September 28, 2014 update: This piece was written in the aftermath of last year's world record at the Berlin Marathon. Despite the record being lowered to 2:02:57 at this year's Berlin race, the author stands 100 percent behind the rationale underlying the article, which remains as it was when published (i.e., it uses numbers based on the world record being 2:03:23). But one new fact to note: Four years elapsed between the first sub-2:06 and the first sub-2:05. It then took five years for the record to go sub-2:04. And then it took six years for the first sub-2:03. The faster the record gets, the more difficult it gets to reduce it by a minute. Sub-2:00 on a record-eligible course is still many years away.

Whenever the men's world marathon record is broken these days, you can count on two things in the immediate aftermath: The new record holder will pose in front of a clock stopped at his new mark, and people will say that a sub-2:00 marathon will be run soon.

Sorry to be a nattering nabob of negativity, but a sub-2:00 marathon on a record-eligible course won't happen for many, many years.

On the surface, it seems reasonable to think a 1:59:XX marathon is imminent. After Wilson Kipsang ran 2:03:23 in Berlin on Sunday, even people as informed as Michael Joyner, M.D., who has calculated world-record progressions, couldn't help themselves from writing things like, "There are only 204 seconds left to get to two hours."

Here's the clearest way to think about it: Kipsang lowered the record by 15 seconds, or approximately .57 seconds per mile. If someone were to lower the mile world record from its current 3:43.14 by .57 seconds to 3:42.57, no one would think, "Gosh, a 3:34.79 mile is just around the corner!"

But that's the equivalent of what's happening with the sub-2:00 marathon talk. The record being lowered by .57 seconds per mile is taken to suggest that taking it down by another 7.78 seconds per mile (204 seconds divided by 26.2 miles) will happen soon.

To further put into perspective what taking 7.78 seconds per mile off a record means, consider that doing so would lower the 5000-meter world record from 12:37 to 12:13, the 10,000-meter mark from 26:17 to 25:29, and the half marathon record from 58:23 to 56:41. Those times might come someday, but nobody knowledgeable about distance running talks as if they're near-future certainties.

If you find this line of reasoning unconvincing, consider a slightly different physiological take, courtesy of the excellent blog The Science of Sport. As Ross Tucker, Ph.D., puts it:

"[T]he currently best runners on the planet are hovering around 59-minutes for half the distance that people expect them to run in a marathon, at the same pace. It's a little like expecting Usain Bolt, with his 19.19s 200m best, to go out and run a 400m, slow down just a little, and run a 41s World Record.

Or it's expecting David Rudisha, who can run a 400m in 45s, to hold a pace of 46s for two laps and run 1:32, rather than his 1:41 for 800m. It just isn't going to happen, and the reason is that the pace we can run for a given distance decreases in a predictable, physiologically 'constrained' manner as the distance increases.

So a man who runs a 59-min half marathon will not be able to sustain two back-to-back 60 min half marathons. It's just not possible. And so therefore, before we can even consider the sub-2 hour marathon, we need to look at the ability over the half marathon. Until humans can run a half-marathon in under 58-minutes (and here, I'm talking low-57), it will not be possible to produce 59:59 twice in a marathon.

This is usually the point where someone counters, "Supposed experts also said breaking 4:00 in the mile was impossible." We'll set aside that those statements were made mostly by medical doctors with no real knowledge of running. Instead, we'll merely point out that, when Roger Bannister ran 3:59.4 for the mile in 1954, the world record for 800 meters, or just short of half a mile, was 1:46.6. Bannister didn't need to run a world-class time just to get to the halfway point of his goal, as someone trying to break 2:00 in the marathon in the near future would have to.

Concludes Tucker, "Bottom line is that talking about a sub-2 hour performance after seeing a 2:03:38 improve to a 2:03:23 is just not feasible. The next barrier is 2:03, and I'm sure will go within five years. Then we can begin to work towards 2:02, which will take another ten years, perhaps."

Scott Douglas Scott is a veteran running, fitness, and health journalist who has held senior editorial positions at Runner’s World and Running Times.

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