A singer should stand freely and easily and should feel as if the chest were leading, but should not feel constrained or stiff in any part of the ribs or lungs.
From the minute the singer starts to emit a tone the supply of breath must be emitted steadily from the chamber of air in the lungs. It must never be held back once.
The immediate pressure of the air should be felt more against the chest. I know of a great many singers who, when they come to very difficult passages, put their hands on their chests, focusing their attention on this one part of the mechanism of singing.
The audience, of course, thinks the prima donna’s hand is raised to her heart, when, as a matter of fact, the prima donna, with a difficult bit of singing before her, is thinking of her technique and the foundation of that technique–breath control.

Luisa Tetrazzini, one of the great coloratura sopranoes of the late 19th and early 20th century