Design and evaluation of a curved computer keyboardfaculty.washington.edu/petej/McLoone,ComfortCurve,Ergonomics2009.pdfpurchasing an alternative keyboard design. The purpose of this

Design and evaluation of a curved computer keyboard

Hugh E. McLoonea*, Melissa Jacobsonb, Peter Clarkc, Ryan Opinac, Chau Heggd and Peter Johnsond

aMicrosoft, Redmond, Washington, USA; b56seven8 design, Seattle, Washington, USA; cInterface Ergonomics of BC Research,Vancouver, British Columbia, Canada; dDepartment of Environmental and Occupational Health Sciences, University of

Washington, Seattle WA, USA

Conventional, straight keyboards remain the most popular design among keyboards sold and used with personalcomputers despite the biomechanical benefits offered by alternative keyboard designs. Some typists indicate thatthe daunting medical device-like appearance of these alternative ‘ergonomic’ keyboards is the reason for notpurchasing an alternative keyboard design. The purpose of this research was to create a new computer keyboard thatpromoted more neutral postures in the wrist while maintaining the approachability and typing performance of astraight keyboard. The design process created a curved alphanumeric keyboard, designed to reduce ulnar deviation,and a built-in, padded wrist-rest to reduce wrist extension. Typing performance, wrist postures and perceptions offatigue when using the new curved keyboard were compared to those when using a straight keyboard design. Thecurved keyboard reduced ulnar deviation by 2.28 + 0.7 (p 5 0.01). Relative to the straight keyboard without abuilt-in wrist-rest, the prototype curved keyboard with the built-in padded wrist-rest reduced wrist extension by6.38 + 1.2 (p 5 0.01). There were no differences in typing speed or accuracy between keyboards. Perceived fatigueratings were significantly lower in the hands, forearms and shoulders with the curved keyboard. The new curvedkeyboard achieved its design goal of reducing discomfort and promoting more neutral wrist postures while notcompromising users’ preferences and typing performance.

Keywords: wrist posture; ergonomics; performance; comfort; productivity

1. Introduction

Alternative keyboards such as adjustable split andsplit-fixed designs have been on the market for overtwo decades; yet, widespread sales and use have notexceeded those of conventional, straight keyboarddesigns. Alternative keyboards were introduced in the1990s with designs based on the findings of severalinvestigators (Kroemer 1972, Buesen 1984, Nakasekoet al. 1985, Ilg 1987). A review article by Rempel (2008)provides a summary of the published research on splitkeyboards between 1926 and 2007. Fixed-split key-boards (Figure 1) reduce awkward postures (Honanet al. 1995, Rempel et al. 1995, Honan et al. 1996,Marklin et al. 1999, Zecevic et al. 2000), muscle strain(Strasser et al. 2004) and overall pain and discomfortas well as improving the functional status of partici-pants with pre-existing hand and wrist pain (Tittir-anonda 1997, Tittiranonda et al. 1999). Further,research has shown the benefit of the fixed-splitkeyboard design in reducing the incidence of newcases of carpal tunnel syndrome and other symptoms(Moore and Swanson 2003). Yet, straight keyboardsare still popular designs among those keyboards

shipped with new personal computers and soldseparately in retail stores.

Many keyboard users have invested time to learnhow to touch type: striking keys without looking andusing all or almost all 10 digits. During this relativelyextensive training process, users have memorised bothcognitively and physically where the keys arepositioned and located. Fixed-split keyboards, by theirnature, physically change the location of keys in space,such that new users must relearn where keys arelocated. This retraining may take only a few minutes ora matter of weeks depending on the typist’s skill andmotivation (Morelli et al. 1995, Tittiranonda 1997). Insome cases, typists on more extreme alternativekeyboard designs may never reach the typing speedsand error rates they experienced with straightkeyboards (Chen et al. 1994, Swanson et al. 1997).

Despite the reported ergonomic benefits ofalternative keyboards and the relatively short learningcurve for some typists, many computer users prefer topurchase and use straight keyboards instead. Internalresearch at Microsoft identified that, among thegeneral population of typists, fixed-split keyboards are

*Corresponding author. Email: [email protected]

Ergonomics

Vol. 52, No. 12, December 2009, 1529–1539

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often perceived as an orthotic or medical device, usedmore often by people with pain and less approachablefor use by otherwise less motivated healthy typists.

As a result of the demonstrated benefits fromalternative keyboards and the challenges associated withtheir perceived poor approachability, a design team wasformed to create anewalternativekeyboard.Thegoalwasto design a keyboard that not only provided theergonomic benefit of reducing awkward wrist postures,but that would also have an approachable designthat would appeal to the masses of straight keyboardusers.

A series of iterative-evaluative, user-centred experi-ments were conducted to attempt to incorporatefurther ergonomic advantages into the straight key-board layout. The research team articulated metrics forsuccess based on a user experience framework ofperformance, comfort and desirability. The metrics forsuccess included determining whether there were anydifferences in typing performance, wrist–forearmpostures, perceived comfort and subjective preferencebetween a straight keyboard and new curved keyboardprototypes developed during this iterative-evaluativeproduct design process. Representative users wereinvited into laboratory settings to evaluate a series ofmodels and prototypes to provide their impressionsand preferences and thus assist with the evolution ofthe new curved keyboard design. The series of threeexperiments presented in this paper exemplified a user-centred product design process.

2. Method

2.1. Experiment 1

2.1.1. Experimental design and protocol

The first experiment was an iterative-evaluativeproduct design research study of preferred keyboardopening angle. A conventional, straight keyboard with08 opening angle and three curved keyboards withcentre opening angles of 88, 108 and 138 were evaluatedby representative users for their visual and tactilepreferences. Figure 2 shows a curved keyboard modelwith the 108 opening angle. As shown in the figure, thegap created in the middle of each keyboard created bythe opening angle was filled by increasing the size ofthe key caps. All keyboards had a 08 slope (i.e. keysurfaces were flat/parallel to the table surface) bydefault and were mechanically operational but notelectrically functional.

To simulate using each keyboard, participants satin an adjustable workstation. In this workstation,participants adjusted the chair so that their feet restedflat on the floor and their thighs were parallel to thefloor and then they adjusted the table so that thehome row of the keyboard was positioned at elbowheight.

The experiment consisted of having the participantssimulate typing a standard text passage on eachkeyboard prototype. When participants formed anopinion of the experience (between 2 and 5 min), theygave feedback on the quality of their experience witheach prototype. Keyboard prototype order wascounter-balanced and, after testing all keyboards, theparticipants were asked to rank the keyboards frommost (‘first’) to least (‘fourth’) preferred and thereasons for their preferences.

2.1.2. Participants

Seven participants (three males, four females) externalto Microsoft were brought into a usability laboratoryto test the four keyboards. The average age of theparticipants was 49 (range 18–62) years and all

Figure 1. Fixed-split keyboard (Microsoft NaturalKeyboard (Elite version)).

Figure 2. (a) The straight keyboard and (b) one of the curved keyboard models (108 split angle shown) tested in Experiment 1.

1530 H.E. McLoone et al.


participants were straight keyboard users. Participantswere not screened for their typing ability. Fourparticipants reported that they used a computer �4 dper week and the other three participants that theyused a computer 7 d per week. The participants wererecruited from a database of people in the Seattlemetropolitan area who were willing to be consideredfor usability research at Microsoft. All participantsgave their consent to participate and received aMicrosoft hardware or software gratuity in exchangefor their participation. Studies followed Microsoft’sstandard organisational procedures for usabilitytesting with human subjects.

2.1.3. Measurements

For both this study and the second one describedbelow, participants were instructed to ‘think aloud’ orotherwise encouraged to express their positive,neutral and negative impressions of the keyboardprototypes and keycap designs. Participants’ impres-sions and rank order preferences were summarised andtallied.

2.1.4. Results

Most of the participants appreciated the three newcurved keyboards. In terms of preferences, five of theseven participants preferred a split keyboard designover the straight keyboard. The prototypes with theopening angles of 88, 108 and 138 received average rankorder preferences of 2.3, 2.1 and 2.0 respectively on aranking scale from 1 (most preferred) to 4 (leastpreferred). The straight keyboard had a generallylower average rank order preference of 3.0. Someparticipants found the new curved keyboards easy toget used to and were able to perceive the benefits of thesplit in the centre of the keyboard. Two participantssaid that the curved keyboards were ‘easy to use’ andhad ‘easy to access keys’. Three other participantsoffered similar comments that the curved keyboardswere ‘natural, comfortable and felt good with the splitangle’. However, the straight keyboard was appre-ciated by two participants for its ‘familiarity’ and for‘easy to use, predictable key locations’. The ‘stretch’keys in the middle were generally well perceived;however, a few participants expressed some concernsabout the non-uniform key size.

2.2. Experiment 2

2.2.1. Experimental design and protocol

The second experiment was an iterative-evaluativeproduct design research study of preferred keyboardgeometry and key cap design.

To evaluate keyboard geometry, five keyboarddesigns were assessed for usability including threedifferent curved keyboards with opening angles of 108,138 and 168 (Figure 2), a conventional, straightkeyboard (a benchmark, Figure 2) and a fixed-splitkeyboard (a second benchmark) with a opening angleof 258 and lateral inclination angle of 88 (Figure 1).The new curved keyboards and the straight keyboardhad 08 lateral inclination angle and all keyboards had a08 slope (i.e. keys were flat/parallel to the tablesurface). The two benchmark keyboards were chosento bracket the range of keyboard geometries currentlycommercially available. The expectation was that, onaverage, participants would give a higher rating to oneor more of the curved keyboards compared to thestraight keyboard representing one extreme and to thefixed-split keyboard representing the other extreme. Asin the first experiment, all models were mechanicallyoperational but not electrically functional. Participantssimulated typing a standard text passage on eachkeyboard (for between 2 and 5 min) until they wereable to provide judgement about the quality of theirexperience with each prototype and to make a decisionabout their preference for each design relative to theother designs. Keyboard order was counter balanced.

In addition to the above keyboard layout designs,the participants evaluated five key cap designs on the108 opening angle curved keyboard. These key capdesigns represented variations on how to fill the spacebetween the keys created by the opening angle.Should the keys remain unchanged and the space befilled with solid plastic or should the keys be enlargedto fill this space? As shown in Figure 3, model P filledthe opening area with stepped keycaps, each key oneither side elongated to fill the gap half way. ModelsQ and S had irregularly sized keys with an obviouscentre line. Model R used identical sized keys with a‘baseball cap’ key design. With this design, the keyshad a secondary lower surface to fill extra space inthe middle of the keyboard. Finally, model T filledthe opening area with a triangular island of plasticsurrounded by irregular sized keys. Model P had the‘B’ key cross the centreline to allow for the opening inthe keyboard and no separating space or islandbetween the keys. Models Q and S had a symmetricalopening between the middle of the keyboard with thecentre keys elongated to minimise the gap in themiddle of the keyboard. Model S also used thestepped keycap design, whereas model Q used a moreconventional gradual slope on the key sides. Thesedesigns were printed full-size on paper and affixed toa foam core poster board for presentation toparticipants. Again, key cap designs were presented incounter-balanced order. A Friedman’s test forordinal, ranked data was used to determine whether

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there were differences in the rankings of the openingangles and keycap designs.

To simulate using each keyboard, participants satin an adjustable workstation and adjusted the chair sotheir feet rested flat on the floor and their thighs wereparallel to the floor and then they adjusted the table sothat the home row of a straight keyboard waspositioned at elbow height. The experiment consistedof having the participants simulate typing a standardtext passage on each keyboard prototype. Whenparticipants formed an opinion of the experience(within 2–5 min), they gave feedback on the qualityof their experience.

The participants were then asked to orient a 2-Dpaper model of a split keyboard into a position thatthey felt was the most comfortable for their hands.The paper model was a printed layout of a full-sizedkeyboard pasted on to heavy cardstock paper andthen cut into two pieces representing two halves of asplit keyboard between the numbers ‘6’ and ‘7’ in thenumeric row and the ‘T’ and ‘Y’, ‘G’ and ‘H’ and‘B’ and ‘N’ keys in the rows consisting of letters.Participants were instructed to keep the ‘6’ and ‘7’keys on the two halves touching as they selectedtheir optimum opening angle, while keeping thepaper model flat on the desk in front of them (that

is, with 08 slope and lateral inclination angles). Thepaper orientation was traced to record eachparticipant’s self-selected opening angle.

2.2.2. Participants

The second experiment brought 20 participants (10men, 10 women) into a laboratory to represent awider cross section of ages and body sizes. Theaverage age of participants was 34 (range 22–50)years. A total of 18 participants were right-handdominant, two participants were left-hand dominantand all were conventional, straight keyboard users.As measured from the distal crease of the wrist totip of middle finger, the average hand size was 17.5(range 16.0–18.7) cm for the female participants and19.7 (range 18.1–21.2) cm for the male participants.All reported that they were touch typists (that is,used all 10 digits and typed without looking at thekeyboard) and did not have any hand or visualdisability that would impact performance whiletyping on a keyboard. They reportedly used acomputer 6 h per day on average (range 2.5–11.0 h).In this experiment, the participants did not knowthat Microsoft was sponsoring the research andreceived a monetary gratuity for their participation.

Figure 3. The non-electrically functional prototype curved keyboard models with the five alternative centre keycap designsassessed in Experiment 2.



2.2.3. Measurements

After using all five of the keyboards, participants wereasked to rank the keyboards from most (‘first’) to least(‘fifth’) preferred and they were asked to place each ofthe prototype keyboards along a 21-point scale withthe benchmark, straight keyboard at the centre ‘zero’point and with ‘þ10’ being the best possible keyboardand ‘710’ being the worst possible keyboard. Thestraight keyboard was chosen as the scale mid-point asall participants used a straight keyboard as theirprimary keyboard. It was left up to the individualparticipant to decide the meanings of ‘best’ and ‘worst’possible keyboard.

For the new key cap designs, in addition to notingand counting the open-ended, positive and negativecomments, the participants were asked to rank the keydesigns from most (‘1’ for first) to least (‘5’ for fifth)preferred.

2.2.4. Results

2.2.4.1. Participants’ preferences for opening angles.In Experiment 2, the keyboard models with 108 and138 opening angles were generally more preferred overthe fixed-split keyboard and the 168 opening anglekeyboard prototype but not the conventional, straightkeyboard (08). The average rank order preferencesfrom 1 (most preferred) to 5 (least preferred) were 2.7and 2.5 for the 108 and 138 opening angles,respectively, 2.8 for the conventional, straightkeyboard (benchmark) and 3.6 and 3.5 for the 168opening angle and the fixed-split keyboard,respectively. These differences in rankings were notstatistically significant but approached significance(p ¼ 0.07).

Based on the ratings utilising the 21-point scale(worst possible keyboard –10 to best possiblekeyboard þ 10), there were significant differences inratings between keyboards (p ¼ 0.02). The mean(SD) ratings for the curved keyboards with 108 and138 opening angles were 1.9 (5.6) and 1.7 (4.9)respectively compared to the conventional, straightkeyboard (representing 0 on the 21-point scale). Thefixed-split keyboard and the curved keyboard withthe 168 opening angle were not rated as favourablyand had average scores of 72.1 (6.8) and 71.3 (6.7)respectively. The curved keyboard with the 108opening angle was rated significantly higher thanthe fixed-split and curved keyboard with the 168opening angle, and the curved keyboard with the 138opening angle was rated significantly higher than thefixed-split keyboard with the 168 opening angle.Based on the positive and negative commentsprovided for each keyboard, both the 168 angle

keyboard and the fixed-split keyboard weretalked about in a neutral way with an equalratio (1 to 1) of positive and negative open-endedcomments. By contrast, the 108 and 138 models weretalked about more positively with a higher 3 to 1ratio of positive to negative open-ended comments.For this group of standard keyboard users,the increase in opening angle to 168 and thelayout of the fixed-split keyboard were deemed tooradical.

2.2.4.2. Participants’ self-selected preference foropening angle. When participants were asked to orientthe 2-D paper model keyboard halves into the positionthat they felt was the most comfortable, the averageself-selected opening angle for the group was 12.38 (SD6.18). This value was consistent with the rankingresults of the keyboards presented in section 5.1, wherethe intermediate keyboard angles of 108 and 138 wereselected over the straight (08) and the more extreme 168opening angles.

2.2.4.3. Participants’ preferences for key cap design.With regard to the preferences for the variouskey cap designs to accommodate the opening angle,most (83%) participants preferred either models P(stepped keys) or Q (irregular shaped keys) for theirfirst choice. Models S, P and Q had the highestaverage (SD) rank order preferences of 2.6 (0.8), 2.5(1.7) and 2.4 (1.4) respectively. There were nosignificant differences between these threedesigns but they were all rated significantly better(p ¼ 0.03) than models R (identical sized keys)and T (centre filled with small plastic triangularregion).

The participants’ reasons for choosing model Pincluded: ‘looked most proportional’; ‘mostproportionately laid out’; ‘more integrated/together’;‘liked flow’. They also liked the key size: ‘centre keysizes are the same (or close) – difference won’tincrease the error rate’; ‘visual curve and shape ofcentre keys look like rest of keys’; ‘key shape similarto straight – would be able to use blend’; ‘others looklike pre-occupied with compensating for the middle’.Their reasons for choosing models Q and S includedthe symmetry, subtle, gradual look and less noticeablekey treatment: ‘gradual’; ‘symmetry, no dead space inthe middle, no odd shaped keys’; ‘treatment not asnoticeable’; ‘smoother/symmetrical’. Models R and Thad lower average (SD) ranks of 3.2 (1.2) and 4.1(1.3) respectively with no differences in rankingbetween these two keycap designs. Model Thad the lowest rating since participants felt the keysdid not aesthetically fill the centre area of thekeyboard.

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2.3. Experiment 3

The two previous experiments used non-electricallyfunctional keyboard prototypes. The purpose ofExperiment 3 was to evaluate the new curved keyboardwith an integrated wrist-rest using a fully functionalprototype of the preferred design embodiments againsta straight keyboard with and without a built-in wrist-rest. As a result of the first two experiments, thepreferred design embodiments included an openingangle of 128 and stepped key design in the centre areaof the curved keyboard. The objectives were todetermine what effect, if any, the preferred keyboardembodiments had on wrist and forearm postures andwhether the same positive subjective impressionswould also be found when subjects used a fullyfunctional prototype.

2.3.1. Participants

A total of 26 straight keyboard users (14 males and12 females) participated in this experiment. Partici-pants were recruited from the Industrial EngineeringDepartment and the Environmental and Occupa-tional Health Science Department at the Universityof Washington. The mean age of the participantswas 31 (range 31–51) years and all participantsreported that they were touch typists who couldtype 40 words per min or higher. The participantswere not aware of who was sponsoring the study andwere paid $15/h in cash for their participation. Thestudy took place at the University of Washington,had the approval of the University Human SubjectsCommittee and all participants gave informedconsent.

2.3.2. Experimental protocol

The experiment consisted of having participants typestandardised text for 15 min on three different key-boards. As shown in Figure 4, the three keyboardsused were a Dell OEM standard keyboard without awrist-rest (P/N 04N454; Dell Computer, Round Rock,TX, USA), a conventional, straight keyboard with abuilt in wrist-rest (Optical Desktop Elite 1.0; MicrosoftCorporation, Redmond, WA, USA) and a fullyfunctional prototype of the new curved keyboarddesign, which was based on the preferred designembodiments identified in the two earlier user-centredexperiments.

The design embodiments incorporated into the newcurved keyboard included a built-in, padded wrist-rest,an alphanumeric keyboard layout with a opening angleof 128 and covering the central split between the twodistinct halves of the alphanumeric portion of the

keyboard with slightly larger, staggered keys in thecentre of the keyboard.

The test workstation where participants typed wasset up according to the ANSI/HFS 100–1988standard to match the participant’s stature (ANSI/HFS 1988). Participants adjusted the chair so thattheir feet rested flat and firmly on the floor, theirthighs were parallel to the seat pan and the chairbackrest firmly supported their back. Then, whencomfortably resting their upper arms at their sidesand forming roughly a 908 angle at the elbow, thetable height for the keyboards was adjusted to be2.5 cm below elbow height. This ensured thatparticipants were comfortably seated, their shoulderswere relaxed and their wrists were in a relativelyneutral flexion/extension position when typing.Participants were allowed to make slight adjustmentsfor comfort.

2.3.3. Measurements

2.3.3.1. Posture measurement. Bi-axialelectrogoniometers (Model XM-65; Biometrics Ltd.,Newport, Gwent, UK) were applied to the right andleft wrists and forearms of participants and calibratedas prescribed by Johnson et al. (2002). Calibrationconsisted of having participants assume a typingposture with their upper arms resting at their side,forearms parallel to the work surface and hands fullypronated. This was to minimise any offset errorsassociated with forearm pronation. As prescribed bythe American Academy of Orthopedic Surgeons(Greene and Heckman 1994), the neutral flexion/extension position of the wrist was defined at theposition where the horizontal plane formed by theback of the hand was in line with the plane formed bythe back of the forearm. The neutral radial/ulnarposition was defined as the position where the thirdmetacarpal was in line with the long axis of theforearm.

2.3.3.2. Typing performance. A program calledTyping Workshop Deluxe (version 6.0; Valusoft, Inc.,Waconia, MN, USA) was used to measure typingspeed and accuracy. In addition, a second programwritten in Labview (version 6.1; National Instruments,Austin, TX, USA) measured minute to minute changesin typing speed. Simple alphanumeric text fromchapters of a novel was used for the typing test. Inorder to become familiar with the operation of theTyping Workshop program, participants were allowed5 min practice with the program using a conventional,straight keyboard different from the conventional,straight keyboards used in the study. Prior to the startof the typing task, participants were asked to balance



speed and accuracy when typing. Thus, allexperimental procedures could be completed within2 h, the typing task consisted of having the participanttype on each keyboard for two 7.5 min blocks (total of15 min). The two 7.5 min blocks were chosen so thatperceived fatigue measurements (see section 2.3.3.3)could be collected at the beginning, middle and end ofeach typing session.

2.3.3.3. Perceived fatigue. Perceived fatigue levelswith each keyboard were measured using the BORGCR-10 scale (Borg 1982) administered before and aftereach of the two 7.5 min typing blocks (at thebeginning, middle and end of each 15 min typingsession). The participant was asked to identify the levelof perceived fatigue in the right and left hands, wrists,forearms, shoulders and neck. Other than the timetaken to fill out the Borg CR-10 scale ratings(*1 min), there was no rest between the two 7.5 mintyping blocks.

2.3.4. Data analysis

During the experiment, the angle data from theelectrogoniometers were collected at 100 Hz and

stored on a portable logger (ME6000-T8; MegaElectronics, Kupio, Finland). After data collection, thedata were downloaded and analysed using an analysisprogram written in Labview. Within each 7.5 minblock of typing, the first and last 45 s were discarded;thus, 6 min records were used for the goniometeranalysis. The 10th percentile, mean and 90th percentileangles from the two 6 min blocks were calculatedfor each participant and group means and standarderrors were calculated and presented for eachkeyboard. With the typing data minute-by-minutetyping speeds, mean typing speeds and typing accuracywere tabulated for each keyboard and group meanvalues were calculated.

The BORG CR-10 scale data were evaluatedbased on relative change across the beginning, middleand end measurements with each keyboard. Calculatingrelative changes involved setting the beginningmeasurement to zero by subtracting the beginning Borgscale rating from beginning, middle and endmeasurements in that particular session. Thus, achange in Borg scale ratings relative to a beginning valueof zero was calculated. This reduced any additive effectsof time that randomisation may not havecounterbalanced.

Figure 4. The functional keyboards tested in Experiment 3 for typing performance, comfort and users’ preferences. (a), aconventional, straight keyboard; (b), a conventional, straight keyboard with built-in wrist-rest; (c), the new curved keyboard.

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Data were then analysed using repeated measuresANOVA using the statistical program JMP (version5.1; SAS Institute, Cary, NC, USA). All values arepresented as mean + SE. Differences were consideredto be significant when p-values were less than 0.05.

2.3.5. Results

2.3.5.1. Wrist posture. Due to equipment failure withone participant, complete data were collected from 25of the 26 participants. When the wrist extension datawere compared between keyboards and hands, therewas a significant difference in mean extension anglesbetween keyboards (p 5 0.01) and between hands(p ¼ 0.04) and a trend suggesting a potential hand bykeyboard interaction (p ¼ 0.052). The statisticalresults for the 10th and 90th percentile dataparalleled the results for the mean wrist extensiondata. As shown in Figure 5, the curved keyboard withthe built-in wrist-rest reduced mean wrist extensionangles by 6.3 + 1.28 (mean + SE) when compared tothe conventional, straight keyboard without a wrist-rest. However, there was no significant difference inwrist extension between this curved keyboard and thestraight keyboard with a built-in wrist-rest. Whencomparing hands, when averaged across all keyboards,participants worked with 3.6 + 1.68 more extension inthe right hand.

In the radial and ulnar plane, there were alsosignificant differences in mean ulnar deviation anglesbetween keyboards (p 5 0.01) and between hands(p 5 0.01), but there was no hand by keyboardinteraction (p ¼ 0.54). Again, the statistical results forthe 10th and 90th percentile data paralleled theresults for the mean ulnar deviation data. The curvedkeyboard reduced mean ulnar deviation anglesby 2.2 + 0.78 compared to the conventional,straight keyboards (with or without wrist-rests)(Figure 5). When comparing hands, participantsworked with 8.7 + 1.38 more ulnar deviation in theleft hand.

2.3.5.2. Typing performance. As shown in Figure 6,data gathered from the typing performanceprogram revealed that the differences in typing speedbetween the three keyboards were not significant(p ¼ 0.08). The mean (SE) typing speeds with thestraight keyboard, straight keyboard with wrist-restand curved keyboard were 51.8 (+3.2), 51.5 (+3.2)and 50.6 (+3.2) words per min respectively.In addition, there were no differences in typingaccuracy (p ¼ 0.77) between keyboards, the mean (SE)accuracy with the straight keyboard, straight keyboardwith wrist-rest and curved keyboard being 93.5(+0.6)%, 93.2 (+0.7)% and 93.1 (+0.6)%respectively.

Figure 5. 10th percentile (%tile), mean and 90th %tile (+SE) wrist extension and ulnar deviation angles by keyboard(KBD) and plotted with regard to hand. Significant differences between keyboards (*) and hands ({) are indicated on thefigure (n ¼ 25). WR ¼ wrist-rest.



2.3.5.3. Perceived fatigue. Perceived fatigue asmeasured by changes in Borg CR-10 ratings withregard to time were analysed for each body part andthe mean values for the changes in ratings are plottedin Figure 7. No differences in perceived fatigue ratingswere observed between right and left sides. As a result,the perceived fatigue data presented in Figure 7, withthe exception of the neck, were based on the averagechanges combining the results from the right and leftsides. Perceived fatigue changed and increased withregard to time with all keyboards (p 5 0.001). As

shown in Figure 7, the curved keyboard with the built-in wrist-rest consistently had the lowest changes/increases in perceived fatigue and the straightkeyboard without a wrist-rest consistently had thehighest changes/increases. The only differences inperceived fatigue ratings that were significant were inthe forearm (p ¼ 0.004), with the curved keyboardhaving smaller changes in perceived fatigue relative tothe straight keyboard without a wrist-rest. Thedifferences in perceived fatigue ratings in the shouldersbetween keyboards approached significance(p ¼ 0.054) with the keyboards with the built-in wrist-rests having smaller changes in perceived fatigue.

3. Discussion

The intent behind the design of the new curvedkeyboard was to promote a more neutral posture whentyping, while at the same time not affecting speed andaccuracy and eliminating the perceived ‘medical device’look of the various alternative ergonomic keyboarddesigns. The major differences between the new curvedkeyboard (Figure 4) and the fixed-split keyboard(Figure 1) are the flat profile and the unbrokenappearance of the alphanumeric section of thecurved keyboard. The fixed-split keyboard has anoticeably visible 258 opening angle betweenkeyboard halves compared to the subtle 128 openingcreated by the shape and curve of the keys on thenew curved keyboard. In addition, the fixed-splitkeyboard has an 88 lateral inclination (i.e. gable) anglebetween key halves to reduce forearm pronationcompared to no lateral inclination on the new curvedkeyboard.

Figure 6. Mean, minute-by-minute typing speed in wordsper minute (WPM) by keyboard. Standard error bars areomitted for clarity (n ¼ 26). WR ¼ wrist-rest.

Figure 7. Mean (+SE) change in the Borg CR-10 perceived fatigue ratings in the hand, forearm, shoulder and neck foreach keyboard (KBD) and plotted with regard to time (n ¼ 26). p-Values in the figure indicate the significance levels ofthe differences between keyboards. WR ¼ wrist-rest.

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The study results indicated that, compared to theconventional, straight keyboards (with and without awrist-rest), the curved keyboard design (incorporatinga wrist-rest) reduced ulnar deviation by 2.28. Rempelet al. (2007) reported a reduction of 0.98 in ulnardeviation when comparing use of this new curvedkeyboard with the conventional, straight keyboard,although their measured difference in ulnar deviationdid not reach statistical significance.

Although the primary interest was determiningwhether the curved keyboard reduced ulnar deviation,it is worth noting that the built-in wrist-rest had afairly substantial effect on wrist extension; on average,wrist extension was reduced by 6.38 compared to aconventional, straight keyboard without a wrist-rest.However, when compared to a conventional, straightkeyboard with a wrist-rest, no significant difference inextension was observed between the straight andcurved keyboards. Compared to a straight keyboardwithout palm rest, Albin (1997) reported an 8.48decrease in wrist extension when typists used a straightkeyboard with a palm rest and Rempel et al. (2007)observed an average reduction in wrist extension of4.28 when comparing use of this new curved keyboardwith the conventional, straight keyboard without awrist-rest. The sources for the small differences in ulnardeviation and extension measured in the present studyand in Rempel et al.’s (2007) study are not known.These may not be significant or could be due tosystematic measurement differences between equip-ment (electrogoniometry vs. video-based joint mar-kers) or differences in the characteristics of theparticipants used in the two studies.

The perceived fatigue measures appear to corrobo-rate the postural measures. The more neutral posturesin the wrist may explain the lower perceived fatigueratings in the hand and forearm with the curvedkeyboard. The short-term changes in perceived fatiguewith the curved keyboard were less than the perceived

changes measured with the straight keyboards. Thisappears to indicate that the participants were able toreadily adapt to using the curved keyboard. Inaddition, perceived fatigue levels in the shoulders werelower with the keyboards with built-in wrist-rests. Thisresult suggests that wrist-rests bear some of the load ofthe arms and reduce discomfort in the shoulder region.Since posture and/or electromyography were notmeasured in the upper arm and shoulder, objectivedata are not available to confirm this hypothesis.

Finally, there were no differences in typingperformance and typing accuracy between theconventional, straight keyboards and the curvedkeyboard.

One potential limitation of this study was that noprior verification was made of whether the participantsin Experiment 3 were touch typists before theirinclusion in the study. However, the group mean (SE)typing speed was 51.3 (+3.2) words per min,indicating that it was likely that the majority of themwere touch typists. In addition, another limitation inExperiment 3 was the short duration of the typingexposure and measuring changes in perceived fatigueover such a short period of time. Small changes inperceived fatigue were measured using the visualanalogue form of the Borg CR-10 scale, but one couldquestion whether the same results would be found overa longer duration of exposure. This could be a goal totest in future studies.

4. Conclusions

While reducing awkward wrist–forearm postures, therelatively extreme geometries of some ergonomickeyboards can be perceived as barriers or are realbarriers to adoption by some computer keyboardusers. Using a series of usability experiments, a newergonomic keyboard design was developed that wasshown to promote more neutral wrist postures, not toadversely affect typing performance and to lowerperceptions of fatigue among a sample of straightkeyboard users. Two iterative experiments, using arepresentative sample of straight, conventionalkeyboard users, identified a 128 opening angle as thepreferred choice when presented with an array ofpossible opening angles (the acceptable range being10–138). In addition, across the five keycap designstested, a ‘stepped’ presentation of keys spanning theopening was the preferred design. This ‘stepped’ keydesign more closely resembled current straightkeyboard designs than the other keycap designs testedand, as a result, was perceived as more familiar andapproachable by the participants. The thirdexperiment used a fully functional prototype of thecurved keyboard to confirm quantitatively the final

Figure 8. Microsoft Optical Desktop Pro Keyboard withcomfort curve design.



design’s effect on wrist postures, typing performanceand perceived fatigue across a sample of representativetypists. The 128 opening angle and curve in the keys inthe alphanumeric section of the keyboard reducedulnar deviation and, relative to a straight keyboardwithout a built-in wrist-rest, the curved keyboard’sbuilt-in wrist-rest reduced wrist extension. Typistsliked the new keyboard design relative to aconventional, straight keyboard. As a result, thedesign goals of creating a keyboard that promotedmore neutral postures, was perceived as less fatiguingand did not adversely affect typing speed and accuracywas achieved. In Autumn 2004, the curved keyboardwas released and marketed as the MicrosoftOptical Desktop Pro with the comfort curve design(shown in Figure 8) and since then additionalkeyboards have been introduced with the curvedkeyboard design.

Acknowledgements

Thanks to industrial designers, model makers and productplanners: Greg Jones, Stiven Kerestegian, Dick Compton,Vince Jesus, Seiya Ohta and Abid Saifee. Hugh McLoone ispresently at Akamai Insights. Peter Clark is presently atProvincial Health Services Authority, Vancouver, BC,Canada. Ryan Opina is presently at Nokia, Richmond, BC,Canada. Experiment 3 was supported by the NationalInstitute for Occupational Safety and Health EducationalResource Centre Training Grant T42/CCT010418, theWashington State Medical Aid and Accident Fund adminis-tered by the Department of Environmental and OccupationalHealth Sciences at the University of Washington andMicrosoft Corporation.

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Documents

Design and evaluation of a curved computer keyboardfaculty.washington.edu/petej/McLoone,ComfortCurve,Ergonomics2009.pdfpurchasing an alternative keyboard design. The purpose of this