Just a thought here….staying "fit" can be nothing but good. Staying marathon runner fit, or cross train contest fit all the time….I'm not sure.
But one thing I did see. When we did the PFI free dive course here in Belize, our instructor wasn't exactly the picture of a gym rat. A bit of a beer gut….not out of shape but.
However, he was doing dives all day. I saw one of 132 feet for over two minutes setting the anchor so we could do our 100 foot dives.
And to the contrary, I've scuba dived with body builder fit guys who sucked air so fast they couldn't do a 17 minute on the bottom (before safety stop), 110 foot dive before running low on air. Meaning, if you train too much, and get super fit, does your body get used to high levels of oxygen? To where you use more? I would guess putting on muscle mass that isn't used for diving is just adding oxygen consuming mass?
Interesting. Free diving is a different thing.