The biggest shoe design innovation in a decade is great for elite athletes, but maybe not so good for the weekend warrior.
On September 25, 2022, Eliud Kipchoge, the legendary Kenyan distance runner, finished the 26.2 miles of the Berlin Marathon in a head-spinning 2 hours, 1 minute, and 9 seconds, breaking his own world record in the process. It’s just the latest dominating performance by the now 38-year-old. In 2019 he ran the fastest unofficial marathon ever in Vienna, completing the race in 1:59:40, an impressive finish.
What’s his secret? It could be the shoes. Since 2016, Kipchoge has raced in shoes from the Nike Vaporfly and Alphafly lines. These lightweight shoes bring together both an ample amount of energy-returning foam and a stiff, slightly curved carbon plate.
Research showed that combining these elements in the first Vaporfly model reduced the energy use of distance runners by an average of about 4 percent, allowing them to run faster with the same rate of oxygen use. Imagine a piece of equipment that could make an already speedy fastball move a couple of miles-per-hour faster or add more than a foot to the length of a long jumper’s leap. That jump in performance is why this kind of footwear, now made by several companies, has been dubbed super shoes.
The shoes were so successful they inspired World Athletics, the officiating body which governs road running and track events, to set rules limiting the thickness of any shoe allowed in competition and the number of stiff plates within their soles, as well as requiring that those shoes be available for purchase for at least four months before a race. But even within those guidelines, the new design’s effectiveness sets up an arms race between the sport’s top performers to compete in expensive, advanced shoes. Some cost well over $200 a pair.
But no matter how effective the shoes may be as performance equipment, they haven’t been convincingly shown to reduce running injuries. Engineers, biomechanics experts, and sports researchers suggest that no matter the footwear or lack thereof, the repetitive pounding of distance running generates forces the body must absorb, and that can make people vulnerable to injuries of one kind or another. And because super shoes do make runners go faster, they’re now spreading beyond the elite performers that may benefit the most from their engineering and be best suited to use them. The proliferation of these shoes presents the most extreme example of a dynamic that’s existed since running shoes were invented, which is the conflict between the conditions in which humans evolved to run, and the modern world’s long-haul sedentary lifestyle that is occasionally interrupted by intense runs on sidewalks and roads.
There is no good evidence available to convincingly show that any particular type of shoe prevents injury, says Chris Napier, a physiotherapist and researcher at Simon Fraser University in Vancouver. “That’s not to say that there won’t be in the future,” he says. “I think one of the issues is that people get very ideological when they talk about running shoes.”
That’s probably because shoes are a relatively modern adaptation for our species.
Sense and sensitivities
Running is evolutionarily ancient. Even before Homo sapiens evolved in Africa about 300,000 years ago, our ancestors were runners. They developed feet, legs and joints that made our bodies well suited to long distance travel on two feet. Early humans would have run, probably at an inconsistent pace, perhaps while tracking an animal. They’d travel over uneven surfaces, first barefoot, then later in simple sandals. To be adept on uneven surfaces, our feet evolved to become sensitive and responsive, says Peter Francis, an exercise scientist at Southeast Technological University in Ireland, who runs most of his miles barefoot on grassy surfaces.
The foot’s bones and nerves work with a collection of muscles and tendons, from the sole to the lower leg, to be responsive to changes on the surface—think of how your body and your foot would react to a pebble on a driveway, or a dip in a grassy field while running.
Wearing shoes blunts the foot’s ability to sense information.
“Your brain knows gravity, it knows your body weight, and it knows how conditioned you are at a moment in time,” Francis says. “I think it regulates your movements, and your speed and so on, according to the combination of that information.” Wearing shoes, he says, blunts the foot’s ability to sense information. As a result, the body becomes less responsive when wearing shoes. Adding a shoe with cushioning may make it less punishing to take stride after stride, running along a hardened surface for miles at a time, but it can also change how the foot strikes the ground. And it affects the way the anatomy adapts to that repetitive strike. Wearing modern running shoes means we don’t build up the kind of muscular strength that allows our bodies to respond effectively to changes in terrain.
However, our modern environment has changed the equation for the best way for us to run, Napier says. “Most of us are running on concrete,” he says. “We’re not off in the savanna running barefoot.”
Although Napier isn’t himself against running in minimalist shoes—the kind that provide no cushioning or hard plates but offer some protection against sharp objects—he wouldn’t use them if he was running 100 miles a week like top competitors might. “You’re just not going to hold up,” he says. Cushioning allows you to land harder without punishing your feet, he notes.
Footwear designs have zigzagged from trend to trend as researchers identified injuries that correlate with certain features and invented strategies to address them. One of the first was to add features designed to protect against the risk of injury when a runner’s foot turns inward as the foot strikes the ground and pushes off. During the early 2000s many runners embraced the back-to-basics potential of minimalist shoes that mimic barefoot running or simple foot coverings worn centuries and eons ago by our ancestors. Today’s super shoes go in the complete opposite direction by adding ample cushioning. This marks a new trend—“probably the first trend that is likely to stick,” says Steph Forrester, a sports engineer at Loughborough University in the United Kingdom.
Since modern running shoes emerged, essentially in the 1970s, top runners have typically used multiple kinds of shoes for different runs. They may have had one set of lightweight racing shoes with limited cushioning. That helps save weight, meaning it takes less energy to take each stride, which helps them go faster over a long race. Runners would then use shoes with more cushioning for the comfortably paced long runs that make up the bulk of their training time. Other types of shoes might also fit into the mix depending on training needs and coaches’ recommendations.
Super shoes take advantage of modern engineering advances in foam to provide the benefits of both extremes by being both lightweight and well-cushioned. Decades ago, research showed that adding 100 grams to the weight of a shoe provided a 1 percent increase in the amount of energy used to move at a given speed. In the 1990s, other research showed that adding a stiff plate to a shoe provided a similar improvement. The trouble was that it felt uncomfortable without cushioning. It would take until 2016 to find a way to combine these two ideas in a shoe design.
It’s gotta be the shoes
Innovation in running shoes seemed to be slow during the ten years prior to the unveiling of the Nike Vaporfly, says Bill Wannop, a sports biomechanics researcher at the University of Calgary. But by the mid-2010s, the Beaverton, Oregon-based company had found a way to effectively combine these features in a way that multiplied their effectiveness. The Vaporfly depended on using a new type of foam, called polyethyl block amide, which goes by the brand name Pebax. It’s extremely lightweight and even though it’s compliant enough to provide cushioning, it returns much more energy than other foams used in shoes.
“It wasn’t really until Nike decided to combine it with more compliant foams that it really seemed to work,” Forrester says.
That cushioning enables runners to benefit from the stiffness of the plate. That stiffness doesn’t allow the big toe to bend, Napier says, which is one way it saves runners some energy. One additional innovation, adding some curvature to the plate, also changes the performance of the ankle joint, Wannop says, making for less energy loss there. Effectively, the shoes feel better to run in.
“Athletes will deliberately use them for hard sessions because they can recover quicker from those sessions by wearing them,” Forrester says.
But that forgiving and propulsive experience may be a false promise. A cushioned shoe feels nicer and it can help you run faster in the short term, Francis says. But, he notes, runners who don’t build up their Achilles tendon and calf and foot muscles are “going to have a lot of issues, because they’re not going to be conditioned.”
For performance and protection against injury, it’s difficult to find a one-size-fits-all solution.
Those kinds of biomechanical consequences can help explain how shoes can feel better and increase performance but also not necessarily protect against injury.
Not even super shoes can stop the forces of running from reaching the body—the repetitive impact of stride after stride pounding the pavement in strike after strike. “They’re not magic,” Napier says. “Those forces are all still there, it’s just the way they’re being distributed is different.”
That redistribution could mean that there would be fewer injuries in the calf and ankle, says Kim Hébert-Losier, a biomechanics researcher at the University of Waikato in Tauranga, New Zealand. But there may be tradeoffs. Super shoes could result in more injuries in the knees and hips. “I personally don’t think they’ll decrease the frequency of injury. They might just change the profile of some of the injuries that we see,” she says. Other researchers agree that research hasn’t revealed the whole picture yet, but anecdotal reports indicate that the hip injuries may be occurring in top level triathletes, Forrester says.
Hébert-Losier and Forrester both note that the super shoe’s design presents a potential issue because the combination of foam and the stiff plate creates a tall shoe. It’s also narrow, to keep weight low. But this raises the risk of twisting the ankle when rounding a corner or during a misstep, especially for people who haven’t built up their strength as much as elite runners.
One issue is that it’s been difficult to systematically and robustly study both the performance and injury-related effects, in part because the shoes are new, and in part because the shoes haven’t necessarily been tested on a broad cross section of runners, says Tom Allen, a sports engineer at Manchester Metropolitan University in the United Kingdom.
Hébert-Losier has studied the way more ordinary runners respond to the super shoes, and she has shown that they also tend to respond with similar performance increases to top performers. But she also sees evidence that there’s variation between individuals.
For performance and protection against injury, it’s difficult to find a one-size-fits-all solution. It’s even harder to prove that something works in environments that aren’t carefully controlled, given variations in individual anatomy and history.
“The human body’s complicated,” Allen says. That affects how it interacts with footwear, as well as how quickly people respond to and accommodate new equipment and training approaches. Those are the kinds of factors that contribute to why running injuries haven’t dropped in the last 40 to 50 years, Hébert-Losier says.
It may be that people benefit most from running in different kinds of shoes in different situations. Francis recommends running most of your miles barefoot, which sounds lovely if you’re running on Irish grass, like he does. He recommends using a thin shoe for fast training runs, and then racing in super shoes if you’re at a high enough level that you need the boost to compete. Napier says that to address different conditions and situations, “it’s good to have an arsenal of shoes if you can.” Durability and cost are also a concern, as the top-of-the-line super shoes aren’t necessarily designed for the kind of durability that an everyday runner might need. For the mass market, and mere mortals, models featuring these foams and stiff plates have added width—and weight. This can offer some protection to runners who haven’t built up the strength that elites have in their springy but stripped down performance models.
The next frontier after super shoes, if there’s no innovation in foam that loses even less energy with further reduction in weight, Wannop says, could be 3D printing. “It would allow us to do a lot of fun things that you can’t do with the classic manufacturing process.”
Forrester says it may be possible to customize other elements such as the curvature and stiffness of the carbon plate for an individual’s anatomy.
Napier thinks future design trends may focus on a different approach altogether, one that adds sensors and wearable technology able to provide feedback on biomechanics and training loads. Rather than designing a shoe to specifically prevent injury, it may be better, he says, “to give that feedback in a way that can advise you to back off or take an easy week.” In this scenario, technology would be used to regain some of that feedback we lost when we began wrapping our sensitive and responsive feet in shoes in an attempt to protect them against the world.
Even if super shoes are the pinnacle of footwear engineering, that doesn’t mean everyone should wear them. If you want to run, find something comfortable, Napier says. “Whatever is going to get you out for that run, go for it. Because the positives are going to largely outweigh the negatives.”