Figure 5 - uploaded by Peter Wallace Johnson
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Index finger width by gender and size percentile as a function of age, data from CHILDATA (24). Both ANSI (28) and ISO (29) standards recommend that keys on keyboards have 19±1 mm spacing, which corresponds to the index finger width approximating the 50th to 95th percentile of adult Western males.
Contexts in source publication
Context 1
... 50th percentile adult male's index finger weighed almost one-third more than the 50th percentile female's; however, the differences in the length of the index finger were smaller, the males' finger being only 6.7% longer than the females'. Figure 5 shows the changes in index finger width by gender and size percentile as a function of age. Current ANSI (28) and ISO (29) standards for keyboards recom- mend a key size and key spacing of 19 (SD 1) millime- ters. ...
Context 2
... ANSI (28) and ISO (29) standards for keyboards recom- mend a key size and key spacing of 19 (SD 1) millime- ters. Figure 5 demonstrates how key size and spacing is probably based on anthropometric clearance issues to accommodate the larger 50th to 95th percentile of adult Western males. ...
Citations
... Differences in the size and shape of conventional mice affected biomechanical loading. With regards to size, Johnson and Blackstone reported no difference in forearm muscle activity when participants used a smaller (88 × 51 × 34 mm) computer mouse [54]. They also reported that participants showed faster performance in a mousing task when using the smaller mouse. ...
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.
... Computer input devices (the computer mouse and keyboard) represent a class of tools where a "one size fits all" paradigm has predominantly been applied (Johnson and Blackstone, 2007). Most of the research and standards on the physical design of computer input devices was conducted in the 1970's and 1980's, long before the advent of the modern computer mouse and keyboard. ...
Studies have shown that there are adverse performance and postural impacts when children use standard, adult-sized computer mice; however, the impact of children using adult-sized keyboards has been less rigorously evaluated. The aim of this study was to investigate whether there were any postural and performance differences when children and adults used the mouse next to a standard 104 key keyboard with a numeric keypad compared to a small, more compact keyboard without a numeric keypad. A total of 42 subjects, including 28 adults and 14 children between the ages 6?8 participated in the study. Subjects were asked to perform a series of standardized point-and-click tasks using a standard-sized mouse with both the standard and small keyboard. During mouse operation arm abduction and forearm rotation were measured using overhead photographs, and mouse performance was characterized by measuring movement times and the time it took to press-and-release (click) the left mouse button. Compared to the standard keyboard, both children and adults had less arm abduction (p < 0.10) and external rotation of the forearm (p < 0.05) when using the mouse next to the small keyboard. When comparing children to adults, children worked with significantly more arm abduction with both keyboards; however there were no significant differences between children and adults in internal and external rotation of the forearm. When comparing performance, children took almost twice as long to move the mouse between targets (p < 0.05) and were slightly faster when operating the mouse next to the small keyboard. In addition, compared to adults, it took children twice as long to press and release the mouse button. The study findings indicate that children would benefit from a postural standpoint if computer manufacturers sold, and schools and parents purchased, computers with smaller keyboards. The two-fold difference between children and adults in the time it took actuate the mouse button indicate that mouse button activation forces may need to be lower for children.
... The aetiology of MSDs is multifactorial and may include workstation parameters, psychosocial stress, posture and forcerelated exposures related to anthropometry (size and strength), rest break schedules and individual differences in motor control strategies. All of these contribute and interact under relatively low biomechanical load conditions (Jensen et al. 1993, Johnson et al. 2000, Wahlstrom et al. 2000, Dennerlein and Johnson 2006, Johnson and Blackstone 2007), which may be sustained for many hours. Although the value of task variation is intuitively appealing, it may therefore be difficult to empirically isolate the effects of variation. ...
... The National Institute for Occupational Safety and Health in the United States of America reviewed the literature on health effects associated with occupational work and concluded that there was strong evidence for an association between static or specific postures of the neck or neck/shoulder and MSDs in these regions (Bernard 1997). Whilst high wrist velocities and accelerations have been reported during keyboard work (Dennerlein and Johnson 2006b), computer tasks generally require a low level of effort ( Johnson 2006a, Johnson and Blackstone 2007) and little movement (Straker et al. 2008c). For example, when a computer-based task was compared to a book/paper-based task, average postures and minimal levels of muscle activity were greater in the computer-based tasks, for both adults (Waersted and Westgaard 1997, Straker et al. 2009c) and children (Ciccarelli et al. 2006, Straker et al. 2008c, 2009d). ...
Computer use by children is common and there is concern over the potential impact of this exposure on child physical development. Recently principles for child-specific evidence-based guidelines for wise use of computers have been published and these included one concerning the facilitation of appropriate physical development. This paper reviews the evidence and presents detailed guidelines for this principle. The guidelines include encouraging a mix of sedentary and whole body movement tasks, encouraging reasonable postures during computing tasks through workstation, chair, desk, display and input device selection and adjustment and special issues regarding notebook computer use and carriage, computing skills and responding to discomfort. The evidence limitations highlight opportunities for future research. The guidelines themselves can inform parents and teachers, equipment designers and suppliers and form the basis of content for teaching children the wise use of computers. STATEMENT OF RELEVANCE: Many children use computers and computer-use habits formed in childhood may track into adulthood. Therefore child-computer interaction needs to be carefully managed. These guidelines inform those responsible for children to assist in the wise use of computers.
Extensive computer mouse use is an identified risk factor for computer work-related musculoskeletal disorders; however, notebook computer mouse designs of varying sizes have not been formally evaluated but may affect biomechanical risk factors.
Thirty adults performed a set of mouse tasks with five notebook mice, ranging in length from 75 to 105 mm and in width from 35 to 65 mm, and a reference desktop mouse. An electro-magnetic motion analysis system measured index finger (metacarpophalangeal joint), wrist and forearm postures, and surface electromyography measured muscle activity of three extensor muscles in the forearm and the first dorsal interosseus.
The smallest notebook mice were found to promote less neutral postures (up to 3.2 degrees higher metacarpophalangeal joint adduction; 6.5 degrees higher metacarpophalangeal joint flexion, 2.3 degrees higher wrist extension) and higher muscle activity (up to 4.1% of maximum voluntary contraction higher wrist extensor muscle activity). Participants with smaller hands had overall more non-neutral postures than participants with larger hands (up to 5.6 degrees higher wrist extension and 5.9 degrees higher pronation); while participants with larger hands were more influenced by the smallest notebook mice (up to 3.6 degrees higher wrist extension and 5.5% of maximum voluntary contraction higher wrist extensor values). Self-reported ratings showed that while participants preferred smaller mice for portability; larger mice scored higher on comfort and usability.
The smallest notebook mice increased the intensity of biomechanical exposures. Longer term mouse use could enhance these differences, having a potential impact on the prevention of work-related musculoskeletal disorders.
