To inhale, one MUST decrease the pressure within the lungs so that it is below the air pressure outside. this is done by expanding the rib cage via the intercostal muscles and by contracting the diaphragm, reducing the pressure between the layers of the pleura, which in turn pulls on the lungs, causing them to expand, reducing the air pressure in the pleura, causing air to flow in. At least - that's a quick summary of what I remember from DeVries and Guyton (physiology textbooks).
The nurse says, "yes, but..."
In order to ACCOMPLISH the air pressure one actually has a choice of using some accessory muscles more than others. One can direct the expansion up into the anterior chest, creating a big expansion there with minimal lateral and posterior thorax movement and minimal abdominal expansion - the way most people breathe when their doctor tells them to take a deep breath. Or, one can do the "abdominal breathing" I was taught in the dojo, being told "it's how babies naturelaly breathe": relaxing the chest and letting the abdomen expand with the inhale, deflate with the exhale. Or, one can focus on lateral and posterior expansion of the thorax, feeling very full and expansive while the chest is relatively quiet and the abdomen still.
(I actually had to show this to a nurse friend recently, with her hands on me, who thought I was nuts when I talked about different ways of breathing - because, indeed, reading texts will NOT teach you what you can actually feel and do as a living breathing being)
So reverse breathing, as I understand it, has to do with abdominal use - essentially contracting on inhale, expanding on exhale, yes? I may be wrong but that's what I think it is- somebody else will jump in and say if that's right or not....