Sort of tiring, but exhilarating:
Spending the entire day in the operating room.
Sometimes difficult, but not too bad:
Spending two hours making patient-related phone calls.
Spending all day in clinic.
Tiring and also painful:
Spending two hours dictating the charts of the day in clinic.
Spending all day teaching six periods of high school health class on the dangers of smoking.
I really respect teachers. How do they do it?