The Cochran-Weiss-Shanteau performance index as an indicator of upper limb risk assessment expertise

Ergonomists and many other professionals apply ergonomics principles to musculoskeletal health problems. This study examines whether there are differences when it comes to judgement expertise concerning upper limb disorders (ULDs) between ergonomists and those with less ergonomics training. The Cochran-Weiss-Shanteau (CWS) performance index combines judgement consistency with discrimination into one CWS index. Fifty-eight professionals working in the musculoskeletal health area, from four different professions, judged the likelihood of staff complaining of ULDs in a number of written work scenarios containing ULD risk factors. A student group (n = 148) taking an introductory ergonomics module was used as a reference. The ergonomists scored higher on the CWS index than all of the other groups, performing significantly better than all but the occupational health advisors. Performance improved with increased training level but not with experience. This study suggests that ergonomists are quantifiably different from other ergonomics advisors in their judgement performance in this context. Given the global cost of musculoskeletal disorders, assessing the expertise of those giving ergonomics advice for the management of musculoskeletal health is of great significance. This study presents a method for assessing judgement performance in ULD risk assessment, an important part of musculoskeletal health management.     

Cycle to cycle variability in a repetitive upper extremity task

The purpose of this study was to examine the variability in muscle activity at rest and work during a repetitive task. A total of 20 participants performed a bimanual push task using three frequencies (4, 8, 16 pushes/min), three loads (1 kg, 2 kg, 4 kg) and two grip conditions (no grip, 30% maximum). The coefficient of variation (CoV) of muscle activity was determined for the anterior deltoid, biceps brachii, extensor digitorum and flexor digitorum superficialis. Faster push frequencies and heavier loads had lower work–rest ratio CoV and higher mean muscle activity (p < 0.01). Sixteen pushes per minute produced the lowest CoV for the anterior deltoid (p < 0.01), while the 1- kg load produced the lowest CoV for the extensor digitorum and flexor digitorum superficialis (p < 0.01). Changes were driven by the rest phase rather than by the work phase, except for grip decreasing forearm muscle CoV. These findings underscore the importance of variability at rest and indicate that low variability of muscle activity is associated with ergonomic risk factors.

Practitioner Summary: Decreased motor variability has been associated with pain and injury. A cyclical push task, evaluated in terms of work and rest phases, found that greater workloads increased variability primarily due to changes in the rest phase. Muscle variability, especially for the rest phase, may provide insight into injury risk.     

The influence of task design on upper limb muscles fatigue during low-load repetitive work: A systematic review

Ergonomic interventions such as increased scheduled breaks or job rotation have been proposed to reduce upper limb muscle fatigue in repetitive low-load work. This review was performed to summarize and analyze the studies investigating the effect of job rotation and work-rest schemes, as well as, work pace, cycle time and duty cycle, on upper limb muscle fatigue. The effects of these work organization factors on subjective fatigue or discomfort were also analyzed. This review was based on relevant articles published in PubMed, Scopus and Web of Science. The studies included in this review were performed in humans and assessed muscle fatigue in upper limbs. 14 articles were included in the systematic review. Few studies were performed in a real work environment and the most common methods used to assess muscle fatigue were surface electromyography (EMG). No consistent results were found related to the effects of job rotation on muscle activity and subjective measurements of fatigue. Rest breaks had some positive effects, particularly in perceived discomfort. The increase in work pace reveals a higher muscular load in specific muscles. The duration of experiments and characteristics of participants appear to be the factors that most have influenced the results. Future research should be focused on the improvement of the experimental protocols and instrumentation, in order to the outcomes represent adequately the actual working conditions.Relevance to industryIntroducing more physical workload variation in low-load repetitive work is considered an effective ergonomic intervention against muscle fatigue and musculoskeletal disorders in industry. Results will be useful to identify the need of future research, which will eventually lead to the adoption of best industrial work practices according to the workers capabilities.     

Cognitive simulation as a tool for cognitive task analysis

Cognitive simulations are runnable computer programs that represent models of human cognitive activities. We show how one cognitive simulation built as a model of some of the cognitive processes involved in dynamic fault management can be used in conjunction with small-scale empirical data on human performance to uncover the cognitive demands of a task, to identify where intention errors are likely to occur, and to point to improvements in the person-machine system. The simulation, called Cognitive Environment Simulation or CES, has been exercised on several nuclear power plant accident scenarios. Here we report one case to illustrate how a cognitive simulation tool such as CES can be used to clarify the cognitive demands of a problem-solving situation as part of a cognitive task analysis.     

The nature of work-related neck and upper limb musculoskeletal disorders

The nature of work-related musculoskeletal disorders of the neck and upper limbs is reviewed using both scientific data and the consensus view of experts, union bodies and government agencies across the European Union. Work-related musculoskeletal disorders describe a wide range of inflammatory and degenerative diseases and disorders. These conditions result in pain and functional impairment and may affect, besides others, the neck, shoulders, elbows, forearms, wrists and hands. They are work-related when the work activities and work conditions significantly contribute to their development or exacerbation but are not necessarily the sole determinant of causation. The classification and the need for standardised diagnostic methods for assessment of neck and upper limb musculoskeletal disorders are reviewed. These disorders are a significant problem within the European Union with respect to ill health, productivity and associated costs. The pathomechanisms of musculoskeletal disorders affecting tendons, ligaments, nerves, muscle, circulation and pain perception are reviewed and conceptual models for the pathogenesis of musculoskeletal disorders affecting the neck and upper limbs are presented. The epidemiological evidence on the work-relatedness of these disorders is discussed. A relationship between the performance of work and the occurrence of neck and upper limb musculoskeletal disorders is evident. Intervention strategies in the workplace for the reduction of both exposure and effect should focus upon factors within the work organisation as well as actively involving the individual worker. The current knowledge is sufficient to enable informed decisions to be made on future research needs and prevention strategies at the societal, organisational and individual level.     

Global optimization method for combined spherical-cylindrical wrapping in musculoskeletal upper limb modelling

In musculoskeletal modelling, many muscles cannot be represented as straight lines from origin to insertion because the bony and musculotendinous morphology of neighboring structures causes them to wrap. The majority of these passive structures can be adequately described as simple geometric shapes such as spheres and cylinders. Techniques for describing smooth muscle paths around multiple obstacles have been developed for modelling use. Until now obstacle-set methods have combined the path of single structures. This does not analytically define the shortest smooth path around multiple objects. When a sphere is included in a multiple-object wrapping algorithm, muscle paths around that sphere are restricted to a bundle of planes containing the sphere center. This assumed restriction can compromise the iterative process for finding the true shortest muscle path that satisfies all restrictions of a smooth path. This can cause model instability. The new method involves the determination of the shortest smooth muscle path in a spherical and cylindrical wrapping algorithm. A typical example is musculoskeletal modelling of the upper limb, where the muscle fibers have to wrap over this combination of obstacles.     

Cognitive simulation as a tool for cognitive task analysis.

Cognitive simulations are runnable computer programs that represent models of human cognitive activities. We show how one cognitive simulation built as a model of some of the cognitive processes involved in dynamic fault management can be used in conjunction with small-scale empirical data on human performance to uncover the cognitive demands of a task, to identify where intention errors are likely to occur, and to point to improvements in the person-machine system. The simulation, called Cognitive Environment Simulation or CES, has been exercised on several nuclear power plant accident scenarios. Here we report one case to illustrate how a cognitive simulation tool such as CES can be used to clarify the cognitive demands of a problem-solving situation as part of a cognitive task analysis.     

Guidelines for occupational musculoskeletal load as a basis for intervention: a critical review

Rationalization efforts in industry, both in the Scientific Management tradition and also based on recent rationalization theories, have as one of their main aims to increase the utilization of workers. Clearly, there is a limit to the amount of physical work each employee can perform without developing musculoskeletal disorders. Such limits are generally set by guidelines for acceptable work load. This paper reviews the physical work load concept, the historical development of guidelines, and current guidelines as found in ergonomics textbooks. The focus is on the change in the aim of the guidelines over time: increased productivity, reduced fatigue and finally improved musculoskeletal health. Current guidelines for physical work load mostly emphazise a reduction in the level of work load, while there are few guidelines that consider the repetitiveness and duration of work load. As the guidelines in general only consider one exposure variable, this is a particular problem in rationalization where all three exposure dimensions may be changed simultaneously. Present guidelines are mainly based on laboratory studies aiming to eliminate short-term physiological or psychological responses. These guidelines are clearly inadequate and may be misleading in view of recent research regarding the relationship between physical work load exposure and the development of musculoskeletal complaints at the work place.     

A computerized method for assessment of musculoskeletal discomfort in the workforce: a tool for surveillance

A musculoskeletal discomfort survey was conducted to assess musculoskeletal discomforts among rural mail carriers in two post offices. Perceived musculoskeletal discomfort was collected directly from the workforce by means of a computerized discomfort assessment system (DAS). This investigation aimed at: (1)assessing the rural mail carrier's perception of DAS; and (2) assessing the rural mail carrier's musculoskeletal discomforts resulting from work. Most participants in the study found the computer tool easy to learn and easy to use. The information collected by DAS was used: (1) to determine the number of participating employees who were experiencing some kind of musculoskeletal problem; (2)to determine subtasks associated with discomfort; (3) to determine the body areas most affected by different subtasks; and (4) to investigate the patterns of discomfort that occurred with time.     

A model for musculoskeletal disorder-related fatigue in upper limb manipulation during industrial vegetables sorting

In the agro-industrial sector there are many activities whose urgent rhythms can cause a considerable exposure to bio-mechanical risk factors. In the vegetable sorting sector the workers are subject to a several biomechanical risks, with due to repetitive movements of upper limbs, and operations that require a remarkable degree of strength.     

Sex differences in upper limb 3D joint contributions during a lifting task

Sex-related differences in work technique may contribute to increasing the risk of musculoskeletal joint disorders among women. In lifting tasks, sex differences have been reported for the trunk and lower limb, although women present a higher prevalence of shoulder disorders. We investigated sex differences in the upper limb technique during a lifting task. Trunk and upper limb kinematics were recorded in 27 women and 27 men lifting a box (6 or 12?kg) from hip to eye level. Work technique was quantified through the three-dimensional contribution of each joint to overall box height. The glenohumeral joint showed a higher contribution in women with a 6?kg box and wrist and elbow joints did with a 12?kg box, compared to men at either 6 or 12?kg. Sex differences occurred systematically above shoulder level. Our results argue for careful consideration of sex during ergonomic intervention, particularly during the overhead task.

Practitioner Summary: We investigated the sex-related differences in upper limb technique during lifting tasks. Results highlight a sex-specific kinematic strategy above the shoulder level on the glenohumeral joint and on the wrist and elbow joints. To help reduce women’s shoulder disorders in overhead task, ergonomic interventions should account for those differences.

Abbreviations: DoF: degree-of-freedom; WR/EL: wrist and elbow; GH: glenohumeral; SC/AC: sternoclavicular and acromioclavicular; TR/PE: pelvo-thoracic     

A study of a light repetitive task

A study carried out on a light repetitive task indicated how the operators' physiological responses were influenced by the regularity and timing of the work. Changes in the cardiac R-R intervals indicated the existence of a warm up period at the beginning of the work. This was followed by a short stable period, after which an increase in R-R intervals took place. Although the length of these periods varied from subject to subject, and from the paced work condition to the unpaced, it was always possible to identify them. The identification was not possible, however, on the basis of the work output patterns. It is suggested that changes in the cardiac variable could be taken into account when setting up rest pauses for light monotonous tasks.     

Quantifying repetitive hand activity for epidemiological research on musculoskeletal disorders--part I: individual exposure assessment

An exposure measurement approach is described for quantifying repetitive hand activity of individual workers in a prospective epidemiological study on work-related upper extremity musculoskeletal disorders. A total of 733 subjects were involved in this study at the baseline. Hand activities were quantified by force and repetition. Force levels were measured by workers' self-reports, ergonomists' estimates based on observation and measurements with instrumentation. Repetition levels were measured by detailed time-motion analyses using two repetitive hand activity definitions and ergonomists' estimates using scales for the American Conference of Governmental Industrial Hygienists hand activity level and the Strain Index. Results showed that the present exposure assessment approach seems to be able to quantify force level and repetitiveness of hand activities. Repetitive hand activity is quantified differently depending on whether forceful hand exertion or repetitive muscle activity is used as the definition. These hand activity definitions may quantify different physical exposure phenomena. Individual exposure assessment is important in epidemiological research of musculoskeletal disorders as there are interactions between the individual subjects and the measured parameters. These interactions may vary between exposure parameters.     

电动负载模拟器的重复控制器的设计

通过分析电动负载模拟器的基本结构和工作原理,建立数学模型并且分析了多余力矩产生的机理,提出一种重复控制和PID控制相结合的复合控制策略,利用重复控制改善系统的稳态特性,利用PID控制改善系统的动态特性.仿真结果表明,所采用的方控制方法能够有效地抑制多余力矩,提高了系统的稳态精度和动态性能.     

MPC as a tool for sustainable development integrated policy assessment

A recent stochastic and multiobjective formulation based on static open-loop optimization has laid the foundations of a quantitative approach to sustainable development policy assessment. Here, the connections between such an approach and model predictive control are explored, and a reformulation that introduces dynamics and addresses closed loop performance and stability is proposed. The approach has wide applicability but it is hoped that it will provide sustainable development practitioners in particular with new insights.     

OCRA: a concise index for the assessment of exposure to repetitive movements of the upper limbs

In the light of data and speculation contained in the literature, and based on procedures illustrated in a previous research project in which the author described and evaluated occupational risk factors associated with work-related musculoskeletal disorders of the upper limbs (WMSDs), this paper proposes a method for calculating a concise index of exposure to repetitive movements of the upper limbs. The proposal, which still has to be substantiated and validated by further studies and applications, is conceptually based on the procedure recommended by the NIOSH for calculating the Lifting Index in manual load handling activities. The concise exposure index (OCRA index) in this case is based on the relationship between the daily number of actions actually performed by the upper limbs in repetitive tasks, and the corresponding number of recommended actions. The latter are calculated on the basis of a constant (30 actions per minute), which represents the action frequency factor; it is valid—hypothetically—under socalled optimal conditions; the constant is diminished case by case (using appropriate factors) as a function of the presence and characteristics of the other risk factors (force, posture, additional elements, recovery periods). Although still experimental, the exposure index can be used to obtain an integrated and concise assessment of the various risk factors analysed and to classify occupational scenarios featuring significant and diversified exposure to such risk factors.     

Working height and parts bin position effects on upper limb muscular strain for repetitive hand transfer

The study examines the influence of workplace layout on localized muscle fatigue in a simulated repetitive seated hand transfer task. Nine task conditions were used consisting of three working heights and three parts bin positions. Six muscles in the right upper limb were monitored bilaterally using surface electromyography. Motion range data on the upper segmental joints were collected along with subjective perception data. Results showed that awkward postures due to workstation setting and high repetitiveness were the major factors affecting upper limb muscle fatigue, especially for the trapezius and anterior deltoid. The percentage of fatigued subjects generally increased when the mean working height became greater. This study suggests that working height should be organized at or below the elbow level with the parts bin position not above the working height when a repetitive hand transfer task is performed.Relevance to industryThis experimental result should be useful in job analysis for the evaluation of muscle activities and workplace layout design for the reduction of muscular load on the upper limbs during repetitive handling of light weight in industries characterized as hand transfer.     

The accuracy of conventional 2D video for quantifying upper limb kinematics in repetitive motion occupational tasks

Marker-less 2D video tracking was studied as a practical means to measure upper limb kinematics for ergonomics evaluations. Hand activity level (HAL) can be estimated from speed and duty cycle. Accuracy was measured using a cross-correlation template-matching algorithm for tracking a region of interest on the upper extremities. Ten participants performed a paced load transfer task while varying HAL (2, 4, and 5) and load (2.2 N, 8.9 N and 17.8 N). Speed and acceleration measured from 2D video were compared against ground truth measurements using 3D infrared motion capture. The median absolute difference between 2D video and 3D motion capture was 86.5 mm/s for speed, and 591 mm/s² for acceleration, and less than 93 mm/s for speed and 656 mm/s² for acceleration when camera pan and tilt were within ± 30 degrees. Single-camera 2D video had sufficient accuracy ( < 100 mm/s) for evaluating HAL.

Practitioner Summary: This study demonstrated that 2D video tracking had sufficient accuracy to measure HAL for ascertaining the American Conference of Government Industrial Hygienists Threshold Limit Value^® for repetitive motion when the camera is located within ± 30 degrees off the plane of motion when compared against 3D motion capture for a simulated repetitive motion task.     

A novel wearable system for the online assessment of risk for biomechanical load in repetitive efforts

Work-related Musculo Skeletal Disorders (WMSD) are considered the third main reason for disability and early retirement in the U.S. and are widespread in many occupations, involving both heavy and light biomechanical loads. In Italy, only taking into account the years 2009–2010, it is estimated an exponential increasing in the number of WMSD reports. In particular a 159.7% increment has been reported compared to the 2006 statistics. In this context, it is clear how important correctly diagnosing this kind of pathology is becoming. Traditional methods for WMDS assessment are based on observational techniques, in which experts manually segment, label and evaluate movements with the help of pro-forma sheets. Since these methods are currently based on visual inspection and subjective judgment, they could benefit from objective measurements in terms of both reliability and repeatability. Moreover an automatic tool for ergonomics assessment would vastly reduce the time that an expert needs to carry out the same assessment manually. In this context a novel wearable wireless system capable of assessing the muscular efforts and postures of the human upper limb for WMSDs diagnosis is proposed. The system, being non-obstructive, can be used to monitor workers in ecologic environment while they are carrying on their everyday tasks. A real-time assessment is obtained according to two of the most common indexes for the analysis of risk factors on workplaces: the Rapid Upper Limb Assessment (RULA) and the Strain Index (SI). The system exploits inertial measurement units (IMUs) to reconstruct the upper limb posture, modeled as a 7 degrees of freedom (DoF) kinematic chain. As far as muscular efforts are concerned, surface EMG sensors are used to assess forearm flexor muscles strain. As an example of the proposed system application the results of a first data collection campaign regarding super-market cashiers during everyday real-life operations is reported.Relevance to industry: The presented system has a high potential impact on industry as a timely intervention on the WMSD factors may reduce pathologies and reduce the recovery of expert workers.     

The occurrence of musculoskeletal alterations in worker populations not exposed to repetitive tasks of the upper limbs

A total of 749 workers (males: 139 aged between 15 and 35 years, and 171 aged &gt; 35 years; females: 176 aged between 15 and 35 years, and 263 aged &gt;35 years) performing tasks not at risk for work-related musculoskeletal disorders of the upper limbs (WMSDs) underwent a clinical examination using a standardized method. The ‘anamnestic cases’ were defined on the basis of pain or paraesthesia present for at least 1 week during the previous 12 months, or appearing at least once a month, and not subsequent to acute trauma. The anamnestic cases among the males amounted to 4.4% (age 15–35 years) and 12.3% (age&gt; 35 years); among the females, 4.6% (age 15–35 years) and 14.2% (age&gt; 35 years). Of the 1498 limbs examined, the prevalent diseases reported were: suspect narrow chest syndrome: 0.3% among the males &gt; 35 years, 0.6% among the females aged 15 35 years, 1% among the females &gt; 35 years; scapulo-humeral periarthritis: 0.3% among the males aged &gt; 35 years, 0.3% among the females aged 15–35 years, 1.3% among the females aged &gt; 35 years; lateral epicondylitis: 0.3% among the males aged &gt; 35 years, 0.2% among the females aged &gt; 35 years; trapeziometacarpal arthrosis: 0.8% among the females aged &gt; 35 years; wrist-hand tendinitis: 0.9% among the males aged &gt; 35 years, 0.9% among the females aged 15–35 years; carpal tunnel syndrome: 2.5% among the females aged &gt; 35 years. No disorders were detected outside the age ranges indicated. Several workers reported more than one disorder. The number of workers with at least one WMSD was: males 0% in the 15–35 years age range, 3.5% in the &gt; 35 years age range; females 2.3% in the 15–35 years age range, 7.2% in the &gt; 35 years age range; 3.9% of the total sample population. The prevalences were on average quite low, particularly among the older workers, hence the authors recommend that even minimal prevalences detected in particular work environments should not be underestimated.