The Composite Strain Index (COSI) and Cumulative Strain Index (CUSI): methodologies for quantifying biomechanical stressors for complex tasks and job rotation using the Revised Strain Index

Comparison of multi-task ergonomic assessment methods for risk of upper extremity and low back musculoskeletal disorders

Work-related musculoskeletal disorder of upper extremity multi-task assessment methods (Revised Strain Index [RSI], Distal Upper Extremity Tool [DUET]) and manual handling multi-task assessment methods (Revised NIOSH Lifting Equation [RNLE], Lifting Fatigue Failure Tool [LiFFT]) were compared. RSI and DUET showed a strong correlation (rs = 0.933, p < 0.001) where increasing risk factor exposure resulted in increasing outputs for both methods. RSI and DUET demonstrated fair agreement (κ = 0.299) in how the two methods classified outputs into risk categories (high, moderate or low) when assessing the same tasks. The RNLE and LiFFT showed a strong correlation (rs = 0.903, p = 0.001) where increasing risk factor exposure resulted in increasing outputs, and moderate agreement (κ = 0.574) in classifying the outputs into risk categories (high, moderate or low) when assessing the same tasks. The multi-task assessment methods provide consistent output magnitude rankings in terms of increasing exposure, however some differences exist between how different methods classify the outputs into risk categories.

A design tool to estimate maximum acceptable manual arm forces for above-shoulder work

There is a need for design criteria for above-shoulder work to prevent shoulder fatigue and supraspinatus injuries. A tool is developed to estimate maximum acceptable manual arm forces for above-shoulder work based on 25th % female strength with adjustments for supraspinatus tendon impingement and shoulder fatigue. The tool equations are presented along with tables of maximum acceptable manual arm forces in 77 locations in the 3 D space above the shoulder that accommodates a 50th % female reach. The largest acceptable anterior force, 140.3 N, occurs at shoulder height, 0.5 m anterior to the shoulder. The largest acceptable superior force, 84.4 N, occurs at shoulder height, 0.1 m anterior and 0.2 m medial to the shoulder. The new tool provides design criteria for arm exertions at a higher level of detail than prior ergonomic tools, making it useful for engineers. Based on sensitivity analyses, the tool is robust to parameter assumptions. Practitioner summary: Above-shoulder work is associated with increased risk for shoulder fatigue and injuries. A new tool is developed that estimates maximum acceptable manual arm forces for work at or above shoulder height. The tool can be used to design acceptable above-shoulder work so that it can be accomplished by most workers. Abbreviations: AFF: arm force field; AP: anterior/posterior; DC: duty cycle; GH: glenohumeral angle; HT: humerothoracic angle; LM: lateral/medial; MAE: maximum acceptable effort; MAF: maximum acceptable force; MAS: manual arm strength; MVC: maximum voluntary contraction; N: newton; OCRA: occupational repetitive action; R: reach distance; RMS: root means square; RULA: rapid upper limb assessment; SF: scale factor; SI: superior/inferior; ST: scapulothoracic angle; T: thoracicKEY POINTSA new design tool is introduced that estimates maximum acceptable hand forces for specific locations above the shoulder.This above-shoulder tool is based on a 50th percentile female anthropometry and 25th percentile female manual arm strength.These base strengths are multiplied by scaling factors that adjust for subacromial impingement and fatigue.The tool was shown to be robust based on sensitivity analysis.

The problem with "ergonomics injuries": What can ergonomists do?

Effects of psychosocial hazards on risk of musculoskeletal disorders (MSDs) are often very substantial, but workplace risk management practices focus largely on biomechanical hazards, as do the risk assessment methods used by ergonomists. Translation of research evidence into more effective workplace practices demands a more holistic risk management framework that encompasses both types of hazard. In this context, we evaluate the validity of different MSD risk assessment methods for different purposes, focusing particularly on requirements for routine workplace risk management. These include choice of fit-for-purpose assessment methods, prioritisation of hazards that are most affecting risk, and control actions as high as possible in the risk control hierarchy. Ergonomists could facilitate more effective workplace risk management by promoting: awareness of the need for change; improvements to guidance from OHS regulators; research on MSD-related workplace management issues; and professional development programs on this topic for ergonomists and other OHS practitioners.

Reliability Analysis of Observation-Based Exposure Assessment Tools for the Upper Extremities: A Systematic Review

(1) Background: The objectives of this systematic review were to (i) summarize the results of studies evaluating the reliability of observational ergonomics exposure assessment tools addressing exposure to physical risk factors associated with upper extremity musculoskeletal disorders (MSDs), and (ii) identify best practices for assessing the reliability of new observational exposure assessment tools. (2) Methods: A broad search was conducted in March 2020 of four academic databases: PubMed, Science Direct, Ergonomic Abstracts, and Web of Science. Articles were systematically excluded by removing redundant articles, examining titles and abstracts, assessing relevance to physical ergonomics and the upper extremities, and article type. (3) Results: Eleven articles were included in the review. The results indicated no singular best practice; instead, there were multiple methodological approaches researchers chose to use. Some of the significant variations in methodologies include the selection of reliability coefficients, rater and participant selection, and direct vs. digital observation. (4) Conclusion: The findings serve as a resource summarizing the reliability of existing observational risk assessment tools and identify common methods for assessing the reliability of new observational risk assessment tools. Limitations of this review include the number of databases searched, the removal of truncation symbols, and the selection of keywords used for the initial search.

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.

Wrist Posture Estimation Differences and Reliability Between Video Analysis and Electrogoniometer Methods

OBJECTIVE

The aim of this study was to determine the inter- and intrarater agreement of estimated wrist angles using video and to compare wrist angles from video analysis to electrogoniometers.

BACKGROUND

Video analysis is used frequently in ergonomic assessments, but factors including parallax and complex angles may influence wrist angle estimates. Electrogoniometers are an alternative to video, but may not be reliable in complex postures. Given the limitations of each method, there is a need to determine the suitability of the measurement methods for field use.

METHOD

Ten participants performed frame-by-frame wrist (flexion-extension, radioulnar deviation) and forearm (pronation-supination) posture estimation for worker tasks from three camera views (top, side, and oblique). Workers were equipped with electrogoniometers to record wrist posture during the tasks. The video estimate data was compared between 2 days and to sensor data.

RESULTS

Percent agreement between participants ranged from 53% to 81% across all ratings. Agreement was highest from the side view (66%, κ = 0.56) for flexion-extension and top view for radioulnar deviation (77%, κ = 0.52) and pronation-supination (69%, κ = 0.58). Video-electrogoniometer agreement was lower, with peak agreement from the top view for flexion-extension (57%, κ = 0.49) and radioulnar deviation (68%, κ = 0.30) and the oblique view for pronation-supination (53%, κ = -0.1).

CONCLUSION

Participant estimate agreement was moderate-substantial overall and aligns with previous reports. Disagreement between video and electrogoniometers may be attributed to camera angle and parallax effects and the small magnitude of wrist motions compared to other joints.

Validation of the Revised Strain Index for Predicting Risk of Incident Carpal Tunnel Syndrome in a Prospective Cohort

The Revised Strain Index (RSI), a model that quantifies physical exposure from individual hand/wrist exertions, tasks, and multi-task jobs, was used to quantify exposure for 1372 incident-eligible manufacturing, service and healthcare workers. Workers were followed for an average of 2.5 years (maximum 6 years) and had an average carpal tunnel syndrome (CTS) incidence rate of 4.6 per 100 person-years. Exceeding the a-priori RSI limit of 10.0 showed increased risk of CTS (Hazard Ratio (HR) = 1.45, 95% CI: 1.11-1.91, p = 0.01). There also was a dose-response relationship using proposed low (RSI ≤ 8.5, HR = 1.00), medium (HR = 1.42 (95% CI: 0.96-2.09, p = 0.08)), and high limits (RSI > 15, HR = 1.79 (95% CI: 1.19-2.69, p = 0.01), respectively. RSI as a continuous variable showed CTS risk increased steadily by between 1.9% and 3.3% per unit increase in RSI (p ≤ 0.03). These results suggest that the RSI is a useful tool for surveillance as well as for job intervention/design and continuous improvement processes.Practitioner Summary The Revised Strain Index (RSI) quantifies physical exposure from individual hand/wrist exertions, tasks, and multi-task jobs. Increased cumulative RSI scores (i.e. daily exposure score) are associated with increased risk of carpal tunnel syndrome (CTS). The RSI is potentially useful as a risk surveillance and intervention design tool.

Lateral epicondylosis: A literature review to link pathology and tendon function to tissue-level treatment and ergonomic interventions

BACKGROUND

Common treatments for lateral epicondylosis (LE) focus on tissue healing. Ergonomic advice is suggested broadly, but recommendations based on biomechanical motion parameters associated with functional activities are rarely made. This review analyzes the role of body functions and activities in LE and integrates the findings to suggest motion parameters applicable to education and interventions relevant to activities and life roles for patients.

PURPOSE

This study examines LE pathology, tendon and muscle biomechanics, and population exposure outlining potentially hazardous activities and integrates those to provide motion parameters for ergonomic interventions to treat or prevent LE. A disease model is discussed to align treatment approaches to the stage of LE tendinopathy.

STUDY DESIGN

Integrative review METHODS: We conducted in-depth searches using PubMed, Medline, and government websites. All levels of evidence were included, and the framework for behavioral research from the National Institutes of Health was used to synthesize ergonomic research.

RESULTS

The review broadened the diagnosis of LE from a tendon ailment to one affecting the enthesis of the capitellum. It reinforced the continuum of severity to encompass degeneration as well as regeneration. Systematic reviews confirmed the availability of evidence for tissue-based treatments, but evidence of well-defined harm reducing occupational interventions was scattered amongst evidence levels. Integration of biomechanical studies and population information gave insight into types of potentially hazardous activities and provided a theoretical basis for limiting hazardous exposures to wrist extensor tendons by reducing force, compression, and shearing during functional activities.

CONCLUSIONS

These findings may broaden the first treatment approach from a passive, watchful waiting into an active exploration and reduction of at-risk activities and motions. Including the findings into education modules may provide patients with the knowledge to lastingly reduce potentially hazardous motions during their daily activities, and researchers to define parameters of ergonomic interventions.

Developing countries and the use of ISO Standard 11228-3 for risk management of Work-Related Musculoskeletal Disorders of the Upper Limbs (WRMSDs-ULs): The case of Chile

Work-Related Musculoskeletal Disorders of the Upper Limbs (WRMSDs-ULs) are one of the most common occupational diseases worldwide. Repetitive motion is one of the main risk factors associated with these conditions. Several efforts have been made within the scientific community in order to develop specific methods to assess the risk that repetitive work represents. Furthermore, internationally coordinated work has resulted in the generation of a series of ISO standards to address issues around ergonomics in the workplace. In 2012, Chile adopted the ISO11228-3 standard checklist in its regulatory process, creating the first technical standard of risk management for repetitive motion. The aim of this study is to present the results of a nation-wide online survey of Chilean Health and Safety Practitioners and Ergonomists, which was conducted in order to identify their level of application experience, most commonly adopted practices, and opinions on the first Chilean Standard for WRMSDs-ULs risk assessment. A second aim is to discuss common issues and possible improvements in public policies, and the adoption of international instruments by developing countries. A total of 331 respondents completed the survey (183 Ergonomists and 148 non-ergonomist). It was observed that a number of the participants consider that the adaptation of the ISO standard has several issues, ranging from simple ones as wording and format to more complex ones regarding overall structure, logic, and ease of use. One of the main issues expressed is the fact that during the adaptation process the instrument is applied in multitask jobs, without providing clear instructions or training. Furthermore, among the top three most used assessment methods were RULA and REBA, which are posture-driven, instead of methods validated for repetitive motion. The issues detected by the Chilean OHS practitioners are common in developing countries, where an intersection of lack of resources, public agency authoritarianism, and poor communication between public-private and public-public organizations contribute to poor consultation, validation, and adaptation processes. Suggestions to improve the current Chilean standard, as well as considerations for developing countries, are presented.

Lean Manufacturing and Ergonomics Integration: Defining Productivity and Wellbeing Indicators in a Human–Robot Workstation

Lean Manufacturing (LM), Ergonomics and Human Factors (E&HF), and Human–Robot Collaboration (HRC) are vibrant topics for researchers and companies. Among other emergent technologies, collaborative robotics is an innovative solution to reduce ergonomic concerns and improve manufacturing productivity. However, there is a lack of studies providing empirical evidence about the implementation of these technologies, with little or no consideration for E&HF. This study analyzes an industrial implementation of a collaborative robotic workstation for assembly tasks performed by workers with musculoskeletal complaints through a synergistic integration of E&HF and LM principles. We assessed the workstation before and after the implementation of robotic technology and measured different key performance indicators (e.g., production rate) through a time study and direct observation. We considered 40 postures adopted during the assembly tasks and applied three assessment methods: Rapid Upper Limb Assessment, Revised Strain Index, and Key Indicator Method. Furthermore, we conducted a questionnaire to collect more indicators of workers’ wellbeing. This multi-method approach demonstrated that the hybrid workstation achieved: (i) a reduction of production times; (ii) an improvement of ergonomic conditions; and (iii) an enhancement of workers’ wellbeing. This ergonomic lean study based on human-centered principles proved to be a valid and efficient method to implement and assess collaborative workstations, foreseeing the continuous improvement of the involved processes.

Personal and occupational factors contributing to biomechanical risk of the distal upper limb among dairy workers in the Lombardy region of Italy

Biomechanical overload in the wrist flexor and extensor muscles, together with awkward hand positions during work activities, can result in occupational wrist and hand disorders. Dairy workers, specifically those that work in the milking parlor, are exposed to highly repetitive and forceful exertions of the upper limb throughout their work shift. There are very few studies that have investigated the determinants that contribute to the risk of distal upper limb musculoskeletal disorders among dairy workers. The purpose of the present study was to identify the variables affecting the biomechanical overload of the distal upper limb among milking parlor workers, define risk profiles, and propose possible interventions to reduce the high physical loads to the distal upper limb during milking activities. Forty male workers from the three most common milking parlor systems in Lombardy Italy were recruited to participate in this study. Multiple correspondence analysis of personal characteristics and occupational risk factors, followed by cluster analysis, led to the identification of three distinct groups of workers. Low, medium and high risk profiles were assigned to each group based on the risk assessments performed using the Strain Index and electromyography of the distal upper limb. The main risk determinants were workstation characteristics, work organization and milking routine. A well-organized milking routine, milking cluster weight below 2.4 kg or the use of supporting arms for the milking cluster may reduce the risk of biomechanical overload.

An Upper Extremity Risk Assessment Tool Based on Material Fatigue Failure Theory: The Distal Upper Extremity Tool (DUET)

OBJECTIVE

Musculoskeletal tissues repeatedly loaded in vitro fail in accordance with material fatigue failure theory, and there is evidence to suggest that the same process occurs in vivo. The current paper presents a new upper extremity risk assessment tool, the Distal Upper Extremity Tool (DUET), predicated on material fatigue failure theory.

METHODS

DUET requires an estimate of force exertion level and the number of repetitions performed to derive estimates of damage and probabilities of experiencing a distal upper extremity outcome. Damage accrued over multiple tasks may be summed to estimate the cumulative damage (CD) accrued over a workday. Validation of this tool was performed using five distal upper extremity (DUE) outcomes (involving medical visits and pain) from an existing epidemiological database involving data from six automotive manufacturing plants. Logistic regression was used to assess the association of the log of the DUET CD measure to DUE outcomes.

RESULTS

Results demonstrated that the log of the DUET CD measure was highly associated with all five DUE outcomes in both crude analyses and those adjusted for site, age, gender, and body mass index ( p < .01). A model relating the continuous DUET log CD score to the probability of the DUE outcome Injury + Pain Last Year was developed, which demonstrated a significant dose-response relationship.

CONCLUSIONS

Results suggest that fatigue failure-based risk assessment techniques are highly associated with DUE outcomes and provide support for the notion that an underlying fatigue failure process may be involved in the development of upper extremity musculoskeletal disorders.

A biomechanical shoulder strain index based on stabilizing demand of shoulder joint

Work-related shoulder joint disorders contribute considerably to absenteeism in the workplace. To identify the tasks that are stressful to the shoulder joint, a strain index was formulated based on the concept of concavity compression-a shoulder stabilizing mechanism. The magnitude and direction of the shoulder joint reaction forces were used in formulating the strain index. A two phase experiment was conducted. In Phase 1, participants performed 30 different manual handling tasks. The tasks were categorized into low, medium and high strain tasks based on their strain index values. In Phase 2, out of the 30 tasks, repetitive exertions of three tasks (low, medium and high strain index values) were simulated using three external loads (0.91, 1.81 and 2.72 kg). The muscle activity data recorded from eight shoulder muscles showed that tasks with higher strain index values induced significantly greater activation and muscle fatigue than tasks with lower strain index values.Practitioner Summary: The strain index developed in this study is a conclusive estimation of the concavity compression required for shoulder joint stabilization. It can be used to identify the activities that may contribute to the risks of shoulder disorders. Abbreviation BLS Bureau of the Labor Statistics.