These stresses create tiny tears in the muscles and tendons, which become inflamed. In extreme cases it can cause permanent tissue damage and disability. RSI is caused by making the same movement over and over again. For computer users RSI can result from poorly designed workstations with keyboards too high, ill-fitting chairs, stressful conditions, extended hours of typing, and using a mouse. The mouse strains the hand by forcing repetitive use of one finger, and is awkward to hold.
Users tend to grip mice too hard, often with the wrist cocked.
According to Dr. Pascarelli, ergonomic computer-related accessories are very hard to find. We couldn't find a single mouse or trackball we felt was safe to use for extended periods of time. The computer keyboard is an ergonomic nightmare. This strains the delicate muscles and tendons of the fingers and wrists, reducing circulation. Unlike workers in yesterday's typewriter-equipped offices, today's users work at a keyboard for hours at time, never varying their activity.