Sports Nut

The Quest for a Sub–Two-Hour Marathon

Eliud Kipchoge almost broke the barrier. What does his race tell us about the limits of human performance?

Eliud Kipchoge
Eliud Kipchoge celebrates the Nike Breaking2: Sub-Two Marathon Attempt at Autodromo di Monza on Saturday in Monza, Italy.

Pier Marco Tacca/Getty Images

A version of this story originally appeared on The Science of Sport.

If the sub–two-hour marathon is the Mount Everest of human endurance performance in 2017, then Eliud Kipchoge has reached the ledge just beneath its summit.

Kenya’s Olympic marathon champion, and the world’s No. 1 marathoner, came within 25 seconds of dipping under the two-hour mark in Nike’s staged test event in Monza, Italy last weekend. That equates to a shade under 150 meters short of running the distance in less than two hours.

Expectedly, the performance has inspired much excitement, and the already lively debate about the prospects of a sub–two-hour race will only intensify as a result. What happens next in the quest to summit this mountain? To continue the analogy, now that Kipchoge has shown the way and put the ropes in place, how long will it take before another runner—or Kipchoge again—returns to finish the climb and reach the summit?

That depends on how flexible you want to be with your standards for what constitutes a legitimate marathon performance. The Nike event was highly stage-managed, and a few of the tactics used to “optimize” the conditions for Kipchoge make it ineligible as an official world record. This is why the world record still belongs to Kenya’s Dennis Kimetto, who ran 2:02:57 in Berlin in 2014, even though Kipchoge is now 2:33 faster over the distance!

The size of that gap between Kipchoge’s “theoretically optimized marathon” and the “real world record” tells you one of two things about the future of the marathon, depending on your perspective. Option one is that Kipchoge is so good that he has shown what is truly possible. “No limits,” as Kipchoge himself said. If you lean this way, then you would expect a genuine sub–two-hour race to happen soon without the carefully designed strategy we saw in Italy. Kipchoge is indeed the world’s dominant marathon runner, having now won seven of his eight races, including the Olympics, London, and Berlin, and scaring the world record once already. If anyone was going to move the event forward, it was him.

Option two is the realization that some of Nike’s tactics were so effective that they were worth between two and three minutes to Kipchoge. If you believe this, then the answer to the question “Where to next?” is that we’ll return to 2:02:30 or thereabouts, just a shade under the current world record, and actually get two to three minutes slower for the foreseeable future. It means that unless Nike (or someone else) designs another staged event like this one, the sub–two-hour barrier will remain safe for a while longer.

Telling these options apart requires that we unpack what we saw from Kipchoge and Nike over the weekend.

My opinion is that the single most effective tactic used on Saturday was to have Kipchoge run most of the distance close behind a Tesla vehicle onto which had been mounted a large wind shield pretending to be a clock.


There was no reason for the size of this clock, or the close proximity of the car to the runners, other than to block air. They even provided lasers to show runners exactly where to run for maximum benefit. This was the most egregious and obvious “cheat” compared to a normal marathon that Nike used in Monza. I’d have no major issue with humans pacing and sheltering another runner, but this was, in my opinion, a step too far, and worth most of the improvement we saw.

The benefit of this protection from the wind cannot be understated, but it’s tricky to calculate with great precision. It’s certainly not as large as you’d get on a bicycle riding in a large peloton, but it is not insignificant either. It is estimated that a runner at two-hour–marathon pace spends around 15 percent of his energy overcoming air resistance, and so reductions in that would be expected to produce time savings by virtue of freeing up more power to actually run. Quite how much is the question.

Have a look at the calculations, which I’ve created based on a highly informative Twitter exchange with Dan Bigham.

Ross Tucker and Dan Bigham

What Bigham did was to estimate the time savings, in seconds, for a runner going at elite marathon pace, with the assumption that 20 percent of the cost of overcoming air resistance can be eliminated.

I’ll try to break down the process for you:

You start with the time and speed. For my calculation, I’ve taken a guy running a 2:02 marathon, which is a speed of 5.76 meters per second.

Next, you need an assumption of what the power output is. This doesn’t make a huge difference to the overall outcome, because it’s all relative anyway, but Bigham has used 5.5 watts per kilogram and a mass of 55 kilograms. That gives you the runner’s power output in watts (302.5).

Now, part of that power output is “running power” and part of it is “aero power.”

Aero power, or the power needed to overcome air resistance, is a function of drag (Cd, the drag coefficient), the athlete’s frontal area (A), and his running speed (V) as described by the equation Aero Power = 0.5 x air density x CdA x V3. For the conditions in Monza, air density is 1.239 kilograms per cubic meter, which I’ve used in the calculations. Using a CdA of 0.4 (the same as an upright cyclist, so a reasonable assumption, I think) gives an undrafted aero power output of 49.9 watts. This is the work required to overcome air resistance in a nondrafted scenario. Note that it is 16.5 percent of the total power output. The remaining 83.5 percent, or 252.6 watts, is the run power in the undrafted situation.

Next, we have to make an assumption about how effective drafting is at reducing that “aero power” component. For this, Bigham has assumed that 20 percent of the aero power can be eliminated by drafting. That means the 49.9 watts comes down by 20 percent, to a new value, called the “draft aero,” of 39.9 watts.

That means the draft run power is now 302.5 – 39.9 = 262.6 watts, which means the athlete can devote an additional 10 watts of power toward running compared to in the undrafted scenario.

Next, we work out a ratio of the two run powers, again using that relationship between power and the cube root of velocity, and that gives us a “run coefficient ratio” of 1.013. This is the factor by which the velocity would increase in this 20 percent drafted scenario.

It means that the velocity of 5.76 meters per second would now be increased by a factor of 1.013, to a new velocity of 5.84 meters per second, thanks to an increase in the run power component when drafting. That in turn means a new marathon time of 7,226 seconds, or 2:00:26, and a time savings, in this scenario, of 94 seconds.

Here’s the big assumption, though: How much does drafting save relative to being undrafted? In the table above, the assumption is 20 percent. To give you a comparison, a cyclist in a peloton saves 40 percent to 60 percent, so this 20 percent assumption is quite conservative, but probably reasonable for a runner behind a large group of other runners.

So, what I’ve done next is show how the time saving would look if the drafting were even more effective. The graph below shows the expected time saving for a range of drafting efficiencies. Here you can see that if you assumed 40 percent saving, the time reduction in the marathon would be three minutes and three seconds.

Ross Tucker and Dan Bigham

Which is likeliest? I don’t know, so I won’t venture a specific answer, other than to say that in the normal marathon scenario, where you have a pack of elite runners accompanied by three or four pacemakers for 25 kilometers, I’ve seen estimates that it’s worth around one minute, or 10 to 15 percent draft efficiency (indicated by point A in the graph).

Therefore, I think it’s reasonable to suggest that running behind six pacesetters and the Tesla for 35 to 40 kilometers would be worth between 20 and 30 percent draft efficiency, which equates to an advantage of between 1:30 and 2:20 (shown by Area C in the graph).

Certain imperfect assumptions must be made, but to be conservative for the sake of a beneficial performance assumption for the runner, you’d say it was worth 1:30 (20 percent efficiency), and the projection would be that Kipchoge’s 2:00:25 was worth around a 2:02:00 had he not been able to rely on the car, shield, and six runners for basically the entire race.

The next avenue that Nike exploited was the shoe. This received much publicity in the buildup to the run, because the company had controversially claimed that it gave athletes a 4 percent advantage. They even incorporated the “4%” into the name: the Zoom Vaporfly Elite 4%.

I believe the International Association of Athletics Federations should ban the inclusion of any devices that may act as springs, and should regulate the midsole cushioning material, precisely because it’s impossible to quantify a performance advantage of this kind of tech. (This is the same logic applied to Oscar Pistorius; you do it on principle, not performance.)

Anyway, on this shoe, I think it’s safe to say that it is not worth 4 percent; if it were, we’d have already seen some eye-popping performances, because that shoe has now been used by enough runners over the past 12 months that we’d know. Remember that 4 percent for an elite male marathon runner is about five minutes. It would be obvious, a bigger effect than doping, if this is what all runners were getting.

That’s not to say that the benefit is zero. I suspect there is a small benefit, though here we have neither data nor theory to even allow an estimation. Adidas previously claimed that its Boost midsole was worth 1 percent in efficiency and around one minute in the marathon. Here, too, data on performance was lacking, but it probably wasn’t worth that alleged 1 percent boost.

Is the Nike Zoom Vaporfly Elite 4% worth an additional 0.5 to 1 percent? Possibly. Runners believe so, as do Nike’s marketing team and scientists. (No surprise there.) It’s also possible that some runners may be getting a little more while others get nothing; having responders and nonresponders to technology is common. I know that previous iterations of shoes incorporating springs have been highly variable, with some people getting worse and some a lot better.

Theoretically, if a runner gets a 0.5 percent advantage, then it plays out in much the same way the air-resistance advantage would. They can run at a given speed using less energy, or could use the same energy to run that little bit faster—this time perhaps 30 to 60 seconds faster in a marathon. The short answer here is that we simply don’t know if Nike’s shoe is worth any time at all, but reports from athletes and researchers says it is, and so this may have helped Kipchoge slightly.

Every runner knows that getting his in-race fuel strategy right in the marathon is key. I’m less convinced that this is a major source of advantage to most of these elite runners, though, because they are mostly getting it right already. There are not many instances of elite marathon runners—particularly when breaking world records—encountering any such limit to either hydration or fuel. Given that most of the marathon world records have been set with faster second halves than first halves, and without any “wobbly parts” where they slow down dramatically, it would seem safe to suggest that running out of energy late in the race is rarely a problem.

So while I wouldn’t dismiss it out of hand, and it certainly is a key factor in runners who are not getting it right, I don’t see much benefit over and above a normal marathon being gained by fancy carbohydrate drinks and free access to them. If this is worth 15 seconds in a marathon, I’d be surprised.

How about the selection of the course in Monza? The choice of track was primarily based on minimizing the number of turns and its pancake-flat gradient. There’s no doubt there is direct time savings when you can eliminate 90 degree turns. For you and I, running at our speed, corners and intersections don’t matter, but at 21 kilometers per hour, you’re looking at perhaps a second (about six meters) every time it happens.

Monza was perfect in this regard—no corners, only sweeping bends—so that may have been worth around 20 seconds in a marathon compared to most courses. (London in particular suffers from many sharp corners.)

We also heard much about the training support provided, but I find it difficult to believe that anything changed in the athletes’ preparation as a result. It was claimed that Lelisa Desisa had changed his approach a good deal based on feedback, but then he had the worst day of the three runners, finishing in 2:14. Performance is complex, so knowing the effect of a general or systemic intervention at the level of training is just about impossible. I think there is an arrogance to sports science that assumes it can improve on generations of wisdom and knowledge that East Africans have acquired about how to prepare for a marathon. Certainly, I doubt whether Kipchoge got any benefit.

Finally, the runners had arm-warmers, and supposedly state of the art clothing, and even wore stickers to reduce drag on their legs. If this was worth even two seconds in a marathon I’d be surprised. They got the Nike swoosh on display, though.

I’d conclude that the drafting effect of a car plus six runners provided the greatest benefit, in the region of 1:30 if you make what is a safe assumption. The course was likely worth up to 30 seconds, bringing a conservative estimate to 2:00 in total. If you want to be more generous, this would increase a bit because of hydration/fuel benefits.

We simply don’t know the effect of the shoes, but if that is worth even 30 seconds, then we have Kipchoge getting a total benefit of 2:30 if we’re estimating conservatively. More if you think the shoe is that effective, less if you are skeptical.

Eliud Kipchoge
Eliud Kipchoge crosses the finish line during an attempt to break the two-hour marathon barrier at the Monza circuit in Italy on Saturday.

Alessandro Garofalo/Reuters

If you settle at 2:30, that means his 2:00:25 is the equivalent of a 2:02:55, which you’ll note is a lot like the current world record of 2:02:57. That is some food for thought. For all the excitement about making a huge leap forward and redefining what humans are capable of in the marathon, his performance may end up reflecting what humans have already shown they’re capable of for the marathon!

It means, in conclusion, that Kipchoge didn’t so much break through the barriers of human endurance as partly bypass them. He did not get close to a sub–two-hour race because he overcame the potential limits of energy cost of running that fast. Rather, those potential limits were shifted slightly, moved aside compared to normal marathons, by the engineers and the Tesla, and then he took full advantage to get close to the summit. It is, to finish the analogy, like getting close to the summit thanks to the benefit of extra oxygen. This is a remarkable achievement, but not one that tells us anything about human potential in the classic sense of what a marathon involves.

As for the original question—“What next?”—I think we get slower before we get faster. I strongly suspect Kipchoge would, on a good day in Berlin, break the world record, and could probably run 2:02:30–ish. That’s my pick for best-case scenario in the foreseeable future, so I hope he runs the Berlin Marathon in good conditions in September.

That 2:02:30 is where we truly are in the marathon, without all the aids provided on Saturday. If Kipchoge does that, then let’s talk about sub–2:02, which might happen within three or four more years. But sub-two, legitimately, is still a ways off.

If we see another marathon “trial/test” like Monza, then I think sub-two might be possible, given the combination of benefits at around 2:30. Whether Kipchoge can do it again, I don’t know. It would have to be him, I think. There’s nobody else in the marathon who can, so it would be fun to see a similar event now, just to test that out.