When do the world records stop

This is something I have been thinking about since the Olympics... at what point will it not be possible for human beings to swim or run any faster. There has to be a point where the human body just can't go any faster, no matter how much you train, what kind of things you put into your body (legal or not), etc. I mean it isn't possible to swim a 400 IM, for example, in 2 seconds (at least I don't think it ever will be) so where does it end? And when will that happen?