Where is the limit to what the body can tolerate?


We humans can run, swim or walk for miles. However, these performances are relatively short and devastate the body's reserves. But is there a limit to how much we can handle if the body is in balance?

There is a limit to how much energy we humans can consume if the body is in balance. Stock Photography.images: Jessica Gow / TT

A few weeks ago, thousands of runners participated in the Stockholm Marathon and ran 4.2 miles. Worse still, Race Across the USA is where unsecured runners run a marathon a day, six days a week, over several months, so that, for 140 days, they travel from California to Washington DC.

But is there any additional limit to human physical performance if we want to last longer than a few hours? How much do we manage people – in fact – by?

Yes, there is a limit. That's what researchers at Duke University in the United States say after studying Race Across the USA participants and other elite ventures such as the Tour de France cycle race.

The result, which was recently published in the journal Science Advances, shows that this limit reaches 2.5 times the resting metabolism, which corresponds to about 4,000 calories per day for a normal-sized person.

Under extreme conditions such as a marathon, we humans can go well beyond that limit. Because during a single marathon, a person burns an average of 15.6 times their own metabolism at rest. For a participant in the Tour de France, the corresponding value is 4.9 and for a person trying to cross the Antarctic ice is 3.5.

But this energy combustion is not sustainable in the long run, say the researchers. Not because the heart or lungs say stop – the intestines.

For example, during a marathon, the runner not only burns his "normal" energy bags, but also his reserve deposits, which consist of muscle and fat, which is not sustainable in the long run. Therefore, it becomes the body's ability to assimilate calories that will be decisive if its systems can remain in balance and in that case the energy consumption can be at most 2.5 times the resting metabolism, according to the researchers.

– You can do really intense things in a couple of days, but if you want to continue longer, you need to relax, says one of the researchers behind the study, Herman Pontzer of Duke University, BBC News.

The researchers also measured energy intake during pregnancy in women and found that this is at most about 2.2 times the metabolism at rest. That is, not far from what researchers call our limit of resistance.


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