Costal or Diaphragmatic Breathing involves breathing from the larger costal diaphragm as opposed to the crural diaphragm. This is a technique sometimes used by opera singers to allow them to sing louder. Using this method combined with deeper tone projection allows people who stammer to speak more powerfully.
An analogy of how this breathing technique works would to imagine a bellows – an item that used to hang near the fire in most houses in the UK. The bellows consisted of two handles and an area that collected air when the handles were drawn apart. When the handles were closed again the air was forced out. When placed near the dying embers of a fire, they would bring that fire back to life.
When we breath using costal breathing we breath in quickly and fill our lungs then we breath out at a much slower pace and speak. A key part of using technique for better speech is to imagine a hole in the chest from which the words now come from. This deeper tone allows us to speak from a place that feels more and anchored and strong as opposed to a high-pitched, throaty sound.
Try this for a moment – breathe in then out of your throat area. Now, take another deep breath and breathe out from your chest. Which feels stronger to you? Costal breathing when used properly brings confidence and better speech to those who stammer and with practice will prove very beneficial indeed.