Using touch-screen keyboards on tablet computers for long periods of time could lead to chronic shoulder problems, suggests a study in the November issue of Applied Ergonomics that compared the musculoskeletal impact of three types of keyboards, The Wall Street Journal reported.
The small study found touch screen, or virtual, keyboards, which lack a feedback mechanism indicating a key has been pressed, require less typing force and finger-muscle activity than conventional keyboards. But tablet users must keep their fingers hovering above the keyboard to avoid accidentally activating the keys. That can lead to prolonged static loading in the shoulders, a form of muscle exertion caused by not moving, the study suggests.
Researchers at Northern Illinois University in DeKalb, Ill., recruited 19 experienced virtual-keyboard users—10 men and nine women in their mid-20s. The subjects typed passages from Grimm’s Fairy Tales during five-minute typing tests on touch-screen, desktop and notebook keyboards. The tests were done twice on each keyboard, while electrodes recorded muscle activity in the forearms and shoulders. A force platform under the keyboards measured keystroke force.
The average typing speed on the desktop and notebook keyboards was 63 words a minute compared with 25 words on the touch screen. Accuracy was also higher on the conventional keyboards. Although muscle activity in the forearms was lowest when the subjects were typing on a virtual keyboard, it was higher in the trapezius muscles in the upper back, which support the shoulders and arms. That may be due to hand and forearm floating while typing, researchers said. The differences in trapezius activity were small but could be important if they accumulate over time, they said.
Caveat: The virtual keyboard screen wobbled slightly during typing, which may have resulted in an underestimation of the typing forces and keystroke duration, researchers said. The study was partially funded by computer company Hewlett-Packard Co.
Title: Differences in typing forces, muscle activity, comfort, and typing performance among virtual, notebook, and desktop keyboards.