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Comment by curun1r | Hacker News Reader

No, plunging 200 ft underwater isn't a physiological marvel. Learning to hold your breath for up to 8 minutes is not some mysterious ability, it just takes training. And anyone who can hold their breath for that long can go down to 60m. Just taking 3 levels of AIDA training will take you down to 40m and another year or two of training will get you to 60-70m depth, which is where these supposed "marvels" from the article dive to.

The medical community has been repeatedly made to look foolish whenever they've speculated on what is and isn't possible for freedivers. These people are no doubt excellent freedivers from the many years of practice they have with it, but nothing in the article suggests they're capable of anything that us normal human cannot do.

FWIW, my PB is 55m (~180 ft), and with a bit more regular training, I feel confident I can go another 15m or so.

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I believe this part of the article addresses that concern:

Diving itself might somehow enlarge the spleen. There are plenty of examples of experience changing the body, from calloused feet to bulging biceps.

Only some Bajau are full-time divers. Others, such as teachers and shopkeepers, have never dived. But they, too, had large spleens, Dr. Ilardo found. It was likely the Bajau are born that way, thanks to their genes.

I know they did. If they had just stuck to the part about genetic tests, that'd be fine. It's the flowery language about how they're adapted to depths that would kill normal human beings that I was objecting to. They should have said that generations of divers have made these people have larger spleens which makes them marginally better at deep diving. But that's less dramatic and, presumably, gets fewer clicks.

It looks worse than that. In figure 1 of the paper[1] they only make a comparison between Bajau and Saluan populations. They show the "enlarged spleens" have volume of ~200 cm^3.

However, if you look at humans overall, apparently even these "enlarged spleens" are much smaller than the average spleen:

>"The mean splenic dimensions were ... 333.6 ± 116.1 cm2 in volume." https://www.ajronline.org/doi/abs/10.2214/ajr.184.1.01840045

[1] http://www.cell.com/cell/fulltext/S0092-8674%2818%2930386-6

EDIT:

They write:

>"We made ultrasound measurements in two planes such that we were able to calculate spleen volumes according to the methodology outlined in Yetter et al. (2003)"[1]

So lets look at Yetter 2003 for their spleen volumes, in table 2 it shows they are >500 cm^3 on average: https://www.ajronline.org/doi/abs/10.2214/ajr.181.6.1811615

So it looks like these "super spleen divers" actually have relatively small spleens...

Is their body mass significantly lower than the overall human population?

If so, then the relevant measure should have been spleen volume to body mass ratio...

The patients in the Yetter paper were all being evaluated for liver disease, so their measurements might not be what you want to use as normal.

Thanks, looking closer at the Yetter paper:

>"Normal cadaveric splenic volumes reported by Loftus et al. [8] are 26–250 cm3 with a mean volume of 110 cm3 and an SD of 70 cm3. Henderson et al. [19] reported a normal splenic volume of 219 cm3 as calculated from axial CT acquisitions."

So an average of 219 cm^3 according to axial CT is still larger than what is seen here. I'm not sure about the cadaver spleens, do they shrink? The Loftus paper only reports maximum length vs actual volume so we can't see that direct correlation.

Some other papers report 184 cm^3 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4549594/) and 214.6 cm^3 (https://www.ncbi.nlm.nih.gov/pubmed/9038125)

Yeah, lines like this are ridiculous.

“I would think, as morbid as it is, that if they didn’t have this, it would kill them,” she said.

Yeah, and by a similar leap of logic, if we didn't have two legs, we'd flop around on the land like fish.

Years of training to dive that deep and hold your breath that long tell me this is something beyond the abilities of most people. Compared to everyone else they are certainly "marvels". Give yourself some credit for having the discipline to accomplish such things!

One could say "it just takes training" for anything that someone becomes really good at. It just takes training to become an Olympic athlete too, but there are only so many of those and their abilities seem almost super-human at times.

FWIW, it took me ~9 mo to go from reasonable swimmer with a 90 second static breath hold to achieving my personal best depth. I think my point was that freediving skill is often attributed to natural aptitude because we go beyond what doctors used to believe was possible in the human body. But having been through the training, I don't think I have any specific natural advantage. I think anyone who's reasonably healthy could achieve what I have in a single year of training. That's a very different situation from an olympian where decades of training are often needed and some sports require a specific body type.

And just for some perspective on what someone who is naturally predisposed to the sport can achieve, I took AIDA 3 with a guy who had taken the courses nearly back-to-back. This meant that he went from untrained to diving to 40m and a 4+-minute static hold in a matter of three weeks.

I guess my overall point is that people with no experience in diving over-mythologize diving ability because the human body is so adaptable that fairly routine changes appear super-human to those that have never experienced them.

Deep diving can kill you, but that's not really what this adaptation is about.

A larger spleen means more time and more activity underwater even if they don't dive for longer. Someone that's say 3% better at finding food is at a significant advantage over a lifetime.

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