Maximum acceptable repetitive lifting workloads for an 8-hour work-day using psychophysical and subjective rating methods

Biomechanical assessment of a passive back-support exoskeleton during repetitive lifting and carrying: Muscle activity, kinematics, and physical capacity

INTRODUCTION

Most people have experienced low back pain (LBP) more or less in their lifetime. Heavier load weight could increase the risk of LBP, especially in repetitive lifting and carrying tasks. The risk could also increase with the frequency of lifting. This study aims to investigate the effects of a passive back-support exoskeleton (PBSE) on trunk muscle activation, kinematics, and physical capacity in a repetitive lifting task and a carrying task in consideration of load weights in a laboratory setting.

RESULTS

Results showed that using the PBSE, the activities of the thoracic erector spinae and lumbar erector spinae muscles were reduced significantly by nearly 7% MVC and 3% MVC in the repetitive lifting task and the carrying task, respectively. There was no significant effect of the PBSE on the spine kinematics and physical capacity.

PRACTICAL APPLICATIONS

This study supports the use of the PBSE to reduce trunk muscle activity in repetitive lifting and carrying tasks.

Evaluation of physiological workload assessment methods using heart rate and accelerometry for a smart wearable system

Work metabolism (WM) can be accurately estimated by oxygen consumption (VO₂), which is commonly assessed by heart rate (HR) in field studies. However, the VO₂-HR relationship is influenced by individual capacity and activity characteristics. The purpose of this study was to evaluate three models for estimating WM compared with indirect calorimetry, during simulated work activities. The techniques were: the HR-Flex model; HR branched model, combining HR with hip-worn accelerometers (ACC); and HR + arm-leg ACC model, combining HR with wrist- and thigh-worn ACC. Twelve participants performed five simulated work activities and three submaximal tests. The HR + arm-leg ACC model had the overall best performance with limits of agreement (LoA) of -3.94 and 2.00 mL/min/kg, while the HR-Flex model had -5.01 and 5.36 mL/min/kg and the branched model, -6.71 and 1.52 mL/min/kg. In conclusion, the HR + arm-leg ACC model should, when feasible, be preferred in wearable systems for WM estimation. Practitioner Summary: Work with high energy demand can impair employees' health and life quality. Three models were evaluated for estimating work metabolism during simulated tasks. The model combining heart rate, wrist- and thigh-worn accelerometers showed the best accuracy. This is, when feasible, suggested for wearable systems to assess work metabolism.

Determining Changes in Electromyography Indices when Measuring Maximum Acceptable Weight of Lift in Iranian Male Students

BACKGROUND

In spite of the increasing degree of automation in industry, manual material handling (MMH) is still performed in many occupational settings. The aim of the current study was to determine the maximum acceptable weight of lift using psychophysical and electromyography indices.

METHODS

This experimental study was conducted among 15 male students recruited from Tehran University of Medical Sciences. Each participant performed 18 different lifting tasks which involved three lifting frequencies, three lifting heights and two box sizes. Each set of experiments was conducted during the 20 min work period using free-style lifting technique and subjective as well as objective assessment methodologies. SPSS version 18 software was used for descriptive and analytical analyses by Friedman, Wilcoxon and Spearman correlation techniques.

RESULTS

The results demonstrated that muscle activity increased with increasing frequency, height of lift and box size (P<0.05). Meanwhile, MAWLs obtained in this study are lower than those in Snook table (P<0.05). In this study, the level of muscle activity in percent MVC in relation to the erector spine muscles in L3 and T9 regions as well as left and right abdominal external oblique muscles were at 38.89%, 27.78%, 11.11% and 5.55% in terms of muscle activity is more than 70% MVC, respectively. The results of Wilcoxon test revealed that for both small and large boxes under all conditions, significant differences were detected between the beginning and end of the test values for MPF of erector spine in L3 and T9 regions, and left and right abdominal external oblique muscles (P<0.05). The results of Spearman correlation test showed that there was a significant relation between the MAWL, RMS and MPF of the muscles in all test conditions (P<0.05).

CONCLUSION

Based on the results of this study, it was concluded if muscle activity is more than 70% of MVC, the values of Snook tables should be revisited. Furthermore, the biomechanical perspective should receive special attention in determining the standards for MMH.

Psychophysical Assessment of Simulated Assembly Line Work: Combinations of Transferring and Screw Driving Tasks

Upper extremity cumulative trauma disorders have been linked to the repeated and/or forceful exertions and/or awkward postures sometimes required by upper extremity intensive work. The combined effect of these physical stressors can be evaluated using psychophysical methods. The purpose of this study was to examine different combinations of repetitive upper extremity work using established psychophysical methods to determine design recommendations for upper extremity tasks. The tasks studied simulated assembly line type work where a part is transferred from a storage bin and attached with a pneumatic tool to another larger part.

Twenty-four experienced industrial workers performed five combination tasks of transferring an object along a conveyor and screw driving using a pistol shaped pneumatic screwdriver: 100% transfer; 75% transfer and 25% screw drive; 50% transfer and 50% screw drive; 25% transfer and 75% screw drive; and 100% screw drive. The cycle time was 24 seconds. Each combination task was performed for an hour. Overall, transferring, and screw driving perceived exertions were measured using 10 cm visual analog scales (VAS) with verbal descriptions at the endpoints. The left and right sides corresponded to “Easiest imaginable work” at 0 cm, and “Hardest imaginable work” at 10 cm, respectively. Body part discomfort surveys were utilized to assess discomfort from each of the tasks.

The overall perceived exertion (VAS) rating increased, as the task utilized more of one upper extremity than the other and involved more of either the transferring or screw driving tasks. The mean overall VAS ratings were 5.3, 4.3, 3.5, 4.4, and 5.3 for the five combination tasks, respectively. As the transferring (or screw driving) proportion of the task increased, the transferring (or screw driving) VAS increased. A repeated measures ANOVA showed that the combination task effect was significant (p<0.01). This psychophysical data can provide guidance in the analysis and design of upper extremity work. Since less varied work which utilized more of one upper extremity than the other had greater overall perceived exertion, upper extremity tasks should be designed as varied as possible utilizing as many body parts as possible. Body part discomfort surveys verified that this decreased discomfort severity and distributed the discomfort more evenly throughout the different body parts. This study provides evidence of the positive effects of work enlargement.

Predicting Endurance Time in a Repetitive Lift and Carry Task Using Linear Mixed Models

Objectives

Repetitive manual handling tasks account for a substantial portion of work-related injuries. However, few studies report endurance time in repetitive manual handling tasks. Consequently, there is little guidance to inform expected work time for repetitive manual handling tasks. We aimed to investigate endurance time and oxygen consumption of a repetitive lift and carry task using linear mixed models.

Methods

Fourteen male soldiers (age 22.4 ± 4.5 yrs, height 1.78 ± 0.04 m, body mass 76.3 ± 10.1 kg) conducted four assessment sessions that consisted of one maximal box lifting session and three lift and carry sessions. The relationships between carry mass (range 17.5–37.5 kg) and the duration of carry, and carry mass and oxygen consumption, were assessed using linear mixed models with random effects to account for between-subject variation.

Results

Results demonstrated that endurance time was inversely associated with carry mass (R² = 0.24), with significant individual-level variation (R² = 0.85). Normalising carry mass to performance in a maximal box lifting test improved the prediction of endurance time (R² = 0.40). Oxygen consumption presented relative to total mass (body mass, external load and carried mass) was not significantly related to lift and carry mass (β₁ = 0.16, SE = 0.10, 95%CI: -0.04, 0.36, p = 0.12), indicating that there was no change in oxygen consumption relative to total mass with increasing lift and carry mass.

Conclusion

Practically, these data can be used to guide work-rest schedules and provide insight into methods assessing the physical capacity of workers conducting repetitive manual handling tasks.

Motion Guides for Assisted Manipulation

This paper explores the use of passive guides to assist a human in manipulating heavy loads. A guide acts as a frictionless rail which confines the load to a one-dimensional curve in its configuration space. In this paper we formulate the problem of designing guides to effectively assist the human, and we apply the formulation to two types of materials handling tasks: pushing a heavy cart and single-arm reaching motions. Guides may be implemented by fixed rails or programmable constraint machines. Initial experiments with humans suggest the potential benefits of guided manipulation.

The influence of task frequency and force direction on psychophysically acceptable forces in the context of the biomechanically weakest links

This study examined the influence of frequency and direction of force application on psychophysically acceptable forces for simulated work tasks. Fifteen male participants exerted psychophysically acceptable forces on a force transducer at 1, 3, or 5 repetitions per minute by performing both a downward press and a pull toward the body. These exertions were shown previously to be strength and balance limited, respectively. Workers chose acceptable forces at a lower percentage of their maximum voluntary force capacity during downward (strength-limited) exertions than during pulling (balance-limited) exertions at all frequencies (4% to 11%, P = .035). Frequency modulated acceptable hand force only during downward exertions, where forces at five repetitions per minute were 13% less (P = .005) than those at one exertion per minute. This study provides insight into the relationship between biomechanically limiting factors and the selection of acceptable forces for unilateral manual tasks.

Performance-integrated self-report measurement of physical ability

BACKGROUND CONTEXT

The technology of self-report measures has advanced rapidly over the past few years. Recently, this technology was used to develop a performance-integrated self-report measure for use with patients with musculoskeletal impairments that may lead to work disability. Psychometric studies of the new measure in patient populations have been successful. A validation study of the measure with adults in good general health is necessary.

PURPOSE

The purpose of this study was to assess the concurrent validity of a new performance-integrated self-report measure, the multidimensional task ability profile (MTAP).

STUDY DESIGN/SETTING

A prospective validation study was conducted in which a self-report measure was administered online, and a physical performance test was administered at various clinics in North America.

PATIENT SAMPLE

One hundred ninety-six (34% male) adult volunteers in good general health participated in this study.

OUTCOME MEASURES

Self-report measure-MTAP. Physiologic measure-EPIC Lift Capacity test.

METHODS

The MTAP was administered online within 1 week of formal testing of lift capacity using a standardized lift capacity test, the EPIC Lift Capacity test. MTAP scores were compared with performance on the EPIC Lift Capacity test. Stepwise regression analysis was used to identify the strength of the relationship between the two measures and the relative explanation of lift capacity variance by the MTAP score, along with gender and age.

RESULTS

The combination of MTAP score, gender, and age demonstrated a regression coefficient of R=0.82, which accounts for 67.3% of the variance in lift capacity.

CONCLUSIONS

The MTAP displayed good concurrent validity compared with actual physical performance as assessed by the EPIC Lift Capacity test. Modern performance-integrated self-report measures, such as the MTAP, have the potential to provide information about functional capacity that is sufficiently useful to confirm status and help guide treatment algorithms.

A estratégia de "redução" e a carga de trabalho dos coletores de lixo domiciliar de uma grande cidade: estudo de caso baseado na Análise Ergonômica do Trabalho

Este trabalho descreve a utilização do método de "redução" como estratégia de trabalho desenvolvida pelos coletores de lixo ("garis") de uma grande cidade e seus reflexos na organização e na carga de trabalho. O método de "redução" consiste de atividade preparatória à coleta de lixo por meio da formação de "estoques intermediários" antes do carregamento nos caminhões. O trabalho dos garis foi estudado utilizando-se a metodologia da Análise Ergonômica do Trabalho (AET), complementada por avaliações de esforço físico. Quanto à organização do trabalho, verificou-se que, ao utilizarem esta estratégia, os garis trabalham em ritmo mais cadenciado, conseguem executar melhor as tarefas de separação do lixo, como os sacos plásticos contendo vidros, podem interagir entre eles e estabelecer relações amistosas com os cidadãos sobre melhores práticas de acondicionamento do lixo. Em relação à segurança e à saúde, ao utilizarem este método, os garis ficam menos sujeitos a riscos de cortes, atropelamentos, quedas e desavenças com motoristas no trânsito, além de realizarem o trabalho com menos esforço físico. Concluiu-se que a utilização da "redução" não apenas diminui o esforço físico e a exposição a riscos de acidentes, mas também melhora a qualidade da coleta de lixo domiciliar.

Surface slope effects on shingling frequency and postural balance in a simulated roofing task

The purpose of this study was to investigate the influence of surface slopes (18 degrees , 26 degrees , 34 degrees ) on the maximum acceptable roof shingling frequency for males performing a simulated roof-shingling task. The psychophysical roof shingling frequency was also compared to the postural sway and trunk motion values. The maximum acceptable roof shingling frequency and selected trunk motion decreased significantly with an increase in slope. Postural sway however increased significantly with an increase in slope. The study also revealed that workers were experiencing a greater postural sway at the earlier phase of task on the steeper surface. This suggests that there might be an adaptation period associated with working on a slope and the body's ability to compensate for a loss of balance. Therefore, more emphasis should be given to the workers in this adaptation period, with additional monitoring and cautionary measures. Collectively, the findings of the study could be utilized for improving work practices on roofs, while reducing the potential risks of falls in roofing construction.

Determination and evaluation of acceptable force limits in single-digit tasks

Acceptable limits derived from psychophysical methodologies have been proposed, measured, and employed in a range of applications. There is little existing work, however, on such limits for single-digit exertions and relatively limited evidence on several fundamental issues related to data collection and processing of a sequence of self-regulated exertion levels. An experimental study was conducted using 14 male and 10 female participants (age range 18-31 years) from whom maximal voluntary exertions and maximal acceptable limits (MALs) were obtained using the index finger and thumb. Moderate to high levels of consistency were found for both measures between sessions separated by one day. Single MAL values, determined from a time series of exertions, were equivalent across three divergent processing methods and between values obtained from 5- and 25-min samples. A critical interpretation of these and earlier results supports continued use of acceptable limits but also suggests that they should be used with some caution and not equated with safe limits. This research can be applied toward future development of exertion limits based on perceived acceptability.

An investigation of perceived exertion via whole body exertion and direct muscle force indicators during the determination of the maximum acceptable weight of lift

The objective of this study was to identify the perceived exertion mechanisms (direct muscle force and whole body exertion) associated with the decision to change the weight of lift during the determination of the maximum acceptable weight of lift (MAWL). Fifteen males lifted a box of unknown weight at a rate of 4.3 lifts/min, and adjusted the weight until their MAWL was reached. Variables such as the predicted muscle forces and heart rate were measured during the lifting exertion, as well as the predicted spinal loading in three dimensions using an EMG-assisted biomechanical model. Multiple logistic regression techniques were used to identify variables that were associated with the decision to change the weights up and down prior to a subsequent lift. Results indicated that the force in the left erector spinae, right internal oblique, and left latissimus dorsi muscles as well as heart rate were associated with decreases in the weight prior to the next lift. It appears that a combination of local factors (muscle force) and whole body exertion factors (heart rate) provide the feedback for the perceived exertion when decreasing the weight. The up-change model indicated that the forces of the right erector spinae, left internal oblique, and the right latissimus dorsi muscles were associated with the decision to increase the weight prior to the next lift. Thus, local factors provide feedback during the decision to increase the weight when starting from light weights. Collectively, these findings indicate that psychophysically determined weight limits may be more sensitive to muscular strain rather than spinal loading.

The psychophysical approach to manual materials handling task design

For approximately three decades, researchers have utilized psychophysics to develop guidelines (weights, forces and frequencies) for manual materials handling tasks. Early work by Stover Snook and his colleagues provided the foundations of the experimental methodologies that would be used by other researchers as well as design data that would be used by practitioners. Currently, there are extensive psychophysical data for designing a variety of materials handling tasks. The current state of psychophysical data will be examined, and the psychophysical approach will be compared to the biomechanical and physiological approaches to setting limits for materials handling tasks. The advantages and disadvantages of the psychophysical approach will be discussed, as will the research needs required to address the current limitations of the psychophysical approach.

Work schedule and task factors in upper-extremity fatigue

We tested the combined effects of work schedule and task factors on upper-extremity fatigue in the laboratory during 8-h and 12-h shift schedules. Participants performed a simulated manual assembly task at three repetition rates and three torque loads and self-adjusted their work cycle duration to maintain fatigue at moderate levels. Work cycle durations decreased with increases in both load level and repetition rate. Fatigue was observed more quickly with increasing time on shifts and during night shifts compared with day shifts. Work schedule effects were most apparent at lighter workloads, with minimal differences at higher workloads. The highest fatigue levels were observed during 12-h night shifts, with similar levels reached by the end of both the week of 8-h night shifts and the week of 12-h day shifts. Overall durations were 20%-30% shorter than in previous short-term studies, which was likely a result of the more realistic work schedules used in this study. Results from this study could be applied to the design of work-rest schedules for manual tasks involving the upper extremities.

Relationships among age, body weight, resting heart rate, and performance in a new test of lift capacity

This study measured the relative contributions of age, gender, body weight, and resting heart rate to lift capacity in 531 healthy employed males and females in a cross-sectional model. The objectives of this study were to measure the contributions to lift capacity that are made by these variables and to develop an appropriate means to express the results of a new test of lift capacity. A formal training program was developed and administered to 110 health care professionals. Subsequently, each trained evaluator performed five tests on healthy volunteers. The effect of the independent variables were studied through the use of multiple regression and analysis of variance procedures. Results indicate that age, resting heart rate, and body weight are significant predictors of performance, with the last variable being the most important. A method to normalize lift capacity is presented in which the maximum acceptable weight lifted is divided by the evaluee's body weight to derive relative acceptable weight, a variable which is normally distributed. Those who use measures of lift capacity to describe performance must consider the effect of these variables in order to make valid interpretations of lift capacity test performance.

A comparison of risk assessment of single and combination manual handling tasks: 1. maximum acceptable weight measures

Many manual handling activities involve combinations of pull, lift, carry, lower and push, yet few studies have investigated how to assess the risk of such combination tasks. Most recommendations assume that a combination task can be split into its components for assessment. The aim of this study was to compare the risks assessed in single manual handling tasks with those in combination tasks. Nine male and nine female students participated in a study to determine Maximum Acceptable Weights (MAWs) in single and combination tasks at different frequencies (1 min-1 and 3 min-1 for combination tasks and 3 min-1 and 6 min-1 for single tasks) and heights (floor, knuckle, shoulder). Combination tasks consisted of one each of the single tasks (pull, lift, carry, lower and push). The MAW of each combination task was compared to the MAWs of the single tasks of which it was composed using repeated measures analysis of variance with specified contrasts. In at least one of the 12 comparisons each single task MAW was found to be different from its related combination task MAW. It was concluded that the current use of single task MAWs to estimate the risk in combination tasks was unacceptable. Prediction models for combination task MAWs based on single tasks MAWs were also developed, using step-wise regression. Although coefficients of determination of around 0.8 were achieved it was argued that owing to their situation-specific nature the prediction of combination task risk using single task MAWs was likely to result in unacceptable risk errors.

The prediction of recommended energy expenditure for an 8 h work-day using an air-purifying respirator

Thirty railway workers executed maximal, or near maximal, stress tests with and without the use of a half mask air-purifying respirator (Spasciani 85 A1 P1) fitted with two combined filters for simultaneous protection from organic vapours and particulate matter. The pressure-flow characteristics of inspiratory and expiratory resistance at airflows in the range 0-90 l.min-1 were established by a continuous flow method on one test mask. Significant differences were found by paired t-test between the two exercises (with and without use of mask), showing reduced values with use of the mask, for breath frequency, ventilation rate, oxygen uptake, carbon dioxide production, maximal oxygen uptake, percentage of maximal voluntary ventilation used at the maximal exercise ventilation. No significant differences were found for tidal volume, respiratory quotient, heart rate, systolic blood pressure, oxygen uptake at anaerobic threshold, and duration of exercise. The predicted energy expenditure recommended for an 8 h work shift, corresponding to 40% of maximal oxygen uptake, is found to be reduced working with respirator and is significantly different from that observed during stress test without mask. The average ventilation rate at this workload is below 25 l.min-1, with predicted inspiratory mouth pressure equal to, or less than, 20 mm H2O. This maximal inspiratory mouth pressure is proposed as a safety limit for prolonged work using a respirator, with a recommended energy expenditure close to 40% of maximal oxygen uptake.

Perception of heavy work operations by tank truck drivers

Seven male tank truck drivers were followed for about 3 h during ordinary work. They rated the perception of heavy work operations on Borg's CR-10 scale. The heart rates were monitored every minute. The hose was pulled out an average of 22.3 m and the corresponding mean rating was 3.2, a little above 'Moderate' on the CR-10 scale. The heart rate averaged 137 beats/min at the end of this operation. When transforming the physiological parameter heart rate to a subjective strain intensity, surprisingly high agreement was obtained between the results from the field study and the predicted ratings. By transforming ordinally scaled data from another study to a scale with ratio properties, the results could be compared with this study. Good agreement was found between the variables.

Calculating relaxation allowances for construction operatives - part 1: metabolic cost

Relaxation allowances are an important part of determining standard times for any task. Traditional methods of calculating relaxation allowances are reviewed and their application to construction operations are discussed. This paper is presented in two parts. Part 1 investigates various methods of determining allowances for metabolic work. Part 2 considers local muscle fatigue and describes an approach that has been developed for determining relaxation allowances for construction operations.

Maximal aerobic capacity for repetitive lifting: comparison with three standard exercise testing modes

A multi-stage, repetitive lifting maximal oxygen uptake (VO2max) test was developed to be used as an occupational research tool which would parallel standard ergometric VO2max testing procedures. The repetitive lifting VO2max test was administered to 18 men using an automatic repetitive lifting device. An intraclass reliability coefficient of 0.91 was obtained with data from repeated tests on seven subjects. Repetitive lifting VO2max test responses were compared to those for treadmill, cycle ergometer and arm crank ergometer. The mean +/- SD repetitive lifting VO2max of 3.20 +/- 0.42 l.min-1 was significantly (p less than 0.01) less than treadmill VO2max (delta = 0.92 l.min-1) and cycle ergometer VO2max (delta = 0.43 l.min-1) and significantly greater than arm crank ergometer VO2max (delta = 0.63 l.min-1). The correlation between repetitive lifting oxygen uptake and power output was r = 0.65. VO2max correlated highly among exercise modes, but maximum power output did not. The efficiency of repetitive lifting exercise was significantly greater than that for arm cranking and less than that for leg cycling. The repetitive lifting VO2max test has an important advantage over treadmill or cycle ergometer tests in the determination of relative repetitive lifting intensities. The individual curves of VO2 vs. power output established during the multi-stage lifting VO2max test can be used to accurately select work loads required to elicit given percentages of maximal oxygen uptake.

An experimental evaluation of psychophysical criteria for repetitive lifting work

Two experiments were performed to test the reliability and validity of psychophysically determined maximum acceptable workloads for setting lifting standards. The perceived workload in a repetitive diagonal lifting task was found to be a positively accelerated function of the weight lifted and of the work pace respectively. A twofold increase in objective workload resulted in a four- to fivefold increase in perceived workload. This relation was independent of previous occupational experience of lifting work. The psychophysically assessed maximum acceptable workloads for this type of lifting task appeared to be satisfactorily reproducible when subjects had to adjust work pace or when they were left free to adjust both the weight and the work pace. However, the results raised several questions concerning the applicability of the psychophysical assessment of maximum acceptable lifting work. Slight changes in the instructions given to the subjects had a definite effect on the selection of workloads. Furthermore, the workloads selected by subjects with previous occupational experience of lifting work - i e, warehouse workers - were systematically lower than those selected by subjects without such previous experience - i e, office employees. At the same time, the warehouse workers rated perceived exertion higher than the office employees, indicating that previous occupational experience of lifting work enhanced the subjective assessment of physical effort. There were no consistent relations between the workloads found acceptable by the subjects and their physical characteristics and performance capacity.

Physiological ergonomics in nursing

The majority of physiological ergonomic studies of nursing are concerned with shift- and night-work and associated circadian rhythm adjustments and influences on job performance. The aerobic demand of medical nursing has not been extensively studied. The aerobic capacity of nurses has not been assessed systematically. Studies of this type are clearly required within an ergonomic framework with particular emphasis on the flexibility and (upper body) strength components of nurses functional capacities in relation to the physical demands of nursing tasks. As health educators, the nursing profession should seriously consider taking a practical lead in espousing the ergonomic process and advocating the health benefits of exercise (together with good diet and smoking cessation.)