To answer your questions:
- A coach / safety will give a signal to the athlete, e.g. pinching of the arm and the athlete will react to it by e.g. lifting a finger.
- Training. You get to know your body and limits very well when training freediving for a longer time. That does not mean that you always avoid blackouts, particularly in competitions they happen but that's what safeties are for. In the end, a free diving competition is one of the safest places to explore your limits.
I've seen people react so instinctively to tap-out signals both in martial arts and sometimes outside of it that I've often wondered if you could fight dirty in a real fight by tapping out and then clocking them or at least breaking a hold during that instant where they start to back off.
I think I have used it successfully both in chiropractic and physical therapy contexts. The thing with really top-shelf pain is that if you're not screaming you can't even talk at all. But your hands still work.
These sorts of little reflexive physical communications are super effective.
yes, i've seen that done in videos of streetfights.
For sure - what I find interesting is that passing out is a disqualification (I assume) so there is a fine line between achieving your utmost limit and being disqualified. Which is like most sports but my understanding is that it is quite easy to accidentally slip under so the guy must have incredible body awareness
Correct. Usually you need to perform a so called surface protocol after surfacing to show you are still conscious enough. This can be e.g. the removal of your mask, an OK sign and saying "I'm OK". Only if you do that within 15 seconds after surfacing your performance will be valid.
And regarding easy to blackout. Yes and no, I personally avoided it for over 12 years, but then again, I'm no world class athlete and only an enthusiastic hobbyist.
In a documentary about freediving they explained that during competitions there are strict rules and steps for the diver to follow after they emerge from the water surface. Only when followed the dive is considered ok.