Profile image
By Alton Parrish (Reporter)
Contributor profile | More stories
Story Views
Now:
Last Hour:
Last 24 Hours:
Total:

Is There A Limit to Human Endurance? Science Says Yes

% of readers think this story is Fact. Add your two cents.

New study reveals how hard humans can push and still keep it up without breaking down.  Some say the breaking point is all in your head, but new research suggests it’s also in your gut

Ironman Triathlon

More than 2,400 Marines and civilians biked 56-miles through base during the Ironman 70.3 Triathlon at Oceanside, Calif., March 30, 2013 130330-M-LD192-533.jpg

Photo Lance Cpl. Sarah Wolff / Wikimedia Commons

From the Ironman triathlon to the Tour de France, some competitions test the limits of even the toughest endurance athletes. Now, a new study of energy expenditure during some of the world’s longest, most grueling sporting events suggests that no matter what the activity, everyone hits the same metabolic limit — a maximum possible level of exertion that humans can sustain in the long term.

When it comes to physical activities lasting days, weeks and months, the researchers found, humans can only burn calories at 2.5 times their resting metabolic rate.

Not even the world’s fastest ultra-marathoners managed to surpass that limit, the researchers found.

“This defines the realm of what’s possible for humans,” said study co-author Herman Pontzer, an associate professor of evolutionary anthropology at Duke University.

Beyond the threshold of 2.5 times a person’s resting metabolic rate, researchers found, the body starts to break down its own tissues to make up for the caloric deficit.

One explanation for this limit may be the digestive tract’s ability to break down food, said team leaders Pontzer and John Speakman of Scotland’s University of Aberdeen and the Chinese Academy of Sciences.

In other words, eating more won’t necessarily help someone make Iditarod history. “There’s just a limit to how many calories our guts can effectively absorb per day,” Pontzer said.

The results appear online June 5 in the journal Science Advances.

For the study, the team measured daily calories burned by a group of athletes who ran six marathons a week for five months as part of the 2015 Race Across the USA, a 3,000-mile race from California to Washington, D.C. The team also considered other feats of human endurance, including punishing 100-mile trail races and pregnancy.

When they plotted the data over time, they found an L-shaped curve. The athletes’ energy expenditure started out relatively high, but inevitably plunged and flattened out at 2.5 times their basal metabolic rate for the remainder of the event.

Co-author Caitlin Thurber analyzed urine samples collected during the first and final legs of Race Across the USA. After 20 weeks of running back-to-back marathons, the athletes were burning 600 fewer calories a day than expected based on their mileage. The findings suggest that the body can “downshift” its metabolism to help stay within sustainable levels.

“It’s a great example of constrained energy expenditure, where the body is limited in its ability to maintain extremely high levels of energy expenditure for an extended period of time,” Thurber said.

“You can sprint for 100 meters, but you can jog for miles, right? That’s also true here,” Pontzer said.

All the endurance events followed the same L-shaped curve, whether the athletes were hauling 500-pound sleds across Antarctica for days in sub-freezing temperatures, or cycling the Tour de France in summer. That finding challenges the idea, proposed by previous researchers, that human endurance is linked to the ability to regulate body temperature.

One limiting factor for endurance events, researchers found, lies in the digestive process — the body’s ability to process food and absorb calories and nutrients to fuel bodily processes.

Interestingly, the maximum sustainable energy expenditure found among endurance athletes was only slightly higher than the metabolic rates women sustain during pregnancy. This suggests that the same physiological limits that keep, say, Ironman triathletes from shattering speed records may also constrain other aspects of life too, such as how big babies can grow in the womb.

As far as the researchers know, no one’s ever sustained levels beyond this limit. “So I guess it’s a challenge to elite endurance athletes,” Pontzer said. “Science works when you’re proven wrong. Maybe someone will break through that ceiling some day and show us what we’re missing.”

This research was supported by Hunter College, Loyola Medical School, Grand Valley State University, Purdue University, the Chinese Academy of Sciences (XDB13030100), the Thousand Talents Plan, and a Wolfson Research Merit Award from the Royal Society of the United Kingdom.

 

Contacts and sources:

Robin A. Smith

Duke University

Citation: “Extreme Events Reveal an Alimentary Limit on Sustained Maximal Human Energy Expenditure,” Caitlin Thurber, Lara R. Dugas, Cara Ocobock, Bryce Carlson, John R. Speakman and Herman Pontzer. Science Advances, June 5, 2019. DOI: 10.1126/sciadv.aaw0341.

Support BeforeitsNews by trying our natural health products! Join our affiliate program
Order by Phone at 888-809-8385 or online at www.mitocopper.com
Get our Free Ebook, "Suppressed Health Secrets" THEY don't want you to know!

APeX - Far superior to colloidal silver in destroying viruses, bacteria and other pathogens.
Ultimate Curcumin - Natural pain relief, reduce inflammation and so much more.
Supreme Fulvic - Nature's most important supplement! Vivid Dreams again! See Testimonials
MitoCopper - First bioavailable copper destroys pathogens and gives you more energy.
Prodovite - The Secret To Healing is in the Blood! Complete absorption in 5 minutes.
Oxy Powder - Natural Colon Cleanser!  Cleans out toxic buildup!
B-12 - Supports healthy metabolism, brain function, hormone balance, red blood cells.
Nascent Iodine - Promotes detoxification, mental focus and thyroid health.
Never Wax Your Car Again - 5 Star Shine protects vehicles for years with dazzling shine!
Smart Meter Cover - Reduces Smart Meter radiation!  See Video.  Protect your family!

Bring Batteries Back to
Life!
Tactical Laser
Bring Dead Batteries Back to life!
New Laser Blinds Attackers Instantly!
Cut Power Bills by 65%
NASA - US Faces 100 Year
Drought!
Discovery Can Cut Power Bills by 65%
NASA - US Faces 100 Year Drought!
Report abuse

Comments

Your Comments
Question   Razz  Sad   Evil  Exclaim  Smile  Redface  Biggrin  Surprised  Eek   Confused   Cool  LOL   Mad   Twisted  Rolleyes   Wink  Idea  Arrow  Neutral  Cry   Mr. Green

SignUp

Login

Newsletter

Email this story
Email this story

If you really want to ban this commenter, please write down the reason:

If you really want to disable all recommended stories, click on OK button. After that, you will be redirect to your options page.