Freediving to 50 Meters: Mouthfill, CO₂ Tolerance, and the System Behind a Clean 50m Dive
- Anthony Feoutis
- 17 hours ago
- 11 min read
AIDA & Molchanovs Instructor Trainer
He is the founder of The Depth Collector and VD Freediving Taiwan. With over a decade of experience, he focuses on solving real-world freediving problems, from equalization to depth adaptation, using practical, field-tested methods.
Before You Read This
This is the third step in the series.
If you haven’t read Freediving to 30 Meters and Freediving to 40 Meters yet, start there first.
My 40 meters were solid, and I had finally started learning and practicing mouthfill.
My progression toward 50 started smoothly. Forty-two, forty-four, forty-six… everything was moving.
Then I reached 47 meters.
And the door closed.
My equalization disappeared. My mouthfill was gone. No more air. On top of that, I started to panic on the way up.
I tried again. And again. And again. I made the stupid mistake of believing I could power through that wall.
Every failed dive made me more frustrated. Every attempt added another little layer of doubt. Then, on one dive, my nose clip got caught on the line during the turn. It came off my nose. Instead of calming down, stopping for a second, and putting it back in place, I rushed my way up, basically praying not to black out.
That dive was horrible.
Free gift from the ocean: a beautiful mental block.
So I had to reassess. I took one month out of the water. For the first two weeks, I completely let go of freediving. For the first time, I started to wonder if maybe I should do something else. That thought made me sad, so I chose to stop feeding it.
Then the urge came back.
The desire to return to the ocean.
During the last two weeks of my break, I resumed dry training and developed a new plan before getting back in the water.
I had to face my own limitations. I needed a better system, one designed specifically for me.
When Equalization Becomes Air Management
At 30 meters, equalization becomes real. You reach residual volume and discover a new feeling.
At 40 meters, equalization needs to be controlled. Small imperfections in the execution can still be tolerated.
But at 50 meters, equalization becomes air management and tension management.
And that changes the game. You cannot keep making the same mistakes anymore.
You are managing a limited amount of air above the glottis. You are protecting it. Moving it. Keeping the glottis closed. Controlling the soft palate. Staying relaxed as the chest gets compressed and the dive continues.
This article is not going to be another warning about not rushing.
We already talked about that.
This one is about building the system that allows 50 meters to happen cleanly.
And for most divers, that system begins with equalization.
More specifically, with mouthfill.
At 50 meters, equalization becomes air management and tension management.
The New Problem at 50 Meters
Freediving to 50 Meters asks more from everything.
The pressure is stronger.
The dive time is longer.
The freefall is longer.
There are more opportunities for small, stressful moments to appear.
So emotional control and body awareness matter more.
Fifty meters is where mouthfill and air management really come into play.
You need to know where the air is and how much you still have left. This means understanding exactly how to direct the air through your Eustachian tubes, how much force to apply, and how to adjust your tongue locks depending on the amount of air remaining. It is not just about pushing randomly and hoping something opens.
That is why I like to think of 50 meters as the beginning of air logistics.
But there is another layer to this.
As you dive deeper, physical tension slowly builds without you even noticing. It does not happen suddenly. It builds gradually along the way.
And that tension makes everything we just talked about more difficult.
Protecting the mouthfill becomes an art.
So, when diving to 50 meters, air management is not only about how much air you have. It is also about how much unnecessary tension you can remove while using it.
I like to set an alarm in the middle of my freefall. It reminds me to perform a quick body scan and release any tension that does not need to be there.
Why Equalization Gets Harder With Depth
Equalization gets harder with depth because every airspace in the body gets compressed.
Simple physics.
When you equalize, you compress air above the glottis and use that pressure to open the Eustachian tubes.
But as you go deeper, the air above the glottis gets smaller.
And smaller.
And smaller.
At some point, either because you cannot bring more air up or because you leak air, your equalization system reaches its limit.
Think about squeezing the last drops out of a wet sponge. At the beginning, water comes out easily. But near the end, you squeeze harder and harder for almost nothing. The system has not disappeared. It has simply reached the edge of what it can give.
Equalization has its own end range too.
It is the point where the air above the glottis has been compressed so much, or your throat, tongue, and jaw are so tense, that you can no longer create useful pressure for equalization.
This is why it starts feeling harder as you go deeper.
Often, you are simply reaching the limit of your current air-management system.
So the solution is not to force harder.
The solution is to improve your control.
That is the whole game.
The solution is not to force harder. The solution is to improve your control.
Mouthfill Is a Strategy, Not a Trick
Mouthfill is not magic.
Its purpose is simple: it gives you more usable air above the glottis once you reach a depth where bringing air back into the mouth is no longer possible.
More air means more time before that air gets compressed to the point where you cannot equalize anymore.
That is why mouthfill is so useful. Thank you very much Eric Fattah.
But mouthfill is not just “take air in the mouth and go deeper.”
That is not a strategy.
That is optimism.
A real mouthfill strategy answers better questions.
When is the best depth for you to charge?
How much air can you take?
Do you top it up? if yes, at which depth?
How often?
How do you use that air to equalize? Constant pressure, Sequential Frenzel? Hands-free, maybe?
Can you keep the glottis closed? In other words, can you prevent air from leaking back into the lungs?
Can you control the soft palate?
Can you relax after the charge and avoid building tension during the dive?
Can you keep equalizing during freefall without being distracted by the depth, the pressure, the silence, your emotions, and whatever little drama your brain wants to create today?
That is mouthfill.
Not one movement.
A whole strategy.
And for 50 meters, you do not need a mouthfill good enough for 100 meters.
This is important.
Some divers get stuck because they think they need to master extreme drills before they are allowed to progress. But the solution to a simple problem is never a complicated answer.
If your goal is 50 meters, you need a mouthfill strategy that works for 50 meters.
That is enough for now.
Then, richer from that success and experience, you can design the next strategy to dive deeper.
Mouthfill is not one movement. It is a whole strategy.
Train the Mouthfill Shallow
Dry first.
On land, you can work on the pieces without pressure, without depth, without stress.
You can train:
Glottis control
Soft palate control
Tongue position
Cheek control
Reverse packs
Small charges, big charges, and stronger charges
Holding the fill without leaking
Relaxing after the charge
Then bring it to the water.
Start shallow.
Very shallow.
Take your mouthfill at the surface, then dive to 10 meters. That can already teach you a lot if you know what you are training.
Then 15.
Then 20.
Then 25.
Then 30.
Learn to manage the fill. Learn to move the tongue. Learn to use the right amount of pressure to open the tubes.
Too much pressure, and you may swallow the air.
Too little pressure, and you will fail to equalize.
On easy 20 to 30-meter dives, you can also practice taking the fill, topping it up, protecting it, and staying relaxed while still having enough mental space to observe what is happening.
That mental space is important.
You cannot learn well when the dive is already eating your attention.
FRC or RV-style exercises can also help. They are tools for simulating compression and training equalization at smaller lung volumes.
Use them intelligently.
The point is to learn how to charge, protect, move, and use the air efficiently.
Build Dive-Time Confidence and CO₂ Tolerance
At 50 meters, dive time starts to matter more.
The dive is longer. The descent is longer. The ascent is longer. You spend more time managing equalization, pressure, movement, and your own little internal cinema.
Depending on the discipline and your speed, a 50-meter dive can easily move toward 1:40, 1:50, or close to 2 minutes.
That time should not surprise your body.
The ocean should not be the first place where you discover what that duration feels like.
This is where pool work becomes useful.
I wrote a full article about this here:
This is exactly where that work becomes useful. You want the right intensity: enough CO₂ exposure to delay contractions, enough technique work to keep building muscle and endurance, and enough control to keep the session building confidence rather than fatigue.
The goal is to make the expected dive time feel normal.
You want CO₂ training that delays contractions, not training that teaches you to suffer through them.
Ideally, you should not experience contractions on the way down. If you do, it usually means your CO₂ tolerance is not yet ready for the task.
Once contractions arrive, they start interfering with everything. The diaphragm moves more. The throat gets tighter. The mouthfill becomes harder to protect. Tension builds up. Relaxation drops.
This is why CO₂ tolerance is not just about “handling the urge to breathe.” At this depth, it becomes part of your equalization strategy.
At 50 meters, CO₂ tolerance becomes part of your equalization strategy.
Train the Way Back Up
Freedivers love talking about the way down, but much less about the way back up.
At 50 meters, the ascent must be incorporated into the training plan. You cannot avoid specific training anymore.
If your legs die, if your arms get heavy in FIM or CNF, the dive becomes expensive.
And when the dive becomes physically expensive, it becomes mentally expensive too.
That is when the mind starts asking questions. I am sure you know the ones I am talking about.
How far is the surface?
Why are my legs made of soup?
Am I going to black out? Shit, no. Do not black out.
Or the worst one of all:
Why the fuck am I doing this to myself?
The problem is simple: the harder your body works, the more oxygen it consumes. If your ascent technique is inefficient, if your muscles are not prepared, or if every kick feels like a negotiation with your quadriceps, your oxygen consumption becomes way too high.
So yes, we must train the way back up.
That work happens in the gym, in the pool, and in discipline-specific training. It is about strength, coordination, muscle endurance, and technique under fatigue.
This does not mean you need to become a gym monster.
It means your body should be prepared for the work you are asking it to do.
I wrote a full article about this here:
I also cover this in more depth in The Science of Strength for Freediving.
Yes, strength matters.
Cardio matters.
Specific endurance matters.
Technique under fatigue matters.
At some point, we need to stop pretending that freediving is only about relaxation. At that depth, the ascent is no longer powered by positive thinking. It is powered by the muscles, coordination, and endurance you trained before the dive.
Relaxation still matters, of course.
But without the body to support it, you are in for a difficult ride.
If you dive bifins, train efficient kicking and the muscles that support it.
If you dive monofin, train the body wave and power without tension.
If you dive FIM, train pulling endurance and rhythm.
If you dive CNF, well, first of all, respect. Second, you already know you chose the spicy path.
Keep your ascent clean: That is real fitness for freediving.
At that depth, the ascent is no longer powered by positive thinking.
How I Would Structure a 50-Meter Training Cycle
This is where the system comes together.
For a 50-meter training cycle, I would not spend most of the time trying to dive to 50. I made that mistake, and that is not real training.
That is shopping for a number.
So when I came back from my break, I organized the work roughly like this:
70% skill dives between 20 and 35 meters.
This is where you train mouthfill setup, top-ups, glottis control, soft palate control, freefall awareness, relaxation, and clean technique. The depth is easy enough that your brain can still learn and experiment with different strategies.
20% adaptation and pool work.
This includes pool sessions for dive-time confidence, CO₂ tolerance, and pressure adaptation through FRC or appropriate exhale work. I also did diaphragm and ribcage mobility three times per week, including breathing-resistance training, alongside physical conditioning for the ascent.
10% depth testing.
This is where you check whether the system works deeper: 40, 42, 44, 46, maybe 48.
Before adding two meters to the line, use short hangs of 5 and 10 seconds to confirm that the current depth is truly under control. I explain this progression concept in more detail in the article on freediving to 40 meters. [Read the 40-meter article here]
Then go to 50, when the system is ready.
Not every session needs to be a breakthrough.
You progress only when the system is clean.
The 50-Meter Mouthfill Checklist
Before seriously attempting training for 50 meters, check the mouthfill system.
Can you charge your mouthfill without tension? YES / NO
Can you relax after the charge? YES / NO
Can you keep the glottis closed all the way down? YES / NO
Can you control the soft palate? YES / NO
Can you top up if that is part of your strategy? YES / NO
Can you equalize without leaking air back into the lungs? YES / NO
Can you release physical tension when it appears? YES / NO
Can you manage the fill while still staying aware of the whole dive? YES / NO
Train Deeper With The Depth Collector
If you want to go deeper into this kind of progression, I explore equalization, CO₂ tolerance, dry training, physical preparation, recovery, and long-term adaptation in much more detail inside The Depth Collector series.
This article is one part of the system. The books are where I organize the full training philosophy: how to build depth step by step, without turning every dive into a stupid little war against yourself.
Final Thoughts: Freediving to 50 Meters
As usual, I had to earn that depth.
I started doing serious pool training. I trained my body. I worked hard on my diaphragm and breathing-muscle flexibility. I also improved my CO₂ tolerance, which I have to admit was one of the things holding me back.
I remember setting the line to 52 meters.
Not 50.
Fifty-two.
I did not want to risk seeing 49.9 on my computer, ahaha. And this time, I was very careful with my nose clip during the turn.
I did the dive in FIM in 1 minute and 47 seconds. When I came up, all my friends were around the buoys, cheering for me. They had stopped their own training while I was underwater and were waiting for me at the surface.
That is a great memory.
At some point in our underwater journey, we all hit a plateau. A wall that seems unbreakable.
And I think there are two kinds of freedivers.
There are those who do not want to put in the hard work to break that wall because, up to that point, everything came easily to them.
And there are the others.
The ones who understand that freediving is a process. Different for everybody. Not always linear. Not always comfortable. Sometimes you need to step back, think, rebuild the system, and come back stronger.
I know which category I belong to.
What about you?
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