@Laotionne - The reason you hear about performers like singers and stage actors doing voice exercises to strengthen their vocal cords is because they are trying to prevent injury to them. Professionals who make a living by using their voices often have a routine of warm up exercises just like athletes have stretches they preform before they go to work.
Even with the precautions they take, plenty of performers end up having to have surgery to repair the damage their careers did to their voices over the years. I think Julie Andrews' voice is one of the best I have ever heard. I loved her in "The Sound of Music." Well, she is one of the actors who had surgery for some type of vocal cord dysfunction. She spent years performing on stage in the theater and that was probably the cause of her condition.