Computer Study Links Mouse Position To Muscle Tension

October 09, 1997

But Simple Solutions Can Ease The Pain

SAN FRANCISCO-- People who use a mouse with their computer suffer more than twice as much muscle tension in their arms, necks and shoulders as those who don't use a mouse, according to research just published by a scientist at San Francisco State University. However, training sessions promoting greater awareness of muscle tension, coupled with frequent one-second breaks from keyboarding, can cut tension levels in half, the study also showed.

The findings appear in the current issue of Ergonomics, and emphasize the apparent connection between greater muscle tension and keyboards that force mouse users to extend their arms for long periods. "Wide keyboards with numeric keypads on one end force the arm to extend farther to use the mouse, and that almost always puts you into trouble," said experimental psychologist Erik Peper, coauthor of the paper and a professor of holistic health at SFSU. "The new, raised ergonomic keyboards are even wider, increasing chronic shoulder tension even more when you use a mouse."

In a separate, ongoing study, Peper and his colleagues have found that about 80 percent of computer stations are set up incorrectly for the user's body. Chairs, keyboards and screens are often at the wrong height or angle, and the muscle tension that results can lead to long-term injuries and chronic pain that is difficult to remedy, according to studies by other researchers. "By the time we are aware of it, it is much harder to reverse," Peper said. Peper suggests that computer users can reduce muscle tension by switching to keyboards with a centrally located trackball or trackpad pointer instead of a mouse, or keyboards compact enough to allow the mouse to be used without extending the arm too much. He finds that reducing the arm extension and taking quick "microbreaks" every minute during computer use minimize muscle tension. An alternative to switching keyboards is to cover the 10-key section to the right with a pad that allows a mouse position less likely to create arm and shoulder muscle tension.

Although he found reduced muscle tension among users of trackball or trackpad pointing devices, Peper noted that there is a low base level of tension any time a computer user approaches the keyboard. People's breathing rates increase, their shoulders often rise, and other indicators of low-level tension appear. "But just because you tense up doesn't mean you'll get sick," he said. With greater awareness of muscle tension, computer users can learn to relieve their muscles and reduce the tension that can result in subsequent pain and injury.

Peper used standard methods of recording tension in four muscle groups with test subjects in four keyboarding positions, and found the greatest reduction in muscle tension among trackball or trackpad pointing device users.

Peper is the director of SFSU's Institute for Holistic Healing Studies, a center which focuses on natural approaches to health. He coauthored the muscle tension awareness study with Richard Harvey, a former SFSU psychology graduate student who won a California State University research competition for this work. Their findings include the development of new ways to apply muscle tension measurements in the design of computer pointing devices and keyboards, and the recommendations for healthier computing practices.
SFSU is a highly diverse community of 27,000 students and 3,500 faculty and staff. It is the second largest of the nationally recognized 23-campus California State University System. Founded in 1899, the University is approaching its 100th year of service to San Francisco, the Bay Area, California and beyond.

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