There's a great, and short, article in this months Runner's World under the Mind+Body section entitled "Think Fast" on page 47. I think it gets to the heart of a few issues that have come up in the last month or so, mainly pacing(negative v. positive splitting), neurological fatigue, and perhaps even quality X. The article has to do with the science of pacing and dealing with fatigue. The article suggests that most people think the best way to finish a given distance in the shortest amount of time without falling apart is to run by feel. "We decide whether to speed up, slow down, or hold steady based on how much discomfort we think we can handle. . . If you petered out midway through a run, most experts would say your body temperature go too high or there was too much lactate circulating in your blood." However, a growing number of experts seem to be hinting that there is something more complex going on. In short, they say when you get into a race your brain is monitoring different systems, calculating the race distance, and then working backwards to where you are in the race and then recalculating what your body can handle for the remainder of the race, either slowing you down, holding you steady, or speeding you up accordingly ... and that this is an almost subconscious process. They coin this 'anticipatory regulation'. The summation of the article suggests that you can over-ride such brain mechanisms by utilizing a couple different training techniques. Three primary suggestions: 1. Run often at race pace, even if for short distance to teach your body the pace, 2. run race pace at/near the end of your training runs to teach your body to deal with fatigue ... frequent experiences of fatigue get your body more in tune with its true limits, and 3. do negative split training runs where you run the 2nd half of your run faster than the first, this will train you to override your mind when it starts to slow down during the 2nd half of a race.
For those of you who don't get Runner's World you can view the article here
http://www.runnersworld.com/article/0,7120,s6-238-244--12848-0,00.html