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Diver vs Doctor

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.


Well-Known Member
Jun 19, 2002
Well I have to say thanks to Simon, for his efforts to communicate and work with us in a complimentary way!

Will be in touch about your ideas for experiments.

I find that a dive for many of us, if not most, is not necessarily most significantly limited by the use of O2 from the lungs. So, where it may be estimated that 42% of our O2 is from the storage of air in our lungs, this does not consider the effect that filling the lungs have on the dive and what proportions of that O2 store are required under various diving techniques. Fundamental to the meaningfullness of specific O2 stores, is when and how do they get accessed, under the various conditions. While diving on exhale most of us have found we can dive for similar lengths of time when compared to our inhale dives.

So, the idea that losing some 28% of our O2 stores, that is mainly accessible to our body core and brain during a dive, may not imply what the number suggests. Most of us here are aware of the difficulties in dealing with bouyancy and changes in bouyancy with depth. These difficulties are generally experienced to have a dramatic overall effect on the dive. Exertion at the surface is maximal and energy consumption is most inefficient, due to the presence of air and inhalations, which hinder the diving reflexes from occuring. The inefficiency comes from leg exertion tapping your O2 stores of the lungs, increases in heart rate as the body prepares for inhale exercise, and increase in metabolism temporarily(?). In general then, it is most likely that we will see a sharp drop in our 42% of O2 stores until we slow down our kicks and settle in to the sinking phase. The significance of the waste of energy is profound, and would be nice to measure in a controlled environment.

To contrast this, in exhale diving, one can weight themself to sinking almost immediately, thereby alleviating this exertion and rise in body activity. Not to mention the induction of diving reflexes as the body senses the prominent apnea conditions that come immediately without the inhale.

As a test try the following: See how long you can hold your breath while laying down on a passive exhale. Then at a similar state of initial relaxation, inhale and hold your breath. Immediately begin a brisk walk while continuing to hold your breath. Stop walking after 20 seconds and continue to hold your breath for max.

This test I would say is close to a comparison of a dive profile under inhale and exhale, without the comparison of diving reflexes.

Regarding myoglobin, due to blood shunting, one can have leg failure at depth if there are inadequate O2 stores in the tissues themselves. So I wonder if it is more important to understand an increase in myoglobin as a relative increase to previous myoglobin levels as opposed to comparing it to your overall body O2 storage. If you increase your myoglobin to double your previous amounts, what increase will this imply to the duration of power supplied by the legs. It is possible that diving on exhale increases myoglobin levels in current tissues, as well under appropriate stress, promotes the development of further muscle tissue with these higher myoglobin levels. So, potential increases to myoglobin stores, should include the tendency to promote the muscle tissue growth as well, correct?

Look forward to discovering whether this occurs and to what effect on top of just the numbers.

Another thing with exhale diving, is that it seems to strongly influence and train your body for diving reflexes. It would be interesting to gather those people who do not get blood shunts very easily while diving, and doing controlled exhale dives, look for increases in effect of diving reflexes and the timeliness of them. In my experience, I could rarely achieve a blood shunt when diving to depths up to 50m. Within a week of practicing exhale dives, I was experiencing blood shunts on all dives greater than 15-20m. I went from feeling exertion on a 50m dive, to feeling the same on a 71m within the next 5 dive sessions, whereas I had previously been diving constantly all year between 30-45m.

Most of this has been said before through this site, but a summary appeared relevant to this thread. Hope it is accurate in representing the ideas throughout our freediving community and that it helps the new people to understand the perspective freedivers are using in some of these concepts.


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Simon Mitchell

New Member
Jun 17, 2004
Hello Tyler,

Thank you for your explanations. It may surprise you to hear that I think that most of what you say sounds plausible. And do you know the best thing about your above post from my point of view? No where in it do you strongly imply that any of these putative physiological advantages for exhale free diving are strictly proven in humans. I have no problems with these types of discussions in which well informed commentators suggest that "x could happen" or "y might happen". It only bothers me when people say "x and y definitely happen" when that is far from certain.

You know, the big problem with all the theories that you propose about blood redistribution (I prefer that word because "shunt" carries specific physiological meaning which is not strictly relevant here) and the benefits of reduced oxygen consumption vs the risk of lowering your oxygen stores is that they are so extraordinarily difficult to test in the real world. The study idea I have had, I believe, circumvents most of the methodological difficulties with trying to prove the individual physiological advantages of exhale free diving methods, and may directly answer the ultimate question: does it work? As I said above, I would prefer not to lay it out here at this stage, but I would greatly appreciate your input to the proposal. Would you mind sending me your email address at [email protected]


Simon M


Well-Known Member
Jan 21, 2004
....what happened with this as I'd really like to know if Simon, Eric, Ben etc collaborated on the experiments that Simon was suggesting and if so what were the results?

Was there a follow up thread that I missed?


Ben Gowland

Ben Gowland

Aplysia gowlandicus
Apr 4, 2002
We had an email conversation for about a week and then the 'line' went dead. From memory, it was mainly Simon, Tyler and myself. Seb had a conflict of interest as he was planning or had executed similar experiments already. I think that when Simon realised this, there was little point in replicating any experiment as that would be a waste of time.
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New Member
Sep 6, 2004
After reading the last 50 posts on this subject i feel really alone and left out. Apparently, i'm the only freediver in the world who inhales before he goes underwater...

Simon Mitchell's tantalizing one-two combinations of learned responses and nasty name-calling leave me breathless (which is very rare for me) and begging for more :)


New Member
Oct 18, 2004
keep up the good work

Your site is very interesting, interesting discussion.

Keep up the good work.

NAUI Instructor #43610
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