In a recent Nike funded study, Hoogkamer et al. 2017 concluded that the Nike Zoom Vaporfly 4%, a shoe embedded with a full-length curved carbon fiber plate, reduces the energy cost of marathon running (i.e. improving running efficiency) by ~4% in comparison to 2 traditional high performing racing shoes (below).
The study, then used a predictive model to suggest that a 4% improvement in running efficiency is equivalent to increasing a 2:54/km paced marathon (2:02:58) by 3.4%. To put this 3.4% performance improvement into perspective, let’s undo a 3.4% improvement from recent marathon running performances that were run in the Nike Zoom Vaporfly 4% shoes:
- Eliud Kipchoge 2:00:25 (Breaking2 at Monza) = 2:04:31
- Galen Rupp 2:09:20 (Chicago) = 2:13:43
- Edna Kiplagat 2:21:52 (Boston) = 2:26:41
Although none of the above performances were run exactly at 2:54min/km pace (where the 3.4% speed improvement supposedly applies), it can be justified that that improvement would clearly NOT correspond to the predictive models estimation. Steve Magness of The Science of Running, predicts (via twitter) that the shoe could be worth 30-60sec for Kipchoge.
This is not to criticise the legitimacy of the studies, but rather to suggest that the predictive model is off, which is also not a shock. Despite this, it’s still worth reminding that this is the classic case of data being disconnected from reality, where a 4% metabolic improvement doesn’t equate to (or anything close to) 4% improved speed. Perhaps not what the general public would expect.
In a sport where performance is highly multifaceted, circumstantial and individualistic, trying to quantify a performance advantage through the boost of a single constraint is similar to pinning the tail on the donkey. Which is why moderating future shoe design will become very difficult, if it comes down to it, as it’s hard in the most scientific sense to quantify a shoes advantage.
Technological advancement is inevitable, and sometimes appears before the existence of the rules which moderate it. Nike’s new shoe is in a grey zone within the rule book, and the question as to whether the advantage is unfair is currently relevant. Running (again) joins a long list of sports which have been posed with a similar question. Take swimming for example, where advancements are represented in the form of performance improvement waterfalls on figure 2.
Unlike running, swimming is a highly inefficient sport where an advancement (in swim suits, pool technology, underwater technique monitoring cameras, etc.) which results in the slightest reduction in drag or improvement in buoyancy, amplifies performance improvements. In 2008, a new full-body swimsuit made from polyurethane material was introduced to the professional swim circuit. Ultimately, in the following year, 43 long course swimming world records were broken, and the suit soon thereafter was banned.
Sometimes advancements are not so much technological as they are opportunistic within the rules of sport. Take Russian high jumper Yuri Stepanov, who in 1957 jumped to a new world record height while wearing shoes with a 25mm thick sole. The IAAF subsequently set the maximum sole thickness at 13mm which still stands today.
Unlike the above 2 examples where the scale of improvement is apparent and homogeneous for competitors, the advantage a shoe like the Nike Zoom Vaporfly Elite (4%) presents a variable within itself. Prof. Ross Tucker advocates: “if you try to legislate against the scale of improvement, you’re heading for disaster, because advances in scale are frequent and simple. Therefore, you should always legislate against concept.”
The nature of running allows the sport to differentiate itself from others in that, at the highest level, technology doesn’t play the deciding factor. There’s beauty in that.