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Exhale Diving

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.
I do a lot of restricted breathing prep before my dynamic on FRC to increase venous return and thus develop a localised 'blood pool'.

Ben, could you explain how you do this.
"On FRV, I start to desaturate earlier (about half way) but desaturate slowly. I think my heart rate is higher on full lung dynamics - this may account for the above. " - Ben

Hi guys,

What Wal and I have found from doing dry tests with my pulse oximeter is that the desaturation curves for us for inhale/FRC/full exhale with reverse packing are all very similar. The more forceful the exhale the earlier the drop or entry point on the curve begins. I'm surprised that Ben finds the desaturation in slower on FRC! Ben have you tested this with a pulse oximeter and if so I'd really like to see the data from an inhale and FRC effort on a stairmaster or static?


Seals exhale on the deep dives because the seals in the past that did not exhale got bent, died, and didn't get to breed more of the same 'stupid' seals. Darwin is responsible

I nearly pissed myself with your bent Seals theory, thanks for that. I was just picturing a bunch of seals looking up PADI dive tables.... :duh :D :D :D

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Some comments on FRC dives:

- Using the mouthfill on FRC you can hit 70m, with the mouthfill + mouth water suck you can hit about 100m. To go beyond that requires a no-mask dive and sinus flooding.

- On FRC dives, the energy on the descent is decreased dramatically, and the energy on the ascent is about the same. This means that you burn far fewer calories on each dive. This explains the shorter recovery time which most people notice. The recovery time on submaximal FRC dives is ridiculously short, especially since there is very little CO2 to blow off.

- Although in my opinion the 'one-dive-max' depth is slightly reduced on FRC, the advantages are numerous, which include:
1. Far greater relaxation during the breathe-up and descent
2. No worry about descent technique, since there is none (just sinking)
3. Dramatically reduced chance of getting bent (DCS) on max depth dives
4. Dramatically reduced chance of DCS on repetitive deep dives
5. Dramatically reduced recovery time between dives, allowing for a greater accumulated bottom time while diving for fun
6. Increased ability to train for deep dives, due to the no-DCS effect (i.e. you can do multiple max depth dives in a row in one training session, for greater specificity of training)
7. Dramatically reduced N2 and CO2 narcosis on deep dives
8. No risk of O2 toxicity on deep dives

Because you don't take a big deep breath before you go down, you don't push blood away from the lungs. This can reduce the risk of a 'shock-squeeze' in the first few meters, although the risk of a deep squeeze is greater.

There are two critical point to remember on FRC dives:
1. The breathe-up must be non-existant. You cannot do any deep breathing before hand, because this blows off CO2. Because of the physiology of FRC dives, you must start the dive with a much higher CO2 level.
2. You must progress gradually to allow the chest a chance to adapt to the increased squeeze.

In some cases, there is no choice but to do FRC. For example, in Vancouver there is an area at Whytecliff park where there are gigantic cloud sponges on a wall, in the 53-65m range. I would like to do repetitive dives on the sponges, which is not possible with max inhale dives, because I would get bent after 2-3 dives. I got to the point where I could do 53-55m recreational dives on this wall, on a full pack in a 5mm suit with 14lbs of lead. But, I can only safely do ONE dive (for DCS reasons)! That SUCKS! The only possibility to enjoy this area of marine life while freediving is to do it on FRC. That takes training and time (for adaptations), and also a thinner wetsuit (or no wetsuit). With no wetsuit, even in the cold local water, I can still do 3 dives before I have to get out---that still beats the ONE dive I am allowed to do to 50m+ on an inhale with the suit....
Walrus et al.,

To set the record straight:
'Exhale' diving is not an end in itself, it is a means to an end....a means to harmony with your element. To use it correctly requires knowing where and when to use it. It was never meant to be used as a simple static exercise of endurance.

I have never suggested or implied that it can be used in 'shallow water', e.g., a pool, and result in 100% avoidance of BOs. Shallow in this case being both relative to the individual but absolute in terms of the point of bronchiolel airway collapse. Indeed, it's central place is not for use in a pool but for depth diving where the benefits of the effects of pressure on the airways can be harnessed. It can, however, be employed to a lesser efficiency for pool training in preparation for ocean diving.
To use 'exhale' diving correctly implies doing a static-dynamic combined and in that sequence.

I have never suggested that it could replace inhale diving for No-limits. In my experience, No limits is not 'free-diving' and we are ill-designed for it. The No-limit dives you often speak of from my time in PNG were done on inhale + buccal pumping. But the object of the game then was to subjectively explore the issue of narcosis and gas-exchange at greath depth, by potentiating it.
Nevertheless, 'exhales' can be used in No-limits, to over 100m; I know this because I've done it. To do this requires an initimate understanding of equalization techniques and appropriate incorporation into a dive. It is also innacurate to suggest that exhale diving cannot be used for spearing. From first-hand experience, I can also confirm that it is possible to equalize a mask (Cressi Super Occhio) to 40m depths

Furthermore, not all seals, whales and porpoises employ exhale diving. The issue here is one of extremes: speed (shallow) vs. endurance (depth). There is also no reasonable point in exhaling or inhaling for endurance when one has relatively easy surface access to revitalize O2 and vent CO2 stores.

It is also not true that the exhale strategy necessitates reaching a passive descent from the onset., althought this is advantageous and desirable because of metabolic particularities in the sequencing od activity and inactivity.

Lastly, to give you an impression as to the scope of possibilities regarding this technique (modesty aside):
Pool:1'45" static to <FRC + 100m (1'50") no fins
Pool:1'45" static to <FRC + 75m (1'50") no fins towing a kick-board underwater
Pool: 150m =FRC; monofin dynamic
Depth: 72m = FRC no fins


For better future relations, I would also ask you to be more considerate in regards mis-quoting, mis-interpreting and then mis-representing me based upon rampant speculation and imagination from bits and pieces you've heard or read about in the media. That includes pbs.
Um.... :confused:
Seb, what rampant speculation and imagination were you referring to ?
If you look at my post I only mentioned your name once and I was trying to correct Brett's impression that you did your no-limits dive on exhale, which is correct ?
Likewise from his post he talks specifically about wanting to do more exhale diving to reduce the risk of blackout and Samba.

One of the reasons I am interested in shifting is basically to avoid the problems of blackouts and samba's (I have had two of these). I guess considering that 99% of these problems occur in the last 5 metres largely the result of expanding lungs, Is it possible that by exhaling one can aleviate this problem by avoiding the expansion.
What are your thoughts?

The reason this makes me and many other divers that I know very nervous is that in my experience with every single diver I know - exhale dives do the exact opposite. Granted I understand now you are talking half exhale, when most of my experience is with full exhale. Still I cannot connect the dots and see how on half exhale or FRC as you call it decreases the risk of Samba or Blackout ?
From even your own PB’s it seems that FRC reduces both Time & Distance ?
From what I understand you are the only person in the world that can dive deeper on FRC then inhale. Because it works for you, you can’t assume it will work for everyone. Why is no-one else capable of doing this, even when some people on this forum have spent quite a bit of time training FRC ?

When you talk spearfishing, people don't dive straight up&down, there is usually either breathold or swimming on the bottom. How does doing this on FRC give you increased depth or bottom time and therefore a greater safety margin ?

Seb I honestly would like to understand, I am totally confused by the whole FRC concept. All my experience and logic tells me that FRC diving would increase the chance of Blackout & Samba. Yes it makes sense to train FRC or use it to warmup for an inhale dive, I can understand that. But I'm actually talking about the FRC dive itself. Likewise I believe this is what Brett was also talking about.

Eric your point on reducing DCS does make sense to me, but you are talking pretty deep dives. ;)

Ulf - stand upright in the pool with the water level just below your lips (so your lungs are as 'deep' as possible. Then breathe in through pursed lips and breathe out without restriction. I do this for about 5 minutes, then breath normally for 1 minute (none of this is at a high breathing rate), then dive/swim.

I understand your warnings, Wal and you are right to point it out for the benfefit of the DB community. However on a more detailed level, I think comparing the two techniques for risk of BO isn't really fair. Each requires adaptation to the changing signs in your own body and being able to judge when to come up. Switching from inhale to empty but retaining your 'end point' is dangerous and a good way to BO - one of the reasons Eric mentioned the reduced ventilation before beginning an FRV dive. In the context we use 'FRV', we aren't intentionally implying that starting lung volume is the only variable here - there are several, and it requires a whole change in the way you assess your dive.

Andy - taking the above two points into account, if you change the way your breathe up, you might see a deviation in the desaturation rate. Your experiences are exactly what you would expect with a smilar breathe up and only changing the starting lung volume. Give it a go and see what happens - you may end up with same result. It would certainly be interesting to hear your results. However - I haven't tested this on an oximeter (I would like to try), I'm just going off the feelings of desaturation that I learnt a few years back (which I could have lost since then with my lack of practice!).

An interesting factoid along the 'superhuman' implications & spearfishing notes above - I have a minescule fraction of the training in this technique that Seb has and I rarely dive deeper than 20m, but I had the chance to dive deep recently and managed several dives to 40m on FRV with my Cressi-superocchio mask....so it is certainly within the grasp of us 'mere mortals', although I doubt I'd have time to shoot anything down there.....
Switching from inhale to empty but retaining your 'end point' is dangerous and a good way to BO - one of the reasons Eric mentioned the reduced ventilation before beginning an FRV dive.

Ben, you are saying that with FRC (half exhale) diving you have to reduce both your depth and time otherwise the chance of BO or Samba is increased ?

This is exactly what I was trying to say. There is so much confusion surounding FRC diving that people actually think they can do the same or increase their depth & time with it. From reading Brett's post he seemed to think that doing the same dive on exhale would reduce his chance of Samba or Blackout. Can anyone else out there understand my concern and frustration on this subject ?

I can see why you are getting wound-up by this, Wal.

Yes - FRV diving undoubtably reduces my dive-times, BUT that doesn't bother me as I'm not really intesred in dive time, but in dive 'quality' and FRV diving certainly increases the 'quality' of my dives (although of course that is a highly subjective criterion, and something I would not have written 4 years ago!).

Yes - If you switch from normal full lung dives to FRV diving and expect to meet your PBs immediately - you are setting yourself up for some nasty accidents!

BUT - FRV diving has not been promoted as an immediate performance boost - although as Brett's comments suggest - it may have been INTERPRETED as such....which I fully agree is dangerous and concerning. Seb is aware of this problem as was demonstrated in 'diver versus doctor' thread. I think seeing a recent student of his arrive on these forums and show these slight, but significant misunderstandings might be an indicator that a bit more care may be needed in how people are introduced to FRV diving - conversely, you can describe things in perfect detail and they will still be mis-interpreted. In this case, neither of us were at the course, so we don't know how much of this is due to the course or due to Brett's interpretation. As long as Seb has explained things clearly on his course - there's not a lot more he can do!

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Originally posted by Walrus
From reading Brett's post he seemed to think that doing the same dive on exhale would reduce his chance of Samba or Blackout. Can anyone else out there understand my concern and frustration on this subject ?

Wal, I agree with you about this. There are probably good reasons for using exhale diving to avoid DCS, and as a way of training. Maybe there has been some misunderstanding about the benefits/risks of exhale.

However, I can say from personal experience and that of my diving friends that the safe time is greatly reduced on exhale.


DCS: many spearos spend hours serial diving to depths of 20-30m (not very deep) + exercise + cold + short surface intervals -> can get bend and indeed many have.

Your wrote: "From even your own PB’s it seems that FRC reduces both Time & Distance ?"
Yes and no! It reduces distance in the pool absolutely, but relatively speaking, if you consider that the static phase of the dive is really the sink phase of a deep dive then am I really going nowhere? I'm certainly not working for it as I'm letting the environment work for me. For me, 1'45", or thereabouts, is equivalent to passively sinking down to a depth of +70m. For the second phase of the dive, i.e, 75m of swimming towing a kick-board simulates (approximately) the ascent phase. I drag the board to duplicate the extra negative buoyancy. It's not perfect but it does the job better than unhidered swimming. Put it together and what do you get? Remember, simulated exhale-and-sink dives in the pool are only a means to an end, i.e., deep diving. Staright out "Dynamics" in the pool are 'unbalanced' dives as they have no turn clear-cut half-way points as gauges to safety, especially if you actively warm-up. Moreover they result in conflict or a tug-of-war between the oxygen conserving response and the oxygen consuming response. I shoulld stope here as I'm detracting here a bit from the crux of the argument.

"From what I understand you are the only person in the world that can dive deeper on FRC then inhale. Because it works for you, you can’t assume it will work for everyone. Why is no-one else capable of doing this, even when some people on this forum have spent quite a bit of time training FRC?"
Certainly, I could be a superhuman freak of nature! But not likely, as I know what I was like when I started and to some exten it would be like saying that we are comparing cats and dogs. It takes time to develop the understanding, the capacities and the ability; not unlike inhale diving I guess. You also have to ask the question are these other people that exclusively use this strategy using the correct sequence of static followed by dynamic or are they simply doing static or dynamic or even dynamic followed by static? This alone makes a world of difference in a world of specific adaptations. Moreover, are they training to +90% of max intensity every session. Do they appreciate the concept of adequate psych/physiological recovery or indeed sensitization versus habituation neurogenic training in the optimal development of such capabilities?

"How does doing this on FRC give you increased depth or bottom time and therefore a greater safety margin? "
"All my experience and logic tells me that FRC diving would increase the chance of Blackout & Samba."

An absolutely smaller lung volume results in an absolutely smaller lung volume re-expansion which necessarily implies a reduced exchange of oxygen molecules that could potentially be 'accepted' by the lungs. Or, alternatively, if a reversed oxygen gradient does not take place because of haemoglobin's very high affinity at low tensions, a view held by some experts, then we may infer that the rate of diffusion of oxygen from lungs to blood is not reduced as much as it would be on an inhale. Why? The rate of O2 diffusion between the lungs and blood is not just an artefact of a concentration gradient that might exist between them but also one of pressure difference caused by a lvolume difference. For example, a pressure difference that exists between two containers will be maintained at higher levels for longer if there is a big difference in volume between the containers. The converse would be true. This means that either more oxygen is ripped off the haemoglobin or less is bound to it.

There are three altogether different sides to the risk of blackouts when comparing inhale vs. exhale. One relates to lung compliance in respect to lung volume. Reduced lung volume, possibly because of a heightened pulmonary blood conjestion which increase lung stiffness, are less amenable to expansion ( and hence re-expansion) than large lungs.
Two: elevated intrathoracic pressures caused by lung re-expansion above and beyond FRC will reduce cardiac output by reducing venous return; more so the larger the lung volume. I would suggest this is not an insignificant effect. Indeed, one may carry more oxygen with the inhale method but it may be to no great benefit if its accessibility is restricted, e.g., cerebral blood flow is restricted because of reduced cardiac output caused by a reduced venous return.
Three: True, the hypercapnic ventilatory stimulus (85% of yoururge to breathe) is much reduced and more is placed on the hypoxic drive (the other 15%). This is not necesarily a bad thing as errors in judgement will be made if high CO2 levels are incurred, as with the inhale method taken to extremes. A reduced ventilatory drive would make the dive more tolerable/comfortable if CO2 levels were lower, as in the exhale method. But you probably say, it gives you less of a reserve for any errors in judgement. Yes, that is the case, but then again exhale diving should not be used for extreme duration dives in depths were there is easy acess to the surface or where a latent and 'trapped' oxygen-rich reserve, induced by an early bronchiole collapse is unlkiely to occur. This 'spare-air'could be formed and reside in the anatomical dead space and later be used when the lungs re-expand thus supporting and maintain consciousness for the final few metres of the ascent. Is there enough oxygen? Yes, if we consider that this dead space contains compressed oxygen and, the metabolic (aerobic) demands are likely to be low at this time (see the dive response). Will airflow from dead space to alveoli occur with simple re-expansion of the lungs. If it was simply a matter of a concentration gradient , probably not. The fact is that there is also a pressure gradient caused by a reduced respiratory quotient which has the effect of 'shrinking' the lungs with elasped time. What is the t value of this critical depth? The actual value largely depends on initial lung volume and secondly 'collapse' depth and an individual's particular physical make-up. For argument sake, let's say this is 15-20m with the exhale method and twice as much with the inhale method. Is this now consequently larger oxygen volume sufficient to maintain consciousness from twice those the exhale depths. Not likely considering that the metabolic demands are likely to be more elevated as a result of a reduced dive response with the inhale method even in hypoxia.

The question to ask then: should the exhale method be used in dives to below such depths. Some might say we could exhale to below FRC and induce a shallower collapse. True, but we also rely on some degree of lung re-expansion to access this spare-air otheriwse we may incur excessive physiologic dead space and a lack of sufficient re-expansion to open the airway and permit inflow. No doubt there is some benefit for 'shallow' diving but one should always remember that bout/serial diving as carried out by spearfishers should not exceed the aerobic dive limit fro want of an excessive surface recovery interval. The name of the game is not to overly tax oxygen stores, so that bottom time to surface intervals in a dive session are as short as possible. This means not extreme endurance dives with this, or indeed, any other method involving shallow 'diving'. Still the question remains, should I inhale or exhale? Simply put , it 's not just about how long you can dive but also how frequently you can dive so that you maximize you bottom time over an entire session,. To do this one needs to accelerate recoveries and also prevent as much as possible the excessive and deleterious metabolites that build-up with anaerobic substrate utilization. That would mean having to resort to the exhale strategy.


PS: Misrepresentation: I was referring to previous threads and not just on this forum. Please appreciate that I am not a competitive threat to you or anyone else here in oz or anywhere else for that matter. I'm not veying to be a world record holder, Australian champion or anything as the media and friends sometimes would seek to perhaps make me in order to satisfy their needs. Indeed, I have no personal interest or aspirations of that nature. I've seen too much been around too long and I'm too old. Instead, I'm simply just doing what I do naturally and if that happens to be more than the next guy whose attempting 'official' records, I'm sorry I can't help that but I certainly wont go back into the forest for fear of putting noses out of joint or take up suggestions of laying low as some 'big' names have suggested...not especially if I may have something interesting to show or say. I certainly can't help it if I happen to be the vehicle by which to demonstrate it. If there was another way it would be preferable and no doubt more comfortable.
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Originally posted by Ben Gowland
Ulf - stand upright in the pool with the water level just below your lips (so your lungs are as 'deep' as possible. Then breathe in through pursed lips and breathe out without restriction. I do this for about 5 minutes, then breath normally for 1 minute (none of this is at a high breathing rate), then dive/swim.
Ben, please tell me if I get the idea: with such an exercise you create a pulmonary errection, which by FRC theory, would cause you to have a higher venous blood O2 saturation without hyperventilating?

Are those 5 minutes also needed for venous blood oxygination? I mean, do you do it more than once per session?

Any difference between this excersize and a few warm-up negative dives in the pool? - it does sound alot safer.

Have you tried breathing through a snorkel and getting your lungs even more submerged? I wonder at what depth it becomes a too great effort to to be helpful...

I thank all of you who are invloved in this thread and other past FRC threads, it's almost as exciting as discovering freediving physiology all over again. :)

Some thoughts:
You could also do a few, but not too taxing, 'Mueller' manoeuvres (reverse Valsalva)whilst immersed to induce pulmonary conjestion which would also increase O2-diffusion.

Proper breathing for exhales (i.e., up-to-the-neck-immersion) involves inducing -ve intrathoracic pressure by active inspiration and more passive expiration. Any forceful expiration will result in an unnecessary +ve intrathoracic pressure and reduction of pulmonary blood volume. The inspirations have to be ample, i.e., deep to counteract the increased physiological dead space that comes with immersion, especially up-to-the-neck-immersion.

The exhale warm-ups are good for bout diving where you're not aiming to set endurance records for yourself. Warm-ups are however detrimental for extreme dives as they prematurely constrict the spleen which has the effect of releasing haemoglobin into the blood stream, delaying vasoconstriction; a necessary early condition for great and extreme diving results

Also I would suggest keeping the head, especially tha face out of the water. Try orientating yourself to the sun before submerging to gain the benefits of a strong and prompt brain water-cooling effect (counter-current heat exchange). A cooler brain consumes a lot less oxygen.

Seb, I didn't understand half of that. The way you talk only adds to the whole confusion of your concept of diving. If that's how you teach a freedive then no wonder someone like Brett is still confused. If your method of diving has some specific areas where it is more safe vs inhale, and others that are not, then why not just say in normal langauge. ie for static it doesn't work, for depth diving it does in case X.
Basically all what I'm reading is theory and the dives you claim to do yourself is not proof of that. I still do not see in any way how FRC diving reduces the risk of Samba or Blackout, which is what this whole thread was about in the first place. Any one I talk to or teach freediving to I will still tell them that exhale diving is less safe. That is based on my experience and not theory. Let's just agree to disagree and not waste other people's time on this forum.

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wasting time?????????

I was glad to see this thread open up to proceed with exploring the nature of exhale diving, something that has been considered, by many, to be an important part of freediving. Yes, where it is applied and the details of how this is done, are varied and controversial. However, it is here to stay, and working together to argue our understandings only helps provide a clearer picture.

Therefore, I think it is grossely inappropriate and mistaken to suggest that ANYBODY'S explanations, experiences, and theories are in any way non-productive. Just because you don't have the time, or interest, to make heads or tails from an explanation does not imply that many of us are not getting valuable information from that, and that we may be the ones to regurgitate it in a more common expression. I think it is absurd that, in prior statements, Wal implies that it may be Sebastien's fault for misinterpretations yet is not satisfied when he attempts to lay it down in the most precise form of explanation. I hope we realize that explanations in common expression are the most open to wide interpretation. You have a larger audience that might think they understand but there is no way to determine if they are correct. Whereas with a more technically specific statement, less audience can understand it, without first learning about what has been expressed, yet if they do, the expression is very precise. There is no quick solution to the problem of misinterpretation.

This thread is about "exhale diving" and I don't think anybody has deviated from that topic (except me?), so how do you make that conclusion Wal?

Wal, it seems you are implying that Sebastien's posts are strictly responses to, and for, you alone!? I don't get that at all and I do not think others do. So, please do not push away a valuable source to our questions and concerns, even if it does not come in the way you want it to, because it may be the way others want it and indirectly it will get to you, the way you want it, if you are patient or explorative yourself.

And finally it seems nobody ever wants to admit, or take notice to, how confused MANY (probably everybody in some area) are when they walk away from most freediving courses in general and yes in dangerous ways as well.
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Let me try to explain a possible way that FRC dives could reduce the risk of blackout.

Case 1: When you do an inhale static on land, your lung volume is constant. The urge to breathe grows gradually. You know where you're at. You can stop at anytime, judging from your urge to breathe (caused by high CO2 and low O2); you may have fading vision (low O2), unclear thoughts (low O2), strong contractions (high CO2), and sometimes a different, more extreme, panic like contraction (low O2 contraction). Similar feelings might occur in dynamic in the pool (still, no lung compression).

Case 2: Inhale dives. Here, the lungs compress at depth. Without some sort of aggressive ventilation at the surface, your CO2 level at the bottom would be insanely high. So, 99.99% of divers take at least a couple of deep breaths before they go down, to counter the pressure-CO2 effect. Beginners often get confused at the bottom, because the urge to breathe may be high; then, during the last part of the ascent, the urge to breathe might decrease, as the CO2 level decreases (with lung expansion). Expert divers, with higher CO2 tolerance, aren't fooled by that phenomenon. Still, who can judge their turn-around point at the bottom based on the feelings in their lungs? It is virtually impossible, because the feelings down there are so strange, and counter-intuitive, in the sense that they DO NOT follow the same progression as for static apnea on the surface, or even dynamic apnea on the surface. So, one of the big problems with inhale dives in the confusing signals your lungs give you when you are down there. This is caused by the dramatically screwed up pressures of O2 and CO2 (high O2 pressure on the bottom, high CO2 pressure on the bottom). On an inhale dive where I have stayed down too long, I will ascend the last 15m, and SUDDENLY FEEL HORRIBLE, as the hypoxia sets in and my lungs re-expand. But it is TOO LATE, I misjudged my bottom time... the vision fades... possibly a samba.

Case 3: FRC static or dynamic in the pool. Here, if you DON'T TAKE ANY DEEP BREATHS BEFORE YOU START, the urge to breathe will follow a logical progression, much like it does for an inhale static or dynamic. Very similar symptoms, they just come a bit earlier. Still, you know when to stop. People who argue that BO hits them without warning on FRC/exhale dives, it is because they are doing deep breathing before they start.

Case 4: FRC depth dives. Here, due to the fact that lung compression is negligible, the breathing stimulus during the dive follows the same pattern as it does in the pool. There are no illusions at depth. When your CO2 gets high, you feel it. When your O2 gets low, you feel it. Thus, it is possible to judge your turn around point on a dive. During the ascent, as you exert yourself, the urge to breathe progresses normally. If you stayed down too long, you'll know it long before you get anywhere close to the surface. There will be no sudden SHOCK in the last 15m as your O2 decreases. Sure, the total dive time & depth may be a bit less, but the urge to breathe (and other symptoms) were the same as on the surface, allowing for more accurate sensing of your energy store....

As an example, when I do MAX inhale dives, I still feel pretty good until the last 15m, when suddenly my vision starts fading and the contractions become huge. My thoughts fade....

When I do max FRC dives, the hypoxic feeling comes much deeper, perhaps at 25m or more. I still remember my first max effort FRC dive. As I ascended, at 25m my vision was already fading, my legs were turning to jello, my thoughts were fading. My last thought around 20m was: F***, I'm 20m down and I can't see SH**, this is going to be a MESSY BLACKOUT. I hope my buddies are ready for it....

....but I made it to the surface CLEAN!!!! I couldn't believe it. What does it say? It just demonstrates that the symptoms appear gradually, as they do in the pool.
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BUT - FRV diving has not been promoted as an immediate performance boost - although as Brett's comments suggest - it may have been INTERPRETED as such....which I fully agree is dangerous and concerning.

I didn't realise this was going to create such a stir. I must point out that I did not believe this would be an immediate performance boost, Sebastien was very clear about this he stated that it does take time to adapt and recondition the body even longer for more experienced inhale divers.

I also must point out I am just a spearo not a competitor freediving. The restriction placed on a relatively speaking novice such as myself is depth, to begin exhale diving its a very slow process adapting to the feeling in the chest when you add depth, this in itself although restrictive helps provide a safer learning platform for a slow progression.

I was just asking for other peoples opinion and/or experiences with this style of diving, as two of my mates have blacked out recently (luckily pulled up) and a few samba's, I am looking at ways to reduce the risk and I am prepared to slowly progress to achieve that, I am not looking for a quick fix as may have been interpreted.

This was only one aspect of the clinic we attended, everyone made excellent improvements over the two days and I spoke to everyone in attendance and they all agreed it was fantastic.
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You asked for an explanation and I gave you one; admittedly I don't claim to be a wordsmith. I can't help your lack of understanding but but if you took the time and effort to read any good text on basic pulmonary physiology it would quickly become apparent that's it's really not rocket science.

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my vote

i consider myself a partial convert to frc diving. the last 6 months i have been doing 90% of my diving frc. mainly because it does feel more relaxing not having to fin down. and also because it seems to keep me in very good shape for deeper diving.
most of my diving is for recreational purposes and in about 25m of water. the passive exhale i do involves completely relaxing the diaphragm at the end of and exhale, and letting water pressure then dictate lung volume.
i agree that samba is certainly not avoided, i have willingly pushed into that area under controlled conditions. but i do feel i'm able to judge the onset of hypoxic well enough to know when to start the ascent. i havent had a mishap yet.
i do think that squeeze is a limiting factor, but mainly if one is not able to do this type of diving on a regular basis. i have increased depths gradually over the last few months and can dive a bit over 30m which is all the depth i need for recreational dives.
dive times at around 25m are typically around 2:30, which is also sufficient for me. it is more than half of my full lung bottom times.(when i started with this type of diving my max was 2:00 but it has steadily risen to just over 3')

other important advantages of this type of diving to me, apart from the relaxation factor, are that firstly, my recovery times are proportionately shorter than on full lungs, meaning i can spend more of every hour underwater.
secondly, i can do many more dives per day without the worry of dcs, which has become a real concern for me.
and thirdly, when i do occasionally choose to do deep dives(which i do on full lungs ) i can go back to those depths at a days notice without having to worry about suffering lung squeeze.

and surprisingly when i do the odd shallow inhale dive my bottom times are longer than they were before i started with the frc diving.(i'm surprised because i would have thought my CO2 tolerance would be pretty low)

i have been very happy with the change of approach. though if i was only able to dive one week out of every six months like some less fortunate people i might stick to inhales?

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