teach English here in Shanghai. Most days we teach four or five classes per day, usually with several breaks in between. A tough schedule would include teaching three classes in a row without a break.
The other day, one of the other teachers at my school was covering some classes for a teacher who was on vacation. She wound up teaching six classes in a row that day. Towards the end of the day, I knew she must have been exhausted. To show my empathy and to give her encouragement, I asked her, "How are you doing? Are you ready to scream?" She stoically replied, "No, my throat is sore," and walked down the hall to her last class.