Nike - Just did it! The sub 2hr shoe debate rages on.

In the Austrian capital Vienna, the Kenyan distance runner Eliud Kipchoge became the first person to complete an unsanctioned world record marathon in a time of 1:59:40, a feat thought impossible 3 years ago. Followed a day later by Kenya’s female distance runner Brigid Kosgei, obliterating Paula Radcliffe’s world record by 81 seconds and personally I feel it’s arguably the greater achievement. Yet there is a feeling that this momentous occasion and the virtue of Kipchoge’s pursuit is tarnished by the unfortunate association with Nike and Ineos.

Chemical giant Ineos who ploughed $19m into this pursuit, are unfortunately the largest producers of non-degradable plastics, a product that threatens the health of our oceans among a number of unethical business practices. Nike have also these last few weeks endured the on-going scandal with coach and founder of Nike Oregon, Alberto Salazar and his performing enhancing exploits. This has unfortunately casted cynicism over the athletic achievement and for some people to ask was this a fortunate and timely PR stunt for two colossus companies?

The real talking point is in fact not the 41 rotating pacemakers, or the electric car with lasers that helped pacing. It was in fact the shoes that Kipchoge and Kosegi wore – the Nike Vaporfly, which the media are hysterically (and with a hint of irony) calling a ‘performance enhancing shoe’. It more accurately appears to have been a hybrid or future version of the next% shoe for the Ineos challenge and the Kosegi WR assault.

Since the introduction of Vaporfly in 2017 we have seen the 5 fastest marathon times, all within the last 13 months and all run in Nike Vaporfly shoes. Pre August 2018 all of these 5 marathon times would have been world records, which is incredible when on average for decades a new marathon world record was only set every 1-3 years for men. This of course has led to cries of a ban, with similarities been drawn to the reduced drag of LZR swimsuits. But is it a fair comparison, when in swimming milliseconds count, over a 4% shoe efficiency? Take a look at the graphs. Clearly the shoe takes nothing away from the magnitude of the achievement from Kipchoge and on a level playing field of the top 5 he’s ahead of the competition. 

This shoe, more specifically Nike Vaporfly 4%, was so named since research from the University of Colorado Boulder’s Locomotion Lab from 2017 had shown that on average, the Nike Vaporfly reduced the energetic cost of running by 4% (thought to be more accurately 4.2%). The Nike Vaporfly Next% was the next generation Vaporfly and building on its success is set to further reduce the energetic cost of running by at least 5%. Check out the link below for an in depth look at the construction of the actual shoe Kipchoge and Kosgei used, a hybrid of the current Next% offered to the public and not yet released.

https://www.runnersworld.com/gear/a29447426/eliud-kipchoge-shoes/

The common DNA of Vaporfly construction features a controversial curved carbon fibre plate embedded within the midsole, alongside a rocker profile and a unique mid sole foam around 31 mm high at the heel. This is around 50 percent thicker than comparable shoes, is exceptionally compliant and resilient with memory, whilst returning most of the energy you apply to it. It is thought to account for 3% of gains and the carbon plate the 1%, again it’s an assumption as the 4% could easily be the sum of its parts and not attainable in isolation.

The bending of the carbon fibre plate stores and returns energy at a rate of 0.007 watts per kilogram with each stride, but the foam returns 0.318 W/Kg around 45 times more than the plate. The foam in fact can move the centre of mass 15mm more vertically than a regular shoe with no extra metabolic energy and increased stride length. We get caught up in the apparent spring effect of the carbon, but in fact the foam is the real spring.

It’s worth checking out Emily Farina and Brett Kirby’s work.

Farina compared no carbon plate and flat-plate shoes, which showed a cost in energy that will only counterbalance the energy saved at the MTPJ. They also looked at a moderate curve to the plate and it was revealed the cost goes down. Lastly, looking at a severe curve, you’re back to parity: your ankle isn’t working any harder than if there was no plate, so you get the best of both worlds. This is fascinating, as the extreme curve reduced energy loss at the MTPJ by 25%, but where does that energy go? The ankle would be the next logical joint for transfer to make up the loss in the system, but it does in fact appear not to need to work any harder!?

Kirby involved 14 runners training for the 2017 Portland Marathon, two roughly equal groups running in either the Vaporfly 4% or the conventional Zoom Pegasus 34. Immediately before and after the marathon blood samples were taken and afterwards they completed a soreness survey. The Vaporfly runners showed lower levels of three blood measures of muscle damage and inflammation by between 15 and 43 percent, as well as reporting significantly less leg soreness.

He additionally in the second part of the study took seven subjects in a random order, trained for two weeks each in the Vaporfly and the Pegasus, doing three standardised training regimes per week with the same intensity each time determined by heart rate. When training in the Vaporfly unsurprisingly the runners ran faster and further, but the most interesting is that the gap widened as the training week progressed. Monday they were 9 seconds per mile faster in the Vaporfly, Wednesday 15 seconds faster and by Friday 35 seconds faster. This suggests that they were able to handle the cumulative training load better and recover more effectively.

The testers subjectively felt less sore and recovered more quickly after training and racing in the Vaporfly. It’s worth mentioning the testers where not blinded to the shoe and we have seen previously in studies the psychological effect this can have. Did they just try a bit harder in Vaporfly over Pegasus?

So, what’s next? in order to sanction a marathon race the shoe needed to be available to the general public, the next generation Next% used in these last two athletes’ races where the new incarnation of the Next% not yet on sale. It’s also interesting how they will market the shoe off the shelf, as body weight is a huge factor. Light runners may not take advantage of the full spring in the midsole, inversely the heavier runners may bottom out the midsole reducing the energy return ability of the Nike VF midsole. Does this mean Nike will optimise the midsole thickness to weight, foot length, strike pattern? Will you buy the Vaporfly in your weight category?

To answer should we ban them? The mere fact that the shoes work can’t be enough, what do you ban - the carbon? The foam? We don’t fully understand why it’s working and so have no clarity over what we are objecting to. Therefore, let’s not ban them but define the maximum geometry of the carbon and foam.

Will we see Vaporfly penetrate middle distance? Triathlon and ultramarathon are particularly interesting, certainly the time savings on an ultramarathon could be huge, but also the savings on the structures of the body in a gruelling 70miles could be life changing.

Runners keep MSK physio’s busy and certainly keep private physio pockets full. Imagine the NHS cost saving of a $300 shoe that reduces stress to anyone training middle distance and further? Vaporfly boosts efficiency, but if they help more people run further in greater comfort then surely they are here to stay - what’s not to like? The only possible issues are those who are new to this shoe not weening onto it properly, with deformation of the sole at 12- 15mm, add in the increased pitch compared to a normal runner, it wouldn’t be a huge leap to predict various foot pathology risks, especially at the TA.

It certainly will be fascinating to see the Next% that is offered to the public and how far Nike can go furthering the efficiencies? They are now sure to dominate the market, with other big brands lagging behind, I look forward to seeing some further research and data as to what exactly is going on and how this could be integrated into various combinations with orthosis, or prosthesis. If you have any thoughts, I would be interested.