As a surfer, I've done a few breathwork classes even though I've never been close to being in conditions that really needed it. There is a tremendous amount of training that you can do to basically change your conscious thoughts in an instant. Going from 180bpm heart rate and anxious panic to a static breath hold for up to a minute while being ragdolled and disoriented, is basically ego death. If you watch some gnarly big wave surfers talk about breathwork, they talk about rapidly flushing out your air in 3-4 big breaths, calming your heart rate, and even laughing, all right before or in anticipation of a pounding. Plus the whole Gerry Lopez yoga and meditation era of the 70s made it clear how important breathing and mental state were.

In any case, this is something every single surfer beyond a certain level is required to master, so I'd love to see data from that kind of cohort. The old lady freedivers of Jeju Island would be cool too.