if you look up freedive fins or watch a spearfishing video you will see they are very different from traditional scuba diving fins, they are designed to magnify

if you look up freedive fins or watch a spearfishing video you will see they are very different from traditional scuba diving fins, they are designed to magnify small movement. The trick is not to descend fast and vigorous, but rather to lazily peddle down, it takes longer but you end up burning less oxygen and end up with more reserve at depth. If I where to take a guess I would say if well trained in controlling muscles and heart rate non-static apnea required 15-25% of the oxygen supply that you would have had if you where doing static. Also the 6 minutes I mentioned has a margin in it as well. I remember reading that totally calm and motionless it's closer to 8 (I have never tried to push past 5, due to the cognitive issue talked about in the article). Most people drown because they panic which can spend it all and get you to black out in as little as 2-3. That is the really interesting thing about spearfishing, it's requires you to be almost meditative in the face of a bunch of stimuli such as you are in water, you are deep, there are predators attracted to what you are doing and the excitement of the hunt. All those have to be put aside because you biggest issue is time, when it runs out none of it matters so you become hyper focused on time and mastering control of your body to extend you time. One time I got pinned between the surface and a nosy tiger shark and it struck me after the event, that I never had an oh crap a 14ft tiger is interested in me moment. Instead every thought was about how to engage in a pissing contents with this shark while I conserve energy. It was a fascinating conversation of variables in my mind and almost meditative and robotic. In the end I decided to use the blowfish defense (Compact yourself into a tight ball with eyes on the shark, then when they come in to bump you, you sprawl out in a X formation fast like a squid or a blowfish, predators in the ocean don't like it when something triples in size right as they approach) as it would be one quick burst of energy, instead of poking it with my gun until it got deterred, which would be a death by a thousand prick by slowly eating my time each time I had to volley with it.