Extreme events reveal an alimentary limit on sustained maximal human energy expenditure, 2019, Thurber et al

[Andy]

Abstract
The limits on maximum sustained energy expenditure are unclear but are of interest because they constrain reproduction, thermoregulation, and physical activity. Here, we show that sustained expenditure in humans, measured as maximum sustained metabolic scope (SusMS), is a function of event duration. We compiled measurements of total energy expenditure (TEE) and basal metabolic rate (BMR) from human endurance events and added new data from adults running ~250 km/week for 20 weeks in a transcontinental race. For events lasting 0.5 to 250+ days, SusMS decreases curvilinearly with event duration, plateauing below 3× BMR. This relationship differs from that of shorter events (e.g., marathons). Incorporating data from overfeeding studies, we find evidence for an alimentary energy supply limit in humans of ~2.5× BMR; greater expenditure requires drawing down the body’s energy stores. Transcontinental race data suggest that humans can partially reduce TEE during long events to extend endurance.

Open access, https://advances.sciencemag.org/content/5/6/eaaw0341

The ultimate limit of human endurance has been worked out by scientists analysing a 3,000 mile run, the Tour de France and other elite events.

They showed the cap was 2.5 times the body's resting metabolic rate, or 4,000 calories a day for an average person.

Anything higher than that was not sustainable in the long term.

The research, by Duke University, also showed pregnant women were endurance specialists, living at nearly the limit of what the human body can cope with.

The study started with the Race Across the USA in which athletes ran 3,080 miles from California to Washington DC in 140 days.

Competitors were running six marathons a week for months, and scientists were investigating the effect on their bodies.

https://www.bbc.co.uk/news/health-48527798

 

[Wonko]

I'm not sure this make sense, according to information I have seen during the middle ages the number of calories expended by a serf was in the region of 5,500 a day, if they were available.

4000 seems awfully low given many people eat considerably more than that when training.

Or are they defining ordinary people as people who don't need more than 4000 kcal a day? In which case the result is unsurprising.

 

[Snow Leopard]

I find this curious as I know some ultramarathoners who can run 500+km in a week... They'd be burning on average about 4000-5000 Cal(kcal) per day on top of their BMR.

The implication is this cannot be maintained for 20 weeks...

 

[arewenearlythereyet]

I think this is interesting, but I struggled to follow the logic in places (mainly due to the extra reading I would have to do).

Looks like it’s observational at this stage rather than any detailed proposal of mechanism. They suggest liver I think, but I wonder about other things more mundane, like down regulation of secretions during exercise (e.g. stomach acid). I’m still a bit confused about the pregnancy bit though?