Metabolism Hits a Ceiling in Athletic Endurance Feats

In long-distance, physically taxing events, the amount of energy athletes can expend appears to peak at about 2.5 times their metabolic resting rate—a maximum likely dictated by how many calories they can digest.

Written byShawna Williams

| 5 min read

Save for Later

Listen with Speechify

0:00

5:00

ABOVE: A runner on the Race Across the USA in 2015
BRYCE CARLSON

We all have limits, and a new study suggests those limits are pretty similar among individual humans—at least at the metabolic level. Researchers tracked runners’ energy expenditure before and after they completed the equivalent of a marathon six days a week for nearly five months straight, then compared their results with studies of other high-intensity activities, and found that the longer the event, the lower the metabolic rate participants were able to sustain.

The maximum metabolic rate for longer-term activities, they report today (June 5) in Science Advances, is about two and a half times an individual’s resting energy use—likely a reflection of a limit on the number of calories the human digestive system is able to absorb.

“Conceptually, people had been looking for one number—they were looking for some level of energy expenditure that is sustainable indefinitely. ...

Interested in reading more?

The Scientist ARCHIVES

Become a Member of

Receive full access to more than 35 years of archives, as well as TS Digest, digital editions of The Scientist, feature stories, and much more!

Join for free today

Already a member? Login Here

Meet the Author

Shawna Williams
Shawna was an editor at The Scientist from 2017 through 2022. She holds a bachelor’s degree in biochemistry from Colorado College and a graduate certificate in science communication from the University of California, Santa Cruz. Previously, she worked as a freelance editor and writer, and in the communications offices of several academic research institutions. As news director, Shawna assigned and edited news, opinion, and in-depth feature articles for the website on all aspects of the life sciences. She is based in central Washington State, and is a member of the Northwest Science Writers Association and the National Association of Science Writers.
View Full Profile