Time--a key issue for musculoskeletal health and manufacturing

Computer simulation as a macroergonomic approach to assessing nurse workload and biomechanics related to COVID-19 patient care

This study uses Digital Human Modelling (DHM) and Discrete Event Simulation (DES) to examine how caring for COVID-19-positive (C+) patients affects nurses' workload and care-quality. DHM inputs include: nurse anthropometrics, task postures, and hand forces. DES inputs include: unit-layout, patient care data, COVID-19 status & impact on tasks, and task execution-logic. The study shows that reducing nurses' biomechanical workload increases mental workload and decreases direct patient care, potentially leading to stress, burnout, and errors. Compared to pre-pandemic conditions, when nurses were assigned five C+ patients, cumulative bilateral shoulder moments and lumbar load decreased by 38%, 36%, and 46%, respectively. However, this was accompanied by increases in mental workload (242%), task waiting-time (70%), and missed-care (353%). These effects were driven by the large increase in required infection control routines. Combining DHM and DES can help evaluate workplace/task designs and provide valuable insights for healthcare system design-policy setting and operational management decision-making.

Is there a u-shaped relationship between load levels and fatigue and recovery? An examination of possible mechanisms

In a previous study, an unexpected u-shaped relationship was observed between load level and fatigue/recovery responses. Moderate load levels resulted in lower perceived discomfort, pain, and fatigue, and shorter recovery times compared to either low or high load levels. This phenomenon has been reported in other studies, but no article has examined the possible mechanisms that might explain this u-shaped relationship. In this paper, we re-examined the previously published data and found that the phenomenon does not appear to be due to the experimental artefact; the u-shape may be due to unexpectedly lower fatigue effects at moderate loads, and higher fatigue effects at lower loads. We then conducted a literature review and identified several possible physiological, perceptual, and biomechanical explanatory mechanisms. No single mechanism explains the entirety of the phenomenon. Further research is needed on the relationship between work exposures, fatigue, and recovery, and the mechanisms related to the u-shaped relationship.Practitioner summary: We examine a previously observed u-shaped relationship between load level and fatigue/recovery, where moderate force resulted in lower perceived fatigue and shorter recovery times. A u-shaped fatigue response suggests that simply minimising load levels might not be an optimal approach to reduce the risk of workplace injuries.

Developing a simulation tool to quantify biomechanical load and quality of care in nursing

Nursing is a high musculoskeletal disorder (MSD) risk job with high workload demands. This study combines Digital Human Modelling (DHM) and Discrete Event Simulation (DES) to address the need for tools to better manage MSD risk. This novel approach quantifies physical-workload, work-performance, and quality-of-care, in response to varying geographical patient-bed assignments, patient-acuity levels, and nurse-patient ratios. Lumbar loads for 86 care-delivery tasks in an acute care hospital unit were used as inputs in a DES model of the care-delivery process, creating a shift-long time trace of the biomechanical load. Peak L4/L5 compression and moment were 3574 N and 111.58 Nm, respectively. This study reports trade-offs in all three experiments: (i) increasing geographical patient-bed assignment distance decreased L4/L5 compression (8.8%); (ii) increased patient-acuity decreased L4/L5 moment (4%); (iii) Increased nurse-patient ratio decreased L4/L5 compression (10%) and moment (17%). However, in all experiments, Quality of care indicators deteriorated (20, 19, and 29%, respectively). Practitioner Summary: This research has the potential to support decision-makers by developing a simulation tool that quantifies the impact of varying operational and design-policies in terms of biomechanical-load and quality of care. The demonstrator-model reports: as geographical patient-bed distance, patient-acuity levels, and nurse-patient ratios increase, biomechanical-load reduces, and quality of care deteriorates.

Multi-task exposure assessment to infer musculoskeletal disorder risk: A scoping review of injury causation theories and tools available to assess exposures

Exposure assessment is critical for understanding musculoskeletal disorder (MSD) risk. Previous reviews summarized the tools available for single-task exposure assessment, however no reviews summarize tools available to assess the accumulation or aggregation of exposure associated with the performance of multiple tasks (i.e., multi-task assessment). We address this gap by using a scoping review methodology to: 1) summarize the theories explaining how multi-task exposures may lead to MSDs, and 2) summarize the models and tools available to assess multi-task exposures, stratified based on prevailing theories. Using a systematic search strategy, 3230 articles were identified, of which 34 were retained for data extraction. Of the retained articles, 13 described MSD causation theories, 12 described mathematical models (not yet accessible as tools), six described readily accessible tools, and three described both theories and a model or tool. We summarized the state-of-the-art in multi-task exposure assessment and highlight the need for more tools that assess muscle fatigue and inform on recovery.

Musculoskeletal disorder risk assessment tool use: A Canadian perspective

Canadian ergonomics professionals from the Association of Canadian Ergonomists (ACE) and Board of Canadian Registered Safety Professionals (BCRSP) participated in a web-based survey of their awareness, use, and factors influencing use of ergonomics musculoskeletal disorder (MSD) risk assessment tools. A total of 791 respondents (21.0% response rate) participated in the survey. Certified ergonomics professionals represented an important subpopulation of MSD risk assessment tool users, however; the vast majority (86.4%) of users within Canada were certified safety professionals. Average tool use varied between ACE and BCRSP groups, where ACE respondents on average use more tools than BCRSP respondents, however the top 10 tools used were similar between the groups. Over 45% of assessment tools were learned at school and average tool use was not influenced by years of experience or continuing education.

Comparing upper arm and trunk kinematics between manufacturing workers performing predominantly cyclic and non-cyclic work tasks

Musculoskeletal disorders (MSDs) are common among manufacturing workers. Exposure to non-neutral postures and high movement speeds associated with MSDs among manufacturing workers may depend on the extent of the variability in the work tasks performed (i.e., predominantly "cyclic" versus "non-cyclic" work). The objectives of this study were to (i) compare mean levels of full-shift exposure summary metrics based on both posture and movement speed between manufacturing workers performing predominantly cyclic (n = 18) and non-cyclic (n = 17) tasks, and (ii) explore patterns of between- and within-worker exposure variance and between-minute (within-shift) exposure level and variation within each group. Inertial sensors were used to measure exposures for up to 15 full shifts per participant. Results indicated (i) substantially higher upper arm and trunk movement speeds among workers performing predominantly cyclic tasks relative to workers performing non-cyclic tasks despite similar postures, and (ii) greater exposure variability both between and within workers in the non-cyclic group.

EMG Characterization and Processing in Production Engineering

Electromyography (EMG) signals are biomedical signals that measure electrical currents generated during muscle contraction. These signals are strongly influenced by physiological and anatomical characteristics of the muscles and represent the neuromuscular activities of the human body. The evolution of EMG analysis and acquisition techniques makes this technology more reliable for production engineering applications, overcoming some of its inherent issues. Taking as an example, the fatigue monitoring of workers as well as enriched human–machine interaction (HMI) systems used in collaborative tasks are now possible with this technology. The main objective of this research is to evaluate the current implementation of EMG technology within production engineering, its weaknesses, opportunities, and synergies with other technologies, with the aim of developing more natural and efficient HMI systems that could improve the safety and productivity within production environments.

A comparison of work-rest models using a "breakpoint" analysis raises questions

OCCUPATIONAL APPLICATIONSDesigning sustainable cyclic work requires attention to both the workload amplitude as well as the duty cycle, the fraction of the work cycle with active workload, that therefore also defines the recovery phase of the cycle. A number of different approaches and models have been developed to calculate the required recovery time for a given load and duty cycle. We present a comparison of three types of models at the "breakpoint" that defines the boundary of load amplitude and duty cycle where fatigue begins to accumulate faster than recovery allows within the work cycle. This comparison shows considerable variation between models of the "allowable" load or duty cycle depending on the method used. Practitioners should thus be cautious applying these models indiscriminately in job design as their results can vary substantially. In particular, differences between the tasks used for model formulation and application may compromise validity, and model application in a given context should be verified before broad application.

Working time and upper limb musculoskeletal symptoms: a longitudinal study among assembly line workers

This study followed assembly line workers during 7 months, comprising a 4-wk season holidays. The main purposes were to determine the potential effect of working time on the presence and intensity of upper limb musculoskeletal symptoms, as to verify the effect of 4 wk of job interruption in the upper limb musculoskeletal symptoms presence and intensity. Data was collected during 6 moments. Generalized estimating equations analyses were used. For the effect estimates, odds ratio with corresponding 95% confidence intervals were reported for each outcome/model. The upper limb musculoskeletal symptoms showed a significant increase (p=0.001), especially after the 4 wk off. In all data collection points there was a significant positive association between the upper limb musculoskeletal symptoms and general health status (p<0.001). Considering symptoms’ intensity, significant relations were found (p<0.001). Work time had a negative effect on the work-related upper limb musculoskeletal symptoms over 7 months (OR 0.909, 95% CI 0.861–0.960, p=0.001). For the intensity of upper limb symptoms, the effect of time was also statistical significant (OR 0.115, 95% CI 1.031–1.220, p=0.008). A 4-wk job interruption did not show an immediately positive effect on upper limb musculoskeletal symptoms presence.

Intraoperative musculoskeletal discomfort and risk for surgeons during open and laparoscopic surgery

BACKGROUND

Surgeon workload is significant both mentally and physically and may differ by procedure type. When comparing laparoscopic surgery and open surgery, studies have reported contrasting results on the physical and mental workload assessed.

METHODS

Wearable posture sensors and pre-/post-surgical questionnaires were employed to assess intraoperative workload and to identify risk factors for surgeons using objective and subjective measures.

RESULTS

Data from 49 cases (27 open and 22 laparoscopic surgeries performed by 13 male and 11 female surgeons) were assessed. More than half the surgeons reported a clinically relevant post-surgical fatigue score. The surgeons also self-reported a significant increase in pain for the neck, upper back, and lower back during/after surgery. Procedural time had significant impacts on fatigue, body part pain, and subjective (NASA-TLX) workload. The objectively assessed intraoperative work postures using wearable sensors showed a high musculoskeletal risk for neck and lower back based on their posture overall. Open surgeries had significantly larger neck angles (median [IQR]: 40 [28-47]°) compared with laparoscopic surgeries (median [IQR]: 23 [16-29]°), p < 0.001) and torso (median [IQR]: 17 [14-22]° vs. 13 [10-17]°, p = 0.006).

CONCLUSION

Surgeons reported significantly higher levels of fatigue and pain in the neck and lower back during or after performing a surgical case. Longer procedural time resulted in more self-rated fatigue, pain, and subjective workload. Open surgery had higher postural risk. Overall, surgeons spent a disturbingly high percentage of time during surgery in high-risk musculoskeletal postures, especially the neck. These results show that intraoperative postural risk is very high and that interventions are necessary to protect surgeon musculoskeletal health for optimal surgeon performance and career longevity.

Self-reported Non-Specific Neck Pain (NSNP) is associated with presenteeism and biopsychosocial factors among office workers

Purpose

The purpose of this paper is to examine the relationship between self-reported non-specific neck pain (NSNP) with presenteeism and biopsychosocial factors in office workers.

Design/methodology/approach

This cross-sectional study was conducted on office workers (n=119) from four workplaces in Sydney, Australia. Data were collected using online questionnaires comprising the Neck Pain and Disability Scale, Neck Bournemouth Index and Stanford Presenteeism Scale 6. Psychosocial factors were explored given their etiological and maintenance roles in musculoskeletal disorders. A combination of linear, generalised linear and ordinal regression models were applied.

Findings

The study found that presenteeism was significantly associated with NSNP. Psychosocial factors such as concentration, emotional stress, anxiety, depression and outlook were found to be associated with increased NSNP.

Research limitations/implications

This research has implications as it expands understanding of the interplay between presenteeism and NSNP and psychosocial factors in the workplace.

Originality/value

The study identified the importance of organisations being able to identify when an office worker may be working while experiencing NSNP and how they may best support their employee’s recovery to prevent long-term disability and work productivity issues. These findings inform workplace policy formation by public health agencies.

The Quick Exposure Check (QEC) - Inter-rater reliability in total score and individual items

The development of musculoskeletal disorders has been linked to various risk factors in the work environment including lifting heavy loads, machine and materials handling, work postures, repetitive work, work with handheld vibrating tools, and work stress. The Quick Exposure Check (QEC) was designed to assess exposure to work-related musculoskeletal risk factors affecting the back, shoulder/arm, wrist/hand, and neck. We investigated the inter-rater reliability of the summary scores and individual items of the QEC by comparing two simultaneous assessments of 51 work tasks, performed by 14 different workers. The work tasks were mainly "light" to "moderately heavy". For total scores, the level of disagreement for shoulder/arm had a Relative Position of 0.13 (95% CI: 0.02; 0.23) and no statistically significant random disagreement. Percentage agreement was 63-100% for individual items and 71-88% for total score. Weighted Kappa of agreement for the individual items rated by the assessors were -0.94-0.77; highest for back motion, and lowest for wrist/hand position. The Swedish translation of the Quick Exposure Check has moderate to very good inter-rater reliability with fair to slight levels of systematic disagreement. There was no statistically significant random disagreement.

Modelling endurance and resumption times for repetitive one-hand pushing

This study's objective was to develop models of endurance time (ET), as a function of load level (LL), and of resumption time (RT) after loading as a function of both LL and loading time (LT) for repeated loadings. Ten male participants with experience in construction work each performed 15 different one-handed repetaed pushing tasks at shoulder height with varied exerted force and duration. These data were used to create regression models predicting ET and RT. It is concluded that power law relationships are most appropriate to use when modelling ET and RT. While the data the equations are based on are limited regarding number of participants, gender, postures, magnitude and type of exerted force, the paper suggests how this kind of modelling can be used in job design and in further research. Practitioner Summary: Adequate muscular recovery during work-shifts is important to create sustainable jobs. This paper describes mathematical modelling and presents models for endurance times and resumption times (an aspect of recovery need), based on data from an empirical study. The models can be used to help manage fatigue levels in job design.

Factors determining workers' pace while conducting continuous sequential lifting, carrying, and lowering tasks

To plan a new manual material handling work process, it is necessary to predict the times required to complete each task. Current time prediction models lack validity when the handled object's mass exceeds 2 kg. In this study, we investigated the effect of workplace design parameters on continuous sequential lifting, carrying, and lowering of boxes weighing from 2 kg to 14 kg. Both laboratory and field experiments were conducted. Results revealed that the box's weight and the lifting and lowering heights influenced the tasks' times. Further, the time to perform a task was influenced by the performance of other tasks in the same work process. New time prediction models were developed using the laboratory experiment data. Our models were found to be more accurate on average than the Maynard Operation Sequence Technique (MOST) and Methods Time Measurement (MTM-1) by 42% and 20%, respectively, for predicting the times of real workers at an actual workplace.

Visualizing stressful aspects of repetitive motion tasks and opportunities for ergonomic improvements using computer vision

Patterns of physical stress exposure are often difficult to measure, and the metrics of variation and techniques for identifying them is underdeveloped in the practice of occupational ergonomics. Computer vision has previously been used for evaluating repetitive motion tasks for hand activity level (HAL) utilizing conventional 2D videos. The approach was made practical by relaxing the need for high precision, and by adopting a semi-automatic approach for measuring spatiotemporal characteristics of the repetitive task. In this paper, a new method for visualizing task factors, using this computer vision approach, is demonstrated. After videos are made, the analyst selects a region of interest on the hand to track and the hand location and its associated kinematics are measured for every frame. The visualization method spatially deconstructs and displays the frequency, speed and duty cycle components of tasks that are part of the threshold limit value for hand activity for the purpose of identifying patterns of exposure associated with the specific job factors, as well as for suggesting task improvements. The localized variables are plotted as a heat map superimposed over the video, and displayed in the context of the task being performed. Based on the intensity of the specific variables used to calculate HAL, we can determine which task factors most contribute to HAL, and readily identify those work elements in the task that contribute more to increased risk for an injury. Work simulations and actual industrial examples are described. This method should help practitioners more readily measure and interpret temporal exposure patterns and identify potential task improvements.

Can a smart chair improve the sitting behavior of office workers?

Prolonged sitting can cause health problems and musculoskeletal discomfort. There is a need for objective and non-obstructive means of measuring sitting behavior. A 'smart' office chair can monitor sitting behavior and provide tactile feedback, aiming to improve sitting behavior. This study aimed to investigate the effect of the feedback signal on sitting behavior and musculoskeletal discomfort. In a 12-week prospective cohort study (ABCB design) among office workers (n = 45) was measured sitting duration and posture, feedback signals and musculoskeletal discomfort. Between the study phases, small changes were observed in mean sitting duration, posture and discomfort. After turning off the feedback signal, a slight increase in sitting duration was observed (10 min, p = 0.04), a slight decrease in optimally supported posture (2.8%, p < 0.01), and musculoskeletal discomfort (0.8, p < 0.01) was observed. We conclude that the 'smart' chair is able to monitor the sitting behavior, the feedback signal, however, led to small or insignificant changes.

Investigation of musculoskeletal symptoms in a manufacturing company in Brazil: a cross-sectional study

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Upper limb MSD were prevalent among manual manufacturing workers.

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Shoulder was the body region with the highest prevalence of symptoms.

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Repetitive work and lack of rest breaks are influential risk factors for MSD.

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Performing work pause was identified as a significant variable.

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MSD had a significant negative impact on workers’ general health.

Background

Musculoskeletal disorders are prevalent and represent the most common health problem among the working population in industrially-developing countries, with considerable costs and impact on quality of life. Despite the high incidence of disability insurance claims among Brazilian manufacturing-sector workers, only a few studies assessed musculoskeletal disorders prevalence.

Objective

To provide information on the prevalence of musculoskeletal disorders among manufacturing-sector workers and to explore the relationship between musculoskeletal disorders and sociodemographic and occupational characteristics in a medium metallurgical company located in Brazil.

Methods

A cross-sectional study was carried out. Data was collected through the use of a specifically-designed questionnaire and the items used to collect musculoskeletal disorders data were based on the Nordic Musculoskeletal Questionnaire. Descriptive statistics were used and multivariate logistic regression analysis (p < 0.02) was performed to explore the associations between musculoskeletal disorders and potential risk factors.

Results

The upper limb was the most frequently affected body region among manufacturing-sector workers: shoulder (24.8%), elbow and/or forearm (15.5%), wrist and/or hand (19.0%). Adjusted logistic regression analysis showed that company experience (p = 0.02), presence of sleep disorders (p = 0.00), self-reported general health state (p = 0.00) and perform work pause (p = 0.00) were significant risk factors for development of musculoskeletal disorders.

Conclusion

Sociodemographic and work-related aspects are influential risk factors for musculoskeletal disorders. These results add comprehension about musculoskeletal disorders prevalence and suggest a need for greater emphasis on prevention strategies.

'Power base' tactics for workplace change - an interview study with industrial engineers and ergonomists

The work activities of industrial engineers (IEs) and ergonomists drive workplace changes. The purpose of this study is to compare the work practices of the two professions and examine (1) how IEs and ergonomists gain influence over workplace changes and (2) whether there are prevailing types of intentional interaction behaviours called Power bases (PB) present in the interaction tactics they employ. The study identified key behavioural strategies used by the interviewees to successfully influence workplace changes; these were then mapped to their corresponding PB. Results showed that IEs and ergonomists were successfully influencing workplace changes using several tactics across the spectrum of PB, with the exception of Reward and Coercion. The study concludes with a list of recommended workplace change agent tactics, and proposes that a PB 'analytical lens' can serve to increase the budding ergonomists' critical and analytical skills when considering possible workplace change tactics. Practitioner Summary: This interview study examines how workplace ergonomics change agents, represented by the two professions: industrial engineers and ergonomists, perceive and exercise their capacity to influence workplace change. Key behavioural tactics that interviewees have found successful are reported, alongside effects on short- and long-term relations with other workplace-influencing stakeholders.

The variability of the trunk forward bending in standing activities during work vs. leisure time

High level of occupational physical activity (PA), contrary to leisure time activities, is generally associated with detrimental health outcomes. We hypothesized that this contrast may be associated with a different pattern of exposure variability in PA, e.g., forward bending of the trunk. The study was conducted on 657 blue-collar workers. Two accelerometers were used to identify the body posture and forward bending of the trunk during work and leisure time. The pattern of forward bending was analyzed using exposure variation analysis (EVA). The recordings comprised of 2.6 ± 0.97 working days in average, with 19.9 ± 8.1 h work and 22.9 ± 8.9 h leisure. The standard deviation and entropy of the EVA profile indicated 11% and 6% (for about 80% of subjects) less variable pattern during work compared with the leisure time, respectively. These new findings contribute to the understanding the paradoxical outcomes of PA during work and leisure.

Measuring elemental time and duty cycle using automated video processing

A marker-less 2D video algorithm measured hand kinematics (location, velocity and acceleration) in a paced repetitive laboratory task for varying hand activity levels (HAL). The decision tree (DT) algorithm identified the trajectory of the hand using spatiotemporal relationships during the exertion and rest states. The feature vector training (FVT) method utilised the k-nearest neighbourhood classifier, trained using a set of samples or the first cycle. The average duty cycle (DC) error using the DT algorithm was 2.7%. The FVT algorithm had an average 3.3% error when trained using the first cycle sample of each repetitive task, and had a 2.8% average error when trained using several representative repetitive cycles. Error for HAL was 0.1 for both algorithms, which was considered negligible. Elemental time, stratified by task and subject, were not statistically different from ground truth (p < 0.05). Both algorithms performed well for automatically measuring elapsed time, DC and HAL. Practitioner Summary: A completely automated approach for measuring elapsed time and DC was developed using marker-less video tracking and the tracked kinematic record. Such an approach is automatic, repeatable, objective and unobtrusive, and is suitable for evaluating repetitive exertions, muscle fatigue and manual tasks.

Changes in division of labour and tasks within public dentistry: relationship to employees work demands, health and work ability

OBJECTIVE

By 2023, fewer dentists are expected in Sweden, at the same time as the demand for dental care is expected to increase. Older people, in particular, are expected to require more dental health than previous generations. To meet this demand, the public sector dentistry in Sweden is moving towards changes in division of labour among dental professionals, including dentists, dental hygienists and dental nurses. However, the impact of this reallocation on the physical and psychosocial wellbeing of employees is unknown. The aim of this study was to compare workplaces with an equal or larger proportion of dental hygienists than dentists (HDH) with workplaces with a larger proportion of dentists than dental hygienists (HD) on the physical and psychosocial work load, musculoskeletal and psychosomatic disorders and sickness presence.

MATERIAL

A total of 298 persons employed in the Public Dental Service in a Swedish County Council participated in this study.

CONCLUSION

The medium large clinics HDH reported 85% of employee's with considerably more high psychosocial demands compared to employees in medium HD (53%) and large HD (57%). Employees in medium large clinics HDH also reported sleep problems due to work (25%) compared with employees in medium large clinics HD (6%), large clinics HD (11%) and small clinics HDH (3%). Clinic size does not seem to influence the outcome of the HD and HD clinics to any great extent. Of all employees, about 94-100% reported high precision demands and 78-91% poor work postures.

The importance of work organization on workload and musculoskeletal health--Grocery store work as a model

We have evaluated the consequences of work organization on musculoskeletal health. Using a postal questionnaire, answered by 1600 female grocery store workers, their main work tasks were identified and four work groups were defined (cashier, picking, and delicatessen work, and a mixed group, who performed a mix of these tasks). The crude odds ratios (ORs) for neck/shoulder complaints were 1.5 (95% CI 1.0-2.2), 1.1 (0.7-1.5) and 1.6 (1.1-2.3), respectively, compared to mixed work. Adjusting for individual and psychosocial factors had no effect on these ORs. For elbows/hands, no significant differences were found. Technical measurements of the workload showed large differences between the work groups. Picking work was the most strenuous, while cashier work showed low loads. Quantitative measures of variation revealed for mixed work high between minutes variation and the highest between/within minutes variation. Combining work tasks with different physical exposure levels increases the variation and may reduce the risk of musculoskeletal complaints.

Design for human factors (DfHF): a grounded theory for integrating human factors into production design processes

The 'design for human factors' grounded theory explains 'how' human factors (HF) went from a reactive, after-injury programme in safety, to being proactively integrated into each step of the production design process. In this longitudinal case study collaboration with engineers and HF Specialists in a large electronics manufacturer, qualitative data (e.g. meetings, interviews, observations and reflections) were analysed using a grounded theory methodology. The central tenet in the theory is that when HF Specialists acclimated to the engineering process, language and tools, and strategically aligned HF to the design and business goals of the organisation, HF became a means to improve business performance. This led to engineers 'pulling' HF Specialists onto their team. HF targets were adopted into engineering tools to communicate HF concerns quantitatively, drive continuous improvement, visibly demonstrate change and lead to benchmarking. Senior management held engineers accountable for HF as a key performance indicator, thus integrating HF into the production design process. Practitioner Summary: Research and practice lack explanations about how HF can be integrated early in design of production systems. This three-year case study and the theory derived demonstrate how ergonomists changed their focus to align with design and business goals to integrate HF into the design process.

Can cognitive activities during breaks in repetitive manual work accelerate recovery from fatigue? A controlled experiment

Neurophysiologic theory and some empirical evidence suggest that fatigue caused by physical work may be more effectively recovered during “diverting” periods of cognitive activity than during passive rest; a phenomenon of great interest in working life. We investigated the extent to which development and recovery of fatigue during repeated bouts of an occupationally relevant reaching task was influenced by the difficulty of a cognitive activity between these bouts. Eighteen male volunteers performed three experimental sessions, consisting of six 7-min bouts of reaching alternating with 3 minutes of a memory test differing in difficulty between sessions. Throughout each session, recordings were made of upper trapezius muscle activity using electromyography (EMG), heart rate and heart rate variability (HRV) using electrocardiography, arterial blood pressure, and perceived fatigue (Borg CR10 scale and SOFI). A test battery before, immediately after and 1 hour after the work period included measurements of maximal shoulder elevation strength (MVC), pressure pain threshold (PPT) over the trapezius muscles, and a submaximal isometric contraction. As expected, perceived fatigue and EMG amplitude increased during the physical work bouts. Recovery did occur between the bouts, but fatigue accumulated throughout the work period. Neither EMG changes nor recovery of perceived fatigue during breaks were influenced by cognitive task difficulty, while heart rate and HRV recovered the most during breaks with the most difficult task. Recovery of perceived fatigue after the 1 hour work period was also most pronounced for the most difficult cognitive condition, while MVC and PPT showed ambiguous patterns, and EMG recovered similarly after all three cognitive protocols. Thus, we could confirm that cognitive tasks between bouts of fatiguing physical work can, indeed, accelerate recovery of some factors associated with fatigue, even if benefits may be moderate and some responses may be equivocal. Our results encourage further research into combinations of physical and mental tasks in an occupational context.

Fatigue and recovery during and after static loading

Subjectively assessed endurance time (ET), resumption time (RT) and perceived discomfort, pain or fatigue (PD), and objectively measured maximum force-exerting capacity were investigated for varying loads and durations of a pushing task with two repeated trials. Beyond the main results quantifying how the load scenario affected ET, RT and PD, three additional results are of note: (1) although the maximum pushing force did not change between trials, shorter ET, longer RT and higher PD indicated accumulation of fatigue in Trial 2; (2) the PD ratings showed a trend with a linear increase during loading and a curvilinear decrease during recovery; and (3) the RT and the load level for different relative loading times were found to have an unexpected U-shaped relationship, indicating lowest fatigue at the intermediate load level. These results can be used to model a more sustainable and productive work-recovery ratio.

An ergonomics action research demonstration: integrating human factors into assembly design processes

In action research (AR), the researcher participates 'in' the actions in an organisation, while simultaneously reflecting 'on' the actions to promote learning for both the organisation and the researchers. This paper demonstrates a longitudinal AR collaboration with an electronics manufacturing firm where the goal was to improve the organisation's ability to integrate human factors (HF) proactively into their design processes. During the three-year collaboration, all meetings, workshops, interviews and reflections were digitally recorded and qualitatively analysed to inform new 'actions'. By the end of the collaboration, HF tools with targets and sign-off by the HF specialist were integrated into several stages of the design process, and engineers were held accountable for meeting the HF targets. We conclude that the AR approach combined with targeting multiple initiatives at different stages of the design process helped the organisation find ways to integrate HF into their processes in a sustainable way.

PRACTITIONER SUMMARY

Researchers acted as a catalyst to help integrate HF into the engineering design process in a sustainable way. This paper demonstrates how an AR approach can help achieve HF integration, the benefits of using a reflective stance and one method for reporting an AR study.

Innovative system for real-time ergonomic feedback in industrial manufacturing

This work presents a system that permits a real-time ergonomic assessment of manual tasks in an industrial environment. First, a biomechanical model of the upper body has been developed by using inertial sensors placed at different locations on the upper body. Based on this model, a computerized RULA ergonomic assessment was implemented to permit a global risk assessment of musculoskeletal disorders in real-time. Furthermore, local scores were calculated per segment, e.g. the neck region, and gave information on the local risks for musculoskeletal disorders. Visual information was fed back to the user by using a see-through head mounted display. Additional visual highlighting and auditory warnings were provided when some predefined thresholds were exceeded. In a user study (N = 12 participants) a group with the RULA feedback was compared to a control group. Results demonstrate that the real-time ergonomic feedback significantly decreased the outcome of both globally as well as locally hazardous RULA values that are associated with increased risk for musculoskeletal disorders. Task execution time did not differ between groups. The real-time ergonomic tool introduced in this study has the potential to considerably reduce the risk of musculoskeletal disorders in industrial settings. Implications for ergonomics in manufacturing and user feedback modalities are further discussed.

Efficient assessment of exposure to manual lifting using company data

The objective of this study, based on an extensive dataset on manual materials handling during scaffolding, was to explore whether routinely collected company data can be used to estimate exposure to manual lifting. The number of manual lifts of scaffold parts while constructing/dismantling scaffolds was well predicted by the number of scaffolders in the team and the type of worksite, in combination with company data of either the number of scaffold parts or the scaffold volume. The proportion of explained variance in the number of lifts ranged from 77% to 92%, depending on the variables in the model. Data on scaffold parts and scaffold volume can easily be obtained from the company's administration, since this is its usual paperwork supporting logistics and customer invoicing, respectively. We conclude that company data can be a promising source of information for ergonomic practitioners and researchers, to support assessment of manual lifting in scaffolding.

Cluster-based exposure variation analysis

Background

Static posture, repetitive movements and lack of physical variation are known risk factors for work-related musculoskeletal disorders, and thus needs to be properly assessed in occupational studies. The aims of this study were (i) to investigate the effectiveness of a conventional exposure variation analysis (EVA) in discriminating exposure time lines and (ii) to compare it with a new cluster-based method for analysis of exposure variation.

Methods

For this purpose, we simulated a repeated cyclic exposure varying within each cycle between “low” and “high” exposure levels in a “near” or “far” range, and with “low” or “high” velocities (exposure change rates). The duration of each cycle was also manipulated by selecting a “small” or “large” standard deviation of the cycle time. Theses parameters reflected three dimensions of exposure variation, i.e. range, frequency and temporal similarity.

Each simulation trace included two realizations of 100 concatenated cycles with either low (ρ = 0.1), medium (ρ = 0.5) or high (ρ = 0.9) correlation between the realizations. These traces were analyzed by conventional EVA, and a novel cluster-based EVA (C-EVA). Principal component analysis (PCA) was applied on the marginal distributions of 1) the EVA of each of the realizations (univariate approach), 2) a combination of the EVA of both realizations (multivariate approach) and 3) C-EVA. The least number of principal components describing more than 90% of variability in each case was selected and the projection of marginal distributions along the selected principal component was calculated. A linear classifier was then applied to these projections to discriminate between the simulated exposure patterns, and the accuracy of classified realizations was determined.

Results

C-EVA classified exposures more correctly than univariate and multivariate EVA approaches; classification accuracy was 49%, 47% and 52% for EVA (univariate and multivariate), and C-EVA, respectively (p < 0.001). All three methods performed poorly in discriminating exposure patterns differing with respect to the variability in cycle time duration.

Conclusion

While C-EVA had a higher accuracy than conventional EVA, both failed to detect differences in temporal similarity. The data-driven optimality of data reduction and the capability of handling multiple exposure time lines in a single analysis are the advantages of the C-EVA.

Performance evaluation of a wearable inertial motion capture system for capturing physical exposures during manual material handling tasks

With a long-term goal of improving quantification of physical exposures in the workplace, this study examined the ability of a commercially available inertial motion capture (IMC) system in quantifying exposures during five different simulated manual material handling tasks. Fourteen participants repeated all these tasks in three 20 min sequential time blocks. Performance of the IMC system was compared against an optical motion capture (OMC) system ('gold standard') in terms of joint angles, angular velocities and moments at selected body parts. Though several significant changes in performance over time were found, the magnitudes of these were relatively small and may have limited practical relevance. The IMC system yielded peak kinematic values that differed by up to 28% from the OMC system. The IMC system, in some cases, incorrectly reflected the actual extremity positions of a participant, and which can cause relatively large errors in joint moment estimation. Given the potential limitations, practical recommendations are offered and discussed.

PRACTITIONER SUMMARY

Use of an inertial motion capture system can advance the quantification of physical exposures in situ. Results indicate a good potential capacity for capturing physical exposure data in the field for an extended period, while highlighting potential limitations. Future system application can help provide better understandings of dose-exposure relationships.

Mechanical exposure implications of rationalization: a comparison of two flow strategies in a Swedish manufacturing plant

The aim of this case study was to (1) investigate differences in mechanical exposure (i.e. mechanical forces arising in the body of the operator) between two production strategies: long-cycle parallelised flow assembly (OLD) and conventional serial flow assembly (NEW), and (2) estimate potential changes in job exposure as a consequence of waste reduction when rationalising a line system. Data on postures, movements and whole body exposure were collected during an ordinary working shift, by means of video recordings synchronised to direct technical measurements of six professional operators. The results revealed the machine paced NEW system to have slower movements with less time spent in movements of high velocity compared to the self-paced OLD system. No significant differences were found between time-median posture levels. 'Disturbances' in the NEW system offered lower mechanical risk exposures compared to direct assembly work. Modelling the removal of wasteful 'disturbances' revealed both an increase in risk-implying fast movements and decrease in recovery-implying periods at low velocity - effectively isolating a work intensification. This study helps expose the complex relationship between rationalizations and mechanical exposure for system operators.

Designing for sustainability: ergonomics--carpe diem

Sustainability is a global issue that has worldwide attention but the role of ergonomics in designing for sustainability is poorly understood and seldom considered. An analysis of the literature on ergonomics, design and sustainability was conducted via a search of electronic databases: Scopus, Business Source Complete, Google Scholar, Emerald Publishing, Academic Search Premiere, Web of Science, Discover and Ergonomics Abstracts, for the years 1995-2012. A total of 1934 articles fulfilled the search criteria, but content analysis of the abstracts indicated that only 14 refereed articles addressed the main search criteria. Of those seven were in ergonomics journals and seven were in other journals (and were not written by ergonomists). It is concluded that the contribution of ergonomics to sustainability and sustainable design has been limited, even though the goals of sustainability and ergonomics are congruent. Ergonomists have not been at the forefront of research contributing to sustainability - and it is time for them to 'seize the day' - 'carpe diem'.

PRACTITIONER SUMMARY

This literature review shows that ergonomics contribution to sustainability is limited but since there is congruence between the disciplines it calls for ergonomists to become more involved and to seize the day - carpe diem.

Ergonomics action research II: a framework for integrating HF into work system design

This paper presents a conceptual framework that can support efforts to integrate human factors (HF) into the work system design process, where improved and cost-effective application of HF is possible. The framework advocates strategies of broad stakeholder participation, linking of performance and health goals, and process focussed change tools that can help practitioners engage in improvements to embed HF into a firm's work system design process. Recommended tools include business process mapping of the design process, implementing design criteria, using cognitive mapping to connect to managers' strategic goals, tactical use of training and adopting virtual HF (VHF) tools to support the integration effort. Consistent with organisational change research, the framework provides guidance but does not suggest a strict set of steps. This allows more adaptability for the practitioner who must navigate within a particular organisational context to secure support for embedding HF into the design process for improved operator wellbeing and system performance.

PRACTITIONER SUMMARY

There has been little scientific literature about how a practitioner might integrate HF into a company's work system design process. This paper proposes a framework for this effort by presenting a coherent conceptual framework, process tools, design tools and procedural advice that can be adapted for a target organisation.

Full shift arm inclinometry among dairy parlor workers: a feasibility study in a challenging work environment

Over the last 20 years, the US dairy industry has experienced a significant transformation from small farm operations to an industrialization of the milking process. This transformation has resulted in improvements in process efficiency and product quality. Milking tasks in large-herd parlors are highly-repetitive involving awkward postures and high muscle loads of the upper extremity. Field-based direct measures of physical exposures have been limited in challenging work settings such as dairies. This study evaluated full-shift exposures of posture and motion of the upper extremity among large-herd parlor milkers using wireless inclinometry. Results suggest large-herd parlor workers may be exposed to high exposure levels (posture, movement velocity, repetition, and inadequate rest) associated with the development of shoulder pathology. Compared to other high-risk occupations involving shoulder-intensive work, parlor workers may have higher exposure levels. These findings warrant the need for continued field-based research with larger sample sizes to facilitate the development of cost-effective intervention strategies.

Variation of force amplitude and its effects on local fatigue

Trends in industry are leaning toward stereotyped jobs with low workloads. Physical variation is an intervention to reduce fatigue and potentially musculoskeletal disorders in such jobs. Controlled laboratory studies have provided some insight into the effectiveness of physical variation, but very few have been devoted to force variation without muscular rest as a component. This study was undertaken to determine multiple physiological responses to five isometric elbow extension protocols with the same mean amplitude (15% maximum voluntary contraction, MVC), cycle time (6 s), and duty cycle (50 %). Sustained (15 %Sus) and intermittent contractions including zero force (0-30 %Int) differed significantly in 19 of 27 response variables. Contractions varying by half the mean force (7.5-22.5 %Int) led to 8 and 7 measured responses that were significantly different from 0-30 %Int and 15 %Sus, respectively. A sinusoidal condition (0-30 %Sine) resulted in 2 variables that were significantly different from 0-30 %Int, and 16 different from 15 %Sus. Finally, ten response variables suggested that varying forces with 1 % as the lower contraction level was significantly less fatiguing than 15 %Sus, while no responses were significantly different from 0-30 %Int. Sustained contractions led to decreased twitch force 24-h post-exercise, whereas recovery was complete within 60 min after intermittent contractions. This suggests that time-varying force may be a useful intervention to reduce local fatigue in workers performing low-load tasks, and also that rest per se did not seem to cause any extraordinary effects beyond those predictable from the force variation amplitude.

Variation between seated and standing/walking postures among male and female call centre operators

Background

The dose and time-pattern of sitting has been suggested in public health research to be an important determinant of risk for developing a number of diseases, including cardiovascular disorders and diabetes. The aim of the present study was to assess the time-pattern of seated and standing/walking postures amongst male and female call centre operators, on the basis of whole-shift posture recordings, analysed and described by a number of novel variables describing posture variation.

Methods

Seated vs. standing/walking was recorded using dichotomous inclinometers throughout an entire work shift for 43 male and 97 female call centre operators at 16 call centres. Data were analysed using an extensive set of variables describing occurrence of and switches between seated and standing/walking, posture similarity across the day, and compliance with standard recommendations for computer work.

Results

The majority of the operators, both male and female, spent more than 80% of the shift in a seated posture with an average of 10.4 switches/hour between seated and standing/walking or vice versa. Females spent, on average, 11% of the day in periods of sustained sitting longer than 1 hour; males 4.6% (p = 0.013). Only 38% and 11% of the operators complied with standard recommendations of getting an uninterrupted break from seated posture of at least 5 or 10 minutes, respectively, within each hour of work. Two thirds of all investigated variables showed coefficients of variation between subjects above 0.5. Since work tasks and contractual break schedules were observed to be essentially similar across operators and across days, this indicates that sedentary behaviours differed substantially between individuals.

Conclusions

The extensive occurrence of uninterrupted seated work indicates that efforts should be made at call centres - and probably in other settings in the office sector - to introduce more physical variation in terms of standing/walking periods during the work day. We suggest the metrics used in this study for quantifying variation in sedentary behaviour to be of interest even for other dichotomous exposures relevant to occupational and public health, for instance physical activity/inactivity.

Mechanical exposure among general practice dentists in Sweden and possible implications of rationalisation

The present study investigates the dental work in terms of time distribution and mechanical exposure in value-adding work (VAW) and non-VAW. Further rationalisation of dental work would typically involve an increase in the proportion of VAW. Information on mechanical exposure within the classes of VAW and non-VAW may be used to predict possible implications of rationalisation. Sixteen dentists were investigated. Using a data logger, postures and movements were continuously recorded for each subject during the 4 h of work, which included the 45 min of video recording. Time distribution and mechanical exposure for the six different work activities identified were evaluated from the video recordings, using a loss analysis technique. VAW, which comprised 54% of the total working time, generally implied significantly more constrained mechanical exposures as compared with non-VAW. The results suggest that future rationalisation of dental work, involving a reduction of non-VAW, may increase the risk of developing musculoskeletal disorders. Statement of Relevance: The present study illustrates the potential effects of rationalisation on biomechanical exposures for dentists. The results highlight the significance of integrating ergonomic issues into the rationalisation process in dentistry in addition to ordinary workstation and tool design improvements performed by ergonomists.

The effect of work pace on workload, motor variability and fatigue during simulated light assembly work

This study investigated the effect of work pace on workload, motor variability and fatigue during light assembly work. Upper extremity kinematics and electromyography (EMG) were obtained on a cycle-to-cycle basis for eight participants during two conditions, corresponding to "normal" and "high" work pace according to a predetermined time system for engineering. Indicators of fatigue, pain sensitivity and performance were recorded before, during and after the task. The level and variability of muscle activity did not differ according to work pace, and manifestations of muscle fatigue or changed pain sensitivity were not observed. In the high work pace, however, participants moved more efficiently, they showed more variability in wrist speed and acceleration, but they also made more errors. These results suggest that an increased work pace, within the range addressed here, will not have any substantial adverse effects on acute motor performance and fatigue in light, cyclic assembly work. STATEMENT OF RELEVANCE: In the manufacturing industry, work pace is a key issue in production system design and hence of interest to ergonomists as well as engineers. In this laboratory study, increasing the work pace did not show adverse effects in terms of biomechanical exposures and muscle fatigue, but it did lead to more errors. For the industrial engineer, this observation suggests that an increase in work pace might diminish production quality, even without any noticeable fatigue being experienced by the operators.

Occupational musculoskeletal and mental health: Significance of rationalization and opportunities to create sustainable production systems - A systematic review

This literature review aims to identify occupational musculoskeletal and mental health effects of production system rationalization as well as organizational-level measures that may improve health outcome ("modifiers" in this review). A short review of the effect of ergonomic interventions is included as background and rationalization is discussed as a theoretical concept. Indicator variables for occupational musculoskeletal and mental health and related risk factors are presented. Variables with a generalized format were allowed in the literature searches (e.g., job satisfaction and absenteeism were accepted as risk factor and health indicator, respectively), suitable for the research fields of work sociology, organization science, human resource management (HRM) and economics research. One hundred and sixty-two studies of rationalization effects on health and risk factors and 72 organization-level modifier results were accepted into the final database. Entries were sorted by rationalization strategy and work life sector, and trends in outcome (positive, mixed, no effect, or negative effect on health and risk factors) were determined. Rationalizations have a dominant negative effect on health and risk factors (57% negative, 19% positive); the most negative effects were found for downsizing and restructuring rationalizations in general (71 studies negative, 13 positive) and for the health care sector in particular (36 studies negative, 2 positive). The rationalization strategy High Performance Work System (HPWS) was associated with the highest fraction positive outcome studies (6 of 10 studies). Other rationalization strategies (lean practices, parallel vs. serial production and mechanization level) reported intermediate results, in part dependent on work life sector, but also on the year when studies were carried out. Worker participation, resonant management style, information, support, group autonomy and procedural justice were modifiers with favourable influence on outcome. It is concluded that production system rationalization represents a pervasive work life intervention without a primary occupational health focus. It has considerable and mostly negative influence on worker health, but this can be reduced by attention to modifiers. The results create a basis for new priorities in ergonomic intervention research.

Influence of three principles of pacing on the temporal organisation of work during cyclic assembly and disassembly tasks

A study was conducted to investigate the influence of different approaches to arranging the pace and temporal organisation of repetitive assembly and disassembly tasks on both average performance and its variability and to compare assembly and disassembly times derived with psychophysical methods to a more traditional methods-time measurement (MTM) approach. The conditions studied were a traditional assembly line arrangement, where assemblies were started at a pace of 110 MTM (repeated on two occasions), a batch condition, where subjects were required to complete 36 assemblies within the total amount of time allowed at 110, MTM and a psychophysical condition, where subjects were allowed to choose their pace (repeated on two occasions). Overall, the results suggest that the mean time spent working in each cycle (the 'on-time') remained fairly constant across conditions, while the idle 'off-time' in between on-times was shorter and of less varied duration in the more autonomous batch and psychophysical conditions. During the second psychophysical (self-paced) condition, subjects completed a significantly higher number of assemblies than during the 110 MTM line condition. The higher pace was achieved through reduction in mean off-times and the potential implications for musculoskeletal risk are discussed. STATEMENT OF RELEVANCE: Higher levels of autonomy over work pace, which intuitively would be beneficial from an ergonomics standpoint, actually led to subjects selecting to organise work such that off-times (idle times) were reduced. In contrast, active 'on' times were not affected much by autonomy. These results point to a reason that piecework would be associated with increased risk for musculoskeletal disorders.

Sustainable MSD prevention: management for continuous improvement between prevention and production. Ergonomic intervention in two assembly line companies

To increase output and meet customers' needs, companies have turned to the development of production management systems: Kaizen, one piece flow, Kanban, etc. The aim of such systems is to accelerate decisions, react to environmental issues and manage various productions. In the main, this type of management system has led to the continuous improvement of production performance. Consequently, such production management systems can have unexpected negative effects on operators' health and safety. Conversely, regulation and control systems focusing on work-related risks have obliged firms to implement health and safety management systems such as OHSAS 18001. The purpose of this type of system, also based on continuous improvement, is to reduce risks, facilitate work-related activities and identify solutions in terms of equipment and tools. However, the prevention actions introduced through health and safety systems often result in other unexpected and unwanted effects on production. This paper shows how companies can improve the way they are run by taking into account both types of management system.

Task selection for increased mechanical exposure variation: relevance to job rotation

It is generally considered that variation in mechanical exposure is beneficial from the viewpoint of preventing musculoskeletal disorders. An approach to quantifying the functional similarity of manual tasks was developed and tested by using three handgrips: power grip (PG); pulp pinch (PP); lateral pinch (LP). Changes in maximal voluntary contraction (MVC) forces were measured during 15 combinations of 2-min duration, 30% MVC isometric contraction in 25 participants. Strength changes in PG were found to be substantially different from LP; when the two grips were alternated, strength dropped to 85.1% MVC whereas after PG alone, strength dropped to 59.3% MVC. The findings suggest that PG and LP are functionally different enough for their alternating use to contribute to increased exposure variation during manual activities. STATEMENT OF RELEVANCE: The paper describes how to determine if two tasks, when performed alternately, are different enough to reduce fatigue, increase work capacity and potentially prevent musculoskeletal disorders. Better understanding of the differences between tasks has the potential to improve job design by allowing better choice of tasks that combine to define a job.

Effect assessment in work environment interventions: a methodological reflection

This paper addresses a number of issues for work environment intervention (WEI) researchers in light of the mixed results reported in the literature. If researchers emphasise study quality over intervention quality, reviews that exclude case studies with high quality and multifactorial interventions may be vulnerable to 'quality criteria selection bias'. Learning from 'failed' interventions is inhibited by both publication bias and reporting lengths that limit information on relevant contextual and implementation factors. The authors argue for the need to develop evaluation approaches consistent with the complexity of multifactorial WEIs that: a) are owned by and aimed at the whole organisation; and b) include intervention in early design stages where potential impact is highest. Context variety, complexity and instability in and around organisations suggest that attention might usefully shift from generalisable 'proof of effectiveness' to a more nuanced identification of intervention elements and the situations in which they are more likely to work as intended. STATEMENT OF RELEVANCE: This paper considers ergonomics interventions from perspectives of what constitutes quality and 'proof". It points to limitations of traditional experimental intervention designs and argues that the complexity of organisational change, and the need for multifactorial interventions that reach deep into work processes for greater impact, should be recognised.