This "top of the lungs" "bottom of the lungs" stuff... are we supposed to take this seriously? Air is a fluid. If you compress the bottom of your lungs, guess which air escapes first. Relatedly, I'm no physiologist, but my impression was that the diaphragm is used to expel air from the lungs in all breathing, whether deep or shallow. Those throat muscles aren't gonna get air out no matter how you use 'em... they are important for producing _sound_, of course, but again that applies equally for normal talking and for projecting. A stub is a stub, I guess, but I'd like to know how this actually works, and this "top of the lungs" story sounds like gibberish to me. Of course, I've been wrong before.

filling the top/bottom of your lungs

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To fill the bottom of your lungs the diaphragm relaxes to allow the air to go down to the bottom and not move the top of your rib cage or shoulders. It involves the stomach going out rather than your chest. This is a technique that singers use. Then yes, you can control the diaphragm, as a muscle, to push it out and expel the air. Singers try to use it to create an even flow of air to support notes that are held. And also, you can fill up separate parts of your lungs, as I can breathe down to the bottom of my lungs (making my stomach go out not my chest) and "feel" full, but then can continue to breathe in by breathing in and making my chest go out also.