Photograph by Nike
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Eliud Kipchoge finishes the Nike Breaking2: Sub-Two Marathon. His time was 2 minutes and 32 seconds faster than the current world record.

Photograph by Nike

Runner Comes Excruciatingly Close to Breaking Two-Hour Marathon Barrier

Science has learned a lot about humans and endurance running. But the goal of going even faster during a race has remained elusive.

Finishing a marathon in under two hours remains a barrier to be broken.

Kenyan runner Eliud Kipchoge fell just 25 seconds short on Saturday, in a marathon that saw three athletes attempt to break the two-hour barrier in Italy.

Kipchoge was trailed by Ethiopian Lelisa Desisa, who has won the Boston Marathon twice, and Eritrean Zersenay Tadese, who holds the world record for the half-marathon.

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Coach Haji Adillo passes water to runners midway through a 22-mile ​(35-kilometer) ​training session on the outskirts of Addis Ababa, Ethiopia. Such ​"​long runs​" ​are a key element of building the muscular and cardiovascular endurance necessary to compete as an ultra-fast marathoner.

Kipchoge did, however, make running history. The previous record for completing the 26-mile run was set by Dennis Kimetto, who ran a marathon in 2:02:57 at the 2014 Berlin Marathon.

The event was staged by Nike, which created the Breaking2 project in 2014 with the goal of breaking the elusive two-hour time barrier. The race, which took place near Milan, on the Monza Formula 1 racetrack, was closed to the public, but hundreds of thousands tuned in to a livestream aired by Nike, and countless more weighed in on Twitter used #Breaking2.

All three athletes plan to continue competing.

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Eliud Kipchoge (center) ​runs ​in cruise control during ​a half-marathon (13.1​-​mile) test attempt, trailed closely by Zersenay Tadese. Setting a high but not-too-fast pace at the beginning of a marathon allows racers to marshal critical reserves they'll require to increase their speed in the second half of the race.

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Lelisa Desisa runs at ​an altitude training camp near the Entoto Forest outside of Addis Ababa, Ethiopia. ​"​Train high, race low​" ​is a central tenet among elite runners, as training at several thousand feet above sea level boosts the body's red blood cell volume​—​​and oxygen carrying capacity​—in response to thinner air.

Asked after the race how he plans to shave 25 seconds off his time, Kipchoge said it would take "good training and good preparation."

Scientists have been working hard in recent years to unlock clues about what makes these elites so fast. Their research is leading to new insights on what sets the best runners apart and how to help them maximize their abilities—as well as keeping hobbyists healthier throughout the miles.

Slow and Steady Wins the Evolutionary Race

In 2004, Harvard University evolutionary biologist Dan Lieberman co-authored a paper which posited that modern humans’ long legs, short toes and muscular rear ends—all useful for walking—also evolved two million years ago as an adaptation for running. A combination of speed and endurance would have allowed ancient hominins to beat rivals to a distant carcass for scavenging, for example, or to wear down prey over time and distance.

Today, Lieberman continues to study the mechanics of human movement, particularly focusing on how running with minimal footwear, or none at all, is more in line with the way our feet evolved to function. (Get tips on barefoot running on National Geographic’s Adventure site.)

In a recent study of the running styles of members of the Harvard track team, Lieberman and his colleagues compared injury rates between runners who mostly land on the ball of the foot and rearfoot strikers, who hit the ground heel-first. Forefoot runners’ legs absorb and distribute strike forces much differently than rearfoot strikers; although forefoot runners weren’t immune to injury, Lieberman found that rearfoot strikers were 2.3 times more likely to become injured.

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A phalanx of racers from Ethiopia and Kenya lead Eliud Kipchoge and Zersenay Tadese down the back stretch of the 13.1-mile test attempt in Monza, Italy. By periodically 'drafting' behind other runners throughout the race, the Breaking2 competitors experience less drag from wind resistance that slows and tires them.

“People today run differently than they used to, between big, cushioned shoes and sitting for long periods of time,” Lieberman says. “Running is a skill, and we don’t teach that anymore.”

Lieberman insists the approach, joined with proper form and technique that could take months or even years to learn properly, could be key in improving performance as well as preventing many common running injuries and ailments. But critics say it just changes the kinds of injuries runners will still ultimately experience.

“Barefoot running has been touted as improving strength and balance, while promoting a more natural running style,” the American Podiatric Medical Association said in a statement in 2014. “However, risks of barefoot running include a lack of protection, which may lead to injuries such as puncture wounds, and increased stress on the lower extremities. Research is ongoing in regards to the risks and benefits of barefoot running.”

The fact remains that no matter their footwear, some runners seem innately able to cover distance very, very quickly, and research into the hidden processes powering their runs is helping us to understand why.

The Big Three

It has long been suspected that there may be some hereditary or genetic aspect to what, exactly, makes East African runners so exceptional. It could also be that running is just a way of life in the impoverished villages from which many of these runners originate—or a path out of poverty, as big race winners bag millions in prize money.

But so far, efforts to identify genetic factors have been inconclusive. Scientists need to catalog and study the genetic makeup of a larger number of runners to determine whether there are combinations of genes that might be responsible for high performance, according to a study by Yannis Pitsiladis, professor of sport and exercise science at the University of Brighton. He’s also leading a separate under-two-hour marathon research project, called Sub2, as well as the Athlome Project, a global effort to characterize healthy human function and disease by studying the genetics and adaptations of elite athletes.

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Lelisa Desisa runs out the dying moments of the day outside of Addis Ababa, Ethiopia.

Genes aside, three physiological elements have emerged as most important for allowing hyper-elite runners to outstrip the pack: oxygen consumption, lactate threshold, and running efficiency. And though there are plenty of examples of athletes with one or two of these kingmakers, all three seem not to exist in one person in an ideal ratio.

In 1991, Mayo Clinic researcher Michael Joyner derived a hypothetical best marathon time possible by someone with maximum values of all three factors. He came up with a time of 1:58:57.

Runners can improve two out of the three. Oxygen utilization can be boosted by training at higher altitudes, which bumps up red blood cell production and allows the blood to carry more oxygen. Resistance and interval training can improve the lactate threshold, or the point at which muscles begin to fatigue and fail. But running efficiency, or economy, didn’t seem to be something that could be improved through training.

Running economy is much like gas mileage in a car: how much energy you expend relative to your speed. It’s different from person to person, and if it improves in an individual, it’s usually over long periods of time. (See how ultrarunners tackled Bhutan’s mountains in “Chasing a Speed Record on One of the World’s Highest, Hardest Treks.”)

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Running behind a group of elite pacers, Eliud Kipchoge calmly moves through the first miles of the 13.1-mile test event in Monza, Italy. One tactic to run a faster marathon: ​R​unners don't go all-out until race day. Careful studies of ​"​tapering,​"​or optimizing the body's exercise and recovery cycles, has resulted in individualized training regimens for each of the three runners attempting the feat on May 6.

“There’s been a concerted effort to maximize the efficiency part of the equation,” Joyner says, adding that the Nike project might be one of the most complete attempts to date to optimize all three values in the three racers. With performance data it has gathered on its runners, Nike’s team of scientists has made customized recommendations for each competitor, including how much, when, and what kinds of carbohydrate-based fuels to consume to keep them powered up during their Italian trial.

Elsewhere on the efficiency front, Joyner points to research that indicates overly long strides may have a negative impact and other studies that show that limber runners may also have reduced economy. “Stiffer muscles and tendons store energy, and there’s some evidence you don’t want to be too flexible if you want to be fast,” Joyner says.

Because scientists can’t exactly run alongside their study subjects and prick fingers for blood every few minutes to test their physiological state, treadmill lab values that predict marathon times well under two hours tend to break down during field trials. But if the intense data-gathering on the elite African runners has not completely filled in the gaps, it has helped identify new areas for study.

Among these unknowns is what makes for endurance. “From a physiological standpoint, there’s a lack of information on what happens with runners later on in a race,” says Andrew Jones, professor of applied physiology at the University of Exeter and a collaborator on Nike’s Breaking2 project.

“Just by numbers, there should be plenty of people out there who could beat that two-hour mark,” Jones says. But clearly, he says, something is changing in runners’ bodies during a long race, and studying these changes could help strengthen endurance, for example by improving nutrition during a race.

And just as athletes in recent Olympic Games have broken world records in part by sporting advanced new gear and tactics, the Breaking2 runners will be shod in a new, lightweight shoe with a carbon-fiber plate. The runners will also employ careful drafting behind pacers, who run ahead for short periods of time to create a smooth slipstream for the competitors. Whether those strategies will translate to significant improvements in performance on the course will have to wait until race day.

Head in the Game

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Lelisa Desisa runs into the rising sun with his training group near Sululta, ​a high-altitude training camp near Addis Ababa, Ethiopia.

A final, relatively understudied area of influence that may have an outsize effect on high-performance runners is psychological training.

Steve Magness, a professional and collegiate running coach and author of the book Peak Performance, says that a runner can almost always give a little bit more than what they believe their maximum effort is. More study is needed on the psychological factors that contribute to—or hinder—that maximum.

“In the marathon, you’re dealing with someone running really hard and fast for two hours,” Magness says. “There needs to be a better appreciation not only of the physical fatigue, but the mental fatigue of being alone in your head for that time and fighting through that effort.”

In the meantime, advises Lieberman, don’t worry about breaking any world records. Just get out there and enjoy doing what your body evolved to do well: Going for a run.

Follow Michelle Z. Donahue on Twitter.

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Kenya's Eliud Kipchoge crosses the finish line of a March half-marathon test event in 59 minutes and 17 seconds. During Nike's Breaking2 marathon event, he narrowly missed breaking the two-hour marathon barrier by 25 seconds.

Editor's Note: A previous version of this article misstated the nationalities of Tadese and Desisa.