Here is a pretty good video of how the respiratory diaphragm functions while abdominal diaphragmatic breathing is happening. The yellow muscle that shows up first is the respiratory diaphragm.
I find that this helpful to understand in the development of the intrinsic muscles, what I call the singer’s muscles. The upward most position of the respiratory diaphragm occurs before we begin to inhale. When we take a breath in, which fills our lungs from the bottom to the top, the diaphragm descends downward toward the lower belly. When we exhale, it rises naturally toward its upward, relaxed position.
From my observation in 35 years of working with singers, many singers quickly fill the lung up before they sing the next line and doing this can have a detrimental effect on their ability to sing, depending on the person’s own body structure. There is quite a bit of air available in the lungs before we take a breath and if we know how, we can utilize that breath to sing for quite some time. But you have to release the fear carried as tension held in the body, especially the chest, neck and abdomen, that is preventing you from using the small emotional, singer’s muscles with complete relaxation and full elasticity.
The Rolfing® Method of hands on education and bodywork that I have used with singers since 1985, can release this tension and reorganize the singer’s body so that singing is done with much more dynamic relaxation, allowing the authentic voice to be accessed.