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Design Features of Alternative Computer Keyboards: A Review of Experimental Data
Abstract
Design of computer keyboards no longer is limited to the flat keyboards that are typically shipped with personal computers. Keyboards now exist that are split into halves and these halves can be slanted away from each other (creating a triangle between the halves), sloped downward toward the visual display terminal, tilted upward like a tent, or simply separated. These design features are intended to alleviate discomfort and possible musculoskeletal disorders that have been suggested to be associated with the extensive use of conventional computer keyboards. The geometry of conventional keyboards requires the wrists to be in 10 degrees to 15 degrees of ulnar deviation and 20 degrees of extension and the forearms to be nearly fully pronated while typing. A review of the available experimental data collected on 10-digit touch typists indicates that (1) keyboards with a slant angle (half of the opening angle) of 10 degrees to 12.5 degrees or keyboards with halves separated to approximately shoulder width are both effective in placing the wrist in near neutral (0 degree) ulnar/radial deviation when typing, (2) wrist extension can be reduced to near neutral (0 degrees) when a keyboard with a negative slope of 7.5 degrees is used, contingent on the wrist rest also sloping with the keyboard, and (3) tilting the keyboard halves 20 degrees to 30 degrees is effective in reducing forearm pronation to approximately 45 degrees. These studies also indicate that experienced 10-digit touch typists readily adapt (within 10 minutes) to these individual alternative keyboard features, and can type with approximately the same speed and accuracy as with the conventional keyboard. While placing the wrist and forearm in a more neutral position could, in theory, reduce the incidence of musculoskeletal disorders, randomized controlled trials are necessary before strong recommendations can be made on the effectiveness of alternative keyboards for the prevention and/or treatment of musculoskeletal disorders. In the absence of these randomized controlled trials, the information in this article provides preliminary guidance to clinicians in their evaluation of computer keyboards and workstations and their recommendations to patients.
... Unfortunately, since this position paper came out, there have been very few studies that have examined the effect of alternative keyboards on musculoskeletal discomfort. While numerous studies indicate that split or angled keyboards effectively alter awkward postures typically associated with musculoskeletal discomfort and MSD [8,9] these studies do not generally evaluate the effect of alternative keyboards on discomfort directly. The studies were cross-sectional and were completed in laboratory settings with ideal workstation setups [10][11][12][13][14][15][16][17][18][19][20], thus, reducing their ecological validity in the workplace. ...
... Despite mixed evidence on their effectiveness, the use of alternative keyboards to prevent and reduce musculoskeletal discomfort continues in practice. Sales for split keyboards outrank standard keyboards in the United States [6], and at least a dozen different designs are available on the market [9]. If alternative keyboards continue to be marketed as a means to address discomfort, additional well-designed trials are needed to determine if they are effective. ...
... Study intervention included replacing each participant's current keyboard with an alternative and standard keyboard provided by the study team. The alternative keyboard was the Microsoft Natural Ergonomics 4000 (version 1.0), which has both a fixed slant angle to reduce ulnar deviation and a fixed tilt angle to reduce pronation [8,9]. The standard keyboard was Lenovo Model No. Ku-0225 (Morrisville, NC); this keyboard is flat and contains a broad, thin wrist rest. ...
There is limited research on the effectiveness of alternative keyboards in reducing discomfort in the workplace.
We hypothesized that participants using a fixed split-angle (alternative) keyboard would report significantly greater improvements in discomfort in comparison to those using a standard keyboard. Additionally, we hypothesized that at 5 months participants would significantly prefer the configuration of the alternative keyboard in comparison to the standard keyboard.
In this randomized cross-over trial 77 symptomatic computer operators used fixed split-angle or standard flat keyboards for five months in their workplace, then switched to the other keyboard. Discomfort was collected weekly using the Weekly Discomfort Survey and usability was measured monthly.
There was no significant keyboard by period effect on any discomfort measure. The number of participants with discomfort decreased dramatically in the first month of use, regardless of keyboard type, and this number remained relatively unchanged for the remainder of the study. Participants' ratings significantly favored the standard flat keyboard for usability.
This study does not support the use of fixed split-angle keyboards over standard flat keyboards to reduce discomfort in the workplace. Further research is needed to evaluate if subgroups of keyboard users might benefit.
... The distribution of physical keys has been investigated by Zhao et al. [9]. Pitch angle ("Slope Angle" [10], split angle ("slant angle" for split keyboards, and tilt angle ("tilt angle") have been extensively studied [10]. In a study with 18 subjects, Monty et al. find a strong influence of different keycap-sets and note the influence of "keycap size and shape, keycap spacing, reflectance of keycaps and housing" [11]. ...
... The distribution of physical keys has been investigated by Zhao et al. [9]. Pitch angle ("Slope Angle" [10], split angle ("slant angle" for split keyboards, and tilt angle ("tilt angle") have been extensively studied [10]. In a study with 18 subjects, Monty et al. find a strong influence of different keycap-sets and note the influence of "keycap size and shape, keycap spacing, reflectance of keycaps and housing" [11]. ...
... Marklin and Simoneau reported on the biomechanical loading effects of keyboard slope angle, opening angle, lateral inclination angle, and separation distance on distal upper extremity region postures and muscle activities as well as performance [60]. They reported that increasing slant angle was effective for reducing wrist ulnar deviation, specifically, that ulnar deviation could be reduced by nearly one degree for every degree increase in slant angle. ...
... Dennerlein also reported on the biomechanical loading effects of keyboard slope angle, opening angle, lateral inclination angle, and separation distance, with a similar interpretation of findings [20]. In line with Marklin and Simoneau [60], Dennerlein reported decreased ulnar deviation with increased slant angle, more neutral wrist postures with both increased separation distance and negative slope angle, and reduced forearm pronation and reduced performance with increased lateral inclination angle. However, in addition, Dennerlein also noted that keyboards with increased separation distance can increase shoulder external rotation. ...
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.
... This posture improvement is intended to minimize lateral arm positioning and reduce ulnar deviations of the hand, which reduce the risk of musculoskeletal disorders. Ergonomic keyboards are typically designed to place the wrists and forearms in a more neutral posture (Baker et al., 2007;Marklin and Simoneau, 2004) and can include slant/tilt features to alter key pressure and response. ...
... Since ergonomic (alternative) keyboards have quickly become the most frequently sold keyboards in the United States (Rempel, 2008), research has increasingly examined their effectiveness in terms of the keyboards' ergonomics and usability. Alternative keyboard use has been studied in relation to wrist/forearm posture, muscle activity, keystroke force, comfort, performance, and a myriad of other topics (Marklin and Simoneau, 2004;Marklin et al., 1999;Rempel et al., 2007Rempel et al., , 2009Smith et al., 1998;Swanson et al., 1997;Szeto and Ng, 2000). Studies have shown initial adoption of alternative keyboards is low because of their differentiation from traditional straight keyboards (Cakir, 1995;Tittiranonda et al., 1999). ...
Obesity in the workplace is associated with loss of productivity, high medical care expenses, and increased rates of work-related injuries and illness. Thus, effective, low-cost interventions are needed to accommodate the size of today's obese office worker while alleviating potential physical harm associated with musculoskeletal disorders. Utilizing a sample of 22 overweight and obese office workers, this pilot study assessed the impact of introducing an alternative, more ergonomically-sound keyboard on perceptions about design, acceptability, and usability; self-reported body discomfort; and typing productivity. Data were collected using self-reported questionnaires and objective typing tests administered before and after the intervention. The intervention duration was six weeks. After switching from their standard work keyboard to an alternative keyboard, all participants reported significant decreases in lower back discomfort (t = 2.14, P = 0.044); although obese participants reported significant decreases in both upper (t = 2.46, P = 0.032) and lower (t = 2.39, P = 0.036) back discomfort. No significant changes were observed in overall typing performance scores from baseline to follow-up. Findings suggest that such interventions may be introduced into the workforce with positive gains for workers without reducing short-term worker productivity.
... Two randomised controlled intervention studies have also demonstrated that the use of a split keyboard can reduce or prevent hand and arm pain and musculoskeletal disorders among computer users (Tittiranonda et al. 1999, Moore and Swanson 2003). The positive health effects of the split keyboards are likely due to the more neutral wrist and forearm postures associated with their use compared to the postures required during typing on a conventional keyboard (Kroemer 1972, Marklin and Simoneau 2004). These keyboards are split into two halves, one for each hand, and include an opening angle to reduce ulnar deviation, a raised centre (gable angle) to reduce pronation and a near flat front-to-back surface angle (slope) to reduce wrist extension (Marklin et al. 1999). ...
... These keyboards are split into two halves, one for each hand, and include an opening angle to reduce ulnar deviation, a raised centre (gable angle) to reduce pronation and a near flat front-to-back surface angle (slope) to reduce wrist extension (Marklin et al. 1999). The underlying health basis for the split design may be from the neutral wrist and forearm postures, which reduce forearm muscle loads and pressures in the carpal tunnel (Marek et al. 1992, Marklin and Simoneau 2004, Rempel et al. 2008). While a number of studies have compared wrist and forearm postures during typing on a split geometry keyboard to a conventional keyboard (Smith et al. 1998, Marklin et al. 1999, Tittiranonda et al. 1999, Zecevic et al. 2000, Rempel et al. 2007), few studies have evaluated the effects of changes in geometry within a split keyboard design (Nakaseko et al. 1985, Honan et al. 1995). ...
Split, gabled keyboard designs can prevent or improve upper extremity pain among computer users; the mechanism appears to involve the reduction of awkward wrist and forearm postures. This study evaluated the effects of changes in opening angle, slope and height (independent variables) of a gabled (14 degrees) keyboard on typing performance and upper extremity postures. Twenty-four experienced touch typists typed on seven keyboard conditions while typing speed and right and left wrist extension, ulnar deviation, forearm pronation and elbow position were measured using a motion tracking system. The lower keyboard height led to a lower elbow height (i.e. less shoulder elevation) and less wrist ulnar deviation and forearm pronation. Keyboard slope and opening angle had mixed effects on wrist extension and ulnar deviation, forearm pronation and elbow height and separation. The findings suggest that in order to optimise wrist, forearm and upper arm postures on a split, gabled keyboard, the keyboard should be set to the lowest height of the two heights tested. Keyboard slopes in the mid-range of those tested, 0 degrees to -4 degrees, provided the least wrist extension, forearm pronation and the lowest elbow height. A keyboard opening angle in the mid-range of those tested, 15 degrees, may provide the best balance between reducing ulnar deviation while not increasing forearm pronation or elbow separation. These findings may be useful in the design of computer workstations and split keyboards. The geometry of a split keyboard can influence wrist and forearm postures. The findings of this study are relevant to the positioning and adjustment of split keyboards. The findings will also be useful for engineers who design split keyboards.
... Short edit-execution cycles, such as numerical parameter adjustments, are unlikely to enter conscious awareness, as this may take up to a few milliseconds. An average typing speed is 60-80 words per minute (wpm), or 3-4 characters per second (Marklin and Simoneau 2004). Short edits may be performed even faster than that, potentially approaching the upper limits of delayed auditory feedback, as the fastest typists can exceed several hundred wpm. ...
This article explores the similarities and differences between live coding and traditional music performances. The focus is on how bodily movements are expressed and whether pre-reflective processes may be activated during a live coding performance. While reports from practitioners vary on percepts of embodiment, the community is missing a theoretical background that reflects on practice. Understanding pre-reflective processes in live coding can benefit performance practices and tool development. As a live coder, I reflect on personal experiences and explore what I call ‘interactivity variations’, a term to denote different gestural manners of interactions during a performance. I observe patterns of embodiment among various live coders who use diverse performance systems from online videos. Out of 11 examples of performance systems, two cases demonstrate interactivity variations that can activate pre-reflective processes while another exploits direct manipulation. I present some implications for the patterns of bodily movement during a live coding performance and discuss how descriptive and prescriptive notation can be important and potentially influence our sensorimotor network. The article contributes a first account of a sensorimotor theory on live coding performances, reflecting on practice and embodied music cognition by presenting an aesthetic analysis of 11 online video examples.
... Decades of research into ergonomic keyboards seem to have had no impact on the procurement of appropriate devices (Turisova and Sinay, 2016). Research has extensively investigated different designs such as angular positions of the hand halves (Tittiranonda et al., 1999;Emerson, Emerson and Fedorczyk, 2021;Otte, 2021), pitch angles (Marklin and Simoneau, 2004;McLoone et al., 2010) or physical key arrangements (Scott et al., 2010;Tasaka and Akioka, 2018;Zhao et al., 2021). ...
Ergonomically designed devices for better workplace design get too little at-tention compared to the annual cost of long-term damage. To help workers better achieve their goals in their work environment, we explore small-step changes that any individual can make with many existing keyboards. We studied the keyboards that users have been using as their daily keyboards for at least a year. In an investigation with baseline and treatment phase we pro-vide the users with 800 keycaps of different shapes, colors and surfaces and let them experiment for 3 months during their daily work. The evaluation shows that users were able to reduce the time for daily operations by 12% and halve the number of looks at the keyboard.
... Repeated stereo-typical movements could lead to upper limb pain (Waersted et al., 2010), although the evidence is limited. Extensive computer keyboard use has been reported to lead to distal upper limb problems (Marklin and Simoneau, 2004), and excessive use of electronic games (Brasington, 1990) and smart phone (Fernandez-Guerrero, 2014) as lead to hand tendon inflammation. However the movement patterns of children with the newer touch screen technology may be different, with different risk. ...
Young children (ages 3 to 5) are using mobile touchscreen technology, including tablet computers, yet little is known on the potential musculoskeletal and physical activity implications of its use. This within-subject laboratory study (n = 10) examined head, trunk and arm postures, upper trapezius muscle activity, and total body and upper limb physical activity during playing with tablets compared to during TV watching and playing with non-screen toys. Overall, this study found that during tablet play children had greater mean head, trunk and upper arm angles compared to both TV watching and toy play. Conversely, compared to toy play, children playing with tablets had lesser trunk, upper arm and elbow postural variation, lesser trapezius activity, more time sitting and lesser physical activity. Thus, to minimize potential musculoskeletal and sedentary risks, non-screen toy play should be encouraged and education and guidelines provided for parents and caretakers to support wise use of tablets.
... Qin et al. [18] studied 10 healthy subjects' internal loads on hand and forearm musculature while tapping in different wrist postures and found that the nonneutral wrist postures resulted in greater muscle stresses than the neutral posture. This association between nonneutral postures during computer work and symptoms was taken into account in ergonomic guidelines, which recommend avoiding non-neutral postures [19][20][21]. ...
Recently, computer, mobile phone, and Internet use has increased. This study aimed to determine the possible relation between self-reported wrist and finger symptoms (aches, pain, or numbness) and using computers/mobile phones, and analyze how the symptoms are specifically associated with utilizing desktop computers, portable computers or mini-computers, and mobile phones. A questionnaire was sent to 15,000 working-age Finns (between the ages of 18–65). Via a questionnaire, 723 persons reported wrist and finger symptoms often or more. Over 80% use mobile phones daily and less than 30% use desktop computers or the Internet daily at leisure. For example, over 89.8% had quite often or often experienced pain, numbness, or aches in the neck, and 61.3% had aches in hips and the lower back. Only 33.7% connected their symptoms to computer use. In the future, the development of new devices and Internet services should incorporate the ergonomics of the hands and wrists.
... Conventionally, in QWERTY keyboards all letters to the left of (and including) hti, hgi, and hvi are mostly typed with the left hand. Instead, all remaining letters are typically typed with the right hand (Marklin & Simoneau, 2004). While our three verb blocks involved more left-than right-sided keystrokes [F(1, 9) = 83.96, ...
... Repeated stereo-typical movements could lead to upper limb pain (Waersted et al., 2010), although the evidence is limited. Extensive computer keyboard use has been reported to lead to distal upper limb problems (Marklin and Simoneau, 2004), and excessive use of electronic games (Brasington, 1990) and smart phone (Fernandez-Guerrero, 2014) as lead to hand tendon inflammation. However the movement patterns of children with the newer touch screen technology may be different, with different risk. ...
... It is anticipated that the postural improvements promoted by the final production mouse will follow the trends of the postural and musculoskeletal health improvements associated with split keyboard designs. With split keyboard designs, early research demonstrated improvements in posture and subjective comfort [17,20,24]. These improvements were later linked with long term comfort benefits and a reduction in the risk of musculoskeletal disorders and symptoms [23]. ...
Background:
Modern computer users use the mouse almost three times as much as the keyboard. As exposure rates are high, improving upper extremity posture while using a computer mouse is desirable due to the fact that posture is one risk factor for injury. Previous studies have found posture benefits associated with using alternative mouse designs, but at the cost of performance and preference.
Objective:
To develop new computer mouse shapes, evaluate them versus benchmarks, and determine whether there are differences in wrist posture, pointing performance, and subjective measures.
Method:
Three concept mice were designed and evaluated relative to two existing benchmark models: a traditional flat mouse, and an alternative upright mouse. Using a repeated measures design, twelve subjects performed a standardized point-and-click task with each mouse. Pointing performance and wrist posture was measured, along with perceived fatigue ratings and subjective preferences pre and post use.
Results:
All of the concept mice were shown to reduce forearm pronation relative to the traditional flat mouse. There were no differences in pointing performance between the traditional flat mouse and the concept mice. In contrast, the fully vertical mouse reduced pronation but had the poorest pointing performance. Perceived fatigue and subjective preferences were consistently better for one concept mouse.
Conclusion:
Increasing mouse height and angling the mouse topcase can improve wrist posture without negatively affecting performance.
... 20 As the repeated use of any tool can cause RMI 9 , the safety of the standard keyboard as a tool deserves evaluation. Studies have found that the standard keyboard forces its users to align their hands, forearms, and fingers in unnatural postures, causing marked ulnar deviation of the wrist and other unnatural postures which can cause a range of repetitive motion injuries 21,22,23,24 While studies in hand kinematics have supported the design of alternative, ergonomic keyboards designed to increase comfort. 25 Keyboard operators have been slow to accept alternative keyboards; the next section explores the issues underlying the question of why. ...
... These non-neutral wrist postures have been associated with arm/hand symptoms among computer users (Wahlstrom, 2005). Ergonomic guidelines recommend avoiding non-neutral postures during computer work (Hedge and Powers, 1995;Occupational Safety and Health Administration, 1997;Marklin and Simoneau, 2004). Despite abundant epidemiologic evidence of association between awkward wrist postures and musculoskeletal symptoms/disorders, little is known about how internal tissue loading is affected by joint posture during computer use. ...
Non-neutral wrist posture is a risk factor of the musculoskeletal disorders among computer users. This study aimed to assess internal loads on hand and forearm musculature while tapping in different wrist postures. Ten healthy subjects tapped on a key switch using their index finger in four wrist postures: straight, ulnar deviated, flexed and extended. Torque at the finger and wrist joints were calculated from measured joint postures and fingertip force. Muscle stresses of the six finger muscles and four wrist muscles that balanced the calculated joint torques were estimated using a musculoskeletal model and optimization algorithm minimizing the squared sum of muscle stress. Non-neutral wrist postures resulted in greater muscle stresses than the neutral (straight) wrist posture, and the stress in the extensor muscles were greater than the flexors in all conditions. Wrist extensors stress remained higher than 4.5 N/cm² and wrist flexor stress remained below 0.5 N/cm² during tapping. The sustained high motor unit recruitment of extensors suggests a greater risk than other muscles especially in flexed wrist posture. This study demonstrated from the perspective of internal tissue loading the importance of maintaining neutral wrist posture during keying activities.
... These studies are summarized by large systematic reviews (Brewer et al., 2006;Verhagen, Karels, & Bierma-Zeinstra, 2006). Through the 2000s, there were more laboratory studies investigating the effects of split geometry keyboard designs on postures and tissue loads (Simoneau, Marklin, & Berman, 2003;Marklin & Simoneau, 2004;Rempel, Barr, Brafman,&Young, 2007;Rempel, Keir, & Bach, in press;Rempel, Nathan-Roberts, Chen, & Odell, in press). These studies tended to evaluate more subtle differences in keyboard design changes on posture than during the previous decade. ...
The author reviews the paper by Kroemer (1972) on the design of the split geometry keyboard and the subsequent 35 years of research on the topic.
It was first suggested in the 1920s that arm strain in the typist could be reduced by splitting the keyboard into two halves and inclining the two halves laterally. The first systematic research on the split keyboard was conducted by Kroemer in the 1960s and published in his 1972 article.
The literature on split geometry keyboards was identified, and the progression of the research was reviewed.
The Kroemer article marked the beginning of a prolonged, worldwide research effort to determine whether and how the split keyboard design might improve comfort and prevent pain in keyboard users.
In the early 1990s, split keyboard designs began to be broadly commercially available. Clear evidence of a health benefit of the split keyboards emerged in the late 1990s. By 2006, a split keyboard was the number one-selling keyboard, of all keyboards sold, in the U.S. retail market.
The history of research on this topic, the challenges to changing the conventional design, and the broader acceptance of the split design are a success story with lessons for all of us.
"Human engineering the keyboard" was the topic of my 1970 technical report (AMRL-TR-69-141), re-printed 1972 in Human Factors 14(1), 51-63. Now, 40 years later, it is of some interest to revisit that topic. Copyright 2010 by Human Factors and Ergonomics Society, Inc. All rights reserved.
Fixed-split, ergonomic keyboards have been shown to reduce awkward wrist postures while maintain typing performance and improve the functional and medical status of those persons with hand pain as well as reduce the likelihood of developing signs and symptoms of musculoskeletal disorders such as carpal tunnel syndrome compared to typists using traditional, straight keyboards. Yet, the design can be improved. This paper describes the basic research, inspiration, and participatory design approach as well as the organizational obstacles in creating the new Microsoft® Natural® Ergonomic Keyboard 4000. The ergonomist had to overcome staid thinking in questioning the fundamental assumptions about the ergonomics of keyboard design and to overcome the product design paradigm of only fixing problems from stated and unstated user needs compared with realizing innovative designs that the average user cannot articulate or consider. An iterative design process resulted in a new ergonomic keyboard with a steeper gable angle, a curved key bed, a taller palm rest, and a palm rest lifter for a truly negative slope.
Knowledge of age-related impairments in vision, hearing, and cognition can aid designers of products, tools, and environments for older users.
Purpose of the study
Niort hospital is getting involved in a preventive approach of musculoskeletal disorders, particularly with the use of keyboard and mouse wrist supports for the administrative staff.
Methods
A prospective satisfaction study was performed among 135 workers concerning the use of these wrist supports. Two questionnaires were filled out before inclusion and after 3 months use.
Results
Global satisfaction was 59.3% for the keyboard support and 81.5% for the mouse support. Symptomatic subjects were more satisfied than the non-symptomatic ones.
Conclusion
Wrist supports could be an effective means of primary prevention of upper-extremity musculoskeletal disorders for computer users.
This study compared the differences between digit joint angles, velocities and accelerations during two typing tasks: one on a standard keyboard configuration and one on an ergonomic keyboard configuration. A marker-based motion analysis system was used to capture digit movements during typing and digit joint angles, angular velocities, and angular accelerations were calculated. Results showed significant differences between the ergonomic and standard keyboard configurations for digit angles, angular velocity, and angular acceleration, particularly for the left metacarpophalangeal joints. Most notably, the ergonomic configuration tended to reduce the angular velocity and acceleration for metacarpophalangeal and proximal interphalangeal flexion/extension and increase these variables for metacarpophalangeal abduction/adduction. The participants showed no significant differences in typing speed and error rate between the two keyboards. This research supports other research, which suggests that an ergonomic configuration can alter keyboard kinematics, but suggests that researchers should evaluate not only the wrist kinematics, but the digit kinematics as well.Relevance to IndustryThis research provides information of interest to people who are considering acquiring an alternative keyboard in the workplace.
The aim of this literature research was to gather information on ergonomic requirements for input devices that are provided
by investigations applying biomechanical criteria. Firstly, international and national standards, guidelines as well as checklist
of this topic had been looked for and their propositions were summarised. Secondly, a query on Internet search engines and
databases had been conducted. A ranking system for the selected articles had been installed in order to comprehensibly rate
the information obtained from each study. For every regarded input device, i.e. keyboard, mouse, trackball, graphic tablet/stylus
and additionally forearm/wrist support, biomechanically based assessment parameters were deducted and outlined. Finally, these
findings were discussed with respect to the recommendations of the standards and an overall ergonomic design of office workplaces
with VDTs. In conclusion, this will lead to the development of a checklist for keyboards and mice that should be evaluated
by occupational health practitioner.
Research has shown that fixed-split, ergonomic keyboards lessen the pain and functional status in symptomatic individuals as well as reduce the likelihood of developing musculoskeletal disorders in asymptomatic typists over extended use. The goal of this study was to evaluate design features to determine whether the current fixed-split ergonomic keyboard design could be improved.
Thirty-nine, adult-aged, fixed-split ergonomic keyboard users were recruited to participate in one of three studies.
First utilizing non-functional models and later a functional prototype, three studies evaluated keyboard design features including: 1) keyboard lateral inclination, 2) wrist rest height, 3) keyboard slope, and 4) curved "gull-wing" key layouts.
The findings indicated that keyboard lateral inclination could be increased from 8° to 14°; wrist rest height could be increased up to 10 mm from current setting; positive, flat, and negative slope settings were equally preferred and facilitated greater postural variation; and participants preferred a new gull-wing key layout. The design changes reduced forearm pronation and wrist extension while not adversely affecting typing performance.
This research demonstrated how iterative-evaluative, user-centered research methods can be utilized to improve a product's design such as a fixed-split ergonomic keyboard.
To compare two postural interventions, a wrist splint and a Wrist Alignment Device (WAD) with a biofeedback mechanism.
Nine right-handed healthy individuals participated in the study.
Using both hands independently a 30-minute office-activity-experiment was performed that consisted of data entry, mouse clicking, text dragging, and mouse scrolling executed one after the other. Joint motion, tendon travel and productivity levels were measured. Participants wore a custom-made flexible electrogoniometric glove (FEG) as three scenarios were tested; namely FEG-only, FEG-Splint, and FEG-WAD. Data analysis was performed using descriptive statistics and ANOVA.
The joint motion results produced insignificant differences (p>0.05) between hands. Both hands showed larger overall tendon travel for the FEG-only when compared with either FEG-Splint or FEG-WAD experiments. Wearing the splint reduced the overall tendon travel by 24% and 10% for the left and right hands while using the WAD further reduced the overall tendon travel for the left and right hands by 51% and 42%. Productivity levels were similar across participants with respect to experiment task and type.
The WAD intervention is the most suitable device to promote a comfortable and non-restrictive neutral wrist posture.
To quantify learning percentages for alternative keyboards (chord, contoured split, Dvorak, and split fixed angle) and understand how physical, cognitive, and perceptual demand affect learning.
Alternative keyboards have been shown to offer ergonomic benefits over the conventional, single-plane QWERTY keyboard design, but productivity-related challenges may hinder their widespread acceptance.
Sixteen participants repeatedly typed a standard text passage using each alternative keyboard. Completion times were collected and subsequent learning percentages were calculated. Participants were asked to subjectively rate the physical, cognitive, and perceptual demands of each keyboard, and these values were then related to the calculated learning percentages.
Learning percentage calculations revealed the percentage for the split fixed-angle keyboard (90.4%) to be significantly different (p < .05) from the learning percentages for the other three keyboards (chord, 77.3%; contour split, 76.9%; Dvorak, 79.1%). The average task completion time for the conventional QWERTY keyboard was 40 s, and the average times for the fifth trial on the chord, contoured split, Dvorak, and split fixed-angle keyboards were 346, 69, 181, and 42 s, respectively.
Productivity decrements can be quickly regained for the split fixed-angle and contour split keyboard but will take considerably longer for Dvorak and chord keyboards. The split fixed-angle keyboard involved physical learning, whereas the others involved some combination of physical and cognitive learning, a result supported by the subjective responses.
Understanding the changes in task performance time that come with learning can provide additional information for a cost-benefit analysis when considering the implementation of ergonomic interventions.
Current best evidence for the conservative management of radial tunnel syndrome (RTS) consists primarily of expert opinion and inferences taken from studies on other nerve compressions and related syndromes. There are limited data reported in the literature of this particular disorder. This article reviews literature on modalities, therapeutic exercise, ergonomic interventions, and cortical reorganization, and how they may be considered for intervention with RTS. The author's preferred method of treatment, as based on theoretical constructs, for RTS is presented. Definitive evidence in the literature to support the conservative interventions suggested is lacking. Suggestions for clinical management and study are included in this therapist's clinical perspective.
The effects of forearm rotation and metacarpophalangeal (MP) flexion on carpal tunnel pressure were investigated in 17 healthy adults who had no evidence of carpal tunnel syndrome (CTS). Pressure was continuously recorded with a saline-filled catheter inserted into the carpal tunnel and connected to a pressure transducer while test subjects slowly rotated the forearm from full pronation to full supination. Forearm rotation was repeated with MP flexion of 0o, 45o, and 90o. Both forearm rotation and MP flexion, and their interaction term, significantly affected carpal tunnel pressure and accounted for most of the variability in the data. Highest mean pressures (55 mmHg) were recorded in full supination and 90o MP flexion and lowest pressures (12 mmHg) were recorded at 45o pronation and 45o MP flexion. These data may be useful in the design of tasks and hand tools in the management and prevention of CTS.
The purpose of this study was to examine differences in experienced typists' performance, posture, and musculoskeletal pain when using a split, adjustable (SA) computer keyboard and when using a standard flat keyboard. In addition, the use of a wrist rest was examined for performance, posture, and musculoskeletal pain effects. Eighteen participants were exposed to the SA keyboard and a flat keyboard in a laboratory study of text typing for four consecutive hours on five days. The results indicated that after just 2 h of orientation and practice, the participants could perform as well on the SA keyboard as on the flat keyboard. The SA keyboard provided advantages for reduced wrist/hand pronation. There was no difference between the keyboards in the level of musculoskeletal pain reported by participants after typing. However, they reported increased pain in the back, neck, shoulders, and wrists from the beginning to the end of each of the experimental periods for both keyboards.
This investigation of current epidemiologic and ergonomic research demonstrates consistent relationships between certain computer-related factors and musculoskeletal disorders.
Carpal tunnel syndrome (CTS) is a cause of pain, numbness, and tingling in the hands and is an important cause of work disability. Although high prevalence rates of CTS in certain occupations have been reported, little is known about its prevalence in the general population.
To estimate the prevalence of CTS in a general population.
General health mail survey sent in February 1997, inquiring about symptoms of pain, numbness, and tingling in any part of the body, followed 2 months later by clinical examination and nerve conduction testing of responders reporting symptoms in the median nerve distribution in the hands, as well as of a sample of those not reporting these symptoms (controls).
A region in southern Sweden with a population of 170000.
A sex- and age-stratified sample of 3000 subjects (age range, 25-74 years) was randomly selected from the general population register and sent the survey, with a response rate of 83% (n = 2466; 46% men). Of the symptomatic responders, 81% underwent clinical examination.
Population prevalence rates, calculated as the number of symptomatic responders diagnosed on examination as having clinically certain CTS and/or electrophysiological median neuropathy divided by the total number of responders.
Of the 2466 responders, 354 reported pain, numbness, and/or tingling in the median nerve distribution in the hands (prevalence, 14.4%; 95% confidence interval [CI], 13.0%-15.8%). On clinical examination, 94 symptomatic subjects were diagnosed as having clinically certain CTS (prevalence, 3.8%; 95% CI, 3.1%-4.6%). Nerve conduction testing showed median neuropathy at the carpal tunnel in 120 symptomatic subjects (prevalence, 4.9%; 95% CI, 4.1%-5.8%). Sixty-six symptomatic subjects had clinically and electrophysiologically confirmed CTS (prevalence, 2.7%; 95% CI, 2.1%-3.4%). Of 125 control subjects clinically examined, electrophysiological median neuropathy was found in 23 (18.4%; 95% CI, 12.0%-26.3%).
Symptoms of pain, numbness, and tingling in the hands are common in the general population. Based on our data, 1 in 5 symptomatic subjects would be expected to have CTS based on clinical examination and electrophysiologic testing.
Computer use is increasingly common among many working populations, and concern exists about possible adverse effects of computer use, such as carpal tunnel syndrome (CTS).
To estimate the prevalence and incidence of possible CTS and to evaluate the contribution of use of mouse devices and keyboards to the risk of possible CTS.
A 1-year follow-up study with questionnaires conducted in 2000 and 2001 at 3500 workplaces in Denmark, followed on each of the 2 occasions by a clinical interview on symptom distribution and frequency.
The questionnaire was sent to 9480 members of a trade union, with an initial response rate of 73% (n = 6943), and 82% (n = 5658) at follow-up.
At baseline, there were 3 outcome measures: tingling/numbness in the right hand once a week or more as reported in the questionnaire; tingling, numbness, and pain in the median nerve in the right hand confirmed by clinical interview; and tingling, numbness, and pain in the median nerve in the right hand at night confirmed by clinical interview. At 1 year of follow-up the main outcome of interest was onset of symptoms among participants who had no or minor symptoms at baseline.
The overall self-reported prevalence of tingling/numbness in the right hand at baseline was 10.9%. The interview confirmed that prevalence of tingling/numbness in the median nerve was 4.8%, of which about one third, corresponding to a prevalence of 1.4%, experienced symptoms at night. Onset of new symptoms in the 1-year follow-up was 5.5%. In the cross-sectional comparisons and in the follow-up analyses, there was an association between use of a mouse device for more than 20 h/wk and risk of possible CTS but no statistically significant association with keyboard use.
The occurrence of possible CTS in the right hand was low. The study emphasizes that computer use does not pose a severe occupational hazard for developing symptoms of CTS.
Manufacturers of ergonomic split keyboards promise maximum effectiveness and comfort as well as a reduction of physical complaints. In order to determine the positive effects claimed, a study was carried out during which 10 male subjects (Ss) participated in standardized working tests. They entered text into a PC, alternatingly using a conventional keyboard and an ergonomic keyboard. Electromyographic activity (EA) of 8 muscle groups was simultaneously recorded during altogether 6 working phases with a duration of 10 min, each. Measurements of the maximum activity, EAmax, via maximum voluntary contractions of the 8 muscles - which were necessary for calculating standardized electromyographic activity (sEA) used to represent muscle strain as a percentage - were always taken at the end of the experiment. Muscle strain varied from muscle to muscle but the level of the sEA-values for the different muscles was reproducible and stable. Also, activation of most muscles acting on the shoulder, upper arm, forearm, and the hand showed differences which, though small in amount, could be statistically secured and associated with the keyboard type. The ergonomic design of the tested keyboard led to objectively verifiable and plausible reductions of muscle strain.
Context Carpal tunnel syndrome (CTS) is a cause of pain, numbness, and tingling
in the hands and is an important cause of work disability. Although high prevalence
rates of CTS in certain occupations have been reported, little is known about
its prevalence in the general population.Objective To estimate the prevalence of CTS in a general population.Design General health mail survey sent in February 1997, inquiring about symptoms
of pain, numbness, and tingling in any part of the body, followed 2 months
later by clinical examination and nerve conduction testing of responders reporting
symptoms in the median nerve distribution in the hands, as well as of a sample
of those not reporting these symptoms (controls).Setting A region in southern Sweden with a population of 170,000.Participants A sex- and age-stratified sample of 3000 subjects (age range, 25-74
years) was randomly selected from the general population register and sent
the survey, with a response rate of 83% (n=2466; 46% men). Of the symptomatic
responders, 81% underwent clinical examination.Main Outcome Measures Population prevalence rates, calculated as the number of symptomatic
responders diagnosed on examination as having clinically certain CTS and/or
electrophysiological median neuropathy divided by the total number of responders.
Results Of the 2466 responders, 354 reported pain, numbness, and/or tingling
in the median nerve distribution in the hands (prevalence, 14.4%; 95% confidence
interval [CI], 13.0%-15.8%). On clinical examination, 94 symptomatic subjects
were diagnosed as having clinically certain CTS (prevalence, 3.8%; 95% CI,
3.1%-4.6%). Nerve conduction testing showed median neuropathy at the carpal
tunnel in 120 symptomatic subjects (prevalence, 4.9%; 95% CI, 4.1%-5.8%).
Sixty-six symptomatic subjects had clinically and electrophysiologically confirmed
CTS (prevalence, 2.7%; 95% CI, 2.1%-3.4%). Of 125 control subjects clinically
examined, electrophysiological median neuropathy was found in 23 (18.4%; 95%
CI, 12.0%-26.3%).Conclusion Symptoms of pain, numbness, and tingling in the hands are common in
the general population. Based on our data, 1 in 5 symptomatic subjects would
be expected to have CTS based on clinical examination and electrophysiologic
testing.
The present study focuses on an ergonomic evaluation of 4 computer keyboards, based on a quantitative analysis of wrist posture and typing performance and on subjective analyses of operator comfort during typing. The objectives of this study are (1) to quantify differences in the wrist posture and in typing performance when the four different keyboards are used, and (2) to analyze the subjective preferences of the subjects for alternative keyboards compared to the standard flat keyboard.
A field experiment is described in which wrist posture, seated posture measured using the RULA method, and musculoskeletal discomfort, recorded by self-report questionnaires, was assessed for 38 office workers while they typed the same text. A pretest survey was conducted to assess the effects of typing with a conventional keyboard on a desk or on an articulating keyboard tray, and with or without wrist rests. Following this, workers were randomly allocated to either a control group (n=15), for whom nothing changed, or a test group (n=23) that used their existing keyboard in a preset tiltdown (PT) system. After some 3 weeks of using the PT system a posttest survey was conducted for both groups. Results showed no significant changes in wrist posture, seated posture, or reports of musculoskeletal discomfort for the control group. Significant improvements in wrist posture, seated posture, and upper body musculoskeletal discomfort were found for workers using the PT system. Workers expressed a strong preference for using a keyboard with the PT system.
Twenty experienced typists participated in a laboratory based study to determine whether wrist and forearm postures changed over a 4 hour period of intensive keyboard use. Subjects were randomly assigned to use a conventional keyboard or a fixed split keyboard. Posture data was acquired using electrogoniometers after a 10 warm-up period and at the end of each hour. Wrist and forearm postures did not change significantly over the four hour period among subjects using the split geometry keyboard. On the conventional keyboard, all joint postures were stable except right wrist extension and left forearm pronation. The right wrist extension increased by 5° over the four hour period (p=.002) and left pronation decreased by approximately 9° (p=.001). Wrist postures among typists exposed for the first time to a split keyboard remained constant throughout a four hour period of intensive typing. On the conventional keyboard, some postures drifted over the four hour period.
Fifty experienced typists participated in a laboratory based repeated measures study with two factors: keyboard height (three) and keyboard configuration (three). The work surface heights tested were 63, 67 and 71 cm. The three keyboard configurations tested were: standard (Apple Extended™), alternative keyboard A (Microsoft Natural Keyboard) and alternative keyboard B (equivalent to Natural Keyboard with Leveler™ extended). Wrist and forearm posture data was acquired using electronic goniometers during 10 minutes of typing at each keyboard/height level. Across all heights tested, wrist extension, wrist ulnar deviation, and forearm pronation were statistically significantly closer to neutral when using alternative keyboard B than when using the standard keyboard.
BackgroundA prospective study of computer users was performed to determine the occurrence of and evaluate risk factors for neck or shoulder (N/S) and hand or arm (H/A) musculoskeletal symptoms (MSS) and disorders (MSD).Methods
Individuals (n = 632) newly hired into jobs requiring ≥ 15 hr/week of computer use were followed for up to 3 years. At study entry, workstation dimensions and worker postures were measured and medical and psychosocial risk factors were assessed. Daily diaries were used to document work practices and incident MSS. Those reporting MSS were examined for specific MSD. Incidence rates of MSS and MSD were estimated with survival analysis. Cox regression models were used to evaluate associations between participant characteristics at entry and MSS and MSD.ResultsThe annual incidence of N/S MSS was 58 cases/100 person-years and of N/S MSD was 35 cases/100 person-years. The most common N/S MSD was somatic pain syndrome. The annual incidence of H/A MSS was 39 cases/100 person-years and of H/A MSD was 21 cases/100 person-years. The most common H/A disorder was deQuervain's tendonitis. Forty-six percent of N/S and 32% of H/A MSS occurred during the first month of follow-up. Gender, age, ethnicity, and prior history of N/S pain were associated with N/S MSS and MSD. Gender, prior history of H/A pain, prior computer use, and children at home were associated with either H/A MSS or MSD.ConclusionsH/A and N/S MSS and MSD were common among computer users. More than 50% of computer users reported MSS during the first year after starting a new job. Am. J. Ind. Med. 41:221–235, 2002. © 2002 Wiley-Liss, Inc.
The effects of forearm rotation and metacarpophalangeal (MP) flexion on carpal tunnel pressure were investigated in 17 healthy adults who had no evidence of carpal tunnel syndrome (CTS). Pressure was continuously recorded with a saline-filled catheter inserted into the carpal tunnel and connected to a pressure transducer while test subjects slowly rotated the forearm from full pronation to full supination. Forearm rotation was repeated with MP flexion of 0 degrees, 45 degrees, and 90 degrees. Both forearm rotation and MP flexion, and their interaction term, significantly affected carpal tunnel pressure and accounted for most of the variability in the data. Highest mean pressures (55 mmHg) were recorded in full supination and 90 degrees MP flexion and lowest pressures (12 mmHg) were recorded at 45 degrees pronation and 45 degrees MP flexion. These data may be useful in the design of tasks and hand tools in the management and prevention of CTS.
Previously presented evidence indicates that carpal tunnel syndrome is related to compression of the median nerve inside the carpal tunnel. Biomechanical arguments in which the extrinsic finger flexor tendons inside the carpal tunnel are characterized as a frictionless pulley-belt mechanism are presented to show quantitatively how wrist size, wrist position and hand position affect forces on the tendons and their adjacent structures.
Self-report data on musculoskeletal discomfort were collected from several hundred VDT users in two agencies of a state government. Aspects of worker posture and workstation design were objectively assessed for 40 of the VDT users. Multiple regression analyses were used to examine the relationship between these ergonomic variables and musculoskeletal discomfort. Effects of ergonomic factors on musculoskeletal discomfort were clearly evident in the analyses. Regression models explained up to 38% of the variance in discomfort at different body sites. Of special interest was that leg discomfort increased with low, soft seat pans, suggesting that postural constraint is more important than thigh compression as a risk factor for leg discomfort in VDT work. In addition, arm discomfort increased with increases in keyboard height above elbow level, supporting arguments for low placement of the keyboard. Finally, high levels of neck and shoulder girdle discomfort observed in the study population suggest the need for further attention to the control of cervicobrachial pain syndromes in VDT work.
Keyboard work consists mostly of dynamic contractions of the small muscles of the forearms and hands. This is accompanied by continuous activity in the arm, shoulder and neck muscles keeping the head and hand in the correct position. Eliminating the weight from the arm by means of support and the position of the arms influences the electrical activity of shoulder muscles when working at a keyboard. We studied the influence of elbow angle; as well as that of different arm supports, on electrical activity of upper trapezius muscle during keyboard work in healthy workers and persons suffering from shoulder pains. The measurements were carried out in the laboratory. EMG activities, which where measured as mean square root (RMS)-values at every 100-millisecond period in trapezius muscle when working, were lower, the greater the elbow angle. Furthermore electrical activity decreased when subjects used arm supports while working. It is evident that the static load to shoulder muscles can be lowered significantly in keyboard work, when the forearms are at an angle of at least 100 degrees and by using arm supports. The most convienient and ergonomic working position can also be found individually be the method used here.
A keyboard concept based on biomechanical considerations was studied with 51 trained typists. The keyboard is split into two half-keyboards. An adjustable model allowed study of the preferred settings of opening angles, lateral inclinations, and distances of the split keyboard. The preferred split keyboards decrease the lateral deviation of the hands, and the use of a large forearm-wrist support is associated with a backwards leaning of the subjects and with an increased pressure of forearm-wrists onto the support. After the typing tasks, about two-thirds of the subjects asserted that they preferred the split keyboard models. Less pain and an increased feeling of relaxation were reported by the subjects when operating the split keyboards.
The standard typewriter keyboard serves as a model for keyboards of teletypewriters, desk calculators, consoles, computer keysets, cash registers, etc. This man-machine interface should be designed to allow high-frequency, error-free operation with the least possible strain on the operator. This paper discusses several feasible biomechanical improvements of the keyboard. Some experimental findings are described which support the following design concepts: (1) the keys should be arranged in a “hand-configured” grouping to simplify the motion patterns of the fingers; (2) the keyboard sections allotted to each hand should be physically separated to facilitate the positioning of the fingers; and (3) the keyboard sections allotted to each hand should be declined laterally to reduce postural muscular strain of the operator.
Video-motion analysis was used to analyse hand/wrist posture for subjects typing at a 101-key QWERTY keyboard on a 68 cm high worksurface. Three conditions were tested: subjects typed at the keyboard without arm support, subjects typed with adjustable full motion forearm supports, and subjects typed with an adjustable negative slope keyboard support system. The average declination of the negative slope keyboard support chosen by subjects was 12 degrees below horizontal, which flattened the angle of the key tops. Ulnar deviation was comparable in all conditions and averaged 13 degrees for the right hand and 15 degrees for the left hand. Full motion forearm supports did not significantly affect any postural measures. Dorsal wrist extension averaged 13 degrees when typing with or without the full motion forearm supports, but this was reduced to an average -1 degree with the use of the negative slope keyboard support system. Subjects chose to sit at a distance of 79 cm from the computer screen when using the negative slope keyboard system compared with 69 cm without this.
The purpose of this study was to explore the relationship between carpal tunnel pressure and fingertip force during a simple pressing task. Carpal tunnel pressure was measured in 15 healthy volunteers by means of a saline-filled catheter inserted percutaneously into the carpal tunnel of the nondominant hand. The subjects pressed on a load cell with the tip of the index finger and with 0, 6, 9, and 12 N of force. The task was repeated in 10 wrist postures: neutral; 10 and 20 degrees of ulnar deviation; 10 degrees of radial deviation; and 15, 30, and 45 degrees of both flexion and extension. Fingertip loading significantly increased carpal tunnel pressure for all wrist angles (p = 0.0001). Post hoc analyses identified significant increase (p < 0.05) in carpal tunnel pressure between unloaded (0 N) and all loaded conditions, as well as between the 6 and 12 N load conditions. This study demonstrates that the process whereby fingertip loading elevates carpal tunnel pressure is independent of wrist posture and that relatively small fingertip loads have a large effect on carpal tunnel pressure. It also reveals the response characteristics of carpal tunnel pressure to fingertip loading, which is one step in understanding the relationship between sustained grip and pinch activities and the aggravation or development of median neuropathy at the wrist.
Concerns have arisen that the keyboard is a causal factor in the development of work-related musculoskeletal disorders (WRMDs) among video display terminal (VDT) operators. A number of alternative keyboard designs have been developed with altered geometry in an effort to improve comfort in keyboard operation. However, few data are available to substantiate whether these new keyboard designs are actually effective in reducing discomfort and musculoskeletal problems in users. The purpose of this study was to provide data on the efficacy of certain alternative keyboard design features (e.g. splitting the keyboard in half, and laterally inclining the keyboard halves) in reducing fatigue and musculoskeletal discomfort among keyboard operators. The study also explored the effects of these design features on performance. Fifty subjects performed a text-entry task for one day on a standard keyboard, then were assigned to one of five keyboard conditions for an evaluation period of two days (i.e. 10 subjects/condition). Outcome measures included performance (i.e. keystrokes/h, errors/h) and self-report measures of discomfort and fatigue. The results indicated an initial decline in productivity when subjects began typing on two of the alternative keyboards, but these productivity losses were recovered within the two-day evaluation period. The results also indicated no significant differences between keyboard conditions in discomfort and fatigue. These results suggest a minimal impact of the keyboard design features examined in this study on productivity, comfort and fatigue, at least after two days of exposure.
Persistent elevations in carpal tunnel pressure may aggravate carpal tunnel syndrome. This study examined the effects of finger posture on carpal tunnel pressure during wrist motion. Carpal tunnel hydrostatic pressure was measured using a saline-filled catheter inserted into the nondominant wrists of 14 healthy individuals. Range of motion tasks of wrist flexion-extension and radioulnar deviation were repeated with metacarpophalangeal (MCP) joint angles of 0 degrees, 45 degrees, and 90 degrees flexion. Pressures were significantly greater with the fingers straight (MCP = 0 degrees) than when the MCP joints were flexed to 45 degrees for all radioulnar deviation angles and from 10 degrees of wrist flexion to all angles of wrist extension tested. Pressures were also significantly higher with MCP joints at 0 degrees than at 90 degrees for wrist extension angles from 10 degrees to 40 degrees. Pressures increased to over 30 mm Hg (4.0 kPa) in some wrist extension and ulnar and radially deviated postures. Finger and wrist postures should be considered when designing splints or evaluating tasks for patients with carpal tunnel syndrome.
Eighty computer users with musculoskeletal disorders participated in a 6-month, randomized, placebo-controlled trial evaluating the effects of four computer keyboards on clinical findings, pain severity, functional hand status, and comfort. The alternative geometry keyboards tested were: the Apple Adjustable Keyboard [kb1], Comfort Keyboard System [kb2], Microsoft Natural Keyboard [kb3], and placebo. Compared to placebo, kb3 and to a lesser extent kb1 groups demonstrated an improving trend in pain severity and hand function following 6 months of keyboard use. However, there was no corresponding consistent improvement in clinical findings in the alternative geometry keyboard groups compared to the placebo group. Overall, there was a significant correlation between improvement of pain severity and greater satisfaction with the keyboards. These results provide evidence that keyboard users may experience a reduction in hand pain after several months of use of some alternative geometry keyboards.
The aim of this study was to perform a comprehensive investigation to document wrist and forearm postures of users of conventional computer keyboards. We instrumented 90 healthy, experienced clerical workers with electromechanical goniometers to measure wrist and forearm position and range of motion for both upper extremities while typing. For an alphabetic typing task, the left wrist showed significantly greater (p < .01) mean ulnar deviation (15.0 degrees +/- 7.7 degrees) and extension (21.2 degrees +/- 8.8 degrees) than the right wrist (10.1 degrees +/- 7.2 degrees and 17.0 degrees +/- 7.4 degrees for ulnar deviation and extension, respectively). Conversely, the right forearm had greater mean pronation (65.6 degrees +/- 8.3 degrees) than the left forearm (62.2 degrees +/- 10.6 degrees). We noted minimal functional differences in the postures of the wrists and forearms between alphabetic and alphanumeric typing tasks. Ergonomists should consider the statistically significant and probable practical difference in wrist and forearm posture between the left and right hand in ergonomic interventions in the office and in the design of computer keyboards. Actual or potential applications of this research include guiding the design of new computer keyboards.
A study was conducted on 90 experienced office workers to determine how commercially available alternative computer keyboards affected wrist and forearm posture. The alternative keyboards tested had the QWERTY layout of keys and were of three designs: split fixed angle, split adjustable angle, and vertically inclined (tilted or tented). When set up correctly, commercially available split keyboards reduced mean ulnar deviation of the right and left wrists from 12 degrees to within 5 degrees of a neutral position compared with a conventional keyboard. The finding that split keyboards place the wrist closer to a neutral posture in the radial/ulnar plane substantially reduces one occupational risk factor of work-related musculoskeletal disorders (WMSDs): ulnar deviation of the wrist. Applications of this research include commercially available computer keyboard designs that typists can use and ergonomists can recommend to their clients in order to minimize wrist ulnar deviation from typing.
Alternative computer keyboards whose halves can be slanted toward each other can reduce a risk factor (ulnar deviation) for work-related musculoskeletal disorders (WMSDs) affecting the upper limbs. Two questions that computer keyboard operators face when using keyboards that can be separated into halves (split keyboards) are: (1) At what angle should the keyboard halves be opened? and (2) At what distance apart should the keyboard halves be placed? The objective of this study was to investigate the effects of the opening angle and separation distance between halves of a split keyboard on wrist ulnar deviation and typing efficiency.
Eleven experienced computer keyboard operators participated in this study and used a split keyboard that was set up in a conventional (nonsplit) format and also in 3 alternative configurations: (1) centers of keyboard halves were separated at 20-cm distance, (2) keyboard halves were separated half of the distance of shoulder width, and (3) keyboard halves were separated at shoulder width distance.
The 3 alternative configurations resulted in ulnar deviation of both wrists that were less than ulnar deviation from typing on a conventional setup. There were no differences in ulnar deviations among the 3 alternative configurations.
The results of this research provide physical therapists and ergonomists with a set of configurations of a split keyboard that they can recommend to their patients or clients. All of the alternative configurations of the split keyboard are beneficial in promoting a neutral wrist position, which theoretically would decrease exposure to WMSDs such as tenosynovitis in the wrist and carpal tunnel syndrome.
A survey was done of employees who were identified as frequent computer users. Although 29.6% of the employees reported hand paresthesias, only 27 employees (10.5%) met clinical criteria for carpal tunnel syndrome, and in 9 (3.5%) the syndrome was confirmed by nerve conduction studies. Affected and unaffected employees had similar occupations, years using a computer, and time using the computer during the day. The frequency of carpal tunnel syndrome in computer users is similar to that in the general population.
The goal of this study was to determine the systematic effect that varying the slope angle of a computer keyboard along with varying keyboard height (relative to elbow height) have on wrist extension angle while typing. Thirty participants typed on a keyboard whose slope was adjusted to +15 degrees, +7.5 degrees, 0 degrees, -7.5 degrees, and -15 degrees. The height of the keyboard was set up such that participants' wrists were at the same height as their elbows, above their elbows, and four cm below their elbows. Results showed that as keyboard slope angle moved downward from +15 degrees to -15 degrees, mean wrist extension decreased approximately 13 degrees (22 degrees at +15 degrees slope to 9 degrees at -15 degrees slope). Keyboard height had a similar effect with mean wrist extension decreasing from 21.8 degrees when the keyboard was lower than elbow height, to 7.3 degrees when the keyboard was higher than elbow height. Potential application of this research includes the downward sloping of computer keyboards, which could possibly be beneficial in the prevention of musculoskeletal disorders affecting the wrist.
Despite widespread recommendations regarding posture during computer use, associations between specific postures and musculoskeletal health are not well characterized.
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.
Keying with an inner elbow angle > 121 degrees, 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 degrees 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.
The results suggest that the risk of musculoskeletal symptoms and musculoskeletal disorders may be reduced by encouraging specific seated postures.
Positioning a computer keyboard with a downward slope reduces wrist extension needed to use the keyboard and has been shown to decrease pressure in the carpal tunnel. However, whether a downward slope of the keyboard reduces electromyographic (EMG) activity of the forearm muscles, in particular the wrist extensors, is not known.
Sixteen experienced typists participated in this study and typed on a conventional keyboard that was placed on slopes at angles of 7.5, 0, -7.5, and -15 degrees. Electromyographic activity of the extensor carpi ulnaris (ECU), flexor carpi ulnaris (FCU), and flexor carpi radialis (FCR) muscles was measured with surface electrodes, while the extension and ulnar deviation angles of the right and left wrists were measured with electrogoniometers.
Wrist extension angle decreased from approximately 12 degrees of extension while typing on a keyboard with a 7.5-degree slope to 3 degrees of flexion with the keyboard at a slope of -15 degrees. Although the differences were in the range of 1% to 3% of maximum voluntary contraction (MVC), amplitude probability distribution function (APDF) of root-mean-square EMG data points from the ECU, FCU, and FCR muscles varied across keyboard slopes.
Wrist extension decreased as the keyboard slope decreased. Furthermore, a slight decrease in percentage of MVC of the ECU muscle was noted as the keyboard slope decreased. Based on biomechanical modeling and published work on carpal tunnel pressure, both of these findings appear to be positive with respect to comfort and fatigue, but the exact consequences of these findings on the reduction or prevention of injuries have yet to be determined. The results may aid physical therapists and ergonomists in their evaluations of computer keyboard workstations and in making recommendations for interventions with regard to keyboard slope angle.
An initial survey showed that typists tended to work with their keyboards higher than is normally recommended in the ergonomics literature and to report discomfort in the shoulders, neck and upper back. An experiment was conducted in which biomechanical stress, subjective comfort and typing performance were evaluated with respect to keyboard height and the presence or absence of a copy stand. Increased keyboard height resulted in increased postural torque about the shoulder joint, decreased torque about the C7 vertebra, and increased discomfort. Keyboard height had no effect on typing performance.
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