Jim, it's pretty common for professional singers to do a vocal warmup before a performance. Joan Baez, for instance, has to do an extensive period of warming up before a performance now or she runs into trouble, according to her. She said that when she was young, she could just open her mouth and belt it out any time at all, but not anymore without warming up first.

Everyone's situation, though, is unique, so different methods would work well for different people, I figure. All Richard needs is warm beer! ;-)

Voice problems can arise out of muscle tension, as you suggested. They can also result from an emotional block which causes muscle tension (as I discovered in my early 20s). A young woman I was in love with decided to marry somebody else, I found out about it, felt devastated, and a short time afterward I found I was losing my singing voice...even my ordinary talking voice. It got worse and worse. I didn't make the connection at first, and I was convinced there was something seriously wrong with my throat, so I went to a throat specialist. He took a good look inside my throat and said, "There is nothing physically wrong here whatsoever."   That was a big relief!

He then said, "Have you had some kind of emotional shock recently, around the time this problem started or shortly before?"

Bingo! I most certainly had.

"Well, he explained,"I've seen this happen a few times with patients who've come to me. You can sustain some kind of emotional trauma and your throat starts to seize up and the vocal chords don't work properly. Now that you know what it was that caused the situation, it should cure itself, because there is really nothing at all wrong with you physically."

The light went on. And it did cure itself within a day or two, and I was singing just fine again.

Interesting story, eh? I lost the girl, all right, but I got my voice back.