Running a marathon in under two hours has become the Holy Grail for the sport.
The apparent difficulty of breaking the two-hour mark has led some to suggest that today's long distance runners have hit some kind of natural barrier in human ability that may not be overcome for decades, if at all.
But a team of researchers from the University of Colorado, Boulder and the University of Houston suggests the goal is within reach, if the conditions are right, and if runners use a special set of techniques.
They published their results Monday in the journal Sports Medicine.
The closest anyone has even come to the mark is Kenyan runner Dennis Kimetto, who set a record of 2 hours, 2 minutes and 57 seconds at the Berlin Marathon in 2014.
Since then, few runners have come even close to the time, and running organizations, fitness companies, and running magazines have contemplated how the record might be broken, and in some cases, thrown their own efforts behind it.
Nike, for example, announced its Breaking2 initiative in December, its effort to help runners beat the time. Nike identified three athletes best poised to achieve the goal: Eliud Kipchoge of Kenya, Lelisa Desisa of Ethiopia and Zersenay Tadese of Eritrea.
Adidas has been said to be working on its own, similar project, and developing a shoe optimized to beat the time.
"People have been thinking about the magical sub-two-hour marathon for a long time," said the study's lead author, Wouter Hoogkamer, a researcher at the University of Colorado in Boulder, in a press release. "Our calculations show that a sub-two-hour marathon time could happen right now, but it would require the right course and a lot of organization."
So what do they think it would take?
Start with lighter shoes.
Hoogkamer and colleagues said the runner would need shoes roughly roughly 3.5 ounces than Kimetto's world record shoes, which were just over eight ounces each. Hoogkamer and colleagues showed in a previous study that simply reducing the weight of shoes to about 4.5 ounces shaved almost a minute — 57 seconds to be exact — off a running time.
The design of the marathon course would also play a big role in helping runners beat the two hour mark.
The would-be record-breaker would also have to run behind a pack of other runners in a straight line — a technique known as "drafting" that helps rude wind resistance and propels runners forward — for about the first half of the race.
Drafting is typically seen more in cycling races than in running, where the formation has been known to dramatically reduce the amount of energy each athlete needs to expend.
The researchers cited a study from 1971 that showed an athlete can reduce wind resistance by 93 percent, simply by running behind another runner. The current study suggests that reducing wind resistance by a mere 36 percent would be enough to earn a time of 1:59:59 for an athlete already capable of finishing a marathon with 02:03:00, which is three seconds longer than Kimetto's record.
It would also help if these first 13 miles of the the marathon's total 26.22 miles took place on a loop that ran through some kind of environment that protected from winds, like a forest.
The second half of the race should follow a slight downhill slope, and the runners would have to continue using the drafting technique, shaving another 3 minutes off the record. Alternatively a 13-mile per hour tailwind could help push the runners forward enough to cut down the total time.
The researchers note that some of these suggestions are not new, but say they are the first to calculate exactly how much time each measure would shave off a total running time.