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First an observation - I noticed that I can not inflate my cheeks with my mouth open. This means that inflating cheeks is not a muscle property and that only pressure of air from lungs trapped inside my closed mouth is responsible for any inflation. Also, once inflated I can move my tongue anywhere and still retain the inflation. This means that tongue is also not responsible for air regulation inside mouth.

Moving on, we all know that we can either inflate both our cheeks, or we can inflate only cheek from one side or we can inflate *portion of face between lips and chin* (I don't know what it is actually called). Put simply, we have complete control over which part of my face would I like to inflate.

I don't understand how this is possible without muscle control? Air has tendency to occupy all space therefore my entire cheeks should get inflated without me having any control whatsoever, but as it turns out I can control and redirect the air to apply pressure only at a particular cheek without any help from tongue. How?

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  • $\begingroup$ Why have you concluded that not being able to inflate your cheeks with your mouth open means the muscles of your mouth and face are not involved in control the space available for inflation? $\endgroup$ – De Novo Nov 8 '18 at 17:27
  • $\begingroup$ I was convinced that facial muscles could only produce inflation and not contraction (mostly because we never feel contraction). A naive conclusion on my part as evident by Bryan's answer. $\endgroup$ – Sarthak123 Nov 8 '18 at 18:30
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Muscles can only "pull" never "push" - that's just how they are organized at a molecular level. We can only push things because we use joints as levers: if you "pull" on the outside surface of your arms, you can push things out with your hands because that pull acts to extend the forearms.

It's not really possible to puff out your cheeks with muscle, because there is nothing floating in the space outside your face to pull against. Your cheeks puff up a bit when you smile, but I think you will agree that's a completely different type of "puffing" and comes from gathering up a bunch of tissue.

However, it's fairly simple to contract muscles in your face (specifically the buccinator) to prevent a cheek from bulging out by tightening the muscles in the cheek. The air pressure you are producing is pretty minimal, so it doesn't take much strength. The cheek bulges out when the muscles are relaxed, and doesn't bulge when the muscles are contracted.

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  • $\begingroup$ Perfect. Just one follow up. When my mouth is closed and cheeks not inflated, are my cheek muscles still contracted? I ask this because when I then attempt to inflate my one cheek I do not notice any significant feeling on my other cheek of contraction or whatever. Is it because muscle contraction is so insignificant that I did not feel it, or because my facial muscles were already contracted before I attempted inflation. $\endgroup$ – Sarthak123 Nov 8 '18 at 18:33
  • $\begingroup$ @Sarthak123 I think you would get your answer reading about muscle tone. In general, though, you don't really feel muscle contraction except when it is unusually forceful (especially a cramp), and even then you may also be feeling the movement of other tissues rather than the force of the muscle itself. Think especially about all the muscles in your back and core that maintain your posture: you probably don't ever notice them and they are doing a lot more work than your cheek muscles would be. $\endgroup$ – Bryan Krause♦ Nov 8 '18 at 18:37
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While it's true that we don't have facial muscles to actively move our cheeks, we DO have muscles to put them under tension (I don't which specific ones that are though).

If we apply both air pressure from our lungs and tensions to (selected) cheeks, we can thereby control which regions to inflate.

As an anecdotal note: building up and using this tension is especially important for musicians playing wind instruments

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