Personally, I've a hard time to judge whether CO2/O2 training really have such a big effect on my diving. Being lazy to a certain extent, I always ask myself how I can be more efficient. My preference is to focus on technique, as this is something which will benefit me on the long run.
Always when I start after a break, I've the impression that it's a good technique which makes the difference in the water. "Getting in the groove", and getting the relaxation straight is the next thing. But here I've the impression that this kind of comes by itself.
What remains is CO2 or O2 training... And here I'm starting to doubt about the real importance... Call me a heretic, and flog me naked through the streets, but I've the impression that this is only of minor importance for recreational freediving. *duck'n'cover* (OK, we might have different ideas about the term recreational... Does +/- 20 m and dive times between 1-2 min sound like the right ballpark?")
CO2 tolerance is a great thing, and I loved to see the progress in DYN. But I always had a hard time to get a good grip on understanding it, and quantifying the training effects. I could never say how much progress I made in DYN or STA, due to CO2 tolerance, since it's also directly tied to relaxation (and technique if applicable). Basically, I have no idea how long it'd take me to build up a good CO2 tolerance, and how long that effect would last... And I'm also pretty sure that I haven't broken into the territory, where I can start even talking about hypoxic tolerance... So any kind of input here is highly appreciated [emoji4]
You sound a tremendously lot like myself. I'm definitely a recreational guy, there isn't a competitive bone in my body (beyond competition with myself). My dives are pretty much always in 15-20m range as where I dive, you need to swim further out with a flag and all that which I find to be more frustrating than fun. For time, my dives are pretty much always in the 1-2 min range. I never dive past the easy stage as I'm just too lazy and don't find the reward of extra bottom time worth the discomfort. Plus, I've never had the opportunity to push myself to know where my limits are and figure that staying within my easy phase is the safest way to approach this. If I lived near the ocean, I would definitely spear, but since that isn't an option, I dive for fun and because I've found I get far more time in the water and move much faster and quieter than with scuba.
Having said all that, I just can't bring myself to bother with tables. I know quite a few divers on here also haven't bothered with it, but perhaps their propensity to spend more time in the water year round makes up for that. . .? Nonetheless, there's just only so much time for training and tables seem like the bottom of the list. Not that they don't have merit, but that I make much more progress learning to relax and getting technique right than to just learn to cope with the breath-hold more. I have a theory that CO2 tolerance is a bit of misnomer. When I read about it, the initial impression I'm left with leads me to believe that people are capable of not feeling it as intensely. . .like a tolerance for hot peppers where you've lost some of the sensation to milder heat (a physical change, not a mental one). I'm starting to think that it is in fact, nothing more than being accustomed to the feeling more and not fighting the awfulness so much. This is somewhat similar to martial arts where you develop a "tolerance" to being hit. It's not that it doesn't hurt as much as when you started, it's just that you don't notice it and focus on it so much anymore. You shove it out of your mind and press on (a mental change rather than a physical one). I asked a question about that on here a year or two ago and never got much of a response, so anyone with a thought on that, please chime in!
Otherwise, I've been equally baffled at what has increased my dive times. Is it that I've actually gotten used to a bit higher CO2 or is that I've learned to relax more and don't produce as much of it over the same time period. . .or a little bit of both? If I could ever figure out which was the real driver in increasing my DYN, I'd finally know what to focus on. As is, it feels like I have to take a shotgun approach and do a little of this and a little of that to make sure that at least one of those techniques actually helps me.
As for hypoxic tolerance. Ha! I could only dream. I just can't last long into the struggle phase to even remotely approach a need for that.
Before I forget, let me tell you the singularly biggest help I've ever had. Last year I bought a pulse oximeter so that I could
see how much oxygen I had left when I felt like I was really struggling. My thought was that being able to confirm that I still had plenty of O2 would help my mental-state. Did it ever. It's surprisingly hard to move the needle on one of those while resting. It takes quite a while of struggling before it starts to drop more than 2-3%. I got tired of messing around with relaxing and breathing and all that when all I really wanted was to get deeper into the discomfort and see how long it took to get the O2 down further. So what I did was to go down to a local soccer field (two fields side by side and walk both their widths and back. I walked out to the field and just took about 3 minutes to collect myself and get the oximeter on, pull out a timer, and get ready to take notes. I didn't do any sort of breathe-up or prep otherwise. Just started. Here's what I found:
1st attempt:
Full lung- 154 yds.
Contractions at 0:39 (around 58-62yds)
Vasoconstriction at 0:43
Total walk time: 1:49
O2 reading at end about 84%
Quite lactic feeling in legs.
Waited approximately 5-8 minutes between attempts
2nd attempt:
Full lung- 154-156yds.
Contractions at 0:42.
Vasoconstriction at 0:50
Total walk time: 1:40.
O2 reading at end about 83%
Very lactic in legs. . .like I had just sprinted the entire distance a couple times.
Note: Urge to breathe diminished noticeably at start of final 3rd of this walk. . around 102 yds, but regained its intensity around 15-20yds from the end.
Those aren't much for numbers, but a prolonged hold wasn't what I was after. Struggling was (hence no prep for the walk, no relaxation, no stretching, breathups, etc). Honestly, I was so surprised that despite being in real agony for a minute, my O2 was still significantly higher than I ever dreamed it would be. That bit of information really freed my mind from concern and in subsequent pool sessions really helped delay the struggle phase as well as make the onset much gentler. I added 25m instantly to both my DYN and DNF without any extra work or struggle to do it . .it was just instantly and always there. Anyhow, just thought I'd throw that out there for what it's worth.