34-year old Kenyan Eliud Kipchoge has become the first man in history to break the fabled two-hour marathon barrier, running 1:59:40 along the streets of Vienna in the early hours of Saturday morning. Although the mark is not an official world record, courtesy of a series of unsanctioned tactics such as an interchanging team of pacemakers, it’s the apex of a new marathon era that dawned on an Italian Formula One track in May 2017. The original Breaking2 attempt, a Nike initiative which was also rendered invalid due to similar tactics, saw Kipchoge fall an agonising 26 seconds short of breaking the barrier. Although purists lamented the attempt due to the carefully engineered environment, there is no denying that it sparked a paradigm shift in the marathon world. Just 16 months later, Kipchoge again surprised pundits by breaking the official world record, running 2:01:39 in Berlin to eclipse the existing record by over a minute. But it wasn’t just Kipchoge who was galvanised. In the months following the original attempt in Monza, the all-time lists have undergone a complete overhaul. In fact, 7 of the fastest 10 times in history have occurred since Breaking2, as well as 6 of the top 10 times by women. In September this year, Kipchoge’s compatriot Geoffrey Kipsang Kamworor broke the world half-marathon world record (58:01). Two weeks later, 37-year old Ethiopian Kenenisa Bekele was just two seconds shy of breaking Kipchoge’s world record in Berlin, in what most are describing as the greatest marathon comeback in history. The new age of marathon running has hit its stride, and it culminated today in Vienna at the INEOS159 Challenge. Although his performance is already being met with familiar scepticism due to the shoes and the pacing strategy, Kipchoge has officially run his way into the unofficial history books.
Armed with the experiences of Monza and Berlin, Kipchoge was on pace from the start and, despite a rough patch just prior to the 30km mark, never looked unlikely to break the barrier. Courtesy of the pacing team, Kipchoge rarely strayed further than two seconds either side of the optimal kilometre splits (official splits pending), and exploded over the last kilometre in typical fashion with a smile on his face. Despite comfortably breaking the barrier, the result was not a forgone conclusion. The spectacle, two minutes faster than the official world record, was a product of careful innovations and interventions that took shape over years.
Proponents of skill acquisition theory (shoutout to my LTU squad) will know that performance is generally limited by elements categorised into three domains - 1) the athlete (their anatomy and physiology), 2) the equipment (in this case, the shoes), and 3) the environment (factors such as temperature, air and wind resistance, and the course). By applying subtle, and not so subtle, manipulations in all three domains, substantial improvements in performance can be made. And that’s exactly what we saw today.
Constraint one: the athlete
Running at 21.1km/hr for two hours is a feat of remarkable physiology. Anybody who owns a Garmin will tell you that there are three pillars of long-distance performance. Maximal oxygen uptake (also referred to as VO2 max) is consistently identified as a determinant of endurance running performance. Elite distance runners have scores in the region of 70-85ml/kg/min, but the VO2 max all-time list is littered with Scandinavians, due in part to their affinity for cross-country skiing. The highest verified score stands at 96.7ml/kg/min set by then 18-year-old Norwegian cyclist Oskar Svendsen. However, the highest ranked Scandinavian is good for only the 166th fastest marathon of all time (a 2:05:48 by Sondre Nordstad Moen, in the months following Breaking2). Unlike VO2 max, running economy is a major source of difference between elite long-distance runners, and is suspected to be the domain where Kipchoge has an advantage over most of his peers. The marker refers to the oxygen cost of running at either a certain speed or for a certain distance. In other words, having a good running economy means having a low oxygen consumption for a given running speed, which allows athletes to use a lower percentage of their VO2 max while running at that pace. Finally, above certain intensity of running, lactate is produced at a faster rate than can be utilised as fuel or removed. The corresponding exponential increase in lactate when passing the so-called lactate threshold is not simply a cause of fatigue, but it does signal a shift in metabolic environment that is unsustainable. As such, the ability to exercise for long periods at a high percentage of VO2 max without overstepping the lactate threshold is a key determinant of marathon performance.
Despite all being fundamental, none of the above measures in isolation quite capture the intricacies of fatiguing exercise or the nuances of marathon performance. That’s why, in the lead-up to the Breaking2, lead physiologist Professor Andrew Jones emphasised the importance of the critical power threshold, using it as a guiding principle for both training prescription and race-pace strategy. Critical power (or critical speed) represents the border between sustainable and unsustainable running. Once an athlete exceeds critical power, they experience an unavoidable upward spiral in oxygen consumption and lactate accumulation, and a drastic decrease in running economy which is catastrophic for performance. According to Jones, it’s currently the most comprehensive marker available for predicting and explaining the physiology, and therefore performance, during fatiguing exercise.
In 1991, Dr. Michael Joyner created a now famous model for a sub-2 marathon. According to his model, an athlete with a VO2 max of 84ml/kg/min, a lactate threshold of 85% of VO2 max and a running economy equivalent to roughly 170ml/kg/km would run a marathon time of 1:57:58. None of these individual values exceed the normal limits expected from elite distance runners. Zersenay Tadese, the former world record holder for the half marathon, was one of three athletes hand-picked by Nike for the original Breaking2 attempt. His VO2 max has been measured at 83ml/kg/min, just 1ml/kg/min short of Joyner’s model. Tadese’s running economy is one of the best ever published at 150ml/kg/km, a whopping 20ml/kg/min more efficient than Joyner’s model. And, although no data is available on his lactate threshold, evidence would suggest that it is between 80-85% of VO2 max, meaning a high fractional utilisation that is within striking distance of Joyner’s model. Given Tedese’s overall physiological proximity to the model, it is conceivable that he could be the man to first go sub, hence his inclusion in the project. But in Monza, Tedese fell off the pace just prior to the half marathon mark, crossing the line in 2:10:41. His marathon PB of 2:08:46 remains over ten minutes outside the hypothetical 1:57:58.
It is entirely plausible, and indeed likely, that Kipchoge has better numbers than Tedese, and therefore a better physiological opportunity to break the barrier. But it’s clear that the model is limited, and so too is the physiology for now – even Kipchoge’s. That explains the willingness of Breaking2 and INEOS159 organisers to operate outside the bounds of regular marathons and experiment with the equipment and environmental limitations.
Constraint two: the equipment
It’s at this stage of the discussion we arrive at a contentious point that rustles the jimmies of even the most infallible purists - Nike’s notorious Vaporfly Next% running shoe and its predecessor, the Vaporfly 4%. For a long time, the conversation circled around whether or not Nike’s claim of a 4% boost in efficiency, by virtue of a reduction in energy cost per stride, was valid. With the emergence of external, peer-reviewed data, there’s now little merit in denying it - the shoe more than lives up to its name by being 4.2% more efficient than the Adizero Adios 3. Even Adidas sponsored athletes are wearing Vaporflys and covering them up. The conversation has since shifted to how the shoes make an athlete faster, and, importantly, whether or not they should be banned.
Nike’s Vaporfly % range has a number of key components, none of which are entirely unique - a carbon fibre plate, a chunky foam midsole and a lightweight construction. Minimising shoe weight has long been reported to substantially reduce running times via improvements in efficiency. Further, the original Vaporfly packed enough Pebax foam to be comfortably the thickest marathon shoe on the market, and the unique combination of compliance and resilience is suggested to largely contribute to the performance benefits by maximising energy return. But perhaps the element most critical to the status of the Vaporfly range is the carbon fibre plate jammed into the foam, although its presence alone is not groundbreaking. In 2006, research validated that a stiff carbon fibre plate created a 1% increase in running efficiency, later suggested to arise through forced straightening of the big toe, which minimises energy lost through a reduction in braking forces. Researchers knew that the carbon fibre plate had even more potential, but benefits in efficiency as a result of toe straightening were diminished by an increase in cost at the ankle joint. With the Vaporfly series, Nike found the sweet-spot by adding an audacious curve to the carbon fibre plate. Not only does this increase efficiency at the big toe preferentially over a straight or even slightly bent carbon plate, but it also entirely removes the additional cost at the ankle joint. The result is quite frankly an astonishing feat of footwear engineering. Preliminary in-house Nike research also suggests the shoes may even reduce subjective and physiological markers of muscle damage and inflammation, which potentially contributed in the late stages of the marathon equation today.
The science is clear – the shoes have a distinct benefit over any others, and were a key driving force behind Kipchoge’s success today, and indeed behind the paradigm shift in marathon running. But here’s the kicker – Kipchoge’s shoes in Vienna were an updated version of the Vaporfly which has no publicly available research data. According to a patent filed in August 2018, the sole may have a structure consisting of four cushioning pods, as many as three carbon fibre plates and two distinct layers of midsole foam. Given Nike’s ability to seize a moment, expect further details soon.
The question with the fewest answers is perhaps the most important – should the shoes be banned? Eminent sport scientist Professor Ross Tucker put forward a strong case for it in 2017, long before the latest prototypes had even touched Kipchoge’s feet. Indeed, the shoes likely explain why organic marathon times are rapidly trending down, despite not reaping the benefits of rotating pacemakers. But Nike aren’t the first to introduce a carbon fibre plate, and they certainly won’t be the last. In order to avoid controversy akin to the swimsuit saga of 2000s, the International Athletics Federation needs to act swiftly based on objective reason and data, or not act at all.
Constraint three: the environment
Look no further than the Doha world championships for proof of the environmental influence on marathon performance. Only 58.8% of women finished their race, which started in 32.7°C and 73.3% humidity. Although conditions were kinder for the men, the race was won in 2:10:40 by Ethiopian Lelisa Desisa (Tedese, the king of running economy, was sixth in 2:11:29). On the opposite side of the spectrum, the 2018 Boston marathon was run in torrential rain, winds and cold temperatures, and won by Yuki Kawauchi in 2:15:58 - a full six minutes slower than the 2017 edition. However, cold conditions (of around 10°C) appear more conducive to marathon performance than warm, particularly when paired with low humidity. The race today started 9°C and ended in 11°C, creating an ideal climate scenario for Kipchoge. In the original Breaking2 attempt, an early morning bout of rain unexpectedly increased humidity on race day. With this in mind, INEOS159 organisers opted to designate a one-week window from which to select race day, in order to adjust appropriately for the weather. Climate was a major factor in the decision to hold the challenge in Vienna, alongside minimising timezone change, as well as minimising altitude (Vienna is only 165m above sea level). The ability to create a primarily straight marathon course was also a major drawcard – it consisted of a 9.6km circuit, 90% of which was straight. Calculations by a team of researchers spearheaded by Dr Rodger Kram indicate that the bends and elevations cost Kipchoge less than 5 seconds across the entire marathon compared to a perfectly straight and flat course.
Beyond careful planning, the climate is difficult to manipulate (unless you can handle an electricity bill the size of Khalifa Stadium). However, one of the protagonists in the pursuit of the barrier was another environmental manipulation intended to reduce the negative effects of drag, known as drafting. Kipchoge was today supported by a 42-strong cast of the leading distance runners in the world, including the Norwegian Ingebrigsten brothers, as well as Australians Jack Rayner, Stewart McSweyn, Brett Robinson and Patrick Tiernan. The pacers typically took shifts of five kilometres at a time, in a seamless flying V formation that would have made the Mighty Ducks proud. Following Monza, modelling from Siemens aero engineers proposed that the pacers combined with the Tesla and gigantic clock mounted on top saved Kipchoge approximately 4.5 minutes over a non-drafted run. However, Kipchoge dismissed this model when he dropped 2:01:39 in a valid marathon attempt in the absence of pacing car, and running alone from around the 25km mark onwards. Unpublished in-house Nike research predicts that Kipchoge saved approximately one minute and fifty-two seconds from the formation utilised today if it performed perfectly, which has been optimised since Monza.
The International Athletics Federation requires pacers to be part of the same race without relaying in and out, and thus this strategy is technically the one that purists should be most concerned with. But following Kipchoge’s official world record in Berlin, researchers proposed a model for legal drafting that would generate a marathon in under two hours – all that’s needed is a team of three athletes participating in a co-operative drafting strategy, all with Kipchoge-level physiology.
The verdict
There you have it - we’re now in uncharted territory. Where did the extra 45 seconds come from over Monza? The shoes, the drafting, a favourable course, possibly a slight upgrade in Kipchoge’s physiology, and a large upgrade in confidence and momentum that comes with the being the leader at the helm of the new age in marathon running.
What’s next? The all-time lists will continue to be repopulated thanks to the sea of Vaporflys visible at the start line of every marathon. Expectations have entirely shifted, but don’t hold your breath for an official sub two-hour marathon within the next season or two. The best shot of an organic breakthrough in the near future would be a battle between Kipchoge and Bekele on the Berlin course renowned for being the fastest major in the world, accompanied by a legal team of pacers up to at least the 25km mark. We may indeed see a battle between the two in 2020, but that is most likely to come in the Tokyo Olympics, where the conditions will essentially guarantee a finish in excess of two hours. In 2020, Kipchoge and Bekele will be in the twilight of their careers (turning 35 and 38 respectively). What are the chances that they’ll forgo the Olympics in favour of one last official attack on the barrier in Berlin a month later? Not large, but I’m sure at least one purist is nervous about it.
But perhaps more importantly, what does today mean for the overall landscape of athletics and sport science? It depends who you listen to. At worst, the event was ‘contrived and annoying’, and hurt the industry by artificially inducing a breakthrough, thus creating a false precedent which sets it up for future disappointment. One of the most vocal critics of the INEOS159 challenge is one of the original minds behind the pursuit of sub-two – Professor Yannis Pitsiladis. Realist Ross Tucker posed (and answered) an important question – are we celebrating a breakthrough in human performance, or a breakthrough in technology and strategy? Tucker is not shy in saying that the advancements in footwear and unsanctioned tactics bypass the physiology. As a self-respecting sport scientist, I almost felt guilty for enjoying the spectacle.
But when I sat back and considered the event at its brilliant best, the attempt today was a fascinating exploration of human (and technological) potential in a sport currently fighting an uphill battle. Given the current state of international athletics – the ongoing Russian doping saga, the Salazar scandal, and USADA alumni going 1-2 in the main event at a World Championships heavily criticised for record lows in attendance – the INEOS159 Challenge today provided a much-needed injection of light. There’s no question that the spectacle was calculated, and that physiology alone was not enough. But there was never a sincere attempt to conceal that fact, and there was never any suggestion that the run be listed as an official time. Today was simply the culmination of a captivating experiment which was large-scale, extremely public and, above all else, successful. Regardless of the reason, we’ve reached new heights, and a whole new audience in the process. When asked pre-race about the controversies, Kipchoge responded that “in a garden there are flowers and there are weeds. In Vienna, we are talking of the flowers...”. For today at least, I chose to listen to Kipchoge.
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**An earlier version of this article incorrectly associated Alberto Salazar with the Oregon Track Club instead of with the Nike Oregon Project. I wish to clarify that there is no connection between Salazar and the Oregon Track Club, who are a community-based organisation that is extremely well respected in the running community. Thank you to Dr. Rodger Kram for highlighting this.