Hand Posture and Force Estimation Using Surface Electromyography and an Artificial Neural Network

OBJECTIVE

The purpose of this study was to develop an approach to predict hand posture (pinch versus grip) and grasp force using forearm surface electromyography (sEMG) and artificial neural networks (ANNs) during tasks that varied repetition rate and duty cycle.

BACKGROUND

Prior studies have used electromyography with machine learning models to predict grip force but relatively few studies have assessed whether both hand posture and force can be predicted, particularly at varying levels of duty cycle and repetition rate.

METHOD

Fourteen individuals participated in this experiment. sEMG data for five forearm muscles and force output data were collected. Calibration data (25, 50, 75, 100% of maximum voluntary contraction (MVC)) were used to train ANN models to predict hand posture (pinch versus grip) and force magnitude while performing tasks that varied load, repetition rate, and duty cycle.

RESULTS

Across all participants, overall hand posture prediction accuracy was 79% (0.79 ± .08), whereas overall hand force prediction accuracy was 73% (0.73 ± .09). Accuracy ranged between 0.65 and 0.93 based on varying repetition rate and duty cycle.

CONCLUSION

Hand posture and force prediction were possible using sEMG and ANNs, though there were important differences in the accuracy of predictions based on task characteristics including duty cycle and repetition rate.

APPLICATION

The results of this study could be applied to the development of a dosimeter used for distal upper extremity biomechanical exposure measurement, risk assessment, job (re)design, and return to work programs.

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.

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.

Biomechanical risk factors associated with distal upper extremity musculoskeletal disorders in endoscopists performing colonoscopy

BACKGROUND AND AIMS

Endoscopists experience upper extremity musculoskeletal injuries. The primary aim of this study was to compare distal upper extremity biomechanical risk factors during colonoscopy with established risk thresholds. Secondary aims were to determine which subtasks during colonoscopy are associated with the greatest risk and to evaluate an intervention to reduce risks.

METHODS

Twelve endoscopists performed 2 to 4 colonoscopies while thumb pinch force and forearm muscle loads of extensor carpi radialis (ECR) and flexor digitorum superficialis (FDS) muscles were collected. Peak exertion values were analyzed using amplitude probability distribution functions. An endoscope support device was evaluated during simulated colonoscopy (n = 8).

RESULTS

Mean endoscopist age was 42.3 years; 67% were men. Peak thumb pinch force exceeded risk thresholds for pinch force (10 N) and percent of time spent in forceful pinch for all colonoscopy subtasks. Peak ECR and FDS muscle activity exceeded the action limit (10% maximum voluntary contraction [MVC]) in both forearms. Peak left FDS, left ECR, and right ECR activity exceeded the threshold limit value (>30% MVC). Peak left FDS and ECR activity were significantly greater during insertion than during withdrawal (P < .05). Peak right FDS and ECR activity were significantly greater during right colon insertion compared with withdrawal (P < .05). The endoscope support device reduced left ECR muscle activity (P = .02).

CONCLUSIONS

Thumb pinch forces and time spent in forceful pinch indicate high-risk exposures during colonoscopy. Left wrist extensor muscle activity exceeded established thresholds with the greatest risk occurring during insertion. An endoscope support device reduced loads to the left wrist extensors.

Physical Ergonomic Improvement and Safe Design of an Assembly Workstation through Collaborative Robotics

One of the key interesting features of collaborative robotic applications is the potential to lighten the worker workload and potentiate better working conditions. Moreover, developing robotics applications that meets ergonomic criteria is not always a straightforward endeavor. We propose a framework to guide the safe design and conceptualization of ergonomic-driven collaborative robotics workstations. A multi-disciplinary approach involving robotics and ergonomics and human factors shaped this methodology that leads future engineers through the digital transformation of a manual assembly (with repetitive and hazardous operations) to a hybrid workstation, focusing on the physical ergonomic improvement. The framework follows four main steps, (i) the characterization of the initial condition, (ii) the risk assessment, (iii) the definition of requirements for a safe design, and (iv) the conceptualization of the hybrid workstation with all the normative implications it entails. We applied this methodology to a case study in an assembly workstation of a furniture manufacturing company. Results show that the methodology adopted sets an adequate foundation to accelerate the design and development of new human-centered collaborative robotic workstations.

Prototype System for Measuring and Analyzing Movements of the Upper Limb for the Detection of Occupational Hazards

In the work environment, there are usually different pathologies that are related to Repetitive Efforts and Movements (REM) that tend to predominantly affect the upper limbs. To determine whether a worker is at risk of suffering some type of pathology, observation techniques are usually used by qualified technical personnel. In order to define from quantitative data if there is a risk of suffering a pathology due to movements and repetitive efforts in the upper limb, a prototype of a movement measurement system has been designed and manufactured. This system interferes minimally with the activity studied, maintaining a reduced cost of manufacture and use. The system allows the study of the movements made by the subject in the work environment by determining the origin of the Musculoskeletal Disorder (MSD) from the movements of the elbow and wrist, collecting data on the position and accelerations of the arm, forearm and hand, and taking into account the risk factors established for suffering from an MSD: high repetition of movements, the use of a high force in a repetitive manner, or the adoption of forced positions. The data obtained with this system can be analyzed by qualified personnel from tables, graphs, and 3D animations at the time of execution, or stored for later analysis.

Biomechanical analysis of users of multi-articulating externally powered prostheses with and without their device

BACKGROUND

Loss of the hand results in significant functional deficits and requires adaptation of movement patterns which may result in overuse injuries. An externally powered prosthesis may improve function of the affected limb and reduce the overreliance on the intact side; however, little research has been done in this area.

OBJECTIVE

Investigate changes in upper limb function and kinematics in individuals with partial-hand amputations performing a functional assessment by comparing results with and without a multi-articulating hand prosthesis.

STUDY DESIGN

Cross-sectional.

METHODS

Three-dimensional kinematics of four- and five-digit limb loss participants were collected as they performed the Southampton Hand Assessment Procedure with and without a prothesis.

RESULTS

Ten males completed the protocol: five with four-digit loss (thumb intact) and five with five-digit loss. Significantly larger joint motions were seen without the prosthesis than with for all participants, which may be an indicator of higher risk for overuse injury. Significant improvement was seen in Southampton Hand Assessment Procedure scores in the five-digit limb loss participants using the prosthesis compared with not using the device (p < 0.05 for 6/7 Southampton Hand Assessment Procedure score categories).

CONCLUSION

The prosthesis reduced functional deficits and decreased joint range of motion in individuals with partial hand loss. Results showed reduced compensatory motions throughout the upper limb and torso which may reduce the risk of overuse injury.

CLINICAL RELEVANCE

Results of this study indicate that externally powered partial hand prostheses can be effective in improving function and reducing compensation in individuals with partial hand loss.

Normal force distribution and posture of a hand pressing on a flat surface

Hand strength data are needed to understand and predict hand postures and finger loads while placing the hand on an object or surface. This study aims to analyze the effect of hand posture and surface orientation on hand force while pressing a flat surface. Twelve participants, 6 females and 6 males ages 19-25, performed three exertions (100%, 30% and 10% MVC- Maximum Voluntary Contraction) perpendicular to a plate in 4 angles (-45°, 0°, 45° and 90° with respect to the horizontal plane) at elbow height. Exertions involved pushing in two postures: (1) whole hand and (2) constrained to only using the fingertips. Inter-digit joint angles were recorded to map hand and finger motions and estimate joint moments for each condition. Participants exerted twice the force when pushing with whole hand vs. fingertips. 72-75% of the total force was exerted over the base of the palm, while only 11-13% with the thumb for exertions at 90°, 45° or 0° plate angles. Males maximum force for pushing at 0°, 45° and 90° plates averaged 49% higher than females for the whole hand and 62% for the fingertips (p < 0.01). There was no significant sex difference (p > 0.05) for the -45° plate. Thumb joint loads were generally higher than the other individual fingers (p < 0.05) in all % MVC and accounted for 12% of total force during whole hand exertions. On average, joint moments were 30% higher during fingertip conditions vs. whole hand. Thumb and finger joint moment magnitudes when pushing the plate at 100% MVC indicated that Metacarpophalangeal (MCP) joint moments were higher (p < 0.05) than Distal Interphalangeal joints (DIP) and Proximal Interphalangeal joints (PIP) under whole hand and fingertips conditions.

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.

The Revised Strain Index: an improved upper extremity exposure assessment model

The Revised Strain Index (RSI) is a distal upper extremity (DUE) physical exposure assessment model based on: intensity of exertion, frequency of exertion, duration per exertion, hand/wrist posture and duration of task per day. The RSI improves upon the 1995 Strain Index (SI) by using continuous rather than categorical multipliers, and replacing duty cycle with duration per exertion. In a simulation of 13,944 tasks, the RSI and 1995 SI showed good agreement in risk predictions for 1995 SI scores ≤3 (safe) and >13.5 (hazardous). For tasks with 1995 SI scores of >3 and ≤13.5, the two models showed marked disagreement, with the RSI providing much greater discriminations between 'safe' and 'hazardous' tasks for various combinations of force, repetition and duty cycle. We believe the RSI is a substantially improved model that will be useful for DUE task analysis, intervention and design. Practitioner Summary: RSI is a substantial improvement over the 1995 SI. It should be a valuable tool for designing and analysing tasks to determine risk of musculoskeletal injuries. RSI is applicable to a wide variety of tasks including very low force and very high repetition tasks such as keyboard use.

Risk assessment of cheese processing tasks using the Strain Index and OCRA Checklist

The purpose of this study was to conduct and compare two ergonomic risk assessment methods often used in occupational health research and practice: the Strain Index (SI) and Occupational Repetitive Actions (OCRA) Checklist. Seven raters used the SI and OCRA Checklist to assess task-level physical exposures to the upper extremity of workers performing 21 cheese-manufacturing tasks. Of the total task exposures assessed with both methods, nearly half (49.1%) were classified as hazardous using the OCRA Checklist while 60.2% were classified as hazardous using the SI. Although the underlying injury risk characterization constructs of the SI and OCRA Checklist differ, the results indicated that the SI and OCRA Checklist often classified job tasks into similar risk categories. The differences in risk classifications determined by the SI and OCRA Checklist for job tasks were likely related to the definition of variables measured by these assessment methods as well as the complexity of tasks evaluated. By design, the SI is specific to the distal upper extremity while the OCRA Checklist accounts for the entire upper extremity including the shoulder. When conducting risk assessments of industrial work tasks, the choice of analysis tools should be based on the purpose of the assessment and the complexity of task functions. Both the SI and OCRA Checklist yield risk assessment ratings that are similar for cheese processing tasks.

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.

Ergonomics and comfort in lawn mower handle positioning: An evaluation of handle geometry

Hand operation accompanied with any combination of large forces, awkward positions and repetition may lead to upper limb injury or illness and may be exacerbated by vibration. Commercial lawn mowers expose operators to these factors during actuation of hand controls and therefore may be a health concern. A nontraditional lawn mower control system may decrease upper limb illnesses and injuries through more neutral hand and body positioning. This study compared maximum grip strength in twelve different orientations (3 grip spans and 4 positions) and evaluated self-described comfortable handle positions. The results displayed force differences between nontraditional (X) and both vertical (V) and pistol (P) positions (p < 0.0001) and among the different grip spans (p < 0.0001). Based on these results, recommended designs should incorporate a tilt between 45 and 70°, handle rotations between 48 and 78°, and reduced force requirements or decreased grip spans to improve user health and comfort.

The inter-rater reliability of Strain Index and OCRA Checklist task assessments in cheese processing

The purpose of this study was to characterize the inter-rater reliability of two physical exposure assessment methods of the upper extremity, the Strain Index (SI) and Occupational Repetitive Actions (OCRA) Checklist. These methods are commonly used in occupational health studies and by occupational health practitioners. Seven raters used the SI and OCRA Checklist to assess task-level physical exposures to the upper extremity of workers performing 21 cheese manufacturing tasks. Inter-rater reliability was characterized using a single-measure, agreement-based intraclass correlation coefficient (ICC). Inter-rater reliability of SI assessments was moderate to good (ICC = 0.59, 95% CI: 0.45-0.73), a similar finding to prior studies. Inter-rater reliability of OCRA Checklist assessments was excellent (ICC = 0.80, 95% CI: 0.70-0.89). Task complexity had a small, but non-significant, effect on inter-rater reliability SI and OCRA Checklist scores. Both the SI and OCRA Checklist assessments possess adequate inter-rater reliability for the purposes of occupational health research and practice. The OCRA Checklist inter-rater reliability scores were among the highest reported in the literature for semi-quantitative physical exposure assessment tools of the upper extremity. The OCRA Checklist however, required more training time and time to conduct the risk assessments compared to the SI.

Requirements for more effective prevention of work-related musculoskeletal disorders

BACKGROUND

Exposures to occupational hazards substantially increase workers' risk of developing musculoskeletal disorders (MSDs) and can exacerbate pre-existing disorders. The effects on MSD risk of the physical requirements of work performance are well recognised, but there is now ample evidence that work-related psychosocial hazards can also have substantial effects; further, some hazards may be additive or interactive. This evidence is not reflected in current workplace risk management practices.

DISCUSSION

Barriers to more effective workplace management of MSD risk include: the widespread belief that risk arises largely or entirely from physical hazard exposures; regulatory and guidance documents targeting MSDs, most of which reflect this belief; risk assessment tools that focus narrowly on subsets of mainly physical hazards and yet generate outputs in the form of MSD risk indicators; and the conventional occupational health and safety (OHS) risk management paradigm, which is ill-suited to manage MSD risk. It is argued that improved workplace management of MSD risk requires a systems-based management framework and more holistic risk assessment and control procedures that address risk from all types of hazard together rather than in isolation from each other, and that support participation by workers themselves. New MSD risk management tools are needed to meet these requirements. Further, successful implementation of such changes is likely to require some restructuring of workplace responsibilities for MSD risk management. Line managers and supervisors often play key roles in generating hazards, both physical and psychosocial, so there is a need for their more active participation, along with OHS personnel and workers themselves, in routine risk assessment and control procedures. MSDs are one of our largest OHS problems, but workplace risk management procedures do not reflect current evidence concerning their work-related causes. Inadequate attention is given to assessing and controlling risk from psychosocial hazards, and the conventional risk management paradigm focuses too narrowly on risk from individual hazards rather than promoting the more holistic approach needed to manage the combined effects of all relevant hazards. Achievement of such changes requires new MSD risk management tools and better integration of the roles of OHS personnel with those of line managers.

General population job exposure matrix applied to a pooled study of prevalent carpal tunnel syndrome

A job exposure matrix may be useful for the study of biomechanical workplace risk factors when individual-level exposure data are unavailable. We used job title-based exposure data from a public data source to construct a job exposure matrix and test exposure-response relationships with prevalent carpal tunnel syndrome (CTS). Exposures of repetitive motion and force from the Occupational Information Network were assigned to 3,452 active workers from several industries, enrolled between 2001 and 2008 from 6 studies. Repetitive motion and force exposures were combined into high/high, high/low, and low/low exposure groupings in each of 4 multivariable logistic regression models, adjusted for personal factors. Although force measures alone were not independent predictors of CTS in these data, strong associations between combined physical exposures of force and repetition and CTS were observed in all models. Consistent with previous literature, this report shows that workers with high force/high repetition jobs had the highest prevalence of CTS (odds ratio = 2.14-2.95) followed by intermediate values (odds ratio = 1.09-2.27) in mixed exposed jobs relative to the lowest exposed workers. This study supports the use of a general population job exposure matrix to estimate workplace physical exposures in epidemiologic studies of musculoskeletal disorders when measures of individual exposures are unavailable.

Biomechanical risk factors for carpal tunnel syndrome: a pooled study of 2474 workers

BACKGROUND

Between 2001 and 2010, five research groups conducted coordinated prospective studies of carpal tunnel syndrome (CTS) incidence among US workers from various industries and collected detailed subject-level exposure information with follow-up of symptoms, electrophysiological measures and job changes.

OBJECTIVE

This analysis examined the associations between workplace biomechanical factors and incidence of dominant-hand CTS, adjusting for personal risk factors.

METHODS

2474 participants, without CTS or possible polyneuropathy at enrolment, were followed up to 6.5 years (5102 person-years). Individual workplace exposure measures of the dominant hand were collected for each task and included force, repetition, duty cycle and posture. Task exposures were combined across the workweek using time-weighted averaging to estimate job-level exposures. CTS case-criteria were based on symptoms and results of electrophysiological testing. HRs were estimated using Cox proportional hazard models.

RESULTS

After adjustment for covariates, analyst (HR=2.17; 95% CI 1.38 to 3.43) and worker (HR=2.08; 95% CI 1.31 to 3.39) estimated peak hand force, forceful repetition rate (HR=1.84; 95% CI 1.19 to 2.86) and per cent time spent (eg, duty cycle) in forceful hand exertions (HR=2.05; 95% CI 1.34 to 3.15) were associated with increased risk of incident CTS. Associations were not observed between total hand repetition rate, per cent duration of all hand exertions, or wrist posture and incident CTS.

CONCLUSIONS

In this prospective multicentre study of production and service workers, measures of exposure to forceful hand exertion were associated with incident CTS after controlling for important covariates. These findings may influence the design of workplace safety programmes for preventing work-related CTS.

Inter-rater reliability of cyclic and non-cyclic task assessment using the hand activity level in appliance manufacturing

This study evaluated the inter-rater reliability of the American Conference of Governmental Industrial Hygienists (ACGIH®) hand activity level (HAL), an observational ergonomic assessment method used to estimate physical exposure to repetitive exertions during task performance. Video recordings of 858 cyclic and non-cyclic appliance manufacturing tasks were assessed by sixteen pairs of raters using the HAL visual-analog scale. A weighted Pearson Product Moment-Correlation Coefficient was used to evaluate the agreement between the HAL scores recorded by each rater pair, and the mean weighted correlation coefficients for cyclic and non-cyclic tasks were calculated. Results indicated that the HAL is a reliable exposure assessment method for cyclic (r̄-bar w = 0.69) and non-cyclic work tasks (r̄-bar w = 0.68). When the two reliability scores were compared using a two-sample Student's t-test, no significant difference in reliability (p = 0.63) between these work task categories was found. This study demonstrated that the HAL may be a useful measure of exposure to repetitive exertions during cyclic and non-cyclic tasks.

RELEVANCE TO INDUSTRY

Exposure to hazardous levels of repetitive action during non-cyclic task completion has traditionally been difficult to assess using simple observational techniques. The present study suggests that ergonomists could use the HAL to reliably and easily evaluate exposures associated with some non-cyclic work tasks.

Pooling job physical exposure data from multiple independent studies in a consortium study of carpal tunnel syndrome

Pooling data from different epidemiological studies of musculoskeletal disorders (MSDs) is necessary to improve statistical power and to more precisely quantify exposure-response relationships for MSDs. The pooling process is difficult and time-consuming, and small methodological differences could lead to different exposure-response relationships. A sub-committee of a six-study research consortium studying carpal tunnel syndrome: (i) visited each study site, (ii) documented methods used to collect physical exposure data and (iii) determined compatibility of exposure variables across studies. Certain measures of force, frequency of exertion and duty cycle were collected by all studies and were largely compatible. A portion of studies had detailed data to investigate simultaneous combinations of force, frequency and duration of exertions. Limited compatibility was found for hand/wrist posture. Only two studies could calculate compatible Strain Index scores, but Threshold Limit Value for Hand Activity Level could be determined for all studies. Challenges of pooling data, resources required and recommendations for future researchers are discussed.

PRACTITIONER SUMMARY

There is a need for standardised measures and measurement protocols of physical exposure for the upper extremity. This study may provide guidance for those planning to conduct an epidemiological study on quantified job physical exposures, or planning to merge physical exposure data from similar studies with some methodologic differences.