It is based on the idea that the glottis remains closed by itself past a certain pressure difference level, and we do not need to generate any kind of tension to “hold” the mouthfill.

For those who wish to know more about the logic and theory behind the exercise, I recommend this article :
Mouthfill : Open / Closed ? What is the natural position of the glottis?

General principle :

The exercise aims to minimize the tensions in the glottis, the oral cavity, and the face while holding a mouthfill at depth. The principle here is not to perform but to OBSERVE. Observe what? To observe the minimal amount of energy needed to hold your mouthfill. You will therefore perform several dives with neutral lungs (possibly empty for the more advanced), during which you will observe and test your glottis. To do this, try to take into account the following principles:

1. Keep the line at a “very-easy” depth: The goal is to have 100% of your attention to observe what is happening in your mouth/glottis without worrying about performance. If you are used to diving at 30m in FRC, I recommend setting the line at 20/22m maximum.

2. “Let it leak”: “Let it leak”: as it is not a question of performance but observation, do not hesitate to release the whole of your oral cavity. You will see what happens; worst-case scenario, it will leak. So what? The exercise aims to redefine the level of tension that you feel necessary to keep the mouthfill, and only an exploration attitude can help you.
   
3. The most important is the time “between” equalizations. The deeper you go, the less frequently you will need to equalize, and the longer the time between equalizations will be. Subsequently, do not hesitate to make a slow dive that will allow you to artificially increase this “non-equalizing” time and focus your attention on this part. Concentrate on relaxing your tongue, jaw, cheeks, and face… It is normal to generate a little bit of tension during an equalization to compress the air; you must make all forms of action disappear between two equalizations.
   
4. Forget about “constant pressure.” If you are normally using this strategy, put aside your habits and adopt (at least for this exercise) a sequential pressure to minimize tensions (see point 3).
   
5. Take a comfortable mouthfill of about ⅔ of your maximum capacity. By maximizing comfort, you will increase your attention level where it matters and be better able to extract the benefits of this exercise.

Conclusion

You have now redefined the level of passivity, of relaxation that your mouthfill requires. You still need tYou have now redefined the level of passivity, of relaxation that your mouthfill requires. You most likely still need training and repetition at easy depth to make it “auto-pilot.” but I hope it will improve the quality of your diving experience and, subsequently, your results.

The article Mouthfill : Make peace with your glottis appeared first on Gaspard Freediving.

I always thought the glottis neutral/natural position was “open”. Like many freedivers, when I encountered leaking mouthfill issues, I assumed that one of the causes was that my glottis was not “strong” enough and had to train it specifically.

However, two years ago, I encountered something strange and counter-intuitive about my glottis. It seemed that on a dry exhale breath-hold, my glottis was remaining closed by itself (without me “keeping” it closed).

After several “tests” on myself, I realized that the glottis was also staying closed on full lung breath-hold. On the opposite, on Neutral lungs (FRC), the natural position of my glottis was “open”.

Let’s play

Before going further, let me detail precisely how you can test it on yourself.

• First, you need excellent glottis awareness. To develop it, you can “cough” very gently multiple times. Playing with the “door” will help you better understand it.
• Then, make a forced exhale (it doesn’t have to be RV, anything below FRC should work). Close your glottis, relax your abdominal muscles, relax your tongue and eliminate ALL the tensions. DO NOT TRY TO HOLD YOUR BREATH; just see what happens with your glottis when you do “nothing” and when you are entirely passive.
• You can do the same with FRC and on full lungs.
• Just to be a bit more precise about Full lung and empty lungs tests: I feel that if I do absolutely nothing, the glottis remains closed, and the breath “HOLD” requires zero energy. However, if I produce a tiny bit of energy to re-open it, the air starts to flow in/out, and the glottis stays open.

Experts opinions

To make sure that my “feeling” of the glottis remaining closed on empty/full lungs was not just me being crazy or having a weird body, I selected three freedivers to replicate the experiment :

Nathan Vinski: Nathan is a good friend, we shared many ideas about freediving, and he is the most knowledgeable person I know about the sport. When I asked him to experiment on himself, he didn’t confirm my hypothesis at the moment. However, a few days later (he kept playing with it independently), he agreed with my observations.

Claire Walsh: Claire is the female Irish national record in multiple depth discipline. I asked her to be a guinea pig for the experience because she also happens to be a professional singer. For sure, she would have a better glottis awareness than me! I had a bit of trouble accurately explaining the “experiment” (it was on video conference call during the first covid wave), but once we were on the same page, she also felt her glottis remained closed on exhale and full-lung. I asked her a percentage of confidence, and she was 100% confident.

Max Gardien: I did an equalization workshop with Max, and this guy is a machine in terms of equalization “raw” skills (dry exercises) and, of course, in the water. The same as Claire, I knew he would be a great help for his glottis awareness. After a few tries and observations on himself, he arrived at the same degree of confidence as Claire: The glottis was remaining closed by itself on full and empty lungs, and he was 100% sure of it.

Interpretation :

My interpretation of those observations is that the main factor is the pressure differences between the lungs and ambient (not necessarily the absolute lung volume).

I base this interpretation on another experimentation you can easily replicate :

Make a forced exhale below FRC (and less than RV to keep the exercise accessible). While you close your glottis, keep your abdominal muscles engaged (and stable) and try to release the tensions of your glottis: this time, the glottis reopens itself.

Having the abdominal muscle engage maintains the lung and ambient pressure balance. Under this condition, the “natural position of the glottis” is “Open.”

Application:

if we look at a “normal” dive using mouthfill, after the last recharge, we can divide the dive into two parts:

1. The parts where our diaphragm keeps rising smoothly and the lung pressure matches with the ambient pressure:

We must intentionally keep our glottis closed during this part as its natural position would be “Open.” BUT we only need to keep it closed very gently because the pressure difference between the mouth and lungs is not so large (if we are not overpressurizing the oral cavity).

2. The part of the dive beyond natural mobility of the diaphragm when lung pressure starts to be “late” (inferior) compared to ambient pressure :

During this part of the dive (which constitutes the last part of the descent), the natural position of the glottis becomes “Closed.” Despite an increased difference in pressure between the mouth and lungs, we do not need to generate tension in the glottis to keep the air in our mouth (unless we need a lot of pressure to open the eustachian tubes, a topic we will come back on in a later article).

I suggest that you focus on the second point: remember, the deeper you go, the less often you need to equalize. It means you can be completely PASSIVE. Trying to “strongly” hold the mouthfill will only generate unnecessary tensions and enhance the leak. You can leave your glottis in peace and let it do the job for you.

To go further

If you want to FEEL the application of this article in your dives, there is a straightforward exercise you can do. I have been using it on my students for the last two years, and there is a high chance it will drastically improve the comfort and efficiency of your mouthfill.

Check this article to find out :
Mouthfill : Make peace with your glottis

The article Mouthfill : Open / Closed ? What is the natural position of the glottis? appeared first on Gaspard Freediving.

“Residual volume is the minimum size of the lungs. From the depth of the residual volume, the air in the lungs stops reducing in volume and it is then the blood shift that comes to protect the lungs.”

There are many errors and approximations in this description, consequences of shortcuts taken at face value. If these errors are not obvious to you, I suggest you read the following article.

A “medical” concept first

First of all, it is necessary to specify that the notions of lung volumes (FRC, RV, TLC…) are prior to apnea which of course borrowed them from medicine. They, therefore, represent medical terms corresponding to “normal” pressure and ventilation conditions.

In this context, the medical definition of residual volume is: “the amount of air remaining in the lungs after a forced expiration”.

The muscles that are mobilized in a forced expiration are the abdominal muscles which when contracted push the diaphragm and compress the lungs (producing expiration).

Thus the limit of a forced expiration is notably given by the limit of an abdominal contraction. However, this does not mean that the diaphragm cannot be pushed further and still compress the lungs. It just means that it cannot be pushed further by the action of the abdominal muscles.

Residual volume in freediving

In apnea, we want to avoid unnecessary tension and contraction. The good news is that the external pressure of the water increases constantly during the descent and pushes the diaphragm instead of our abdominal muscles which can (and must !) remain relaxed. Under the effect of the hydrostatic pressure, the diaphragm can therefore be pushed BEYOND its position that corresponds to the residual volume from a medical point of view.

Thus, the purely “medical” definition of residual volume does not really make sense during deep immersion and the only situation in which this concept can be really useful is in the context of those who choose to load/reload their mouthfill by abdominal contraction.

“Freediving Residual volume”

However, many of us have “experienced” the residual volume in terms of Frenzel equalization: personally, I remember that a few weeks after I started freediving, at 27m depth I had no more air in my mouth to equalize and I had to turn around. Compared to my apnea courses, this corresponded well to my “medical” (or theoretical) residual volume. But for some people, this phenomenon occurs as early as 10m while for others, they can continue to Frenzel normally beyond 40m.

The reason for this difference (all things being equal) is the abdominal tension that “holds back” the diaphragm. To realize this, you can perform the following maneuver on dry:

Contract your abdominal muscles (as if you were expecting someone to punch you in the stomach) and perform a series of Frenzel equalization while letting a little air escape through one nostril at each equalization (you should ear a little “pshiit” at each equalization). You will notice quite quickly that there is no more air available in your mouth to equalize. Release the abdominal tension and resume the equalization (still letting air escape): finally, there was air available!

Of course, in the water, abdominal tensions are rarely that big, but they can still significantly affect the passive mobility of your diaphragm and therefore affect what we can call our “freediving residual volume”. Our “freediving residual volume” can be way deeper or way shallower than our medical residual volume: it mostly depends on our freediving adaptation and the quality of our training.

And once the diaphragm can no longer rise then?

Through advanced equalization techniques, it is still possible to dive beyond the “freediving residual volume” (maximum passive mobility point of the diaphragm). Nevertheless, the air in our lungs does not stop shrinking. However, it is the way the air is compressed that will change. This is where the blood shift comes into play (even if it can start earlier) : by inflating the capillaries with blood, the air in the lungs will continue to be compressed and thus decrease in volume. This will have the effect of maintaining the pressure balance between the surrounding water and the air in the lungs and keeping us safe.

In summary

The residual volume as defined medically does not correspond to the minimum air volume of our lungs during apnea. In a trained freediver, the passive mobility of the diaphragm will continue to compress the air as the external pressure increases. Even after the point of maximum diaphragm mobility, our “freediving residual volume”, the volume of air in the lungs will continue to decrease due to blood shift.

What use ?

A better theoretical understanding of freediving can always help us in our training. In my case understanding better this concept gave me the confidence to adopt a non-traditional equalization strategy that includes mouthfill refills deeper than my “medical residual volume” but still shallower than my “freediving residual volume”. However, before you start to play with it make sure you also include some pressure adaptation sessions in your training and that you only do what feels right and comfortable for you so you do not jeopardize your safety.

For those that might need some extra clarifications, there has been some interesting discussions around this article in the “Freediving science” facebook group :

https://www.facebook.com/groups/freedivingscience/permalink/2135721613270215/

To go further

The understanding of residual volume will also help you understand better Frenzel equalization and why it stops working at 10m for some while other people casually use it to 40m : more in this article

The article Residual volume: some clarifications appeared first on Gaspard Freediving.

As we saw in an article published last year, contrary to some popular beliefs, as long as we are relaxed, air travels naturally from the lungs to the mouth, regardless of whether we are head up or head down. The main reason is that the lungs are much more flexible than the head and the oral cavity. Therefore, the external pressure is released first in the lungs, and the air travels in the direction “high pressure to low pressure”. For more details, I invite you to read or re-read this article.

However, this demonstration does not explain a phenomenon that most freedivers have observed: it is easier to equalize when “head up.”

In this article, I will present the two explanations that I believe to be the most relevant to explain this phenomenon for the Frenzel equalization. You may already be familiar with the first of these explanations. The second one is the result of my work on the subject, and I have never heard it formulated by anyone else. However, a hyperbaric doctor (Dr. Heikal) has confirmed its relevance.

A little reminder

Before going any further, let’s look at the mechanics of equalization. An equalization (except BTV) consists of generating pressure at the entrance of the eustachian tubes to open them. Once opened, air naturally comes to lodge in the middle ear. The amount of pressure you have to generate you may know if you have already used an EQ tool (not an otovent). As an indication, we can consider an average of this value at about 30 millibars (this value is not definitive, and there are several ways to decrease it, starting with good hydration). Nevertheless, it is essential to understand that this value is not absolute. It is 30 millibar PLUS the ambient pressure. It means that if I am in a hyperbaric chamber with 2 bars, 3 bars, or 10 bars of ambient pressure, I should always generate 30 millibars of additional pressure to open my tubes.

Explanation 1: more blood pressure head down

Our blood is subject to gravity, and when we are head down, the blood pressure towards our head increases. The eustachian tubes being flexible enough, they accumulate more blood. It makes them “heavier,” and we need more pressure to open them. To better understand this, you can think of the eustachian tubes as swinging doors that you have to push open. The heavier a door is, the more force and pressure you need to generate to open it. This extra pressure to generate makes equalization head down more difficult.

Explanation 2: higher ambient pressure when we are “head up”.

Let’s imagine a head down diver whose head is at precisely 10 m depth and whose abdominal area is 9.5 m. As we explained in the introduction, the head does not deform under pressure and therefore cannot reproduce the external pressure. Thus the “natural” pressure in the oral cavity will be 1.95 bar. If our diver goes head up while keeping his head at a depth of 10m, his abdominal area is now at a depth of 10.5m, and the “natural” pressure in the oral cavity increases to 2.05 bar. It gives us an extra theoretical ambient pressure difference of 0.1 bar. “Theoretical” because two mechanisms that are difficult to quantify and that I will not detail here largely attenuate this value. Nevertheless, we are in order of magnitude comparable to the 0.03 bar (30 millibars, remember) that we need to equalize. So to use the analogy of the swinging door, it’s as if you had a strong wind pushing against this door all the time, so you need to generate less force to open it. 

A little perspective

For those who have trouble picturing all these values and who may not realize how much of an impact a 50 cm (estimated sternum to head) water gap can have (it is REALLY easier to equalize head up), it may be interesting to ask ourselves how many meters this pressure gap represents in the open air, at the surface… 500 meters! In terms of pressure, a 50cm water column is similar to a 500m air column. In terms of pressure again, 1m75 of water (size of a human) represents about 1750m of air. Yes, this is a lot, and it shows us how necessary it is to look at how external pressure is exerted on the different parts of the body if we want to understand equalization.

What applications?

The first and main application is to feed the curiosity of those who like to understand “how things work” and that is by itself lot in my opinion.

However, we can find a pedagogical application: 

Personnally, since few months, once a beginner student is comfortable with the head-up equalization, rather than doing a head-down “test” or adding depth to make him go deeper head-up, I keep the line at the same depth while instructing him to generate more pressure in his equalization, to be a little more “aggressive”. It allows to simulate the subsequent dives the student will have to make in comfort and, it constitutes an intermediate step increasing the chance of success for head down dives.

The article Frenzel : Why is it easier to equalize head up ? appeared first on Gaspard Freediving.

The challenge is to determine at what depth the last equalization of the mask will take place to ensure that the maximum amount of air is available for your ears while excluding the risk of injury at the targeted depth.

To do this, we can perform a simple calculation…
First of all, you will have to make a dive in which you will keep your nose pinched as soon from the surface and never release your fingers (so do not equalize the mask at all). Then stop at the depth at which your mask becomes uncomfortable and remember the depth.

Once at the surface, convert this depth into pressure. For example, if at 10m the mask becomes too oppressive, note 2 bars of pressure. Since the surface pressure is 1 bar, this means that with this mask you can withstand a pressure multiplication by 2 without having to equalize it.

You then need to know the depth you are aiming for in your training cycle and convert this depth into pressure. For example, 5 bars if you are aiming for a depth of 40m.

Then divide these two values. In our case: 5bars / 2 = 2.5 bars
Finally, convert the result into depth: 15m

In our case, this means that if I stop equalizing my mask at 15m, I can continue my descent to 40m without risk of injury while ensuring maximum air supply for my ears.

The interest of doing this exercise at the beginning of the training cycle is to be able to quickly get into a habit and avoid having to make last-minute changes that are likely to penalize you when the goal is getting closer.

The article Until what depth should you equalize your freediving mask? appeared first on Gaspard Freediving.

1. The fluidity of your mucus (sinus secrets): A large part of beginners are confronted with this problem without being aware of it! In fact, if you are not properly hydrated, your mucus (in the sinuses and at the entrance of the eustachian tubes) will be more “dry” and will be more likely to form congestion (which will not necessarily prevent you from breathing normally but which will be present). This small congestion is able to drastically increase the pressure needed to compensate for what can make things particularly uncomfortable. Conversely, if you are well hydrated, your mucus will remain fluid and even if you are slightly “cluttered” a few descents and the air movements that accompany them will help you get rid of this excess once on the surface which will make it easier for you to clear for the following dives.
2. A better bloodshift/haemocompensation (pulmonary erection for intimates): the blood is composed of about 50% water (contained in the plasma), being properly hydrated will make your blood less dense, more fluid which will help promote your Blood shift. I’m not going to detail here how a good bloodshift promotes compensation but let’s say that the more air in your lungs can compress (thanks among other things to your blooshift), the better!
3. Better recovery and less stress on the body: Even if it is an aspect often overlooked by us apneists, the accumulation of nitrogen in the body is a factor to be taken into account. If there are “rules” to follow: interval between dives and total depth per session, the practice of depth can generate a very specific fatigue that will be even greater with poor hydration. This physical fatigue stresses the body and can have an impact on your freshness the next day without you necessarily realizing it directly. If you then find yourself diving when you are not in your best physical shape, it may be quite “normal” that the discomfort generated by this fatigue turns into tensions that will negatively affect your compensation. Good hydration drastically reduces the effects of nitrogen absorption and your recovery will be even better: this physical freshness will necessarily result in better relaxation and therefore easier compensation.

I would like to end with what it means to hydrate properly: it is not a matter of drinking like crazy before, during and just after his session, hydration is an ongoing process that must be maintained and maintained throughout your stay (and even before very high preference!). To give you a quantitative idea on the number of litres recommended, in Dahab when you are on a training period: minimum 4 liters of water in winter and 6 liters in summer all distributed throughout the day (and not I exaggerate anything). And for the smart kids at the bottom: no coffee is not a moisturizing drink;-)

The article Hydration and equalization appeared first on Gaspard Freediving.

While talking with experienced divers or through interviews, I often notice a certain “reluctance” to teach mouthfill. We often hear sentences like “you don’t need the mouthfill to go to XXm”, or “it’s too early to learn the mouthfill”. Some instructors even refuse to teach it in detail during an AIDA4, considering that it is more “penalizing” than anything else… If I can somehow “understand” this kind of reflections, I find that they are often awkwardly stated with an almost laughable effect reminding us of those “grandmasters” full of mystery who, facing the hero at the beginning of the movie, would say “he is not ready” without any further explanation.
I will therefore try to discuss with you logically how to identify the right moment to learn this equalization technique and why learning it too early is likely to penalize you more than anything else. I will also start from the assumption (which is of course not mandatory) that you want to progress in your freediving practice.

What is mouthfill ?

The mouthfill is an equalization strategy. It consists of transferring a large quantity of air into your mouth at the beginning of the dive (usually between 10m and 30m) and using this air (and only this air) to equalize for the rest of the dive. This is a powerful strategy whose main advantage is to eliminate any air transfer between the lungs and the mouth after exceeding the depth corresponding to our residual volume.

Is mouthfill difficult to learn ?

Learning and mastering the mouthfill is complex, it requires the control of muscles that we are normally not consciously using, it also requires total control of what is happening in our mouth as the volume of air available is reduced, we must adapt the movements of the tongue and cheeks to continue to be able to pressurize this air while keeping the soft palate in a neutral position. I am aware that stated like that, it can seem complicated. And let’s be clear, it will probably be complicated at first. But it is not “very complicated”. In fact, if you start by practicing a few exercises, if you put all your attention during your dives the technique itself will come pretty quickly. Of course, it will always be perfectible and a total mastery will take years of practice, but learning an efficient base is not at all difficult.

Why do so many freedivers encounter problems in learning mouthfill ?

As I explained above, learning the mouthfill requires that you be able to give it your full attention during your dives. For this, your dives without mouthfill must already be complete and perfect. Duck dive, line orientation, body position, finning technique, freefall timing, freefall position, relaxation during freefall, turn… All these basic elements that make up a dive must not only be mastered but must also be done on “autopilot”, with an empty mind and without requiring any focus on your part. If you are not 100% on autopilot during your dives, you will simply not be able to concentrate fully on your mouthfill, and from “difficult to acquire”, this new technique will become “very difficult to acquire”. You then risk encountering serious blockages and lose a lot of time in your progression. Yes, there is an “order” in which to learn and this order is not just there to annoy you, it is mainly there to facilitate your progress. The mouthfill is one of those things that you should learn last and learning it too early is the number one source of difficulties generally encountered in the acquisition of the technique.

What will happen if I try to learn mouthfill too early ?

In the beginning, in addition to being complex, the mouthfill can be particularly uncomfortable. It will take time and many dives to make it really enjoyable. If you learn it too early, your lack of relaxation (potentially linked to a too perfectible technique) will add exponentially to this new sensation and your dives may become a negative experience in terms of pleasure. This negative experience will create tension and frustration which will penalize you even more for your future dives and you risk entering a potentially endless vicious circle. Learning the mouthfill too early can be like trying to learn to jump when you can hardly walk: you might not find it very funny and it might “traumatize” you more than anything else. For my part, I clearly learned the mouthfill too early in my career, I was not yet on “automatic pilot” in my dives, and learning the mouthfill turned out to be a particularly unpleasant experience that took me a long time to make acceptable and then enjoyable. During all this time, I was never really able to increase my results in a satisfactory way and it is only a change of attitude and philosophy towards apnea in general and equalization in particular that allowed me to “unblock” myself regarding this technique.

So, how deep do you have to be in Frenzel before learning mouthfill?

This is generally the way things are presented and personally, I’m not a fan of it… To partially answer this bad question, at the risk of shocking some people, my answer would be 30m. Why 30m? Because if you are neutrally buoyant at 10m, it means that you already have about 10 seconds of freefall and that you are already doing “full” dives. But as I explained, I think this is the wrong question… Indeed, more than a depth, it is your attitude and the quality of your dives in terms of relaxation that counts. In fact, if you are “stuck” at 30m and want to learn the mouthfill to be able to go deeper, then you are absolutely not ready and you should try to increase the quality of your dives and your relaxation (by being relaxed, the frenzel will easily take you to 40m). On the other hand, if you are diving in a perfectly relaxed way at 30m and want to learn the mouthfill by curiosity and extend your knowledge to favor your long term progression, then you will have no problem and it is absolutely not too early to start practicing this new technique. In the same idea, even if you are able to dive to say 45m in frenzel but that these dives are always in “challenge mode” and that you do not take full advantage of your freefall, you are still not ready to learn mouthfill in good conditions and improving the quality of your sensations must become your priority, mouthfill will come next.

Why learning mouthfill then ?

It is perfectly possible to dive to more than 70m without mouthfill and wanting to learn mouthfill only to increase your depth is not necessarily the best entry point to have. However, the mouthfill remains an indispensable equalization technique to master for any serious freediver. Indeed, it is the technique that (with equal relaxation and general technique) limits the risk of injury the most. Moreover, if its practice may seem unpleasant and unnatural at first, I assure you that with practice, eliminating the transfer of air between your lungs and your mouth will make your dives so much more pleasant and you will naturally be able to increase your depth in complete relaxation. And yes, in the end, a controlled and pleasant mouthfill equalization along with good training will allow you to dive deeper.

Conclusion

Relying on a depth to decide whether or not to learn mouthfill doesn’t really make sense, what matters most is that you are able to dedicate 100% of your attention to it. 30m seems to me to be a minimum because if you dive shallower, it means that you still have other skills to acquire in priority. Not following this order of acquisition of skills and learning mouthfill too early will clutter your mind during your dives and the whole of your diving will be penalized. If you have too many things to think about, you won’t be able to do any of them properly. On the other hand, if you learn the mouthfill at the right time and in the right conditions, you will limit the risks of stagnation and will keep the pleasure in the practice of your favorite sport.

The article When is the right time to learn mouthfill? appeared first on Gaspard Freediving.

Introduction

Whilst talking with some instructor friends I recently realized that even on this type of « shallow » dives we do not always use the same equalization technique:

On a personal basis (I’m not the only one, I assure you) I just repeat in the Frenzel a sequence of « equalization, release, equalization, release… ». (I will come back later on what that means exactly). I do not think about the air in my mouth, it comes naturally, all by itself. Others add a step to this sequence, «reload» the air in their mouth regularly (so that they can make a few equalizations or just one), and start again once this air is gone.

In discussing this difference with equalization specialists I was told that « my » version was theoretically impossible and that I simply should not be aware of bringing air back into my mouth. The two reasons I was given for this (by different people) were as follows:

1st reason: « Air has a natural tendency to come to the surface, so upside down it’s impossible for it to go down into the mouth. »

2nd reason: « The air naturally goes where there is the least pressure (diffusion principle) and the mouth being deeper than the lungs (upside down), it naturally goes in the direction mouth => lungs » (with the idea that the pressure is created first at the lowest point).

Proponents of one (or both) of these arguments therefore suggest that « my » version is theoretically only possible by diving feet first, otherwise there must be an « action » to transfer air.

Let’s take a closer look at these two reasons…

1st reason: As we saw in a previous article, the natural behaviour of air is to occupy all the space available. It is not because we are under water that the air in our body « floats », there is no fluid to make this air ‘float up’ in our lungs. On the other hand, air has mass, and in the presence of gravity, even when it is floating up in the water column, an air bubble continues to exert pressure (an extremely small one) downward ; It is only rising to the surface because Archimedes’ thrust is greater than this force. In other words, when you are « losing » in arm wrestling, your force is always present in the opposite direction of the movement you are observing: it is the same for everything you can see floating, including the air. This argument is therefore not at all admissible. I understand that it is counter-intuitive, but please take the time to think about it : air is not « pulling » you up, it’s water that is PUSHING you up. This video explains it better than i ever could

2nd reason: Now it gets interesting … This time the logic is good and I agree 100% with the idea that the pressure difference between 2 spaces is the only thing to look at to understand the natural direction of the air! However, although good, this logic is unfortunately misused here and forgets a crucial element …

A small (easy) trick question: if I dive with my closed metal flask full of air to a depth of 5m, what will be the air pressure inside? 0.5bar? 1bar ? 1.5bar ? 2bar ?

If you answered 1.5bar, you have fallen into the trap.

It is the decrease in volume that generates the pressure…

A metal flask is a very difficult object to compress and 0.5bar extra (down to 5m) of external pressure will not be enough to deform it: and without compression (without volume decrease) there is no pressure increase! The pressure inside our flask has not changed; it is still at 1bar, as it would be on the surface!

If you are a maths addict (category to which I do not belong):
P (pressure) = K (quantity) / V (volume)

Our metal flask is closed so the quantity of air did not move, and because of its elasticity (very very low) the Volume did not move either… Therefore, the pressure remains the same!

« But the human body is flexible » you may say!

Well, it depends… Not all areas have the same flexibility, sinuses for example are not at all flexible where the lungs are flexible as long as the diaphragm can move up (bloodshift also plays its role in the propensity to compress the air). Anyway, to understand in which direction the air goes it is not so much a question of knowing if an area is flexible or not, but more importantly if it is MORE flexible than the area to which it is connected or not… In other words, imagine our metal flask at the end of which we attach a plastic bottle: whether I dive with my assembly in one direction or the other, the air inside this space will always go from the plastic bottle to the flask. Indeed, the air in the plastic bottle will increase in pressure due to the compression of the plastic bottle and will therefore move towards the flask whose air would otherwise have remained at surface pressure (the pressure naturally balances in the same volume).

Here the example is extreme on the differences in rigidity (metal Vs plastic bottle) but the principle will be the same regardless of the materials used: what matters is to know which will first transmit the external pressure to compress the air, and then the air will travel naturally in the direction « high pressure => low pressure » until equilibrium. To be a little more precise, we can easily add as a parameter the additional external pressure of the deepest part: if we consider a gap of 50cm (the deepest part would be 50cm « lower » than the shallowest part), this means an additional pressure of 0.05 Bars (0.05kg per cm2). In summary, if you have a zone A connected to a zone B that would be 50cm deeper (the whole forming the same volume), to understand in which direction the air will « naturally » go as our volume goes down in depth, we must solve the following equation:

RIGIDITY A – (RIGIDITY B – 0.05kg/cm2)

-If you get a positive result, this means that by combining its properties with the excess external pressure, zone B transmit the pressure first and therefore the air goes in the direction B => A (which would be the case for example if A and B had exactly the same properties).

-If you get a negative result, it means that despite the excess external pressure, zone B will transmit the pressure AFTER zone A and therefore the air goes in the direction A => B.

-Finally, if you get 0, it means that the 2 zones compress at the same rate and that the air does not need to move according to the principle of diffusion between the 2 zones.

I’m sure there are much more elegant ways of presenting things and if someone has the background to do so, he is more than welcomed. However, I think the idea behind it is quite simple and I leave it to you to make it your own.

Coming back to the human body, I do not have any precise and « official » scientific data on the subject but I will bet (which seems quite reasonable to me) that the belly (and the propensity of the diaphragm to rise) has the capacity to be more flexible than the oral cavity (protected by our jaw and larynx). I think that this flexibility gap is potentially large enough to absorb the 0.05Kg/cm2 of extra pressure on the oral cavity. Moreover, this demonstration does not take into account the bloodshift which contributes to decrease the volume of the lungs and thus to increase the pressure (there is no equivalent mechanism in the oral cavity) which again favours the diffusion of air towards the mouth.

So as long as the lungs first transmit the external pressure the natural direction of the air is to travel in the direction « Lungs => Mouth », even head down.

The 2 stages of the Frenzel: equalization and general release.

Since you started reading this article, how have you been breathing? It’s a good bet that you are breathing through your nose. This means that by default when you are relaxed, your soft palate and glottis are open, it’s good news you’ll see! Moreover, the equalization consisting in a contraction of the tongue/larynx to decrease the air volume of the mouth, allows us to affirm without too much of a problem that when our mouth is « relaxed », it has a greater volume of air (still speaking « basic » equalization without mouthfill !).

After each equalization, there is an increase in volume when you release the pressure (the tongue is relaxed again) but with a smaller amount of air than before (this air now being in your ears).

An increase in volume combined with decrease in quantity => decrease in pressure in the oral cavity.

Because of this decrease in pressure the air will travel by itself into the mouth if the glottis relaxed and you will be able to repeat the operation.

In addition to the « natural » direction of the air going towards the mouth the post-equalization release creates a reduction in pressure accentuating the phenomenon!

If you are an equalization nerd, it is the exact same mechanism of a reverse pack (decreasing pressure in the oral cavity). Just done in a « natural » way.

Equalization issues…

« Well, that’s all well and good, but why am I out of air in my mouth at 5m/10m/15m/20m/25m/30m while I know I can equalize in Frenzel? »

Well I don’t know how to answer this question directly, there are several possibilities, let’s explore them together:

1. You have two separate volumes instead of one. If your glottis is tense and therefore closed and tight it means that you create a strong separation between the volume of your mouth and the volume of your lungs. The diffusion cannot therefore take place and it is normal that the air does not recharge itself. The glottis only needs to be closed during the equalization action, keeping it relaxed the rest of the time you will allow the air to flow naturally to your mouth. Solution: dive more relaxed! Don’t be « afraid » to breathe out underwater, if you have your mouth closed it won’t happen, especially at depth. To persuade you, observe how you need very little energy to hold your breath: you can thus have fun doing short (20 seconds will be enough) static breath holds in neutral lungs (FRC) while using the absolute minimum of tension to « hold » the air. You will see that it still works with very little amount of tension !

2. You « refuse » the pressure: remember, the key point is the difference in elasticity between two spaces. The trick is that this difference is not « constant and guaranteed » as it evolves as you go down (full lungs compress much more easily than empty lungs) and with your general level of relaxation; if you have tension in your abdominal area, this will decrease the elasticity of the space that is supposed to generate the pressure. Less elasticity -> less pressure generated -> less pressure difference with the mouth -> less diffusion -> less air naturally in the mouth! Solution: Dive more relaxed! Forget your stiffness: only your legs have to work (in constant weight), the rest of your body (especially your belly) has no reason to be mobilized and can behave in a neutral way as if you were on a « walk ». You can also probably work on your freefall position and make sure you are « slouched » when you do it; imagine the walking position of an old man with his knees bent and his upper body curled forward.

3. You don’t relax your mouth/tongue enough after an equalization: for X reason, once your Frenzel equalization is done you don’t (or not enough) relax your tongue. So even with a relaxed glottis and belly, the space of your mouth remains considerably reduced (potentially reduced to its minimum even) so the air has nowhere to go and it’s normal that you can’t continue to equalize. Solution: dive more relaxed! What position is your tongue in right now? It is possible that « by default » it is already contracted and stuck to your palate. If this is the case, take the time several times a day to relax your entire oral cavity (jaw, tongue, larynx, and glottis): then become aware of the sensation. During your next sessions, pay attention to the reproduction of this release of tensions after each equalization.

If we want to extend the question to deeper dives: up to 45m let’s say but there is absolutely no « rule » behind this number:

4. Lack of flexibility: yes, another term for elasticity! Your diaphragm exercises and intercostal muscle stretches will have a direct impact on the propensity of the air in your lungs to compress! Being more flexible will directly improve your equalization as the air pressure in your lungs will be able to continue to increase more easily and for longer periods of time.

5. Depth adaptation / bloodshift. If we assume that a person who is trained has a « better » bloodshift than someone who is less experienced, then in addition to the elements already mentioned, physiological depth adaptation also has a role to play in equalization. The bloodshift also contributes to compressing the air in the lungs and thus increasing the pressure in the lungs: be patient and give your body time to create the necessary adaptations to what you are asking of it.

For those who would like to read some pertinent discussions around this article, you can check the post on the freediving science Facebook page

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