Running Shoes With Carbon Plates May Help Your Performance And Has Potential to Reduce Certain Injuries
by Eric Oliver, PT, Founder, Running Specialist, USATF Level 1
Carbon plated running shoes (the carbon is in the midsole) are becoming more ubiquitous in the running world. It started with Nike’s VaporFly shoes and continues with their yet to be released AlphaFly shoe. In the meantime, the other major shoe companies are also jumping on the carbon bandwagon. Nike’s carbon shoe has been used to break several records in the marathon distance, most notably helping Eliud Kipchoge to run 26.2 miles under two hours for the first time in human history. Ever since Nike’s VaporFly shoes have hit the market with their carbon plate, runners of all types and experience levels have been purchasing them with the belief that running in these shoes will give them an extra boost in their running. People have even been referring to Nike’s VaporFly’s as “magic shoes” because it feels like it provides a little more spring to their step. These shoes, with their purported ability to improve one’s running performance by up to 4%, are filled with all kinds of tech, and they are priced accordingly. So are they worth it?
The fact that records are being broken by runners wearing the Nike VaporFly/AlphaFly shoes is pretty telling evidence that these shoes have the ability to positively improve your performance. This has been a point of contention in the running world, though, because there are people who believe the carbon plate provides a mechanical advantage to the user allowing the runner to supplant tech over skill and training. There was even talk of banning these shoes from competition due to the belief that these types of “springy” shoes provide extra propulsion that is unfair. But, does the carbon fiber plate actually “spring” you forward, or is there something else at play that improves a runners performance while wearing them.
The great ban on Nike’s carbon-plated shoes never materialized, and at the US Olympic Team Trials (where I was both spectating and supporting one of my athletes) I noticed that these shoes were quite popular amongst many of the athletes, all of whom received a free pair of the black/green Nike AlphaFly Next% for being a participant at the race. Although Nike wasn’t the only carbon shoe represented on that start line, they were obviously the shoe of choice.
Women’s starting line at the 2020 Olympic Team Trials Marathon in Atlanta, Georgia.
I had the opportunity to preview the AlphaFly Next% shoes while in Atlanta for the US marathon Team Trials. They are an interesting shoe, to say the least. First impression upon holding them is they are extremely lightweight, and the midsole is quite stiff thanks to the carbon plate. In keeping with the design of the VaporFly shoes, the midsole of the AlphaFly is comprised of Nike’s thick, lightweight foam. New to the AlphaFly Next% model are air pods integrated into the shoe, presumably to provide additional cushioning. When it comes to explaining why these shoes are “magic”, I am not a believer that the carbon fiber actually springs you forward. In delving into research, I was able to find a theory and scientific explanation for why these shoes are effective in allowing someone to run faster. Rather than springing you forward, these shoes most likely help reduce the energy cost of running and reduce your susceptibility to fatigue.
There is a research study that came out in November 2019 by Cigoja, et al, called, ‘Does increased midsole bending stiffness of sport shoes redistribute lower limb joint work during running?’ (1). This study found that placing a full carbon plate in a shoe reduces the amount of work at the knee joint and places that work back into the foot. This is relevant because a previously published study by Sanno et al (2) has shown that as runners fatigue during a long run, there is a shift in work from the ankle to the knee. When there is a shift in work from the ankle to the knee your body begins to rely on muscles and muscle-tendon units of the knee that are not as good in storing and releasing energy as those of the ankle. Therefore, reliance on the muscles of the knee for propulsion is significantly more energy taxing.
What Sanno’s study suggests is that if a runner can reduce the work redistribution away from the knee and back to the ankle as he/she fatigues, that runner can theoretically reduce the onset of fatigue by reducing energy expenditure. All this is to say that a runner could run faster for longer periods of time if something existed to control the work distribution in the joints of the knee and ankle/foot. Well, guess what? That “something” is putting a carbon plate in a shoe, and that is what was found by Cigoja, et al. They found that placing a carbon plate in a running shoe redistributed the work from the knee and returned it to the foot, thereby improving the runner’s efficiency of movement. In fact, the redistribution of work away from the knee was ~2%, and an additional ~2% of work was placed on the first toe. Over several thousand steps in a race, this total redistribution of ~4% of work can make a huge difference in preserving running economy.
Other studies (3, 4, 5) have demonstrated the positive effect of increasing stiffness in shoes, showing improvement in other biomechanical and kinetic metrics such as joint energy, jump height, and sprint performance. Interestingly, in the above mentioned study by Cigoja, et al, the researchers also tested electrical signals of various muscles while subjects ran in the carbon plated shoes and the control shoes. They found that there were not any significant systematic differences in muscle activation when wearing shoes with a carbon plate versus shoes without a carbon plate for the entire subject group, but when looking at the data of individual runners they did see differences in their own EMG activity. This is all to say that some runners used their muscles differently when wearing carbon-plated shoes. Further analysis of this EMG data as well as future studies are needed, though, before concrete interpretation can be made on the effect of carbon shoes on muscle recruitment. Studies are also needed to better understand what happens at the muscular and cellular level when running with carbon plated shoes to determine metabolic efficiency when running with these types of shoes.
So, should you buy a carbon plated shoe? If you don’t mind the hefty price tag, then the Nike VaporFly/AlphaFly may allow you to optimize your running, albeit from improving your kinematic and kinetic efficiency and not by literally springing you forward. I believe that wearing these type of shoes is no different than putting a carbon fiber disc wheel on a bike for improving aerodynamics and efficiency when cycling. When riding a bike with a disc wheel, you are still the engine that produces the power. The results of the above studies appear to suggest that the carbon plate is not propelling you forward when running any more than a carbon fiber wheel propels a cyclist. You are still the engine when running in carbon shoes. Therefore, if a 2-4% improvement in efficiency allows you to be more competitive against other racers or against time qualification standards, you may want to consider a carbon plated shoe as your go-to racing shoes. Just as with any tech purported to improve performance these shoes do not take the place of good ol’ fashioned training. You still have to do the work to reap the full benefit of maximally optimizing your running capacity. If you are considering shelling out $250+ on racing shoes, though, maybe you should also do a self check on whether or not you are doing everything else from a training, recovery, and nutrition standpoint to better your performance and reduce your risk of injury. If you incorporate the extra injury prevention and performance training habits, these carbon plated shoes can be the cherry on top.
Lastly, from my own clinical viewpoint, I wonder if these carbon plated shoes can reduce enough work to the knee—thereby reducing repetitive stress—in order to decrease knee pain or lessen your risk of developing runner’s knee symptoms. This is a direction of study that researchers will likely build towards (if not already) from these latest studies. If so, then maybe physiotherapists will start prescribing these shoes for knee and leg pain and not just performance gain.
About the Author:
Eric is a physical therapist and the founder of Beyond Exercise, a holistic health and fitness business that specializes in physical therapy, sports performance, and integrative health solutions. Eric is a certified running coach with USA Track & Field and the Road Runner’s Club of America. He specializes in rehabbing and developing running athletes.
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