I'm watching the women's long jump at the 2015 Beijing world athletics championship, and don't understand why they keep using the phrase, "It's a fast track so some of the girls are struggling with it." Surely the track is the same length as other tracks? It has to be flat, so it would not be down hill. I can't understand what would make it faster then other tracks. Is it simply that there is a strong back wind pushing them forward thus adding more momentum?
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.
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. 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.
Specifically for the long jump, the issue for the competitors is their starting marks. They set themselves up very carefully for their jumps in order to make their last stride as close to the board as possible without being on it (i.e. fouling).
As @steelerfan's answer explains, a "fast" track or runway is giving the athlete more "return" for the force they apply to it, which means more of the energy they produce goes to pushing them forward (instead of being absorbed by the track). This usually means a track which feels "harder," because it is pushing back more on the athlete. A softer or springier track usually isn't as "fast". The differences are usually incredibly small.
If the runway is "faster" than they expect, they're getting more energy return from the runway and taking slightly longer strides than they allowed for when setting their mark. This very small additional distance, repeated for each stride, could put their takeoff onto the board and cause a foul.
So while a "fast" runway is nominally a good thing, it can lead competitors in the horizontal jumps (long jump and triple jump) to foul more often.