There is a limit to human endurance just before your body starts to eat itself

Until where can one push the human body? This is an issue that you could ask yourself during a 5 km run or a morning gym session, but a new study indicates that there is a definite limit to the number of hours in the morning. Human endurance – beyond which our body begins to decompose.

For long-term stress levels, this limit is to burn calories at 2.5 times our resting metabolic rate, regardless of your level of fitness or training. Beyond that, our body starts to feed on its own tissues and fat reserves to run its engines.

To determine our limits, a team of researchers analyzed data from different endurance challenges and life events, ranging from an ultramarathon from one ocean to the other 4,957 km (3,080 miles) to the requirements of pregnancy on the human body. .

"This defines the realm of the possible for man," said one of the team members, the evolutionary anthropologist Herman Pontzer, of Duke University in Carolina. North.

"There is just a limit to the number of calories that our guts can effectively absorb per day."

Part of the new study was tracking the energy expenditure of six race competitors across the United States: a grueling five-month run in which runners ran six marathons a week. The researchers also examined previously published data on the Tour de France, Arctic expeditions and other events.

The same L-shaped curve was noticeable for all types of effort. Although we can spend energy on many occasions, our resting metabolic rate is very fast – up to 15.6 times for a single marathon, 4.9 times for a professional cycling event or 2 , 2 times for a pregnancy, for example – possibly up to 2.5 times the limit in.

"You can do really intense things for a few days, but if you want to last longer, you have to remember it," Pontzer told James Gallagher at the BBC. "All data points, for each event, are all mapped onto this magnificent barrier of human endurance."

"These are very interesting data," said Michael Price, an evolutionary biologist, Daniel Lieberman of Harvard University, who had not participated in the study. Science. "This shows very convincingly that" at the limits of human endurance, the limit is strict. "

It seems that the human body can actually reduce its calorie consumption in order to stay at a sustainable limit, where we do not use energy faster than it can be restored. This study shows that this is possible in the short term, but our bodies eventually decide to put the brakes.

The researchers suggest that the digestive system is one of the biological bottlenecks: at one point, our body simply can not turn food faster into fuel.

For athletes who train for high endurance events, these new discoveries could help them plan the best way to work under this 2.5x cap. However, researchers have not ruled out the possibility that some people will pierce it.

"So, I guess it's a challenge for elite athletes," Pontzer said. "Science works when we prove that we are wrong, maybe someone will exceed that ceiling one day and show us what we are missing."

The search was published in Progress of science.