THURSDAY, July 3 (HealthDay News) -- Doing mental or physical work while exhausted may harm your health, a new study shows.

Researchers at the University of Alabama at Birmingham found that fatigued people had bigger spikes in blood pressure than well-rested people while doing a memorization test.

When fatigued people regard a task as worthwhile and achievable, they increase their effort to compensate for their diminished capability, explained study author and psychologist Rex Wright. As a result, a tired person's blood pressure increases and remains elevated until the task is completed or the person gives up.

"Our findings are relevant to health because of links that have been established between cardiovascular responsiveness and negative health outcomes, including hypertension and heart disease," Wright said in a prepared statement.

"Individuals who experience chronically exaggerated cardiovascular responses are believed to be at greater risk than individuals who do not. Thus, the implication is that chronic fatigue may pose a health risk under some performance conditions," he explained.

In this study, Wright and colleagues told 80 volunteers they could win a modest prize by memorizing two or six nonsense trigrams (meaningless, three-letter sequences) within two minutes. Compared to volunteers with low levels of fatigue, those with moderate fatigue had stronger blood pressure while doing the two-trigram memorization task.

"Presumably this was because the moderately fatigued subjects viewed success as relatively hard, but still possible and worthwhile. Subjects who reported moderate fatigue had relatively reduced blood pressure increases in the six-trigram condition, presumably because they view success there as impossible or too difficult to be worth the effort," Wright said.

Volunteers with high levels of fatigue had low blood pressure increases in both the two- and six-trigram tasks. This likely means they viewed both tasks as too difficult to attempt, the researchers said.

The study was published in the July issue of the International Journal of Psychophysiology.

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