Kind of a mundane topic, but I noticed the other day that I can’t tell what muscle I’m using to puff out my cheeks (the ones in my face, wiseguy).
Is it my tongue? It doesn’t seem like it, because I can puff my cheeks without really moving my tongue.
Your diaphragm.
I think it’s just air. Close your mouth and nose and try to exhale. Your cheeks will puff unless you try to hold them in.
Well not always. Once the air is in your mouth you can push it around w/your tongue.
There’s no way it’s the diaphragm. I’m not using any stomach muscles at all.
It is the diaphragm. If you doubt that, try to puff your cheeks with your mouth open.
Actually, now that I’m playign around with it, it seems that I can puff my cheeks by either closing my jaw (reducing the volume of my mouth) or pushing my tongue up (also reducing the volume) while preventing air from going back into the lungs. The diaphragm is still being used to balance out the backpressure, but the jaw muscles or the tongue also play a role.
If you can’t purse your lips, you’re gonna have a hard time keeping the air in your mouth. Orbicularis oris, to the rescue! (The muscle of the oral sphincter).
It can’t be the diaphragm since I can puff out my cheeks while still breathing through my nose.
Seems to me that your cheeks puff out simply due to increased air pressure in the mouth cavity. In the throat, the glottis (I think) closes to prevent air from rushing down into the lungs or stomach. The lips, of course, stop air from being expelled through the mouth.
You’re using your tongue and or jaw, assuming your throat/windpipe are sealed off as you do it.
Try it with your mouth open - you can expel a noisy puff of air with a “hhhhhwwwwtt” sound, as if you were about to spit. That’s the front of the tongue coming up to touch the palate, thus forcing the air out. Alternatively, you can move your whole lower jaw up, to the same effect.
If you leave your windpipe open, you can inflate your cheeks using your diaphargm to blow out, but this feels different, somehow.
I think there’s more than one way to do it. You can do it by pushing the air around in the oral cavity with your tongue or jaw (and the facial muscles might come into play as well), OR you can do it by expelling air into the oral cavity with the diaphram. You HAVE to somehow increase the air pressure, either by making the cavity smaller or adding more air.
I think it’s all pneumatics. The pump (diaphragm), the valve (throat) that redirects air into or out of the mouth, and the jaw.
I don’t see what the tongue has to do with it though. The tongue is just moving around in there - you can’t use it to push air into the mouth, or out of it.
Actually, you can. You can use the tongue as a sort of combination one-way valve and bellows.
Place your entire tongue flat against your upper palette. Now, while keeping your glottis closed, lower the back half of the tongue to the floor of the mouth, but keep the front half in its current position. This will cause a small amount of air to be pulled into the mouth through the nose. Next, raise the very back of the tongue to the roof of your mouth again. Now you have the very tip and very back of the tongue touching the upper palette, with a small quantity of air trapped in between. Finally, loosen the contact between the tip of the tongue and the upper palette, and raise the entire tongue to once again be flat against the palette. The air that you had trapped is now below your tongue, and you’re back where you started. Repeat until your cheeks are sufficiently puffed out.
Notice that this won’t work if you pinch your nose, because you are using your tongue to actively draw in air.
Tongue. Diaphragm not necessary for this specific maneuver.
QtM, MD
But by arching the tongue, you can effectively decrease the size of the oral cavity, and redirect the air pressure into the cheeks. At least that’s what is feels like I’m doing. If you squeeze one end of a balloon, the other end will puff out, even though the net air in the system is the same.
The tongue’s not necessary either, though! (You can puff your cheeks even if you keep your tongue stationary).
But you are closing your jaw, right? I can’t seem to do it without doing at least one of these things:
a. pushing air up from the diaphragm
b. arching the tongue
c. closing the jaw
I know that it feels like you’re using some kind of cheek muscles, but if you try to puff your cheeks without your mouth completely closed, you’ll find you can’t do it. It’s your lungs.
::sigh:: And pursing the lips! 
Otherwise, that’s just how I do it. Push air into sealed mouth (diaphragm), using the tongue to keep air from escaping backwards into the nasal cavity, and out. Once the mouth is filled with air and sealed off on both openings, I can continue breathing through the nose without effort. If I plug my nose, I can leave my tongue flat, and inflate my cheecks, again by pushing up with my diaphram, noting that I feel definite pressure in my nose and behind the eardrums.
Well, I may be weird, but I can also puff using my cheek muscles. Try this: seal the back of the throat with the tongue and take a gulp of air into the mouth. Seal your lips, clamp your jaws shut, and hold the tongue still. Now “swish” the air from cheek to cheek. As one deflates, the other inflates.
Done only with cheek muscles, but it is the cheek contracting on one side that inflates the other.