the entire pursuit revolved around one question: How can we help the world's most elite distance runners be faster? And not just incrementally, but faster than any distance runner ever. When you're trying to shave minutes—not seconds—off the world's fastest times, you need all that science has to offer. Skin temperature monitors and muscle imaging to inform hydration and sugar intake. New types of apparel to help minimise drag. And of course, the Nike Zoom Vaporfly Elite footwear. To understand how we got here, on the precipice of our historic quest to break the two-hour marathon barrier, we need to start at the beginning.


ATHLETE SELECTION To identify the runners most likely to run under two hours in the marathon, our science team tested many of Nike's elite distance athletes, measuring three primary factors that help predict performance: Exercise Capacity: an athlete's maximum capacity for exercise, expressed as VO2 Max, or the maximum rate of oxygen consumed. Running Economy: how much energy a runner needs to run a kilometre at a given speed. Sustainable Velocity: the speed a runner can sustain for a long period of time without needing to slow down. Of the athletes initially screened, three emerged as the most promising: Eliud Kipchoge of Kenya, Lelisa Desisa of Ethiopia and Zersenay Tadese of Eritrea. The testing process yielded key physiological data that allowed our science team to project each athlete's potential. The team compared each athlete's personal records against their projections in order to identify areas of focus, and began brainstorming strategies to close these gaps for race day. For example, while Eliud had refined his hydration techniques over his competitive years, Zersenay, the world record holder in the half marathon, hydrated minimally. Given Zersenay's incredible running economy, but the slower marathon personal record of the three athletes, his hydration was a factor the team worked to improve. Another example was nutrition strategy. "Marathoners can hit a wall at 30 or 35K", said Brett Kirby, Lead Physiologist of the NXT Generation Research team in the Nike Sports Research Lab. "This is commonly associated with depletion of their muscle sugars. So, how do we keep those sugars up? We started looking at that and working towards a personalised solution for each athlete."


Before the team could work with the athletes to refine their training and conditioning, we needed to understand their current training schedules. In order to do so, our science team met the athletes and their coaches at Nike's World Headquarters in Beaverton, Oregon. At this first team camp, the science team provided each athlete with GPS watches and heart rate monitors to begin tracking the training load of each athlete. In addition, each athlete was connected to internal Nike performance prediction analysis software. This helped to facilitate individualised athlete learnings, as well as forecast future running performances.
Next, the science group teamed up with the product group and went to the athletes' home training grounds in Kenya, Ethiopia and Spain. They tested and integrated insights across the Nike Breaking2 project, gathered new data and observed first-hand the athletes' daily training regimens and lifestyles, constantly looking for avenues where support could be provided.


At the first team camp, the science team introduced hydration and nutrition strategies, which were then regularly adjusted month by month. Skin temperatures and sweat rates were monitored. Fit details for the revolutionary Nike Zoom Vaporfly Elite shoe and race-day apparel were obsessed over. And the closer we got to the attempt, the more important temperature became for our team.
For the success of Breaking2, the most important temperature reading was the difference between the body's internal core temperature and skin temperature. This is known as the temperature gradient.
"We're looking at what core body temperature does in relation to skin temperature and we want those two numbers to be as far apart as possible", Brad Wilkins, Director of the NXT Generation Research team in the Nike Sports Research Lab, said. "That means that the gradient—the temperature gradient—from the core to your skin is really high." In order to maintain a high temperature gradient for each runner, the team focused on optimising the environmental conditions for race day. During our half marathon test event, internal and external monitors were used to measure core temperature and skin temperature, respectively. This provided the constant data needed to understand the impact of thermal factors on each athlete's performance. To try and optimise for temperature, cloud cover and wind, the race was planned over a three-day "launch" window. Over that three-day window, the team picked the optimal morning for the race based on the maximum core-to-skin gradient, which allowed for the least impact of thermal factors on the athletes' performance outcomes.
Another important factor that's affected by environment is hydration. Throughout training, the team weighed the runners before and after their runs, which told the team how much water each individual runner had lost through sweat. Then, our team observed how the body of each runner responded to their respective fluid strategies—a carefully crafted sugar-water liquid mixture. Other tests, like muscle imaging, showed how much sugar was in the athletes' muscle. This was crucial, because sugars could help the runners avoid the burnout that is synonymous with the marathon. Alternatively, taking in too much could upset their stomach and throw them off their game.


The next step in race-day optimisation brought us to the wooded setting of the Autodromo Nazionale Monza, 13 miles north of Milan, for the marathon track. Monza's flat track with gradual curves, as well as Northern Italy's temperate climate, made it a good location for the attempt. The half marathon test event was not a race for the athletes to test their fitness. Rather, it was a test of how the Breaking2 team will manage the Breaking2 attempt, logistically.
The team asked the athletes to run at a 60-minute half-marathon pace. Small alterations, such as Eliud having a beetroot bar with carbohydrates as opposed to beet juice as a pre-run meal, were tested at the trial run. Temperature gradient and, of course, the footwear and apparel were also tested.

All of this data has been collected before, but never with athletes of such calibre with the intent of breaking this barrier. Even without hitting the two-hour barrier, these key data points help all athletes look towards what's next.


We used a dynamic formation with pacers to reduce wind drag for our athletes and made sure that the athletes were getting the perfect hydration for each of them. And of course, we developed a shoe—the Nike Zoom Vaporfly 4%—designed to turn every advantage into performance.

Breaking2 wasn't just a race or an experiment. It's now a model for how much faster we can go when cutting-edge science meets unwavering passion and commitment to the goal. After years of research and development, Breaking2 debuted a system of ground-breaking innovation that has the potential to elevate every runner.