By Brian Metzler
Most marathoners will agree that the emergence of shoes with energetic midsole foams and carbon-fiber propulsion plates have been a triumphant innovation in running.
That new “supershoe” design paradigm has proven, both in laboratories and on race courses, to return a high percentage of the energy a runner puts into a stride and, as a result, have allowed athletes to run more efficiently and race faster than ever before.
Nike was the first brand to commercialize the concept in 2017, and since then every brand has developed its own versions. Supershoes have led to several world records in the marathon, including the new women’s mark of 2:11:53 set by Ethiopia’s Tigst Assefa wearing Adizero Adios Pro Evo 1 shoes on September 23 in Berlin and the new men’s mark of 2:00:35 set by Kenya’s Kelvin Kiptum wearing a pair of Nike Alphafly 3 prototypes (pictured above) on October 8 in Chicago.
But one of the big questions being asked with more regularity is whether or not those shoes make runners more susceptible to injuries. To date, no substantive academic research has been done on biomechanical impacts of carbon-fiber shoe technology on a runner’s gait as it relates to injuries. But elite athletes and recreational runners alike, as well as some coaches and medical professionals close to the sport, have become increasingly concerned about the correlation between those types of shoes and running injuries. We have seen anecdotal evidence of foot pain, Achilles tension and sprained ankles associated with the use of supershoes.
Back in February, Sports Medicine published a scientific opinion piece that opened a dialogue about the possibility that runners might be susceptible to foot injuries from running in shoes with carbon-fiber propulsion plates. In the report, led by Adam Tenforde, M.D., a Boston-based physician at Mass General Brigham’s Sports Medicine program and medical director of the Spaulding National Running Center, researchers studied the cases of five athletes who had been diagnosed with stress injuries to the navicular bone – a bone at the medial side of the highest point of a runner’s arch – to determine if there might be a biomechanical plausibility tied to the novel stresses related to shoes with carbon-fiber plates.
Tenforde, working with peers at the Sports Medicine Department of the Palo Alto Medical Foundation in Palo Alto, California, and the Institute of Interdisciplinary Exercise Science and Sports Medicine in Hamburg, Germany, made clinical observations of three teenage middle-distance track runners in Europe and two athletes in their late 30s who competed in running races and triathlons in North America. They determined that three of the athletes developed foot pain after little or no adaptation to the racing shoes, but two of the athletes reported chronic pain after extensive training time in carbon-plated shoes.
While the report was essentially based on a series of singular case presentations – there was no control group and no testing specific protocol for each of the athletes – Tenforde says he believes it can be a valuable first step for runners, the running shoe industry and the medical community to understand the altered biomechanical demands of running in shoes with carbon-fiber plates.
“It was important for us to at least document our observations and to at least validate the greater running community for those that are observing these kinds of changes in how they're feeling when they incorporate this footwear,” Tenforde says. “And of course there's a great appetite in the running community to understand how to choose the right shoes – identifying the shoes that will allow individuals to run at faster speeds, to perform at a high level and to recover optimally.”
Tenforde believes the published work can help to increase cautionary awareness in the running community about the need for a slow and gradual transition to shoes with carbon-fiber plates. He hopes it will serve as a catalyst for deep-dive research projects related to carbon-fiber plate technology and injuries, as well as being something footwear manufacturers could consider as they develop new shoe models.
While there isn’t yet definitive research connecting carbon-fiber running shoes to injuries, what is commonly understood in both the running shoe industry and the medical community is that, generally speaking, runners move differently while running in carbon-plated shoes.
That’s mostly because the curved rigid plate inside those shoes keeps a runner’s forefoot and toes from flexing while also stabilizing the ankle, according to a 2022 article in the Journal of International Exercise Science. That results in runners activating different muscle groups and exposing their feet and lower legs to different forces and load distributions than they’re used to when wearing traditional shoes that have foam midsoles, rubber outsoles but no plates.
Shoes with carbon-fiber plates usually result in similar or even lower peak load forces, but the loading rates are considerably faster because of how a runner’s foot accelerates through the gait cycle as the plate levers forward as it reacts to the hyper-responsive midsole foam, says Jay Dicharry, a Bend, Oregon, physical therapist and running gait analyst who has studied running biomechanics as it relates to running shoes. A runner can adapt to those increased loading rates of carbon-plated shoes but it must happen gradually over time, he says – similar to how runners can gradually adapt to the higher peak load forces from minimalist shoes with lower heel-toe drops.
Dicharry has first-hand knowledge of elite-level athletes who have sustained injuries that likely resulted from running in carbon-plated racing shoes without properly adapting, including two that missed the opportunity to run in the 2020 U.S. Olympic Trials. But, he points out that it doesn’t necessarily mean those injuries are directly related to the carbon-fiber plated shoes, he says, because there are numerous other factors that could be contributing to a runner’s specific injury circumstances.
“The issue is real,” Dicharry says, “It's about how you absorb or lose energy in your tissues. And those shoes change the timing and the rate of loading of those tissues quite a lot. If you’re somebody who is on the cusp of (some kind of injury), is that enough to throw you over the edge? For sure. But I wouldn't say the shoes are causative, I'd say they're different. It gets into wording and not jumping to conclusions. But I think that those shoes, all of them together, are definitely putting a runner into a different environment.”
Amol Saxena, a leading sports podiatrist in Palo Alto, California, told journalist Jonathan Beverly recently that the problem with the carbon-plated shoes is that your foot is individualized, and the carbon plates are not. “So if the shape or length of your metatarsals line up differently than where it has to bend, or your plantar fascia is less flexible, you can get stressed in those areas—that’s why people are breaking down. I’ve had people break or tear things just in one run in the shoes.”
In other words, carbon-plated racing shoes put runners in less stable situations compared to their training shoes, Dicharry says, and that can put a runner’s feet, lower legs and knees into compromised positions as they roll through the gait cycle that makes it even harder to absorb those increased loading rates. And, given that the stride pattern of most runners tends to be somewhat unstable to very unstable to begin with, wearing carbon-fiber shoes too often without optimal adaptation can increase the likelihood for a variety of stress-related injuries.
The bottom line is that runners should adapt gradually before deciding to do speed workouts, tempo runs and long runs in carbon-plated racing shoes, Dicharry says. But if you have poor running mechanics or unstable foot placements and start running in those shoes without adapting, it will greatly accentuate the problem.
“If you’re a runner who doesn’t have good body control and you throw yourself in an environment that's even more unstable, you shouldn't expect good things to happen,” Dicharry says. “If you show up and you gradually adapt to a new environment and you’re able to be more stable in those shoes, you can do quite well. And obviously people do quite well, but, generally speaking, they need to take the time.”
One of the other challenges of the new carbon-plated shoe design paradigm is that there’s also no universal understanding about how those shoes impact runners outside of the front of the pack.
“I think what this creates is an opportunity for us, not just to think about the navicular bone stress injury, but to think about the general trends we might observe in running related injuries,” Tenforde says. “I don't want people to lose sight of the excitement of the sport. It's more what can we do from a sports medicine community to at least highlight concern for injury? What can we do then to transition people into these shoes in a more rational way? What can we do to come up with strategies around developing footwear that might allow individuals to get the training benefits without the injury risk, or to minimize the injury risk, or even to create, you know, kind of the whole possible, whole new footwear line, which could transition people into these shoes more safely.”