True, if Elvis was only performing one show a night...but he was doing 2 shows a night, 6 nights a week in Las Vegas and 1 show on the 7th day. That's 26 shows in 14 days....definitely a lot of pressure for Elvis to keep up, especially with the energy he exerted on stage.
And again, let's not forget that one of the reasons for the hectic schedule is because rumor has it The Colonel had huge gambling debts to pay off and if Elvis wasn't working, he wasn't making money. And as we all know, The Colonel was only after one thing...
Another aspect of that is the ticket prices that The Colonel charged for an Elvis Presley show. Elvis was always of the mind that the ticket prices needed to be kept low so that his fans could afford to see his concerts. If Elvis were touring today, certainly a ticket to one of his shows would cost exorbitantly more than they did in the 70's.
This, of course, also plays into the whole situation of The Colonel booking Elvis for as many shows as he possibly could. With the lower ticket prices that Elvis required, The Colonel needed Elvis to perform as much as possible to make as much money as possible!
TCB!
Mike