A person get tired when he stand for 2-3 hours holding a briefcase as he do not cover any distance

Do you have a question? If it's about the definition of work in physics and how is it that a man can do no work and yet get tired the reason is because even though no work is done on the briefcase the man's muscles are are expending energy maintaining tension. It's a consequence of the inefficiency of the human body. Similar to how an automobile sitting motionless in a parking lot with its engine idling performs no work, and yet it will eventually run out of gas.