Changes in upper extremity biomechanics across different mouse positions in a computer workstation

Shoulder kinematics during cyclic overhead work are affected by a passive arm support exoskeleton

PURPOSE

We investigated the influence of passive arm-support exoskeleton (ASE) with different levels of torque (50, 75, and 100%) on upper arm osteokinematics.

METHODS

Twenty participants completed a cyclic overhead drilling task with and without ASE. Task duration, joint angles, and angular acceleration peaks were analyzed during ascent and descent phases of the dominant upper arm.

RESULTS

Maximum ASE torque was associated with decreased peak acceleration during ascent (32.2%; SD 17.8; p < 0.001) and descent phases (38.8%; SD 17.8; p < 0.001). Task duration remained consistent. Increased torque led to a more flexed (7.2°; SD 5.5; p > 0.001) and internally rotated arm posture (17.6°; SD 12.1; p < 0.001), with minimal changes in arm abduction.

CONCLUSION

The small arm accelerations and changes in osteokinematics we observed, support the use of this ASE, even while performing overhead cyclic tasks with the highest level of support.

Effects of a passive upper-body exoskeleton on whole-body kinematics, leg muscle activity, and discomfort during a carrying task

OBJECTIVE

To compare whole-body kinematics, leg muscle activity, and discomfort while performing a 10-min carrying task with and without a passive upper-body exoskeleton (CarrySuitⓇ), for both males and females.

BACKGROUND

Diverse commercial passive exoskeletons have appeared on the market claiming to assist lifting or carrying task. However, evidence of their impact on kinematics, muscle activity, and discomfort while performing these tasks are necessary to determine their benefits and/or limitations.

METHOD

Sixteen females and fourteen males carried a 15kg load with and without a passive exoskeleton during 10-min over a round trip route, in two non-consecutive days. Whole-body kinematics and leg muscle activity were evaluated for each condition. In addition, leg discomfort ratings were quantified before and immediately after the task.

RESULTS

The gastrocnemius and vastus lateralis muscle activity remained constant over the task with the exoskeleton. Without the exoskeleton a small decrease of gastrocnemius median activation was observed regardless of sex, and a small increase in static vastus lateralis activation was observed only for females. Several differences in sagittal, frontal, and transverse movements' ranges of motion were found between conditions and over the task. With the exoskeleton, ROM in the sagittal plane increased over time for the right ankle and pelvis for both sexes, and knees for males only. Thorax ROMs in the three planes were higher for females only when using the exoskeleton. Leg discomfort was lower with the exoskeleton than without.

CONCLUSION

The results revealed a positive impact on range of motion, leg muscle activity, and discomfort of the tested exoskeleton.

Impact of a passive upper-body exoskeleton on muscle activity, heart rate and discomfort during a carrying task

OBJECTIVE

The goal of this study was to compare erector spinae muscle fatigue, upper limb muscle activity, body areas discomfort, and heart rate during a 10-min carrying task with and without a passive upper-body exoskeleton (CarrySuitⓇ) while considering sex influences.

BACKGROUND

Passive exoskeletons are commercially available to assist lifting or carrying task. However, evidence of their impact on muscle activity, fatigue, heart rate and discomfort are scarce and/or do not concur during carrying tasks.

METHOD

Thirty participants (16 females and 14 male) performed a 10-min, 15kg load-carrying task with and without the exoskeleton in two non-consecutive days. Heart rate, and erector spinae, deltoid, biceps and brachioradialis muscle activity were recorded during the carrying tasks. In addition, erector spinae electromyography during an isometric hold test and discomfort ratings were measured before and after the task.

RESULTS

While without the exoskeleton upper limb muscle activity increased or remained constant during the carrying task and showing high peak activation for both males and females, a significant activity reduction was observed with the exoskeleton. Low back peak activation, heart rate and discomfort were lower with than without the exoskeleton. In males muscle activation was significantly asymmetric without the exoskeleton and more symmetric with the exoskeleton.

CONCLUSION

The tested passive exoskeleton appears to alleviate the physical workload and impact of carrying heavy loads on the upper limbs and lower back for both males and females.

A first step towards a framework for interventions for individual working practice to prevent work-related musculoskeletal disorders: a scoping review

BACKGROUND

Work-related musculoskeletal disorders (WMSDs) are a key topic in occupational health. In the primary prevention of these disorders, interventions to minimize exposure to work-related physical risk factors are widely advocated. Besides interventions aimed at the work organisation and the workplace, interventions are also aimed at the behaviour of workers, the so-called individual working practice (IWP). At the moment, no conceptual framework for interventions for IWP exists. This study is a first step towards such a framework.

METHODS

A scoping review was carried out starting with a systematic search in Ovid Medline, Ovid Embase, Ovid APA PsycInfo, and Web of Science. Intervention studies aimed at reducing exposure to physical ergonomic risk factors involving the worker were included. The content of these interventions for IWP was extracted and coded in order to arrive at distinguishing and overarching categories of these interventions for IWP.

RESULTS

More than 12.000 papers were found and 110 intervention studies were included, describing 810 topics for IWP. Eventually eight overarching categories of interventions for IWP were distinguished: (1) Workplace adjustment, (2) Variation, (3) Exercising, (4) Use of aids, (5) Professional skills, (6) Professional manners, (7) Task content & task organisation and (8) Motoric skills.

CONCLUSION

Eight categories of interventions for IWP are described in the literature. These categories are a starting point for developing and evaluating effective interventions performed by workers to prevent WMSDs. In order to reach consensus on these categories, an international expert consultation is a necessary next step.

The role of at home workstation ergonomics and gender on musculoskeletal pain

BACKGROUND

The recent mandate for university faculty and staff to work-from-home (WFH) during the COVID-19 pandemic has forced employees to work with sub-optimal ergonomic workstations that may change their musculoskeletal discomfort and pain. As women report more work-related musculoskeletal discomfort (WMSD), this effect may be exacerbated in women.

OBJECTIVE

The purpose of this study was to describe university employee at-home office workstations, and explore if at-home workstation design mediates the effect of gender on musculoskeletal pain.

METHODS

University employees completed a survey that focused on the WFH environment, at home workstation design and musculoskeletal pain. Descriptive statistics and regression analysis were used to analyze the responses.

RESULTS

61% of respondents reported an increase in musculoskeletal pain, with the neck, shoulders and lower back being reported most frequently. Women reported significantly greater musculoskeletal pain, but this relationship was significantly mediated by poor ergonomic design of the home workstation. Improper seat-height and monitor distance were statistically associated with total-body WMSD.

CONCLUSIONS

WFH has worsened employee musculoskeletal health and the ergonomic gap between women and men in the workspace has persisted in the WFH environment, with seat height and monitor distance being identified as significant predictors of discomfort/pain.

Association between comprehensive workstation and neck and upper-limb pain among office worker

OBJECTIVES

Our study aimed to investigate the association between comprehensive workstations and neck and upper-limb pain (NUP) among office workers.

METHODS

This cross-sectional study included 307 office workers (median age, 39 years; 88% men). Workstations (presence of armrest, armrest position, number of monitors used, mouse position, mouse usage, keyboard usage, and keyboard position) were investigated in terms of 17 items and judged as "adequate" or "inadequate." NUP was assessed using a numerical rating scale. NUP locations included the neck, shoulder, elbow, and wrist. In the statistical analysis, outcome variables were the presence of pain in each part, while explanatory variables were the number of inadequate workstations. Logistic regression analyses were conducted with adjustment for age, gender, working duration, and exercise habit.

RESULTS

The prevalence of neck pain was 47% (n = 143), shoulder pain was 50% (n = 153), elbow pain was 7.2% (n = 22), and wrist pain was 13% (n = 40). In the adjusted model, the number of inadequate workstations had significant positive associations with elbow pain (odds ratio [OR], 1.39; 95% confidence interval [CI], 1.06.1.81) and wrist pain (OR, 1.80; 95% CI, 1.17.2.26). However, the number of inadequate workstations was not significantly associated with neck pain or shoulder pain.

CONCLUSIONS

Workstation-related factors (presence of armrest, armrest position, mouse usage, and keyboard usage) were significantly associated with elbow and wrist pain. Our findings suggest that workstations can contribute to elbow and wrist pain in office workers.

Mouse with your arm™: Facilitating forearm support using the chair armrest to prevent and mitigate musculoskeletal disorders

BACKGROUND

Musculoskeletal disorders (MSDs) can be prevented by avoiding trauma caused by poor posture, compression, force, and repetition. Neutral postures are recommended to avoid MSDs.

OBJECTIVE

This study introduces Mouse With Your Arm™ (MWYA) methodology which promotes sitting back in a chair, using the chair's armrest for forearm support at relaxed elbow height, matching surface and armrest height, and keeping the mouse on the surface edge. This position allows optimal task chair use, facilitates movement and neutral postures, avoids compression and contact stress, and is effective in mitigating MSDs.

METHOD

MWYA was applied and measured in the field for more 23 years providing over 3,500 individualized assessments to integrate a participant's unique characteristics, reported health concerns, tasks, tools, and environment to achieve and sustain whole-body neutral and comfortable working postures.

RESULTS

Previous research has consistently recommended use of forearm support by a desk, apparatus, or wrist rest, and resulted in non-neutral, static postures and measured health consequences. By using armrests for support, MWYA avoids the potential of MSDs as can be caused by these previously endorsed postures.

CONCLUSION

By applying the five MWYA principles, computer users comprehend neutral posture and put forth the effort essential to creating healthy human computer relationships.

Evaluating biomechanics of user-selected sitting and standing computer workstation

A standing computer workstation has now become a popular modern work place intervention to reduce sedentary behavior at work. However, user's interaction related to a standing computer workstation and its differences with a sitting workstation need to be understood to assist in developing recommendations for use and set up. The study compared the differences in upper extremity posture and muscle activity between user-selected sitting and standing workstation setups. Twenty participants (10 females, 10 males) volunteered for the study. 3-D posture, surface electromyography, and user-reported discomfort were measured while completing simulated tasks with each participant's self-selected workstation setups. Sitting computer workstation associated with more non-neutral shoulder postures and greater shoulder muscle activity, while standing computer workstation induced greater wrist adduction angle and greater extensor carpi radialis muscle activity. Sitting computer workstation also associated with greater shoulder abduction postural variation (90th-10th percentile) while standing computer workstation associated with greater variation for should rotation and wrist extension. Users reported similar overall discomfort levels within the first 10 min of work but had more than twice as much discomfort while standing than sitting after 45 min; with most discomfort reported in the low back for standing and shoulder for sitting. These different measures provide understanding in users' different interactions with sitting and standing and by alternating between the two configurations in short bouts may be a way of changing the loading pattern on the upper extremity.

Assessing ergonomic risks of software: Development of the SEAT

Software utilizing interaction designs that require extensive dragging or clicking of icons may increase users' risks for upper extremity cumulative trauma disorders. The purpose of this research is to develop a Self-report Ergonomic Assessment Tool (SEAT) for assessing the risks of software interaction designs and facilitate mitigation of those risks. A 28-item self-report measure was developed by combining and modifying items from existing industrial ergonomic tools. Data were collected from 166 participants after they completed four different tasks that varied by method of input (touch or keyboard and mouse) and type of task (selecting or typing). Principal component analysis found distinct factors associated with stress (i.e., demands) and strain (i.e., response). Repeated measures analyses of variance showed that participants could discriminate the different strain induced by the input methods and tasks. However, participants' ability to discriminate between the stressors associated with that strain was mixed. Further validation of the SEAT is necessary but these results indicate that the SEAT may be a viable method of assessing ergonomics risks presented by software design.

A literature review of the effects of computer input device design on biomechanical loading and musculoskeletal outcomes during computer work

BACKGROUND

Extended use of conventional computer input devices is associated with negative musculoskeletal outcomes. While many alternative designs have been proposed, it is unclear whether these devices reduce biomechanical loading and musculoskeletal outcomes.

OBJECTIVE

To review studies describing and evaluating the biomechanical loading and musculoskeletal outcomes associated with conventional and alternative input devices.

METHODS

Included studies evaluated biomechanical loading and/or musculoskeletal outcomes of users' distal or proximal upper extremity regions associated with the operation of alternative input devices (pointing devices, mice, other devices) that could be used in a desktop personal computing environment during typical office work.

RESULTS

Some alternative pointing device designs (e.g. rollerbar) were consistently associated with decreased biomechanical loading while other designs had inconsistent results across studies. Most alternative keyboards evaluated in the literature reduce biomechanical loading and musculoskeletal outcomes. Studies of other input devices (e.g. touchscreen and gestural controls) were rare, however, those reported to date indicate that these devices are currently unsuitable as replacements for traditional devices.

CONCLUSIONS

Alternative input devices that reduce biomechanical loading may make better choices for preventing or alleviating musculoskeletal outcomes during computer use, however, it is unclear whether many existing designs are effective.

Influence of Input Hardware and Work Surface Angle on Upper Limb Posture in a Hybrid Computer Workstation

OBJECTIVE

We evaluated the effect of work surface angle and input hardware on upper-limb posture when using a hybrid computer workstation.

BACKGROUND

Offices use sit-stand and/or tablet workstations to increase worker mobility. These workstations may have negative effects on upper-limb joints by increasing time spent in non-neutral postures, but a hybrid standing workstation may improve working postures.

METHOD

Fourteen participants completed office tasks in four workstation configurations: a horizontal or sloped 15° working surface with computer or tablet hardware. Three-dimensional right upper-limb postures were recorded during three tasks: reading, form filling, and writing e-mails. Amplitude probability distribution functions determined the median and range of upper-limb postures.

RESULTS

The sloped-surface tablet workstation decreased wrist ulnar deviation by 5° when compared to the horizontal-surface computer when reading. When using computer input devices (keyboard and mouse), the shoulder, elbow, and wrist were closest to neutral joint postures when working on a horizontal work surface. The elbow was 23° and 15° more extended, whereas the wrist was 6° less ulnar deviated, when reading compared to typing forms or e-mails.

CONCLUSION

We recommend that the horizontal-surface computer configuration be used for typing and the sloped-surface tablet configuration be used for intermittent reading tasks in this hybrid workstation.

APPLICATION

Offices with mobile employees could use this workstation for alternating their upper-extremity postures; however, other aspects of the device need further investigation.

Developing and validating a self-report assessment tool for software biomechanics

BACKGROUND

There are many effective methods for decreasing the likelihood of repetitive strain injury (RSI) for those who work at a computer in an office environment. This study is focused on the highly repetitive task of interpreting seismic data. The skilled geoscientists who perform this work are very well compensated, and their work is vital to the success of the oil company. However, RSIs are still occurring in situations where effective methods of mitigating injuries have been successfully implemented and this has been occurring very frequently for geoscientists. This suggests that there are other elements contributing to the development of these injuries and one element could be the software interaction design. However, it is difficult for software designers to determine this because most measures associated with muscle activity require expensive data collection methods.

OBJECTIVE

This paper describes research conducted to determine if survey-based subjective measures might be used to assess the potential for RSI for software programs.

METHODS

In laboratory and field settings, data were collected using three different survey instruments (NASA-Task Load Index, Latko's Busiest Hand Activity Level Scale, and the Borg CR10 Rating of Perceived Exertion Scale) and conventional measures of muscle activity (sEMG). Correlations between the surveys and muscle activity were then calculated.

RESULTS

For both the laboratory and the field, people were able to provide reliable self-report information related to their muscle activity. However, the effect sizes were not large.

CONCLUSIONS

These results suggest that self-report tools could be utilized to identify software interaction designs related associated with risks of RSI.

Evaluating the effect of four different pointing device designs on upper extremity posture and muscle activity during mousing tasks

The goal of this study was to evaluate the effect of different types of computer pointing devices and placements on posture and muscle activity of the hand and arm. A repeated measures laboratory study with 12 adults (6 females, 6 males) was conducted. Participants completed two mouse-intensive tasks while using a conventional mouse, a trackball, a stand-alone touchpad, and a rollermouse. A motion analysis system and an electromyography system monitored right upper extremity postures and muscle activity, respectively. The rollermouse condition was associated with a more neutral hand posture (lower inter-fingertip spread and greater finger flexion) along with significantly lower forearm extensor muscle activity. The touchpad and rollermouse, which were centrally located, were associated with significantly more neutral shoulder postures, reduced ulnar deviation, and lower forearm extensor muscle activities than other types of pointing devices. Users reported the most difficulty using the trackball and touchpad. Rollermouse was not more difficult to use than any other devices. These results show that computer pointing device design and location elicit significantly different postures and forearm muscle activities during use, especially for the hand posture metrics.

Effects of forearm and palm supports on the upper extremity during computer mouse use

The use of forearm and palm supports has been associated with lower neck and shoulder muscle activity as well as reduced musculoskeletal discomfort during keyboard use, however, few studies have investigated their effect during computer mouse use. Eight men and eight women completed several computer mousing tasks in six arm support conditions: Forearm Support, Flat Palm Support, Raised Palm Support, Forearm + Flat Palm Support, Forearm + Raised Palm Support, and No Support. Concurrently, an infrared three-dimensional motion analysis system measured postures, six-degree-of-freedom force-torque sensors measured applied forces & torques, and surface electromyography measured muscle activity. The use of forearm support compared to the no support condition was significantly associated with less shoulder muscle activity & torque, and the raised palm support was associated with less wrist extension. Forearm supports reduced shoulder flexion torque by 90% compared to no support. The use of either support also resulted in lower applied forces to the mouse pad. Participants reported less musculoskeletal discomfort when using a support. These results provide recommendations for office workstation setup and inform ergonomists of effective ways to reduce musculoskeletal exposures.

Ergonomic Design of a Computer Mouse for Clients With Wrist Splints

OBJECTIVE. We explored effects of cutaneous feedback and hump position on efficiency and comfort in mouse use with a splint. We also analyzed the relationship between anthropometric measurements (width of hand and length of hand, palm, and index) and the task performance.

METHOD. Thirty participants performed a computer task with two forms of mice (front hump and rear hump) and two kinds of wrist splints (dorsal and volar). Movement time and satisfaction scores were recorded.

RESULTS. No interaction effect (Hump Position × Splint Type) was found on movement time. Movement time was shorter for rear-hump mouse users than for front-hump mouse users. Movement time was also shorter for wearers of dorsal wrist splints than for wearers of volar wrist splints. Limited differences existed in the satisfaction scores. Participants with a longer index finger had shorter movement time.

CONCLUSION. Both dorsal wrist splints and rear-hump mice are recommended. Length of index finger positively correlated with task performance.

Self-selected duty cycle times for grip force, wrist flexion postures and three grip types

Performance and health issues are common in industry. On-the-job productivity gains related to good design, which could help justify ergonomics intervention, are often not considered. More quantitative data are needed to model the discomfort/productivity relationship for upper limb activity in simulated repetitive assembly type work. Eighteen participants completed an experiment, simulating a repetitive upper limb task with force, posture and grip type recorded as independent variables. Duty cycle time and discomfort were recorded as dependent variables. Participants performed 18 experiment combinations (block designed around force); each treatment lasted 35 min, including breaks. Analysis indicated a significant two-way interaction between posture and grip type. Results from this experiment were used to model the effect of these variables on operator discomfort and performance.

Shoulder and neck muscle activities during typing with articulating forearm support at different heights

Use of forearm support is known to reduce physical stress of computer users, but research about how to properly position the forearm support is insufficient. This study was aimed to determine whether the height of forearm support influences muscular loads during typing. Twenty four subjects performed a typing task with a pair of articulating forearm support at three different heights as well as without any support, while shoulder, neck and forearm muscle activities and posture data were recorded. Typing with the support at resting elbow height produced significantly (p < 0.05) lower shoulder and neck muscle activities than that of no support condition. Typing with the support at heights higher than the resting elbow height produced significantly greater shoulder and neck muscle activities compared to the no support condition. Results suggest that forearm support can help computer users lessen physical stress in typing, but only when the supports are positioned at resting elbow height. Practitioner Summary: Use of forearm support is known to alleviate physical stress of PC users in computer works such as typing. This experimental study addressed the importance of proper positioning of forearm support by comparing neck and upper extremity muscle activities between conditions with varying heights of forearm support in keyboard typing.

Observed differences in upper extremity forces, muscle efforts, postures, velocities and accelerations across computer activities in a field study of office workers

This study, a part of the PRedicting Occupational biomechanics in OFfice workers (PROOF) study, investigated whether there are differences in field-measured forces, muscle efforts, postures, velocities and accelerations across computer activities. These parameters were measured continuously for 120 office workers performing their own work for two hours each. There were differences in nearly all forces, muscle efforts, postures, velocities and accelerations across keyboard, mouse and idle activities. Keyboard activities showed a 50% increase in the median right trapezius muscle effort when compared to mouse activities. Median shoulder rotation changed from 25 degrees internal rotation during keyboard use to 15 degrees external rotation during mouse use. Only keyboard use was associated with median ulnar deviations greater than 5 degrees. Idle activities led to the greatest variability observed in all muscle efforts and postures measured. In future studies, measurements of computer activities could be used to provide information on the physical exposures experienced during computer use. Practitioner Summary: Computer users may develop musculoskeletal disorders due to their force, muscle effort, posture and wrist velocity and acceleration exposures during computer use. We report that many physical exposures are different across computer activities. This information may be used to estimate physical exposures based on patterns of computer activities over time.

Changes in posture through the use of simple inclines with notebook computers placed on a standard desk

This study evaluated the use of simple inclines as a portable peripheral for improving head and neck postures during notebook computer use on tables in portable environments such as hotel rooms, cafés, and airport lounges. A 3D motion analysis system measured head, neck and right upper extremity postures of 15 participants as they completed a 10 min computer task in six different configurations, all on a fixed height desk: no-incline, 12° incline, 25° incline, no-incline with external mouse, 25° incline with an external mouse, and a commercially available riser with external mouse and keyboard. After completion of the task, subjects rated the configuration for comfort and ease of use and indicated perceived discomfort in several body segments. Compared to the no-incline configuration, use of the 12° incline reduced forward head tilt and neck flexion while increasing wrist extension. The 25° incline further reduced head tilt and neck flexion while further increasing wrist extension. The 25° incline received the lowest comfort and ease of use ratings and the highest perceived discomfort score. For portable, temporary computing environments where internal input devices are used, users may find improved head and neck postures with acceptable wrist extension postures with the utilization of a 12° incline.

Developing a framework for predicting upper extremity muscle activities, postures, velocities, and accelerations during computer use: the effect of keyboard use, mouse use, and individual factors on physical exposures

Prediction models were developed based on keyboard and mouse use in combination with individual factors that could be used to predict median upper extremity muscle activities, postures, velocities, and accelerations experienced during computer use. In the laboratory, 25 participants performed five simulated computer trials with different amounts of keyboard and mouse use ranging from a highly keyboard-intensive trial to a highly mouse-intensive trial. During each trial, muscle activity and postures of the shoulder and wrist and velocities and accelerations of the wrists, along with percentage keyboard and mouse use, were measured. Four individual factors (hand length, shoulder width, age, and gender) were also measured on the day of data collection. Percentage keyboard and mouse use explained a large amount of the variability in wrist velocities and accelerations. Although hand length, shoulder width, and age were each significant predictors of at least one median muscle activity, posture, velocity, or acceleration exposure, these individual factors explained very little variability in addition to percentage keyboard and mouse use in any of the physical exposures investigated. The amounts of variability explained for models predicting median wrist velocities and accelerations ranged from 75 to 84% but were much lower for median muscle activities and postures (0-50%). RMS errors ranged between 8 to 13% of the range observed. While the predictions for wrist velocities and accelerations may be able to be used to improve exposure assessment for future epidemiologic studies, more research is needed to identify other factors that may improve the predictions for muscle activities and postures.

User discomfort, work posture and muscle activity while using a touchscreen in a desktop PC setting

An experimental study was conducted to evaluate physical risk factors associated with the use of touchscreen in a desktop personal computer (PC) setting. Subjective rating of visual/body discomfort, shoulder and neck muscle activity, elbow movement and user-preferred positions of the workstation were quantified from 24 participants during a standardised computer use task with a standard keyboard and a mouse (traditional setting), with a touchscreen and the standard keyboard (mixed-use condition) and with the touchscreen only. The use of a touchscreen was associated with a significant increase of subjective discomfort on the shoulder, neck and fingers, myoelectric activity of shoulder and neck muscles and percentage of task duration that arms were in the air. Participants placed the touchscreen closer and lower when using touch interfaces compared with the traditional setting. Results suggest that users would need more frequent breaks and proper armrests to reduce physical risks associated with the use of a touchscreen in desktop PC settings. Statement of Relevance: In this study, subjective discomfort, work posture and muscle activity of touchscreen desktop PC users were quantitatively evaluated. The findings of this study can be used to understand potential risks from the use of a touchscreen desktop PC and to suggest design recommendations for computer workstations with the touchscreen.

Evidence-based guidelines for the wise use of computers by children: physical development guidelines

Computer use by children is common and there is concern over the potential impact of this exposure on child physical development. Recently principles for child-specific evidence-based guidelines for wise use of computers have been published and these included one concerning the facilitation of appropriate physical development. This paper reviews the evidence and presents detailed guidelines for this principle. The guidelines include encouraging a mix of sedentary and whole body movement tasks, encouraging reasonable postures during computing tasks through workstation, chair, desk, display and input device selection and adjustment and special issues regarding notebook computer use and carriage, computing skills and responding to discomfort. The evidence limitations highlight opportunities for future research. The guidelines themselves can inform parents and teachers, equipment designers and suppliers and form the basis of content for teaching children the wise use of computers. STATEMENT OF RELEVANCE: Many children use computers and computer-use habits formed in childhood may track into adulthood. Therefore child-computer interaction needs to be carefully managed. These guidelines inform those responsible for children to assist in the wise use of computers.

Effects of a feedback signal in a computer mouse on movement behaviour, muscle load, productivity, comfort and user friendliness

To study the effects of a tactile feedback signal in a computer mouse on reduction of hovering behaviour and consequently on changes in muscle load, productivity, comfort and user friendliness, a comparative, experimental study with repeated measures was conducted. Fifteen subjects performed five trials with different mouse actions and a standardised task, once with a mouse with the feedback signal and once with a mouse without the feedback signal. Holding the hand just above the mouse caused higher muscle loading than clicking and scrolling. Holding the hand on the mouse caused higher muscle loading than resting the hand on the desk. The feedback signal effectively decreased hovering behaviour. It also led to a more dynamic activation pattern of the extensor muscles of the forearm. The overall opinion of the feedback signal for future use was rated as somewhat variable. No effects on discomfort or productivity were found. The use of a mouse with a tactile vibrating feedback signal seems promising for preventing arm complaints, although more research is needed to establish the clinical relevance.

Procedure-related musculoskeletal symptoms in gastrointestinal endoscopists in Korea

AIM: To determine the prevalence and risk factors of work-related musculoskeletal disorders in gastrointestinal endoscopists in Korea.

METHODS: A survey of musculoskeletal symptoms, using a self-administered questionnaire, was conducted on 55 endoscopists practicing in general hospitals or health promotion centers.

RESULTS: Forty-nine (89.1%) endoscopists reported musculoskeletal pain on at least one anatomic location and 37 (67.3%) endoscopists complained of pain at rest. Twenty-six (47.3%) endoscopists had severe musculoskeletal pain defined as a visual analogue score greater than 5.5. Factors related to the development of severe pain were (1) standing position during upper endoscopy, (2) specific posture/habit during endoscopic procedures, and (3) multiple symptomatic areas. Finger pain was more common in beginners, whereas shoulder pain was more common in experienced endoscopists. Sixteen percent of symptomatic endoscopists have modified their practice or reduced the number of endoscopic examinations. Only a few symptomatic endoscopists had sought professional consultation with related specialists.

CONCLUSION: The prevalence of musculoskeletal pain in endoscopists is very high. The location of pain was different between beginners and experienced endoscopists. Measures for the prevention and adequate management of endoscopy-related musculoskeletal symptoms are necessary.

Effect of horizontal position of the computer keyboard on upper extremity posture and muscular load during computer work

The distance of the keyboard from the edge of a work surface has been associated with hand and arm pain; however, the variation in postural and muscular effects with the horizontal position have not been explicitly explored in previous studies. It was hypothesized that the wrist approaches more of a neutral posture as the keyboard distance from the edge of table increases. In a laboratory setting, 20 adults completed computer tasks using four workstation configurations: with the keyboard at the edge of the work surface (NEAR), 8 cm from the edge and 15 cm from the edge, the latter condition also with a pad that raised the work surface proximal to the keyboard (FWP). Electrogoniometers and an electromagnetic motion analysis system measured wrist and upper arm postures and surface electromyography measured muscle activity of two forearm and two shoulder muscles. Wrist ulnar deviation decreased by 50% (4 degrees ) as the keyboard position moved away from the user. Without a pad, wrist extension increased by 20% (4 degrees ) as the keyboard moved away but when the pad was added, wrist extension did not differ from that in the NEAR configuration. Median values of wrist extensor muscle activity decreased by 4% maximum voluntary contraction for the farthest position with a pad (FWP). The upper arm followed suit: flexion increased while abduction and internal rotation decreased as the keyboard was positioned further away from the edge of the table. In order to achieve neutral postures of the upper extremity, the keyboard position in the horizontal plane has an important role and needs to be considered within the context of workstation designs and interventions.