[curun1r]

> Lung capacity can only be improved a little bit with training (we're talking 5-10% range)

Do you have a source for this, because it doesn't sound right to me. For one, the packing technique has been shown to add an extra 10-15%. So right off the bat, there's a training technique that can increase lung capacity by more than your figure. Also, my anecdote matches GPs...since I started training freediving, exercising my diaphragm on a regular basis and practicing three-zone breathing with the corresponding stretches, the amount I can exhale into a balloon has increased significantly.

[jacobjuul]

some interesting reading on the topic:

https://www.ncbi.nlm.nih.gov/pubmed/29174581 https://www.ncbi.nlm.nih.gov/pubmed/28168782

(you can find more by searching PubMed). Granted I have mostly done research on cyclists. What we tend to see is an increase in the strength of respiratory musculature which leads to an increase in functional lung capacity and this capacity would not vary much between individuals (even between pro cyclists and high-level amateurs). More important than lung capacity for performance is your diffusing capacity (how fast you can move oxygen from lungs to your red blood cells). In sports other than swimming, it's always possible to breathe faster, which benefits from a strong respiratory musculature.

when it comes to freedivers, it's slightly different. They are forcefully stretching their lungs (which doesn't happen with normal aerobic training or breath holding to the same extent)

in this study https://erj.ersjournals.com/content/41/3/760.long they stretched their lungs as much as +800 ml.

[curun1r]

Unless I’m reading it wrong, it looks like the paragraph above the one that lists 800ml is the more interesting. The 2004 reading was 2.4L above expected, or 192% of expected.

Also, the freediving exercises are not just about stretching the lungs, they’re also about opening up the rib cage, since it constrains lung volume, and exercising the diaphragm, since the further down it can flex, the more air is pulled into the lungs. Freedivers also train the ability to stretch the diaphragm up since lung volume decreases significantly under pressure.

Anyway, it’s an interesting topic. And since you mentioned cycling, there’s one other area where apnea training intersects with the world of professional cyclists. You mentioned that the speed at which you can perform gas exchange in the lungs was the most important, and to a certain extent that’s true, but also important is the blood’s ability to hold oxygen and deliver it to organs/muscles. And, as I understand it, increasing the blood’s ability to hold oxygen is the primary effect of the banned substance EPO that cyclists frequently use to cheat. Now what’s interesting is that apnea training has a similar effect to EPO as well as increasing the body’s ability to reduce haemoglobin oxygen affinity. What I gather that to mean is that repeated exposure to hypoxic conditions triggers adaptations that allow freedivers to store more oxygen in the blood and, once reserves are running low, deliver more of that oxygen to the organs where it’s needed. The original study where I read this has since gone paywalled, so I’m not sure I’ve still got the correct link to give you, but one of the conclusions was that the effects of apnea training could likely be beneficial to the performance of endurance athletes like distance runners and cyclists.