I suppose that technically, these are two separate topics, but for swordwork in particular, they are intimately bound up with one another. Have you ever read books where it seems that the hero has all the time in the world to swing a sword around, or where one of the people in a swordfight seems unfeasible quick compared to another? It seems unrealistic that someone should have so much of an advantage, doesn't it?
It's not fiction, though. It does happen. I have had the joy of fencing against a few internationals now, and on occasion, it really did seem like they were moving twice as fast as I was. So fast, in fact, that I was stuck between moves while they hit me. When I attacked, it seemed like they had all day. They weren't really that quick, of course. They were simply slightly closer or further away than I thought.
Despite what some martial artists occasionally think, one thing is true: in the absence of contact to control an attacking limb/blade, if the other person is close enough, they will hit you almost regardless of what you do, because you simply do not have the time to react. If the other person is far enough away, by contrast, you will have all day to plot your defence.
That's why in swordplay, a big part of what the best people do is based on using tricks such as acceleration, rapidly changing direction (by bouncing in the case of much sport stuff) and generally creeping up to completely control the distance between them and their opponent. They show up slightly closer than you expect when they attack, and they keep you right on the edge of distance defensively, so that you think you're close enough to attack, but you aren't. So the next time you want one of your heroes to seem impossibly fast, just have him move forward a bit first.