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    • When I read or hear about unbelievable physical feats of endurance I am both awestruck and curious. This article distills some current scientific study. It is quite short, so well worth a read.

      "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."

      Duke University conducted this study.

      "You can do really intense stuff for a couple of days, but if you want to last longer then you have to dial it back," Dr Herman Pontzer, from Duke University, told BBC News.

      He added: "Every data point, for every event, is all mapped onto this beautifully crisp barrier of human endurance.

      "Nobody we know of has ever pushed through it."

      The study suggests that it is the human digestive system, not the heart, lungs, or muscles that is really critical. Apparently our bodies cannot sustain a higher level of energy use because we can't digest, absorb and process enough calories and nutrients.

      Here are the detals of the study:

    • So, what happens with parenteral nutrition - bypassing the gut and injecting nutrients intravenously? Will this alter the thesis stated above?

      It is interesting question, as I have discussed before about how important cooked foods were in human selection and evolution in a very tough environment in East Africa.. Specifically Richard Wranghams's book - "Catching Fire - How Cooking Made Us Human" - which suggested that the inherent limitations of mastication and digestion in most primates limited nutrition, and how cooking allowed the human precursors to evolve differently from their gorilla cousins, by pre-digesting food before mastication, by cooking it, that was unavailalbe to earlier primates with just their jaws and guts - both meat and plant based foods.

      Effectively, human ancestor species spent much much less time collecting and masticating food, and despite spending less time, aquired a diet with much more energy and protein to power larger brains, and provide greater endurance, and also the time to use and train their brains. Cooking food literally made us human - at least that was Wrangham's hypothesis, and one he presented compelling evidence for, I think. He also spend a fair amount of time describing how cooking may have contributed to human pair bonding with different social roles for sexes - a topic that is sensitive to discuss for some today, and highly debated by some - but not all primates species pair bond either, so....

      The article linked above says humans are limited to 2.5 times their daily basal metabolic rate for sustained long term energy expenditure, even though they can over short periods go as high as 8-10 time their BMR. But that their ultimate limit is how much nutrition they can aquire orally through their gut endothelium... Cooked food makes much more nutrients available than just mastication. Primitive man did not have high speed blenders to masticate their food before ingestion, so cooking MAY be less important today than hundreds of thousands of years ago.

    • This is more interesting than I thought it would be. In the end for endurance events that last weeks or months, it comes down to the stomach. That begs the question, what diet allows the stomach to absorb the most calories over the weeks and months for races like these.

      It feels like the Tour de France teams measure everything and have the most to say about what works. It appears from what they say that easy digesting carbs with not much fat or fiber works best to absorb all the calories they have to absorb.

    • That sounds like a very interesting book. Somewhere in all my reading I saw an article about cooked foods versus raw and which are most nutritious. The way I remember it, raw foods have more nutrition because some nutrients are lost in the cooking. But cooked foods are more absorbable. They calculated nutrients before eating and after pooping (yuck, poor researchers) to find out how many nutrients were absorbed.

      The results varied depending on the nutrient. Lycopene is the red caratanoid in red peppers and tomatoes and it didn't absorb well from eating them raw, but it absorbed really well when cooked. Overall, they recommended eating both raw and cooked foods because overall absorption was the same, but varied by ingredient.

      I'm pretty sure I remember water cooking in soups was best because a lot of nutrients go into the water and the temperature wasn't high enough to destroy many nutrients or create a cancer-causing blackening.

    • I did Race Across America in 2001. Interesting at that time we knew the limit was 4,000ish/day due to the absorption rate. I was not a top level racer just one out to survive and finish but we knew enough to realize we had to have a liquid diet since we could not spare anything for digestion. Personally, I have never liked the idea of intravenous fluids etc as I believe you need to be able to survive on a natural process but I suppose liquid diets might push that limit.

      Anyway, it is an interesting study and a very interesting question. Would it be doping? Not buy the rules but is it unnatural and beneficial to ultra performance? I would have to assume so.

    • What an accomplishment, hitch. Oh my God. Is this one of those things you do once in a lifetime and look back on forever with satisfaction, being able to say "I did that"? I'm afraid that's what it would be for me. I'd like to do it once.

      I know a lot of people who go do the same race year after year and for some reason I'm not wired that way. I want to try them all, each year something different, accumulating stories to tell and new perspectives. I've always wondered about Race Across America.

      Welcome to Cake, btw. 🎂

    • it comes down to the stomach. That begs the question, what diet allows the stomach to absorb the most calories

      I know I'm being pedantic, but the absorption all happens in the small intestine. Mechanical digestion of food starts in the mouth (and chemical digestion of carbohydrates starts with saliva). In the stomach the chewed food is mixed with bile, which starts chemical digestion. Muscles in the stomach aid in further mechanical digestion by mixing the food with the bile to break it all down into what's called chyme. The chyme then moves into the small intestine and starts the absorption process.

      So it's all down to the small intestine, really. I can't help with the diet part of your question, unfortunately. I don't really know that much about nutrition.

    • I know for several elite ultramarathoners and Mark Allen, the six-time World IronMan champion, their nutrition was Boost. It’s the drink for old people who have trouble absorbing nutrition. Cat Bradly, the 2017 Western States 100 champion, eats frosting from a can for her calories. 😳