Running as we know it may have changed with the recent performance by Eliud Kipchoge in running 1.59.40 in the INESO 1:59 Challenge in Vienna, Austria last month. Many, including myself, believe this run was more about a leap in shoe technology rather than a leap in pure marathoning ability. Don’t get me wrong, I think Eliud Kipchoge is the best marathoner in history but we need to protect the sports integrity and this seems to be more about advances in technology which may prove to be outside the rules of footwear set down by the IAAF (International Amateur Athletics Federation).

There have been many points raised by the doubters about why this performance isn’t legal; things such as the loop course, the different pacers jumping in and out every 5k, the pace car with a laser beam in front of the runners at 2mins 50 per k, the fact that a man on a bike was jumping in and out handing Kipchoge his drinks. All of these valid points aside, it is the shoes on his feet that need closest attention as none of these other factors will be allowed in a normal running race, but the shoes are and have been since the first pair came out in 2016. Now we need to consider how much technology in a running shoe is too much, and do races like the INESO 1:59 make it more a victory for technology rather than human performance and ability.

Even the founder of the original project to run a marathon in less than two hours has warned that “technological doping” is in danger of wrecking distance running. 

In going sub 2 hours for the marathon in Vienna, Kipchoge was wearing a prototype version of the Nike ZoomX Vaporfly Next%. One day later Brigid Kosgei took a staggering 81 seconds off Paula Radcliffe’s 16-year-old marathon world record in a different version of the Vaporfly. Since the first version of the Vapourfly’s came out in 2017, with the sole purpose of improving running economy and speed, we have seen the five fastest official times in history  (including Kipchoge’s official world record of 2:01:39 set in Berlin in September 2018), ran in a version of this shoe. One would say Nike have succeeded in their mission!
Like other sports before it, running may have to begin to consider introducing limits on technological innovations assisting athletes. We have seen this happen with tennis rackets, cricket bats, golf balls and probably the best comparison was the polyurethane-based swimsuits (LZR Racer) that were banned starting in 2010 after many world records were set wearing them. Like running, swimming is a sport essentially based on the physical performance and ability of the athlete, and the suit (which in essence made a swimmer more buoyant) was more beneficial to some swimmers than others, creating an uneven playing field. In cases like this, if all athletes would benefit equally, and have equal access to the item, then it is unlikely the swimsuit would have been banned.
Right now, we may not be seeing the runner with the best physiology winning a running race!

It is important to note that footwear as described by the IAAF is purely to protect the foot. It was not envisaged that footwear would become a performance aiding tool. We do actually have a precedence already in athletics, related to a rule change that was instigated to limit technology. Yuri Stepanov set a world record in 1957 in the high jump while wearing shoes with a 25mm thick sole. The IAAF subsequently set the maximum sole thickness in high jump shoes at 13mm which still stands today.

In the case of INESO 1:59, the prototype shoe Kipchoge wore isn’t available to the public, and none of the runners pacing him were even given that shoe to wear.

The IAAF Footwear Rule:

“Athletes may compete barefoot or with footwear on one or both feet. The purpose of shoes for competition is to give protection and stability to the feet and a firm grip on the ground. Such shoes, however, must not be constructed so as to give athletes any unfair assistance or advantage.” It also says “ Athletes may not use any appliance, either inside or outside the shoe, which will have the effect of increasing the thickness of the sole above the permitted maximum, or which can give the wearer any advantage which he would not obtain from the type of shoe described in the previous paragraphs.”

The most technologically advanced shoe yet – fair? You be the judge! This is an example of the Nike  Vaporfly Next % shoe. – Kipchoge’s was even more advanced than this!

Limits are needed in shoe design!

I was put onto a great podcast by a client of mine when we were discussing the Kipchoge performance and the shoes. Given my intrigue with the shoes, I found the podcast to be so on point that I thought I would write a summary combined with my own thoughts for you all to ponder. 

After listening to this podcast, which aligns with my own thoughts on the fairness of competition and testing the limits of the human body, I am convinced that the governing body needs to set criteria for restrictions on footwear. As highlighted in this podcast, as in the high jump example above, the issue really all comes down to a shoes “stack height”. 
“Stack Height” refers to how much material is between your foot and the ground. It is basically the thickness of the midsole in your shoe. The issue is the bigger the stack height the greater the space that companies like Nike have to insert technological materials like the carbon fiber plates in these controversial shoes. The other factor to consider is if you can increase stack height without adding to the mass of the shoe, you are potentially giving the wearer a biomechanical advantage as well. 
I will keep my technical analysis of the shoes to a minimum as our podiatry team is going to follow this article by metaphorically stripping back the shoe to describe how it is working for you.
There have been several iterations of the Nike Vaporfly since the original version in 2017 which have since taken the marathon world by storm. The original version was aptly named the 4%ers largely as a result of lab results showing that the energy cost of running was 4% less at the same pace in these shoes. The obvious change in each new model of the shoe, culminating in the current prototype shoes worn by Kipchoge in his sub 2 hour race(I believe they will be called Alphafly, but they have patents pending before they will become available to general public) is the stack height keeps increasing to the point where we now have a bizarrely tall shoe with a stack height close to 50 millimetres.
The two key pieces of technology that our podiatry team will analyse in detail are the carbon plate located within the mid sole which is shaped a little like a spatula, and a new mid sole foam. The key factor in a racing shoe is to be able to keep the weight of the shoe down and Nike have been able to do this with the ultralight and responsive foam dubbed Zoom X (Pebax).
Other companies had been changing mid sole material in their shoes with claims that they also were energy saving but studies showed that any saving was no better than the natural variance in normal energy cost of running from day to day. The material Nike are using has been shown to offer greater energy return than any previously used material.
So much of the talk about these shoes has focused on the carbon plates but it may actually be the mid sole material that is the key, both because of its energy return (think spring) factors but also its lightness which is allowing Nike to increase the shoes stack height without adding weight to the shoe. They then have more space to be able to play around with variations in the carbon plate/s used. The carbon plates may largely be providing stability so that the very soft foam in the mid sole does not make the shoe too unstable especially as it builds up to approaching 4cm’s in the current model.
We are now at the point where other non-Nike sponsored athletes are making complaints to the IAAF (athletics governing body) that they are not on a level playing field. More research is now being done to investigate the merits of the shoe and whether they may actually be providing an unfair advantage. Like the swimsuits discussed earlier, if it is shown that the Vaporfly’s benefit a certain type of runner and not others then it forces the question of whether they should be permitted, or at the very least, restrictions put in place. 
There may well be an uneven playing field in the case of these shoes, as they have been found to be more energy saving for those who are rear foot strikers than forefoot strikers. They also are more beneficial to athletes who spend less time on the ground during their running gait. Coincidentally decreased ground contact time has been shown to be a key factor accredited to many African runners who have dominated the marathon event over the past 20 years.
So what’s the answer?
The obvious one that has been raised by Professor Ross Tucker in this podcast and also by biomechanist, Geoffrey Burns in the British Journal of Sports Medicine is that the stack height is limited in all shoes just like they did in the high jump, probably back to something around 30mm which is a common stack height seen in a running shoe
Other Pitfalls
Putting my physio hat back on and ignoring the performance benefits of these shoes I thought I should finish by posing whether these shoes may eventually lead to injury concerns for those who have overused them. As I explain to patients all the time, whenever we do something to unload a particular part of the body there is usually a flip side to that where we overload something else. We have actually seen this in many shoe models previously where technological changes in the shoe has resulted in extra load on achilles tendons or big toes etc. In this case the carbon plate decreases the natural spring mechanism done by the arch of the foot and the big toe as it performs this role by rocking the runner forward off their big toe. We wait to see whether in the long term we will see runners paying a price for this if they use them for all their running and not just race days. I certainly would recommend those interested in using this shoe to limit it to race days only and use another shoe for training. The fact that they can cost in excess of $300 should make it easier to convince people to wear them as little as possible!!

For anyone really keen to have a listen you can find the podcast at: The Real Science of Sport, 23rd October, “The Shoe That Broke Running”.

This has been quite a along article, but I’m sure you’ll agree it is quite a controversial topic and one that needs a lot of discussions with the decision makers in athletics and running sports! For now, it’s a matter of “watch this space”!

Rob O’Donnell
SSPC Physiotherapist