I appreciate the modesty, but talking about completing an Ironman and having the phrase “really wasn't all that fit” anywhere near it is comical.

Getting through any one of the stages of an Ironman (or heck even a half of each stage) represents a level of fitness most adults do not have and will never attain.

Not necessarily true, I think. It’s a mental barrier more, than a physical one. Tell someone you ran 100 m in 12 seconds and they go “meh”. Tell them you did a marathon and they go “i could not do that, awesome, how could you etc.” whereas an average person can do a marathon with a years worth of training and never achieve that sprint time.

It took for me 21 months of training to go from effectively zero to a half ironman and the biggest barrier was swimming, which is very technical in nature. I still can’t swim very well. I was in no shape at all and overweight. If you look at the speeds required to stay within ironman time limits, they are quite low and a person in a slightly better than average condition would be able to sustain them with relative ease. The barriers might be swimming technique (which one might have from training as a kid) and things like biking position and running technique but not necessarily fitness as such. In fact, I see quite a few people visually in much worse shape than I am (i.e. fatter) doing long IMs and beating me at shorter distances.

The person you're replying to spoke of what levels people do and will reach, not can reach.

Just as the ability to learn how to fly planes within a year doesn't change the fact that most people aren't and won't become pilots.

Sure, but my point was really to suggest I’m just a regular guy who did an Ironman very slowly. There are physiological freaks at Ironman events, but I was certainly not one of them. Regular people with a plan and appropriate training can do it.

How much running training did you do and if you don't mind sharing what was your marathon time?

When I started I was able to run a 5k and that was about it. I trained for 21 or 22 weeks.

I think my marathon was a 5:30 or something like that. Lots of walking, but I never stopped moving.

Respect for achieving that in 21 weeks.

The idea that fat efficiency can be improved via diet or training is often said, but the people I have known who both tried it and carefully measured it couldn’t.

Also there are perfectly ordinary ways to figure out you need to eat more, Ive coached some pro cyclists and done a decent amount of my own triathlon and cycling adventures and if someone gave me a free vo2 machine I don’t think I would ever use it.

This is probably not exactly what you mean by diet, but Rob Gray (an Ultraman world champion) says:

in the 10 days before the race I would predominantly eat a high fat diet. Based on all the testing I’ve done, what you eat in this window has a large impact on how your body uses fat vs carb on race day

https://robgray.org/ironman-arizona-nutrition-report/

Carbo loading can be done prior to a race. The day before is usual. But even carbs in the morning before a race is effective.

The fat burning starts when you empty the glycogen chambers, but there is a sweet spot in terms of energy output, because as other people has pointed out, you can't do high intensity work on fat.

So it makes sense as an ultra endurance athlete that you try to pack som fat before a race, because it will be effective as a slow burning resource.

Another interesting thing at the moment are the ketones supplements one can drink.

Which pro cyclists have you trained ?

> the calculation of an athlete's Vo2 max really isn't all that useful

I can hear thousands of Garmin owners screaming about this comment as they obsess over their VO2 Max.

A friend of mine does keto and after running a marathon reported that they did not experience "the wall". Presumably this is because they were using fat to begin with, not after mile 15 or whatever.

For those interested, Jeff Volek's team published a study in 2016, "Metabolic characteristics of keto-adapted ultra-endurance runners" [1] that compared fax oxidation. One of the "fat adapted" participants Zach Kibbter, an ultra-marathon record holder, posted a personal writeup that included a table of his fat usage at various VO2 Maxes (a ridiculous 98% fat usage at 75% VO2max and 76% even at 84% of VO2max!)[2]

[1] https://www.sciencedirect.com/science/article/pii/S002604951...

[2] https://web.archive.org/web/20201111190720/https://zachbitte...

What would those numbers be for the general population or someone who is slightly fit but not a freak?

I don't know the numbers for the general population, but Fig2 [1] illustrates the difference between the high-carb and low-carb arms between the elite athletes, and Fig3 [2] shows the difference in absolute fax oxidation rates between the groups. If you're interested in finding out more, I'd also recommend doing a literature search for "maximal fat oxidation" (MFO, FATmax) - eg, here's a recent (2018) review w/ Fig1 that shows MFO peaking at 0.72g/min [3] (the FASTER trial cohorts avgd 0.67g/min for the HC arm, and 1.54g/min for the LC arm)

If you're interested in some of the other physiological impacts of keto adaptation, here's a presentation Volek gave a couple years ago that helps contextualize both the FASTER trial and a related TANK trial his team ran, as well as some other interesting related performance research: https://www.youtube.com/watch?v=BeS_dhM8dsY

[1] https://www.sciencedirect.com/science/article/pii/S002604951...

[2] https://www.sciencedirect.com/science/article/pii/S002604951...

[3] https://www.frontiersin.org/articles/10.3389/fphys.2018.0059...

At that effort, close to 0. Maybe 20% for someone with great genetics.

It all has to do with intensity. We obviously can't tell from the information provided, but if they ran at a slow pace, that would also skew the fueling towards fat.

Exactly. While the marathon is an endurance event, the intensity when racing is often higher than 65% VO2 max - the "fat max" or point at which fat oxidation peaks. For example, for a 3 hour marathoner (or faster), the intensity would be around 74-84% VO2 max or 80-90% max heart rate. It has also been observed that going on keto reduces your running economy (so you end up running slower for the same effort).

As for "hitting the wall", this often happens around 20 miles as this is where your stored glycogen is depleted. To avoid this happening, you'd be better off to "train the gut" to handle consuming ~60g carbs per hour while running at your target pace/intensity.

AIUI 60g/hr is for pure glucose, thanks to co-transport another 50% can be handled as fructose (i.e. 2:1 glucose:fructose ratio)

Not to be an idiot but you're implying 90g just to confirm the math.

Yup

Generally competitive endurance athletes try to shift their metabolism to match the length of their target event. For the longest ultra endurance events you have to be pretty well fat adapted because if you relied mostly on glycogen you wouldn't be able to take in enough carbohydrates during the event to avoid hitting the wall. But for shorter, high intensity events you're going to be burning mostly glycogen and barely touching your fat stores. It's a spectrum.

There is this concept of “fat adapted” after you’ve been on keto for long enough periods of time. I would assume that’s what was happening.

Will this device actually tell you fat versus glycogen metabolism the way a real exercise lab test would? From the description it doesn't seem so. I think all it really tells you is the amount of oxygen used.

Just a note, it's probably "Coeur d'Alene"

Unless you're dealing with mail, in which case you're more likely to succeed with "Coeur D Alene". Our city name apparently isn't sufficiently American in some contexts.

Yep. Sorry for transposing a few letters. It’s a tremendously beautiful and friendly place. I’d love to go back one of these days.

:) wasn't trying to criticize. Sorry if it came off that way.

Not at all! And CDA deserves to be spelled correctly, anyway. All good.

I would say vo2 max is fairly useful but maybe not in a tactical way which you are describing. Its a longer term trend identifier for efficiency of your respiration process.

Well sort of. But you can train VO2 Max in ways that don't result in higher performance. What most athletes really care about isn't VO2 Max per se, but rather ability to sustain a high percentage of VO2 Max for a longer period.

could you kindly elaborate on why Vo2 max isn't useful for an athlete?

naively, it seems measuring oxygen consumption would be useful.

It’s been a while since I’ve read much about this but one explanation I’ve heard is that Vo2 was elevated to importance because it could be accurately measured and therefore studied.

Also unlike aerobic fitness, which can be improved with year after year of consistent training, an athletes peak Vo2 max (for their given fitness) can be maxed out over 4 - 6 weeks of specific training. Doing much more specific Vo2 training can result the athlete (at least in running) becoming ‘flat’.

That said Vo2 measurement can provide a great deal of useful information but for most recreational athletes getting the basics right is more important than having an exact Vo2 measurement.

It’s not useful because it’s not really an indicator of one’s ability to perform and can’t really be affected through training. It’s primarily affected by genetics and weight.

That said, it does provide some correlation to an athletes performance “ceiling”, and you’ll typically find elite endurance athletes are naturally blessed with an impressive Vo2 max. You’re not going to win the Tour de France with a Vo2 max of 50 no matter how hard you train, just like you’ll never play Center in the NBA if you’re 6’1.