The DANGERS of Carbon-Plated Shoes TO High Mileage Runners

Long distance running is evolving rapidly. Shoe technology is evolving with it, but with each new technology comes risk to the athlete. Modern race shoes have been affectionately nicknamed “super shoes” for their almost unbelievable boost to racing performance. However, when it comes to running in carbon plated shoes long term, they cause weakness in foot and calf muscles leading to injuries.

The modern carbon-plated shoe most commonly has a curved carbon plate throughout the outsole. In professional athletics there is a one plate limit and as such most commercial shoes also follow this rule. Some examples of modern carbon-plated shoes include the Nike Vaporfly, the Nike Alphafly, and the Adidas Adizero Adios Pro series’ of shoes. The curved nature of the modern carbon plates leads to the rocker effect that is sought after by manufacturers and athletes. Many people focus too much on the stiffness of the plate however stiffness is only helpful if it pushes the athlete forward. The rocker effect is what helps the athlete’s foot roll through their stride while the stiffness gives them a boost at the end. A flat plate doesn’t do this and as such the performance returns are much lower. This distinction is the reason the flat carbon plate is no longer relevant and not included in the carbon-plated shoes produced and studied today.

The shoe’s redistribution of load is the primary concern when it comes to weakness. Weakness in the context of elite and consistent runners is seen on a completely different scale to that of a normal person. The most dangerous weakness is not the overall weakest muscle in a runner, it is the weakness with the most disparity compared to the surrounding muscles. These kinds of weaknesses lead to the overuse of the surrounding muscles and a much higher risk of injury. 

A person with two weak hips is less likely to get injured than a person with one weak hip because of our bodies ability to overcome issues by cheating for a short time. If a redistribution of load is done because of a weakness it causes short term gain, because the athlete can continue to run, but often ends in an injury because the areas that are suddenly under greater stress eventually fail and pick up an injury of some sort. If load redistribution is done by something else, a different type of shoe for example, the end result is the same. Any area that suddenly comes under greater stress will eventually fail and become injured. 

Injury risk is something that every athlete tries to minimize. For most athletes this includes being smart on their playing field but for long distance runners it is about maintaining strength throughout all muscles, no matter how small. Muscle strength disparities in localized areas have been proven to increase the risk of injury. One of the most crucial ways of avoiding this is maintaining a consistent form. On an athlete by athlete basis many different shoes cause issues including ankle eversion. Ankle eversion is when a person’s sole moves away from the body’s midline, or if an athlete picks up the outside of their foot and only uses the inside. This can be a very small change and go unnoticed but over time it can create new or exacerbate old muscle imbalances.

Overuse injuries are the kind of injury most common for long distance runners. The term overuse injuries is a broad overarching term that includes many different types of injuries. For runners these injuries are often not from pure overuse but quick redistribution in load to a new muscle that can not handle it for the type of mileage most long distance runners run in their weekly training. These injuries are the main focus of studies when talking about distance running due to acute injuries being much more similar to a game of chance. Coaches and trainers have a much better chance at preventing overuse injuries and as such they focus their efforts on doing so.  Overuse injuries exclude some of the most common injuries in the normal world and instead are made up of injuries like stress fractures, strains, and aggravated muscles, tendons, and nerves. They are often nebulous and difficult to pin down.

Long distance is often defined in race distance and is 5000 meters or more. Training as a long distance runner has weekly mileage goals and to be considered an experienced long distance runner the bare minimum is 40 miles a week. Less than that is good for inexperienced or shorter distance runners and does not constitute long term or heavy use of a carbon plated running shoe. For consistent use one must run in the carbon plated shoe for at least 6 miles at a time. The use of the shoe should be proportional to the weekly mileage. 15 miles a week for a 40 miles a week total athlete is consistent use whereas for an 80 mile a week runner it is purely complementary use. At minimum 40 percent of weekly mileage needs to be in the carbon plated shoe for it to be considered consistent use and this must be maintained for at least a month to see long term effects. To study the effects, shorter distances can be used but will fail to fully encompass all long term effects for a long distance runner.

The standard use of a carbon plated running shoe is to use them during workouts and races and not during recovery or steady state runs. Steady state consists of runs that are not for the purpose of recovery or to workout, essentially a neutral run. This style of usage is typically minimal and reduces the risk. Training in this way was encouraged by the fact that most shoes with carbon plates were expensive and geared toward racing and performance. As more people start to enjoy the benefits of running in a carbon plated shoe however, more shoes have carbon plates. 

One example of a shoe that is closer to a recovery shoe, than a race shoe is the Nike Zoom Fly 5. The earlier generations of this shoe were widely considered good workout shoes, but the Zoom Fly 5 was different. It was heavier and had a less fast foam. Whether that be through a miss on Nikes part or a calculated move towards every day trainer, the result was increased day to day use. With the shoe feeling more like a recovery day trainer people started racking up the mileage. Another example is the previous generation, the Nike Zoom Fly 4. This had no issue being a fast workout shoe but was so well liked by many that they stretched the usage. This had the same result as the Zoom Fly 5, people were wearing a shoe with a carbon plate more than they had in the past. This is the type of consistent use that can lead to injuries. Training that isn’t mindful and the overuse of workout shoes may be acceptable for hobby joggers but over 40 miles a week this can become a real issue that most certainly constitutes consistent and long term use.

Long distance runners have to be very careful with how they manage their training load in order to avoid injury. Making sure the training load is distributed in a way their bodies can handle is important. One important part of this is managing the load in a given area.

One way the load in a given area can change in a way that leads to injury is through form fatigue and alteration. Form fatigue occurs when an athlete is tired. They may know the best way to run but when an athlete is tired they may start to cheat or become unable to run in their normal style due to fatigue. According to a study done by the Institute of Biomechanics and Orthopaedics in Cologne, Germany there is a significant increase in rearfoot and ankle eversion. High levels of ankle eversion was found at a much higher level in injured runners in a study done by Azusa Pacific University and California State University. A study done by the Department of Health and Sport Science at Wake Forest corroborated this claim in their own independent study. These three studies show that form changes can and do lead to overuse injuries. The more one runs the more important it is to keep form consistent. A study done by a group of fellows from a variety of sports medicine fellowship programs shows that increases in training load comes with greater risk of injury. This can be attributed to the lower margin of error when the training load is high. With a high training load there is significantly less room for error in form and training. Sudden changes in either can lead to the mismanagement of load to areas of the body that can’t handle it. After years of training the muscles become used to the load that is put on them. If an inexperienced runner attempted to start running 80 miles a week they would get injured. The same principle applies if an experienced runner tries to put 80 miles of training load onto a new muscle or joint. The muscle or joint is not prepared for the huge increase in load and therefore injuries are very common. 

Form can be altered by footwear as well. One of the most common reasons for an injury is inadequate footwear. Typically that comes in the form of dead shoes or the misapplication of shoe type. For the average person one or two runs in sneakers would not hurt them. For runners with high mileage and training load the misapplication of footwear is much more nuanced and volatile. No one recommends doing high mileage in sneakers. An inexperienced runner may however do consistent mileage in a shoe not meant for consistent use. Shoes mainly fall into three categories: everyday wear, workout shoes, and race shoes. Carbon plated shoes typically fall into the latter two but recently they have become much more widespread. This leads to inexperienced runners using carbon plated shoes in new applications.

Carbon plated shoes have been studied many times for performance but there are minimal studies looking into the long term effects. One study done by the Chemnitz University of Technology (CUT), had their subjects run for 10 kilometers in carbon plated shoes reported that there was significant form alteration by the final kilometer. They reported that the runners altered their form to optimize the load on their lower extremities while still maintaining performance. This alteration helps with performance but over time could lead to weaknesses and injuries. 

Slight weaknesses and instabilities in the foot and ankle affect the whole leg. A study done by the American Podiatric Medical Association found that altered or malfunctioning foot alignment has far reaching repercussions like the changing of gait. The changing of gait can lead to weakness, instability, and eventually injuries. One of the more interesting studies was done by the University of Salzburg in partnership with the Red Bull Athlete Performance Center . That study was done on an experienced elite female endurance athlete and showed a change in footfall patterns over short distances. The study emphasized the essential nature of individualized training because when that particular athlete used the carbon plated shoes an old injury cropped up. When the carbon plated shoes altered the form of the athlete it forced her into her old injury and caused pain. Injuries like these are what leads people to the anecdotal evidence that carbon plated shoes lead to long term problems. Individualization makes studies on distance running difficult. Individualized training is becoming more and more common and with it comes many individual challenges. Athletes who have a high training load have to make sure that the shoes work for them because if they don’t the consequences can hurt a career long term.

When paired with the study done by CUT that showed that form changed more over time there is a reasonable worry that having athletes run more in carbon plated shoes could lead to injuring them. Studies like the ones done by CUT and the University of Salzburg that show clear changes in gait and footfall patterns also show increases in injury risk and should be used to show the need for caution when using carbon plated shoes. 

Ankle load redistribution is a key part of the story when it comes to the risks of using carbon plated shoes. Multiple studies including the one done by CUT, a study done by the University of Calgary ,  another study done by California State University, and one done by Iowa State University (ISU) found significant redistribution of load on the ankle. Unfortunately the limited number of studies and the gradual nature of the issue, mean that the studies have not been able to find specific areas of the ankle that are loaded differently. The ISU study found increased ankle aversion with carbon plated running shoes, however the sample size was not enough that they could confidently reject the null and say that it was the carbon plated shoes specifically. Ankle eversion is one of the main causes of peroneal tendinopathy according to a study published in the Physical Medicine and Rehabilitation Clinics journal. If indeed the widely confirmed significant ankle redistribution is ankle aversion then it would be a significant factor in the long term increase in injury risk when using carbon plated shoes. 

As studies on super shoes have come out, two different ideologies have formed. One group believes that super shoes increase injury risk over time, but the other group believes the complete opposite. They point to the reduced stress and improved ability to handle overall training load, to show that shoes with a carbon plate reduce injury risk. 

An article in the MIT Technology Review considers this exact position. They interview David Kirui, a physical therapist that treats many of Kenya’s top marathon runners. He estimated that overuse injuries were down by around 25% due to the increased use of super shoes. His ideology was supported by Jonathan Maiyo, an experienced racer and elite road runner since 2007, who said that “in the old shoes, after 10 marathons you’d be completely exhausted.” He sees a huge change in this and now says that “10 marathons are like nothing.” The group of Kenyans coach Claudio Berardelli estimated that his athletes do at least 60% of their mileage in super shoes. 

Kenyan distance runners subscribe to the high mileage strategy completely. Weekly mileage for world class marathon runners like the group mentioned is often around 220 kilometers or about 137 miles. The late Kelvin Kiptum who had a meteoric rise to prominence reportedly had a regular mileage of 280 kilometers or about 173 miles a week. That equates to 24 miles a day and is clearly high mileage. If the group interviewed ran the estimate of 137 miles and we take the low estimate of 60% of mileage in super shoes, it would tell us that they run around 80 miles a week in carbon plated shoes. 

It would make sense if, because of the high volume, these athletes saw an increase in injuries over time. There are a few different reasons I think we don’t see this. First is the reduction of stress professional athletes see when they go pro. Especially in Kenya athletes are often doing a huge training volume without proper equipment before they go pro. Kelvin Kiptum is a prime example of this. Before he became one of the most well known marathon runners in the world, he was doing his training barefoot. While there have been some documented benefits to training barefoot, it is widely known that high mileage barefoot is unsustainable. When he went pro it can be reasonably assumed that there was a huge reduction in musculoskeletal stress for the same amount of training. A similar reduction should be found when super shoes are introduced. The difference is that over time the redistribution of load increases the risk. 

Another reason we don’t see this increase in that group in particular could be the other training they do. Their exact training is unknown because different teams hide their training to avoid copycats cropping up, but it should include strengthening outside of running. If their coach, who has a background in sports science, is smart he can adjust their strengthening regimen to strengthen the regions necessary before it becomes an issue. If the area the load is redistributed to is already strong then an injury is far less likely to occur. This wouldn’t show up in most studies because the average person doesn’t have a coach that does that. Even most coached athletes don’t have a coach that is able to do that. That kind of training needs to be backed by a coach that knows the athlete well. Super shoes are a mass market product that are marketed to everyone. The problem is still there even if careful training outside of running can mitigate the additional risks.

The third reason that the group doesn’t see the increase in injuries predicted by studies is the difference in the individual. While the study done by the Department of Sport and Exercise Science at the University of Salzburg and the Red Bull Athlete Performance Center in Austria, showed an example of an athlete responding poorly it’s possible that this group is an example of a group that responds well to the shoes. 

The MIT article mentions individualism when it comes to performance but it holds true for health too. They look to a study done by Wouter Hoogkamer that revealed a 4% range in performance improvement. Hoogkamer also commented on why he believes athletes respond so differently to super shoes. He thought there were around 20 variables affecting the response to the shoes including weight, calf strength, and the strike pattern of the runner. The strike pattern of an athlete is usually categorized into forefoot, midfoot, and rearfoot with the location being the first point of contact between the foot and the ground. While it can be broadly categorized into those three categories there are countless other subcategories including the natural level of eversion and inversion on impact. 

Abdi Nageeye, a Dutch marathon runner that finished second in the Tokyo Olympic marathon and won the 2024 New York City marathon earlier this month, is a heel striker. He struggled significantly with the first two versions of the Nike Alphafly because they forced his stride into a different pattern that felt unnatural. He described the change as a “skip” in his stride. In contrast to his struggles with the first two versions, the third version of the Alphafly worked well for him. He won his first ever major marathon in the shoes. As a Nike athlete the Alphafly was what he had to race in even when his stride was being changed unnaturally. Changes in form increase injury risk and could have caused injuries. 

Small case studies like these have huge variation. Just like the variation in the shoes performance the variation in the effect on the runner is large. Studies with large sample sizes help to even this out. There are more and more studies coming out with results that point towards increased injury risk. Alone there isn’t a study that proves the argument one way or the other. There are case studies going both ways. Put together the scientific studies only point one way. They point towards increases in injury over time and the potential for long term problems. 

References

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