Working beyond our capacity is something we're all intimate with, from the executive with back-to-back tasks the boss wants "yesterday" to the single mother with young child and full-time job. Few of us can afford to defer work for the morrow, when we are fresher and better rested.
Now a new study tells us that working hard when already fatigued can raise blood pressure significantly. In the long term this can contribute to various problems including cardiovascular stress.
Rex Wright and his team at the University of Alabama used a simple experiment to correlate fatigue and blood pressure. They had 80 subjects perform a memorisation test with a chance of a small prize.
The volunteers were given two minutes to memorise either two or six trigrams (random three-letter sequences like airport codes, such as DXK). During those two minutes the researchers measured heart rate and blood pressure response. Before the test, the volunteers were asked to describe their level of fatigue, using a standard questionnaire.
Wright's team found that of those asked to memorise just two trigrams, moderately fatigued subjects saw a greater rise in blood pressure than those with low fatigue. Of those asked to memorise six trigrams, the moderately fatigued had a relatively small blood pressure response. And those who reported high fatigue had a small blood pressure rise whether told to memorise two or six trigrams.
The results indicate a cost-benefit analysis happening in the minds of the subjects. "Presumably," Wright said, "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 viewed success there as impossible or too difficult to be worth the effort."
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In other words, if a goal looks both achievable and worthwhile, even a fatigued person will increase effort to compensate for decreased capability. If, however, a person is very fatigued, he will withdraw effort: even an easy task appears difficult and not worthwhile.
It is studies like this that call the attention of employers and taskmasters to the physical stress they can cause. The prevalence of office gyms and the changing responsibilities of HR departments and consultants are a partial result of such common-sense science.