From Advanced Marathoning, by Pete Pfitzinger, page 125.

Most runners shouldn't try to run dead-even splits, because during the marathon you'll gradually fatigue your slow-twitch muscle fibers and will start to recruit more of your fast-twitch A fibers to maintain your pace. Unfortunately, these fast-twitch fibers tend to be less economical than your slow-twitch fibers in their use of oxygen. Therefore, your running economy will tend to decrease slightly as well. The result is that your optimal pace will be reduced during the latter stages of the marathon. 

For example, if your goal is to run 2:39 (notice that Pfitzinger puts a 2:39 runner in your hobby jogger category) for the marathon, then even splits would require you to run 1:19:30 for each half of the race. To run even splits, you would have to increase your oxygen consumption and lactate level as your fatigue level increases during the second half of the race. A more efficient pacing strategy would be to go through halfway in 1:18 because doing so would allow you to slow by 3 percent during the second half and still achieve your goal (So that would be a first split of 1:18 and a second one of 1:21. A difference of 3 minutes for a 2:39 runner). If you ran negative splits for the marathon, chances are that you ran more slowly than optimally during the first half of the race and could have had a faster finishing time. 

Brad, I'm in no way saying that there are no other ways to do things and that you are wrong. You are certainly a very successful runner, so you're doing something that works great for you. All I'm saying is that it's possible to do things differently and still be successful. In 15 marathons, I have never had a 20 minute positive splits, like you imply. My positive splits range from 2 to 6 minutes and fall within the Pfitzinger 3% allowance. It obviously works for me, as I've never met the proverbial wall, no crash, no nothing, and I've always finished in good enough times to allow me to BQ, despite still having some medical problems. Like you, I have always hit my goals (except twice, because of heat), I've done it 15 times. I also know how to read a book.

You're right that you're no master of the universe, because I had also predicted that that guy was not going to hit his 3:00 goal. It had nothing to do with his pacing. It had everything to do with his goal which was way too lofty based on his marathon training.

My best (and fastest) marathons have had negative splits.  If I have a positive split it's because my lungs are in trouble.  There is no way I can run on pace in the first 3-4 miles of a marathon.

 

Every runner is different and we all bring our history/medical conditions to the table. We must apply what works best for us.

True.  I was just giving it as an example of how different we really are.

 

OK, I'm never on RWOL, but I had to go find that thread. Yes his question was about pace bands, but in his OP he mentioned the races he has done, and his goal finish time. And when questioned on why he thought he could turn a 1:30 half into a 3:00 full with no experience at the distance & insufficient training, he stated he knew his capabilities, had motivation & determination, and that the basis for his goal time was  being challenged by someone. I don't think there's anything wrong with telling someone running their first marathon that those things may help you finish, but it is physically impossible to will yourself to a certain goal time if you do not have the fitness. He also said he welcomed people's comments, and they should feel free to rub it in if he did not meet the goal.

But he never listed his HM time or any of the PRs he had, which is why I assumed this thread spilled from marathoners or from another thread.

I wonder how much he thought about that thread in the last miles of that marathon??

From Advanced Marathoning, by Pete Pfitzinger, page 125.

 

Most runners shouldn't try to run dead-even splits, because during the marathon you'll gradually fatigue your slow-twitch muscle fibers and will start to recruit more of your fast-twitch A fibers to maintain your pace. Unfortunately, these fast-twitch fibers tend to be less economical than your slow-twitch fibers in their use of oxygen. Therefore, your running economy will tend to decrease slightly as well. The result is that your optimal pace will be reduced during the latter stages of the marathon. 

 

For example, if your goal is to run 2:39 (notice that Pfitzinger puts a 2:39 runner in your hobby jogger category) for the marathon, then even splits would require you to run 1:19:30 for each half of the race. To run even splits, you would have to increase your oxygen consumption and lactate level as your fatigue level increases during the second half of the race. A more efficient pacing strategy would be to go through halfway in 1:18 because doing so would allow you to slow by 3 percent during the second half and still achieve your goal (So that would be a first split of 1:18 and a second one of 1:21. A difference of 3 minutes for a 2:39 runner). If you ran negative splits for the marathon, chances are that you ran more slowly than optimally during the first half of the race and could have had a faster finishing time. 

I know how to read a book, but would prefer not to.  

That said that blurb from Pfitz leaves me wanting more, thanks for posting it!

I've read Pfitz... his opinion only reflects one school of thought.  There is no consensus on negative splits.  I think even or slightly negative splits are the way to go on a flat course.  It really depends on the course.  If it's a big downhill from the start and hills late in the race (like Boston), it makes no sense to run negative splits as you would be leaving chunks of time on the first half of the course.

 

As far as sharing race goals, I'm not afraid to share them but like to be a little vague

No consensus on negative splits, therefore no reason to be arrogant about it. 

ok, point taken

 

everybody, just do what works for you.  But if I was unhappy with my results, I'd be a fool not to try something new and different.

 

I wasn't implying that YOU are arrogant. I had someone else in mind.