CO2 tolerance vs O2 efficiency - or how not to train for blackout?

Penyu · Dec 13, 2016

Hi everyone,

When thinking about my training I keep coming back to one problem time and again. Everyone who starts reading a bit about freediving will pretty soon come across the inherent dangers of hyperventilation and why not to do it. We don't want to meddle with our alarm system, i.e. artificially lower our CO2 levels, and miss the moment when we need to breathe. How come then, that most training advice revolves around building up CO2 tolerance? Doesn't that amount to permanently skew our alarm system to warn us ever closer to the moment when we run out of O2? It surely does. Ideally we would leave our CO2 tolerance where it is and instead of learning to dive with more CO2, we should increase our dive time by reducing the rate at which we burn our O2. Relaxation and proper technique are key and I guess the entire FRC school is about oxygen efficiency. My question to this wise forum now is: how do you train your O2 efficiency?

Best regards!

cdavis · Dec 13, 2016

VERY GOOD POINT!

I think C02 tolerance is often stressed for two reasons, 1) its fairly easy to make relatively large gains and 2) most divers don't realize how much their breathhold time will increase with modest C02 training. Your point is well taken anyway. Too much co2 tolerance is a path to BO, IMHO.

Training 02 tolerance is more tricky than c02 tolerance and takes a lot longer. Seems like there are again two avenues, 1) improving your dive reflex and 2) actually increasing your bodies ability to function in a low 02 situation. I've followed number 1, diving FRC (which includes learning to start the dive with more c02 not less) and practing frequent short dry statics to teach faster onset of DR have worked for me. I think number 2 is harder. Eric Fattah reported on improving low 02 ability connected with extreme statics ( lots of them). If I remember right, one thing he was doing was a full exhale, hold to the first contraction, then very small slow inhale, like the volume of one pack, intermittantly. Search his old posts for more info. Its worth the time to read them all, quite an education. He is one of the very few divers who have thought seriously about and experimented with low 02 tolerance. Short of that technique, it seems like any activity that includes breath hold and works the body hard enough so that it is operating in anerobic mode should help.

Another way hi level competitive divers cope with low 02 and n2/co2 toxicity is practicing their moves until it is unconscious. I've heard stories of divers coming up with a tag that were so narked at depth they could remember nothing. Similar thing for static.

I could be wrong, but pretty sure that the most bang for the buck comes from improving DR and technique.

Penyu · Dec 14, 2016

cdavis said:
Training 02 tolerance is more tricky than c02 tolerance and takes a lot longer. Seems like there are again two avenues, 1) improving your dive reflex and 2) actually increasing your bodies ability to function in a low 02 situation.

Without knowing anything about the actual training done for option 2 I do suspect though that spending lots of time in a hypoxic state in order to function in that situation can't be too healthy a thing to do. Intuitively I prefer option 1, improving the dive reflex. Got some question about that too.

1.) I do think I have read somewhere that dive reflex and onset of contractions are correlated. I certainly can notice a sharp decline in heart rate (sometimes as low as the high 40s) with the onset of contractions (for me at around 2 minutes). Does that mean though, that DR is always linked to contractions or can I learn to trigger DR before - maybe even before the dive?

2.) Do you know if the slow build up of longer dive times and later onset of contractions during a session is due to a short term building up of CO2 tolerance or stronger DR? Wrt the danger of blackout this would be crucial to know, since it would grow in the first and decrease during the session in the second scenario.

3.) I just did a personal trainer session at the Y-40 pool in Padova/Italy (www.y-40.com). Great experience, particularly since I was not aware of all the subtleties of body position and movement. Thought I moved quite well, but now learned so much about head and shoulder position, optimal finning etc.. All this fine tuning technique mean great improvements in hydrodynamics with the obvious advantages for O2 consumption. Having said that, how would you weigh the relative importance of DR, CO2 tolerance, technique, cardiovascular fitness and mental relaxation against each other? Just interested to see what people are focused on. There are surely various paths to improve ones diving.

Curious to hear what you think!

Cheers.

cdavis · Dec 15, 2016

3) a strong and early DR is far more important than anything else. The other things contribute to DR. Importance ranking probably varies with the diver. For me, DR, relaxation, technique, fitness and co2 tolerance, in that order. Note: I hate diving into pain. If its uncomfortable (my co2 tolerence is lousy), I come up.

2)The buildup of time and depth over a dive session is hard to pin down. I think a lot of things are going on, cumulative DR, release of blood buffers that aid co2 tolerance, probably cumulative effect of hyperventilation (for many divers), increasing relaxation making DR all the more effective, almost certainly some physiological changes not yet identified. Hard to say what all and I've seen no research on the subject.

1) One of my favorite subjects. Rising c02 levels kick off DR, and correlates with contractions, but its not just about co2. You can definitely get a start on DR before the first contraction. Decreasing lung size with depth is a strong factor. Low levels of exertion early in the dive are really important Practice is a strong factor. Something not well known, under some circumstances (FRC diving for sure) blood shift, a major part of DR, is cumulative. Between dives, not all the blood pooling in the core exits the core. Cumulative blood shift dramaticly improves depth ability and, almost certainly, dive time and dive comfort. Good technique and relaxation contribute to cumulative blood shift . Full inflation of the lungs certainly works against it.

It is possible to train a divers DR to come on earlier and stronger. Not much research on this, but a fair amount of anecdotal data. Appears to be very individual. For me, training seems to work. 3 or 4 times a week, I do a series of reverse pac negatives (dry) and I can feel blood shift in my arms and legs. Practice and it gets stronger and, I think, comes earlier, well before the first contraction. At my level of training improvement is very slow, but it continues. I do a half lung dry static at the end of exactly the same series of statics. Time to first strong contraction keeps getting longer. I also seem to get a modest amount of blood shift during 25 yard dynamics with a good rest period between runs.

Peter123 · Dec 18, 2016

I did a lot of co2 training in the last years. I read here at deeperblue something about one breath tables. Way better than normal co2 tables. I like the static as well the dynamic version.

"How to not train for blackout"
I am training weekly freediving since 3 years and never blacked out.
I have accomplished several times 100m no fins dives. However for me its very hard to keep pushing. The emotions that rise up during a maximum attempt are totaly different compared to co2 training. At the last turn "the alarm is ringing" in my head so loud and I feel very lactic.

I dont realy think that training neither co2 or dive response would help me overcome this problem :-/ Any recommendation?

Jaap · Dec 22, 2016

As far as the diving reflex goes, there are a lot of individual factors that influence this.

1) As cdavis says, decreasing lung size has to do with it. From what I recollect it is actually the flexing of the diaphragm upwards that triggers the dive reflex (a consequence of decreasing lung size).

2) Having water on your face. There are lots of nerve endings around the eyes that, if submerged in water, trigger the dive reflex. Try breathing without your mask on (through your snorkel) for a few minutes before you dive. Colder water commonly excites a stronger dive reflex. This is the reason you pull someones diving mask off and blow air over their face if they blackout, it tells the body that the face is out of the water and can start to breathe again.

3) Perhaps high PaCO2, but only in combination with 1 and 2. High PaCO2 also happens during sprints, and won't trigger the dive reflex unless you are also submerged in water etc. There are no receptors in the body that monitor O2 levels to my knowledge.

The diving reflex can be trained, and associated to specific conditions as well. If you have a pre-dive ritual, the ritual alone may cause your spleen to contract prior to dives, your heart rate to slow down, but only after you have done lots of dives and always included the ritual. Before a training session, I make sure I get to a 3 min static comfortably, because that way I know that for me the diving reflex is triggered. If I have no time for that (it's cold outside etc.), I'll do two short exhale statics up to two contractions, and that makes my initial dives much more comfortable. If I don't, I need about 4 dives (10 -12 minutes) to warm up to 80% capability.

Bloodshift, as far as I know is impossible to measure during dives and may be confused with muscle fatigue, although it definitely is a consequence of the dive reflex.

For me personally, the onset to contractions varies dramatically, from 1:30 to 3:30 depending on what I've eaten, stress levels, fatigue, warmup, and so forth. If I meditate prior to statics the contractions come much later, and this is the most consistent influence on my comfort during statics.

Jaap

cdavis · Dec 22, 2016

Jaap, could you elaborate on flexing the diaphragm to help DR? Where does thatinformation come from? I've found that flexing the diaphragm on the way down seems to help max equalization depth, comfort level and dive time, but did not know why.

Do you meditate before open water sightseeing or spearfishing type dives? Does it help?

Jaap · Dec 22, 2016

I think the only way that your body realizes that your lungs are empty are the nerves in the diaphragm/at the base of the lung - there are nerves in the lungs -alveolar stretch receptors but they only work to prevent over-inflation of the lungs:

https://en.wikipedia.org/wiki/Pulmonary_stretch_receptors

In contrast there are many nerves surrounding the diaphragm (the celiac/solar plexus is right there) and it is by virtue of these nerves that your body knows that your lungs are empty. I cannot find a direct reference for this, but remember it was in part of the intermediate PFI teaching material. The result is that once your diaphragm flexes upward you have an increased urge to breathe, and an increased dive reflex. You may have noticed that once you get to FRC you experience an increased urge to breathe, despite PaO2 being higher. My guess is that this is a combination of the upward flexing of the diaphragm and PaCO2, and for me happens around 25 m.

For me meditating is calming and does have a big effect. I often dive both for fun and depth training after work and my dive times and depth are much less than what they are if I dive without having the stress of work before hand. If I meditate prior to a dive session(15 - 45 minutes, guided or unguided) my performance is better, and more importantly it is much more relaxing. This goes for any type of diving. Some people don't like to meditate though, and maybe in that case you are better off listening to 15 min of your favourite relaxing music or something.

Flexing the diaphragm on the way down will help equalizing if your epiglottis is not totally closed, because air won't escape back to the lungs. If it is fully closed it shouldn't make a difference, because the air in your mouth will stay right where it is.

Jaap

cdavis · Dec 23, 2016

Good info, thanks. I dive half lung and can't mouthfil, so the diaphragm flex should apply to me.

I had stopped flexing the diaphragm, thinking the effect was just mental and the co2 cost of extra muscle contraction wasn't worth it. I'll start again and play with it.

Jaap · Dec 23, 2016

Interesting. I think flexing your diaphragm also ensures your epiglottis is closed because you create some negative pressure on the lungs. I've never thought about, or felt, the extra CO2 cost though.

Going back to the original question by Penyu (perhaps we flew off topic a bit...), while diving it is quite hard to get hypoxic because of the pressure. If you dive to 20 m, and have 6% O2 left in the lungs, that will react as if it is 6% * 3 atm = 18%. In this case you would black out upon surfacing. Training hypoxia tolerance does help for very long dives, but it is very hard to notice the effect while diving for leisure. The only way I've ever noticed it (never had a BO or samba while diving), was being lightheaded upon surfacing and seeing funny colours in my vision. The funny colours appear when I'm at 70% PaO2. That did not impact my ability to do a good surface protocol though.

The story is different for statics.

The best thing you can do in my opinion is to do gradual training on a line so that you become comfortable with your own abilities and limits, and keep a detailed training log.

cdavis · Dec 23, 2016

Apologies if I stole the thread but, I think improving DR does go directly to Penyu's question.

Having had to play safety diver or assist on 3 spearfishing BOs and two other near BOs, I'm more than a little paranoid about co2 tolerance (all those guys had great c02 tolerance) and VERY interested in Penyu's question. I agree that training 02 tolerance for recreational diving is problamatic, thats part of why I've concentrated on improving DR. I'm thinking that playing with diaphragm flex is going to help my DR. There is likely to be some strategy and technique to find the best combination of timing and muscle intensity to get the most effect with the least o2 cost. Thanks again.

Jaap · Dec 23, 2016

Didn't mean to say you did steal the thread. I think it's a great discussion. Good luck with that diaphragm flex. You will probably want to engage it just prior to reaching functional residual volume on a deep dive, maybe earlier if you do a shallower dive.

cdavis · Dec 24, 2016

Stealing threads is half the fun.

Your idea of timing fits my experiance. When I was doing that, it was roughly between 30 and 60 ft, then relax as increasing pressure squeezed me down till I could not equalize any more, somewhere between 80 and 105 ft. I'm going to try starting earlier and harder to see if that improves blood shift by the time I reach my equalization limit.

I'm a spearo and sight seeer, never was much interested in really deep dives or serious line diving.

Jaap · Dec 25, 2016

We unfortunately don't have anything worth spearing around Vancouver in my opinion. Most of my dives are for sightseeing, but I like line diving because it's an easy and safe way to try out new techniques and to track progress. We need it around here because the visibility is usually horrendous. We usually can't see each other diving from the surface. I was not able to equalize with a Sphera at 25m+ (85ft+) because the nose pocket was too small for me and it pulled my soft palate up as the air in my mask shrunk. Maybe that's something to be aware of too.

xbuster · Dec 26, 2016

Jaap said:
I was not able to equalize with a Sphera at 25m+ (85ft+) because the nose pocket was too small for me and it pulled my soft palate up as the air in my mask shrunk. Maybe that's something to be aware of too.

I think I'm getting the same thing, but deeper! How you overcome this problem? Even when I use mouthfill and my chicks are full of air my soft palate is not allowing me to equalize.

Jaap · Dec 26, 2016

xbuster said:
I think I'm getting the same thing, but deeper! How you overcome this problem? Even when I use mouthfill and my chicks are full of air my soft palate is not allowing me to equalize.

I wasn't able to overcome it, so I use a different mask now, a Salvimar Noah.

Sent from my iPhone using Tapatalk

xbuster · Dec 26, 2016

Jaap said:
I wasn't able to overcome it, so I use a different mask now, a Salvimar Noah.

I find Sphera by far most comfortable mask because of it's minimal weight and large silicon surface that fits the face just perfectly. Why you've chosen the Salvimar Noah? Is it similar to Sphera?

growingupninja · Dec 27, 2016

Re: mask and eq...
if you want to dive past RV in a mask you need to really keep it topped off, and actively equalize it. You can do this with mouthfil air (open soft palate, keep glotis closed, and use tongue to push air out through nose) but I find it easier to just over pressurize mine almost to the point of leaking air when I am taking a deep mouthfill and then forget about it. Although Sphera is advertised as not needing EQ, at a certain point like any mask it will screw things up if you don't keep it pumped up. The Sphera is nice but fragile even if we'll taken care of and of course lousy for spearing. Before the lenses popped out I had my Sphera down to almost 200', that was a while ago, now I easily go past that in a regular low volume glass spearing mask.

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Jaap · Dec 27, 2016

The Sphera has a very low internal volume so it doesn't need EQ as fast or often as most other masks. I use the Salvimar Noah because it is fairly low volume, tempered glass lenses and decent field of view . Xbuster, masks are personal, they may fit you or not. You're going to have to test them.

xbuster · Dec 27, 2016

growingupninja said:
I find it easier to just over pressurize mine almost to the point of leaking air when I am taking a deep mouthfill and then forget about it.

After the mouthfill (and mask equalization) you're keeping the nose pinched all the way down or release the pinch after each equalization?

CO2 tolerance vs O2 efficiency - or how not to train for blackout?

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