Here is a really good article on this subject:
When a track is designed for Olympic competition, the designers are going to make the track as “fast” as possible — which usually means that the track will provide a great deal of grip, but will be as hard as possible to allow the runners, especially sprinters, get the best push-off from the track.which usually means that the track will provide a great deal of grip, but will be as hard as possible to allow the runners, especially sprinters, get the best push-off from the track.
Now there’s one other trade-off that needs to be made. Sprinters typically want the track as hard as possible, while distance runners would like to see a bit softer surface. Sprinters are only on the track for a matter of seconds in their races, so they would prefer a very hard surface to get the most speed out of the track. Distance runners are racing on the track longer and would prefer more cushion. When the designers sit down to create the running surface, they need to decide if they’re going to make a preference toward sprinters or distance runners.
Anecdotally speaking, I’ve heard that some Olympic tracks — like Atlanta’s– were designed more with sprinters in mind so while many sprint records were set there, distance runners felt a little beat-up after racing on it. In Barcelona, I heard the opposite, that the distance runners really liked the track, but the sprinters didn’t feel it was fast enough.
So the Bird’s Next in Beijing? If you’re hearing that the track is “very fast”, you can probably read that to mean “very hard” — and very favorable to sprinters.If you’re hearing that the track is “very fast”, you can probably read that to mean “very hard” — and very favorable to sprinters. As we see lots of world records fall, like Usain Bolt’s world record in the 100M, it is probably an indication of a great surface for sprinters.