alan little’s weblog

gas exchange yoga

4th October 2005 permanent link

I was thinking whilst cycling to work the other day[*] about something David Williams said at the yoga course I went to with him in July: he wouldn’t be surprised if as much oxygen passed through the body in one hour’s ashtanga yoga practice as in the other twenty three hours in the day of other activities.

(Unfortunately for me, perhaps,) I’m not the sort of person that hears a claim like that and just thinks “wow, cool”. Instead I think “wow, that would be interesting if it were true. Now show me the numbers”.

According to yoga anatomy guru David Coulter, a normal resting breath for a “healthy young male” is about half a litre, and the maximum possible breath is a little under 5 litres. So a factor of 10 difference – quite a lot, but less than 23x. And that's the theoretical upper limit of what would be possible for a super-yogi who breathed at the maximum possible throughout their yoga practice, and an absolutely relaxed resting breath the rest of the time. I don't think such a person exists.

In ashtanga vinyasa yoga, we don’t in any case attempt to breath the absolute maximum possible volume of air. We are supposed hold muscle locks in the lower abdomen throughout our practice – bandas – one effect of which is to prevent breathing into the abdomen and instead keep as much of the breathing action as possible up in the diaphragm and ribcage. This serves a number of purposes, some of which are:

Really? That’s interesting. Let’s look for some support for that claim too. What does google think about “lung region gas exchange efficiency”? It thinks there is a handful of medical papers that do indeed seem to be in the right general area, but they don't appear to contain the answer to this particular question. Skimming them anyway, I discover that “ventilation/perfusion ratio” appears to be the key technical term – how much air is getting into a particular region of the lung, versus how much blood supply is there to exchange gases with it. Lots of papers about how to measure it, how it deteriorates in emphysema cases, etc. etc., but nothing clearly saying here’s how it varies in different parts of a normal healthy human lung.

So (pulling numbers out of my ass since I couldn’t find them anywhere else) let’s assume a hypthetical ideal ashtangi is breathing using two thirds of their maximum lung capacity, but the third they’re not using is only half as efficient as the rest. But wait – resting breath also uses almost entirely the less efficient lower part of the lungs. So our ashtangi is breathing seven times the volume of a resting breath, but using parts of the lungs that are “twice” (?) as efficient. So the answer could be 14.

That’s per breath. What about breathing rate? I’ve timed my breaths during practice at four per minute during seated meditation at the end, around twenty per minute in strenuous arm balancing postures. Presumably somewhere in between the rest of the time. Where in between? No idea. My resting breath rate? No idea, have never counted it. Probably also somewhere between four and twenty. Does a higher breath rate mean more gas exchange anyway? I guess not necessarily; the air probably has to be in the lungs for a certain amount of time for gas exchange to occur. Coulter has a chart saying something about this too, but I didn’t understand it and I don’t have the book in front of me right now anyway.

Too many unknown variables to actually come up with an answer. It looks as though David Williams’ factor of 23 is on the high side if taken literally, but he’s on to something. A factor of 10 might be vaguely credible.

Couple of links stumbled across whilst “researching” this entry: a huge bibliography of books and research papers on the physiological effects of yoga, one of which is an interesting-sounding book entitled Science of Breath.

[*] Not having yet reached an elightened state of being fully absorbed in the activity of the moment at all times.

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