Susan wrote in with a comment and question about pre-performance nerves and how the physical signs of such anxiety could affect a dancer's performance:
"I have often wondered if the adrenaline rush that comes with pre-performance anxiety is in some way helpful to dancers. For other types of performers it really gets in the way: public speakers or singers find their voices are shaky, musicians find their hands are shaky. These can be devastating problems. They have to try to override the adrenaline (talk about using rituals and superstitions!). But if you are about to go out on stage and move, can you make use of that extra jolt of energy?"
I'd have to say that for dancers it's much the same as for musicians or public speakers. I've definitely felt that nervous, trembly feeling before going onstage, and have worried that I would have trouble executing my choreography because of it. However, the difference is that as dancers, because our means of expression and performing involves moving the entire body, we are trained to "take charge" of our physicality and move with assertion. Therefore, that nervousness or shakiness will usually disappear instantly once a dancer steps onstage-- or at least as soon as they have to start moving and dancing. Breathing deeply (which you have to do in order to move with amplitude) and moving your body so fully automatically erases the tremors of an over-adrenaline rush. Very convenient! It is true, though, that the adrenaline gives you extra energy, or at least keeps you from thinking about being tired. That is one down side to performing a role or a ballet a million times over-- you can get so comfortable with it that the adrenaline rush is gone, and then you really feel how tiring it is!