Dr. Matt Walker

There's no need to take it to the extreme.

But

I don't think there's any good evidence yet in humans that firstly that's the case and nor is the strong enough evidence to make any recommendations.

But I just bring it up because it's in the data and it's starting to emerge that if you were to ask me about sleeping position and are there any recommendations, those are the two pieces of descriptive advice I would give you.

They are not prescriptive pieces of advice.

so there are at least four competing theories of yawning that we have and i think there is probably a emerging clear winner the first theory was that it was just tiredness that yawning is simply a sign of you being tired and it turns out that that's not true because many people can yawn when they're bored

and they are not tired and they've been very well rested.

So that doesn't seem to be true.

The next one was one that seems to be very logical, which is it's about trying to rebalance your blood gases and specifically oxygen and carbon dioxide.

And you would think that perhaps when you yawn with that sort of, when you, and you inhale a huge volume of oxygen, what you're trying to do is rebalance

pump back up the oxygen in your bloodstream, or when you sort of and the exhale, maybe it's about exhaling more carbon dioxide.

Exactly.

Yeah.

And so that was a theory that maybe you're trying to balance these blood gases.

And there was some very clever experiments where they took individuals and they artificially increased the oxygen levels, but more specifically, they increased the carbon dioxide levels bi-directionally.

They tried to manipulate it and they asked, did those individuals start to yawn more?

Because the idea would be if your blood oxygen

is coming down and your carbon dioxide is starting to rise, if this theory is correct, you should start yawning with greater frequency.

And there was no difference whatsoever.

That's probably also the reason that you don't see people yawning on a treadmill or when they're going into more of an oxygen debt and higher levels of carbon dioxide.