Working hard when tired is not good for your health. Doing mental or physical work while exhausted may harm your health, according to a study from University of Alabama at Birmingham and published in International Journal of Psychophysiology.

In the study, fatigued people had bigger spikes in blood pressure compared to 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. As a result, the blood pressure of a tired person increases and remains elevated until the task is completed or the person gives up.

In this study, Wright and colleagues told 80 volunteers they could win a modest prize by memorizing 2 to 6 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.