THE ALEXANDER TECHNIQUE...
is a fascinating discipline that helped me with back problems and vocal strain, and as a certified teacher of the Technique, I consider it the basis of my approach to performing and to teaching voice.
Click on these links to read my articles on the Alexander Technique (pdfs):
What Is the Alexander Technique? (an introduction)
Constructive Rest (a teaching handout)
The Unified Field of Awareness (a teaching handout, with credit to Frank Pierce Jones and David Gorman)
What Is the Alexander Technique? (a collection of statements and definitions by teachers and authors)