I want to warn you not to practice any breathing exercise to such an extent that you make your heart beat fast or feel like strangling.
Overexercising the lungs is as bad as not exercising them enough and the results are often harmful.
Like everything else in singing, you want to learn this gradually. Never neglect it, because it is the very foundation of your art. But don’t try to develop a diaphragm expansion of five inches in two weeks.

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