting session was significantly lower when wearing the PLAD for the TES (91% vs 3%) and the LES (104% vs 16%). The median frequency (MF) drop was also significantly lower when wearing the PLAD for TES and LES. The PLAD delayed the onset of fatigue in women by requiring less muscular effort.Relevance to industryThere are numerous industries that still require repetitive manual materials handling tasks to be performed by humans. Repetitive lifting fatigues the musculature involved and may lead to an increased risk of injury. The PLAD reduced fatigue on several measures. This device appears to have potential for industries where women perform repetitive, fatiguing lifts.

Longer lifting hooks for forestry workers: An evaluation of ergonomic effects

This study analysed the load-reducing effects of using lifting hooks that were 0.09 m longer than those conventionally employed by forestry workers. A method for recording and analysing repetitive lifting movements is also presented. Nine experienced workers performed a standardized sagittal symmetric repetitive lifting task, with the Long and the Standard types of hook. To simulate the aerobic stress during motor-manual cutting, a 17-kg log was lifted 15 lifts·min −1. Heart rate, oxygen consumption, sagittal body movements, vertical force plate measurements, and vertical movement of the log lifted, were recorded continuously. Sagittal load moments and forces in hip and L5-S1 segment were calculated. The subjects also rated their overall, low-back and thigh exertions. The use of the Long hook resulted in a 12% reduction in O 2 consumption. Mean and peak load moments in hip and L5-S1 were reduced by 14% and 9% respectively. The loads were rated significantly lower with all three assessments. The movement analyses showed a significant difference in movement pattern between the two types of hook, and that the kinematic variables were related to each other and to the VO 2 measurements in a consistent way.

The Role of Dynamic Three-Dimensional Trunk Motion in Occupationally-Related Low Back Disorders

Current ergonomic techniques for controlling the risk of occupationally-related low back disorder consist of static assessments of spinal loading during lifting activities. This may be problematic because several biomechanical models and epidemiologic studies suggest that the dynamic characteristics of a lift increase spine loading and the risk of occupational low back disorder. It has been difficult to include this motion information in workplace assessments because the speed at which trunk motion becomes dangerous has not been determined. An in vivo study was performed to assess the contribution of three-dimensional dynamic trunk motions to the risk of low back disorder during occupational lifting in industry. More than 400 repetitive industrial lifting jobs were studied in 48 varied industries. Existing medical and injury records in these industries were examined so that specific jobs historically categorized as either high-risk or low-risk for reported occupationally-related low back disorder could be identified. A triaxial electrogoniometer was worn by workers and documented the three-dimensional angular position, velocity, and acceleration characteristics of the lumbar spine while workers lifted in these high-risk or low-risk jobs. Workplace and individual characteristics were also documented for each of the repetitive lifting tasks. A multiple logistic regression model was developed, based on biomechanical plausibility, and indicated that a combination of five trunk motion and workplace factors distinguished between high and low risk of occupationally-related low back disorder risk well (odds ratio: 10.7). These factors included 1) lifting frequency, 2) load moment, 3) trunk lateral velocity, 4) trunk twisting velocity, and 5) the trunk sagittal angle. This analysis implies that by suitably varying these five factors observed during the lift collectively, the odds of high-risk group membership may decrease by almost 11 times. The predictive power of this model was found to be more than three times greater than that of current lifting guidelines. This study, though not proving causality, indicates an association between the biomechanical factors and low back disorder risk. This model could be used as a quantitative, objective measure to design the workplace so that the risk of occupationally-related low back disorder is minimized.