We discovered the absolute limit to human endurance

The human body cannot burn more than a certain number of calories per day, which means that human capacities have an insurmountable ceiling, reports a new study. A ceiling linked to metabolism which would also explain … the duration of pregnancy.

We are used to seeing world records fall in sports competitions such as the Olympic Games or the World Championships in Athletics. Many scientists have questioned the limit impassable that the human body could not exceed. We can thus observe that the number of sports records has been in free fall since the 1990s. " In pole vault, for example, we went very quickly from the 5m mark (in 1963) to 6.14m by Sergei Bubka in 1994. But it took twenty years to break this record thanks to Frenchman Renaud Lavillenie, in 2014 "Reports Jean-François Toussaint, professor of physiology at Paris-Descartes University. However, we have never been able to formally establish a theoretical limit.

The body cannot assimilate more than 4,000 calories per day

However, this is what a team of researchers from Duke University in California has just discovered. In a study published in Science Advances on June 5, they established that even the best athletes in the world cannot overcome a certain endurance capacity in the long term. According to their calculations, the total energy expenditure (TED) cannot exceed 2.5 times the basic metabolic expenditure (DMB), or about 4,000 calories per day for an individual of normal build.

Previous studies had however estimated this ceiling at a much higher threshold: 4 to 5 times the BMD for the 23 days of the Tour com France, 9.4 times for an 11 hour triathlon, 8.5 times for an ultramarathon of 25 hours or 6.6 times for a trek Arctic 10 days. But to achieve this performance, the body draws on its reserves and "self-consumes" even if it is supplied with additional calories, reports Herman Pontzer, anthropologist at Duke University and co-author of the study. In the long term, the expense is therefore unsustainable.

An energy expenditure in logarithmic curve

To arrive at the figure of 2.5, the researchers compiled the results of previous studies and added their own data from a 140-day race across the United States (transcontinental Race Across the USA, or Rausa), and, more surprisingly, the pregnancy andfeeding with milk, "A kind of ultimate endurance activity," smiles Herman Pontzer. They drew a declining logarithmic curve tending towards 2.5: during a 100 meters, one can naturally burn calories at a very high pace, but you won't be able to run a marathon at this speed. During the Tour com France, cyclists can thus consume 7,000 to 8,000 calories per day, but after a while, the body can no longer assimilate these additional calories. " It is actually less a limit to the effort than a limit to the digestion capacity Explains Herman Pontzer.

However, the body has an incredible ability to adapt. During the first five days of the Transamerican race, athletes spend an average of 6,202 calories per day, or 3.76 times the BMD. But during the last week, while the pace of the race is almost unchanged, energy expenditure drops to 4,906 calories per day, or 2.81 times the DMB. The body thus learns to "save" theenergy. But this saving capacity therefore reaches a fate limit of 2.5.

Is pregnancy the last endurance race?

Another surprising discovery: energy expenditure during pregnancy is 2.2 times the BMD, barely below that of athletes during an endurance trek. " That would explain why babies can't get bigger and why pregnancy lasts so long "Say the researchers. Exceeding the 2.5 threshold would mean for the mother draw from its own reserves, which would be dangerous for its survival. " The question is: this rate of 2.5 seems to regulate the whole metabolism is it the cause or the consequence of the duration of pregnancy ? Asks Herman Pontzer.

A drug that increases endurance by more than 50% in mice

Article by Janlou Chaput published on 07/16/2013

Mice that received the drug with the code name SR9009 were more enduring by more than 50% in running. While this compound may help people with pathologies severely limiting activity physical (including L'obesity), the authors already fear that this product will soon be sought by those involved in the fight against doping./strong>

Sport is good for health. Everyone knows it. Unfortunately thephysical activity is a nightmare for some people, suffering from disorders greatly limiting their possibilities of movement. This is the case ofobesity and aging, among the most frequent examples, but also of debilitating diseases such as chronic obstructive pulmonary disease orheart failure Congestive.

Scientists are trying to find solutions to help all of these patients. Among those that inspire hope, one molecule named SR9009. Because according to a study published in Nature Medicine, this drug candidate would give endurance to laboratory mouse, and would transform them into runners seasoned.

Endurance improved by 50%

This compound is said to have a particular affinity for cellular receptors called Rev-Erb-α. Previous research, published in March 2012 in the journal Nature, showed that it is involved in the metabolism of lipids and glucose the level of liver, that it synchronizes the activity of the body according to the 24-hour day-night alternation cycle and that it helps obese mice lose weight.

In this work, researchers from the Institut Pasteur com Lille first tested the muscle activity of rodents who don't have the famous Rev-Erb-α receptors. Their performance in running are significantly lower than their congeners with receptors. These first elements therefore suggest that SR9009 could improve physical capacities.

Wild-type mice then received the drug, which activates Rev-Erb-α. As well in vitro thatin vivo, the metabolism of muscular skeletal has been increased. In terms of performance, running capacities have been improved by more than 50% compared to the same untreated animals, not only in terms of deadlines, but also in terms of distances traveled. Huge progress.

SR9009, the drug that turns muscles

On closer inspection, the authors noted that the muscles of these laboratory rodents had assumed the appearance of those of trained athletes, capable of withstanding strong oxidation. Indeed, the expression profile gene very similar to what is found in athletes.

According to this work, the activation of Rev-Erb-α receptors by SR9009 would lead to the synthesis of new mitochondria, the energy centers of the cell, which make it possible to maximize the energy obtained from glucose thanks to oxidation reactions. In return, the mitochondria failing, and potentially harmful to the muscle cell, would be destroyed by autophagy (digestion by the cell).

In addition to improving athletic performance, the molecule could help lower the level of triglycerides. It would help give the body the illusion that it is trained tophysical exercise, making it possible to increase energy expenditure.

Scientists are already concerned about possible drifts

Encouraging results for a whole section of the population affected by the difficulty of practicing physical activity. But obviously, when we talk about improving performance, we inevitably think of one of the scourges of sport: doping. At a time when suspicion hangs over the yellow jersey of the Tour com France cyclist Christopher Froome (the controversy arose because of his ease on the bike, and not because of analyzes confusing him) and while American sprinters and Jamaicans come to admit having been taken by the patrol, the cleanliness in the sport very high level remains debated. It is also obvious that these are not the only disciplines affected.

Interviewed by the Florida daily Sun Sentinel, Thomas Burris, one of the researchers of the study, admits feeling frightened at the idea that its use could be diverted for the benefit of cheaters, and almost regrets the effectiveness of the molecule that he himself put on point.

However, it is not yet known whether the results obtained in mice can be extrapolated to humans. In addition, there is the question of possible health risks. Only clinical tests could rule on the interest of such drug, and these are not yet programmed. This gives the anti-government authorities a little time doping to find a way to detect traces of SR9009, in case it shows promise.

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