I think doing 8 shows a week can be compared to top-sport.
The show takes over your whole life.
I have been in a few professional musicals and it is one of the hardest jobs there is. Mainly because of the 8 show-a-week schedule. My voice doesn't feel the same every day, and I basically have to live like a "nun". Make sure I get at least 8 hours of sleep every night, and eat healthy. I couldn't go out for a drink after a show, trying to speak in a bar with loud music would affect my voice and my performance for the next day. That's not me being paranoid, that's just a fact that I noticed at many occasions. Every birthday, visit to a bar, wedding, little cold, is a huge problem. Not sleeping 8 hours is a problem too. Even little things like hiccups or eating too fast can ruin a show. Or a tickle in your throat after kissing someone or having sex (there are thousands of innocent viruses that can affect your singing, or when you have to cough every now and then because of a little cold, etc). I can't visit my family and speak and play with my little nephews all day and then give that vocally demanding performance at night. Doing a show and doing it well takes over your whole life. Especially if it's a vocally demanding role.
We are all human. So I don't expect people to give 8 great performances a week, and nobody should expect that. It's the responsibility of the producers and the actors to be reasonable about it. I think 5 great shows a week is the maximum. If you push someone to give 8 great shows a week you have to deal with the quality loss, and the paying public deserves a great show every day. That's why I think there are certain roles that should have alternates.
Updated On: 5/20/13 at 12:44 PM