An Interview With Michael Flynn, Regional Manager, Big River Running Company
As a runner, you’ve likely heard the buzz about carbon and nylon plated running shoes (aka “super shoes”), which burst onto the scene in 2017 with the groundbreaking Nike Vaporfly 4%—worn by elite athletes at the 2016 Rio de Janeiro Olympics.
These innovative shoes have undoubtedly elevated race performances across the board, but they aren’t a one-size-fits-all solution for every runner.
To explore this topic further, we sat down with Michael Flynn, the regional manager of Big River Running Company and a seasoned shoe expert. Read on for Mike’s insights!
Q: What defines a super shoe?
A: The combination of a highly responsive midsole foam plus a carbon fiber plate. Shoe tech has advanced a lot over the years. The midsole is the majority of what most people think of as the sole. The outsole is the rubber on the outside that’s more durable, kind of like the tread. Think of a car tire for the outsole.
The midsole provides all the cushioning, and then some shoes also have a smaller layer, the topsole, on top that helps with just like shoe fit or fine-tuning things. But the super shoes have foam in the midsole that has much more energy return than other foams that are used in more conventional shoes or historically have been used in shoes.
When our feet hit the ground, energy dissipates. So, your designers want to return as much of that back into the body to propel the runner forward. There are different terms out there. There’s super critical foam or Pebax [a lightweight plastic polymer] foam. Largely, those are talking about the same thing, but something that’s highly responsive.
And then I would say that all the true super shoes have a rigid carbon fiber plate that’s sandwiched in the midsole. That serves two purposes: one, it provides some structure and stability to that foam, which is often very squishy and can create a very wobbly unstable feeling shoe. Also, the rigidity and the shape of the carbon fiber plate will provide leverage, which changes the way that the foot interacts with the ground and helps improve running economy.
Q: What about the difference between the straight-up carbon fiber plated shoes and the nylon plate? What are the different variations of plated shoes?
A: So, a lot of shoe companies are now using nylon plates. I would call that category more like a “super trainer” category, which we should definitely circle back to because, for a lot of runners, those might make more sense than the carbon plated.
The carbon fiber is extremely rigid. So, if you were to cut open a shoe—which we have a couple of plates at the [Big River Running Company] store that we have cut open over the years—these were worn-out, used shoes, but we kind of dissected them. The carbon is extremely rigid. You get a stiff lever. It doesn’t flex, or if it does flex out of the shoe, it only flexes in one direction, but not the other, and so the way that the foot interacts with it is incredibly stiff.
The nylon plates sometimes have an identical shape to the carbon plate, and in other shoes, it’ll be an even different shape. Those are much more flexible, so they’ll still provide some structural benefits in the shoe to kind of balance out the energy return properties of the foam, provide some stability to the sole, and a little bit of that leverage motion, but not nearly as much.
They [nylon plates] aren’t as aggressive or as stiff. The benefit of that is far less stress on the bones and the foot. The downside to that is you don’t get as much energy return.
Q: What is the injury risk with carbon plated shoes?
A: With carbon plated shoes, there is an injury risk, and researchers are still discovering exactly what that is. Anecdotally, for a few years now, some professional running groups and shoe manufacturers have learned that if you spend too much time running in a carbon fiber shoe, you can either get stress fractures on the navicular bone in the foot, which is one of the bones near the ankle, or on the metatarsal head behind the big toe because that stiff rigid plate puts a lot, it concentrates a lot of pressure right behind the big toe and then the forces in the way that the foot interacts with the ground in the super issues is not natural.
So, to speak, it changes the running dynamics and can create some torsional stresses on the navicular. That’s more of a “Don’t train in it every day, 40-plus miles a week, week after week” type risk. Also, a “Don’t go from never using them to just putting them on and running a marathon right out of the box” type risk.
There are a couple of scientifically specific articles [linked below], and the recommendation in one or two of those [articles] is that runners should gradually build up to doing mileage in carbon-plated shoes and that they’ll also mix in other shoes into that rotation. [For example, occasional workouts or long runs in carbon-plated shoes with most of the rest of the mileage done in regular trainers].
Other downsides are cost and durability. In a lot of carbon-plated shoes, you’re spending a lot of money for something that’s maybe only good for one to two hundred miles. On the other hand, nylon-plated super trainers are good for three hundred to four hundred miles, more in line with a typical training shoe. The nylon shoes don’t put as much stress on the foot.
Q: Are there any other variations of the plate besides carbon and nylon plates?
A: Kind of. Hoka’s Mach X2 has a Pebax plate or PEBA plate, but that’s basically plastic. I classify [different material plates] into flexible plates and then carbon fiber plates.
Q: As a coach, I would think that over time you’re conditioning your biomechanics to not put the same force into the ground if you’re training too much in carbon-plated shoes or super trainers. Is there any research to support that theory?
A: Some of what I’ve read says muscle atrophy is a risk of spending too much time in the super shoes because they do de-emphasize the workload on your soleus muscle and achilles tendon, which can lead to some weakening of those over time.
The upside to that is improvement in recovery, and you can do more miles and not feel as beat up after hard workouts. Personally, I kind of like the idea of doing a good amount of work not in a super shoe, and then putting [the super shoes] on provides a performance boost.
Q: Is a super shoe a good selection for all athletic abilities, or when is it a good idea to dive into the super shoe world as a runner?
A: The benefits vary a little bit with speed. The faster you are, in most cases, the more you’re going to gain from using specifically the carbon-plated shoes. The shape of the plate and the way the shoes are built—many of those are optimized for people running 5:30-6 [minutes] per mile or faster. Whereas a lot of the nylon-plated or super trainer shoes are going to give a benefit at 8-9 minutes per mile or faster.
So, there’s more to gain on the table the faster you are, and even the percentage in running economy increases.
Somebody though who’s trying to break 2 hours in the half marathon, or 4 hours in the marathon, they’re going to get a benefit from the shoes too. This often looks like a two to four percent performance increase.
That can add up over time and can take minutes off race times. With the super trainers, as opposed to carbon-plated shoes, they often are in the 180 to 200-dollar ballpark. The typical running shoe right now is 140 to 160. That’s not a huge cost increase. A lot of the carbon-plated shoes are in the 250 to 300 ballpark. It’s a big investment.
Q: What about the athletes who normally run in a stability shoe? Can they use super shoes?
A: One of the studies [linked below] talks about runners who are neutral versus those who overpronate, and neutral runners benefit far more [from super shoes]. The person who over-pronates has minimal benefit, and in fact, at the rate of walking, it’s a detriment.
You walk slower in a super shoe than you do in a normal shoe. That’s because of the high stack height and the wobbly cushioning foam. If you’re someone who’s in the five-plus-hour ballpark for a marathon, and especially if you feel like you’re going to end up doing some walking or a substantial amount of walking throughout the race, that’s not going to go very well if you’re using one of the super shoes with a narrow heel.
Q: What is the best way to incorporate super shoes into training?
A: About a month and a half to two months away from race day, if not sooner, start incorporating them into some of your workout runs in the middle of the week, just so you’re getting familiar with how your foot reacts with the ground in those shoes.
I typically tell people to do a medium to somewhat long-distance run for a marathon in them. That would be in the 15-to-18-mile range; it doesn’t need to be the longest run on your block, but it should be a longer run.
For a half marathon, do something that’s 10 or more miles [in the super shoes] just to get in some serious miles in the shoe and make sure nothing is rubbing or blistering that you need to be aware of ahead of time on race day.
In that run, I’d also work in some race pace work just so you’re getting some time at race pace in the shoe ahead of time.
Q: Are there any injuries that make you think someone is not a good candidate for super shoes?
A: Yes, weak ankles. Routine ankle sprains would be a big risk. Someone who has a history of something like posterior tibial tendonitis might do well with some shoes and really poorly with other shoes. I’d be careful with plantar fasciitis too.
Most of the shoes will accommodate some type of aftermarket insert, which can help provide a degree of stability. If you have a runner who moderately over-pronates and is typically running in a stability or motion control shoe, putting an insert into a super shoe sometimes might give them the stability they need.
Other times, you’re now putting something that’s rigid and supportive on top of something that’s squishy and wobbly, and that can potentially even cause new problems.
In those cases, I would certainly look for one [super shoe] that has a broad, wider heel. If they stand up and feel stable, that’s a good sign. To check, do you notice your ankles dipping in when you’re standing, or are they vertical? If you can get good orientation of the ankle joint while standing in the shoe, then it’s probably going to be okay. But yeah, the energy return and running economy vary a little bit.
Runner to runner, neutral runners are going to benefit more, while over-pronators are going to benefit less. Some of that is a comfort thing for the over-pronator.
Q: What about research around long-term studies? We’ve talked a little bit about super shoes being so new to the market and how we don’t really know too much about the long-term effects and injuries that could pop up way down the road from wearing them a lot. What do you know about that?
A: I think there are some question marks there. I think it’s telling that a lot of the pro groups and the college groups don’t train in them every day. That’s where a lot of the anecdotal stuff was coming from a couple of years ago—college teams where everybody was running in their super shoe five or six days a week.
When Camille Heron went after the 100-mile world record a couple of years ago, she ran it in the Hoka Rincon, which doesn’t have a plate in it at all. Afterwards, she kind of said, “I had any Hoka shoe available to me, and I chose to do it in a non-plated shoe because I was going to be on my feet for so long and all day.”
The community and the industry have recognized that there are injury risks. The science is catching up with that.
How does this impact muscle strengthening, the kinetic chain, long-term muscle development, and atrophy, and all those things? It’s probably going to be a while before we know a lot.
Q: Would you advise an athlete to use a super shoe during an ultra-marathon?
A: It would depend on the nature of the ultra, and that’s a good question. So, if it’s a road ultra or a rails-to-trails type of ultra, the people who are running and winning those races and setting records are doing them in carbon-plated super shoes. Oftentimes, they’re doing them in the road shoe on well-groomed trails.
Trail shoes like Hoka’s “Tecton,” which is their carbon-plated trail racer, have a plate that is very different. It consists of two parallel plates to allow for adaptation and some flex with the uneven terrain underfoot.
There are trail super shoes. Those came out a couple of years ago, and a lot of them are deviating from that super rigid, stiff plate that most of the road super shoes have.
So, Hoka has the two parallel plates that allow some flexion of the sole. Another brand has a half plate, so it’s not under the heel; it’s just under the forefoot to give you some levering up there. Another brand, “Speedland,” which is mostly direct-to-consumer, has a removable plate. You pull the mid-sole out of the shoe, the plate twists, and you can pop it off. Then you can also put it back in.
I used those for my 100k Black Canyon last year, where I was on my feet for close to 17 hours. I ran about half the race and walked the other half. I didn’t notice any detriment from that plate, but the way that the plate is placed in the shoe is very low, below the mid-sole, so it has less of an effect than if it were in the middle of the mid-sole or higher up above more foam.
Q: How does shoe foam react over time to just like sitting in your closet? Like if I stock up on my favorite Alpha Fly model and just put them in my closet for a year, will the foam break down just sitting there?
A: So, my understanding is that those Pebax foams are really shelf stable. They’ll do fine over time. It’s more compression cycles where they break down and start to stiffen up, firm up, and lose their integrity quickly.
On a typical running shoe, you know, most of those are shelf stable for probably five to ten years before you truly have to worry about the foam, the sole falling off, or separating.
But a lot of the super shoes, because they’re trying to go with a really lightweight upper and cut weight to maximize performance, the glue might be a concern because there isn’t going to be as much glue on the shoe.
The bonding’s not going to be as great. They’re cutting some corners to bring the weight down. So, the long-term durability, I’m not really sure. I’ve had some super shoes at home for over three years before I’ve used them, and they at least look the same and feel the same.
I can’t standardize what their performance is because my fitness has differed drastically over the past five years.
Q: Is there anything else that you think we should include?
A: There are some shoes on the market that, if you’re trying to win prize money in certain races, you’re not allowed to use. World Athletics has a stack height restriction of 40 millimeters for road racing. There are some shoes in the super trainer category, not in the elite racing category, but there are some shoes with 45 or 50 millimeters stack heights out there.
The rationale was that, because the Pebax foams are so responsive, adding more and more foam was magnifying the performance benefit.
So, World Athletics said we’re capping things where they are at. And at the time, I think the Vapor Fly was at 39.5 millimeters. They said 40 millimeters is the ceiling; you can’t go taller than that.
You can buy [the disqualified] super shoes, and most of us can run in them and race in them, and nobody’s going to care. But if you’re going after prize money, you can potentially get disqualified because your shoe is illegal.
Thank you Michael Flynn for taking the time to give us the scoop on super shoes!
References:
https://link.springer.com/article/10.1007/s40279-023-01818-z
https://www.livescience.com/can-carbon-plated-running-shoes-cause-injury
https://www.health.com/thick-heels-running-shoes-injuries-study-8770094
