Have you ever been in a fight that went longer than 30 seconds? Hell, have you ever been in a wrestling match with your brother or best friend that went longer than 30 seconds? It's a fucking nightmare for the cardiovascular system with all that tussling and jockeying for position. At the end of it all you're out of breath, sweating profusely and -- depending on your possible state of inebriation -- in need of a good yack. It's enough to make you tired just thinking about it.
Add about ten pounds of hockey equipment, some ice skates, thousands of screaming fans and a running time of over two minutes and you get the following video. Kind of adds a new element to the whole "Shit, I'm tired!" aspect don't you think?