Anticipating the vibration of the sound column from your heels fosters your verticality and brings a rich and consistent voice throughout the tessiture, reflecting the body-space trade amplified by your instrument : the invariance of this body attitude ensures an easy emission of lower and higher notes as well.
Laryngeal vibrations form fundamental tones, while the harmonic shower of sparks associated with the fundamentals, rich in higher frequencies and reinforcing the initial sound considerably, depends on the skeleton.
There are many advantages to the activation of this bony resonance. The energy that is dispensed is extremely important. Ample, warm, dense sounds are made with minimum effort.
It takes some work to get the feeling of ascending the scale without expending any energy at all. You have to learn to differentiate between the kind of energy that seems necessary to rise in pitch, and tension in the larynx.
It is easy to confuse going up in pitch, with its attendant naturally increasing intensity, with the need to employ effort, which is entirely unrelated. The intensity of sound comes from avoiding any pushing, so that the larynx is free to drop slightly lower. (…) the sensation of support will shift lower in the body at the same time.
Alfred Tomatis, The Ear And The Voice
(translated by Roberta Prada and Pierre Sollier)