Turns Out Your Mental Exhaustion Can Impact You Physically

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Turns Out Your Mental Exhaustion Can Impact You Physically

By: Chris O'Shea

There have been countless studies that showed that when we're physically tired, our capacity to perform mental tasks suffers greatly. Anyone who has tried to drive after an all-nighter, or take a test after drinking one too many Zimas can attest to that. Our tired bodies just can't seem to make our brain kick into gear. But what about the opposite? Does mental fatigue impact our physical functioning? According to a trio of specialists in Britain, it does.

Samuele Marcora, Walter Staiano and Victoria Manning of Bangor University in the United Kingdom set out to determine how our bodies react when our brains are tasked. "The aim of this study was to test the hypotheses that prolonged mental exertion 1) reduces maximal muscle activation and 2) increases the extent of central fatigue [fatigue that takes place in both individual muscles and the central nervous system], induced by subsequent endurance exercise," the team wrote. Their report, set to be published in the March print edition of the Journal of Applied Physiology, shows that our bodies and our minds are much more connected than we ever thought possible.

To come to this conclusion, the team asked 16 healthy participants to ride a stationary bike once while feeling mentally fatigued and once while feeling mentally fit. To make sure they isolated the brain's functioning level, the team made sure the people had the same amount of sleep, food and drink before each experiment. To fatigue the participants' brains, the experts had them complete a 90 minute barrage of mental tests, which measured attention levels, memory and more. The non-fatiguing test was not unlike a high school class being taught by a sub: They merely sat and watched a documentary.

After each of the 90-minute sessions the participants mounted their bikes. They each rode until they reported feeling exhausted ("the point when they could not maintain a cadence of at least 60 revolutions per minute for more than five seconds"). As the people rode their bikes, Marcora, Staiano and Manning tracked their physical levels. The results? Those who took the 90 minute brain stumped tests stopped exercising about 15 earlier than those who watched the film.

As one of the researchers noted, the most interesting takeaway from this experiment is "that maximal force production is not altered by mental fatigue but endurance performance is altered, and this alteration is closely linked with a higher feeling of perceived exertion." In other words, mental fatigue doesn't impact strength, only endurance. So all those times you say you can't go to the gym because you worked too hard? Not cutting it anymore. But it's a totally valid excuse to skip any long runs.  

[Pic via Flickr - Brian Hillegas]

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