The way we use the breathing machine during speech is very complicated. Luckily, like most complicated actions such as walking and eating, breathing to communicate is an automatic function we’re born with. After all, babies don’t have to think twice about how to use their breath to vocalize in a way that gets our attention very quickly!
Like any system run by “fuel”, the vocal fuel supply needs to be replenished regularly. As you discovered during your CVO experiment, breathing in to replenish the air supply occurs automatically when you stop squeezing the lung-compressing muscles: then the lower torso can relax to let the diaphragm do its work of breathing in. Let’s get acquainted with the breathing parts by exploring their locations and actions…
The diaphragm is the main muscle that lets us breathe in. It works with the ribcage-lifting muscles to expand the lung cavity. You can identify the location of your diaphragm by feeling your bottom rib and tracing it all the way around your body. The diaphragm is a large sheet of muscle attached to the bottom ribs. It divides your torso into two compartments: the upper compartment houses the lungs and heart; the lower compartment is where all the other “guts” live. In rest position, the diaphragm is deeply dome-shaped. When it contracts to help us breathe in, the diaphragm flattens and pushes against the lower-compartment guts, expanding the lung cavity vertically.
Now, with your hand, feel the abdominal muscles do their work as you experiment with “Hm!” again: feel how the lower guts squeeze in to start the vocal motor; then notice them relax and push out against your hand to let the new breath in as your diaphragm lowers.