Well, I’m the lead singer in a bar band. We play mostly hard rock, with some heavy metal thrown in there. Which means I really have to belt out the high notes I’m on stage nearly four hours a night, for three nights a week. How do I do it?
Practice, practice, practice.
Okay, that sounds like a cliche, but it’s true. Way back when I first tried to sing with a choir, when I was about 14 years old, I couldn’t sing a note any higher than the A below middle C. But I got into heavy metal, and strongle desired to sing that kind of music. So I tried, and tried, and tried, and kept doing it until I could do it. I managed to develop my range to the E a tenth above middle C.
As I’ve had no formal voice training (I was always in the band at school) this was painful much of the time. I could hit the notes, but it was a strain. Especially when many of the songs were literally screamed. Over time, though, I learned how to “sing from the diaphragm”. All the power in my voice comes from there, not from my throat. I learned how to keep my neck and throat muscles mostly relaxed, and to let my diaphragm drive the notes. And like cdhostage said, I learned how to tighten those muscles only as much as necessary.
The result is that I can go all night, full bore. Even when I have to scream, or use a raspy-sounding voice, it doesn’t hurt or wear me out.