The following post is heavily influenced by the work of Ron Murdoch, an AT teacher and voice teacher from Nova Scotia. I've never met him but I greatly admire his writing.
To make sense of any approach to singing or the use of the voice in general, is to understand what the voice is and how it works. It all starts with a desire to communicate, and in the case of singing, the desire to communicate beautifully.
The communication level required to sing well, needs to be on a very large scale and to be overtly emotional. It is this exaggerated level of communication of feeling that actually sets in motion and coordinates the vast, complex muscle structures of the singing instrument. This puts a very great physical demand on a singer, as great a demand, in fact as that of an athlete.
The singing instrument goes from the crown of the head to the soles of the feet. Working with the whole produces a good voice, either for singing or for talking.
The singer is always his own instrument. A singer has to establish the poise and direction and shape of his instrument each time he sings and it is entirely susceptible to his moods and thoughts. And remember this instrument goes from the crown of the head to the soles of the feet. Alexander once said, “ I made no progress with the ability to free the tension in my neck until I had sorted out what what I was doing with my feet and legs.”