Ergonomic studies in computer-aided design

This paper describes the results of an ergonomic survey on interactive graphics workstations for computer-aided design (CAD). A work-sampling study was carried out to characterize the use of keyboard, digitizer tablet and video display. Subjective impressions of CAD software, CAD hardware and health aspects were collected by means of a questionnaire. Working methods and working postures were recorded on videotape. The two most important differences in comparison with other office terminals are: (i) dynamic working methods result in an absence of constrained postures in CAD operators and allow full-body exercise; (ii) CAD operators spend more time (46-68 per cent of working hours) viewing the video display than the average office terminal operator. Some ergonomic recommendations have been deduced for the construction of CAD terminals, as well as for the ergonomic improvement of existing workstations.     

Ergonomic analysis of musculoskeletal discomforts among conversational VDT operators

VDT tasks are rapidly increasing as the office automation prevails. Despite its numerous benefits, occupational hazards such as visual fatigue, eye strain, radiation and musculoskeletal stresses have emerged as an important issue. This study was designed to investigate the effects of work postures and anthropometric differences upon the musculoskeletal stresses experience by operators involved in conversational VDT tasks. Evaluation of the level of muscoloskeletal discomfort was performed for 297 VDT operators from three divisions of telecommunication company in Korea. The ergonomic variables of the VDT tasks and the operators' anthropometric variables were evaluated for 70 out of the 297 VDT operators. Factor analysis is used for identifying underlying pattern of discomfort and multiple regression analysis were performed to examine the relationship between the measured ergonomic variables and the musculoskeletal discomfort. This study indicates that the ergonomic variables have influences on the musculoskeletal discomfort. It is important to provide the workers with fully adjustable workstations so that they can maintain their work postures most suitable for the sustained VDT work. Furthermore, in order to achieve the best working conditions, VDT operators should be given a proper training for the adjustment of their workstations.     

Behavioural data in the design of ergonomic computer terminals and workstations—a case study

Abstract

Manufacturers of office automation equipment, in their design of ergonomic computer terminals and office furniture, are encountering needed design data which is sometimes weak, absent, erroneous or inapplicable to the office-worker situation under consideration. In some instances, office automation manufacturers simply follow standards. In others, manufacturers make assumptions as to the best design, and in others, design decisions were based on testing results and conclusions.This paper reviews the ergonomic tools and features incorporated into the design of one office automation manufacturer's terminals and workstations. The short fall of applicable design data relevant to comfort versus extremes of motion in biomechanics, to keyboard home row height and slope angle to viewing distance, as well as to reverse video and surface colour are presented, along with the design resolution of these parameters. Further, certain aspects of posture recently published are discussed.     

Ergonomics study and analysis of workstations in Tunisian mechanical manufacturing

The workers’ performance in the mechanical manufacturing sector is the main factor for the improvement of productivity and quality. At present, it seems that the available information on the ergonomics and the working environment of the mechanical manufacturing actors is scarce. This study deals with the relationship between the working method and the workstation in injection mold manufacturing. An original methodology, based on the survey of operators using participatory ergonomic tools, is proposed in order to evaluate the ergonomic performance of 3 workstations: milling, turning, and drilling. The surveys concerned 3 operators. Obtained results showed that ergonomics play a key role in improving mechanical manufacturing. The results obtained from the analysis showed that ergonomics has a key role in the quality of the various tasks performed by operators. Using the Rapid Entire Body Assessment (RULA) and Rapid Entire Body Assessment (REBA) investigation tools, the examination of the workstations revealed 4 machining operations and 12 operator postures that have a direct influence on the performance of all machining stations. In addition, data from the analysis conducted on injection mold manufacturing revealed that neither the workstations were ergonomic nor the operators complied with the ergonomic rules. Based on the results obtained, a new standardized score is proposed for the RULA and REBA calculations. This score was applied and validated through another study conducted in a leaf spring manufacturing plant. The results of these studies were concretized by proposing the digital factory where CATIA software was used for the virtual design of the ergonomic workstations and their environments.     

Visually deficient working conditions and reduced work performance in office workers: Is it mediated by visual discomfort?

IntroductionThe main purpose of this cross-sectional study was to investigate whether visual discomfort acts as a mediating factor between perceived visual ergonomic working conditions and self-rated visual performance among office workers who carry out administrative tasks and computer-based work at the Swedish Tax Agency.MethodsA questionnaire was sent to 94 office workers addressing: 1) perceived visual quality of the visual display units; 2) prevalence of eye symptoms; and 3) self-rated visual performance. Eighty-six persons (54 women (63%), 31 men (36%), and 1 of unspecified sex) answered the questionnaire. Multiple regression analysis investigated the association between visual ergonomic working conditions and visual performance, both with and without visual discomfort as a mediator.ResultsThe group mean of the Indexed survey questions indicated a reasonably good quality of visual ergonomic working conditions, a relative absence of eye symptoms, and acceptable self-rated visual performance. Results from multiple regression analysis showed a significant association between perceived visual ergonomic working conditions and self-rated visual performance (r² = 0.30, β = 0.327, p < 0.01). When visual discomfort was used as a mediator, the association between perceived visual ergonomic working conditions and self-rated visual performance remained the same (r² = 0.32, β = 0.315, p < 0.01).DiscussionIt was remarkable to discover that self-rated visual performance was independent of visual discomfort. Possible explanations include exposure factors not included in the current study, such as dry air and sensory irritation in the eyes, psychosocial stress, time spent performing near work activities, or time exposed to visually deficient working conditions.Relevance to industryThe strong connection between satisfaction with visual ergonomic working conditions and productivity in this study has implications for workplace profitability and staff satisfaction. If productivity is enhanced by better visual ergonomic working conditions, then managers of workplaces may be able to improve work outcomes by optimizing the physical work environment.     

Risk assessments of work-related musculoskeletal disorders among the TFT-LCD manufacturing operators

The thin film transistor liquid crystal display (TFT-LCD) industry is one of the major industries in Taiwan, yet few studies addressed its work-related musculoskeletal disorders (WMSDs). Thus, this study aims to evaluate the risk of WMSDs among the operators of a TFT-LCD manufacturing company in Taiwan by using the subjective questionnaire and ergonomic assessment tools. First, the NMQ survey was conducted among 393 operators, accounting for 94% of all operators in the TFT-LCD plant. The results showed that the prevalence of WMSDs was 31.8%. Among the various body parts, the highest prevalence of WMSDs was found in neck and shoulders (20.4%), while upper limbs were with the lowest prevalence (9.2%). Besides, the prevalence of WMSDs tends to be affected by both work factors and operator factors. Those who were more experienced, working in day shift and involved in the Array process tend to have a higher prevalence of WMSDs. Further, female and domestic operators reported a higher prevalence of WMSDs than male and foreign operators. Moreover, the jobs of 50 employees were analyzed using ergonomic assessment tools including OSHA MSDs, BRIEF, OWAS, 3D SSPP, and NIOSH lifting equation. The findings indicated that inadequate working height, restricted working space, awkward postures, overweight load, and high repetition were the major risk factors of WMSDs. Thus, countermeasures such as redesigning the workstations and material handling carts, proactive training of manual material handling, and providing safety clearance are recommended to enhance the occupational health and safety of the TFT-LCD operators.     

A Study of Computerized Offices in Greece: Are Ergonomic Design Requirements Met?

In this study, an investigation was conducted into the extent to which ergonomic requirements for work on computers are met in Greek office workstations. The ergonomic requirements considered were those included in Council Directive 90/270/EEC (1990) of the European Union and the ISO 9241 (1997) standard. 593 office workstations were assessed using an assessment tool consisting of 70 assessment points. The assessment results show that the ergonomic requirements that are independent of the specific characteristics of individual work spaces and environments (e.g., design standards for seats, monitors, and input devices) are adequately met. Ergonomic requirements that should take into consideration the specific characteristics and constraints of individual work content, work spaces, and environments (e.g., requirements dealing with workplace layout, environmental conditions, software, and work organization) are inadequately met. Based on these results, issues are indicated on the effort ergonomists should focus to improve working conditions in computerized offices.     

Ergonomic assessment of office worker postures using 3D automated joint angle assessment

Sedentary activity and static postures are associated with work-related musculoskeletal disorders (WMSDs) and worker discomfort. Ergonomic evaluation for office workers is commonly performed by experts using tools such as the Rapid Upper Limb Assessment (RULA), but there is limited evidence suggesting sustained compliance with expert’s recommendations. Assessing postural shifts across a day and identifying poor postures would benefit from automation by means of real-time, continuous feedback. Automated postural assessment methods exist; however, they are usually based on ideal conditions that may restrict users’ postures, clothing, and hair styles, or may require unobstructed views of the participants. Using a Microsoft Kinect camera and open-source computer vision algorithms, we propose an automated ergonomic assessment algorithm to monitor office worker postures, the 3D Automated Joint Angle Assessment, 3D-AJA. The validity of the 3D-AJA was tested by comparing algorithm-calculated joint angles to the angles obtained from manual goniometry and the Kinect Software Development Kit (SDK) for 20 participants in an office space. The results of the assessment show that the 3D-AJA has mean absolute errors ranging from 5.6° ± 5.1° to 8.5° ± 8.1° for shoulder flexion, shoulder abduction, and elbow flexion relative to joint angle measurements from goniometry. Additionally, the 3D-AJA showed relatively good performance on the classification of RULA score A using a Random Forest model (micro averages F1-score = 0.759, G-mean = 0.811), even at high levels of occlusion on the subjects’ lower limbs. The results of the study provide a basis for the development of a full-body ergonomic assessment for office workers, which can support personalized behavior change and help office workers to adjust their postures, thus reducing their risks of WMSDs.     

Effect of sampling interval on the reliability of ergonomic analysis using the Ovako working posture analysing system (OWAS)

In industry, the Ovako working posture analysing system (OWAS) is applied using different sampling intervals. However, it has not yet been established what influence the sampling interval has on the reliability of the data collection. For this purpose, the sampling interval of an existing ergonomic analysis of working postures using OWAS with 20,601 observations was varied between 2 and 90 s to investigate the effects of deviation from the original sampling interval of 1 s. Based on these comprehensive industrial data, which was statistically analyzed with regression analyses, it can be concluded that in the ergonomic analysis of working postures using OWAS, direct observations should have a sampling interval of 20 s, and video-based observations should have a sampling interval of 10 s or less.Relevance to industryThe Ovako working posture analysing system (OWAS) is a practical and frequently selected method for the ergonomic analysis and evaluation of working postures. However, the selection of a suitable method is as least as important as the definition of a sampling strategy providing reliable values obtained through observation. For this reason we investigated the effect of the sampling interval and recommend using 20 s for direct observations and 10 s or less for video-based observations.     

Working conditions of Iranian hand-sewn shoe workers and associations with musculoskeletal symptoms

The working conditions and the prevalence of self-reported musculoskeletal symptoms among 180 Iranian hand-sewn shoe workers were evaluated in this cross-sectional study. Data were collected using both questionnaire (for assessing musculoskeletal symptoms and associated risk factors) and direct observations of posture (by the Rapid Upper Limb Assessment [RULA] method). The prevalence and severity of symptoms was very high among the study population. The mean RULA grand score of 6.2 indicates that in most cases the workers' postures at their workstations need to be investigated and some changes are required immediately. Multiple logistic regression models indicated that the job experience, daily working hours, duration of continuous work without breaks, feeling pressure due to work and working postures were significantly associated with musculoskeletal symptoms of different body regions. The results are discussed in terms of their implications for hand-sewing tasks. These findings can help to better understand the working conditions of those jobs involving hand-sewing operation and highlight the potential for ergonomic interventions to reduce musculoskeletal symptoms among these working groups.

Practitioner Summary: Working conditions of hand-sewn shoe workers and their musculoskeletal symptoms were investigated. The prevalence and severity of musculoskeletal symptoms was very high among the study population. Poor working postures, feeling pressure due to work, long duration of work without breaks and prolonged daily working hours were positively associated with musculoskeletal symptoms.     

Activity in neck-shoulder and lower arm muscles during computer and smartphone work

Relevance to industryThere is emerging evidence of musculoskeletal problems related to smartphone work and a rapid transition to mobile workplaces, where smartphones are key working tools. Aim: The study's aim was to compare muscle activity during computer work with smartphone work and to see what possible effects ergonomic recommendations for smartphone usage have on muscle activity.MethodsActivity was measured bilaterally from the upper trapezius muscle and from lower arm muscles on the right hand side, on twelve participants with surface electromyography who performed e-mail work on the computer using ergonomic recommendations, smartphone in a self-chosen way of working and on smartphone with ergonomic recommendations. Effects on productivity was not assessed in this study.ResultsActivity in m. trapezius and m. extensor digitorum was significantly higher during computer work (p < 0.05) than during the two smartphone usages and activity in m. interossei dorsalis 1 was, vice versa, significantly higher during smartphone work (p < 0.05). Comparison of smartphone in self-chosen way of working and smartphone with ergonomic recommendations showed no significant differences.ConclusionsPrevious research has highlighted the benefits of variation of work postures. This paper indicates that replacing the computer with a smartphone gives the trapezius muscle an opportunity to rest.     

Perception and visualization of human posture information for computer-aided ergonomic analysis

This article reports three experiments that examined the effects of photographic method, computerized visualization scheme, and posture complexity on posture perception and specification for computer-aided ergonomic analysis. The subjects were presented with photographs of working postures, and were required to manipulate human forms generated by an ergonomics software program to match the postures in the photographs. The first experiment showed a clear advantage of using a three-dimensional (3-D) human form graphic with two photographs when complex, asymmetric postures were analysed. However, the use of a 3-D human graphic display and two photographs jeopardized the subjects' posture specification performance when simple, symmetric postures were analysed. The results of the second and the third experiment demonstrated the importance of achieving congruency between photographic and computer display perspectives in improving posture specification performance. Implications for ergonomic job analysis and ergonomics software design are discussed.     

The feasibility of repositioning ability as a tool for ergonomic evaluation: effects of chair back inclination and fatigue on head repositioning

Poor posture has been suggested as one of the main factors contributing to the high prevalence of neck pain in video display unit (VDU) users, but no clear association between pain and any particular resting neck posture has been found. Postural awareness of the neck, as indicated by the repositioning accuracy, may therefore be an appropriate measure and potentially useful assessment tool. The objective of this study is to examine whether posture and fatigue affect the head repositioning ability in typical VDU usage.

A group of 20 healthy participants reproduced a normal comfortable posture for forward, upright and backward chair back inclinations in random order both before and after fatigue of the upper trapezius muscles. Ten repetitions of the posture were recorded for 2 s each, and the angular and translational deviations from the original head position were measured with regard to the external environment (head in space repositioning) and with regard to the trunk (head on trunk repositioning). Analysis by repeated measures ANOVA showed significant effects and interactions of fatigue and chair back inclination on the repositioning errors in the sagittal plane, which typically showed systematic trends towards certain postures rather than random errors around a mean position.

While further work is required to examine the ergonomic impact of impaired repositioning ability, head repositioning is sensitive to ergonomic factors such as seating configuration and fatigue, and may therefore be a useful tool for evaluation of static working postures.     

Evaluation of ergonomic working conditions among standing sewing machine operators in Sri Lanka

BackgroundStanding Sewing Machine Operators (SSMOs) are engaged in highly repetitive operations, and work while standing during their entire working hours. This leads to discomforts and Musculoskeletal Disorders (MSDs). However, there is a dearth of research in SSMOs’ working conditions.Objective: Aim of the study is to evaluate the prevalence of MSDs and related ergonomic risk factors among SSMOs in the Sri Lankan textile industry.Methods: The sample included 552 female sewing machine operators. Data were collected through self-reported questionnaires which included demographic, job-related factors and Cornell Musculoskeletal Discomfort Questionnaire [CMDQ], along with the application of validated ergonomic tools (Rapid Entire Body Assessment [REBA] and Strain Index [SI]) to assess the ergonomic risks amongst them. The inter-rater reliability test ensured the reliability among observers. An individual regression model was developed for each body parts to assess the associated risk factors.Results: The highest occurrence of musculoskeletal symptoms were in knee, foot, thigh, lower leg and lower back of SSMOs. REBA grand score (4–11) indicated that workers’ postures were at medium, high and very high risk levels necessitating evaluation to change. Moreover, SI indicated medium and high risk of upper extremity disorders. Finally, regression models revealed associated risk factors with musculoskeletal symptoms among various body parts including age, Body Mass Index (BMI), marital status, SSMO experience, job satisfaction, job stress, daily walking distance to the boarding place/factory, interest in job rotation and satisfaction with the design of sewing machine.Conclusion: The findings highlighted that the prevalence of discomfort and MSDs in the lower limbs were higher than in the upper limbs among SSMOs. The findings revealed the working conditions of SSMO and emphasised the need for ergonomic interventions to minimise the MSDs among them.Relevance to industryThe findings highlighted ergonomic risks among SSMOs and associated risk factors which will help managers and researchers better understand the working conditions of SSMOs. The identified risk factors could be considered during the implementation of standing sewing operation layouts and during the selection and allocation of new employees.     

Effects of positioning optimization in an alternative computer workstation for people with and without low back pain

The aim of this study was to measure the impact of positioning optimization on typing performance and user comfort for people with and without low back pain (LBP) in alternative working postures. Participants completed a series of typing tests in each of five randomly ordered alternative working postures ranging from upright to fully supine. Typing accuracy and typing speed were recorded as were subjective measures of overall comfort and body part discomfort. The impact of positioning optimization of the monitor, keyboard, and arm supports was determined by comparing results from an “Optimized” test study protocol (n = 27) with those from a “Non-Optimized” test study protocol (n = 26). The results indicate a significant improvement in user comfort with the optimized positioning, but no significant differences in typing performance between the two test protocols. However, in both tests the slowest typing speeds occurred in the fully reclined and zero gravity working postures. Results of the user comfort scores indicated that for the Non-Optimized test, all alternative working postures were less comfortable than the upright posture. Whereas, in the Optimized test the tilted and reclined postures were comparable to the upright working posture and only the zero gravity posture was viewed as less comfortable.

Relevance to industry

Understanding the importance of position optimization for VDT operators in alternative working postures will provide valuable information toward the development of more comfortable and more accommodating computer workstations.     

Kinematics differences between obese and non-obese workers during vertical handling tasks

Obesity is highly prevalent in the workforce but little is known about its effects on musculoskeletal disorders risk factors, such as the posture adopted during work activity. Vertical Handling Tasks (VHT), including manual lifting and lowering loads, are quite frequent in industrial settings and are considered to be a major cause of Work-Related Musculoskeletal Disorders (WMSD). Therefore, the main objective of this study is to compare and analyse the strategies and postures adopted during VHT between obese and non-obese subjects. A kinematics study with the VICON® system was conducted within a convenience sample of 8 non-obese (4 women and 4 men) and 8 obese (4 women and 4 men) volunteers participants. Different occupational conditions were tested over 8 trials of VHT. When developing VHT, the obese group presents kinematics significant differences (p < 0.05), compared with non-obese, namely: a decrease in the duration of the tasks, an increase in the horizontal distance between the load and the body worker, and an increase of the trunk sagittal flexion. This study demonstrates that obese individuals are exposed to a higher level of WMSD risk, during VHT performance.Relevance to industryThe findings are relevant to ergonomic workstations/job design for obese workers. This study defends that obesity can be a WMSD risk factor during VHT frequently found in industry, pointing to the need of companies to include this factor during ergonomic interventions on workstations and to adopt obesity prevention measures.     

Postures and the design of VDT workstations

With the introduction of VDTs many office employees became part of a man-machine system with close physical binding to the workstation. Constrained postures associated with muscle fatigue and sometimes with impairments involving joints or tendons can occur.

Field studies revealed a certain incidence of physical discomfort in the neck-shoulder-arm-hand area. These troubles may also occur in other strenuous office jobs. An increased incidence of physical discomfort'and medical findings is observed when keyboard levels are too low, when forearm and wrists cannot rest on an adequate support and when the design of the keyboard itself is too high.

A study of preferred settings and postures at adjustable VDT workstations under practical conditions revealed the need for relatively wide ranges of adjustable dimensions. The operators prefer postures similar to those of car drivers: they lean backwards with upper arms kept higher than expected and slightly opened elbow angles. Recommendations are drawn from these studies for the proper design of VDT workstations concerning the ranges of adjustability, the leg room and the chair.     

Effectiveness of the C-Sharp: reducing ergonomics problems at VDTs

The use of visual display terminals (VDTs) has been associated with complaints of visual fatigue and body discomfort. In an effort to eliminate some of these problems, an ergonomic emphasis has been placed on the design of computer workstations. A new device, the C-Sharp, has been developed to help reduce some of the ergonomics problems related to long-term VDT usage. The C-Sharp was designed to alleviate visual strain and temporary myopia by reducing the amount of muscular work associated with accommodation and convergence to near targets. It was also designed to eliminate glare. The present study is an ergonomics evaluation to determine whether the C-Sharp meets accepted standards and guidelines. Specifically, the objectives of the research are to determine the effects of the C-Sharp on operator reading and search performance, perceived comfort, body posture, and visual acuity. The C-Sharp is compared with mesh-glare filter and no-glare filter device conditions. Subjects were blocked into three groups based on age and type of vision correction (with or without bifocals). Results indicate that the C-Sharp meets the recommendations of the Americal National Standard for human factors engineering of visual display terminal workstations. No differences in objective performance were found between the three glare device conditions. The C-Sharp allowed bifocal wearers to keep their necks in natural postures rather than tilted backwards. Post-session far visual acuity worsened regardless of the device condition.     

Effect of alternating postures on cognitive performance for healthy people performing sedentary work

Prolonged sitting is a risk factor for several diseases and the prevalence of worksite-based interventions such as sit-to-stand workstations is increasing. Although their impact on sedentary behaviour has been regularly investigated, the effect of working in alternating body postures on cognitive performance is unclear. To address this uncertainty, 45 students participated in a two-arm, randomised controlled cross-over trial under laboratory conditions. Subjects executed validated cognitive tests (working speed, reaction time, concentration performance) either in sitting or alternating working postures on two separate days (ClinicalTrials.gov Identifier: NCT02863731). MANOVA results showed no significant difference in cognitive performance between trials executed in alternating, standing or sitting postures. Perceived workload did not differ between sitting and alternating days. Repeated measures ANOVA revealed significant learning effects regarding concentration performance and working speed for both days. These results suggest that working posture did not affect cognitive performance in the short term.

Practitioner Summary: Prior reports indicated health-related benefits based on alternated (sit/stand) body postures. Nevertheless, their effect on cognitive performance is unknown. This randomised controlled trial showed that working in alternating body postures did not influence reaction time, concentration performance, working speed or workload perception in the short term.