The Science of PEBAX Shoes and Carbon Fiber Plates: What We Know Now

By Chief Editor Matthew Klein PT DPT PhD OCS GCS SCS FAAOMPT

In April of 2020, we posted a critical review diving into the research and evidence around the quickly emerging carbon fiber-plated and/or PEBAX-based footwear. We discussed several things including early thoughts on carbon plates, newer foams, geometries, interactions between them, and most importantly how much we do not know about what was truly going on. In a short two years, there has been a large amount of research into these topics. While there are still significant holes in our understanding due to research being so far behind current industry trends and development, we decided to create an update to address this new information. As this is an update, those wanting the original research should check out the original article HERE so we can focus on all the new research since that time.

Then and Now: Updated Research on Super Shoes

The original studies on the Nike Vaporfly Next% demonstrated clear economic improvements over traditional racing shoes (Hoogkamer et al., 2019; Hunter et al., 2019). However, original testing of these shoes were done with elite athletes and all known research was done on flat treadmills. Several questions rose out of this, including whether or not these shoes would still benefit slower runners, who/how many people actually would respond to this type of footwear and whether they would still be beneficial on hilly roads. The answers to both these questions were addressed in three separate studies.

A study with Dustin Joubert on its team found that while slower runners running at slower speeds still experienced some benefit with super shoes (specifically the Nike Vaporfly Next% 2), it was far less than previous research suggesting 3-4% economy improvements (Dominy & Joubert, 2022). The improvements were 0.9-1.4% and while they are technically better, there are other factors to consider over the longer periods of time these athletes will be on their feet. Given the far smaller magnitudes of improvement in economy, runners going above 4 hours may want to consider other important factors like comfort instead of shoes with economy improvements. Although we have absolutely no evidence on them yet, this is where the new super trainers (New Balance Fuelcell SC Trainer, Asics Superblast, Adidas Prime X) may come in.

Following up on whether slower runners would also benefit from these shoes, additional research has looked into whether the majority of recreational runners will actually experience the 4% economy improvements seen in the Vaporfly studies. Given that the testing and research was done on those with fairly fast racing times, it was uncertain whether the subject testing pool was too narrow. Heyde et al. (2022) studied a group of 32 recreational runners and found that while the group average was 4%, the variability in response was high. This response was suggested to occur in only 25% of recreational runners, with others have greater or lesser responses. This further suggests that there will be those who respond to these shoes and those who do not, further emphasizing our continued concept that shoes are tools. Different people will need different tools to optimize their unique biomechanics, which may or may not respond to these footwear types.

A study on up and downhill in Nike Vaporflys was performed by Whiting et al (2022). They found that while there were economy improvements compared to a control shoe (Nike Streak), it was less than reported for the economy improvements on flat/level ground. The study suggested that while these new super shoes may provide significant benefit on certain courses, their overall benefit would be reduced on hilly courses. This would not be a major issue for larger road marathons, but suggests that super shoe development on trails may need to come from a different angle to maintain the same improvements seen on road.

Carbon Fiber Plates: Important, but Still Not the Sole Factor

We received a large number of angry emails and messages over our quoting of older research that stated that the overhyped carbon plates contributed at most 1% economy improvements and were negligible compared to the improvement from newer foams. However, newer research has continued to tell the same story. This has continued to be the case, with researchers cutting the plate in vaporflys and finding no changes in economy improvements (Healy & Hoogkamer, 2022). This does not mean the plates are useless, but that their mechanism is different than often advertised. Thus far, evidence suggests that the plates stabilize the foams and help facilitate motion, rather than return it (Agresta et al., 2022; Healy & Hoogkamer et al., 2022). On a runner-specific scale, Dustin Joubert was able to compare a variety of carbon fiber-plated racing shoes and found only the shoes with special foams seemed to make a major difference in running economy compared to a non-plated control (Joubert & Jones, 2022). The carbon plated only racing shoes had little difference if any from the non-plated control, again suggesting the importance of the foams.

To follow up on the Mcleod et al., (2020) study on certain people responding to different levels of longitudinal bending stiffness, it appears that in order for people to benefit from plates, the flex point needs to line up with the 1st MTP joint (Agresta et al., 2022;?Hébert-Losier & Pamment,?2022;?Ortega et al., 2021). This would make sense given that this is a major pivot point for the body as it transitions from the support to the propulsive phase of running gait. Additional studies have explored plate location and plate shape. Studies looking at top-loaded or insole-based carbon plate versus embedded plates found that the embedded plates improved economy with significant differences while the insole-based and top-loaded plates did not (Ortega et al., 2021). Curved plates, much like the ones that are seen in the more elite racing shoes on the market, have also been found to facilitate motion as they tend to line up with the metatarsophalangeal joint axises more efficiently (Agresta et al., 2022;?Hébert-Losier & Pamment,?2022;?Nigg et al., 2021; Ortega et al., 2021).

Thus, while the plates may not be contributing the most to the major economy and performance improvements seen in the top racing models, they are still important. That importance is based heavily on their location, shape and geometry within the shoe.

Learn more about the impact of foam and our thoughts on the correct execution of super shoes based on research in our full PEBAX shoe feature.