The science behind Adidas’s new world-record running shoe

Before most people had eaten breakfast, Peres Jepchirchir had smashed a world record. On September 5 at around 7.25am, the Kenyan runner set a new women’s-only record for the half marathon, completing a 21.1km course in Prague in 65 minutes and 34 seconds. She knocked 37 seconds from the previous fastest time – completing each kilometre in around three minutes and six seconds.

Like in most recent long-distance running world records, Jepchirchir was wearing a fluorescent pair of trainers. But contrary to other current records, the shoes were created by adidas and not its arch rival Nike. The US firm has dominated distance-running records since 2017, when it released its first trainers containing carbon-fibre plates that help people run more efficiently.

But now adidas is striking back with its Adizero Adios Pro. For the last two years, around 50 staff at adidas have been working on the Adios Pro. The trainer is a performance running shoe that’s designed for long-distance racing and running.

It’s the company’s first real response to Nike’s new-found distance dominance, and goes on sale today for £170. And unlike the vast majority of top-end running shoes, it doesn’t include a full-length carbon-fibre plate. “We’ve seen the sport of marathon racing changing, and lots of product innovation happening,” says Sam Handy, vice president of design at adidas running. “But of course we don’t launch things until they’re ready.”

Since Nike released its first Vaporfly 4% shoe the rest of the running world has been mimicking its carbon-fibre plate. Rival brands Saucony, On, Brooks, Hoka One One, Asics have all released their own racing shoes that include the plates.

However, adidas has done something different with the Adios Pro. Running throughout the shoe are a series of curved carbon-infused rods. These are wedged between two chunks of the company’s energy-returning Lightstrike Pro foam.

“The origin of the energy rod is to try and mirror the metatarsal bones of the foot,” Handy says. As shown below the rods run down the length of each bone in the foot and are curved to follow the shape of the foot. These rods have been stiffened to help give the greatest possible energy return when combined with the foam and other parts of the shoe. The company tested “hundreds” of different prototypes of the shoe with different length rods, positioning them differently, and with different stiffness.

Handy says that the company experimented with full-length carbon fibre plates as well – some of its other shoes do use them – but ultimately the carbon-infused rods came out on top. The best place for the reinforcement is where the bones are, he says. “You don’t really need it anywhere else,” Handy adds. “We found that it gives the shoe a much more natural gait than when you have a big carbon plate.”

In rod we trust: the carbon-infused energy rods mimic the structure of the foot

adidas

While independent studies have verified that Nike’s Vaporfly line-up does make runners more efficient, we don’t know the exact reason why. The combination of its carbon-fibre plate and its ZoomX foam contributes to overall efficiency gains, but neither one of these alone can be picked as the supercharging feature. To unlock exactly why the shoes are more efficient would involve controlled scientific studies where the shoes are tested with and without the carbon-fibre plates (and plates made of other materials) to see where the gains come from.

Handy says that a carbon-fibre plate isn’t necessarily needed to increase the efficiency that running shoes can provide. Instead it’s more about all of the elements in a shoe. Each individual component can bring marginal gains to the efficiency of a shoe. “You read the amateur science that the plates do all the work, but they don’t,” Handy says.

What matters is how quickly the foam in the shoe will degrade, the radius of any rocker design and the amount of stiffness that’s added back into the foam with the internal components. “They are all connected,” says Alberto Uncini Manganelli, general manager of running at adidas. “They work together, they should work in sync. When you change a parameter, you need to adjust the other to get the best possible performance. So the equation was advanced.”

While sports companies can pump millions into creating the most efficient shoes possible, there’s another key element: the runner wearing them. To date, only professional athletes sponsored by the sports firm have been training in and helping to develop the shoe. At Jepchirchir’s world record in Prague, the half marathon was made up entirely of adidas runners – all of them in the new shoe. (In the men’s event fellow Kenyan Kibiwott Kandie ran the fifth fastest half marathon of all time in 58:38.)

The number of records set by carbon-fibre plated shoes forced World Athletics to introduce new shoe rules in January this year – and the body is continuing to investigate their impact on the sport.

Some critics say shoes with increased efficiency are a form of technological doping, and records set with using them should be discounted. In some cases athletes have been keen to distance their performances from the capability of their shoes. After setting the world record last week, Jepchirchir acknowledged the technology helped. “I was exhausted for the last five kilometres,” she said, “but the new shoes have helped me set a record.”

Any tech built into a shoe has to be comfortable to run in, and just because a shoe performs highly in efficiency tests in the lab doesn’t mean it will be something distance runners want to wear while pounding the pavements for hours. “What you measure as a mechanical benefit in percentages might be too much or too little for an athlete when they’re actually running in a shoe,” Handy says.

The Adios Pro isn’t completely carbon-fibre-plate-free though. There’s a mid-length plate that sits in the shoe’s heel area. This gives a glimpse into the importance of foams used in running shoes – particularly how they need to be protected against the forces imparted each time a runner hits the ground.

The most efficient running form comes when athletes land on either their forefoot or midfoot. As a result, those at the top of the sport largely run on their forefeet. But this can change as they get fatigued during a run and their form reverts to landing on their heels. When this happens more force is put through the heel. “We need to make sure that the shoe isn’t becoming more deformative over time – that’s why the plate is in the heel,” Handy says.

Adidas may also have one extra trick to play with the energy rods. Unlike a carbon-fibre plate, the shape, length and position of each rod can be more easily adapted. They can be moved to a higher or lower vertical position in a running shoe, their stiffness can be adapted, and they can be spread out more easily or individually adjusted to create the most efficient performance.

Handy refuses to say whether each of the current energy rods is set up in exactly the same way. But in the future their composition may change. “We definitely want to see them appear in more products and be taken further,” he says. “We will try various different stiffnesses and differences around these components as well. They’re very tuneable. There’s lots of scope for us to do more with them.”

Matt Burgess is WIRED’s deputy digital editor. He tweets from @mattburgess1

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