Picture by Chris Lawrence
Here we are…
The Nike attempt to break the 2-hour marathon barrier will happen very soon, most likely the 6th, 7th or 8th of May. It will be possible to watch the race live (though I don’t know where it will be broadcasted yet) and, hopefully, get a full understanding of the strategies chosen by the Nike team (including pacing and nutrition).
A crucial part of the strategy was/is the choice of the Monza Fromula 1 track, rather than a more traditional city location. Nike justifies the choice of Monza as follows :
The temperature hovers around 12 degrees Celsius and vapor pressure is under 12mmHg. Additionally, skies are typically overcast (minimizing heat load on the runners) and air currents don’t exhibit drastic directional shifts — thanks to the course being perfectly situated off shore and amid many trees.”
But another interesting feature for me is the fact that the course is a loop. A very short loop of 2.4 km. For official marathons, IAAF rule 240 states that aid stations should be available at least every 5 km; and in fact, there are mostly located every 5 km in major marathon events. Here, Nike runners will pass by an aid station every 2.4 km : could that make a difference? Nike indeed mentions the length of the loop as an optimal length for a “perfect management of […] hydration, (and) nutrition“. What does science say about this claim?
1/ Is dehydration in elite runners a performance-limiting factor?
There is a long and furious debate about what “adequate” hydration for endurance performance actually means. I don’t want to get into this today, but one thing is certain: losing a lot of body weight (presumably due to water and glycogen loss) doesn’t seem to be a problem for elite runners.
In an interesting study, sports scientists of the University of Glasgow examined the drinking behaviour of 10 elite marathon runners during a race. And by the way, among these 10 elites, 9 won and 1 finished 2nd of some of the major city marathons (average finishing time of 2:06:31). The study found that these elite runners drank on average during 25.5 seconds in the race, resulting in a fluid intake of about 0.5 Liters / hour. The authors estimated that such fluid intake would result in about 9% of loss of body weight, and confirmed this by measuring an almost 10% body weight loss in the 2009 Dubai marathon winner.
Ok, you may think “just because the winners finished highly dehydrated doesn’t mean that this is the best strategy… Maybe they would have done better in a well-hydrated state?”
Well, not sure… Lots of studies have tried to measure the impact on endurance performance of drinking “naturally”, i.e. according to thirst, vs drinking more, i.e. to prevent a loss of body weight above 2%. The results are, like often, mixed, but the general consensus is that 1/ drinking according to thirst is usually an optimal strategy, 2/ losing a lot of body weight during a race does not necessarily lead to a poor performance (at least not in elite runners).
In conclusion, there is not so much data around to support that a better hydration status during the race enhances performance in elite athletes (I am not talking about amateur runners here). There is even a striking prevalence of dehydration (or at least loss of body weight) in top marathon runners.
Picture by Robert F. Bukaty
2/ If it’s not about drinking more, is there something about drinking/eating more often?
Is it more efficient to drink X mL per hour in small sips or in a few big ones? As basic as the question may sound, there are not many studies on this question in elite runners. So… we need to rely on gut feelings. I would say it is most probably a good idea to segment fluid and food intake in small bites or sips to reduce gastrointestinal load. Keeping the fluid and nutrients coming at a constant rate to the stomach may reduce gastrointestinal stress and increase intestinal absorption. Still, whether there is a real difference in gastrointestinal comfort or intestinal absorption when you drink every 2.4 km instead of 5 km is just not known.
In real life, grabbing a bottle at each round will likely cost a few seconds or at least, some energy to slow down and accelerate again. If drinking at each loop is the strategy followed by the Nike runners, they will most probably have the pacers collect the bottle for the 3 main runners.
3/ Do frequent aid stations help cooling?
We all know the effects of air temperature on endurance performance and the importance to keep the core temperature down. But Monza has in part been chosen because the temperatures are in the 10 to 14°C range in the mornings of May. Thus, atmospheric conditions should be optimal without active cooling. Whether supplemental cooling during the race may improve performance in race conditions that already are near optimal remains unknown. There may be some practical real life data on this, but no published studies to my knowledge.
In a major marathon, aid stations are staggered every 5 km, meaning that elite runners get the opportunity to drink every 15 minutes. In Monza, the Nike runners will get the opportunity to refuel twice more often. There is really not enough published data in the scientific literature to conclude whether the more frequent availability of fluid and nutrients improves performance in elite runners. But in the context of a sub 2hr attempt, each second may count… so even in the absence of scientific literature published, Nike may want to try things out based on the runners’ feelings or their own collected data. And beyond nutrition, a small loop might be ideal for the Nike runners to get frequent feedback about their pace, inputs from their team, changes of pacers…
Let’s see how all this unfolds!