Developing a framework for assessing muscle effort and postures during computer work in the field: the effect of computer activities on neck/shoulder muscle effort and postures

The present study, a part of the PROOF (PRedicting Occupational biomechanics in OFfice workers) study, aimed to determine whether trapezius muscle effort was different across computer activities in a field study of computer workers, and also investigated whether head and shoulder postures were different across computer activities. One hundred twenty participants were measured continuously for two hours each while performing their own computer work. Keyboard activities were associated with the highest intensity of left and right trapezius muscle efforts, and mouse activities were associated with the smallest variability in left and right trapezius muscle efforts. Corresponding trends in head and shoulder postures included that the greatest head flexion and left and right shoulder internal rotation was observed during keyboard activities, and that the smallest variability in head flexion, head lateral tilt, and right shoulder internal rotation was observed during mouse activities. Identifying which muscle efforts and postures are different across computer activities is the first essential step for developing prediction rules for muscle efforts and postures, which can be used to link muscle efforts and postures to musculoskeletal symptoms in epidemiological studies.     

Postural assessment of school children: an input for the design of furniture

During the last decades of the previous century, school desks with a tilt top have disappeared. The chairs have been designed for sitting upright, with the hip, knees and ankles all at right angles. However, the erect posture cannot be maintained for more than one or two minutes, after which it will result in fatigue, discomfort or poor posture. The main aim of project is to identify the type of furniture that most effectively contribute to adequate neck and back postures of the school children, by carrying out a postural analysis of a sample of school pupils when using three different types of furniture. The postures adopted by school pupils were monitored by video during several activities, such as reading, writing and painting tasks, copying from a blackboard and listening the teacher. Additionally, the characteristics of the adopted postures were assessed by registering the head tilt, flexion of the neck, trunk and hips position. All these aspects were classified and the results were recorded for future analysis. The obtained results seem to point out that the use of a school desk with a tilted table surface resulted in a reduction in trunk and neck flexion, preserving the natural lordosis in the lumbar and cervical regions. Accordingly, it can be concluded that there are alternatives to consider in the furniture design in order to eliminate tensions and, consequently, to improve children's wellbeing.     

Long-term effects of forearm support: computer users working at conventional desks

Recent research has demonstrated that forearm support might be preferable to working in the traditional "floating" posture for computer users. A previous field study in a call centre reported a significant decrease in discomfort following 12 weeks of using a conventional desk for forearm support. The aim of this follow up study was to determine the long-term effect (21 months post intervention) of forearm support on reported musculoskeletal discomfort in the previous sample of intensive computer users. METHODS: The follow-up sample consisted of 33 females and 2 males (59% of original group). Data were collected via self-report questionnaires and workstation assessments. RESULTS: Despite a significant reduction in discomfort for most body regions following the initial intervention, the only significant decrease in discomfort over 21 months was for the neck. Reported discomfort for all other body regions had decreased, apart from the shoulder in which there was a reported increase in discomfort. The results of this follow up study indicate that forearm support has a positive effect on the reduction of neck discomfort. The increase in shoulder discomfort indicates that a concave desk may be preferable to the conventional desk if the forearm support posture is to be adopted.     

Notebook computer use with different monitor tilt angle: effects on posture, muscle activity and discomfort of neck pain users

This study aimed to evaluate the posture, muscle activities, and self reported discomforts of neck pain notebook computer users on three monitor tilt conditions: 100°, 115°, and 130°. Six subjects were recruited in this study to completed typing tasks. Results showed subjects have a trend to show the forward head posture in the condition that monitor was set at 100°, and the significant less neck and shoulder discomfort were noted in the condition that monitor was set at 130°. These result suggested neck pain notebook user to set their monitor tilt angle at 130°.     

The gap between exposure and implementation of computer workstation ergonomics in the workplace

The population of people using computers is increasing in home, school and work environments [20,21]. Research suggests that more computer usage may lead to increased incidence of upper extremity cumulative trauma disorder (UECTD) and other work related musculoskeletal injuries [8]. Yet, proper computer workstation ergonomics training is not readily available. This pilot study attempts to better understand the gap between ergonomic interventions and the initiation of work-practice change. The pilot study used self-report through an anonymous Internet survey to explore university faculty and staff training in computer workstation ergonomics, assess UECTD and other computer-use related symptoms, and learn about the respondents' success implementing their knowledge of computer workstation ergonomics. The 55 respondents ranged in age from 21 to 65, and spent an average of 5.3 hours at the computer during a typical workday. Over 70% of respondents experienced symptoms associated with excessive computer use. Although 60% of respondents had exposure to computer workstation ergonomics information, less than 10% reported implementing their knowledge of computer workstation ergonomics in their tasks. This paper looks at organizational and individual issues preventing the implementation of computer workstation ergonomics in the workplace. The Transtheoretical Model for Health Behavior Change [25,27] is used to further evaluate effectiveness of ergonomic interventions. Recommendations for interventions and future evaluations are presented.     

The effect of Video Display Terminal (VDT) mouse use on muscle contractions in the neck and forearm

This study used surface electromyography (EMG) to examine the percent of maximum voluntary contraction (%MVC) of the upper trapezius, the flexors of the wrist/fingers and extensors of the wrist/fingers during Video Display Terminal (VDT) mouse use with the mouse positioned either next to the computer or on a lapdesk. Thirty participants, between the ages of 18 and 40, used a VDT mouse to follow a prescribed pattern for three trials at each location. Although there was a trend towards the lapdesk location producing lower %MVC than the computer location for the trapezius and wrist/finger flexors (lapdesk: trapezius M 4.71%, wrist/finger flexors M 3.53%; computer: trapezius M 5.74%, wrist/finger flexors M 3.94%) a two way ANOVA controlling for sequence and order found no significant difference between the means. There was no trend for the effects of location for the wrist/finger extensors. These results suggest that changing the position of the mouse may not significantly reduce muscle contractions.     

Ergonomics evaluation of a government office building

An ergonomics team from the US Army Center for Health Promotion and Preventive medicine evaluated 465 video display terminal (VDT) workstations in a Government office building over an 18-day period. Each workstation evaluation involved an assessment of the worker, the chair, the desk, the keyboard, the pointing device, the monitor, and the office environmental conditions. The team also collected worker pain and injury information. The problems seen during the evaluation were characteristic of most office environments where VDT workstation furniture was purchased before the advent of mouse-driven software. The majority of furniture evaluated was not designed to meet the demands of intensive mouse use for prolonged periods of time. Much of the workstation furniture was not adjustable, chairs lacked adequate back support, and workers assumed non-neutral postures. As a result, more than 35% of the workers evaluated complained of on-the-job pain. New office furniture that is adjustable, adequate desk space and storage space were among the solutions recommended by the ergonomics team.     

Ergonomic evaluation in a values transportation company in Venezuela

The objective was to analyze the work activity and identify risk factors that could account for musculoskeletal disorders in the upper extremities, shoulder and neck of workers of a transport values company in Venezuela. The methods used were: collective interview, tasks observation, evaluation of posture with RULA method and evaluation of repetitive motions with the OCRA method. Five workstations were evaluated. Main problem perceived by workers was: exposure to chemical and biological hazards when handling paper money and coins; inadequate chairs and close supervision. The postures level risk was 1 or 2 for the RULA scale. Only two workstations showed ligth and medium risk level by OCRA method. Conclusion: The factors identified that could explain the musculoskeletal changes were: wrist repetitive flexion and extension, shoulder elevation, lifting weight above shoulder height, elbow repetitive flexion and extension, neck flexion, extended work journey, work overload, high responsibility and strict supervision by a video camera.     

Effects of a ball-backrest chair on the muscles associated with upper crossed syndrome when working at a VDT

This study examined the effect of a ball-backrest chair on the weakness and tightness of muscles associated with upper crossed syndrome when working at a visual display terminal (VDT). The surface electromyography (EMG) was recorded from the serratus anterior, middle trapezius, and upper trapezius muscles of 20 adults as they performed VDT work, which are known as the weakened and tightened muscles of upper crossed syndrome. The recorded signals were averaged and normalized to the mean amplitude of the EMG signal obtained during submaximal reference voluntary contractions. The significance of differences between the use of a general-purpose backrest and a ball backrest was tested by paired t-test, with the significance cutoff set at alpha=0.05. The activities of the serratus anterior and middle trapezius muscles increased and that of the upper trapezius muscle decreased when sitting in a ball-backrest chair compared to when sitting in a chair with a general-purpose backrest (p<0.05). These results indicate that the use of a ball-backrest chair reduces the risk of patients with upper crossed syndrome developing muscles soreness or injury related to overuse when working at a VDT.     

Furniture dimensions and postural overload for schoolchildren's head, upper back and upper limbs

The aim of this study was to evaluate how the fixed furniture dimensions match with students' anthropometry and to describe head, upper back and upper limbs postures and movements. Evaluation was performed in 48 students from a Brazilian state school. Furniture dimensions were measured with metric tape, movements and postures by inclinometers (Logger Tecknologi, ?karp, Sweden). Seat height was high for 21% and low for 36% of the students; seat length was short for 45% and long for 9% and table height was high for 53% and low for 28%. Regression analysis showed that seat/popliteal height quotient is explained by 90th percentile of upper back inclination (β=0.410) and 90th percentile of right upper arm elevation (β=-0.293). For seat/thigh length quotient the significant variables were 90th percentile of upper back velocity (β=-0.282) and 90th percentile of right upper arm elevation (β=0.410). This study showed a relationship between furniture mismatch and postural overload. When the seat height is low students increase upper back left inclination and right upper arm elevation; when the seat is short students decrease the upper back flexion velocity and increase right upper arm elevation.     

The effectiveness of a home-based ergonomics intervention on the proper use of computers by middle school children

A study was conducted in the homes of middle school children (average age = 12.7 years, SD = 0.52 years) to determine if an educational intervention would increase both the children's and their parents' knowledge of ergonomically correct setup of a computer workstation and computer use. Six children and their parents (n = 6) participated in this study. The study consisted of two data collection sessions over a two-week period. Results suggest a significant (p < 0.05) increase in knowledge of computer use and workstation setup for both parents and children, however, no significant changes in posture were noted between sessions. It was concluded that education is an effective method to increase knowledge of ergonomics in both middle school children and their parents but more research is indicated to understand the linkage between ergonomic understanding and durable accomodations.     

Long periods with uninterrupted muscle activity related to neck and shoulder pain

The aim was to analyze the relationship between periods with uninterrupted neck muscle activity for ≥ 4 min and neck and shoulder pain. The trapezius muscle activity was recorded bilaterally on 40 young workers and students during a full shift. Neck and shoulder pain, mechanical work load and decision control were reported at the same time as the muscle activity recording and 6 months later. A dose-response relationship was found between uninterrupted muscle activity and neck and shoulder pain, with a ten-fold higher risk for the group with more than half, compared to less than a third, of the shift with uninterrupted muscle activity. Self-reported mechanical work load showed a small but protective effect related to pain. Gender and decision control did not emerge as important risk factors in this model. In conclusion, this study indicates that work or other exposures that contains long periods with uninterrupted neck muscle activity of 4 min duration or longer should be minimized to reduce risk of neck and shoulder pain.     

Co-variation in time between near-far accommodation of the lens and trapezius muscle activity

Visual strain and discomfort may contribute to the generation of work-related musculoskeletal disorders among e.g. computer workers. A positive correlation on a group level between eye-lens accommodation and trapezius muscle activity has been reported. In this study we investigated the possibility of a direct, fast, connection between lens accommodation and trapezius muscles activity. The subjects focused alternately on Near and Far targets, with a mean switch time of 5 s, through four different lenses. The cross-correlation, R(tau) was computed, between the time signals of accommodation and electromyography (EMG) from 23 subjects. In the overall mean R(tau) of 736 curves, a small but significant correlation peak (0.019) with a delay (of the EMG signal) of about 0.3 s, revealed a small common component in the two signals. Among the lenses, the positive lens (3.5 D), showed the highest correlation peak (0.040). The correlation may be caused by a direct "hard-wired" connection between the ciliary and trapezius muscles. But it could also be caused indirectly by the subject's need for a more stable head in a more demanding visual task. The latter is supported by the result that the correlation was the highest in the positive lens condition. The present correlation is however weak and it has probably a low practical importance.     

Fundamental study on relationship between human injury probability due to fall and the fall height

Many fatal accidents due to falling from height have happen at construction sites in Japan. The purpose of this study is about to seek new prevention methods of fatal accidents due to falling. For the first step, this study was carried out to find out "cause of death" in labor accidents by using past statistics data and was analyzed it. For the second, Butt dropping tests were carried out to measure impact load and acceleration of human head and neck by using simplified human model. After that, relationship between the human injury probability and the fall height was discussed by comparing with experimental results and some impact tolerance values for human. From the results of this study, impact force might be able to head trauma involved not only skull fracture but also cervical spinal cord injury. These results suggest needs to explore new protection equipment for head and cervical injuries prevention.     

Level of self-reported neck/shoulder pain and biomechanical workload in cleaners

The aim of the present study was to investigate the relation between self-reported pain, muscular activity and postural load during cleaning tasks. Eighteen cleaners performed usual cleaning tasks in both a laboratory and a lecture room. The level of perceived pain in the neck-shoulder region during the last 7 days was recorded. Bipolar surface electromyography (SEMG) was recorded bilaterally from upper trapezius and erector spinae muscles during cleaning. Root mean square (RMS) and permutation entropy (PE) values representing amplitude and complexity of SEMG time-series were estimated. A tri-axial accelerometer package was mounted on the low back (L5-S1) to measure postural changes during cleaning tasks. The 10th, 50th and 90th percentiles of the angular distributions were computed to characterize postures and movements. Pain tended to play a significant role on RMS of left/right trapezius and left erector spinae muscles (P≤0.08). Cleaners with low pain level exhibited higher muscular activity during cleaning. Pain played or tended to play a significant role on PE of left and right erector spinae muscles (P≤0.08). Pain played a significant role on the 10th, 50th and 90th percentile (P<0.05) of lateral flexion angle (side bending). The present study emphasizes biomechanical adaptations occurring in presence of neck-shoulder pain during cleaning tasks.     

Kinematic analysis of post office employees' workstations

This study analyzed a post office clerk's tasks, comparing two workstation models. The clerk was facing the client in one, and seated at 45 degrees to the counter in the other. We analyzed the most frequent tasks and those presenting the most critical points: 1) payment of a postal order; 2) accepting a registered letter, breaking them down into subtasks. We used an optoelectronic system for kinematic analysis, and calculated the range of motion of the trunk and arms in the three spatial planes. The 45( position required less torsion of the trunk and head when using the printer, placed to the left of the employee. A larger worktop improved the workstation, leaving more room for equipment and allowing the worker to sit frontally to the monitor. However, this solution involved a shorter distance between the worker and the client with longer extension of the shoulder and elbow and less trunk flexion. These findings suggested a modification in the layout that shortens the distance between the worker and client.     

Effects of a participatory ergonomics intervention computer workshop for university students: a pilot intervention to prevent disability in tomorrow's workers

A participatory approach was used to create a computer ergonomics workshop for college students, incorporating an instructional systems design process and adult learning inquiry perspectives. The primary objective of this participatory ergonomic pilot intervention was to involve students throughout the training design process in solving computer workstation ergonomic problems and adopting healthy computing behaviors. Students' level of participation included becoming part of the training design team, a co-facilitator, or a student trainee. A second objective was to examine the translation of an industrial office ergonomics training program into a college computer ergonomics training program. The long term goal was to reduce upper extremity symptoms and disability. The program was piloted at one private university. The three student trainees significantly increased their knowledge of computer ergonomics from 69% of test items answered correctly pre-training to 82% post-training. Trainees were also successful in conducting computer ergonomic evaluations of students' computing work areas. They achieved 100% accuracy in identifying ergonomic problems and proposing solutions in five ergonomic workstation assessments in the field. This approach was successful in creating a sense of ownership among the student developers and facilitators as reflected in their self-reports during a post-intervention debriefing. The results of this pilot study justify formal controlled trials of this intervention in university students, who will become tomorrow's workers.     

An analysis of VDT monitor placement and daily hours of use for female bifocal users

A population of 72 bifocal wearers was studied to determine the relationship between VDT (video display terminal) placement for those who reported musculoskeletal pain and those who did not. The mean hours worked was 50.4 minutes (p=0.003) greater for those who reported head/neck pain versus those who did not and 48.6 minutes (p=0.004) greater for those who reported shoulder/arm pain that those who did not. There was no statistically significant difference between the means of monitor height, distance, or angle for those who reported pain symptoms versus those who did not. This study indicates that, self reported pain symptoms are correlated with hours of VDT work and that there appears to be a threshold at approximately five hours for pain symptoms among bifocal wearers. No such correlation can be made for monitor placement     

Ergonomics in the operating room

Surgical staff is considered to have several ergonomic risk factors, but their physical workload and musculoskeletal health have seldom been evaluated. Clinical examinations of neck and upper extremities were performed in 99 theatre nurses and 93 assisting nurses, all females. Their physical workload was assessed by questionnaire, and by technical measurements of postures, movements and muscular load in subgroups of both categories. The prevalences of diagnoses in neck/shoulders were not remarkably high in the nurses, compared to other occupational groups. In elbows/hands though, the prevalence was rather high among assistant nurses, 13 vs. 5 % in theatre nurses; POR 3.0 (CI 95 % 1.0 - 8.9). Theatre nurses experienced prolonged static postures in the questionnaire, whilst assistant nurses reported high physical load. Accordingly, the technical measurements showed more strenuous working postures in the theatre nurses, but lower wrist angular velocities. The time proportion of muscular rest in m.trapezius was rather high in both groups. Although both groups had some stressful loads they had relatively low prevalence of diagnoses in neck/shoulders. The high proportion of muscular rest may be protective. The elevated risk of elbows/hands diagnoses among assistant nurses may be explained by strenuous work tasks of short duration.     

Physiological stress assessment of female workers at kitchen workstation

This paper explores the extent of the physiological stresses of female workers at kitchen workstation while performing the various activities. For this a survey of eighty homemakers and experiment on sixteen respondents having similar physical and physiological parameters was done. Five activities in which the respondents faced maximum problems were selected and were standardized. Physiological stresses including cardiovascular, muscular, and energy expenditure during these activities were then assessed. Study revealed that fatigue during the selected five activities i.e. cutting, grating, rolling, kneading, dish washing, was felt mainly at the wrist, fore arm, followed by discomfort in the shoulders, upper arm, lower back and neck. Energy expenditure for these activities ranged from 7.0 to10 kJ\min, total cardiac cost of work (TCCW) was between 200.81 to 364.30 beats, physiological cost of work (PCW) was 12.82 to 26.26 beats\min; maximum for grating and minimum for rolling. The percent increase in heart rate was maximum for grating 38.56 and minimum for rolling 16.20. Reduction in grip and pinch strength of right hand was found more as compared to the left hand.