A shift in the power spectrum of surface electromyographic (EMG) activity, recorded during machine-paced keyboard operation and indicative of localized muscle fatigue in the forearms, clearly distinguished two groups of operators who sorted mail in accordance with different work practices. The group exhibiting these fatigue-related changes in EMG activity also (1) had much greater difficulty in meeting the accuracy requirements of the keyboard function; (2) rated visual, mental, and keying-related workload as objectionably high; (3) exhibited greater tremor in a post-work test of hand steadiness; and (4) reported greater physical discomfort in the fingers, hands, wrists, and arms. These results demonstrate that physiological data can increase our understanding of the effects of occupational stress on performance in the workplace.
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