My daughter can chase me around the living room like this for hours on end. Just around and around and around. For maximum fun I have to stay about three feet ahead and act perpetually panicked. It's just as funny to her the 200th time around as it is the first. Eventually I have to call a halt because she will seriously never get tired of it.
Now before you think this is going to be some kind of tired Erma Bombeck horseshit about how my kid wears me out, and "where in the world do they get all the energy", it's not. For one thing, I don't believe for a second that a small child can actually "wear you out". The day a three year old can physically run me to the ground you may as well bury me there. Take a little kid and put them in any pick-up basketball game anywhere and see how long they last. I guarantee you that inside ten minutes they'll be either crying or taking a nap in mid-court.
So let's just put that one to rest right now: your kids don't tire you out because they have all this tremendous energy. They tire you out because they have all this energy for incredibly boring shit.