This refers to the amount of time a person holds a static position to perform a given task. The longer the same muscle or muscle group is used, the greater the likelihood of both localized and general fatigue. This is why rest breaks or changing tasks is so important to decrease prolonged static postures, and thereby reduce the risk of injury. Also important is the use of position aides, such as foot rests, copy holders, adjustable chairs, and keyboard trays to minimize fatigue to muscle groups not directly involved in the computer work activity.
Repetitious work (working at the computer) is very fatiguing on your upper extremities as well as your eyes. It is important that breaks from working at the computer be taken every 20 to 40 minutes in order for your body to rest and recover. Taking a short break (3 to 5 minutes) does not mean you have to stop working, other activities such as talking to a co-worker, making copies, filing, etc. could be done during breaks from typing.
It is also important to change positions periodically. Sitting in one position or leaning on your arms for an extended period of time can interfere with circulation.