Arne Aarås

Musculoskeletal, visual and psychosocial stress in VDU operators before and after multidisciplinary ergonomic interventions

The study has a parallel group design with two intervention groups (T and S) and one control group (C) of VDU operators. Three serial interventions were carried out in the T and S groups, first a new lighting system, then new workplaces and last an optometric examination and corrections if needed. The new lighting gave significantly increased illuminance levels, increased luminances of the room surfaces and better luminance distribution. The two intervention groups reported significant improvement of the lighting conditions, as well as of the visual conditions and significantly reduced visual discomfort and glare. Significant reduction of headache was found in one of the intervention groups. Optometric corrections reduced the visual discomfort in both the intervention groups. When looking at those given new corrections, a significant reduction was found in the T group and a clear tendency was also found in the S group. The C group reported no improvements for any of these health outcomes. The workplace intervention gave the operator the possibility to support the whole forearm and hand on the table top. Before the intervention there were no significant differences between the three groups regarding shoulder pain and static trapezius electromyographic (EMG) load. Two years after the intervention, a significant reduction of shoulder pain was reported in the T and S groups in parallel with a significant reduction in static trapezius load, while no such reduction was found in the C group. At the same time, both static trapezius load and shoulder pain were significantly lower in the T and S groups compared with the C group. Pain in the forearm and hand showed no significant changes in any of the groups during the study period. However, there seem to be a relationship between pain in the forearm and hand and the time the operator used the mouse. The C group reported significantly higher intensity of pain and used the mouse significantly more than the S group.

Postural load during VDU work: a comparison between various work postures

The aim of this study was to compare the postural load during VDU work in the following work postures: (1) Supporting and not supporting the forearms on the table top, (2) Sitting and standing positions, and (3) Sightline to the centre of the screen at an angle of 15 degrees and 30 degrees below the horizontal. The muscle load from the upper part of musculus trapezius and from the lumbar part of musculus erector spinae (L3 level) was measured by electromyography (EMG). Postural angles of head, upper arm and back were measured by inclinometers. The load on m. trapezius when using the keyboard was significantly less in sitting with supported forearms compared to sitting and standing without forearm support. Further, the time and number of periods when the trapezius load was below 1% MVC was significantly greater with support versus no support. The load on the right erector spinae lumbalis was also significantly less and the time when the load was below 1% MVC was significantly longer in a sitting work position with support versus standing without support. In addition, when using a mouse supporting the forearms reduced the static trapezius load in sitting. The results from this study document clearly the importance of giving the operator the possibility of supporting the forearms on the table top.

Musculoskeletal, visual and psychosocial stress in VDU operators before and after multidisciplinary ergonomic interventions. A 6 years prospective study--Part II.

A prospective epidemiological field study covering a 2 years period has earlier been published. The study has a parallel group design with two intervention groups (T and S) and one control group (C) of Visual Display Unit (VDU) operators. The present paper covers the period from 2 to 6 years of the study. After 3.5 years, the C group got the same intervention in terms of new lighting system, new workplaces and at last an optometric examination and corrections if needed. The C group reported a significant reduction in visual discomfort after interventions while the two groups (T and S) continued to report significant reduction of visual discomfort after 6 years. By supporting the forearm on the table top, the C group reported significant reduction of shoulder and neck pain while the T group reported significant reduction in shoulder and back pain after 6 years. Organizational and psychosocial factors at work and outside work did not show any significant changes during the study period.

Postural angles as an indicator of postural load and muscular injury in occupational work situations

Abstract This paper explores the use of information on the position of the upper arm and head as an indicator of load on the shoulder and of risk of shoulder injury for workers performing electromechanical assembly work. Two tests were used in the evaluation of the method, examining whether or not: (1) the development of musculo-skeletal injuries among groups of workers could be related to postural angles of the upper arm, and (2) there was a correlation between the two indicators of shoulder load, position of upper arm and upper trapezius EMG. Postural angles of flexion/extension and abduction/adduction of the right upper arm in the shoulder joint as well as flexion/extension of the head and back were measured using potentiometer-sensed pendulums. In most subjects, electromyography (EMG) was simultaneously recorded from upper trapezius muscles. The magnitude of the postural angles of the shoulder joint influenced the shoulder load. However, several parameters not quantified by postural angle measurements...

Relationship between trapezius load and the incidence of musculoskeletal illness in the neck and shoulder

Abstract A relationship between m. trapezius load measured by electromyography (EMG) and the incidence of musculoskeletal illness in the neck and shoulder regions, was investigated both for assembly workers and VDT operators. For assembly workers, the static trapezius load (probability 0.1 of the amplitude probability distribution function, APDF) was significantly reduced from 4.3% MVC (Maximum Voluntary Contraction) to 1.4% MVC as a group median value after an ergonomic adaptation of their work places. Musculoskeletal sickleave was significantly reduced from 22.9 days to 1.8 days as a medium duration per-man-labour year for the same group. Three groups of VDT operators were examined in terms of trapezius load and pain intensity and duration before and after an ergonomic intervention. All groups reported significant less intensity or duration of pain either in the neck or in the shoulder regions after the intervention. The trapezius load was reduced for all groups post vs. prior intervention. This reduction was measured in terms of a decrease in the static level of APDF and an increase in the number of periods per minute and total duration of muscle activity below 1% MVC. The results from this study indicate that the trapezius load may be a predictor for development of musculoskeletal illness in the neck and shoulder regions.

Reproducibility and stability of normalized EMG measurements on musculus trapezius

The reliability of normalized EMGrms (root mean square value of the electromyographic signal) measurements from musculus trapezius were evaluated in a field study. The reproducibility and stability of the method as well as the reproducibility of the results for nine variables were examined. The variables were: static, median and peak values of the ADF (amplitude distribution function) and the total time and number of periods when the muscles load was below 1, 2 and 5% of MVC (maximum voluntary contraction). Twelve data operators, performing entry work, were measured twice with an interval of a week. Coefficients of repeatability were calculated. The coefficient of repeatability for 5 of the variables showed that 95% of the differences between measurements 1 and 2 for each subject were less than two standard deviations from the group mean. The same was true for the other four variables if the result of one of the twelve measurements was removed. The agreement index, twice the standard deviation of the difference between the two measurements divided by the mean of the two measurements was low only for the static value of the ADF and the number of periods below 5% MVC. Six data operators performing entry work were examined six times at weekly intervals. The stability ratio SDmm/SDv was less than 1 for all variables except for time and number of periods when the muscles load was below 5% MVC. SDmm is the standard deviation of the difference between minimum and maximum value for each of the subjects for the six measurements. SDv is the average of the standard deviations of the six measurements at each visit. Two groups, each consisting of 24 VDU operators doing similar work were compared using the results from one EMG measurement on the trapezius. No significant differences were found between the groups for any of the nine variables (0.07 < p < 0.87).

The impact of ergonomic intervention on individual health and corporate prosperity in a telecommunications environment

This paper is a summary of several papers published in different journals and conference proceedings. The contents deal with the incidence of load related musculoskeletal illness of female workers exposed to various workloads. Furthermore, the changes in workload due to improved workplace design and the effect on the incidence of musculoskeletal illness was evaluated. The sick-leave due to musculoskeletal illness was reduced from 5.3% to 3.1% and the reduction in turn-over from 30.1% to 7.6%. The cost and the benefits of this ergonomic intervention were analysed, and showed that an investment of NOK. 350,000 produced total savings of NOK. 3,200,000. Postural load was assessed by recording electromyography (EMG) on the upper part of musculus trapezius, postural angles of the upper arm and flexion/extension of the head and back. A quantitative relationship was found between the static trapezius load and the development of musculoskeletal sick-leave, related to the length of employment. Indications were found that certain factors were associated with reduced incidence of musculoskeletal illness. These were: increasing the number and total duration of trapezius load below 1% to 2% MVC (Maximum Voluntary Contraction); reducing the magnitude of flexion angle of the upper arm in the sagittal plane and distributing the work between flexors and extensors; and a more dynamic work pattern of the upper arm. The relationship between postural load and musculoskeletal injury was studied in comparable groups of female workers with respect to age, working hours per day and time of employment. Psychosocial problems, spare time activities and living habits of the workers did not show any significant differences across the groups. The results from this study indicate that: the static trapezius load must be kept at a minimum; a median arm flexion should be less than 15 degrees and a median arm abduction less than 10 degrees. These values seem roughly to approach an acceptable arm position; and a forward median flexion of the back of less than 20 degrees seems not to lead to a higher rate of low back pain for workers with long periods of employment.

Workload When Using a Mouse as an Input Device

A newly developed mouse, which seemed to give the operator a more neutral forearm position was compared with a traditional mouse. The muscle load was recorded by electromyography from the extensor digitorum communis, extensor carpi ulnaris, and trapezius muscles. The muscle load of the forearm was significantly less when using the new mouse compared with the traditional one. This was true for the extensor digitorum communis regarding the static (p = .0005) and the median (p = .001) values of the amplitude distribution function (ADF) and the number of periods per minute when the muscle load was below 1% of maximum voluntary contraction (p = .03). The same dear tendency was also found regarding the static muscle load from the extensor carpi ulnaris (p = .06). These results indicate the need for reducing the pronation of the forearm when, working with a mouse.

Work With the Visual Display Unit: Health Consequences

This article is a review of the international literature regarding health consequences for visual display unit (VDU) workers. The 2 main problems reported by VDU workers, visual discomfort and musculoskeletal pain, are particularly focused. Important factors for designing the lighting system and workplace are given. A procedure for optometric corrections is discussed. This article emphasizes the importance of multidisciplinary cooperation to reduce visual discomfort and musculoskeletal pain.

The Effect of an Ergonomic Intervention on Musculoskeletal, Psychosocial and Visual Strain of VDT Data Entry Work: The Polish Part of the International Study

A group of routine data entry operators (female) was included in the Polish MEPS (musculoskeletal—eyestrain— psychosocial—stress) study. Before the intervention, ergonomic assessment revealed improper working conditions such as inadequate lighting, uncomfortable chairs, and lack of forearm and wrist support while medical examination revealed that trapezius muscle load along with upper arm, head and back angles were higher than advisable. Subjects complained about neck and shoulder pain, visual problems, and psychosocial conditions. The ergonomic intervention included installation of new luminaires and Venetian blinds, new chairs, repair of ventilators, and optometric corrections. The results after the intervention showed mainly improvement in chair comfort, lighting conditions, visual strain, and sitting posture. However, financial limitations did not allow satisfactory completion of the intervention leading to a mixed interpretation of the results.