If you ’re redact your consistence through a test of survival , whether it ’s running an ultramarathon or crossing Antarctica , is it “ mind over matter ” or is there a physical limit ? A young cogitation shows that your breakage point is not only a matter of psychological science , there might actually be a hard boundary to human endurance .

As reported in the journalScience advance , even the tough and best - trained endurance athlete are ineffectual to burn calories at more than 2.5 times their resting metabolic pace for a free burning time . Beyond this point of accumulation , the body starts to break down its own tissue to make up for the thermic shortage .

It is possible to break this 2.5 verge for   a limited period . As the study note , some 11 - 60 minutes triathlon athletes burn large calorie at 9.4 times their basal metabolic rate . However , your consistency is not capable of digesting enough gram calorie needed to sustain this level of survival without the body draw on its reticence DOE supplying . Your   " gasoline tank " is almost   running on empty at this pointedness and you ’ve only get limited time left before it ’s totally game over .

" There ’s just a limit to how many calories our guts can effectively take in per day , " discipline co - source Herman Pontzer , an associate professor of evolutionary anthropology at Duke University , said in astatement .

" you may sprint for 100 cadence , but you may even up for miles , right ? That ’s also true here , " Pontzer add .

The squad of researchers track   legion athletes ’ metamorphosis by addinguncommon isotopes of elementsin their drunkenness water and then analyzing pee sample after the project at hand . In doing so , they tracked the rate of   carbon dioxide their trunk was get and , ultimately , increases in metabolism and energy expenditure .

A number of other activities were shown to really labour the curt - term bound of metabolic rate . For example , cyclists in the Tour de France were line up to burn calories 4.9 times their resting metabolic rate , while trekking across the Antarctica saw hikers sunburn calories at 3.5 times the resting charge per unit .

Interestingly , pregnant women hold up around 2.2 times their resting metabolic rate . This go to show how taxing this effort can be on the body , demanding a sustain stream of DOE expenditure that ’s only just less   than thesustainable free energy outgo found among endurance jock .

An understanding of this 2.5 room access could even be used to explain howphysiological limit point are stopping certainspeed records from being shattered , as human endurance may have   an ultimate limit . That say , while the squad argue that the 2.5 mark is likely the current surd limitation for human , it is n’t unimaginable   that some   individuals , somehow , might be capable to march beyond it .

" So I guess it ’s a challenge to elect survival athletes , " Pontzer concluded . " Science work when you ’re evidence wrong . perhaps someone will break through that cap some day and show us what we ’re missing . "