[prox]

That is because he got it from the Buddhist Tummo techniques.

>It has similarities to Tibetan Tummo meditation and pranayama, both of which employ breathing techniques.[25]

https://en.wikipedia.org/wiki/Tummo

I won’t say he appropriated it, because he is quite open about it and adapted it, but it did not originate with him.

[bmj]

The article doesn't mention it, but there is a long tradition of hesychastic prayer[0] in Christianity, starting with the desert Fathers, and continuing in the practice of the Jesus Prayer. Some teachings about the Jesus Prayer which emphasize the importance of breath also include serious warnings about the possibility of bodily harm if the prayer is not done correctly. While early practitioners likely saw this as God's judgement on the unrighteous, current practitioners better understand the physiological effects of breath work, and the potential dangers if done incorrectly.

[0] https://en.wikipedia.org/wiki/Hesychasm

[1] https://en.wikipedia.org/wiki/Jesus_Prayer

[mettamage]

I don't think so. I know that he was interested in Buddhist stuff (source: some documentary).

But when I talked to him, he told us (part of the Radboud experiment in 2014, I think) that he just jumped into cold water and was forced to learn how to breath in such a way that he wouldn't freak out.

Note/edit: As you can see from my writing my memory isn't pinpoint accurate. Given that the article was published in 2014 [1], I'm sure I'm probably wrong in the year when I talked to him as it then most likely would've been April 2013 since I had to keep the results of the study a secret for at least a year.

[1] https://www.pnas.org/content/111/20/7379

[prox]

I am quite sure he mentioned it as inspiration (or he even learned it somewhere, on that count I am not sure) in some interview.

Things do not exist in a vacuum, though. Especially something such as breath would be pretty universal despite in what cultural context.