Can confirm - I went on a bunch of dives with a former Navy Seal and he used less than half the air on any given dive than the rest of us (who were all only regular or advanced certified) did. His explanation was that he'd just mastered the meditative mindset/breathing technique to use as little air and energy underwater as possible.
Mindset and breathing technique is certainly important in minimizing open circuit gas consumption, but it's not the only factor. Some people just have a naturally higher tolerance for CO2 loading (the instinct to breathe is driven more by increase in CO2 levels rather than lack of O2). Perfect buoyancy control helps a lot since you're not wasting energy on depth keeping. Equipment configuration should be streamlined to minimize drag. A high level of physical fitness also allows you to keep your breathing under control during periods of exertion, like finning against a current.
But I've also seen former military divers who had relatively high gas consumption. Some units mainly use closed circuit rebreathers or surface-supplied gas where breathing rate doesn't matter.
That’s true, but irrelevant in this case as in the short term people are O2 limited not CO2 limited which is why the world record for holding ones breath goes up by breathing pure oxygen.
It’s also one of the reasons I was asking for examples as I assumed you where making assumptions that didn’t apply.
For the vast majority of people that's just wrong. The urge to breathe is driven primarily by increasing blood CO2 levels (hypercapnia). You can learn to tolerate higher levels but to reach the point where pre-breathing pure O2 makes a difference takes extensive dedicated apnea training.
Anyone can extend breath hold times at least a little by hyperventilating first to drive down CO2 levels, thus surpressing the urge to breathe. That can be dangerous underwater as it becomes easier to go hypoxic before the urge to breathe gets overwhelming.
> For the vast majority of people that’s just wrong.
>That can be dangerous underwater as it becomes easier to go hypoxic before the urge to breathe gets overwhelming.
Again true on both counts but irrelevant, there is no reason to suppose people in 800BC where average divers. Pearl diving goes back to ~2000BC so demonstrating a very long tradition of people pushing these limits and it’s exactly the people pushing such limits that might try bringing an air supply underwater.
Sure this depiction is almost guaranteed to be a floatation device, but you build something like that and spend your life around water and people are going to try stuff.
