Effects of negatively sloped keyboard wedges on risk factors for upper extremity work-related musculoskeletal disorders and user performance

Several changes to computer peripherals have been developed to reduce exposure to identified risk factors for musculoskeletal injury, notably in keyboard designs. Negative keyboard angles and their resulting effects on objective physiological measures, subjective measures and performance have been studied, although few angles have been investigated despite the benefits associated with their use. The objective of this study was to quantify the effects of negative keyboard angles on forearm muscle activity, wrist posture, key strike force, perceived discomfort and performance and to identify a negative keyboard angle or range of keyboard angles that minimizes exposure to risk factors for hand/wrist injuries. Ten experienced typists (four males and six females) participated in a laboratory study to compare keyboard angles ranging from 0 degrees to -30 degrees , at 10 degrees increments, and a keyboard with a 7 degrees slope, using a wedge designed for use with standard QWERTY keyboards. Repeatability of exposures was examined by requiring participants to complete two test sessions 1 week apart. Dependent variable data were collected during 10 min basic data entry tasks. Wrist posture data favoured negative keyboard angles of 0 degrees (horizontal) or greater, compared to a positive keyboard angle of 7 degrees , especially for the flexion/extension direction. In general, the percentage of wrist movements within a neutral zone and the percentages of wrist movements within +/-5 degrees and +/-10 degrees increased as keyboard angle became more negative. Electromyography results were mixed, with some variables supporting negative keyboard angles whilst other results favoured the standard keyboard configuration. Net typing speed supported the -10 degrees keyboard angle, whilst other negative typing angles were comparable, if not better than, with the standard keyboard. Therefore, angles ranging from 0 degrees to -30 degrees in general provide significant reductions in exposure to deviated wrist postures and muscle activity and comparable performance.     

Effects of psychosocial and individual factors on physiological risk factors for upper extremity musculoskeletal disorders while typing

Psychosocial factors are hypothesized to contribute to work-related musculoskeletal disorder (WMSD) development, although previous research has been largely epidemiological or has focused primarily on the shoulders, back and neck. The objective of this study was to quantify the effects of mental workload and time pressure on perceived workload and physiological responses of the distal upper extremity. A total of 18 typists completed nine 5-min typing sessions representing three levels of time pressure and mental workload. Levels were manipulated by adjusting typing speed and by requiring participants to perform arithmetic tasks while typing. Outcomes were measured in muscle activation levels, wrist postures and movements, key strike force and subjective assessments of workload. In general, increased time pressure increased muscle activation, key strike force and wrist deviations; and increased mental workload increased key strike force. Mental workload and time pressure mediated physical risk factors during typing to increase WMSD risk for the distal upper extremity.     

Effects of psychosocial and individual factors on physiological risk factors for upper extremity musculoskeletal disorders while typing

Psychosocial factors are hypothesized to contribute to work-related musculoskeletal disorder (WMSD) development, although previous research has been largely epidemiological or has focused primarily on the shoulders, back and neck. The objective of this study was to quantify the effects of mental workload and time pressure on perceived workload and physiological responses of the distal upper extremity. A total of 18 typists completed nine 5-min typing sessions representing three levels of time pressure and mental workload. Levels were manipulated by adjusting typing speed and by requiring participants to perform arithmetic tasks while typing. Outcomes were measured in muscle activation levels, wrist postures and movements, key strike force and subjective assessments of workload. In general, increased time pressure increased muscle activation, key strike force and wrist deviations; and increased mental workload increased key strike force. Mental workload and time pressure mediated physical risk factors during typing to increase WMSD risk for the distal upper extremity.     

Effects of a vertical keyboard design on typing performance, user comfort and muscle tension

To circumvent the awkward pronated hand position inherent to conventional horizontal keyboards, a vertical, split keyboard was designed with flexible cushions supporting the wrists, allowing relaxed hand and arm postures. During eight twice-weekly 30-min training sessions, the performance and subjective comfort of nine experienced typists were tested. Typing speed and error percentage, and surface electromyographic activity of six forearm muscles and two postural muscles were recorded in separate sessions at the end of each week. Typing speed rapidly recovered to the preset rate of 300 keystrokes/min and error percentages were similar for the two keyboards. The vertical keyboard caused lower muscular activity in especially finger extensor muscles, did not increase postural muscle activity, and self-reported comfort was higher. Thus, the vertical keyboard was easily mastered, was experienced as comfortable, and caused less stress on muscles sensitive to repetitive strain injuries.     

Effects of keyboard tray geometry on upper body posture and comfort

The effects of a downward-tilting (DT) keyboard tray on wrist posture, seated posture and self-assessed musculoskeletal discomfort were investigated in a field experiment. Thirty-eight professional office workers were studied. A pretest assessed how they typed using either a conventional keyboard on a desk or on an articulating keyboard tray, and with or without wrist rests. Workers were randomly allocated to a control (n= 15) or test group (n= 23) that used their existing keyboard in a DT system. A post-test was conducted 3 weeks later. Results showed no significant changes in wrist posture, seated posture or reports of musculoskeletal discomfort for the control group, and ? 50% of typing wrist movements put the hand in a neutral zone. There were significant improvements in wrist posture, seated posture and upper body musculoskeletal discomfort for the test group using the DT system. Over 80% of typing wrist movements put the hand into a neutral zone with the DT arrangement. Reactions to using a conventional keyboard on a DT system were positive.     

Vibration of portable orbital sanders and its impact on the development of work-related musculoskeletal disorders in the furniture industry

The wood furniture industry has a strong presence in Canada, where it employs over 100,000 workers. Because of the extensive number of manual tasks required in this industry, several studies have been undertaken to characterize the health and safety risk factors to which these workers are exposed, such as awkward postures, repetitive movements and the application of undue force. However, very little research has been done on workers’ exposure to vibration from portable orbital sanders, one of the most common tools used in this industry. Vibration is responsible for a specific occupational disease called vibration syndrome, but is also recognized as a risk factor that increases the prevalence of more common work-related musculoskeletal disorders (WMSDs). This study proposed to determine the level of vibration to which sanders of furniture parts are exposed, and to analyze its impact on the risk of WMSDs. The results show that the level of vibration to which the workers are exposed is well above acceptable levels defined by recognized standards and directives and that this vibration is combined with many other risk factors, thus representing a risk for the development of WMSDs.     

A test of two training interventions to prevent work-related musculoskeletal disorders of the upper extremity

We investigated, on behalf of a large electronics manufacturer, two types of worker training interventions for their efficacy in preventing unnecessary muscle tension and the symptoms of work-related musculoskeletal disorders. The first intervention, Muscle Learning Therapy (MLT), used electromyographic (sEMG) feedback and operant conditioning to decrease muscle tension during complex work tasks. The second intervention used adult learning and cognitive behavioral techniques in small group discussion to advance the worker's capabilities for symptom and stress management and problem-solving. Workers were randomly assigned to a control group or one of the two treatment conditions. Prior to training, baseline data were collected using symptom diaries and sEMG recordings of the trapezius and forearm muscles of the left and right arms. The training interventions were conducted for 6 weeks with reinforcement training provided at 18 and 32 weeks post-baseline. Follow-up data were collected after the initial 6-week training period and at 32 weeks, prior to the reinforcement training. Symptom outcomes demonstrated significant differences at 6 weeks, increasing in severity for the control group and declining modestly for the educational group, with little change for the MLT group. These differences were not maintained at further follow-up. The MLT group was consistently effective in reducing muscle tension in the trapezius areas after 6 and 32 weeks, and was partially effective for the forearms. Further testing is recommended of these training interventions, especially with the inclusion of strategic, periodic reinforcement of the worker's learning.     

The nature of work-related neck and upper limb musculoskeletal disorders

The nature of work-related musculoskeletal disorders of the neck and upper limbs is reviewed using both scientific data and the consensus view of experts, union bodies and government agencies across the European Union. Work-related musculoskeletal disorders describe a wide range of inflammatory and degenerative diseases and disorders. These conditions result in pain and functional impairment and may affect, besides others, the neck, shoulders, elbows, forearms, wrists and hands. They are work-related when the work activities and work conditions significantly contribute to their development or exacerbation but are not necessarily the sole determinant of causation. The classification and the need for standardised diagnostic methods for assessment of neck and upper limb musculoskeletal disorders are reviewed. These disorders are a significant problem within the European Union with respect to ill health, productivity and associated costs. The pathomechanisms of musculoskeletal disorders affecting tendons, ligaments, nerves, muscle, circulation and pain perception are reviewed and conceptual models for the pathogenesis of musculoskeletal disorders affecting the neck and upper limbs are presented. The epidemiological evidence on the work-relatedness of these disorders is discussed. A relationship between the performance of work and the occurrence of neck and upper limb musculoskeletal disorders is evident. Intervention strategies in the workplace for the reduction of both exposure and effect should focus upon factors within the work organisation as well as actively involving the individual worker. The current knowledge is sufficient to enable informed decisions to be made on future research needs and prevention strategies at the societal, organisational and individual level.     

Reproducibility of a self-report questionnaire for upper extremity musculoskeletal disorder risk factors.

A self-report questionnaire was developed to evaluate the potential for assessment of possible risk factors for musculoskeletal disorders. Visual-analog and categorical scales were designed to represent responses relating to primary work as well as a second job and hobbies or non-work activities. 71 tree nursery workers completed the scales twice in consecutive weeks. Agreement between means of the two questionnaire administrations was 0.80 or higher for all scales. Intraclass correlation coefficients ranged between 0.59 and 0.69 for the primary job hand/wrist responses and between 0.49 and 0.82 for non-work/hobby neck and upper arm scales. These results show potential for future application of similar scales in industry or temporary and seasonal work to evaluate exposure to upper extremity risk factors.     

The influence of VDT work on musculoskeletal disorders

Relationships between visual display terminal (VDT) use and musculoskeletal problems were examined in a group of 353 office workers, using data from medical and workplace investigations as well as questionnaires. There were no general differences between VDT and non-VDT users as to the occurrence of muscle problems. Combinations of specific VDT work situations such as data entry work or work with a VDT for more than 20 h/week and the presence of some other factors were, however, associated with excess risks of certain muscle problems. The extraneous factors involved in the definitions of such risk groups were: use of bifocal or progressive glasses at a VDT; stomach-related stress reactions; limited rest break opportunity, repetitive movements; non-use of lower arm support; and possibly the vertical position of the keyboard; and presence of specular glare.     

The effect of upper extremity support on upper extremity posture and muscle activity during keyboard use

Forearm support during keyboard use has been reported to reduce neck and shoulder muscle activity and discomfort. However, the effect of forearm support on wrist posture has not been examined. The aim of this study was to examine the effect of 3 different postures during keyboard use: forearm support, wrist support and "floating". The floating posture (no support) was used as the reference condition. A wrist rest was present in all test conditions. Thirteen participants completed 20 min wordprocessing tasks in each of the test conditions. Electromyography was used to monitor neck, shoulder and forearm muscle activity. Bilateral and overhead video cameras recorded left and right wrist extension, shoulder and elbow flexion and radial and ulnar deviation. The forearm support condition resulted in significantly less ulnar deviation (p < or = 0.007), less time spent in extreme ulnar deviation (p = 0.002) and less reports of discomfort than the "floating" condition (p = 0.002). The wrist support but not the forearm support condition resulted in less trapezius and anterior deltoid muscular activity (p < 0.007). These findings indicate that typing with upper extremity support in conjunction with a wrist rest may be preferable to the "floating" posture implicit in current guidelines.     

Comparison of self-report, video observation and direct measurement methods for upper extremity musculoskeletal disorder physical risk factors

The prevention of work-related musculoskeletal disorders has become a national priority in many countries. Increasingly, attempts are made to quantify those exposures that increase risk in order to set exposure limit values. This study used commonly employed field measurement methods and tools in order to perform an inter-method comparison between three primary methods of risk factor exposure assessment: self-report questionnaires, observational video analysis and direct measurement. Extreme posture duration, repetition, hand force (estimated from electromyography) and movement velocity were assessed for 18 subjects while performing each of three jobs processing tree seedlings. Results indicated that self-reports were the least precise assessment method, which consistently overestimated exposures for each of the measured risk factors. However, adjustment of the reports as psychophysical scales may increase agreement on a group level. Wrist flexion/extension duration and repetition were best measured by electrogoniometer. Electrogoniometric measures of wrist deviation duration and frequency were less precise than video analysis. Forearm rotation duration and repetition, grip force and velocity appeared to be best quantified by direct measurement as measured by electrogoniometer and electromyography (EMG) (as root-mean-square amplitude). The results highlight the fact that it is as important to consider and report estimated measurement error in order to reduce potential exposure misclassification in epidemiologic studies.     

Comparison of self-report,video observation and direct measurement methods for upper extremity musculoskeletal disorder physical risk factors

The prevention of work-related musculoskeletal disorders has become a national priority in many countries. Increasingly, attempts are made to quantify those exposures that increase risk in order to set exposure limit values. This study used commonly employed field measurement methods and tools in order to perform an inter-method comparison between three primary methods of risk factor exposure assessment: self-report questionnaires, observational video analysis and direct measurement. Extreme posture duration, repetition, hand force (estimated from electromyography) and movement velocity were assessed for 18 subjects while performing each of three jobs processing tree seedlings. Results indicated that self-reports were the least precise assessment method, which consistently overestimated exposures for each of the measured risk factors. However, adjustment of the reports as psychophysical scales may increase agreement on a group level. Wrist flexion/extension duration and repetition were best measured by electrogoniometer. Electrogoniometric measures of wrist deviation duration and frequency were less precise than video analysis. Forearm rotation duration and repetition, grip force and velocity appeared to be best quantified by direct measurement as measured by electrogoniometer and electromyography (EMG) (as root-mean-square amplitude). The results highlight the fact that it is as important to consider and report estimated measurement error in order to reduce potential exposure misclassification in epidemiologic studies.     

The development of the Quick Exposure Check (QEC) for assessing exposure to risk factors for work-related musculoskeletal disorders

This paper describes the development and evaluation of the Quick Exposure Check (QEC), which is an observational tool developed for Occupational Safety and Health (OSH) practitioners to assess exposure to risks for work-related musculoskeletal disorders and provide a basis for ergonomic interventions. The tool is based on epidemiological evidence and investigations of OSH practitioners' aptitudes for undertaking assessments. It has been tested, modified and validated using simulated and workplace tasks, in two phases of development, with participation of 206 practitioners. The QEC allows the four main body areas to be assessed and involves practitioners and workers in the assessment. Trials have determined its usability, intra- and inter-observer reliability, and validity which show it is applicable to a wide range of working activities. The tool focuses primarily on physical workplace factors, but also includes the evaluation of psychosocial factors. Tasks can normally be assessed within 10min. It has a scoring system, and exposure levels have been proposed to guide priorities for intervention. Subsequently it should be used to evaluate the effectiveness of any interventions made. The QEC can contribute to a holistic assessment of all the elements of a work system.     

Assessing exposure to risk factors for work-related musculoskeletal disorders using Quick Exposure Check (QEC) in taxi drivers

Work-related musculoskeletal disorders (WMSDs) are a common health problem throughout the world. This study aimed to examine the risk factors that are involved in the development of WMSDs in taxi drivers. In total 382 taxi drivers were observed using Quick Exposure Check (QEC) observational tool, which allows practitioners and workers to assess four key areas of the body. Results of the QEC scores were found to be very high for the shoulder/arm, wrist/hand and neck, whereas the scores for the back were found to be high for static use and moderate for moving. The results also showed that the occupational risk factors for WMSDs were associated with restricted postures, repetitive movements, vibration, work related stress. Essential ergonomic interventions are needed to eliminate risk of exposures to WMSDs in taxi drivers.Relevance to industryThe study results have relevance for ergonomists, health and safety practitioners as well as the drivers themselves, and helpful for estimating the main physical risk factors for WMDSs before choosing a method prior to an ergonomic intervention in industry.     

Investigation of oil palm harvesting tools design and technique on work-related musculoskeletal disorders of the upper body

The oil palm industry is one of the important sectors in Malaysia. The growth and development of this industry shows that Malaysia is the world second-largest oil palm producers. However, in the fresh fruit bunch (FFB) harvesting process, the harvesters are exposed to many types of work-related musculoskeletal disorders (WMSDs). The FFB harvesters tend to develop WMSDs especially the shoulders and trunk. Hence, it is important to identify the exposure levels, awkward postures and the reaction forces of muscle activity based on the posture and movement of the harvesters when using pole, chisel and loading spike during the harvesting process. The objective of this study was to investigate the effect of the design of oil palm FFB harvesting tools on WMSDs of the upper body. Rapid Upper Limb Analysis (RULA) was used to investigate and assess the exposure level on the harvester body during the harvesting process. The assessment showed that the shoulders and trunk have high exposure level and undergo awkward posture. Human Musculoskeletal Model Analysis (HMMA) was used to identify the reaction force exerted on the muscle during the FFB harvesting process. In this study, 4 muscles were analysed including Triceps, Biceps, Erector Spinae and Psoas Major. The highest reaction force of 16.36 N was found on the left triceps when handling a loading spike. In conclusion, it is important to address the risks by reviewing all possible aspects that contribute to the WMSDs and interventions on the tool design, task and working shifts may be required.     

Effect of key size and activation area on the performance of a regional error correction method in a touch-screen QWERTY keyboard

Manual text entry, which is one of the main features of mobile communications devices, decreases the competitive advantages of full touch-screen interfaces over physical interfaces. Especially for small full QWERTY keyboards, text entry becomes more problematic because of the small size of the virtual keys, absence of tactile feedback, and occlusion of virtual keys by fingers. One solution to this problem is the regional error correction, which is a predictive text entry method that activates the key corresponding to the actual activation point and also other keys within an activation area. This study investigates how the size of keys and of the activation area affect the accuracy of the regional error correction and compares the regional error correction method with the conventional finger touch method, for a touch-screen QWERTY keyboard. The regional error correction reduced both the time and the number of touches required to complete text entry when keys were small, but no difference was observed when keys were large. Users’ subjective assessments of ease of use and preference indicated greater satisfaction with the regional error correction method than without it, regardless of key size.Relevance to industry: The result of this study can be used to speed and simplify text entry in mobile devices with full-QWERTY virtual keyboards.     

Updating reference values and predictive models of the OCRA method in the risk assessment of work-related musculoskeletal disorders of the upper limbs

A database has been established combining existing data for 23 groups of workers with different level of exposure to repetitive movements of the upper limbs. For all groups, data were available regarding an exposure index (OCcupational Repetitive Actions - OCRA index) and clinically determined UL-WMSDs outcomes (PA = Prevalence of workers affected by one or more UL-WMSDs; PC = Prevalence of single diagnosed cases of an UL-WMSDs). Using these data, new critical values of the OCRA index have been estimated for discriminating different exposure levels (green, yellow, red areas) and new forecasting models of expected PA and PC in exposed populations based on OCRA exposure indexes. The new critical values of the OCRA index were estimated by an original approach in which data for the effect variable (PA) in a reference population not exposed to the relevant risks are combined with the regression function between OCRA and PA. The best simple regression functions between OCRA exposure indexes and health outcomes variables (PA; PC) were researched to obtain forecasting models of effects starting from exposure. Discussion of the results obtained considers their intrinsic limitations, as they are based on prevalence studies, as well as providing recommendations and cautions in the use of the proposed classification system and forecasting models when the OCRA method is applied.     

Comparison of OWAS,RULA and REBA for assessing potential work-related musculoskeletal disorders

This study compared three representative observational methods for assessing musculoskeletal loadings: Ovako Working Posture Analysis System (OWAS), Rapid Upper Limb Assessment (RULA), and Rapid Entire Body Assessment (REBA). The comparison was based on 209 cases of upper-body musculoskeletal disorders (MSDs) diagnosed by medical doctors. The most awkward/stressful posture in each participant's tasks was assessed using these techniques. Postural loadings were rated more highly by the RULA than by the OWAS and REBA (p < 0.01). The chi-square test and logistic regression analysis showed that only RULA grand score and action level, and REBA action level were associated with MSD work-relatedness (p < 0.01, p < 0.05, and p < 0.05, respectively). The percentage concordant values of the logistic model for the RULA grand score and action level were 52.4% and 44.8%, respectively, while the percentage concordant value for the REBA action level was 22.1%. Therefore, the RULA may be the best system for estimating the postural loads and work-relatedness of MSDs.Relevance to industryWork-related musculoskeletal disorders are the leading cause of workplace disability in the developed countries. For preventing the disorders, quantification of musculoskeletal loads is required.