Dynamic Apnea

[trux]

Originally Posted by flying_spanner

I don't get any real contractions while doing statics or dynamics. I may try this later to see how it feels.

Well, there indeed are people who do not get any contractions, but at most of them it is just because they either hyperventilate (although they are persuaded they don't), or they do not push enough. To test yourself, try a 8-10 minutes hypercapnic series of breath-holds of the same length, but with only a single breath between (one exhalation, one inhalation). You can make the subsequent breath-holds longer, but the next one should never be shorter than the previous one. For example, you can try 8 times 1 minute. If you do not get any contractions at the end, try little longer.

And you can do this hypercapnic table in dynamics in the same way too - just replace the time with distance - for example do dynamic apnea swims of ~15m with a single breath between them, during 10 minutes.

If you do not get any contractions during this exercise, then you are likely one of the few who simply do not get them. Now the question is, whether it is good or not. The contractions, besides being an important body signal about progressing diving response, and although consuming some oxygen, help with the oxygen supply of the core, by increasing the blood pressure, avoiding so a blackout. The oxygen consumption of the contraction is not necessarily important, because (if the diving response works well), the muscles driving it already work in anaerobic mode, hence consuming only little oxygen (if any) - that's why your diaphragm may feel so tired (lactic) after a hard session of apnea.

What I wanted to tell with it is that you should think about contractions positively. Many beginner freedivers freak out and start panicking when getting strong contractions, or try avoiding them (suppressing so the diving reflex), while they really should think about them as their best friends.

[chrismar]

Originally Posted by trux

Well, there indeed are people who do not get any contractions, but at most of them it is just because they either hyperventilate (although they are persuaded they don't), or they do not push enough. To test yourself, try a 8-10 minutes hypercapnic series of breath-holds of the same length, but with only a single breath between (one exhalation, one inhalation). You can make the subsequent breath-holds longer, but the next one should never be shorter than the previous one. For example, you can try 8 times 1 minute. If you do not get any contractions at the end, try little longer.

And you can do this hypercapnic table in dynamics in the same way too - just replace the time with distance - for example do dynamic apnea swims of ~15m with a single breath between them, during 10 minutes.

If you do not get any contractions during this exercise, then you are likely one of the few who simply do not get them. Now the question is, whether it is good or not. The contractions, besides being an important body signal about progressing diving response, and although consuming some oxygen, help with the oxygen supply of the core, by increasing the blood pressure, avoiding so a blackout. The oxygen consumption of the contraction is not necessarily important, because (if the diving response works well), the muscles driving it already work in anaerobic mode, hence consuming only little oxygen (if any) - that's why your diaphragm may feel so tired (lactic) after a hard session of apnea.

What I wanted to tell with it is that you should think about contractions positively. Many beginner freedivers freak out and start panicking when getting strong contractions, or try avoiding them (suppressing so the diving reflex), while they really should think about them as their best friends.

I don't think the contractions themselves are good, instead they are a sign (that not everyone gets) that your body is in conservation mode. I can now mentally block them, similarly Will T also blocks them, though its actually more painful than just letting them happen. Personally, the dive reflex is even stronger when I block them.

[trux]

Originally Posted by chrismar

I don't think the contractions themselves are good, instead they are a sign (that not everyone gets) that your body is in conservation mode. I can now mentally block them, similarly Will T also blocks them, though its actually more painful than just letting them happen. Personally, the dive reflex is even stronger when I block them.

Yes, they are good. Well, "good" is perhaps not the best term to describe them, because they have also some negative effects (for example increased risk of hemoptysis {lung squeeze} when experiencing contraction at depth), but they definitely have other positives than just being a signal of the diving reflex. It was already discussed here on DB, and there are also some scientific studies (I am just unable to find the references right now). The contractions indeed help increasing the pressure both in lungs and in the brain, hence helping with the gas exchange in the lungs, and with supplying the brain with oxygen despite progressing hypoxemia, protecting you so from the blackout.

[Mullins]

Then presumably those who do not get involuntary contractions should contract their diaphragms voluntarily in the latter stages of their dives?

[billieball]

Excellent question! I'd love to hear the response!
--Billie

[trux]

Originally Posted by Mullins

Then presumably those who do not get involuntary contractions should contract their diaphragms voluntarily in the latter stages of their dives?

It sounds reasonable, but the question is whether the additional stress and muscle work won't distract you mentally and physically too much. It may need some serious drilling. I think you are one of the few ones who can test it and tell us whether it helps you pushing further. Perhaps it may be best done in cooperation with an experienced freediving physiologist who can plug you on some devices to see what's going on. I bet that most of the docs working in this area would love to cooperate on such project with you, Dave.

[trux]

BTW, strangely, in this document (Hemoptysis Provoked by Voluntary Diaphragmatic Contractions in Breath-Hold Divers -- Kiyan et al. 120 (6): 2098 -- Chest), the authors apparently use the term "voluntary diaphragmatic contractions" for the contractions that I definitely do not consider voluntary. Not sure why it is so, but I dared mentioning it to avoid possible misunderstanding when reading some similar documents or discussing with physiologist. I do not know though if it is common to call the contractions so, or whether it is rather a deviation at this specific research team.

[trux]

OK, this similar article seems to explain the voluntary diaphragmatic contractions better. They tell:

... all of the divers performing in these military exercises did the same maneuver: voluntary diaphragmatic contraction at the depth. Breathhold divers to increase the breath-hold time use this maneuver

So unless the authors are inexperienced and completely misunderstood the mechanism of contractions during apnea, it indeed looks like the voluntary contractions are used by some freedivers to push the breath-hold further.

At the first document, I was quite confused, because at least at the second and third cases, it did not sound like voluntary contractions to me - at the second, it was written "he experienced voluntary contractions". Personally, at indeed voluntary contractions, I would not use the verb "experienced", but rather "performed" or similar. And at the third case, they wrote "had diaphragmatic contractions just before the ascent (because of short surface interval)", which also sounds more like the classical contractions to me, than realy voluntary ones.

[chrismar]

When I mentally block contractions, Brachycardia is more pronounced. A training partner of mine has been having contractions later and later recently, resulting in longer dives. And before you ask, it's not a comfort thing, I'm talking hypoxia as the limiting factor here.

I'll read the articles when I get a chance, but I have my doubts about contractions increasing pressure in the heart and lungs in a meaningful way and even more doubts about that having a positive effect.

[trux]

Yes, of course, getting the contractions later during the terminal phase of the apnea is certainly better than experiencing them already early in the breath-hold. There is a threshold when the negative aspects of the contractions (mental stress and physical effort, hence higher oxygen consumption) will overweight the positive effect. So when the contractions are too early, they may limit you more than helping.

[Mullins]

Originally Posted by trux

OK, this similar article seems to explain the voluntary diaphragmatic contractions better...

So unless the authors are inexperienced and completely misunderstood the mechanism of contractions during apnea, it indeed looks like the voluntary contractions are used by some freedivers to push the breath-hold further.

I would expect that the test subjects were performing the contractions (if they were voluntary...) not to increase the efficiency or potential duration (time to BO) of the breathhold, but as in order to make themselves more comfortable or distract themselves from the discomfort.

I would be interested in testing this sort of thing, but I am somebody who gets early contractions. You need a subject who gets none, so that they can try voluntary contractions to see what difference it makes.

[trux]

Originally Posted by Mullins

I would expect that the test subjects were performing the contractions (if they were voluntary...) not to increase the efficiency or potential duration (time to BO) of the breathhold, but as in order to make themselves more comfortable or distract themselves from the discomfort.

Yes, I guess you are right.

Originally Posted by Mullins

I would be interested in testing this sort of thing, but I am somebody who gets early contractions. You need a subject who gets none, so that they can try voluntary contractions to see what difference it makes.

Ah! I though you did not get any - had to confuse you with someone else. AFAIK Mifsud does not get any, but I though one of you the top freedivers and residents on DB is the same case.

[Mullins]

Contractions @50m

[trux]

On the back way. or going down? In any way, it seams rather dangerous - you never suffered lung squeeze because of the contractions in such depth?

[Mullins]

Sorry - in dynamic. Usually get contractions as I begin to ascend in CW. I've had some pretty heavy ones at depth with no lung squeeze problems.