June 17, 1996
Chair-mounted split keyboard helps reduce typing risks
Although expensive and complicated to adjust, a split keyboard mounted onto the arms of a worker's chair can help reduce a typist's risk of carpal tunnel syndrome (CTS) and other cumulative trauma disorders, according to a new Cornell University study.
"Using the 'floating arms' keyboard (FAK) can reduce the time a typist's hands spend in deviated postures that increase risks for carpal tunnel syndrome," said ergonomist Alan Hedge, Ph.D., professor of design and environmental analysis and director of the Human Factors Laboratory in Cornell's College of Human Ecology. He pointed out that although there are several split keyboard designs on the market, the FAK is the only one that actually attaches to one's chair.
"The FAK can improve upper body posture, compared with a regular keyboard on a conventional articulated flat holder, especially if the FAK is tilted down to put the hands and wrist in a neutral position," he added.
Hedge, with graduate student Gregory Shaw, used an electrogonimeter and video-motion measurements, observer reports and questionnaires to analyze how useful the FAK was in reducing risk with 12 experienced typists.
Their findings are summarized in a new report issued by the Cornell Human Factors Laboratory, Effects of a Chair-Mounted Split Keyboard on Performance, Posture and Comfort.
The most dramatic postural improvement with the FAK was in how much typists deviated their wrists side to side (ulnar deviation); when using a conventional keyboard, the typists' wrists were in high risk positions 14 percent of the time, compared with only 0.5 percent when using FAK. But unless the FAK is properly adjusted, the hands can still be in vertical deviation (wrist extension) for the same amount of time as with a conventional keyboard.
Typists also generally improved the posture of their shoulders, upper arms and forearms with the FAK. "Overall, it was easier for some typists to work in more neutral and supported postures with the FAK than with the conventional keyboard arrangement," Hedge said.
When the FAK was adjusted to a 15-degree downward angle, it scored even better because the typists' hands were much closer to a desirable neutral position. In previous research, Hedge had found that when regular keyboards are placed on a lowered, preset angle tilted down keyboard holder, workers made 60 percent more typing movements within a low-risk zone compared with the same keyboards on desks and other keyboard holders.
"This study confirms that working with a keyboard that's just below elbow level and tilted away slightly lets you type in a relaxed posture, while keeping your hands in a wrist neutral position," Hedge said. "The FAK is probably the best of the alternative keyboard designs we have studied so far for touch typists."
The keyboard does have its drawbacks, however, Hedge pointed out. It is difficult for hunt-and-peck typists, awkward for small users to use, interferes with chair accessibility, makes it more difficult to reach paper documents, fits only certain kinds of chairs, costs much more than conventional keyboards, and correctly setting up the FAK requires some professional help.
During the 1980s, the number of personal computers in the United States jumped by a factor of 10; during the same period, the incidence of reported cumulative trauma disorders in the upper body, such as carpal tunnel syndrome, also jumped tenfold.
"Most keyboard injuries apparently occur because of long term working on repetitive tasks while sitting in a poor upper body posture with the hands in deviated positions," Hedge said. "Lowering and reorienting the keyboard seems to substantially reduce these problems."
The report, Effects of a Chair-Mounted Split Keyboard on Performance, Posture and Comfort, is available for $15. The report can be ordered by calling (607) 255-2168, or by fax, (607) 255-0305. For further details, contact Dr. Alan Hedge, Human Factors Laboratory, DEA, MVR, Cornell University, Ithaca, NY 14853, phone (607) 255-1957 or e-mail firstname.lastname@example.org. More information on the Human Factors Laboratory and its research is available on the World Wide Web at
The FAK was donated by Workplace Designs, Inc., of Stillwater, Minn.