It seems to me that the thing being missed out from a lot of this discussion is periodisation. Several people have said that to race fast you have to train fast. Well, that's true to a certain extent, but you also have to build the reserves of endurance and aerobic fitness - conditioning, basically - that will allow you to absorb the effects of harder training effectively and without getting injured. I've seen lots of my clubmates who have read all about their three key sessions - tempo run, intervals and long run - and go on doing the same things week after week. And then they wonder why they plateau!

For a lot of amateur runners, it isn't necessarily true that you have to train faster to race faster. For someone with a relatively low volume of mileage in their background, it may well be that they can get faster simply by improving their aerobic fitness and endurance: I've done this myself. I think it's more accurate to say that you have to train fast to race fast assuming that you already have a high level of aerobic conditioning.

Aerobic/endurance training works over months and years. Speed training works over weeks. A good training programme will include a period of high-volume, low-intensity aerobic work, followed by higher-intensity threshold work, followed by sharpening interval work in the weeks before a race. Lots of runners are looking for the one key session that they can do week after week in order to keep improving. It doesn't exist. A training plan should be based on progression: you won't be doing the same things at every stage of the training.