The effect of six keyboard designs on wrist and forearm postures

There is increasing evidence that alternative geometry keyboards may prevent or reduce arm pain or disorders, and presumably the mechanism is by reducing awkward arm postures. However, the effect of alternative keyboards, especially the new designs, on wrist and arm postures are not well known. In this laboratory study, the wrist and forearm postures of 100 subjects were measured with a motion analysis system while they typed on 6 different keyboard configurations. There were significant differences in wrist extension, ulnar deviation, and forearm pronation between keyboards. When considering all 6 wrists and forearm postures together, the keyboard with an opening angle of 12 degrees , a gable angle of 14 degrees , and a slope of 0 degrees appears to provide the most neutral posture among the keyboards tested. Subjects most preferred this keyboard or a similar keyboard with a gable angle of 8 degrees and they least preferred the keyboard on a conventional laptop computer. These findings may assist in recommendations regarding the selection of keyboards for computer usage.     

An evaluation of the ergonomics of three computer keyboards

The influence of keyboard design on hand position, typing productivity and keyboard preference was evaluated by comparing two segmented alternative designs with the linear standard keyboard. The FIXED alternative keyboard featured a split angle of 12 degrees and a moderate lateral inclination angle of 10 degrees. The adjustable OPEN alternative keyboard was used with a 15 degrees split setting, which resulted in a marked 42 degrees of demiboard lateral inclination. Sixteen typists, who completed 10 h of training on both alternative keyboards, were videotaped while typing set texts on all three keyboards. Forearm and wrist angles based on three-dimensional video analyses were significantly different (p<0.05) among the three designs tested. Both alternative keyboards placed the forearm and wrist closer to neutral positions than did the standard keyboard. While the OPEN keyboard reduced pronation, it simultaneously increased radial deviation. The FIXED keyboard kept the forearm in moderate pronation and the wrist closer to neutral. More time was spent in neutral and moderate ranges of wrist motion when subjects typed on the FIXED compared with the other two designs. With respect to the standard keyboard, typing productivity was reduced by 10% on the FIXED and 20% on the OPEN designs. No significant difference in preference was found between the standard and FIXED keyboards, both of which were preferred over the OPEN. It was concluded that, of the three keyboards evaluated, the FIXED design incorporated moderate changes to the standard keyboard. These changes promoted a more natural hand position while typing thereby reducing the potential for cumulative trauma disorders of the wrist. In addition, the FIXED design preserved a reasonable level of productivity and was well accepted by users.     

Design and evaluation of a curved computer keyboard

Conventional, straight keyboards remain the most popular design among keyboards sold and used with personal computers despite the biomechanical benefits offered by alternative keyboard designs. Some typists indicate that the daunting medical device-like appearance of these alternative ‘ergonomic’ keyboards is the reason for not purchasing an alternative keyboard design. The purpose of this research was to create a new computer keyboard that promoted more neutral postures in the wrist while maintaining the approachability and typing performance of a straight 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 of fatigue when using the new curved keyboard were compared to those when using a straight keyboard design. The curved keyboard reduced ulnar deviation by 2.2° ± 0.7 (p < 0.01). Relative to the straight keyboard without a built-in wrist-rest, the prototype curved keyboard with the built-in padded wrist-rest reduced wrist extension by 6.3° ± 1.2 (p < 0.01). There were no differences in typing speed or accuracy between keyboards. Perceived fatigue ratings were significantly lower in the hands, forearms and shoulders with the curved keyboard. The new curved keyboard achieved its design goal of reducing discomfort and promoting more neutral wrist postures while not compromising users' preferences and typing performance.     

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

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

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

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

Wrist and forearm postures of users of conventional computer 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.     

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

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

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

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

Guidelines for wrist posture based on carpal tunnel pressure thresholds

OBJECTIVE: To develop work guidelines for wrist posture based on carpal tunnel pressure. Background: Wrist posture is considered a risk factor for distal upper extremity musculoskeletal disorders, and sustained wrist deviation from neutral at work may be associated with carpal tunnel syndrome. However, the physiologic basis for wrist posture guidelines at work is limited. METHODS: The relationship of wrist posture to carpal tunnel pressure was examined in 37 healthy participants. The participants slowly moved their wrists in extension-flexion and radioulnar deviation while wrist posture and carpal tunnel pressure were recorded. The wrist postures associated with pressures of 25 and 30 mmHg were identified for each motion and used to determine the 25th percentile wrist angles (the angles that protect 75% of the study population from reaching a pressure of 25 or 30 mmHg). RESULTS: Using 30 mmHg, the 25th percentile angles were 32.7 degrees (95% confidence interval [CI] = 27.2-38.1 degrees) for wrist extension, 48.6 degrees (37.7 -59.4 degrees) for flexion, 21.8 degrees (14.7-29.0 degrees) for radial deviation, and 14.5 degrees (9.6-19.4 degrees) for ulnar deviation. For 25 mmHg, the 25th percentile angles were 26.6 degrees and 37.7 degrees for extension and flexion, with radial and ulnar deviation being 17.8 degrees and 12.1 degrees, respectively. CONCLUSION: Further research can incorporate the independent contributions of pinch force and finger posture into this model. APPLICATION: The method presented can provide wrist posture guidelines for the design of tools and hand-intensive tasks.     

The split keyboard: an ergonomics success story

OBJECTIVE: 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. BACKGROUND: 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. METHODS: The literature on split geometry keyboards was identified, and the progression of the research was reviewed. RESULTS: 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. CONCLUSIONS: 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. APPLICATION: 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.     

Acceptance of the adjustable keyboard

The acceptance of a split keyboard with a user-adjustable angle (adjustable keyboard) and its impact on postural discomfort and general comfort of users was tested in a comparative laboratory experiment with 26 typists as subjects. The comparison was made with a standard keyboard. The results were interpreted using the findings of an earlier field study with another split keyboard with a fixed angle between the halves of the device. Both split keyboards improved postural comfort; however, the period of familiarization was much longer with the fixed-angle split keyboard. Since the adjustable keyboard allows a change, in the angle from 0 to 30^°, a person's posture can be adopted on a step-by-step basis. Thus, the new adjustable design has much better prospects of being accepted in practice than former attempts where the value was more academic than practical. The analysis of throughput and errors, under self-determined angles of the test object and with an angle comparable with those of fixed-angle split keyboards, reveals that users in work situations are not likely to accept fixed-angle split keyboards (30°) since throughput is substantially reduced during the long period of familiarization, accompanied by a substantial increase in errors. The results of this study confirm the assumption that new adjustable split keyboard design, once accepted by the users, may improve postural comfort, general comfort, and reduce fatigue. These effects could be demonstrated both in a short-term experiment and a long-term field study. The basic design feature of the adjustable keyboard, adjustability, is in agreement with the conclusions of recent studies on the introduction of ergonomically designed keyboards.     

The effect of handle angle on MAWL, wrist posture, RPE, and heart rate

In manual material handling tasks, the handle serves as the interface between the human operator and the box (the materials). Handle angle design can affect both wrist posture and lifting ability. This study was designed to evaluate the effect of handle angle on maximal acceptable weight of lifting (MAWL), perceived whole-body exertion, whole-body workload, wrist posture, and perceived wrist exertion. The results indicate that handle angle had a significant effect on wrist posture and wrist rating of perceived exertion (RPE). A box with a 0 degrees handle angle induced the greatest ulnar deviation and the highest wrist RPE. A 75 degrees handle angle induced the greatest radial deviation and a relatively high wrist RPE. A 30 degrees handle angle resulted in the greatest MAWL and the lowest level of wrist RPE. Overall, these findings suggest that 30 degrees and 45 degrees handle angles can provide favorable coupling conditions for the cutout-type handhold container handle. Actual or practical applications include the ergonomic design of container handles for manual material handling tasks industry.     

Physical exposure differences between children and adults when using standard and small computer input devices

By the age of five years, 75% of the children in the USA are using computers and at this age they are only one-half to two-thirds the size of and about one-fifth as strong as their adult counterparts. Fourteen children between five and eight years of age and their same-gender biological parents (giving a total of 28 subjects) were evaluated using both a standard and a smaller, child-proportional input device during standardised mouse and keyboard tasks. Typing and computer mouse performance were measured with tracking software, wrist posture was measured with an electrogoniometer and electromyography was used to measure finger flexor and extensor muscle activity in the right arm. With the small mouse, both children and adults performed the mouse task significantly faster and made significantly fewer errors. When using the standard-sized mouse and keyboard, children worked with significantly greater ulnar deviation and significantly less extension than their adult counterparts. When children used the smaller mouse, finger flexor muscle activity, finger extensor muscle activity and ulnar deviation significantly decreased, with little change in wrist extension compared to the standard mouse. No significant differences were observed between the standard and small keyboards for children or their parents. Compared to their adult counterparts, children had to apply twice the relative force, as a percentage of their maximum capacity, to activate the buttons and keys on the input devices. These measured differences may have application in the design of computer input devices for children.     

Physical exposure differences between children and adults when using standard and small computer input devices

By the age of five years, 75% of the children in the USA are using computers and at this age they are only one-half to two-thirds the size of and about one-fifth as strong as their adult counterparts. Fourteen children between five and eight years of age and their same-gender biological parents (giving a total of 28 subjects) were evaluated using both a standard and a smaller, child-proportional input device during standardised mouse and keyboard tasks. Typing and computer mouse performance were measured with tracking software, wrist posture was measured with an electrogoniometer and electromyography was used to measure finger flexor and extensor muscle activity in the right arm. With the small mouse, both children and adults performed the mouse task significantly faster and made significantly fewer errors. When using the standard-sized mouse and keyboard, children worked with significantly greater ulnar deviation and significantly less extension than their adult counterparts. When children used the smaller mouse, finger flexor muscle activity, finger extensor muscle activity and ulnar deviation significantly decreased, with little change in wrist extension compared to the standard mouse. No significant differences were observed between the standard and small keyboards for children or their parents. Compared to their adult counterparts, children had to apply twice the relative force, as a percentage of their maximum capacity, to activate the buttons and keys on the input devices. These measured differences may have application in the design of computer input devices for children.     

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

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

Wrist and forearm postures and motions during typing.

Awkward upper extremity postures and repetitive wrist motions have been identified by some studies as risk factors for upper extremity musculoskeletal disorders during keyboard work. However, accurate body postures and joint motions of typists typing on standardized workstations are not known. A laboratory study was conducted to continuously measure wrist and forearm postures and motions of 25 subjects while they typed for 10-15 min at a standard computer workstation adjusted to the subjects' anthropometry. Electrogoniometers continuously recorded wrist and forearm angles. Joint angular velocities and accelerations were calculated from the postural data. The results indicate that wrist and forearm postures during typing were sustained at non-neutral angles; mean wrist extension angle was 23.4 +/- 10.9 degrees on the left and 19.9 +/- 8.6 degrees on the right. Mean ulnar deviation was 14.7 +/- 10.1 degrees on the left and 18.6 +/- 5.8 degrees on the right. More than 73% of subjects typed with the left or right wrist in greater than 15 degrees extension and more than 20% typed with the left or right wrist in greater than 20 degrees ulnar deviation. Joint angles and motions while typing on an adjusted computer workstation were not predictable based on anthropometry or typing speed and varied widely between subjects. Wrist motions are rapid and are similar in magnitude to wrist motions of industrial workers performing jobs having a high risk for developing cumulative trauma disorders. The magnitude of the dynamic components suggests that wrist joint motions may need to be evaluated as a risk factor for musculoskeletal disorders during typing.     

Wrist and forearm postures and motions during typing

Awkward upper extremity postures and repetitive wrist motions have been identified by some studies as risk factors for upper extremity musculoskeletal disorders during keyboard work. However, accurate body postures and joint motions of typists typing on standardized workstations are not known. A laboratory study was conducted to continuously measure wrist and forearm postures and motions of 25 subjects while they typed for 10 – 15 min at a standard computer workstation adjusted to the subjects' anthropometry. Electrogoniometers continuously recorded wrist and forearm angles. Joint angular velocities and accelerations were calculated from the postural data. The results indicate that wrist and forearm postures during typing were sustained at non-neutral angles; mean wrist extension angle was 23.4 ± 10.9 degrees on the left and 19.9 ± 8.6 degrees on the right. Mean ulnar deviation was 14.7 ± 10.1 degrees on the left and 18.6 ± 5.8 degrees on the right. More than 73% of subjects typed with the left or right wrist in greater than 15 degrees extension and more than 20% typed with the left or right wrist in greater than 20 degrees ulnar deviation. Joint angles and motions while typing on an adjusted computer workstation were not predictable based on anthropometry or typing speed and varied widely between subjects. Wrist motions are rapid and are similar in magnitude to wrist motions of industrial workers performing jobs having a high risk for developing cumulative trauma disorders. The magnitude of the dynamic components suggests that wrist joint motions may need to be evaluated as a risk factor for musculoskeletal disorders during typing.     

Factors related to working posture and its assessment among keyboard operators

Video analysis of 15 keyboard operators was conducted over two four-hour periods to determine the effects of symptoms of over-use injury, the adjustability of the workstation, the type of keyboard, time of day and sex on working posture. The only factor which significantly affected posture was the type of keyboard, with operators at typewriters adopting a more extended shoulder position, reduced elbow flexion and increased wrist flexion, than those working at a VDU terminal. Analysis of the components of variance associated with repeated observations revealed that to minimise the variance associated with recording the posture of these subjects, and therefore obtain a representative mean posture, required at least nine observations for wrist angle, four for elbow angle, six for shoulder angle and three for trunk incline. The mean posture adopted by this group of operators was similar to the 'right angles' posture, with the trunk reclined 4 degrees , shoulder extended 1 degrees , elbow 92 degrees and wrist extended 7 degrees .     

The effect of viewing angle on wrist posture estimation from photographic images using novice raters

Observational assessment of wrist posture using photographic methods is theoretically affected by camera view angle. A study was conducted to investigate whether wrist flexion/extension and radial/ulnar deviation postures were estimated differently by raters depending on the viewing angle and compared to predictions using a quantitative 2D model of parallax. Novice raters (n = 26) estimated joint angles from images of wrist postures photographed from ten different viewing angles. Results indicated that ideal views, orthogonal to the plane of motion, produced more accurate estimates of posture compared to non-ideal views. The neutral (0°) posture was estimated the most accurately even at different viewing angles. Raters were more accurate than model predictions. Findings demonstrate a need for more systematic methods for collecting and analyzing photographic data for observational studies of posture. Renewed caution in interpreting existing studies of wrist posture where viewing angle was not controlled is advised.     

Effect of computer keyboard slope and height on wrist extension angle

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.