Physical workload on neck and upper limb using two CAD applications

Wearable Motion Capture Devices for the Prevention of Work-Related Musculoskeletal Disorders in Ergonomics-An Overview of Current Applications, Challenges, and Future Opportunities

Work-related musculoskeletal disorders (WMSDs) are a major contributor to disability worldwide and substantial societal costs. The use of wearable motion capture instruments has a role in preventing WMSDs by contributing to improvements in exposure and risk assessment and potentially improved effectiveness in work technique training. Given the versatile potential for wearables, this article aims to provide an overview of their application related to the prevention of WMSDs of the trunk and upper limbs and discusses challenges for the technology to support prevention measures and future opportunities, including future research needs. The relevant literature was identified from a screening of recent systematic literature reviews and overviews, and more recent studies were identified by a literature search using the Web of Science platform. Wearable technology enables continuous measurements of multiple body segments of superior accuracy and precision compared to observational tools. The technology also enables real-time visualization of exposures, automatic analyses, and real-time feedback to the user. While miniaturization and improved usability and wearability can expand the use also to more occupational settings and increase use among occupational safety and health practitioners, several fundamental challenges remain to be resolved. The future opportunities of increased usage of wearable motion capture devices for the prevention of work-related musculoskeletal disorders may require more international collaborations for creating common standards for measurements, analyses, and exposure metrics, which can be related to epidemiologically based risk categories for work-related musculoskeletal disorders.

Mind the gap - development of conversion models between accelerometer- and IMU-based measurements of arm and trunk postures and movements in warehouse work

Sensor type (accelerometers only versus inertial measurement units, IMUs) and angular velocity computational method (inclination versus generalized velocity) have been shown to affect the measurements of arm and trunk movements. This study developed models for conversions between accelerometer and IMU measurements of arm and trunk inclination and between accelerometer and IMU measurements of inclination and generalized (arm) velocities. Full-workday recordings from accelerometers and IMUs of arm and trunk postures and movements from 38 warehouse workers were used to develop 4 angular (posture) and 24 angular velocity (movement) conversion models for the distributions of the data. A power function with one coefficient and one exponent was used, and it correlated well (r2 > 0.999) in all cases to the average curves comparing one measurement with another. These conversion models facilitate the comparison and merging of measurements of arm and trunk movements collected using the two sensor types and the two computational methods.

Effects of Sensor Types and Angular Velocity Computational Methods in Field Measurements of Occupational Upper Arm and Trunk Postures and Movements

Accelerometer-based inclinometers have dominated kinematic measurements in previous field studies, while the use of inertial measurement units that additionally include gyroscopes is rapidly increasing. Recent laboratory studies suggest that these two sensor types and the two commonly used angular velocity computational methods may produce substantially different results. The aim of this study was, therefore, to evaluate the effects of sensor types and angular velocity computational methods on the measures of work postures and movements in a real occupational setting. Half-workday recordings of arm and trunk postures, and movements from 38 warehouse workers were compared using two sensor types: accelerometers versus accelerometers with gyroscopes-and using two angular velocity computational methods, i.e., inclination velocity versus generalized velocity. The results showed an overall small difference (<2° and value independent) for posture percentiles between the two sensor types, but substantial differences in movement percentiles both between the sensor types and between the angular computational methods. For example, the group mean of the 50th percentiles were for accelerometers: 71°/s (generalized velocity) and 33°/s (inclination velocity)-and for accelerometers with gyroscopes: 31°/s (generalized velocity) and 16°/s (inclination velocity). The significant effects of sensor types and angular computational methods on angular velocity measures in field work are important in inter-study comparisons and in comparisons to recommended threshold limit values.

Are Measures of Postural Behavior Using Motion Sensors in Seated Office Workers Reliable?

OBJECTIVE

In this study, the reliability of measures of upper body postural behavior (head, thorax, neck, and arm) during sustained office work was evaluated.

BACKGROUND

Although there has been a substantial body of research examining the technical aspects of posture measurement in office workers using motion sensors, there is a paucity of literature examining whether posture-related behaviors are actually consistent among office workers in the field on different days and times.

METHOD

Thirty one office workers performed their usual work for three, 1-hr sessions (two morning sessions and one afternoon session) while wearing wireless motion sensors. Reliability coefficients of the derived measures of postural behavior were calculated.

RESULTS

Most (30/31) of the postural behavior measures demonstrated modest to excellent reliability (ICC 2.1: 0.48-0.84). Reliability appeared to be mildly affected by factors such as the time of day recordings were taken and variations in desk setups.

CONCLUSION

The findings suggest these measures may be a reliable method for evaluating postural behavior in the office work environment in future studies.

APPLICATION

Postural measurement using a technical motion sensor described an acceptable reliability to be used for risk assessment in the workplace. Consideration of assessment time and desk setting would increase the accuracy of postural measurement.

Associations of screen work with neck and upper extremity symptoms: a systematic review with meta-analysis

Objectives

It has often been suggested that screen work (ie, work on desktop, laptop, notebook or tablet computers) is a risk factor for neck and upper extremity symptoms. However, an up-to-date overview and quantification of evidence are lacking. We aimed to systematically review the association of exposure to screen work with neck and upper extremity symptoms from prospective studies.

Methods

An electronic database search (PubMed, Embase, Cinahl and Scopus) for prospective studies on the association of exposure to screen work and musculoskeletal symptoms was conducted. Studies were synthesised regarding extracted data and risk of bias, and meta-analyses were conducted.

Results

After screening 3423 unique references, 19 articles from 12 studies (with 18 538 participants) were included for the current review, with the most recent exposure assessment reported in 2005. Studies described duration and input frequency of screen work (ie, computer, keyboard and mouse use, assessed using self-reports or software recordings) and musculoskeletal symptoms (ie, self-reported neck/shoulder and distal upper extremity symptoms and diagnosed carpal tunnel syndrome [CTS]). Although there was overall an increased occurrence of musculoskeletal symptoms with larger exposure to screen work (relative risk: 1.11 [1.03 1.19]), findings were rather inconsistent with weaker (and statistically non-significant) risks when screen work was assessed by software recording (1.05 [0.91 1.21]) compared to with self-report (1.14 [1.03 1.19]).

Conclusions

We found an increased risk of musculoskeletal symptoms with screen work. However, the evidence is heterogeneous, and it is striking that it lacks information from contemporary screen work using laptop, notebook or tablet computers.

Comparison of muscle activity from upper trapezius and wrist extensors between dominant and non-dominant upper limbs during computer-based tasks

BACKGROUND

Sustained low-level muscle activity occurring during computer-based tasks is associated with the development of WMSDs (work-related musculoskeletal disorders) and this biomechanical exposure may be different between limbs.

OBJECTIVE

To compare muscle activity from dominant and non-dominant upper trapezius (UT) and wrist extensors (WE) during computer-based tasks in real work settings.

METHODS

Forty-five workers were monitored during two hours while performing their usual administrative tasks. Surface electromyography (sEMG) was recorded from UT and WE muscles in both sides. Rest and general exposure variables were calculated.

RESULTS

The 50th percentile demonstrated little muscle activity demand, for both dominant and non-dominant UT and no difference between sides was observed. The dominant WE muscles had lower measures of rest and higher muscle activity when compared with the non-dominant side.

CONCLUSIONS

Differences in sEMG between upper limbs were only found in WE muscles, probably due to the use of the mouse. The overall low-level muscle activity suggests a constant activation of the same motor units for the entire data-collection period, which can be considered harmful for musculoskeletal health.

Electromyographic analysis of relevant muscle groups during completion of computer tasks using different computer mouse positions

BACKGROUND

We analyzed muscular activity for different computer mouse positions during the completion of a timed computer task and determined whether the different mouse positions could affect muscular activity, productivity and perceived fatigue.

METHODS

The subjects were nine healthy young men. Two mouse positions were studied: the distal position (DP), with the forearm rested on the desk; the proximal position (PP), with only the wrist rested on the desk. The subjects performed a 16-min task in each position. Surface electromyography data were recorded for the upper back and shoulder muscles. Work productivity and muscular activity were measured for each mouse position. A visual analog scale was used to assess subjective fatigue.

RESULTS

Muscular activity was higher in muscle (m.) deltoideus (posterior) for the DP, while it was significantly higher in m. inferior infraspinatus for the PP. The visual analog scale score was significantly higher and work productivity was lower in the PP.

CONCLUSIONS

We found that using a mouse in the DP rather than the PP leads to less activity of the external rotators, less perceived fatigue and more productivity. This suggests that the DP is preferable to the PP for computer work involving a mouse.

Intraoperative workload in robotic surgery assessed by wearable motion tracking sensors and questionnaires

BACKGROUND

The introduction of robotic technology has revolutionized radical prostatectomy surgery. However, the potential benefits of robotic techniques may have trade-offs in increased mental demand for the surgeon and the physical demand for the assisting surgeon. This study employed an innovative motion tracking tool along with validated workload questionnaire to assess the ergonomics and workload for both assisting and console surgeons intraoperatively.

METHODS

Fifteen RARP cases were collected in this study. Cases were performed by 10 different participants, six primarily performed console tasks and four primarily performed assisting tasks. Participants had a median 12 (min-3, max-25) years of surgical experience. Both console and assisting surgeons performed robotic prostatectomy cases while wearing inertial measurement units (IMUs) that continuously track neck, shoulder, and torso motion without interfering with the sterile environment. Postoperatively, participants completed a workload questionnaire (SURG-TLX) and a body part discomfort questionnaire.

RESULTS

Twenty-six questionnaires were completed from 13 assisting and 13 console surgeons over the 15 cases. Postoperative pain was reported highest for the right shoulder and neck. Mental demands were 41 % higher for surgeons at the console than assisting (p < 0.05), while physical demands were not significantly different. Assisting surgeons worked in demanding neck postures for 58 % of the procedure compared to 24 % for the console surgeon (p < 0.01). Surgeons at the console were primarily static and showed 2-5 times fewer movements than assisting surgeons (p < 0.01).

CONCLUSIONS

Postures were more ergonomic during console tasks than when assisting by the bedside; however, the console may constrain postures leading to static loads that have been associated with musculoskeletal symptoms for the neck, torso, and shoulders. The IMU sensors were effective at quantifying ergonomics in robotic prostatectomies, and these methods and findings have broad applications to other robotic procedures.

Biomechanical Stresses in Computer-Aided Design and in Data Entry

A study of the risk factors of musculoskeletal disorders (MSDs) of the upper limbs was carried out on 2 populations, 1 performing a computer-aided design (CAD) task and the other performing a data entry task. A questionnaire on MSD complaints and working life was completed by a sample of each population. Biomechanical measurements of the forces, the angles, and the repetitiveness of movements of the upper limbs were carried out on some operators in each sample. It emerged that complaints of the upper limbs seem to be linked to the use of input devices. The grip forces exerted when using the keyboard and mouse were higher in CAD than in data entry.

Biomechanics and performance when using a standard and a vertical computer mouse

OBJECTIVE

to compare the biomechanics and performance while using a vertical computer mouse (VM) and a standard mouse (SM).

METHODS

muscle activation (electromyography), forearm movements (electrogoniometers), performance (Fitts' Law test) and satisfaction (questionnaire) of 16 subjects were evaluated.

RESULTS

there were significant differences between the VM and the SM, respectively, on motion (28° vs. 42° pronation, p = 0.001; 5° ulnar vs. 7° radial deviation, p = 0.016) and muscle activity (13% vs. 16% of extensor carpi activity, p = 0.006; 10% vs. 13% extensor digitorum activity, p = 0.001). VM user satisfaction was good (68); however, time to target was longer (4.2 vs. 3.4 s, p < 0.001).

CONCLUSIONS

using the VM decreased wrist pronation and lowered wrist extensor muscle activity, but additional training and familiarisation time may be required to improve user performance.

PRACTITIONER SUMMARY

Using a vertical mouse can decrease the exposure to biomechanical risk factors for computer mouse use-related musculoskeletal disorders. Using a vertical computer mouse resulted in less wrist pronation and lower wrist extensor muscle activity. But, training and familiarisation are required.

Bias and imprecision in posture percentile variables estimated from short exposure samples

Background

Upper arm postures are believed to be an important risk determinant for musculoskeletal disorder development in the neck and shoulders. The 10^th and 90^th percentiles of the angular elevation distribution have been reported in many studies as measures of neutral and extreme postural exposures, and variation has been quantified by the 10^th-90^th percentile range. Further, the 50^th percentile is commonly reported as a measure of "average" exposure. These four variables have been estimated using samples of observed or directly measured postures, typically using sampling durations between 5 and 120 min.

Methods

The present study examined the statistical properties of estimated full-shift values of the 10^th, 50^th and 90^th percentile and the 10^th-90^th percentile range of right upper arm elevation obtained from samples of seven different durations, ranging from 5 to 240 min. The sampling strategies were realized by simulation, using a parent data set of 73 full-shift, continuous inclinometer recordings among hairdressers. For each shift, sampling duration and exposure variable, the mean, standard deviation and sample dispersion limits (2.5% and 97.5%) of all possible sample estimates obtained at one minute intervals were calculated and compared to the true full-shift exposure value.

Results

Estimates of the 10^th percentile proved to be upward biased with limited sampling, and those of the 90^th percentile and the percentile range, downward biased. The 50^th percentile was also slightly upwards biased. For all variables, bias was more severe with shorter sampling durations, and it correlated significantly with the true full-shift value for the 10^th and 90^th percentiles and the percentile range. As expected, shorter samples led to decreased precision of the estimate; sample standard deviations correlated strongly with true full-shift exposure values.

Conclusions

The documented risk of pronounced bias and low precision of percentile estimates obtained from short posture samples presents a concern in ergonomics research and practice, and suggests that alternative, unbiased exposure variables should be considered if data collection resources are restricted.

Using pliers in assembly work: short and long task duration effects of gloves on hand performance capabilities and subjective assessments of discomfort and ease of tool manipulation

The present study investigated the effects of wearing typical industrial gloves on hand performance capabilities (muscle activity, wrist posture, touch sensitivity, hand grip and forearm torque strength) and subjective assessments for an extended duration of performing a common assembly task, wire tying with pliers, which requires a combination of manipulation and force exertion. Three commercially available gloves (cotton, nylon and nitrile gloves) were tested and compared with a bare hand condition while participants performed the simulated assembly task for 2 h. The results showed that wearing gloves significantly increased the muscle activity, wrist deviation, and discomfort whilst reducing hand grip strength, forearm torque strength and touch sensitivity. The combined results showed that the length of time for which gloves are worn does affect hand performance capability and that gloves need to be evaluated in a realistic working context. The results are discussed in terms of selection of gloves for industrial assembly tasks involving pliers.

Injury risk associated with physical demands and school environment characteristics among a cohort of custodial workers

Few epidemiological studies have investigated the relationship between work exposures and injury risk among custodians. The relationship between injury risk and occupational physical demands (e.g. pushing/pulling, lifting) and school environment characteristics (e.g. school type, season) was investigated among a cohort of 581 school custodians over a 4-year period. In the final Poisson regression models, the risk of injury was associated with time spent in pushing/pulling tasks in a dose-response manner increasing to a five-fold risk among the highest quartile of exposure (risk ratio = 5.15, 95% CI 1.00, 26.5). Injury risk was also associated with working during the school year compared to the summer, working in a school with grass vs. gravel grounds and working in a school with detached classrooms. Results help to target interventions such as alternative methods for floor cleaning to reduce the pushing/pulling demands of custodial work and to support decisions for alternatives to detached classrooms and grass surfaces. Statement of Relevance: This study examines ergonomic factors (physical demand exposures, school environment characteristics) associated with injury risk among custodial school workers. The findings help schools to target interventions to reduce the physical demands associated with injuries and to design school environments to reduce exposures.

A review of direct neck measurement in occupational settings

No guidelines are available to orient researchers on the availability and applications of equipment and sensors for recording precise neck movements in occupational settings. In this study reports on direct measurements of neck movements in the workplace were reviewed. Using relevant keywords two independent reviewers searched for eligible studies in the following databases: Cinahal, Cochrane, Embase, Lilacs, PubMed, MEDLINE, PEDro, Scopus and Web of Science. After applying the inclusion criteria, 13 articles on direct neck measurements in occupational settings were retrieved from among 33,666 initial titles. These studies were then methodologically evaluated according to their design characteristics, exposure and outcome assessment, and statistical analysis. The results showed that in most of the studies the three axes of neck movement (flexion-extension, lateral flexion and rotation) were not simultaneously recorded. Deficiencies in available equipment explain this flaw, demonstrating that sensors and systems need to be improved so that a true understanding of real occupational exposure can be achieved. Further studies are also needed to assess neck movement in those who perform heavy-duty work, such as nurses and electricians, since no report about such jobs was identified.

Increased physical work loads in modern work--a necessity for better health and performance?

Shifting workforce proportions to sedentary occupations and technology developments in traditionally physically demanding occupations have resulted in low physical workloads for many workers. Insufficient physical stress is known to have detrimental short- and long-term effects on health and physical capacity. It is argued herein that many modern workers are at risk of insufficient physical workload. Further, it is argued that the traditional physical ergonomics paradigm of reducing risk by reducing physical loads ('less is better') is not appropriate for many modern occupations. It is proposed that a new paradigm is required, where 'more can be better'. The potential for work to be seen as an arena for improving physical health and capability is discussed and the types of changes to work that may be required are outlined. The paper also discusses challenges and responsibilities presented by this new paradigm for ergonomists, employers, health and safety authorities and the community. The majority of workers in affluent communities now face the significant threat to health of insufficient physical workload. Ergonomics can design work to a prescription that can not only reduce injury risk but enhance health and capacity. However, this will require a change in paradigm.

Precision of measurements of physical workload during standardized manual handling part III: goniometry of the wrists

Goniometry of the wrist is a feasible method for studying wrist movements in most hand-intensive work. The precision and accuracy of the method per se is good. For the knowledge on validity of field measurements, the size of imprecision is of importance. This study evaluated this condition during standardized circumstances. Six women performed three different hand-intensive work tasks: 'materials picking', 'light assembly', and 'heavy assembly', repeated during three different days. Variance components between-days (within subjects) and between-subjects were derived for positions (flexion/extension and deviation) and movements, including angular velocities, % of time with very low velocity (<1 degree /s), as well as repetitiveness. For positions, the average standard deviations in the three tasks were, both between-days and between-subjects, 3-4 degrees . For movements, the coefficients of variation of angular velocities were about 10% between-days, and could to a great part be explained by differences in work rate. Between-subjects variability was higher, 20-40%. The variability was larger at low velocities than at high ones. The precision of the measured positions was good, expressed as small between-days and between-subjects variability. For movements, the between-days variability was also small, while there was a larger between-subjects variability. The imprecision of goniometry is consequently lower and comparable with inclinometry but lower than for EMG.

Design and validation of a desk-free and posture-independent input device

This study investigates variations in performance, postures and strains on the hand-arm-shoulder musculature during the operation of a wireless mouse, trackpad and a new input device. The device is held between the flexed index and middle fingers with the palm facing sideways. The buttons and wheels are activated by flexion and/or rolling of the thumb. Eleven males and nine females participated in the study. All subjects performed an aiming task to test the pointing and dragging functions. The results of this study reveal that the new pointing device allowed users to adopt more ergonomic postures and has the advantage of reduced muscular loadings of the upper extremities. Mean (SD) muscular activities (%RVC) using the wireless mouse, the trackpad and the new input device were as follows: trapezius: 3.0 (1.7), 4.4 (2.9) and 1.4 (1.0), and extensor carpi ulnaris: 7.3 (4.4), 14.5 (8.4) and 5.6 (3.1), respectively. The device was used in a variety of hand positions, alternatively. The size of the working area was far greater when the new input device was used than when the two conventional analogues were used. Although reasonable performance was not achieved, the results support recommendations concerning the redesign of the device. The ergonomic efforts in the design of the input device are of heuristic value, providing a basis for future development.

Effects of pace and stress on upper extremity kinematic responses in sign language interpreters

Sign language interpreters suffer from high levels of upper extremity disorders and burnout due to the physical and cognitive demands of interpreting. The objective of this research was to quantify the wrist kinematics of interpreting and to assess how speaker pace and psychosocial stress influence wrist kinematics. Professional interpreters interpreted a pre-recorded lecture, while the speaking pace of the lecture varied. One group of subjects was exposed to environmental conditions intended to induce stress. Several wrist kinematic variables of interpreting exceeded previously established high risk benchmarks for development of upper extremity disorders in industrial tasks. Wrist velocity and acceleration increased significantly with pace, with increases ranging from 10.7-18.6%. Increased psychosocial stress resulted in significant increase of left hand (non-dominant) wrist velocity and acceleration, with increases ranging from 14.8-19.5%. These results provide an objective assessment of the biomechanical demands of interpreting and support earlier research into different types of work, which found deleterious effects of psychosocial stress on the biomechanical responses of the lower back.

The influence of body posture, arm movement, and work stress on trapezius activity during computer work

The study aimed to determine the influence of arm posture and movement on trapezius activity of computer workers, considering the full workday. A second aim was to investigate if work periods perceived as stressful were associated with elevated or more sustained muscle activity pattern. Twenty-six computer workers performing call-center (n=11), help desk (n=7), or secretarial (n=8) work tasks participated. Bilateral trapezius surface electromyographic (sEMG) activity and heart rate was recorded throughout the workday. Simultaneous inclinometer recordings from left thigh and upper arms identified periods with sitting, standing, and walking, as well as arm posture and movement. Perceived work stress and tension were recorded on visual analog scales (VAS) every hour. Trapezius sEMG activity was low in seated posture [group median 1.8 and 0.9% of activity at maximal voluntary contraction (%EMGmax) for dominant and non-dominant side] and was elevated in standing (3.0 and 2.5% EMGmax) and walking (3.9 and 3.4% EMGmax). In seated posture (mean duration 79% of workday) arm movement consistently influenced trapezius activity, accounting for approximately 20% of intra-individual variation in trapezius activity. Arm elevation was on average not associated with trapezius activity when seated; however, considerable individual variation was observed. There was no indication of increase in trapezius activity or more sustained activity pattern, nor in heart rate, in high-stress versus low-stress periods, comparing periods with seated posture for the subjects reporting contrasts of at least two VAS units in stress (n=16) or tension (n=14) score.

Differences in physical workload, psychosocial factors and musculoskeletal disorders between two groups of female hospital cleaners with two diverse organizational models

OBJECTIVES

To clarify if differences in the physical workload, the psychosocial factors and in musculoskeletal disorders can be attributed to work organizational factors.

METHODS

The physical workload (muscular activity of m. trapezius, positions and movements of the head, upper arms and wrists and heart rate) was assessed in 24 female hospital cleaners working in a traditional work organization (TO) and in 22 working in an extended one (i.e. with an enlarged work content and more responsibilities; EO). The psychosocial work environment was assessed as job demand, decision latitude and social support in 135 (TO) and 111 (EO) cleaners, and disorders of the neck and upper extremity by a physical examination.

RESULTS

The EO group was associated with lower physical workload, in terms of heart rate ratio (23 vs 32; P<0.001), head and upper arm positions and movements (right upper arm, 50th percentile, 35 degrees/s vs 71 degrees/s; P<0.001) and wrist movements (20 degrees/s vs 27 degrees/s; P=0.001), than the TO group. The EO group reported higher decision latitude and lower work demand than the TO one, while we found no difference in social support. The prevalence of complaints and diagnoses in neck/shoulders were lower in the EO group (diagnoses 35% vs 48%; P=0.04). Moreover, the prevalence of subjects with at least ten physical finding in elbows/hands was lower in the EO group (10 vs 29; P<0.001).

CONCLUSION

Hospital cleaners have a high prevalence of neck and upper limb disorders and a high physical workload. Comparing two groups of cleaners, with differences in the way of organizing the work, lower physical workload, more beneficial psychosocial factors and a better musculoskeletal health was found in the group with an extended organization. Hence, the differences found can be attributed to the organizational factors.

Characterization of a laboratory model of computer mouse use - applications for studying risk factors for musculoskeletal disorders

In the present study, we assessed the wrist kinetics (range of motion, mean position, velocity and mean power frequency in radial/ulnar deviation, flexion/extension, and pronation/supination) associated with performing a mouse-operated computerized task involving painting rectangles on a computer screen. Furthermore, we evaluated the effects of the painting task on subjective perception of fatigue and wrist position sense. The results showed that the painting task required constrained wrist movements, and repetitive movements of about the same magnitude as those performed in mouse-operated design tasks. In addition, the painting task induced a perception of muscle fatigue in the upper extremity (Borg CR-scale: 3.5, p<0.001) and caused a reduction in the position sense accuracy of the wrist (error before: 4.6 degrees , error after: 5.6 degrees , p<0.05). This standardized painting task appears suitable for studying relevant risk factors, and therefore it offers a potential for investigating the pathophysiological mechanisms behind musculoskeletal disorders related to computer mouse use.

A new input device: comparison to three commercially available mouses

This study was conducted to simultaneously compare the postural demands and performance of a new human-centred computer input device to three devices currently on the market. It was hypothesized that the new device would perform as well as the commercial devices while requiring less postural strain. A total of 24 experienced computer users performed a series of modified Steering and Fitts' Law Tests while their postural behaviour was captured using an opto-electric system. Analysis of the postural data revealed strong similarities between the new device and the commercially available devices, including some similarities that are not suggested in the literature. Analysis of the performance data reveals no significant difference between the new device and most commercial devices and suggests further examination of the difference between familiarity and mastery. This study has shown that it is possible to use the new device in a relaxed posture and yet achieve the same accuracy as commercial devices at no more postural risk than when the traditional mouse is used at a customized, ergonomic workstation.

Should office workers spend fewer hours at their computer? A systematic review of the literature

Worldwide, millions of office workers use a computer. Reports of adverse health effects due to computer use have received considerable media attention. This systematic review summarises the evidence for a relationship between the duration of work time spent using the computer and the incidence of hand-arm and neck-shoulder symptoms and disorders. Several databases were systematically searched up to 6 November 2005. Two reviewers independently selected articles that presented a risk estimate for the duration of computer use, included an outcome measure related to hand-arm or neck-shoulder symptoms or disorders, and had a longitudinal study design. The strength of the evidence was based on methodological quality and consistency of the results. Nine relevant articles were identified, of which six were rated as high quality. Moderate evidence was concluded for a positive association between the duration of mouse use and hand-arm symptoms. For this association, indications for a dose-response relationship were found. Risk estimates were in general stronger for the hand-arm region than for the neck-shoulder region, and stronger for mouse use than for total computer use and keyboard use. A pathophysiological model focusing on the overuse of muscles during computer use supports these differences. Future studies are needed to improve our understanding of safe levels of computer use by measuring the duration of computer use in a more objective way, differentiating between total computer use, mouse use and keyboard use, attaining sufficient exposure contrast, and collecting data on disability caused by symptoms.

Musculoskeletal disorders among female and male air traffic controllers performing identical and demanding computer work

Operators with identical, demanding computer work (90 female and 97 male air traffic controllers) were found to have high prevalences of disorders (assessed by questionnaire and physical examination) in neck, shoulders and upper back. In spite of the identical work, the women displayed higher prevalences than the men (e.g. neck diagnoses 21% vs. 4%). Disorders in elbows, wrists and hands were less common, with similar rates in both genders. Generally, the psychosocial work environment (assessed by questionnaire) was found to be good, but with large inter-individual variation. Women experienced lower decision latitude than men, particularly regarding influence and freedom at work, but perceived higher social support. Physically, the work was characterized by relatively low angular velocities of upper arms (measured by inclinometry) and wrists (right: < 1 degrees/s during 19% of time, measuring by goniometry), dynamic muscular activities and high time fractions of rest in the trapezius and forearm extensor muscles (measuring by electromyography). There were only minor differences between the genders.

Precision of measurements of physical workload during standardised manual handling. Part II: Inclinometry of head, upper back, neck and upper arms

For measuring the physical exposure/workload in studies of work-related musculoskeletal disorders, direct measurements are valuable. However, the between-days and between-subjects variability, as well as the precision of the method per se, are not well known. In a laboratory, six women performed three standardised assembly tasks, all of them repeated on three different days. Triaxial inclinometers were applied to the head, upper back and upper arms. Between-days (within subjects) and between-subjects (within tasks) variance components were derived for the 10th, 50th and 90th percentiles of the angular and the angular velocity distributions, and for the proportion of time spent in predefined angular sectors. For percentiles of the angular distributions, the average between-days variability was 3.4 degrees , and the between-subjects variability 4.0 degrees . For proportion of time spent in angular sectors, the variability depended on the percentage of time spent in the sector; the relative variability was scattered and large, on average 103% between days and 56% between subjects. For the angular velocity percentiles, the average between-days variability was 7.9%, and the average between-subjects variability was 22%. The contribution of the measurement procedure per se to the between-days variability, i.e., the imprecision of the method, was small: less than 2 degrees for angles and 3% for angular velocity.

Comparison of three computer office workstations offering forearm support: impact on upper limb posture and muscle activation

The aims of the study were: 1) to determine whether resting the forearms on the work surface, as compared to chair armrests, reduces muscular activation; 2) to compare the sensitivity of different electromyographic (EMG) summary parameters. Eighteen healthy subjects performed computer work (with keyboard and mouse alternately) for 20 min while resting their forearms on a work surface adjustable in height (Workstation A), on the chair's armrests with an adjustable workstation (Workstation B) or on their chair's armrests with a non-adjustable workstation (Workstation C). The EMG amplitude of the trapezius and deltoid muscles was little influenced by the workstations, whereas their EMG variability increased with Workstation A, which was interpreted as a positive effect. However, the EMG amplitude of the mouse-side extensor digitorum muscle was higher with Workstation A. Alternating between resting the forearms on the work surface and on the chairs' armrests could solicit different muscles during computer work, and could be considered as a strategy for preventing musculoskeletal disorders. The new exposure variation analysis summary parameters used were sensitive to small workstation changes, thus supporting their use in future studies.

Validity of self-assessed reports of occurrence and duration of occupational tasks

To obtain quantitative estimates of the physical workload in epidemiological and intervention studies of musculoskeletal disorders, there is a need to extend task based exposure data to job exposure profiles. For this purpose a work task diary was developed and evaluated. This was validated against direct observations of a day's work for twenty-two female office workers and twenty female hospital cleaners. There was a good agreement regarding the occurrence of the main tasks. However, the less time-consuming tasks were under-reported. Moreover, about two thirds of the changes between tasks were not reported. The difficulties of defining tasks that function as occupational entities seems to be a major reason for the lack of agreement. The underestimation of the duration of breaks/pauses was most pronounced for the cleaners. Still, the diary would be useful for the calculation of job exposure, by time-weighting task exposure data, when the tasks and/or their duration vary between days.

Measurements of wrist and forearm positions and movements: effect of, and compensation for, goniometer crosstalk

Flexible biaxial goniometers are extensively used for measuring wrist positions and movements. However, they display an inherent crosstalk error. The aim was to evaluate the effect, of this error, on summary measures used for characterizing manual work. A goniometer and a torsiometer were combined into one device. An algorithm that effectively compensated for crosstalk was developed. Recordings from 25 women, performing five worktasks, were analyzed, both with and without compensation for crosstalk. The errors in the 10th, 50th and 90th percentiles of the flexion/extension distributions were small, on average <1 degrees. The ulnar/radial deviation distributions were weakly dependent on forearm position. The flexion/extension velocity measures were, for the 50th and 90th percentiles, as well as the mean velocity, consistently underestimated by, on average, 3.9%. For ulnar/radial deviation, the velocity errors were less consistent. Mean power frequency, which is a measure of repetitiveness, was insensitive (error <1%) to crosstalk. The forearm supination/pronation angular distributions were wider, and the velocities higher, than for the wrists. Considering wrist/hand exposure in epidemiologic studies, as well as for establishing and surveillance of exposure limits for prevention of work-related upper extremity musculoskeletal disorders, the crosstalk error can, when considering other errors and sources to variation, be disregarded.

The impact of working technique on physical loads - an exposure profile among newspaper editors

The aim of this study was to investigate the possible associations between working technique, sex, symptoms and level of physical load in VDU-work. A study group of 32 employees in the editing department of a daily newspaper answered a questionnaire, about physical working conditions and symptoms from the neck and the upper extremities. Muscular load, wrist positions and computer mouse forces were measured. Working technique was assessed from an observation protocol for computer work. In addition ratings of perceived exertion and overall comfort were collected. The results showed that subjects classified as having a good working technique worked with less muscular load in the forearm (extensor carpi ulnaris p=0.03) and in the trapezius muscle on the mouse operating side (p=0.02) compared to subjects classified as having a poor working technique. Moreover there were no differences in gap frequency (number of episodes when muscle activity is below 2.5% of a reference contraction) or muscular rest (total duration of gaps) between the two working technique groups. Women in this study used more force (mean force p=0.006, peak force p=0.02) expressed as % MVC than the men when operating the computer mouse. No major differences were shown in muscular load, wrist postures, perceived exertion or perceived comfort between men and women or between cases and symptom free subjects. In conclusion a good working technique was associated with reduced muscular load in the forearm muscles and in the trapezius muscle on the mouse operating side. Moreover women used more force (mean force and peak force) than men when operating the click button (left button) of the computer mouse.