I never believed that...the 10 or 20lbs swords that I'd heard about. Not even as a kid. Of course, kids these days will base what they know off of the latest video game...take Skyrim for example. Your average singlehand sword weighs in at around 12-18lbs depending on what its made of; two handed swords can get upwards of 30lbs. I guess in a game that's cool, but in real life? NAAAAHHHH.
One of my old favorites is Ladyhawke and I like watching it now because they really tried to bring some life into that old 10lbs greatsword type of fight...now, it is hilarious to watch. And I could almost believe that the swords used by the actors must've weighed nearly that much, judging the movements and obvious exhaustion from wielding those monstrosities.