Ultimate limit of human endurance found

We might need a deep dive on this one @chad @Nate @Jonathan

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So what happens if you train over 2.5x your basal metabolic rate for a long consecutive period of time? Does your metabolism shut down or something to stop you from keeping up the intensity? Or does performance slowly fade off. Anyone got a tl;dl for lazy folk like me :smiley:

Say my BMR is around 1700 - that means I’m basically capped at exercising 4250cals a day. Is the 4250 total calories = exercise + BMR, or is that purely exercise calories alone you’d be able to do?

Fascinating, thanks for sharing!

I’d also be interested to know what “not sustainable” actually means

How I imagine most of you fine folk reacting:

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I had a look through my history, and my biggest day on the bike was a measly 3.1 times my BMR. Can’t believe I held back so much, considering marathon runners do 15x in 1 day and tdf riders do 4.9x over the 23 days…

(I calculated my rmr with an online calculator)

I would take it as that is the limit you can stay at for an extended period. in a day you can go much higher, like the marathon runners, but over a long period you will slowly fizzle out.

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Not sustainable - They say at first, the body starts to consume itself (loss of fat and muscles). It also adapts by bringing BMR down. I’d imagine at some point you simply can’t go any faster, will need longer breaks, sleep etc. You’ll also likely get ill.

As most events don’t take that long, I doubt most people will reach the absolute limit. There seem to be higher limits for shorter durations though (eg the 3 weeks of GT).

What I find interesting though is the relationship to overtraining - 4000kcal doesn’t sound that much out of reach if you train a lot (especially long slow excercise), and because you think of it as training, it can easily go on for months.

I was reading this earlier and Im a bit confused by the article tbh, and its typical BBC I think, they say 2.5 is an unbreakable barrier for extended period of time but then point out a TDF rider is nearer 4.9, now thats for three weeks. Im assuming thats not the race winner, who will be higher, and then doesnt explain how riders can complete multiple grand tours in a year.

And then you have athletes like Ross Edgely, the guy that swam round britain last year, who described it as an exercise in eating with a bit of swimming thrown in, was consuming up to 10000 calories a day for 3 nearly three months.

Its a nice headline but contradicts itself.

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Oh yeah, didn’t think about that. What about Amanda Coker who was riding for a year solid, over 200 miles a day. That must have been over 2.5x her BMR and she seemed to be doing great 12 months in.

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Exactly!!! This reminds me of the 2-hour marathon impossibility debate.

I’d be really interested for the tr folks to interview Mark Beaumont on this.

Perhaps a TR virtual grand tour is in the cards - burning 5x calories over 90 days.

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+1

The study (which is linked in the BBC article if anyone wants to read it) says that there is a relationship between time and total energy expenditure. The shorter the time, the more energy can be used. At long durations (multiple weeks), it flattens out at about 2.5× BMR. Most of the data in the study comes from RAUSA runners, with estimates about other endurance events. The three weeks of grand tour are not sufficient to reach the flattening out stage.

I agree it would be nice to include estimates from Mark Beaumont’s or Amanda Coker’s records, but the trendline they have from their other events seems pretty robust, so I wouldn’t expect any surprises. I seem to remember looking at one of Amanda’s rides and being surprised by the low heart rate, which would be an indication of a fairly low energy expenditure.

The interesting bit is that the authors link this limit to the amount of food that can be turned into energy, long term. In other mammals, the limit is usually due to heat dissapation, but this didn’t seem to be the case with humans/the activities considered. The other interesting bit is that it is just slightly higher than the TTE during pregnancy, which might be another evolutionary driver for this limit.

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.

So when you go and read the actual paper, you find out what “long term” actually means, and it’s basically a full year. It’s a logarithmic curve asymptotic at 2.5xBMR. If you’re going for a shorter time frame, like say a measly 100 days, you can still crank out around 4xBMR.

Given all the discussion of nutritional issues here and in the podcast, people may find this summary of a study on the limits of human endurance interesting. Basically, the conclusion is that humans can burn calories up to a limit of 2.5x the resting metabolic rate. I haven’t read the original study yet but will dig it out.

Interesting article on BBC News about a research article titled Extreme events reveal an alimentary limit on sustained maximal human energy expenditure. “They showed the cap was 2.5 times the body’s resting metabolic rate, or 4,000 calories a day for an average person.”

The 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.

Looks like the pinnacle of endurance over the long term is women who are pregnant and/or lactating— so if you are and you’re doing training on top of that, you are double-hands down a tougher human then I could ever comprehend being :slight_smile:

your last paragraph may hold a lot of truth - look at the performance of jasmin paris last year on the 269 mile pennine montane spine race. just given birth, was expressing milk for her baby at aid stations and beat the (male) course record by 12 hours. Needless to say she won. Not taking anything away from her as she is a very accomplished ultra runner, but this was an exceptional performance by anyone’s standards.

Regards the article I have a problem with anyone trying to cap or categorise anything to do with performance, barriers are there to be broken.

Pre 1954 it was thought impossible to beak a 4 minute mile, there were (are) scientific papers explaining why it would never be accomplished and that the body would pretty much destroy itself by running at that pace. Needless to say Roger Bannister took no notice of these reports, and as soon as he broke the record the floodgates were open and other runners followed and accomplished the sub 4 minute mile.

Ive successfully help coach quite a few cyclists in the past and the one thing thing Ive always pushed forward is Dont Limit Yourself. As soon as you constrain or limit yourself, or say I can’t, you won’t. No one ever won a gold medal by saying theyre better than me or I cant.

The calorie restriction im not sure is a restriction as such but maybe a ‘levelling out’. As we get fitter the enginee will become more efficient nd require less fuel for the same workload that previously required, Im quite sure the people I read about being morbidly obese are on a lot more than 2.5 their bmr… again its about extremes and pushing boundaries.

I don’t think the intention of that article is to ‘cap’ what’s possible. It’s more a generalized trend that will on average hold true. There will always be individuals,that at certain times, can go above that. Note that the authors don’t even quantify the exact x BMR factor the ‘limit’ is, they just say the trendline ‘flattens out below 3 x BMR’.

Good article from Alex Hutchinson (author of Endure) discussing the research:

Amanda without a doubt exceed the 2.5 “limit” during her record setting ride. She consumed at least 6k calories per day for 423 days straight and didn’t gain/lose any weight. Her BMR is far lower than the 2400 required to keep her at the 2.5 limit. In fact, t’s closer to half that. She performed at over 4, and closer to 5x her BMR.

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The authors did state that they do not know of anyone who has exceeded the limit (which from what I remember was 2.5 RMR beyond 275 days. Read that on the writeup at Discovery magazine and I’ll try find a link for the quote tonight.

I tried to follow Amanda Coker’s Strava account to see her rides but she hasn’t accepted, so it’s hard to do any real number crunching there. However like Chris above is saying, I think she is one candidate who maybe has broken their limit and it could be a terrible oversight on their part, invalidating the study on the grounds that people simply haven’t been doing those sorts of efforts so they haven’t been able to plot that sort of data.