Rethinking CO₂ Tolerance Training: An Interview with Nathan Vinski
- Anthony Feoutis
- 3 days ago
- 25 min read
A conversation from Pillar One of The Depth Collector Book One on the urge to breathe, smarter CO₂ training, equalization, and why harder is not always smarter.
This interview originally appeared in Pillar One of The Depth Collector Book One, the section dedicated to CO₂ tolerance training. I am republishing it here as part of Depth Talks, a series of conversations with freedivers, coaches, and ocean people whose experience shaped the way I think about training, performance, and depth.
Nathan Vinski is one of the best coaches out there when it comes to CO2 tolerance training.
His innovative approach is, without a doubt, the starting point for the future of training in this field. Through meticulous analysis of sports performance and crafting customized training programs, Nathan mentors freedivers worldwide. He aids them in enhancing their freediving skills, making the process enjoyable and seemingly effortless. Find more information about his training methods and the man himself at: https://www.trainfreediving.com/
I'm thrilled to have had the opportunity to interview him.
In This Interview |
Rethinking CO₂ Tolerance
Your approach to CO2 tolerance training stands out. Can you elaborate on the foundational principles and experiences that have shaped your methodology?
Nathan: My approach to developing CO2 tolerance is, first of all, impacted by how I 'define' CO2 tolerance. For me the definition of tolerance is how much of a 'substance' or 'stimulus' you can be exposed to BEFORE it creates a reaction. Therefore, CO2 tolerance specifically deals with how much CO2 we can accumulate in the body BEFORE there is a significant reaction, or in other words, before it creates a strong urge to breathe with contractions. This, is in my view, is VERY DIFFERENT to 'urge to breathe tolerance,' which looks at how long you can sustain a breath-hold AFTER the urge to breathe and contractions start. When it comes to developing CO2 tolerance (i.e., delaying and weakening the urge to breathe), the key principle for me is designing exercises which work with the 'onset' of the urge to breathe and contractions. To put that simply, tables are designed so that the recovery times and hold times/dive distances are balanced so that the diver spends as much time as possible right around the point where contractions/urge to breathe are JUST ABOUT to start, but not going beyond that point and actually experiencing contractions and a strong urge to breathe.
I started to realize that this concept of working 'up to and around' the onset of urge to breathe was beneficial because I saw myself, and many divers around me, training beyond this point all the way to near-maximal urges to breathe for months and years and never achieving a later urge to breathe. It was clear by looking at everyone around me that going hard DOES NOT delay or weaken the urge to breathe. It might do other things, but it certainly doesn't benefit your CO2 tolerance. Later on, as I became more interested in general sports training, I started to see this pattern over and over. The best way to become more flexible is to stretch to the point of 'feeling it' but not to the point of 'pain.' Lactic onset is delayed by bringing the muscles to the point of feeling lactic start to build up, not to the point of lactic failure or burn. And this list can go on and on. Long story short, adaptations are made by training up to and around the ONSET of a particular sensation, and not by going to the maximum tolerable amount of the sensation. So, again, for CO2 tolerance, this means training up to and around the ONSET of urge to breathe and contractions to delay them, NOT pushing to the maximum amount of urge to breathe you can tolerate.
How does CO2 tolerance influence a freediver's performance? Is there a correlation between CO2 tolerance and deep equalization?
Nathan: In my opinion, CO2 tolerance (a delayed and weakened urge to breathe) is the foundation of freediving. We all say that 'relaxation' is the most important quality for a freediver, and that the more relaxed you are, the greater your maximum performance will be. I agree and tend to see that this is true. So, maximize your relaxation by delaying your urge to breathe before thinking about other things. Remember, the urge to breathe is our 'built-in warning system.' The later this warning system starts, the less fight-or-flight responses we will have during our dive, and obviously these responses are the antithesis of relaxation. Of course, I also see good CO2 tolerance as a base and foundation for all other types of training. 2'30" RV STA is better hypoxic training than 1'45" RV STA, but only if you can get there with good composure and no fight-or-flight response. 10x50m reps with 30s recovery is better muscle conditioning than 8x50 with 1'30" recoveries. A 2'00" FRC dive to 25m is better blood shift training than a 1'00" FRC dive to 25m. So, better CO2 tolerance allows all other types of training to be done with greater performance and quality (no flight or flight) giving you a much greater response and training effect. With equalization, there is both a mechanical and psychological advantage to having a good CO2 tolerance. Mechanically, CO2 (no matter how tough you think you are) will create muscle tension in the diaphragm, abs, and intercostals. At depth, this tension equals 'negative pressure' and will, of course, make equalization harder and more dangerous. On top of this, one of the pre-contraction reactions to CO2 is the urge, often uncontrollable, to swallow, which complicates Frenzel and ruins mouthfill. Psychologically, it's hard to feel relaxed (no fight or flight) when you're experiencing contractions halfway down your descent with 75% of the dive still remaining… and we all know: no relaxation = no equalization. For me, the 'minimum' CO2 tolerance required for deep diving is that you feel ZERO signs of CO2 until reaching at least the bottom. This isn't always easy to develop, especially as you approach 80m, 90m, and 100m+ depths, but as someone who used to get contractions on the WAY DOWN to 30m, and finally achieved 90m with contractions at 20-25m on the WAY UP (diving with current to the plate), it's 100% possible to develop this level of CO2 tolerance. When people ask me the most important or beneficial thing I did for my equalization, I jokingly say (I'M 100% NOT JOKING), "Improving my no-contractions max DYN." Honestly, nothing has made a more noticeable positive impact on my equalization than achieving 115m and 90m FRC without contractions in the pool during a 'given' training cycle.
Blood Volume and the Urge to Breathe
If we increase the volume of blood, would it dissolve more CO2 and consequently delay the urge to breathe? If so, how would that work? Nutrition? Special workout? What do you think about that?
Nathan: In theory, yes, increasing your total blood volume would allow more space for CO2 to dissolve in the plasma, and typically there would also be an increase in total RBCs and hemoglobin to bond with CO2 as well. The more total CO2 we can fit into the blood, the greater the increase in total CO2 required to shift blood pH toward acidity. So yes, increased blood volume and increased RBCs would delay the urge to breathe.
Typically, endurance training is the primary way in which we see both an increase in volume and RBC count, but according to the studies I could find, this takes A LOT of training, and the increases are typically in the 3-3.5% for both volume and RBC count. Now, if you consider that both volume and RBC count can have a positive impact on CO2 tolerance, we can say there's (POTENTIALLY) a net increase of 6-7% in CO2 tolerance by having this extra blood.
Are these adaptations worth pursuing?
Nathan: I think if you ALREADY have a base or history in endurance sports, and then take up freediving, these adaptations will benefit you. But if you're already freediving and think that increasing your blood volume is worth pursuing, probably it's a waste of time. With good quality freedive training, you can often more than double your no-contraction time, which is significantly more than the (potential) 6-7% you'll gain by increasing blood volume. The other drawback is that the AMOUNT of endurance training required to make these increases is like 'full-time' focus on endurance; you'll have to take so much time away from freediving that you won't really see any sport-specific benefit since your overall freediving abilities will decrease back to baseline. My view is that freedivers should do enough endurance training to keep themselves cardiovascularly healthy, but not try to pursue these elite-level endurance adaptations that require full-time focus.
Diet-wise, I think there's more to gain here. Your daily blood volume can go up and down quite a lot based on hydration levels. So getting plenty of water and sodium (salt) is going to help keep your hydration levels up. Actually, the reason salt is often associated with high blood pressure is that it increases the amount of fluid or blood volume you have, and, as the system gets filled up, your blood pressure increases. Obviously, don't overdo the salt, but getting enough is probably helpful.
Building Effective CO₂ Training
Among the numerous CO2 training exercises available, which ones do you find most effective for enhancing tolerance? Could you also highlight some pivotal dry exercises for CO2 tolerance training?
Nathan: Ultimately, I don't like to say that any exercise is more effective than another at developing CO2 tolerance. What's MOST important is the WAY any exercise is done.
For example, a classic CO2 table performed with the maximum-tolerable urge to breathe is NOT going to improve your CO2 tolerance (delayed onset of urge to breathe and contractions).
On the other hand, a classic O2 table, performed up to a hold time where the diver only experiences 1 or 2 soft contractions over time, will help delay their 1st contraction, indicating an improved CO2 tolerance.
That being said, my preference for CO2 training (in DYN or STA) is to perform relatively short holds (25-50m or up to 50% STA) with relatively short recoveries. What's important is that the total number of holds, the specific recoveries used, and distance/duration allow the diver to frequently experience the onset of the urge to breathe without passing into contractions and strong 'urge to breathe zone.'
My favorite dynamic example is what I call a 'reverse CO2 table,' where the 'reverse' means that the recovery increases through the table instead of decreasing. An example could be 8x25m with (2, 2, 3, 3, 4, 4, 5) breaths between each lap. The point is to quickly get close to the 'onset' point, and then slowly add recovery to maintain contact with this onset point (but without passing it) during the 8 laps.
An interesting STA example is what I call 2-part holds (this also does a lot to train hypoxic tolerance once your CO2 tolerance gets good enough, so a 2-birds-1-stone exercise). The way I perform it is to hold on either FRC or RV until 1st contraction, inhale to full, and then continue to full lungs until the first contraction. On the one hand, it gives you two opportunities on two different lung volumes to experience the 'onset zone,' and these tend to be surprisingly long, while also training the mind to 'accept' longer and longer times without contractions. As a bonus, as your CO2 tolerance improves, you'll get some hypoxia towards the end of the exhale part of the exercise and get an O2 training effect.
Of course, those are just two examples, but really any combination of dives, holds, distances, and recoveries that get the athlete frequently and repeatedly up to the 'onset point' will do a great job of developing CO2 tolerance.
My breath-holds are always more demanding the days following a hard workout in the gym. Can you explain why?
Nathan: The first thing to remember is that CO2 comes from burning O2, and we 'measure this' as CALORIES. So the more O2 you burn during your dive, the more calories you are burning. Why does this matter?
There's lots of evidence that after a hard workout, we can experience EPOC (excess post-exercise oxygen consumption) or increased calorie burning at rest for up to 72 hours after exercise!
Basically, in this situation, our metabolism is burning more O2 and therefore producing CO2 at a faster rate at rest (increased metabolism) and, of course, during diving (increased metabolism + effort).
That being said, outside of competition or peaking dives, the BENEFITS of good quality gym and fitness training completely outweigh the negatives, so no, I'm NOT giving everyone an excuse to not exercise. All I would say is to tone down your workouts before important training sessions and try to have at least 2-3 days off between final gym workouts and PB or competition dives.
Long term, exercising and experiencing this EPOC will actually contribute to improving your CO2 tolerance; it's just in the short term that you can feel some 'negatives.'
Cross-training for CO2 tolerance: What types of additional fitness should freedivers do to improve their CO2 tolerance in the water?
Nathan: My experience has been that, of course, keeping fit and healthy is going to have an overall benefit to your breath-holds, making them more comfortable overall. This could be 'CO2 tolerance' or just simply that, when you're more fit, it requires less O2 to perform the same dives (less O2 burned = less CO2 produced).
What I tend to notice is that cardio/endurance training seems to have a positive impact on your STA CO2 tolerance. Every time I rebuild or improve my 'cardio,' my 1st contraction in STA seems to come later. That being said, I see almost ZERO benefits in depth or dynamic.
Where I've gained the most noticeable improvement in depth/dynamic is with strength and power training. Doing heavy compound movements (squat, deadlift, etc) with weights that I can only lift for 2-5 repetitions always seems to delay my urge to breathe in DYN/depth the most.
Of course, in all disciplines, the real improvements come from freedive-specific CO2 tolerance training on breath-hold. But when it comes to 'session #1,' having the best baseline CO2 tolerance to build on (the latest contraction without apnea training), cardio, strength, and power tend to have the most benefits overall.
Why is it recommended not to practice both CO2 and O2 tables on the same day?
Nathan: In my opinion, the reason is that the 'classic' tables are too hard for most people. Imagine a diver who does their 8x50% CO2 table with lots of hard contractions, barely being able to finish, and then does their +15s until 80% O2 table with hard contractions starting on the 4th hold. That's a lot of effort, and for most people, doing 16 holds, with maybe 8-10 hard ones, is simply too much volume at that level of intensity and will over-stimulate the nervous system.
That being said, if we made the workout level-appropriate, for example, CO2 at 40% and O2 up to 65% (imagine this is for an individual who can complete both tables with only one contraction on the last hold of each table), there's probably no problem doing this.
Actually, when I'm writing programs for my athletes, I very frequently include both hypoxic and hypercapnic stimulus on the same workout, and often on the same exercise. On top of that, I frequently include multiple repetitions, or 'sets,' of each type of table I'm writing. So once the effort level is correct, you can tolerate A LOT more volume and variety in each workout.
When it comes to breath-holding frequency, I've noticed that the vast majority (95%+ of divers I've worked with) do best with any type of training at a frequency of 3-4 breath-holding sessions (of any kind: STA, depth, dynamic) per week. Once we start doing 5-7 apnea days per week, the volume per session needs to be so low to recover that there's almost no measurable improvement over weeks, or even months. With CO2 tolerance training in particular, I've had the best results (biggest increase in no-contraction time) with my athletes training CO2 specifically 1-2x per week and focusing on other things for the other 2-3 apnea days.
Progress Tracking: How can freedivers effectively track their progress over time, and when should they consider advancing to more challenging exercises?
Nathan: For me, progress is measured in terms of QUALITY. Which quality depends on what the exercise is trying to achieve; in the case of CO2 tolerance, it's going to be a later or lesser urge to breathe. In other words, if your 1st contraction is coming LATER, your CO2 tolerance is progressing.
Moving to more challenging exercises is a common 'mistake.' Actually, all of your exercises should have the built-in possibility to be made more or less challenging, so we can stick with the SAME exercise(s) throughout a training cycle and just adjust it or them as our fitness or level improves. I'll give two dynamic examples to show my last two points.
Let's go back to the 8x25 with (2, 2, 3, 3, 4, 4, 5) breath exercises. Imagine today, your first time doing this, you get one contraction on laps 3 and 4. You do this table 2 sessions later: no contractions, but you're close. The week after, you do it again with only very minimal CO2 feelings. Perfect, you progressed.
Now you can modify the table to (2, 2, 2, 3, 3, 4, 4), getting one contraction on laps 4 and 5. Repeat this progression until you have only a minimal feeling of CO2.
But if instead, you did (2, 2, 3, 3, 4, 4, 5) with one contraction, and next week you do (2, 2, 2, 3, 3, 4, 4) with five contractions, and the week after (1, 2, 2, 2, 3, 3, 4) with ten contractions, you DID NOT progress, only the exercise did.
So the point is that each 'exercise' can be adjusted (distance, volume, recovery) to fit your CURRENT level of adaptation (in this case, the onset of the urge to breathe, since we're specifically talking about CO2 tolerance). As you require longer distances, more reps, or less recovery to achieve this 'onset,' you must adjust your exercises to match your ability.
The most important thing is that your exercise(s) FOLLOW your adaptation, and not the other way around. Don't make an exercise harder until you see evidence that you're adapting to it, which is that the exercise consistently feels easier to do than when you started it.
When introducing newcomers to freediving, how do you ensure that CO2 training is both effective and approachable? How should they adapt or modify these exercises to continue pushing their limits safely?
Nathan: I think across all levels, the most important aspect of CO2 training is the 'sensations' that the diver experiences. For CO2 tolerance, the sensations are the urge to breathe and contractions. Too many 'sensations' beyond the onset of a strong urge to breathe and 1st contractions is going to be inappropriate for improving CO2 tolerance for divers of all levels.
That being said, especially with beginners, we need to consider the 'stress' response to these sensations. Perhaps, for a beginner, even the 1st contraction is already into the stage where things feel stressful. In this case, the level (recovery, duration, volume) needs to be reduced to the point where the diver stops just before the 'onset' of the stress response, training to the edge of their comfort zone.
Another way to adapt to beginners is to make a game of it. Instead of being 'serious' and over-structured with the training, you can have them do things like, "How quickly can you do 8x25 WITHOUT any contractions?" allowing them to build their awareness, confidence, and CO2 tolerance without the rigidity of a structured exercise (like fixed amounts of recovery between laps). As they improve and also become more consistent, you can start implementing the more structured approach of 'this many laps, with this much recovery,' etc.
For top-tier freedivers, how does CO2 training adapt to meet their advanced needs? Is CO2 tolerance a continuous focus, or do they shift towards aspects like hypoxic resistance?
Nathan: In my opinion, CO2 tolerance is really the 'base' of all apnea training, and just like the 'jab' in boxing, it should be something that's always worked on and developed. With that being said, at a certain point of experience with proper CO2 training, it takes less and less time to rebuild your CO2 tolerance at the start of every new training cycle. Then, as you said, other things become more and more important, like hypoxia, chest pressure, lactic, stamina, etc.
However, I do want to make a very clear point which I already made previously. Good CO2 tolerance is the foundation of good 'other' training. Why?
How can you get proper lactic on 25m or 50m repetitions if you break because of the urge to breathe? How can you become hypoxic on 25m RV dynamics if you need +45s to recover just to finish 8 laps? Is a 30s hang or 1'15" hang at 25m on FRC better for developing bloodshift?
Of course, the 1'15" at depth is better, but only if you can do this safely and without contractions.
So for me, continuously building and maintaining CO2 tolerance is going to make the rest of your 'more advanced' training much easier, more sustainable, and more effective.
To illustrate my point further, near the end of one of my best training cycles, I did a 16x30m DYN (30m pool) and my 'limit' was actually that I was starting to develop LMC symptoms (laryngospasm) and severe lactic acid at around lap 11-13, and I had to pull back my pace. This was on FULL LUNGS; I wasn't having any contractions and had only a moderate urge to breathe. So, with good CO2 tolerance, even conventional full-lung 'urge-to-breathe' tolerance tables can become hypoxic and lactic training.
Tracking Progress and Adjusting the Training
How do you tailor CO2 training to individual divers considering their unique physiological responses and goals?
Nathan: Again, the three basic ways of tailoring, or adjusting, CO2 (or really any kind of training) is to manipulate one or more of these variables: dive duration (depth, distance, time, speed), recovery time, or volume (total number of dives, dives per set, or sets). Depending on how you adjust these up or down is going to affect if the exercise is easier or harder (objectively). Then, with the right tweaking, you can match that objective difficulty to the diver's subjective experience. To train CO2, we want the diver to be experiencing one contraction right at the end of the table/sets/reps. But of course, person to person, we will need different distances, recovery times, total number of reps, etc. to achieve this.
That being said, it's clear that there are lots of different 'physiologies.' Some divers RESPOND better to more volume or less volume per set or table. The trick and challenge is finding out what type of 'responder' you're dealing with and then adjusting the training to suit that person. For example, 6x25 with 3 breaths between laps for 3 sets vs. 10x25m with 5 breaths for only 2 sets; maybe two divers could complete either workout with 1st contraction on the last lap of each set. But one would respond better to the 6x25 and the other to the 10x25m. By 'respond better,' I mean how quickly (in weeks or months) this training produces a significantly later contraction in their 'actual' diving, like a 1-rep max in competition or recreational/general dives.
Of course, we can look at goals, or really the diver's 'level,' as well. A 200m+ DYN diver might need sets of 6x50m for CO2 training instead of the 8x25m that might be more suitable for 100-150m divers. Again, it's all about being LEVEL- and INDIVIDUAL-appropriate. What distances and recoveries should we use to get the maximum effect for each person?
We can also look at what type of environment the diver will be diving in. A pool diver might use dry full-lung STA CO2 training, but a depth diver doing dry STA would probably want to include a bit more CO2-style training on half or even empty lungs to mimic the sensations they would experience at depth.
Again, individual differences come into play, and some divers RESPOND better to one lung volume over another, or do better with 50m reps with medium recoveries vs. another diver who does better with 25m reps with very short recoveries. Coaching-wise, this tends to be a little bit trial and error, but if you know what to look for and once you find out what your diver is responding best to, you can bias toward that and away from the things that have less effect.
Hydration, Nutrition, and Metabolism
Dehydration and Diving: How does dehydration, which leads to reduced blood volume, affect a diver's CO2 tolerance and performance?
Nathan: I personally think and feel that proper hydration is extremely important overall, but also that, yes, it does affect CO2 tolerance as well. Part of it is related to blood volume as discussed above, but there's actually another, maybe even more important, aspect of hydration, and that's just 'body water' or 'muscle water.'
The more water in the muscle tissue, the more of these products the muscles themselves can absorb during exercise; therefore, it takes even longer before they start to build up and 'pour' into the blood. Think of a well-hydrated (and conditioned) muscle as a sink for CO2 products, keeping them localized and not going into the core, where they cause the urge to breathe.
Of course, when it comes to hydration, in general, we need to consider that hydration only 'counts' when the water is absorbed by the body. Chugging a liter before diving is only going to make you pee more in your wetsuit. Proper hydration involves drinking 3-4L of water per day, every day, and ensuring you're getting enough sodium (salt) in your diet to actually retain that water.
Having high blood sugar by eating a high carbohydrate (more than 125-150g of carbs per day) or regularly snacking on carbs (eating more than 3x per day) will also lead to dehydration, as your kidneys produce urine to remove excess blood glucose.
Also, remember that coffee, tea, and alcohol are diuretics, so if you consume these drinks (I drink coffee and the occasional beer), you'll need to be closer to +4L of water per day and up your sodium intake even more to compensate. On top of that, muscle hydration, which I think is even more important, is going to be 3-4L per day, lots of sodium, AND CREATINE, which specifically helps the muscle cells retain proper amounts of water. Most people need around 3-5g of creatine per day at a maintenance level, and there's around 4.5g of creatine in 1kg of muscle meat. Personally (as you'll see in my nutrition response), I noticed that I feel and perform the best (with the best CO2 tolerance) on a diet where around 80% of my calories are coming from mostly red meat; therefore, on a daily basis, I get around 3.5-4.5g of creatine, directly from my food.
That being said, if you don't want to eat 800-1,000g of meat every day, at least supplement with 3-5g of creatine monohydrate powder. Personally, my preference is to get everything my body needs directly from my diet and not rely on supplements. But yes, long story short, both your blood volume and muscle water will increase with proper hydration and diet/supplements, and this will have a positive impact on your CO2 tolerance. Just remember, hydration is more than just drinking water. You need the right minerals (mainly sodium) and the right nutrients (mainly creatine) to actually retain the water correctly at a cellular level.
Does diet play a role in CO2 tolerance and, if so, what nutritional guidelines do you suggest for freedivers? Is an alkaline-oriented diet beneficial?
Nathan: In my opinion, yes diet does play a role. But before I respond to this I need to say that I've researched this stuff A LOT, but I'm a freedive coach/expert, not a nutritionist, and because of that I'm going to keep things to my experience.
I've been going through a process of finding out which foods make me feel (in general) and perform the overall best. I'm NOT saying these things are 'facts,' but in my experience, this is what helps me feel the best overall and in the water.
My diet (source of calories) is around:
- 80-85% high-fat animal products: Red meat, eggs, dairy, other meats
-15-20% fruits- 0-5% 'other' (usually wheat and beer); I feel best when this is at 0%
If I go 'off' diet for a few days, I notice a +/- 10% earlier urge to breathe, and just generally not feeling that great.
The main idea here (based on research) is that by having a fat-dominant (source of calories) diet, you end up with lower insulin levels, allowing your body to lean more on stored and dietary fat to produce energy. Also, by focusing on fruits instead of grains and starches as the source of carbohydrates, the liver processes the fructose (fruit sugar) and turns it into glucose and glycogen (stored in the muscle directly) as needed. So, even though the total carbs in my diet are relatively low (less than 500 calories of carbs per day, instead of a conventional 1250 calories of carbs), they get processed and stored in 'proper' places instead of being absorbed as excess glucose, spiking insulin, and getting converted to fat that you can't burn since your insulin levels are too high.
Why does increased fat-burning improve CO2 tolerance?
Nathan: When you burn fat, you simply produce less CO2 per unit of O2 consumed. Burning carbs, you'll be at 1.0 CO2s per O2. Pure fat, 0.7 CO2s per O2. And on a 'mixed' burn, anywhere in between.
The question is, "Why not eliminate carbs completely and aim for the 0.7 ratio?" In my experience, this actually DOES produce the latest urge to breathe, but you'll also tend to see a significant decrease in hypoxic tolerance (much earlier blackout, as well), and terrible lactic build-up in the legs. For me, the 'lower' carbohydrate way of eating (80-125g of carbs per day) promotes that 'middle' ratio of 0.85, and with significantly healthier metabolic function (low insulin and controlled blood glucose), but leaves you enough carbs (glucose and glycogen) in the tank to function correctly at the lower O2 levels, as well.
Anyway, all of that being said, whatever your 'dietary beliefs,' it's probably a good idea to limit processed garbage like seed oils (canola, corn, sunflower, etc.), processed carbohydrates (sucrose, corn syrups, isolated starches), and chemical additives (coloring, thickeners, artificial sweeteners, etc). These things just mess up your metabolism and insulin and damage your body, creating inflammation. I'm not saying 0%, because a treat every once in a while is nice, but there's a reason pro athletes don't eat these things. The body functions much better without them, and my experience has been experiencing the earliest urge to breathe on a processed garbage diet.
The Future of CO₂ tolerance training
Given the ongoing advancements in sports science, where do you see CO2 training for freediving heading in the future?
Nathan: So far, I've had a lot of 'push back' from many coaches in the community, but I think as more and more freedivers realize they aren't progressing with the no-pain-no-gain approach to CO2 training, and slowly start to switch over the style of working upto and around the 'onset' of urge to breathe and 1st contraction, the more this will become the norm.
I'm already seeing a small shift toward this approach in the community, and everyone that gives this a proper shot tends to be surprised at how much more comfortable they can make their diving, and that their absolute performance (PBs) increase, too.
Long term, I think that this type of CO2 training (what I consider actual CO2 training, 'not urge to breathe training') is going to become the 'foundation' of apnea training. Similar to other sports like running or cycling, where a good base of 'steady state' endurance is always developed BEFORE switching to lactate threshold, VO2 max, lactic, speed work, etc. We will see a similar shift in freediving, where the initial goal is to maximize the 'no contractions and mild urge to breathe zone,' and then, once that's up to a certain acceptable level, build the rest of the training on top of that. If we're throwing out numbers for the 'future,' I think that ANY freediver with the right CO2 training training can achieve a solid base of 90-100m DYNB, 3'30"-4'00" STA, and 45-50m CWTB without any contractions, and that this should be prioritized before looking at working on other 'more advanced' things or more advanced numbers.
What I like to remind people is that I'm not doing or proposing anything 'new.' It's actually really 'by the book' if you look at other sports and how level-1 adaptations (improving comfort zone) are prioritized as the foundation for both short and long-term development. It's freediving that seems to be a little backward, or 'behind,' in that even beginners are being given really hard training tables and workouts, pushing to their breaking points, and then wondering why 2-3 years later, their PB is the same as when they started with an earlier urge to breathe.
The Psychology of the Urge to Breathe
Beyond the physiological benefits, how does CO2 training mentally prepare divers? As contractions are inevitable, what's your advice on accepting them?
Nathan: In terms of psychological benefits, I think we need to make something very 'clear.' You CANNOT relax. Relaxation is simply the ABSENCE of tension, stress, doubt, and fear. This distinction is really important, because we need to identify what's causing (most) divers to feel tension, stress, doubt, or fear… Remove that problem, and then allow them to experience the 'absence' of these issues: What we call 'relaxation.'
My point is, think about your own diving and your own experiences. On a max DYN, are you afraid that your fin is going to fall off or stop working, or suddenly remember you left the stove on and panic that your house will burn down?? No; 99% of the time, if your mind gets messed up it's usually because you're worried about how hard the dive is going to feel and wonder if you're going to be able to 'push' through it until the end.
Fix the CO2 problem, delay your urge to breathe, and suddenly these dives aren't' so scary and you're actually 'allowed' to relax. When it comes to actually 'dealing' with contractions for me this is a whole other 'interview' about 'urge to breathe tolerance' training. But in short, there are a few key points:
1: Used 'FIXED' amounts of urge to breathe in training. 20s of contractions in STA. Hang at 20m until the 1st contraction. Do 105m DYN (not 100, not 110: One ZERO FIVE). This will help you learn to commit and stay focused in the urge to 'breathe zone,' and again, applying similar principles to CO2 training: only doing 'amounts' that you can CURRENTLY deal with, without feeling anxiety or 'panic,' and increasing these 'amounts' ONLY as you improve.
2: Do these 'harder' trainings infrequently. For me, a 'harder' exercise once every 4-5 sessions, only lasting a few repetitions or 1-2 sets, is optimal. You should feel 'motivated' to do them to 'challenge' yourself, but you need to re-build that motivation to do these workouts WELL, with good focus and commitment by spacing them out as much as YOU need to.
3: Very infrequent HARD-effort workouts: maybe 2x in a 3-month training cycle, I'd recommend doing something at full-ish effort. I typically do these as 'you-vs.-the-clock' exercises. 16x25m as fast as you can. Shallow hang (10-20m) PB. How many ':00" or 1'30" STAs can you do with 1 or 2 breaths in between? These are exercises where the diver gets to challenge themself in a way that is different to their training goal (max DYN is NOT good for training the urge to breathe during a max DYN) so they don't affect their confidence or 'flow' on the thing they are training for. These 2x 'really hard' efforts help 'prove' to the diver how far they are capable of going, but doing it super infrequently so that there's no loss of motivation to do these harder efforts. All of that being said, I don't think that contractions are 'inevitable' with the right CO2 training.
When I started diving I was getting contractions at around 25m on the way down. 30m was a pretty painful dive for over 4 years. By 2021, I did an 85m PB with ZERO contractions, and an 88m competition dive in heavy current with contractions (4 of them total) starting only after passing 30m on the way up. My 'limit' when I did 90m a few days after the 88m was narcosis and some health (diet and gut) issues causing sleep and chronic fatigue problems.
My fiancee and partner with 'Train Freediving,' Sarah (also my first test subject with these concepts), started freediving with a 75m DYN PB with a mild LMC (laryngospasm) and hard contractions starting at 55-60m. Also, in 2021, she did 150m without contractions or more than a mild urge to breathe, and her limit on this dive was hypoxia for the first time since the 75m.
So I do believe that a diver with a good approach right from the start can experience, during key moments of the year when they are peaked and ready for max performances, only a moderate urge to breathe and minimal contractions during even max dives.
Train the Adaptation, Not the Suffering
What I like about Nathan’s approach is that it rejects one of freediving’s worst habits: treating suffering as proof that training is working. Contractions, short recoveries, and brutal tables may make a session feel serious, but difficulty alone does not create adaptation.
This is very close to my own training philosophy. Every exercise should have a clear purpose, and the intensity, volume, recovery, and progression should serve that purpose. Nathan and I may use different methods, but we share the same foundation: quality matters more than brutality, and training should follow the athlete’s adaptation, not the athlete’s ego.
If months of painful CO₂ tables are not delaying your contractions or making your dives easier, perhaps you do not need to become tougher.
Perhaps you need to train smarter.
Connect with Nathan
Nathan is, in my opinion, one of the best freediving coaches around. Take a few minutes to explore his website and discover the impressive work he is doing, the way he approaches training, and everything he has to offer to freedivers who genuinely want to progress.
Further Reading
My own approach to CO₂ tolerance training shares some of the principles discussed in this interview, particularly the importance of controlled intensity, clear objectives, and progression based on adaptation.
For readers interested in exploring my training framework in more detail, CO₂ Tolerance Training for Freediving is available on Amazon.
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