Effect of four computer keyboards in computer users with upper extremity musculoskeletal disorders (original) (raw)
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Use of keyboards and symptoms in the neck and arm: evidence from a national survey
Occupational Medicine, 2001
The objective of this study was to examine the relationship between upper limb symptoms and keyboard use in a population survey. A questionnaire was mailed to 21 201 subjects aged 16-64 years, selected at random from the registers of 34 British general practices. Information was collected on occupation and on regular use of keyboards (for >4 h in an average working day), pain in the upper limbs and neck, numbness or tingling in the upper limbs, headaches, and feelings of tiredness or stress. Associations were explored by logistic regression, with the resultant odds ratios converted into prevalence ratios (PRs). Among 12 262 respondents, 4899 held non-manual occupations. These included 1871 regular users of keyboards (e.g. computer operators, data processors, clerks, administrators, secretaries and typists). Pain in the neck or upper limbs and sensory symptoms were common in the non-manual workers overall (with 1 week period prevalences of 30 and 15%, respectively), and were associated with older age, smoking, headaches and tiredness or stress. After adjustment for these factors, regular keyboard use was significantly associated with pain in the past week in the shoulders (PRs 1.2-1.4) and the wrists or hands (PR 1.4), but not with elbow pain or sensory symptoms over the same period, or with neck or upper limb pain that prevented normal activities in the past year. Disabling symptoms were somewhat less prevalent among symptomatic keyboard users than among other symptomatic workers. We conclude that use of keyboards was associated with discomfort at the shoulder and wrist or hand, but risk estimates were lower than generally reported in workplace surveys. Previous estimates of risk in the occupational setting may have been biased by shared expectations, concerns, or other aspects of illness behaviour.
The effect of six keyboard designs on wrist and forearm postures
Applied Ergonomics, 2007
There is increasing evidence that alternative geometry keyboards may prevent or reduce arm pain or disorders, and presumably the mechanism is by reducing awkward arm postures. However, the effect of alternative keyboards, especially the new designs, on wrist and arm postures are not well known. In this laboratory study, the wrist and forearm postures of 100 subjects were measured with a motion analysis system while they typed on 6 different keyboard configurations. There were significant differences in wrist extension, ulnar deviation, and forearm pronation between keyboards. When considering all 6 wrists and forearm postures together, the keyboard with an opening angle of 121, a gable angle of 141, and a slope of 01 appears to provide the most neutral posture among the keyboards tested. Subjects most preferred this keyboard or a similar keyboard with a gable angle of 81 and they least preferred the keyboard on a conventional laptop computer. These findings may assist in recommendations regarding the selection of keyboards for computer usage. r
Applied Ergonomics, 2004
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 (op ¼ 0:007), less time spent in extreme ulnar deviation (p ¼ 0:002) and less reports of discomfort than the ''floating'' condition (p ¼ 0:002). The wrist support but not the forearm support condition resulted in less trapezius and anterior deltoid muscular activity (po0:007). 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. r
Keyboard Design? Postural behavior evaluation during interaction with keyboards and typewriters
2008
The study has evaluated macro and micro postural analysis and angular relationships of the main anatomical segments involved in the activity of typewriting in old typewriters and current computer keyboards. Our protocol consider this objects with the goals to identify and to rescue structural benefits of the old typewriters that were not incorporated in the current design of keyboards for computers, as well as those activities' aspects and properties. As results, we have that some old typewriters' attributes which were not considered for the design of new computer keyboards can contribute to reduce the wrist overload.
An assessment of alternate keyboards using finger motion, wrist motion and tendon travel
Clinical Biomechanics, 2000
Objective. To assess the biomechanical impact of commercially available alternate keyboard designs. Design. A repeated measures study was conducted in a laboratory setting, with planned comparisons of Pitch, Roll and Yaw angles of the keyboards. Ten keyboard conditions were tested. Dependent measures included tendon travel, wrist deviations, and wrist and ®nger kinematics. Background. Various alternate keyboard designs have recently been introduced, which vary Pitch, Roll and Yaw angles, separation distance between keyboard halves, and include other novel features such as cup-shaped depressions for the keys. Yet little objective research has been conducted regarding the biomechanical implications of these various design features. This study attempts to quantify the keyboard designs in terms of several recognized risk factors associated with cumulative trauma disorders that arise with repetitive typing. Methods. Wrist and ®nger goniometers were used to measure joint motions during a standardized typing task. 15 experienced typists (8 women, 7 men) served as subjects. Regression equations were used to generate estimates of tendon travel. Results. Tendon travel was aected primarily by Pitch but not Roll or Yaw angles while wrist deviations responded to changes in all three angles. Males had signi®cantly greater amount of tendon travel than female subjects; this dierence was only partially accounted for by anthropometry. Dierences in joint motion may have a greater impact on the amount of tendon travel. Conclusions. Alternate keyboard designs can aect tendon travel by as much as 11%. Relevance As various alternate keyboard designs are marketed, quanti®able biomechanical data such as that provided by this study, will help to assess their impact on the risk factors for cumulative trauma disorders.
Journal of Occupational Rehabilitation, 2010
Introduction This cross-sectional study examined the effect of structural changes caused by rheumatoid arthritis (RA) on computer keyboarding style to provide insights on how changes may affect worker performance. Method Computer keyboarding styles, as measured by the keyboard-personal computer style instrument, were compared between 45 keyboard operators with RA and 29 without. A severity of structural changes score (SSCS) was assigned after recruitment by observing subjects' hands while operating a keyboard. Significant differences between each item of keyboarding style by diagnosis were identified through Chi square analyses. Logistic regression models with age, diagnosis, SSCS, and touch typing training as the predicators further evaluated the effect of structural changes on each item of personal keyboarding style. Results Significantly more keyboard operators with RA used high force keystrokes, did not use a wrist rest, moved their hands to strike keys, maintained their wrists and fingers in a fixed position and used fewer than two fingers to activate keys. The amount of variance explained by each model varied from 8 to 56%. SSCS was the most common predictor of keyboarding style (54% of significant models), followed by age (35% of significant models), diagnosis (19% of significant models), and touch typing training (15% of significant models). Conclusion Severity of structural changes and age are significant predictors of keyboarding style for computer operators with RA. The keyboarding styles used by computer operators with RA appear to reduce typing productivity and have the potential to put stress on joints already affected by RA. Computer operators with RA may benefit from worksite modifications that address keyboarding style such as alternate keyboards.
Effects of a Multitouch Keyboard on Wrist Posture, Typing Performance and Comfort
PsycEXTRA Dataset, 2005
The design of computer keyboards is rapidly evolving as portable computing becomes increasingly ubiquitous due to wireless networking and the increased popularity of personal digital assistants and notebook computers. However, there is a balance between mobility and productivity, in terms of text-entry accuracy and speed, which needs to be maintained as computer keyboards become smaller and slimmer through the introduction of ultra low-profile designs. In addition, the ergonomic benefits, in terms of the reduction of awkward wrist postures and user comfort, of ultra-low profile designs are unclear. This study tests a new prototype ultra-low profile MultiTouch keyless keyboard (MTK) that uses a MultiTouch surface to create an extremely thin typing environment that requires no force to register a keystroke and allows mousing and gestural input on the same surface. In this study, the MTK was tested against a conventional keyboard (CK) for typing speed, accuracy, wrist postures and user comfort. It was hypothesized that the lack of key travel would increase speed and accuracy, while the ultra-thin design would reduce the amount of wrist extension, which could decrease the risk of a wrist injury or other hand and wrist musculoskeletal disorder. Finally, it was hypothesized that there would be a significant short-term learning effect on typing speed and accuracy for the MTK. A laboratory experiment was conducted with 6 males and 6 females typing using two QWERTY keyboard designs: a CK and a MTK. Subjects visited the lab for 1.5 hours for 2 non-consecutive days in the same week, for a total of 3 hours. Each visit consisted of eight randomly assigned 7.5-minute typing tasks of text passages of similar difficulty and identical length. Quantitative measures of typing speed and accuracy were collected using Typing Quick and Easy 13.0 and qualitative measures of user preference and comfort were gathered by self-report questionnaires. A wrist glove electrogoniometer system was used to record right-hand wrist positioning data, which was analyzed to assess the risk of injury. The two keyboards were evaluated in a repeated measures withinsubjects factorial design. Subjects, typed slower (F 1,11 = 41.86, p=0.000) and less accurately (F 1,11 = 23.55, p=0.001) on the MTK during the typing tasks. Subjects preferred the CK and reported a higher level of ease (F 1,11 = 49.732, p=0.00) and enjoyment (F 1,11 = 51.129, p=0.00) during its use. Mean wrist extension was lower for the MTK (F 1,11 = 10.205, p=0.000) while radial and ulnar deviation did not differ significantly between the two keyboards. The MTK had a lower percentage of highest-risk wrist extension (F 1,11 = 6.437, p=0.028), and conversely, a higher percentage of neutral wrist posture (F 1,11 = 12.947, p=0.004). A significant positive linear trend was observed across the within-subjects scores for speed (F 1,11 = 9.308, p=0.011) and accuracy (F 1,11 = 11.903, p=0.005) across tasks in the MTK condition. Limitations to this study include practice effects, due to the naïve subjects' lack of training on the MTK and the limited duration of exposure to this novel keyboard. Fatigue effects may have also been a factor, even though the experimental conditions were spread out over two non-consecutive days in the same week. Future research directions include additional testing of the unique mousing and gestural capabilities of the MTK. Other research suggests that practice and extended exposure to the MTK may raise performance to comparable levels associated with CK devices.
American Journal of Industrial Medicine, 2002
BackgroundDespite widespread recommendations regarding posture during computer use, associations between specific postures and musculoskeletal health are not well characterized.Despite widespread recommendations regarding posture during computer use, associations between specific postures and musculoskeletal health are not well characterized.MethodsSix hundred and thirty-two newly hired computer users were followed prospectively to evaluate associations between posture and neck or shoulder (N/S) and hand or arm (H/A) musculoskeletal symptoms and musculoskeletal disorders. Participants' postures were measured at entry and they reported symptoms on weekly diaries. Participants reporting symptoms were examined for specific disorders. Multivariate Cox regression models were used to estimate associations between postural variables and risk of symptoms and disorders, controlling for confounding variables.Six hundred and thirty-two newly hired computer users were followed prospectively to evaluate associations between posture and neck or shoulder (N/S) and hand or arm (H/A) musculoskeletal symptoms and musculoskeletal disorders. Participants' postures were measured at entry and they reported symptoms on weekly diaries. Participants reporting symptoms were examined for specific disorders. Multivariate Cox regression models were used to estimate associations between postural variables and risk of symptoms and disorders, controlling for confounding variables.ResultsKeying with an inner elbow angle > 121°, greater downward head tilt, and presence of armrests on the participants chair were associated with lower risk of N/S symptoms or N/S disorders. Keying with elbow height below the height of the “J” key and the presence of a telephone shoulder rest were associated with a greater risk of N/S symptoms or N/S disorders. Horizontal location of the “J” key > 12 cm from the edge of the desk was associated with a lower risk of H/A symptoms and H/A disorders. Use of a keyboard with the “J” key > 3.5 cm above the table surface, key activation force > 48 g, and radial wrist deviation of > 5° while using a mouse was associated with a greater risk of H/A symptoms or H/A disorders. The number of hours keying/week was associated with H/A symptoms and disorders.Keying with an inner elbow angle > 121°, greater downward head tilt, and presence of armrests on the participants chair were associated with lower risk of N/S symptoms or N/S disorders. Keying with elbow height below the height of the “J” key and the presence of a telephone shoulder rest were associated with a greater risk of N/S symptoms or N/S disorders. Horizontal location of the “J” key > 12 cm from the edge of the desk was associated with a lower risk of H/A symptoms and H/A disorders. Use of a keyboard with the “J” key > 3.5 cm above the table surface, key activation force > 48 g, and radial wrist deviation of > 5° while using a mouse was associated with a greater risk of H/A symptoms or H/A disorders. The number of hours keying/week was associated with H/A symptoms and disorders.ConclusionsThe results suggest that the risk of musculoskeletal symptoms and musculoskeletal disorders may be reduced by encouraging specific seated postures. Am. J. Ind. Med. 41:236–249, 2002. © 2002 Wiley-Liss, Inc.The results suggest that the risk of musculoskeletal symptoms and musculoskeletal disorders may be reduced by encouraging specific seated postures. Am. J. Ind. Med. 41:236–249, 2002. © 2002 Wiley-Liss, Inc.
Occupational and …, 2005
To examine the effect of two workstation and postural interventions on the incidence of musculoskeletal symptoms among computer users. Methods: Randomised controlled trial of two distinct workstation and postural interventions (an alternate intervention and a conventional intervention) among 376 persons using computer keyboards for more than 15 hours per week. The incidence of neck/shoulder symptoms and hand/arm symptoms during six months of follow up among individuals in the intervention groups was compared to the incidence in computer users who did not receive an intervention (comparison group). For individuals in the intervention groups, study staff adjusted workstations, where possible, and trained individuals to assume the intervention postures. Individuals reported musculoskeletal symptoms in a weekly diary. Participants who reported discomfort intensity of 6 or greater on a 0-10 visual analogue scale or who reported musculoskeletal symptoms requiring use of analgesic medication were considered symptomatic. Results: There were no significant differences in the incidence of musculoskeletal symptoms among the three intervention groups. Twenty two (18.5%) participants in the alternate intervention group, 25 (20.2%) in the conventional intervention group, and 25 (21.7%) in the comparison group developed incident arm or hand symptoms. Thirty eight (33.3%) participants in the alternate intervention group, 36 (31.0%) in the conventional intervention group, and 33 (30.3%) in the comparison group developed incident neck or shoulder symptoms. Compliance with all components of the intervention was attained for only 25-38% of individuals, due mainly to the inflexibility of workstation configurations. Conclusions: This study provides evidence that two specific workplace postural interventions are unlikely to reduce the risk of upper extremity musculoskeletal symptoms among computer users. Keyboard shoulder abduction of 210˚to 20N Keyboard inner elbow angle of 80˚to 100N Keyboard wrist ulnar deviation of 210˚to 10N Keyboard wrist extension of 210˚to 10N Keyboard wrist rest present N Mouse wrist ulnar deviation of 210˚to 10N Mouse wrist extension of 210˚to 10N Armrest present N High quality chair present Policy implications N The study provides no empirical basis for recommendation of one posture versus another for prevention of musculoskeletal symptoms among computer users. Main message N No differences in risk of musculoskeletal symptoms were observed among participants randomly assigned to two workstation and postural interventions in comparison to participants who received no workstation or postural intervention. *Head tilt angle is defined as the angle formed between a line defined by the tragion of the ear and the infraorbitale of the eye and the horizon. To clarify the meaning of head tilt angle values, increasing neck extension results in larger values for head tilt angle and increasing neck flexion results in smaller (including negative) values. **Characteristics of high quality chair: easily (pneumatically) adjustable for height, adjustable height backrest, full contoured backrest, adjustable seat pan angle, round waterfall seatpan edge, five legged base. 10a