Here's the part that the press picked up: in addition to comparing racers to sleep-deprived controls, the paper also compares the results from one race to another - specifically, to the shorter Ultra Trail du Mont Blanc of 2009, which is "only" 100 miles, with 40% of the elevation change of the TdG. Counter-intuitively, runners in the shorter race showed more fatigue and inflammation than in the longer race. Interesting! The authors go on to discuss reasons why this might be, mainly that the pace in a longer race is slower, which is less punishing. Specifically, the pace in the longer race here was 15% slower, and some of the wear-and-tear parameters were 50% or more lower!
That does make sense, but it raises another interesting question they don't address about inter-individual exercise response differences - which I think is more likely to be relevant here than in most experiments. We can't be sure the difference is because of any difference in the race experiences themselves, because the racERS are different too. The longer the event, the more systematically different the racers are from racers in shorter events. Not only will people train differently; more importantly, in these groups of racers at the margins of human endurance, you are certainly enriching for genetic variants that allow this kind of performance and which are likely to affect the response to this kind of stress. You're out at the very end of a long tail, many standard deviations away from the mean. The harder the race, the more you're enriching. Basically, they're a bunch of mutants! Consequently, the clearest support for this theory would require that they sample the same runners. This would be hard to pull off, but it might make a difference.
Below: a few of the Tor des Geants runners. Get it? From screenrant.com.
Granted, the difference between people who run 200 miles versus 300 miles is probably not as great as the difference between people who road marathons and 100-milers. And, it was probably hard enough getting this data for any runners, let alone the same runners in multiple events - and try getting a budget to train people and an ethics board to approve your experimental endurance race. But interesting study and look forward to further results from this crew.
1. Saugy J, Place N, Millet GY, Degache F, Schena F, Millet GP. (2013) Alterations of Neuromuscular Function after the World's Most Challenging Mountain Ultra-Marathon. PLoS ONE 8(6): e65596. doi:10.1371/journal.pone.0065596
2. Millet GY, Tomazin K, Verges S, Vincent C, Bonnefoy R, Boisson R, Gergelé L, Féasson L, Martin V. (2011) Neuromuscular consequences of an extreme mountain ultra-marathon. PLoS ONE 6: e17059. doi: 10.1371/journal.pone.0017059