When people are out of breath from exercising, instead of breathing normally they partially obstruct their expirations by blowing out instead of breathing out.

Why is this?

EDIT: This photo illustrates what I'm referring to.

  • $\begingroup$ I'm not sure I understand your question. You have to breathe out in order to breathe in again… $\endgroup$ – canadianer Oct 9 '15 at 23:02
  • $\begingroup$ I don't. I start panting. This is opinion based I guess. $\endgroup$ – AliceD Oct 9 '15 at 23:23
  • $\begingroup$ @canadianer: You don't understand the difference between blowing and breathing out normally? $\endgroup$ – EmmaV Oct 10 '15 at 1:56
  • $\begingroup$ Why did 'AliceD' mark this question as 'unclear what [I'm] asking', when her comment shows that she understood the question perfectly? I give up. No one is capable of answering, or, it seems, even understanding my simple question. $\endgroup$ – EmmaV Oct 10 '15 at 21:25
  • $\begingroup$ @EmmaV, after a while, thinking about it, I now understand what you are asking. Alice is clearly saying that the answer(s) would be opinion based and thus not constructive and hence put a block on any further answers. In my opinion based answer, I would say I do that so the strong air flow does not go through my teeth because it gives me a strange feeling when it goes through my teeth... Like others, I think the question could have been better expressed. $\endgroup$ – Alexis Wilke Oct 11 '15 at 0:19

Trying to rephrase the question

If I understand the question (and what you missunderstand) correctly, I think one could rephrase the post as

When one spends some time under water and come back to the surface, one usually breath out and then breath in. This is surprising to me because I would expect the person to be out of air and therefore wouldn't need to breath out before breathing in.

Let me know if I failed to understand your question and misunderstandings


We don't incorporate the air we breath in our lungs. We only use the molecules of oxygen $O_2$ from the air (which takes ~20% of the total volume). This molecule goes in the blood, reach the cells and react with sugar to produce energy. The waster of this reaction is another molecule $CO_2$ that needs to be exhaled through the lungs.

So, really the volume and of air that we have in our lungs doesn't vary much (It actually increase a little bit as we had some carbons). Only the composition of the air that we have in our lungs changes. After some time, we need to renew this air and for this purpose we first need to breath out the air that is contain a high density of $CO_2$ before breathing in.

This is why when sticking the head out of the water many people first breath out and then breath in. Note, however that one can breath out all its air underwater and then only has to breath in when back at the surface.


Are you asking why do we contract our lips during sport?

If yes, I think it very much depend from one person to another. There is probably no physiological advantage/disadvantage at doing so and it probably is just a consequence of expressing pain on our face.

  • $\begingroup$ That's not what I mean. When people are out of breath, they breath more heavily than normal, but instead of expiring gently as normal, they 'blow'. By this I mean they partially close their mouth so that there's a small opening and blow through it, often making thier cheeks bulge. Inspirations are still normal, albeit deeper. Here's an image I found quickly: watchfit.com/wp-content/uploads/2015/07/… $\endgroup$ – EmmaV Oct 9 '15 at 23:45
  • $\begingroup$ Your comment seems very unrelated to your post...but ok. I tried to answer to what might be your question (still unclear to me) in an edit in my answer above. $\endgroup$ – Remi.b Oct 9 '15 at 23:50
  • $\begingroup$ My comment is an elaboration on my question. I'm not asking why we contract our lips during sport. I personally 'blow' when out of breath because a rapid expiration when out of breath is uncomfortable. This is doubtless why others do it too. I thought that there must be a physiological explanation for it. $\endgroup$ – EmmaV Oct 10 '15 at 0:13
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    $\begingroup$ Note also btw that I don't have a PhD (yet) as I am currently a PhD student. I'll delete my answer once I'll understand your question (and will then try to suggest an edit to your post). $\endgroup$ – Remi.b Oct 10 '15 at 2:10
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    $\begingroup$ And so is you question, why do we need to inhale and exhale more air when we are exercising? $\endgroup$ – Remi.b Oct 10 '15 at 2:32

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