How to tell if your running shoes are illegal in 2025

The boom of "supertech" shoes in the running universe is relentless: every year we see new models with higher heights, more foam, multiple carbon plates and cutting-edge materials that promise to improve our running economy and reduce fatigue. However, what for many runners is an opportunity to perform better, for the bodies that regulate elite athletics this becomes a sensitive issue: to what extent can a shoe offer us an advantage without undermining sporting fairness? If you have heard of the term "illegal shoes " and don't quite know what it's all about, here at RUNNEA we clear up your doubts and show you how to find out whether or not your running shoes fall within the regulations to officially compete in 2025.

The origin of "technological doping": Why does World Athletics regulate running shoes?

The history of the regulation of running shoes by World Athletics (formerly IAAF) dates back to the controversies that arose when elite athletes began to use models with carbon plates and very advanced foams, capable of improving running economy by significant percentages. The most resounding case was that of a legend like Eliud Kipchoge breaking the barrier of 2 hours in a marathon (an achievement not homologated as a record: in Vienna with the INEOS 1:59 Challenge, 2019) using a prototype of the first version of the Nike Alphafly NEXT%. These eye-catching Nike shoes, with an extraordinarily thick sole and several stiff elements, raised suspicions that the line between technological innovation and so-called "mechanical doping" might be being crossed.

Since then, World Athletics has decided to set limits to ensure fairness in top-level competition. It is not a matter of banning progress, but of ensuring that all athletes compete under uniform standards in terms of equipment. Otherwise, the difference between having the latest prototype and not having access to it could make a significant difference in final performance.

• Key objective: Avoid disproportionate advantages and maintain the integrity of the sport. Technological advances, such as new foams and carbon plates, should not become more of a determining factor than the physical preparation and athletic ability of the runner.

World Athletics ground rules for 2025

World Athletics (WA) has been fine-tuning their restrictions in recent years. While the first regulation was made official around 2020 (coinciding with the Tokyo Olympics), there have been constant updates. As of February 6, 2025, IRONMAN has also aligned itself with these rules in its long-distance competitions. To make it clear to you whether your shoes are within the legal framework, take a look at these conditions:

Maximum sole height

• For road events (marathons, half marathons and other approved events), the thickness of the midsole must not exceed 40 mm.
• For track spikes, the limit is 20 mm.

Rigid plates

• Only one plate is allowed along the length of the midsole, which must be in a single plane and not overlap with other additional plates.
• This plate can be carbon, fiberglass, TPU or any other material, but the key is to have no more than one.

These rules apply mainly to federated and elite competitions, but have started to be extended to events where strict compliance is required (recognized marathons, official local championships, etc.). An amateur runner could be disqualified from an elite race if he or she wears a model that violates the rules.

We gut an 'Illegal' running shoe

I want you to get an inside look at an "illegal"running shoe and how its innovative design can influence a runner's biomechanics.

New types of foams

The heart of this type of shoes is its advanced foam, usually composed of Polyether Block Amide (PEBA), known commercially as Pebax. This material is used in foams such as Nike's ZoomX; Saucony's Pwrrun PB; PUMA's Nitrofoam; New Balance's Fuelcell; and ASICS' FF Blast Turbo. We are already finding these types of foams (at different densities) in both racing shoes and everyday training shoes. And of course they are appearing in "illegal" shoes as one of their strong points.

PEBA-based foams lead the way in the concept of energy return, i.e. more reactive foams. To begin with, they are lighter than TPU and softer and more elastic than traditional EVA. Each brand then adjusts the compression and responsiveness of its foam to offer specific benefits for each model. For example, heavier runners with heel landings will need a firmer midsole in the heel area to avoid sinking into a foam that is too soft.

Geometry

Another key to the design of these shoes lies in the geometry of each model. In that curved profile, which in our world is known as 'rocker'. This curvature, similar to a rocker or rocking chair, extends from the heel to the toe. In shoes with a more accentuated rocker it is very characteristic to see the considerable height from the toe of the shoe to the ground. The rocker geometry is fundamental in the manufacture of this type of shoes with such a thick sole, as it allows for a smoother transition during the stride cycle, avoiding above all stiffness in the forefoot.

Shoe designers adjust the inflection points of these rockers according to the runner's pace and stride type, thus influencing transition time. Although the most aggressive rockers are found in racing shoes, their presence in supershoes is essential to ensure comfortable transitions.

Carbon plate

It's true that not all super shoes have a plate in the midsole, but it's a trend we're seeing more and more of on the market. A plate, whether TPU, EVA, PEBA, carbon fiber, fiberglass, adds rigidity to the midsole and mainly provides additional stability and support. Consider that in a midsole with profiles above 40 mm, it is necessary to stabilize the foot strike cycle. This can be done by tweaking foam densities, but it is often more efficient to incorporate a semi-rigid plate. In addition, it can increase the feeling of momentum, but its main function is to stabilize the shoe. For example, the adidas Adizero Prime X 2 Strung carries up to two carbon-infused rigid plates due to its high heel height.

Scientific Evidence: How much does a super shoe really improve performance?

One of the claims most supported by existing scientific evidence is the improvement in running economy, a term that refers to the energy required to maintain a steady pace. A highly regarded study published in 'Sports Medicine' in 2020 revealed that shoes with advanced carbon plates and foams improve running economy by an average of 4%. This improvement can translate into a significant reduction in running times, especially over longer distances.

Beyond times, another significant advantage of these shoes is the reduction in perceived exertion during the run. This means that a runner can maintain a faster pace with the same, or even lower, level of effort compared to traditional shoes. This benefit, which has a direct impact on fatigue, is particularly important in long-distance running.

While we see benefits in terms of performance, the evidence on the impact of these shoes on injury prevention is less conclusive. Some podiatrists suggest that prolonged use of shoes with such radically different cushioning and design may require biomechanical adaptation and may not be suitable for all types of runners.

Who are these "illegal" shoes aimed at?

• Professional athletes: First and foremost, these shoes appeal to high-performance runners looking for a competitive edge. Despite restrictions in professional competitions, many elite athletes choose to train in them to take advantage of their benefits in terms of efficiency and recovery. They are particularly popular with those chasing personal bests or qualifiers for prestigious events such as the Boston Marathon.
• Runners looking for new experiences: On the other hand, they are also an option for popular runners looking to enhance their running experience. They are not athletes who necessarily compete at the highest level, but value advanced technology that allows them to run more comfortably and efficiently, especially over longer distances.
• Runners looking for performance and comfort: In addition, "illegal" shoes are ideal for those who prioritize comfort and want to reduce the impact on joints and muscles during their workouts, especially long runs. Their maximalist design and advanced cushioning technology offer a smoother running experience, making them appealing to runners looking to reduce muscle fatigue.
• Geeks: With all due love and respect, these shoes appeal to the most passionate running who are always looking for the latest fashions.

The potential risks of super shoes

At RUNNEA, we always seek to offer a complete and professional vision of trends in the world of running. That's why we have relied on the experience and knowledge of our podiatrists, Rut Delgado and Toni Fernández Sierra, to better understand the risks and benefits of this type of footwear.

Rut Delgado, a podiatrist who regularly collaborates with sports brands in the development of footwear, stresses the importance of good technique and high paces for the optimal use of carbon plate shoes. In her opinion, these shoes can cause injuries if not used correctly, mainly due to their greater instability compared to other models. She advises not to use them daily in all training sessions, but to alternate them with shoes without a carbon plate, finding them most useful in series training and pre-race days.

According to Delgado, although super shoes can help avoid certain muscle overloads thanks to their greater reactivity and efficiency in the propulsion phase, they also reduce proprioception of the sole of the foot. The latter is especially relevant for runners with impaired plantar sensitivity, where the use of shoes with high cushioning may not be the most appropriate.

For his part, Toni Fernández Sierra provides a critical perspective on the studies that support the improvements in performance and reduction of muscle fatigue thanks to these shoes. He points out that these studies are mostly focused on elite runners with advanced technique, well-trained and balanced musculature, so the results cannot be extrapolated to all runners.

In addition, he points out that the use of these shoes can also generate instability and, consequently, an increased risk of overloads and injuries if the runner's body is not prepared to counteract it. He stresses the importance of choosing the right model that fits the individual characteristics of each runner, including pace, stride type, and adequate training to assimilate the benefits of these very special shoes.

The 7 illegal super shoes that you won't be able to compete with this 2025

And we could not finish this report without referring to the list of banned shoes for 2025, which IRONMAN has published:

New Balance Fuelcell Supercomp Trainer v3

As the name suggests, the New Balance FuelCell Supercomp Trainer v3 is a training shoe with a carbon plate and FuelCell foam. It offers great cushioning and energy return. Not approved for its midsole height of 47 mm, exceeding the established limit of 40 mm.

ASICS Novablast 5

The ASICS Novablast 5 is presented as that versatile model with improved and more durable FF Blast Max foam; and it does not have the famous plate. It has a wider last and better stability. Not approved for exceeding the sole height limit, since they have 41.5mm. height in the heel.

Saucony Kinvara Pro

This standout option from the Saucony Kinvara Pro is another daily training shoe with a carbon plate and Speedroll technology. It combines PWRRUN and PWRRUN PB foams. Not homologated for its 42 mm thickness in the heel, exceeding the allowed limit of WA.

HOKA Skyward X

The innovative HOKA Skyward X has been all the rage recently. The reason? The U.S. 100-mile championships in Nevada. In this sporting event, Rajpaul Pannu crossed the finish line at first place, but ended up being disqualified when it was detected that his shoes exceeded the midsole height limit set by the regulations by 8 mm. The model chosen was this Skyward X from HOKA, which has an elevation of 48 mm. in the heel and 43 mm. in the forefoot, thus exceeding the measurements allowed for the competition.

PUMA MagMax Nitro

Highly rigid torsion system and voluminous midsole are the main hallmarks of these new PUMA MagMax Nitro. It offers stability with sidewalls and a large outsole extension.

Adidas Adizero X Prime Strung 2

Get ready for a feeling unlike anything you've ever experienced, because running in the adidas Adizero Prime X 2 Strung offers that feeling. A height of 50 mm in the heel area, 2 carbon plates, a spectacular upper and a running biomechanics that encourages you to land midfoot or forefoot. It requires a good running technique and that your weight is not too high because it is the least stable of the 3, although the most radical in all aspects. For lively runs where we seek to minimize the impact on joints and reduce fatigue as much as possible.

Are your shoes legal or not, and does it really matter?

What is really relevant is that the World Athletics regulations affect official road running competitions. If you're a grassroots runner not looking for international race rankings, wearing a shoe with a 45mm sole or two carbon plates isn't going to be a violation in most races. That said, in elite events or marathons with labels (Gold Label, etc.), they can apply controls and disqualify you.

"Illegal" shoes have exploded as an interesting niche market: an ultra-comfortable option, with top foams and often multiple plates, geared to maximize comfort and performance, without worrying about 40 mm limits or homologation. Is it worth it? It depends on your profile: if you are looking for maximum joint protection on long rides and don't mind the price, you may enjoy its benefits. If you compete in approved marathons and are aiming for an official result, the most sensible thing to do is to stick to an approved model.

Of course, in 2025 technology in the running world will continue to advance, but World Athletics has already set boundaries. You, as a runner, must decide whether to stay within those boundaries or cross them for your personal use, knowing that you may not be able to use those very specific shoes in certain official races. The most important thing is that the model you choose fits your biomechanics, your goals and helps you run with less risk of injury. In the end, running shoes are just one part of the whole that makes you a runner, and the passion for running is fueled by much more than just the thickness of the midsole.

Enjoy every stride, whether it's "legal" or not for top competition!