Kenya's Dennis Kimetto running in the 2013 Tokyo Marathon.

Aflo Co. Ltd./Alamy Stock Photo

What will it take to break the 2-hour marathon?

*Update, 8 May, 12:21 p.m.: On Saturday, Kenyan runner Eliud Kipchoge came closer to breaking the 2-hour marathon barrier than any person in history, racing 42.2 kilometers in just 2 hours and 24 seconds. The feat—more than 2 minutes faster than fellow Kenyan Dennis Kimetto’s record-setting run at the 2014 Berlin Marathon—capped years of work by scientists in Nike’s Breaking2 project, an effort to engineer runners and racetracks to blow through the elusive barrier. Still up for debate is whether Kipchoge’s performance will be recognized by the body that ratifies marathon times, the International Association of Athletics Federations. While they deliberate, find out what researchers are doing to engineer the perfect runner, as detailed in this story below, originally published online 3 March.

The 4-minute mile, Tony Hawk’s 900, Babe Ruth’s home run record: The statistical calculus of sport contains barriers that once seemed to be iron but proved to be glass. Will the same hold true of the 2-hour marathon? Scientists and engineers in a group called Sub2 have been pushing toward the goal for years now, and in the past few months, major players like Nike and Adidas have announced projects aimed at bringing down the barrier. But running 42 kilometers in 120 minutes remains elusive.

So what will it take to push athletes over the hump? Science interviewed marathon experts to learn what makes this challenge so difficult, and whether we’re truly nearing a watershed moment for the sport.

How much faster do we need to get?

Kenya’s Dennis Kimetto holds the world record for the marathon at 2:02:57. Two other runners, Kenenisa Bekele and Eliud Kipchoge, have recorded times below 2:03:10. Shaving 3 minutes off those times amounts to roughly a 2.5% performance improvement. Although that might not seems astronomical to the casual runner, Ross Tucker, a sports scientist at the University of Cape Town in South Africa, points out that professional marathon runners are far from casual. “That magnitude (2.5%) of improvement in performance at the elite level is absolutely enormous.”

To get faster, the runner must either become more powerful or more efficient, or the course must become easier.

How do we make the runner more powerful?

The main measurement of a runner’s power is VO2 max: the maximum volume of oxygen per unit of body weight that the athlete can use in a minute. Elite marathon runners tend to use about 80% of maximum during a race. Average people can increase their VO2 max by training at high intensity over sustained time periods, but the ceiling for VO2 max is determined primarily by genetics, and there isn’t much that can be done to raise it without turning to performance enhancing drugs.

Blood doping, especially with erythropoietin, can increase VO2 max by artificially inflating hemoglobin levels, but the practice is illegal in marathon running, and all the groups claim they’re commited to cleaning up the sport of running. That means runners will probably have to become more efficient instead of more powerful.

How do we make the runner more efficient?

Running is filled with inefficiency. Only about 45% of the power generated by our legs actually pushes us forward; the rest is dissipated as the foot strikes the ground. One way to improve a runner’s efficiency is to return more of that energy to the legs with every stride, perhaps with some sort of spring-loaded footwear. “Nike has applied for a patent recently for springs in shoes,” says Tucker, “and I think that’s what they’re gonna do.”

At the Dubai Marathon in the United Arab Emirates at the end of January, Bekele ran with a new prototype Nike shoe that insiders, including Tucker, thought may have contained just such a new spring technology based on its thicker midsole. But Bekele fell early in the race and did not finish.

Last Friday, Adidas introduced a new shoe—the Adizero Sub2—that doesn’t rely on springs but uses a special kind of foam the company claims is 1% more efficient than other footwear. This “Boost” technology has been around for a few years now, but the new Sub2 shoe is 150 grams lighter, which Adidas thinks could be worth another 1%. Kenya’s Wilson Kipsang snagged first place at the Tokyo Marathon last weekend (yet still fell nearly 4 minutes short of the 2-hour barrier) in the new Adidas shoes and set the record for the fastest marathon ever run on Japanese soil.

Still, Peter Weyand, a biomechanist at Sub2, doesn’t think springy shoes are going to be the answer for breaking the barrier. “I would say that there’s a long, long history of trying to put springs in shoes that has had either a minimal benefit or none at all,” he says. “That’s not an easy trick.”

The Sub2 project is focusing on improving physiological performance rather than footwear, says Yannis Pitsiladis, the founder of the Sub2 group and a researcher at the University of Brighton in the United Kingdom. He thinks the marathon performance is far from optimized, noting that many elite East African runners do not make use of new technologies like fitness trackers or perfectly optimized training and diet schedules. He points to hydration as an area neglected in the sport until now, but like spokespeople for other projects, he’s cagey about the specifics. Ultimately, he says that it won’t be one major advance, but many small ones across multiple areas of science that bring the 2-hour barrier down.

How can we make the course easier?

An all-downhill course in ideal weather—preferably a stiff tailwind—might do it. Running below sea level could also help, because oxygen concentration increases as altitude decreases, making breathing more efficient. Pacers could run part of the course at a sub–2-hour pace, allowing the racer to cut air resistance by running in their wake. “That might be worth 1% or 2%,” Tucker says.

The downside of such measures is that the International Association of Athletics Federations might not certify a record-setting run. In their pledge to break the 2-hour barrier sometime this year, Nike admitted that their time would not be record eligible. Tucker and the Sub2 group suspect that the company plans to manipulate the course and conditions in their favor. Nike did not respond to a request for comment.

Is this a realistic goal for the near future?

Performance jumps of about 2% are not unprecedented in modern sports. Usain Bolt has brought the record for the men’s 100-meter sprint down from 9.74 seconds to 9.58 (1.7%), for instance. But Tucker points out that there has already been a 2% increase in marathon performance over 15 years. “We’ve already seen 2 minutes taken off it, and now we want to see another 2.5 minutes or 3 minutes taken off?” Tucker says. “We want to do a double Usain Bolt on the marathon record?”

Still, Pitsiladis is optimistic. If all goes well and his team can secure enough funding, he thinks that it can break the 2-hour barrier by 2020 without relying on spring shoes or other gimmicks. “Whatever we do, we will be guided very much by what will be a record that will be ratified,” he says. “I have no doubt whatsoever that this will be done.”