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Exhale (FRC) Adaptation

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.
Yeah, sure why not. I asked for permission to partake in the constant-ballast (fins) world champs in France this year, considering that I could make the cut of 61m. Unfortunately, the organisers were insistant that I'd have to wear fins as this was the law. Personally, I couldn't see the logic.

This meant that I'd have to organize an individual attempt which I believe to be an unnecessary waste of money, time and, considering the previous fiascos of the past involving other athletes it put it strictly out of the question.

Moreover, it became apparent that since the cut-off for Hct is 52% for males, so I'm told, I'd be wrongly accused of blood-doping!

That being the case its clear that its now far more productive for me to do these dives as part of scientific experiment for my postgrad.

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Dear Sebastien Murat
First of all thank you very much for your kind reply.I will be very glad if you can mail the references to me when you return home.
I will make short field study about reaching 12 coursiers,if not I will look to other possibilities.
Thank you all for the very nice tread here!
Just a small practical question from me,
How do I know I've got the Functional Residual Capacity right?
It appears for some tough to find the right exhale.

For instance, when I breath out I can follow the following steps:
1 relaxing the chest (goes down due to the gravity), 2 relax my diafragm, 3 force my chest to collapse more, 4 force my diafragm upwards.

Can someone tell me how to do it right?


I think it's phase two by your description. That's atleast how I do it whenever I do it.
yeah, i think of FRC as when you let out air to where your chest and diaphram are completely relaxed
I give it a try yesterday... short breath up, passive exhale, 30 sec hold, and 30 sec dynamic. The last 10 sec of the breath hold where promising a difficult dynamic, but strange enough it was much easier than expected.

Later I try exale+ light inverse packing, 10 sec hold, and 32m dynamic (length of the pool)... to find out that my diaphragm need some serious stretching if I want to keep going deeper using a mono. Must mention my first contraction doing dynamics: strong and painful.

It is surprising how easy is the dynamic phase and how clean is the exit. Still, I feel like I need more recuperation in between the dives than on full lungs.

The buoyancy changes more than expected and I keep hitting the pool floor, specially on forced exhales. I find myself swimming with my arms on the sides to finish some of the dives... In general I was swimming at 1m/s instead my normal 1.2-1.3m/s: something to work on!

It seems like I get colder on the water doing exhale dives.

Definitely something to explore... sadly we didn't make the numbers to flight Seb down to NZ for a much anticipated course :waterwork. I feel a bit out of boundaries and it will be nice to get some "in the water" advice!
My humble suggestion:
No breathe-up, break-point breath-hold followed by dynamic. It is a fundamental mistake to reverse/inverse-pack and have a pre-conceived time in mind.

Warm-up => aerobic => very quick recovery which is faster than on 'inhale'
Serial diving = no muscle fatigue

No warm-up => aerobic (vital organs) + anaerobic (non-vital organs + locomotors) => very long recoveries which are slower than on 'inhales'
Max performances must = muscle failure


I attended a course Sebastian recently ran in Perth. I mainly dive to spear. While I have some reservations, like Pablo, I have noticed benefits by FRC diving under suitable conditions.

I personally prefer to be conscious of the time, and increase the time gradually. I'd be interested to know Sebastian why you consider having a time in mind is a fundamental mistake?

Brett started off initially by saying his depth was limited by lung squeeze. Are there signs to watch out for that signals when lung squeeze is excessive (beside coughing up blood)?
Sebastien,Thank you for your kind reply about the exhale adaptation references,I have gotthem
Hi Derek,

Having a time in mind, like having a distance/depth to reach, is a "fundamental" mistake because it throws the static to dynamic phase out of balance. A preoccupation with time means that divers learn very little about sensing their way through the dive, a much more reliable indicator. More often than not, the experienced diver prolongs the static phase at the expense of the dynamic phase, by overriding contractions. This means that he/she overreaches, possibly beyond the 'point of of no return'. There are many ways to fool the body into thinking that the urge to breathe has not been reached before swimming off, e.g., counting, looking at the watch, swallowing, etc.

On the other hand, with novices there is a tendency to cut short the static phase (mental overload) and aim to swim far, e.g., "must get to the wall" or a constant looking for the wall. If suffient time hasn't elapsed blood flow to the muscles will be kept patent resulting in a rapid, out of control desaturation of O2 and blackout, that is, if the diver continues beyond the sensation to surface.

When that youg fella from your club had a BO he did made two fundamental mistakes: he went through several, possibly many, contractions in the static phase, indicated by the prolonged duration compared to everyone else, and secondly, looking for the wall as a goal to reach on numerous occasions. It is possible that he could of been excessively warm, which would of delayed the contractions to much later but I think it is unlikely considering his low body fat and the quite cool temperature of the water (~27 degrees + shade).

Signs of possible lung squeeze: mild pressure on the chest....quite noticeable.
Most bleeds involve reverse packing under already elevated -ve chest pressures. All this does is put excessive pulling pressure on both sides of the closed glottis.

Some preliminary results on experiments we've been carrying out here on the east coast: exhale dives resulted in significantly more elevated end-dive O2 tensions than with inhale dives.
Though the results should be taken with some caution, as they were obtained from my particular case, they do indicate the potential merit of the strategy considering the observations many of us have noticed in the clinics, i.e., that most divers achieved similar results with inhale and exhale after just two days parctice. Of course, I'm not referring to doing static breath-holds, but actual dives.

Although today's experience with 56'F water reminded me how much I doubt I will be diving until it warms up, this thread remiinds me of some questions that I had back toward the end of last years diving season. When I first tried exhale diving, I experienced a rapid, semi-uncontrolled descent which resulted in a feeling of pressure in my chest which persisted until I reached the surface and started breathing again. The whole experience intrigued me as I did not cough blood or plasma, and was confused about what I had experienced. I started practicing exhale dives regularly with generally thereafter feelings of pressure which incresed with depth, and eventually running out of air and having to surface. It seems like if the pressure kept increasing eventually something would just break, but I don't really know.

So now I still don't understand. I read here that provided the genetic capacity is there, over a long enough period of time the feeling of pressure will go away entirely with the development of blood shift adaptation and capaillary flexibility. Does that mean that I should keep practicing minimizing the depth to the depth at which the feeling of pressure starts, and over time that depth will increase? Does it mean that if I keep going I really will get a lung squeeze? There needs to be a manual for this sort of thing. I feel simultaneously scared to take it too far, and intolerant of my reservation.

I did not notice any increases in the depth of of pressure sensation onset inspite of weekly devotion last year. Maybe I wasn't 'stretching' hard enough.

Some possible suggestions from my own experiences:

Practice, practice and then more practice. When I first started training for exhales I was typically doing upto 20 drops to depths of 15-20m every other day. Sometimes I had 2 days off and noticed better tolerance. I kep this up for as long as a year. It was easy then as I worked on a liveaboard and could shoot through for some practice in the late afternoon after work.

It will get easier, if you remember that intrathoracic pressure changes are largely non-linear with depth (Boyle's Law) so that great distension and engorgement is required in the first 10-30m after which volume changes are relatively small with increasing depth. If you were to put it in perspective, a 30m exhale dive, for example, is equivalent to an 80m inhale dive, pressure wise. Therefore, a 30m exhale need not be an extreme dive and should be quite manageable with practice. Even Micki, my partner, was puling off 10m exhale after just 4 days parctice and her friend was doing 15m with no previous experience or practice and with apparently no discomfort.

Some factors to consider: keep a cold periphery for a better blood shift(diver's often overlook this pre-requisite); don't do an excessive number of forced equalizations as this will prevent venous return and impede a good blood shift; don't drink too much before diving and don't take aspirin, as all of these will predispose to squeezes.

Thanks for your responses Sebastien.

sebastien murat said:
Hi Derek,

Signs of possible lung squeeze: mild pressure on the chest....quite noticeable.
Most bleeds involve reverse packing under already elevated -ve chest pressures. All this does is put excessive pulling pressure on both sides of the closed glottis.

I understand you are saying that you stop your descent as you as you feel lung squeeze. Is that correct?

In the past I have experienced lung squeeze while inhale diving. I found relaxing relieved the feeling of squeeze, rather than trying to fight it by pushing out with the lungs. Is this other peoples experience?

sebastien murat said:
Some preliminary results on experiments we've been carrying out here on the east coast: exhale dives resulted in significantly more elevated end-dive O2 tensions than with inhale dives.

What do you mean by 'more elevated end-dive tensions'? Are you saying there was more oxygen in the blood? Can you give more detail on how the tests were carried out?
I go by a simple axiom when it comes to pressure tolerance: if it hurts stop as it wont get any better. I see a lot of divers who simply "hammer" their diving with packing, reverse packing, forceful equalization, bleeds and pro-active descents. In my experience, its all unnecessary and counterproductive. A softer, effortless approach to depth progression is much more effective. This may sometimes be difficult for terrestrially adapted divers whose frame of mind is usually one of aiming to increase effort output to new highs. Optimal freediving, on the other hand, should strives for physical inactivity.

Your right when you say relaxation helps. Physiologically, if you tense (isometrically), perhaps because of incorrect equalization, you reduce the flow of blood returning to the lungs, which is needed to tolerate mounting pressure.

In regards to the end-dive O2 tensions I'm referring to alveolar oxygen and carbon dioxie concentratrions. The tests were done in a pool just the other day whilst trialing some exhaled gas collection gear, in preparation of some ocean diving experiments we're due to undertake next month on the GBR. Basically, the dives involved simulating the various phases & durations of vertical dives with both inhale vs. exhale dives. Moreover, one dive was done after hyperventilation and 'exhaling' with interesting but highly controversial results. If you can wait another month or so, at least till we've sampled a few divers, I'll make the data and our interpretations more readily available.

I like your approach to assessing pressure tolerance. Thanks for taking the time out to give a detailed response.

The tests sound interesting. I take it you strap a tank onto someone and when they exhale after a dive, it measures the O2/CO2 concentrations. Look forward to hearing the results in due course.
Hi Seb,

Can you explain what you mean when you say that drinking too much water before diving can lead to lung squeeze? I would have thought that in general, a hydrated person would be better off that a dehydrated one. Or is that not what you mean?


Vancouver, BC
My problem thus far is that the sensation of pressure doesn't hurt per se. It's more that it is not something I experience in everyday life. I can simulate the feeling by reverse packing, or via the yoga exercise Uddiyana Bandha, which I practice nearly anytime I realize that my stomach is empty enough for it. Perhaps I was not monitoring the data closely enough last year to see any changes. This year will be different. I have a dive logger, and will use it diligently. The real conundrum is that yes, due to the nature of the relationship between pressure and depth, depth acheivment will increase exponentialy , which is to say slower than linarly at first, and 2) the deeper you are the faster you sink, making this an exercise to be carried out experimentally with the assistance of a line.
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