The rarity of the negative split in marathons, and the art of blowing up

One of the most common tips virgin marathoners hear is that they should try to run negative splits. That is, you should run the second half of the marathon, miles 14-26, faster than you ran miles 1-13. This has a few different levels. It means you shouldn't go out in a pace you can't maintain, and it means you should have enough left in your tank to run strong in those painful late miles. Patience to go out sanely, endurance to push through the end.

In theory, it sounds wonderful. In practice, it appears to be really, really damn tough. In my three marathons -- each of which I was undertrained for, I admit -- it was impossible. I'm a Blow Up Right Around Mile 20 All-Star; I've never had a positive split less than 10 minutes in my fulls. And I'm not alone. I pulled the results data for the 2012 California International Marathon run a few weeks back. (This was the race in which "swum" was more accurate than "run.") Of the 3,330 male finishers whose splits were properly recorded and displayed in the final results, 2,928 ran positive splits. That's 89 percent of the male finishers who ran slower in the second half than in the first.

So much for the negative split.

Of course, it makes sense that most runners would run slower in the second half despite all advice to the contrary. Injuries happen. Lots of people finish through injuries, but obviously are forced to slow down. The Wall is real, and so few runners train beyond 20 or 22 miles in a marathon run-up that suffering from late-race exhaustion seems widespread. There's also the possibility that despite all of the advice to go out slow and sane we don't follow through. That was my problem at San Francisco last July. I was crazy undertrained, went out loving life and attacking the hills during the beautiful half of the course and fell completely apart.

It appears this happens to a lot of us. For what it's worth, the average positive split among male finishers at CIM was 16:19. That's a big split. The average negative split was 3:18. Barring inaccurate splits -- always a possibility -- there were five negative splits of more than 20 minutes. Four of those five dudes were master's runners. Two were older than 60. Of course. Wise men.