A two-hour marathon has long seemed unthinkable. But these charts show we're almost there.

Running a two-hour marathon requires running fast. Insanely, nearly unbelievably fast.

Each mile needs to take, on average, 4 minutes and 36 seconds to cover, moving at  a pace of about 13 miles per hour (just about a comfortable cruising speed for biking around a city). To put this in perspective, the current world record for the one-mile race is 3:43. A 2-hour marathon requires running each mile less than a minute slower — but doing it more than 26 times in a row. The average marathoner in most large races takes more than 4 hours to complete the course.

But some awesome new charts from Runner's World show how the 2-hour marathon actually doesn't seem totally crazy anymore. The world record marathon time has dropped quickly and consistently since 1998:

(Runner's World)

If a 2-hour marathon is going to happen, it will likely take some very specific conditions. Runners essentially need an assist from an easy course and perfect weather. Runner's World notes that most world records are set during cold-weather races; elite runners have their best races at 38.9 degrees Fahrenheit

The course will also need to be really boring, and flat. Marathoners, unsurprisingly, have faster times when they're not trekking up big hills. This is what makes famous courses like Boston and New York unlikely places for the 2-hour mark to be broken. This is the elevation profile of the New York course (which tens of thousands of marathoners are currently running in today's New York Marathon).

(Runner's World)

The course's record holder, Kenya's Geoffrey Mutai, was able to cover 95.9 percent of the course in 2 hours. Courses that have fewer 90-degree turns also tend to be faster, as runners don't have to slow down to switch directions. These things are small, but they matter when you're trying to run the world's fastest marathon.

This is why Runner's World settles on a little-known Polish course as the possible home for the world's first 2-hour marathon:

One unheralded race is in the tiny Polish town of Debno, where, since 2000, elite runners have finished 79.2 seconds faster on average than they do on other courses. Who knows what might happen if top racers showed up for a sub-two attempt in Debno, whose course follows straight country roads, and which comes in early April, when the average temp is just 42°F?

Check out the full Runner's World package here.

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