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PubMed1994

Effects of two types of chairs on stature change and comfort for individuals with healthy and herniated discs.

The objective of this study was to determine if stature change and perceived comfort are significantly different for individuals with either healthy or herniated discs when seated in a conventional chair or a sit-stand chair. Sixteen subjects were studied (5 young/healthy, 6 old/healthy, 5 old/herniated). Subjects performed a search task on a computer screen during two 2 h sessions for two consecutive days, with a different chair each day. Changes in stature were measured with a stadiometer. General comfort and body parts discomfort rating scales were administered every 30 min. The main findings were: (1) for all subjects, the sit-stand chair produces less height loss than the conventional chair; and (2) for both chairs, subjects with herniated discs lost more height than subjects with healthy discs. A positive correlation was observed for height loss and age with the sit-stand chair. Subjects with herniated discs felt relatively more uncomfortable in the conventional chair and more comfortable in the sit-stand chair compared to subjects with healthy discs. Both old healthy and young healthy subjects felt more comfortable in the conventional chair in comparison to the sit-stand chair. But, old healthy subjects had a relatively greater perception of comfort in the conventional chair compared with the younger subjects.

Adult↗

PubMed1994

VDT work, oculomotor strain, and subjective complaints: an experimental and clinical study.

Two studies, one experimental and one clinical, are presented. Study I examines the effect of three hours of continuous VDT work (text-editing) on a set of optometric and health-related variables in an experimental design with two matched groups, one experimental (n = 18) and one control group (n = 19). Doing the same keyboard activities for 3 h as the experimental group, the control group was looking out of a window instead of at the display while working (distance viewing). There were significant group differences in work related effects on the eyes' ciliary and extraocular muscles and on subjective symptoms, indicating that not only visual symptoms but also muscle pain in the head, neck, and upper back regions may result from near-point induced oculomotor strain. Study II shows the health effect of optical corrections on symptomatic VDT workers (n = 14). There is a significant pre-post reduction in symptoms, indicating that visual anomalies contribute to work-related symptoms. The results of both studies are discussed in a visual ecological perspective.

Adult↗

PubMed1994

Musculoskeletal problems in VDT work: a review.

This paper discusses the possible causes of musculoskeletal pain in VDT workers and outlines strategies to minimize it. The paper reviews workstation, chair, and keyboard design, and makes recommendations to improve user comfort. Also discussed is worker selection, training, posture, conditioning, and rest breaks. Short term musculoskeletal discomfort is experienced by many VDT operators in the telecommunications industry and chronic disability may result in the long term. It is important that the ergonomist and office manager work together to improve the working conditions in this important occupational area.

Back Pain↗

PubMed1995

Effects of lensed-indirect and parabolic lighting on the satisfaction, visual health, and productivity of office workers.

A pre- and post-renovation survey evaluated the reactions of office workers to two office lighting systems: a parabolic downlighting system and a ceiling suspended, lensed-indirect uplighting system. Questionnaire data on work content, perception of ambient environmental conditions (including office lighting), work-related health symptoms, job stress, job satisfaction, and self-reported productivity, and environmental data on illumination, air temperature, and relative humidity were collected. The lensed-indirect lighting system was more favourably rated on several subjective lighting impressions scales, and for computer work workers reported fewer screen glare problems, and fewer and less frequent problems with tired eyes and eye focusing. Productivity was less hindered by the lensed-indirect lighting, and satisfaction with office lighting and ratings of lighting quality were significantly higher for this system. These reactions were not associated with any differences in levels of illumination between the lighting systems. Ratings of lighting satisfaction and lighting importance were inversely related. Overall, some two-thirds of workers indicated a preference for working under the lensed-indirect lighting system.

Adult↗

PubMed1995

Wrist postures while keyboarding: effects of a negative slope keyboard system and full motion forearm supports.

Video-motion analysis was used to analyse hand/wrist posture for subjects typing at a 101-key QWERTY keyboard on a 68 cm high worksurface. Three conditions were tested: subjects typed at the keyboard without arm support, subjects typed with adjustable full motion forearm supports, and subjects typed with an adjustable negative slope keyboard support system. The average declination of the negative slope keyboard support chosen by subjects was 12 degrees below horizontal, which flattened the angle of the key tops. Ulnar deviation was comparable in all conditions and averaged 13 degrees for the right hand and 15 degrees for the left hand. Full motion forearm supports did not significantly affect any postural measures. Dorsal wrist extension averaged 13 degrees when typing with or without the full motion forearm supports, but this was reduced to an average -1 degree with the use of the negative slope keyboard support system. Subjects chose to sit at a distance of 79 cm from the computer screen when using the negative slope keyboard system compared with 69 cm without this.

Adult↗

PubMed1995

Use of visual perception in estimating static postural stresses: magnitudes and sources of errors.

Very little is known about the magnitudes and sources of errors associated with the visual estimation of postural classification displayed on TV screens. This study was conducted to address this issue. Sixty-three subjects participated in the experiments. The findings indicate that: (1) subjects found it difficult to evaluate upper extremity postures (particularly the elbow and the wrist), while the postures around the lower back were the easiest to evaluate; (2) the lower extremity positions affected the ability of the subjects to accurately classify postures around the wrist, elbow, shoulder, neck, and lower back, with the estimates being > 70% for sitting and > 60% for standing (except for the elbow); and (3) in general, flexion and extension are easier to evaluate than neutral and non-neutral postures.

Adult↗

PubMed1996

Accommodation, convergence, pupil diameter and eye blinks at a CRT display flickering near fusion limit.

This study investigates possible effects of temporally modulated light stimulation near critical fusion frequency (CFF) when subjects observe a cathode ray tube (CRT) operated at different refresh rates. Various visual functions were measured in a series of tests of 2.5 min duration. In experiment 1, at a repetition rate of 50 Hz mean pupil size was 0.055 mm smaller than at 300 Hz. The precision of convergence and accommodation in binocular vision was not affected. In experiment 2, 300 Hz was compared with the lowest frequency that did not produce visible flicker for each subject. At the lower rate (55 to 90 Hz), mean accommodation in monocular vision was 0.06 D weaker, median eye blink duration was 6% shorter, and mean eye blink interval was 15% longer. Individual differences and possible fatigue effects of intermittent light at visual display units are discussed.

Accommodation, Ocular↗

PubMed1996

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 muscle's 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 muscle's 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).

Adult↗

PubMed1996

Source document position as it affects head position and neck muscle tension.

Measurements of head position, mechanical load at C7, and level of muscle EMG activity in the muscles of the neck were compared across six document positions in both a reading task and a typing (word processing) task. Source documents, identified as a primary visual task, were placed in two positions in front of the subject, flat on the table to each side of the keyboard, and on a document stand at each side of the keyboard. Each of the 20 subjects performed both a reading task and a typing task in each of these document positions while measurements were taken. It was found that the greatest variations in head position occurred in head rotation with documents flat on the table. This document position on each side also produced the greatest level of muscle tension in both the neck extensors and, to a lesser degree, the sternocleidomastoid muscles. In addition, greater variability between document position measures was found in the typing condition.

Adult↗

PubMed1996

Attention-related muscle activity in different body regions during VDU work with minimal physical activity.

The purpose of this study was to characterize regional variation in task-irrelevant muscle activity. Surface EMG was recorded at 20 different muscle sites during a complex choice-reaction task. Up to ten muscle sites were recorded in parallel and always including the upper trapezius muscles. The experimental setting was designed to minimize the physical activity while performing a VDU-based task demanding continuing attention. Consequently, the label 'attention-related muscle activity' has been adopted. The presence of this activity varied between subjects and between the different muscle sites. It tended to decrease in a caudal direction and to be low in the muscles of the extremities, with the exception of the extensor muscles of the hand and foot. Attention-related activity was prevalent in the frontalis and upper trapezius muscles. This result is discussed with respect to a potentially harmful health effect of task-irrelevant muscle activity.

Adult↗

PubMed1996

Viewing distance variation and related ophthalmological changes in office activities with and without VDUs.

This experimental study was conducted on 14 volunteer female clerks to measure viewing distance variation and related ophthalmological changes in office activities with (session 1) and without (session 2) VDU. A video camera connected to an electronic elaborator was used to determine eye-screen distance of the VDU operators during the task. Before and after each of the two work sessions far refraction, far phorias, near point of accommodation (APP), and fusional convergence were measured. Blinking rate of each subject was measured by a transducer only during the "VDU session'. The objective measurements of the eye-screen distance, whose range was between 48.42 and 65.33 cm, allowed a precise quantification of the occupational visual load during session 1. The accommodation was about 1.5-2D on average and the fusional convergence 10-13 delta on average. The symptomatology shows a number of disturbances in session 1 (71.4%) clearly higher than in session 2 (35.7%). The study of refraction before and after the task has shown a slight excess of accommodation compared to the theoretical value in both sessions, more marked in session 1. The APP shows no statistical significative variation. A tendency to exophoria was registered at the beginning and at the end of the trial and the fusional convergence clearly decreased, especially in the first session.

Accommodation, Ocular↗

PubMed1996

Upper-arm elevation during office work.

The present aim was to measure and quantify upper-arm elevation and to find how changed work organization and work tasks influence arm movement during a working day. Sixteen female office workers participated in the study. Their main work was statistical data entry. Upper-arm elevation was measured on two occasions separated by 18 months, i.e., before and after a change of work organization. The measurements were performed during the whole of one ordinary working day. The differences between the two measurements were mostly non-significant. Arm elevation remained essentially below 30 degrees during the main time of the working day, and the subjects worked with limited arm movements. Despite new alternative office tasks, they did not achieve a change in their habitual arm postures, or in their neck-and-shoulder disorders.

Adult↗

PubMed1997

Induced pupillary hippus following near vision: increased occurrence in visual display unit workers.

Using a quasistatic method, it has been found previously that one-third of normal subjects retained pupillary constriction under empty-field conditions for a substantial period following a near-vision task. This pupil after-effect was dissociated from adaptation of tonic accommodation. In this paper, essentially the same method was used to investigate further the effects of near vision on pupil response in VDU (Visual Display Unit) workers with complaint of general fatigue and/or asthenopia. In some cases, large and slow pupillary oscillation accompanied by miosis was noted after near vision. Pupillary oscillation is a well-established phenomenon that has a broadly spread frequency spectrum with an occasional component 'hippus' at approximately 0.2 Hz. A proportion of subjects (30 out of 100) showed hippus, a consistent oscillation of 0.22 Hz (SD = 0.03 Hz) in VDU workers, while only one out of 24 normal subjects showed this. Occurrence of pupillary hippus following near vision increased in VDU workers. It was suggested that this hippus is concerned with cumulative asthenopia and/or general fatigue although the origin of hippus is still unknown.

Accommodation, Ocular↗

PubMed1997

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.

Adult↗

PubMed1998

Preferred position of visual displays relative to the eyes: a field study of visual strain and individual differences.

At office workplaces equipped with visual display units (VDU) that were adjustable to various positions relative to the eyes short and long viewing distances from the eyes to the screen were imposed (mean value of about 63 and 92 cm) at two levels of screen height so that the visual target was either at eye level or 18 cm below, on the average. The change from far to near viewing distance produced a larger increase in eyestrain when the VDUs were at eye level. High screens resulted in greater eyestrain than low screens, as shown by correlations over subjects. When operators were free to adjust the most comfortable screen position, the group of 22 participants preferred viewing distances between 60 and 100 cm and vertical inclination of gaze direction between horizontal and -16 degrees downwards. However, within most subjects the range of preferred screen positions was much smaller. Between 3 days during a 1-month period the test-retest correlations of the preferred screen positions were highly significant, both for viewing distance and vertical gaze inclination. When operators were forced to work at a shorter distance than their preferred viewing distance they reported more visual strain. Thus, operators appear to prefer an individual adjustment of the screen relative to the eyes in order to avoid visual strain and discomfort at VDU work.

Adult↗

PubMed1998

Frontal midline theta rhythm and eyeblinking activity during a VDT task and a video game: useful tools for psychophysiology in ergonomics.

The necessity of psychophysiological research in ergonomics has gradually been recognized in Japan. In this paper, frontal midline theta rhythm (Fm-theta) and eyeblinking are recommended as tools in this field, especially for assessing workers' attention concentration, mental workload, fatigue, and interest during VDT work at the workplace and playing video games at home. In experiment 1, Fm-theta and eyeblink rates were measured in 10 Japanese abacus experts (Group E) and 10 normal students (Group C) during a visual search task with VDT. Memory load affected all measures. The amount of Fm-theta appeared more in Group E than Group C, but blink rate was lower in Group E than in Group C. As abacus experts have such highly developed skills in concentration, the result indicates that the amount of Fm-theta would be a good index of attention concentration in VDT workers. The second experiment was done with 10 school-aged children as subjects during three visual tasks: video game, mental test and animation. Amounts of Fm-theta and the degree of blink inhibition were maximum while playing the video game, which all subjects reported they most preferred, and minimum while watching animation, which eight subjects reported to be most boring. An interesting task would seem to provoke Fm-theta and inhibit eyeblink activity. From these two experiments, Fm-theta and eyeblink rate would appear to be good indices of attention concentration and task pleasantness of a mental task using VDT.

Adolescent↗

PubMed1998

Research on pelvic angle variation when using a pelvic support.

A pelvic support consisting of a forward sloping wedge of foam has been tested as an addition to conventional office seating for VDT work. In experiment 1 a questionnaire investigation was carried out on the impressions of 10 male and 10 female subjects who sat using pelvic supports. A general result from the questionnaire was that the waist and pelvis were felt to be stable and the evaluation was more positive with the support than without. In experiment 2, pelvis and chest inclinations were measured during sitting with and without the pelvic support. Over a long work period, significant differences were not observed. In both cases, subjects were able to move freely and there were no significant changes in posture. In experiment 3, pelvis and chest inclinations were measured in conditions of no pelvic support and with supports of 10, 20 and 30 degrees. The experiment demonstrated that a support angle of 10 degrees was stable and comfortable. In this research, it was found that the change of inclination of the pelvis can be measured continuously using an angle of inclination sensor. Imposing a forward slope of 4 to 10 degrees on the seat pan surface using the pelvic support had a positive effect, while angles of 20 and 30 degrees had a negative effect.

Adult↗

PubMed1999

Wrist and forearm postures and motions during typing.

Awkward upper extremity postures and repetitive wrist motions have been identified by some studies as risk factors for upper extremity musculoskeletal disorders during keyboard work. However, accurate body postures and joint motions of typists typing on standardized workstations are not known. A laboratory study was conducted to continuously measure wrist and forearm postures and motions of 25 subjects while they typed for 10-15 min at a standard computer workstation adjusted to the subjects' anthropometry. Electrogoniometers continuously recorded wrist and forearm angles. Joint angular velocities and accelerations were calculated from the postural data. The results indicate that wrist and forearm postures during typing were sustained at non-neutral angles; mean wrist extension angle was 23.4 +/- 10.9 degrees on the left and 19.9 +/- 8.6 degrees on the right. Mean ulnar deviation was 14.7 +/- 10.1 degrees on the left and 18.6 +/- 5.8 degrees on the right. More than 73% of subjects typed with the left or right wrist in greater than 15 degrees extension and more than 20% typed with the left or right wrist in greater than 20 degrees ulnar deviation. Joint angles and motions while typing on an adjusted computer workstation were not predictable based on anthropometry or typing speed and varied widely between subjects. Wrist motions are rapid and are similar in magnitude to wrist motions of industrial workers performing jobs having a high risk for developing cumulative trauma disorders. The magnitude of the dynamic components suggests that wrist joint motions may need to be evaluated as a risk factor for musculoskeletal disorders during typing.

Adult↗