[Speaker 1]

Welcome to the Freedive Cafe, episode 155 with Erika Shaigetai. My name is Donnie. I’m the host of the Freedive Cafe.

The Freedive Cafe is the long form interview podcast that explores the backstories, the training, the challenges and the combined wisdom and personal philosophies of the world’s freedivers. You can find this podcast at FreediveCafe.com, Freediveandthrive.com and on all good podcast players. And the video version of the show is available on YouTube at Freedive and Thrive.

If you’re a Patreon supporter, thank you 10 million times. And the extended version of this podcast, including the Desert Island questions section, is available now over on your Patreon dashboard. Patreon supporters get early access, exclusive episodes and extended episodes.

So if you appreciate what I’m doing here with the Freedive Cafe and you want to say thanks, head over to Patreon.com slash Freedive Cafe. As far as news and updates are concerned, all I can say is that I’m doing great. I’m training for the next competition in five weeks, which is happening here in Dahab in the Blue Hole.

I’m very happy with the way the little blue has turned out. I’m really enjoying having this amazing location from which to teach and feeling blessed every day to work next to the amazing Red Sea. I know it was another long wait between episodes, but they should be appearing a little bit more regularly now.

After this one, I have another last episode coming out, retrieved from the Mists of Time, an exclusive Patreon episode that we lost during the COVID period and have rediscovered. Then we’ll have the latest interview I recorded recently with Stefan Thurow. And finally, Lotte Eriksson, one of the most important and influential characters in freediving, will be coming on the show.

Many of you will be glad to hear that she’s finally coming on. On today’s episode, we are having another discussion about the science of freediving. We are joined by Erika Shagetai for the second time.

Erika originally appeared on episode 42 of the show. So it’s been five years since that conversation and definitely time for a catch up and time to dive a little deeper into some of those freediving science topics and learn about some exciting new research she’s been doing. Erika was here in Dahab for this one.

You can watch the interview on YouTube, as I mentioned before, on the Freedive and Thrive YouTube channel. OK, let’s head over to the dive lab in Dahab and chat with Erika

Shagetai. Let’s dive.

OK, Professor Erika Shagetai, welcome back to the Freedive Cafe. It’s been five years, I think, five or six. Yeah, it’s yeah, it sounds a long time.

It’s surprising. But yeah, really nice to have you back on our first episode, which, despite the pure audio quality, was very it’s a little bit exciting because I think that was the first time that you really had like a sort of in-depth discussion on things like the dive response in that media format for for the freediving community. And so that was episode forty two.

So if someone wants to go back and listen to it, they can check it out at the on the Spotify. And because of the audio quality, we also had a full transcript of that one as well, which you can read on the website Freedive Cafe dot com or Freedive and Thrive dot com. So we are first of all, before I start, I want to give a shout out to two people.

First of all, Nathan McClatchy, who saved my ass today because he let me borrow a screen for the laptop because I destroyed the screen on my laptop. So thank you very much, Nathan. And also a big shout out to Joe, who is visiting from Barcelona with Mireya, who’s a big supporter of the podcast and is over here doing a bit of training right now.

So I told you I’d give you a shout out, Joe. So there you go. OK, Erika, we’re in the Dive Lab.

Tell us about the Dive Lab in Dahab. We started building it two years ago to be able to test a lot of divers, because Dahab is one of the best places, of course, in the world to find training divers. You’ve been coming here.

You’ll come here a few times a year and you’ll conduct some research. And you were just doing some tests yesterday. You were telling me about the ramp test that you’ve been developing for apnea, this apnea ramp test.

So I’m familiar with the ramp test in terms of a kind of a graded exercise test, maybe like a VO2 max test, similar kind of idea to test the the upper aerobic threshold in runners and cyclists and things like that. So what is an apnea ramp test and what are you going to use this data for? What is the goal of the research?

Well, in most of the sports where many people are involved, they have standardised tests to see where you are at your performance cycle. And then you can train what you see is missing. And in breath-hold diving, there is no such test.

So we are trying to develop one. So what does a test look like if I was to come and do a test tomorrow? What would you what kind of thing would you make me go through?

Because some of the ramp tests that I’m familiar with are quite challenging tests. Is the apnea ramp test also quite challenging? Well, it can be challenging for beginner divers because they have to hold the breath for one minute, rest for two minutes, hold the breath for two minutes, rest two and then hold the breath for three minutes.

And we measure a lot of very important variables like the diving response, some things that have to do with the blood. And we can see and compare between different individuals and also between the same individual at different locations how well you are performing because the time is limited. You can really see the oxygen cost for a three minute apnea, for instance, for a beginner or for a very qualified diver.

So what what have been the you know, obviously you haven’t finished the research yet, but what kind of results have you had from doing these tests so far? What are you seeing? The first thing we have seen is we have tested about 100 divers now here in the hub and we have been able to divide them in three groups and see who is very fast desaturating and who is very sustainable.

So there are some people that after three minutes of apnea, they don’t desaturate at all. So even if they don’t breathe, they don’t have any visible effect of that. That means they have huge oxygen stores or and or very, very low metabolic rate.

And also we can predict a little bit who is sensitive to a severe hypoxia. And this is one of the aims of our studies to see who is at risk for blackout, especially among beginners. So if you see someone becoming desaturated very quickly, you you think they may have a higher risk for blackout as they continue in their journey in freediving.

Let’s say they’re a beginner and they would do this test and then you can see, OK, maybe this person is going to have a higher risk of hypoxia sooner than a person who is showing really high saturation after three minutes. Yeah, that that is true. And one of our aims and also one of our main sponsors is interested in preventing blackout deaths.

And that is mainly happening in beginner and recreational freedivers, not in competition divers. So we are very concerned to see what is the individual limit and how should you plan your diving. And if we can have a standardised test, then you can also preset your kind of diving pacing strategy because recreational freedivers, they do repeated diving.

Yeah, yeah. As a coach for for divers, especially some people who are halfway across the world as well, it would be quite I do baseline tests anyway, like for people’s mobility, for their strength, capacity and and then obviously I get their personal best and things like that. But this kind of test would be like a really nice thing to know the results to set somebody up on their next kind of coaching block, I would say, or even the first coaching block.

Yeah. And I think also for even for elite divers, it could be useful to know which factors

are optimal already and which factors are maybe lagging behind that you should train. I don’t know, CO2 tolerance or hypoxia tolerance or you should train your spleen or you should train your diving response.

And we know pretty much about how to train these things. But if you make an overview of what you need to be even better as a competition diver, you could also use this test. OK, all right, so fascinating.

And then so you’re testing so you’re testing complete beginners. Yeah. As well as trained freedivers, all the range in between, all the range in between.

And you’re seeing that some people are all the trained freedivers. Do they all have really good tolerance to hypoxia or do you see completely untrained people with really good tolerance and trained people with really low tolerance? It’s a good question.

And actually what we have seen in a lot of research through the years is that everything comes both through genetics and through training. So there are some cases of pure beginners that have a very high oxygen reserve. They have a high tolerance to hypoxia and they have an ability to lower their metabolic rate is that these three things that make you a good diver.

And among trained people, it is harder to see the difference. But of course, when you look at the really top people, they have all these things at the top. Yeah, top level.

But then you still but then you still can’t know if they started because you were only doing these tests now, so you don’t know if they started with this advantage or whether this advantage was trained over the years. Right. With some of the elite divers today, I have studied them also 20 years ago.

So I actually know a little bit about it. I haven’t published it yet. I remember I was at I was in Gili Islands.

I was I know that the next day I had to go and do a requirement for my instructor course, but I passed by like a bar on the way home to have an early night’s sleep. And I heard the music and I’ll go and see what’s happening in there. And I went in and met this bunch of people and started socialising with them and they asked what I was doing.

And I was like, you know, I’m doing an instructor course, free diving. And then I had them all, you know, we’re all drunk, you know, so got everyone to start holding their holding their breaths. Not in the water, fortunately.

But there was one guy there. He just he just sat down. He took a breath and he just held his breath for four minutes sitting there right in front of me, like without any discomfort whatsoever.

And the guy had never done any apnea or breath holding before. So, yeah, I have the same experience. And I, for instance, tested some of the best skiers in Sweden.

Sweden is kind of a skiing nation, not a diving nation so much. But some of the really best skiers, they could also hold their breath for four minutes, which is interesting because they can tolerate discomfort to some extent. So you will continue doing the testing over the.

What point do you reach a conclusion? When will there be a ramp test that we can all use? Right now, we are analysing the hundred divers that we have measured.

And it’s about 60 percent men, like 60 men and 40 women. And they will probably come back in the fall to try to do another 20 or 30 women, because they also want to know if there is a difference. We don’t see a difference at this point, but there could be things that we want to know about gender differences.

But we’re also developing a dynamic apnea ramp test. And that is what we are just beginning to doing now. That’s why I’m in the hub now to do a test that is swimming one lap in a 25 metre pool and two laps and three and four, which is 100 metres with five minutes resting in between.

And we are measuring a few different things, including lactate, which is a typical variable that you measure in this kind of performance tests in other sports. Yeah, that would be especially important in the dynamic disciplines. Right.

This ability to clear lactate through the course of a long dive. Well, at least to not use your anaerobic capacity too early on. So there is something called the lactate threshold.

It’s very often used to describe marine mammals performances. And they can use their aerobic capacity for short dives to do a lot of repeated dives. But if they want to do one single exploratory dive, they have to also tag their anaerobic capacity.

And the anaerobic capacity of humans in breathhold diving is not known. So that is one of the goals also to understand better what is what is the kind of this fascinating level. I follow some like triathlon stuff.

You know, I follow those guys, you know, the difference between a runner, the difference between somebody that can run like a two and a half hour marathon compared to a four hour marathon is that these people, when they’re running, you know, at your sprinting speed are still not crossing over that threshold, building up lactate yet. So could the implications there be that that that same kind of training that they are doing to to for anaerobic, for aerobic training, for long distance aerobic efforts, for example, that it could feed into freediving training, too? I think running is good.

I think aerobic exercise is good. I think anaerobic training is good. But I think there are

also differences with freediving and aerobic stuff.

OK, so recently we had a really interesting article with Frank Burnett, who is soon going to defend his thesis. He’s a PhD candidate and he has his thesis is titled Hypoxic Blackout in Serial Freediving, Protective Mechanisms and Risk Factors. I have read the abstract and I have a few questions about it, but perhaps you can tell us exactly what Frank’s work is all about.

Well, the task that he set out to answer was, why is it so common among recreational freedivers to blackout? And some of them drown. So he decided to study serial freediving, not like maximum performance freediving.

But when you do repeated diving, also like spearfishing, spearfishing, fun diving, fun diving, snorkelling, underwater photography, that kind of thing. Yeah. And one of the factors that has been known for some time to be a risk factor is hyperventilation.

But then you think of hyperventilation like really consciously overventilating before you do maybe a maximum performance. But what he has found is that it is very, very important not to hyperventilate also when you do serial diving. And even a very small period of a few breaths of overventilation will lead to accumulation of an oxygen depth in your tissues.

And that means you will desaturate much faster in the second or third and fourth and fifth dive. And this also happens unconsciously. OK, this is very fascinating information, because when I think of an oxygen depth, OK, first thing is I’m thinking of, let’s say we do a maximum effort, anaerobic effort, like a sprint.

Let’s say we’re going to run up a hill at full speed. And of course, we are able to, you know, tap directly into our ATP to produce that effort. So we kind of bypass the oxygen system, the glucose system, whatever.

And we have that maximum effort. But when we get to the end of the run, we’re going to have to stop and we have to pay off this oxygen debt that we have. Right.

So this is I’m thinking right here. [Speaker 2]
Right.
[Speaker 1]

So then if I think, OK, how can we accumulate an oxygen debt if we’re doing such easy dives where we don’t feel this kind of need to compensate at the end of the dive? If we just do an easy 10 metre dive and come back up. What is it about hyperventilation that makes the difference?

Well, even if you just hyperventilate very, very little, you can extend your dive time to a little bit into the anaerobic phase. And that means that you accumulate lactate. And lactate, you have to use oxygen when you come back to the surface to process it.

So I know this because I have been also trying to follow the AMA divers of Japan and they dive for four hours straight in the morning and they spend about 50 percent of the time underwater and they do dives of 40 seconds, which sounds like a ridiculous short time, but they also manage to rest only 40 seconds and then they go down again. And this to me when I was following them was kind of easy for five, six, seven dives. But after 10 dives, I was exhausted.

I had to spend 10 minutes on the surface. And that was because I was always tagging a little bit the anaerobic system to do what they were doing professionally within their aerobic diving limit. And this is so interesting because how do they know exactly when to surface again to not tag the anaerobic system?

So it comes back again to this ability to clear lactate. Yeah, to clear lactate is very important, but it’s even more important to not create any lactate, to keep within your aerobic diving limit like most marine mammals do when they forage dives. In this context of serial diving, lots of shallower dives over a longer period of time.

So it seems then that deep diving, the maximal effort dives that we do, they’re basically easy then, right? Well, then you can rest all you want.

[Speaker 2]
You can rest all you want. You can rest the whole day. [Speaker 1]

You can put everything on one cart and you don’t have to dive for the rest of the day or the week, but the AMA divers and the Bajau divers, they have to be able to dive again very soon. And the only thing that matters for them is the bottom time. Uh-huh.

And then it’s much smarter to make very short dives and to have very, very short recovery time. I wonder then if we’re doing very deep dives, but we’re still doing a session that includes several dives, we might have some warm up dives, we might have one or two warm ups, we might have a maximal effort dive. And then at the end of the session, we might have some shallower technical dives, drills or something like that.

Might be a typical session for somebody who’s maybe not peaking just before a competition, but somewhere in the middle of their training. Then it’s also something to consider then that the rest times between the dive, it’s not just nitrogen related, that we need time to clear nitrogen, but also that this could be a factor related to lactate. Absolutely, yes.

Because, yeah, I have heard it’s quite common to hear recently around here that people are sort of incorporating hyperventilation into their diving and deep diving as well, you know, and sort of promoting that a little bit as a technique that can be used by people to increase their comfort and things like that. Well, 20 years ago, everyone was hyperventilating like crazy before competition dives. But people have figured out that it has a downside to it.

And that is if you hyperventilate too much, you don’t oxygenate your brain very efficiently and you actually need the high CO2 in the end of the dive to stay awake because that opens your vessels to your brain. Yeah. And most people know that now.

But 20 years ago, nobody knew it. And everyone was completely into hyperventilating. And they even black out from hyperventilating.

Yeah, I think a lot of people still have in their mind that CO2 is a waste product. And I tend to tell my students that it’s not really a waste product. Of course, we need to get it out.

But we also need to have the perfect amount of CO2 in the system to maintain this homeostasis in the blood, this pH pH balance that that leads to the right uptake of oxygen, right? Yeah. Actually, there was a question from one of the patrons, maybe now is a good time to bring it in, because so this is from Tom.

Tom Way, thank you for the question. He was asking, you know, does anyone know if there is a pH level or a level of CO2 in the blood that is optimal for availability of of oxygen? Is it just our normal breathing, our tidal breathing is doing that or with a little bit more CO2 be more optimal?

I would definitely say the normal one when you are resting and breathing. I would bet on that. Yeah, not that I have done comparative studies, but I think that would be evolutionary.

A good answer that. We are getting that when we don’t over or underventilate. Yeah, a few billion years of evolution.

So that did a good job. And I think another thing that was interesting, one of the notes that I took from from Frank’s thesis was that it was you hyperventilation was also observed often in those divers who were trying to avoid it. Yes.

It’s quite easy to hyperventilate by mistake. Yeah, that’s true. When you do serial diving as recreational divers and snorkelers usually do, you will hyperventilate without noticing, and that means if you make very many dives in a row, you should take a little bit longer break just on the surface, just relaxing, playing on your back, breathing.

So maybe when you have done five dives, you should take a five minute surface break.

And that would prevent, we think, a lot of these accidents that we see today. All right, so did you have anything else you wanted to add about Frank’s stuff?

Well, he’s also shown that we can detect hyperventilation by using a chest strap. And beginner divers, if they would use that, they would have a kind of warning that now you should take a longer break and now you’re hyperventilating, that it could be a risk. Of course, they should also really learn how to have a proper safety.

But I mean, when competition divers always know about safety and train divers from diving schools, a lot of recreational divers, they don’t even understand that. And the first advice would be to go to a diving school to learn about safety systems. But there could also be a technical device, for instance, a dive computer that says, OK, now stop for five minutes and then they start again.

And then even if they have involuntary hyperventilation after five dives, OK, take a five minute break. This is something we are considering and this is something that our sponsors are very interested in to make a diving computer that is also good for recreational divers. How does this work with the chest strap?

What exactly is being measured with this strap? We first tried to measure CO2 in your exhale air, which would be the ideal version to determine if you hyperventilate or not. Not so convenient in water because you have to carry it.

We thought we would put it in the snorkel, but many freedivers don’t use even snorkel. But then we said that what if you can pick it up from just this chest circumference? And Frank has developed a system to compare that.

We did it first in the lab and then in the field lab to see how your breathing movements correspond with your CO2 levels. And if you have a baseline for an individual, you can easily see when they overventilate and then you can see if that is really correlating well with your CO2 levels. And he found that it does.

That’s also in his thesis. So that could be the basis for developing a safety system. Maybe a very easy to put on string that will say, peep, peep, take a five minute break because you’re accumulating in oxygen depth.

Fascinating. OK, tell us about the research that you were doing with the deep dives, with the pulse oximetry at depth. For very many years, we have done a lot of research with pulse oximetry, which is measuring heart rate and saturation.

But the problem was there is no underwater version of this thing. So I’ve been sitting on platforms in world championships. And when people come up and they do their protocol and they are OK, and then they wipe the hand and they put it on.

And then if I’m lucky, I get the nadir value. If they have been 200 metres, it will be

maybe 80 percent or. But now through contacts with underwater technology professor, we have developed an underwater pulse oximeter.

And it’s not just to case a normal pulse oximeter and put it underwater. But you have to start from the really beginning with the interface being water. And we have a reflective monitor now that is measuring on your forehead instead of on your finger.

And we have succeeded now to measure oxygen saturation in your blood down to around 100 metres. And this is very, very rewarding because we can compare all the results to what we have done by simulating dives in the lab. When you do a lab measurement, you have the ideal condition for measuring stuff, but you have to mimic a real dive.

And now we can actually send the device down mounted on the diver. So they have a small sensor on the forehead. They have a small cable through the hood in the neck.

And this cable is just transporting all the information to the small logger. And when they come up, we can see what happened across the whole dive. So the saturation information is still coming from the finger?

No, it’s coming from your forehead. Forehead. OK, so what kind of conclusions have you reached then from finally having this ability to do the pulse oximetry at depth?

Well, one of the things we wanted to know was that if a diver goes down to a deeper depth, they will be, first of all, hyperoxic because when the air is compressed, also the oxygen pressure will be higher. So actually, when you deep dive, you will take up more oxygen from your lung supply than you can on the surface, which is good. But then when you start ascending, it will be the reverse situation that then suddenly your partial pressure of oxygen will go down and then suddenly you can even have the reverse flow from your blood back to your lungs of the oxygen.

And that means you are rid of oxygen in your brain. And this is known since the 60s or even before. But we could see that some divers, they start desaturating already when they are going down and when they are at depth.

And this is very peculiar because this is when they should really saturate the blood that is going to the brain with oxygen. And this is indicating that some divers, they have a compromised gas exchange in the lungs when they are at depth. And this can be caused by at least two different factors.

It could be that you have lung atelectasis, that some of the lung is collapsing, the alveoli are not working anymore, or it could be by pulmonary edoema, that is the swelling of the lung, that it doesn’t have any gas exchange anymore. And this is likely partial, but these divers, they come up with a very low saturation level. And they are also at risk for blackout.

And that that point about the and I’m going to have to because the atelectasis, atelectasis, atelectasis.

[Speaker 2]

I don’t know how to pronounce it.

[Speaker 1]

It’s a very tricky word. But this is the the atelectasis is this the lung collapses in some areas. Yes, there are a few reasons why that would happen.

But when it collapses, then it can no longer take up place. And and we discussed when we spoke a couple of days ago that there could be some again, there could be some kind of genetic variation in people that makes this desaturation more possible, but also that the injury or the edoema, pulmonary edoema or barotrauma could be more more common in these divers, correct? It could be that some type of lungs are sensitive to compression in that way and some others are not.

And it’s quite well known that some people they squeeze easily and some people they can go to either depth and they don’t squeeze. And there are a lot of other factors that affect, of course, the the actual depth where you squeeze. It’s a lot of with stretching and training and so on.

But also with lung diseases, it’s known that you have different kinds of varieties of lungs genetically. So it’s not only about training. It could be that people come in two or even more varieties, some that are susceptible to squeeze and some that are not.

And you also mentioned that what you see is that in these very deep dives and elite divers that the dive response, I think you said, is getting weaker. Well, it was taught before from laboratory studies that when you go deeper, your diving response kicks in even more and it would kind of balance the effect of going deeper and the exertion level and so on. But what we found was that you get less of a diving response when you go deep.

So. It’s just adding to the problem that you don’t have a protective diving response. And this is because you have to put more effort, especially when going up again in deep diving.

First of all, of course, when you swim against buoyancy, when you go down and then you freefall. But when you turn, you have to put so much effort that you compromise your diving response. And that is adding on to the problem of gas exchange that has to do with the partial pressure of oxygen changing so much.

And so there the problem with deep diving is multifactorial. It’s not only the gas

exchange problem. It’s also that you don’t have the same protection as you have with shallow.

And what we mean with shallow is like 20 metre diving. When you said that you measured that on the on the descent, you already see some of these deep divers desaturating. Was that a surprise to them that they were desaturating so early?

Good question. I don’t think we discussed it with them, but they know they have a problem sometimes with the risk of blackout or samba. So probably they will say that they were aware of it, but they wouldn’t be aware of the cause of it, because most people, they saturate even better when they are in the beginning of the dive, when they are down at their maximal depth.

It’s only when they come up that they desaturate. Fascinating. From Eric’s studies, we also found that there is a separate cause of blackout that we didn’t think of before, and that is arrhythmia.

OK, yes, I do have a note here to cover this. Yes, that there are not just pure hypoxia that can lead to blackout. Yeah, because when you talk about hypoxia, you usually think of your brain being too hypoxic and then it kind of closes down.

But if your heart is sensitive to hypoxia, it can be compromised. The pumping function from the heart can be compromised before the brain shuts down. But when the heart doesn’t work properly, you will have a drop in your blood pressure and then the brain will shut down.

So that could explain why people blackout despite having the same saturation. Some people blackout, many people don’t blackout. And this is one other individual factor that we think can be crucial when it comes to who is blackout, blacking out.

Should I say it again? I’m having a bad day with this microphone. That then also makes me think about blood pressure and how blood pressure affects our free diving.

Do you have any thoughts on that? If someone is like has a low blood pressure or high blood pressure, is it affecting this this ability to saturate? What changes?

Well, blood pressure has to be regulated within a special range for you to perform in any kind of sport. And I think it’s important in freediving as well. If you have a very high blood pressure, it could be straining when you hold your breath, especially in static.

If you have a high blood pressure, it could be straining in static because in static we know that blood pressure is increasing a lot. And in deep diving, we don’t actually know so much because most of the studies are done in the laboratory where you simulate deep diving, which you don’t do very well in lab. This is also something we hope to look more into with wearable technology.

Yeah, I test my blood pressure at home not every day, but most days I have one of these little things I sit on the table because I noticed that it’s quite a lot of variation, you know, from day to day in my blood pressure. It could be quite low and healthy. And then on some days and it can be I’m testing, you know, in the morning when I’m rested, so it’s usually quite similar conditions each day.

But then it can also be outside of the healthy range on some days for no apparent reason. So it might be cause if we know more about that to also have to be checking more regularly our blood pressure. And and I could inform a little bit what we do on a training session, for example.

It could be. It could very well be. But if everything, of course, when you go into the water from air, everything that has to do with blood pressure changes.

This is important to realise. So even your baseline changes when you go just immersed to the neck. And on that topic, that this, you know, arrhythmia could occur that could lead to the heart not functioning, not pumping well, pumping well, then because we discussed this a couple of days ago, you know, there there are certain people who like this idea of, let’s say, let’s go and train together in the pool.

And since the dives that we’re going to do are very easy, now we just do our dives at the same time. We don’t have to provide safety for for those dives. And I’ve always really had a serious problem with this.

To be frank, I think it’s stupid. I think it’s stupid because it is there are there are just because you’re a hundred and fifty metre diver in the pool doesn’t mean that something is not going to happen, you know, what you might call a black swan event. You know, you know, this arrhythmia or some aneurysm or pneumothorax, whatever it is, could all, you know, so many random factors could occur.

So I very strongly like discourage people from a personal standpoint not to do any of these no safety dives just because you think it’s very submaximal or very easy. Yeah, I absolutely agree with you. And I also know of some accidents, lethal accidents in recreational freediving where people were confident with doing like many 25 metre laps all at the same time.

And they’re not good. Yeah, I know you don’t know what’s going to happen. You don’t know what’s going to happen.

Yeah, I think a lot of people forget that as safe as freediving is when you are with a body, the consequences of a blackout when you’re not with a body can be, you know, life changing. It’s very likely it is life ending. Yes, yes, yes.

Don’t forget that, guys. We covered the dive response in detail in the first interview. One of the things I’ve always remembered about that, because I’m still struggling with the

education materials from Ida Molchanov, you know, is that I really like how you said that the spleen contraction was not part of the dive response, which I’m still trying to convince people of.

It doesn’t matter what you call it. But I mean, it is a completely different response and it’s doing different things. The diving response is conserving oxygen.

The spleen response is increasing the oxygen storage. And it is kicking in when you have a first hypoxic event. So when you do serial dives or a warm up, then you need the first dive to really make it happen.

And then you have a larger oxygen supply. And then the diving response will kick in after that to try to conserve your oxygen. So it’s completely physiologically different.

And something else that I remembered wrongly about that and also Frank and I had a good discussion about that on the last the recent interview that we did. But something that I remembered incorrectly about that was that I had thought that it was rising CO2 that stimulated the spleen contraction, which always led me to tell people, you know, another good reason not to hyperventilate then. But you you told me that it’s it’s it’s mainly hypoxia.

It’s mainly hypoxia and CO2 contributes a little bit because we have compared also high altitude hypoxia where you have a very low CO2 with apnea hypoxia. And we see that with apnea, the spleen contracts much more. And then we have done experimental runs where we see that also the hypercapnia is increasing the spleen contraction a little bit.

So it would be even stronger toward the end of the apnea when you have the hypercapnia. Yeah, it sounds to me like what you’re saying, again, is that normal breathing, normal blood pH level before a dive is, again, optimal for producing all the benefits that we want from the spleen contraction, from the dive response, everything like that. Thanks to evolution.

Thank you, evolution. I think I think people evolved to do different things, run and walk and climb. And and that includes diving.

Absolutely. Yeah, the dive response is the dive response affected the the strength of the dive response, is it affected by hyperventilation? No, not much.

But when you hyperventilate, you also have to use some oxygen for your respiratory muscles. So actually you start off with a worse situation where you already consume a lot of oxygen if you hyperventilate. If you’re doing the kind of like active hyperventilation that requires you to actively breathe.

Right. But probably if you’re just doing that kind of subconscious quiet hyperventilation, it’s not going to make much of a difference. Not so much, not as much, I would say.

OK, OK. Because in my mind, I thought that that vassal constriction is going to be the amount of vassal constriction is going to be important for hemo compensation, especially in the lungs. But that’s not the case.

With hyperventilation. Explain how you think it could work. Because then the my point be that.

All right, guys, let’s just take a little minute here to hear from our friend over in the U.S. of a Ted Hardy about freediving training secrets.

[Speaker 2]

Hello, freedive cafe listeners. There are a lot of awesome reasons to tune in to the freedive cafe podcast, one of which is to improve your own freediving performance by gleaning pearls of wisdom from some of the best in our sport. Another way to dive deeper and feel more comfortable when you’re down there is to actually implement a training plan.

So what are you currently doing to improve your freediving performance and abilities? When I ask most people this, they say, well, you know, Ted, I go diving whenever I can, but it’s hard because of the spouse, the kids and the job. Let’s be clear.

Diving whenever you can is not a training plan. And that’s why I created freediving training secrets. It’s my newest online course where I’ll put you on a six week training programme you can do from home without having to go to the pool or the ocean.

Each week you’ll unlock a new video where I’ll tell you exactly what to do, why you’re doing it and what to focus on during the exercises. You’ll be happy to know that the traditional O2 and CO2 tables didn’t even make it into my top 10 dry land training exercises. If I thought they were awesome, I’d use them.

You’ll notice that as you go from week to week, you’ll be building on what you did, the previous week and unlocking new exercises. So you won’t be stuck doing the same thing over and over again. To learn more about the programme, visit freediving training secrets dot com or click the link in the show notes.

Life’s safe out there. It’s not even that hard. [Speaker 1]

Thanks, Ted. OK, let’s go back to Erica. That we would need that CO2, I was thinking the CO2, the CO2 level was somehow contributing to the extent of vasoconstriction.

But that’s not not so much. I would say it’s only an extreme situation. Don’t make up your own science, guys.

That’s the lesson there. OK, good. Just to clarify a couple of points on on dive response and especially blood shift.

It was my belief that the strongest blood shift would be happening. And I’m thinking of blood moving into the capillaries, into the chest, around the alveoli, that this would be happening more as we’re getting deeper. But this is maybe not the case.

I think the main blood shift happens actually when you go from air into water. So when you put your body in water, when you just jump in the water, that’s when most of the blood concentration in your thorax and in your body happens, because then that’s when you remove the gravity effects on your whole body when you are standing on land. But then when you hold your breath, you will have the diving response start that will squeeze in even more blood to your middle of your core.

And if you reach depth, it will be enforced even more because that’s when you are actually sucking in blood from your extremities to your chest. So it’s a whole kind of spectrum of steps. Yeah, but but what you said there, I think that’s a really interesting point for people to understand is the idea that as soon as you get in the water, you have this redistribution of blood because gravity is removed from the equation.

Right. Most of the time we have blood kind of pulling in our legs and feet. And we are, you know, the heart keeps the blood moving around so that we don’t end up just with it and also the temperature change.

So it would be four factors that focus your blood in your in your abdomen and in your chest. Fascinating. OK, so I cleared up a few points there about about the dive response for myself, and I hope that was interesting for everyone else as well.

OK. What’s going on with myoglobin? Do we have it?

Do some people have more than others? Can we what is it for a start? Myoglobin is something that is similar to haemoglobin that is carrying oxygen in our blood.

It’s the red stuff in our blood. And myoglobin is kind of a local oxygen supply in our muscles. And in terrestrial animals, it’s usually considered as just a station to transport oxygen to our mitochondria that are using it.

But in marine mammals, it’s known that the myoglobin is very, very high. And when they have a strong, strong diving response, when they dive, the muscles have their own local oxygen supply so they can keep in the aerobic part of the dive on their own, so to speak, without having a blood oxygen delivery. And it’s not known if humans can accelerate the myoglobin very much, but it has been observed in divers in one study by Anthony Salia that actually it seems like we can have a higher level of myoglobin when we are trained divers.

And it has also been seen in high altitude populations that they have higher myoglobin content in their muscles. So that’s kind of corresponding. And it’s very little done on it.

And I actually wanted to do it many years ago. I even had the ethics for it. But to do these studies, you have to actually take a muscle biopsy from skilled divers.

And most skilled divers, you can find them on competitions and they absolutely don’t have time to be on land after such a sampling for several days. So these muscle biopsies, and for those who don’t know, are quite invasive and painful procedures. You can have a local anaesthesia, but of course you have a small wound because you need to take out some muscle tissue.

I don’t do it myself. There are experts that do it. But still, I think it’s quite it’s a quite important study that maybe some really skilled freedivers should consider being in, that we can eventually understand if people have the same ability as seals.

Seals have 10 times more myoglobin in their muscles than terrestrial animals. Yeah, that would be fascinating. Maybe grab 10 or 20 elite level freedivers in the off-season and take them out for a drink.

No, but if they volunteer to be in the study, if we have 10 of them, I can arrange a study like that. Talking of studies that could be arranged, we also discussed in our pre- conversation for the interview about the effects of caffeine on the dive response and what the possibilities could be there. Thank you for the question from the Patreon supporter.

I forget who it was, but thank you for the question. So we obviously, you know, if caffeine is increasing the heart rate, then it could counter the bradycardia that comes with the dive response.

[Speaker 2] For sure. [Speaker 1]

That seems like common sense. But there could be some other interesting dynamics going on there between caffeine in the dive response or caffeine in diving in general. What kind of study would you conduct?

Like, how would you do that if you wanted to find out more? We could easily find out. I couldn’t answer your question.

I would say that the basic heart rate would go up a little bit. I don’t know what the diving response would do, actually. Probably the overall heart rate would be a little bit higher.

But we could easily do the same kind of study that we did with beetroot juice or with fasting, where you have a weighted design and you have people do static apnea before without caffeine or with caffeine, preferably blinded, that you have some decaf coffee or some coffee coffee. You need some good decaf coffee to fool the coffee drinkers. And also, I think it has to do with who is using caffeine on a regular basis.

Because if you read people that are really addicted to caffeine from caffeine, they might perform worse. So I think this is always a thing that is difficult to determine. But we could do the study here in that habit if people are interested.

I’m sure a lot of people would be interested in that because that’s one of those things that, you know, a lot of people are unwilling to give up in any sport or anything that people want to achieve. Coffee is one of the last possibly negative habits that they are unwilling to give up. And it’s also about the amount, of course.

I mean, if you drink very much coffee all the time, maybe it’s a good idea to minimise it a little bit. But I mean, half a cup of coffee in the morning before you dive, if you really like it. I think it’s a psychology as well.

Yeah, I mean, even with that kind of low level addiction, I think that obviously, if you have like a habit of caffeine, even if you’re just having like one coffee a day again, if you’re coming towards the peak point in your training block or just before a competition and you suddenly decide to cut out coffee, there might be some rebound, you know, neurones might just not be firing as efficiently in the brain because you skipped your coffee, you know, and maybe it’s actually beneficial to to control the caffeine. I don’t think you should stop just before a competition.

I think you should know what you’re doing ahead of time. [Speaker 2]
Yeah.
[Speaker 1]

Yeah. And what about alcohol? You said that you already did some study with alcohol.

We had the question from an insurance company if really alcohol is making people drown or if it just makes them fall overboard because they found that many people that drowned had alcohol in their blood and we had a low volume of alcohol for the people like one beer. And we saw that that compromises the diving response a lot. So alcohol for sure.

It’s making it almost impossible to constrict your vessels to the degree that you save oxygen for your brain. So I think we have shown that we haven’t published it, though. It

was a student work.

I did it 20 years ago or so. But it was quite clear that even a low amount of alcohol, it made it compromised your diving response. Because of vasodilation caused by alcohol.

And something that was funny was that we actually tested this might come out wrong, but we actually tested that in trained freedivers. And this is what I was referring to. But also we trained it in completely novel people that didn’t even try to hold their breath before and they performed better, which is a risk factor in itself, because they didn’t listen to the warning signals to stop breath holding.

So this is also a kind of bad idea to start breath hold diving when you have some beer. Maybe that’s why the guy in Indonesia held his breath for four minutes because he was so drunk. Didn’t get enough warning signals.

But I mean, also for a competition diver, it’s very clear that you perform worse. So the novel person would hold their breath a little bit longer, but the competition diver would hold their breath for a shorter time. This is what we saw.

Interesting. OK, so there was, no, we have this that we put on the table from Pontus. Yeah, Pontus Holmström about the high altitude tolerance, da, da, da, da.

And there was a question from the Patreon supporter. Who was it now? It was from Peter.

Thank you for the question, Peter. Well, we decided not to because you were asking about some medication. We decided not to discuss pharmacology.

That is not really your area. But you did mention some interesting things about high altitude in relation to to freediving. And we discussed, I think a lot of people also want to know if high altitude is a good place to train for freediving, if it’s beneficial to be at a an environment where the partial pressure of oxygen in the atmosphere is lower.

I think high altitude could work as a kind of pre a pre-setting for freediving, for advanced freediving. And the other way around as well. You could train for high altitude by holding your breath because very many factors are, in fact, the same when you when it comes to hypoxia.

Even though breath holding is like acute hypoxia and the high altitude is chronic hypoxia. I think that was Peter’s question. Actually, part of it was that, you know, could you train for high altitude using something like CO2 tables or O2 tables or O2 tables, I would say CO2 tables is unnecessary because when you are in high altitude, you have very low CO2 because you need to breathe a lot.

But we actually found that you can do an apnea test to determine who is tolerant or not

to high altitude. And that shows that inside the body the same things are working when you go to high altitude and when you’re diving. And it used to be thought to be completely the opposite things if you go high or if you go deep.

But it seems like you’re recruiting the same defence systems in your body. Both low oxygen situations, right? And then when you say you can use an apnea test for that, would that be like the ramp test?

It would be similar to the ramp test we have done with the maximal apneas. But then we’re talking about people that never dive. So people that are going to high altitude, if they get to hold the breath first one minute and then two maximal breath holds, and then we measure the diving response and the spleen response and the blood response, we can divide them into groups who will be prone to develop high altitude sickness and not.

And those that have a strong diving response, they will not have altitude sickness at a given level. I mean, at 4,000 metres. Right.

Yeah. Because explain again for me what is actually what the adaptation is taking place, because you had this interesting description of the adaptation that takes place when we we go to base camp, for example, on Everest. Like why we have to stay there for two weeks, like what the changes are taking place in the body.

You explain very nicely. I can barely speak English right now, so I do my best to ask this question. But that there’s something very interesting happening with CO2.

And well, the first thing when you go to altitude is that you have to breathe more because you get hypoxic and then you get rid of more CO2. And when you sleep, for instance, at high altitude, the first night at 3000 metres or so, you will have periodic breathing because that you sort of stop breathing, hold your breath and then you start breathing when you are really hypoxic and then you have to breathe so much that you go very low in CO2 again and your brain is set on the CO2 signals to arrange your breathing in an imbalanced way. But when you adapt to high altitude, you start using more the signals that come from your hypoxic sensors in your blood vessels and you can just forget about the CO2 and your kidneys will set your pH in your blood right again.

So over two weeks, you just listen to your hypoxia and not to your hypercapnia and at high altitude you will need to breathe more. So it’s very important that you can still keep your blood pH at a good level. So, yeah, once again, like another ten points for evolution doing an amazing job even when we go into those extreme environments.

But it makes me wonder also what the maybe you have some thoughts on this. If we take a group of very highly trained freedivers, obviously, this is kind of what you’ve been doing. But if we take a group of very highly trained freedivers and untrained freedivers,

how much how different are they?

On a deep level, physiologically, how deep are they? We compare like, you know, top level marathon runners, for example, they have very different physiologies than the average person. I wouldn’t say different.

I think they have just pushed a few of the systems to to the edge. Like with other sports, it’s not so specific, I think. But there are other things that are important.

If you have to be a good runner, then if you have to be a good freediver. So I think it has more to do with the level you train, because athletes in other sports as well are really pushing toward a side where they usually have to start with the genetics to develop and then they train as much as they can. And with the very specific training methods and then they can go to the to the very top level.

So I don’t think they are different, but they are they are trained in a different way and they have different specific characteristics. But it’s also not it’s also not contradicting to be a good runner and to be a good freediver, I don’t think. Yeah, I don’t think so either.

I mean, I come from a background of long distance running and I think obviously training for an ultra marathon at a higher level is going to contradict the training for the freediving quite because you have to train a different thing because you have to spend 20, 30 hours a week running around in the hills when you you should be diving. Right. But at the same time, the benefits of the improved, you know, the vascular mobility, the improved heart respiratory function, all of the improved functions of the body that come from this kind of running exercise or cycling or swimming or whatever it is, is going to be beneficial to your health in general, which is going to be good for your freediving.

I’m going to a conference in Belgium in the end of June together with an anthropologist also that thinks that swimming and diving was a prerequisite for being a good runner, evolutionary speaking. So we have a kind of swim run hypothesis of human evolution. Swim run hypothesis.

I didn’t learn to swim until I was 34 years old. I was running before that. But it has to do with how our systems are promoting one thing or the other.

Then I’m going to ask you some fun questions that you can that you can fire off. These are called the Desert Island questions. I put them into the interview for the Patreon supporters like a little extra fun thing, and it’s just fun.

First question before we do that last question from Tom. He’s asking if someone wanted to work in your field of research, what educational pathway would you suggest? I’m now in sports sciences, but I’m a biologist.

So either kind of physiology or biology. OK, I’m running a programme that is called

Master by Research where you can do two year project in our group in sports physiology now at Mid Sweden University. So if you have a bachelor exam in something like that with physiology in it, then you can apply for that.

OK, that would be one way. OK. OK.

Desert Island questions. What is your perfect morning routine? This section of the podcast, Desert Island questions is a little addition we put on for the listening pleasure of the Patreon supporters.

It’s about eight, nine questions. I asked the guest fun questions, things like if you could take three books with you to a desert island, what would they be? If you could only eat one meal for the rest of your life, what would it be?

If you could meet one famous person from history, who would that be? Questions like this. If you want to hear the answers, you can consider supporting the show and supporting me on this free diving journey by going to Patreon dot com slash free dive cafe.

OK, thank you for answering those questions. Final question. The question we always ask on the show, why do you free dive?

I free dive because it gives me a lot of calm and pleasure. And I started when I was 13 and I couldn’t stop. Good answer.

Have you done much diving when you’ve been here this time? Every day, two hours, but not really not deep diving or anything. We dive.

We have a it’s a moorish line somewhere close to where we stay. So we pull down to 15 metres and just float up. I don’t do any deep diving now.

I have done 100 feet some years ago with Lotta. But I enjoy free diving also in the north of the Scandinavian Sea and I see the lakes and everywhere. So and I have been enjoying it always.

So you’ve got your own little private mooring out here down on this side of the bay. Yeah, we don’t even have to put the buoy, you know. Yeah, you know, we were also stuck up in the lighthouse area there as free divers.

We need to expand out a little bit sometime. OK, well, thank you so much for this conversation, Erika. It’s really fascinating.

I think there’s like, you know, you’re one of the very few people doing this research. It means a lot for our community because it’s, you know, see, free diving is such a unique sport, but so understudied and probably we’ll never have the kind of research that we deserve, I think. No, but it couldn’t be done with all the support from all the free divers.

And I’m so happy that so many people volunteer to to be in our studies. And then we hope that we can give back some understanding of what everyone is doing. Yeah.

Yeah. And there’s already been a couple of things here from this conversation that are completely new to me and also a lot of clarifications I have as an instructor, as a coach, it’s very, very useful. So thank you very much.

And maybe once we have a few more things to talk about, we can do it again. And yeah, let’s keep each other informed. And yeah, nice talking to you and dive safe.

Yeah, dive safe. Nice talking to you. Nice talking to you.

That was a Shagatai, absolutely fascinating discussion that we had there. I hope you enjoyed listening to it as much as I enjoyed producing it. If you have any questions or comments or you want to get in touch for any reason, you can email me at Donnie at free dive and thrive dot com on social media.

I am at free dive and thrive and you can find out information about free diving courses, coaching sessions, remote coaching and all that kind of stuff at free dive and thrive dot com. That’s the mothership mothership website for everything that I do. OK, guys, love you all.

Thank you a million times for listening and have a wonderful day or evening or afternoon wherever you are and of course, dive safe.