[ad_1]
The maximum metabolic activity of the human being during extraordinary endurance feats is limited by his biology.
iStock.com/Pavel1964
By Michael Price
Athletes who can run the equivalent of 117 marathons in a few months may seem unstoppable. It turns out that the biggest obstacle is their own body. A new study quantifies for the first time an unsurpassed "ceiling" for endurance activities such as running and cycling over long distances. It also reveals that the metabolic rate of pregnancy is similar to that of an ultramarathon.
"These are very interesting data," says Daniel Lieberman, a biologist at Harvard University's evolving university, who was not involved in the work. "He is very convincing that at the limits of human endurance, there is a hard limit."
Physiologists and athletes have long been interested in the fact that the human body can surpass itself. There is plenty of evidence to suggest that most people, and mammals, reach about five times their basic metabolic rate (RMO) or the amount of energy they spend at rest. Herman Pontzer, an anthropologist of evolution at Duke University in Durham, North Carolina, explains how the use of energy by humans during long endurance activities is another question.
Pontzer took the opportunity to answer this question when Bryce Carlson, an endurance athlete and former anthropologist at Purdue University in West Lafayette, Indiana, organized the 2015 Across the USA Race. Runners traveled 4957 kilometers during a series of marathons extending from Los Angeles, California to Washington, DC
Pontzer, Carlson and his colleagues replaced the normal hydrogen and oxygen of their drinking water with harmless and unusual isotopes of these elements, deuterium and oxygen 18. Scientists can calculate the amount of carbon dioxide produced by the athlete by chemically tracing the way these isotopes flow into the urine, sweat and exhaled breath. This measure is directly related to the number of calories burned.
The Pontzer team measured the initial BMRs of six riders, five men and one woman. Then, they collected energy expenditure data during the race to determine the number of calories burned per day. Researchers have mapped these data over time and analyzed them, as well as metabolic data previously collected during other endurance events, including triathlons, 160 km ultramarathons, long distance races. like the Tour de France and expeditions in the Arctic.
Whatever the event, they found that energy expenditure had strongly stabilized after about 20 days, eventually reaching about 2.5 times the BMR of the athlete. At this point, the body burns calories faster than it can absorb nutrients and convert them into energy, which represents a biologically determined ceiling for human performance, researchers report today. Progress of science. When an athlete reaches this ceiling, his body needs to tap into fat reserves to get energy. "It was just one of those beautiful moments of discovery for which you live as a scientist," says Pontzer. "We ended up tracing the very limits of human endurance, the envelope of what humans can do."
Brent Ruby, an exercise physiologist at Montana University in Missoula who did not participate in the study, says the new findings support what many ultra-endurance athletes already know: they need to accumulate their reserves of energy. fat before a long run.
In a second conclusion, the authors report that human pregnancy – the energy expenditure of which has been measured in previous studies – requires about the same level of energy as long sports endurance events. It is also governed by the same metabolic constraints. "Thinking of pregnancy in the same terms as we consider cyclists and triathletes in the Tour de France makes you realize how extremely demanding pregnancy is for the body," said Pontzer.
Some researchers, including Lieberman, have hypothesized that humans have developed bodies capable of traveling long distances to track large calorie-rich animals, and that these same metabolic adaptations could have allowed mothers to give birth. to bigger babies with a bigger brain. Since pregnancy and endurance activities work according to the same metabolic rules, this could have been the opposite, says Pontzer: Maybe humans have evolved to have babies with bigger brains , which then gave our species more stamina.
Lieberman is not convinced on this point. "It's a very big jump to go, and we need a lot more evidence to confirm it," he says. "Let's do things one step at a time, like a marathon."
[ad_2]
Source link