Muscles can do one thing – they can contract. If they are not contracting, they are relaxing. For this reason, muscles generally come in pairs. Think tricep and bicep. If you engage both at once, you get isometric effort, which is great for exercising and terrible for making music!
When does your diaphragm contract? It’s primarily muscle so it can only contract in one direction.
Teachers who say “support with the diaphragm” are implying that one engages the diaphragm to exhale. In other words, this little bit of advice suggests that the diaphragm contracts to push the air out of the body.
This is backwards. The diaphragm contracts as you inhale, not as you exhale. The diaphragm is the primary muscle of inspiration. Upon exhalation, the diaphragm is actually relaxing. Furthermore, this sort of advice is confusing because one can’t directly feel the diaphragm. When students hear this kind of dialogue they are not quite sure what to think so they smile and nod as though they know what you are talking about. They don’t want to be the one student who doesn’t quite understand…
I suspect this scenario is more common than we would like to think. The teacher says “breathe from the diaphragm” (because that’s what we always say!) and all the good little children smile and nod as thought they understand completely what this means. In reality, however, the students are trying to figure out where the diaphragm is and how it works in order to breathe with it.
Try this: don’t talk to young students about the diaphragm. Talk to them about creating a beautiful tone and give them lots of great examples so they understand what a beautiful tone is.