The other day, I did a post looking at the likelihood of a sub-2 hour marathon, inspired by an interesting article published in the Journal of Applied Physiology. That was part 1, focusing on the historical evolution of world records, not only in the marathon, but over shorter 10km and 21km distances, because I'm of the opinion that a 2-hour marathon will only be possible when the 10,000m times and half-marathon times improve by at least 30 seconds and 90 seconds respectively. So, contrary to the JAP paper, which suggested that the barrier would be broken in between 15 and 25 years, I think it will take many, many more years.
Today sees the promised Part 2, looking more at the physiology, and specifically the running economy that will be required in order to reel off 42,195 m at an average pace of 2:50/km. It's a conceptual post, so bear with the length and the "unanswerable" questions.
And I must emphasize the point, picked up by some of you, that physiologically, our ability to separate a 2:03:59 from a 1:59:59 is limited. Both performances are close to the "limit", and given that elite athletes are rarely tested and measured in the laboratory, and that the physiological variability is larger than the difference in performance we're looking for, you won't reach the end of this kind of discussion with a concrete answer. However, it's an interesting process, nonetheless.
Running economy re-introduced
Way back in 2007, we did a short series on Running Economy, the first post of which can be read here. Running economy is a measure of how much oxygen you use when running at a given (sub-maximal) speed. The more economical the runner, the less oxygen is used, and this is crucial, because it is a characteristic of great runners that they are much more economical.
The graph below, which is redrawn from a paper by Foster and Lucia (2006), shows the running economy of a few different groups of runners.
Here, running economy has been measured as the volume of oxygen used per kilogram to run one kilometer (think of fuel economy in a car - one gallon takes you x-kilometers). So, the Europeans shown by the pink line in the above graph are using approximately 210 ml/kg to run 1 kilometer. You can convert this to the actual VO2 quite easily, if you know the running speed. For example, at 20km/hour, 1 kilometer takes 3 minutes, and so these European athletes are using 70ml/kg/min at that pace.
The Africans, shown in red, are considerably more economical (this is one of the more interesting debates in physiology - there are obviously overlaps, but generally, African runners appear more economical than Europeans). The VO2 of the Africans at 20km/hour is equal to 190 ml/kg/km, or around 63 ml/kg/min, about 10% lower than the Europeans.
Can economy and capacity predict performance?
So, knowing this, we can begin to project what kind of physiology is required in order to run a sub-2 hour marathon. The method used is very similar to that used for cycling, when we looked at the power outputs achievable during the Tour de France in our recent Tour coverage.
There are of course assumptions that must be made, but as I tried to explain for cycling, if you make the "conservative" assumptions, you still produce an interesting picture of what is physiologically plausible. This is an exercise in theory, not proof. It is the first word in a debate, not the last, so bear with some assumptions and let's see what the picture reveals.
The assumptions
The first assumption that you have to make is what relative intensity an athlete can sustain for a given period, two hours in this case.
This is not too much of a guess for elite athletes, but it does vary considerably with training - an elite athlete is usually able to sustain running speeds that require about 85% - 90% of VO2max for about one hour. Marathons are usually run at an intensity corresponding to approximately 80% of VO2max, while 10,000m is run at around 95% of VO2max.
So for a two-hour marathon, we can make the assumption that the intensity will be equal to between 80% and 85% of maximum.
Next one has to assume VO2max, the "capacity". This is more of a lottery, because the range, even in elite athletes, can be quite wide. Zersenay Tadese of Eritrea was measured at 83 ml/kg/min, but some elite runners have been measured as low as 70 ml/kg/min (the reason they are still competitive, incidentally, is likely due to exceptionally good running economy).
And then finally, you must assume running economy. This is the key assumption, because as the graph above shows, it varies quite considerably. The east Africans have been measured as having running economies in the range of 180 to 190 ml/kg/km. Zersenay Tadese was reported to be the most economical runner in history, using only 150 ml/kg/km. This is so low that I'm actually skeptical about the value. (For more on this, check out this post from 2007, and see later in this post)
Nevertheless, using three assumptions, we can create quite an interesting picture of what the sub-2 hour marathon runner will look like, at least in terms of his 'engine'.
The graph below is the first step towards bringing all three assumptions together. It converts running economy into a VO2 (in ml/kg/min) at 2-hour marathon pace (± 2:50/km).
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