For most people, I think the increased heart-rate of doing the big breathing motions would nullify the theoretical gain. So it feels easier, but you can't reall

For most people, I think the increased heart-rate of doing the big breathing motions would nullify the theoretical gain. So it feels easier, but you can't really hold any longer, you just pass out unexpectedly. The best way to get better is to do "co2 tables", just slouch in your couch and do the intervals of breathing/holding, and learn to control your body. When actually diving, we never push our limits, compared to what we know we can handle on land. Like, I can hold my breath for 5 minutes, but would seldom be more than a minute underwater. Co2 tables are actually very meditative. After the first convulsions, if you manage to calm your body down, it's quite a weird headspace to be in for the next minutes.