Some people suffer more damage than others, but it may not slow them down.
A few weeks ago, a press release hit the wires with a curiosity-provoking title and subtitle: “Are your muscles genetically prepared to run a marathon? The way is open for the use of genetics in training.”
The press release described a study by researchers at the Exercise Physiology Laboratory of Camilo José Cela University in Spain, published in PLoS ONE, looking at markers of muscle damage after running a marathon. Some people, previous studies had found, seem to suffer much greater damage than others despite similar training; the new study linked these differences to seven gene variants – and in the process, the press release proclaimed, demonstrated “that genetics plays an essential role in success when completing this long distance”.
This topic interests me, in part because of my own limited experience with the marathon. I ran one in 2013 – and I suffered. While I’m always sceptical of self-diagnosis, my impression was that my training, pacing and fuelling were all fine, but that my quads were simply shredded. So can I blame genetics for my abnormally acute muscle damage? And can this knowledge somehow allow me to do better next time?
The study followed 67 runners at the Rock ’n’ Roll Madrid Marathon, who gave blood samples and completed some simple tests immediately before and after the race. In particular, they measured levels of two proteins – creatine kinase (CK) and myoglobin – that leak into the blood when muscles are damaged.
The runners were also assigned a ‘gene score’ out of 14, reflecting whether they had zero, one, or two copies of each of the seven gene variants associated with lower susceptibility to muscle damage.
Sure enough, the marathoners who had relatively low post-race CK levels (below 400 units/litre) also had higher gene scores: an average of 5.2 out of 14, compared to 4.4 in those with higher CK levels. Using myoglobin to divide the low- and high-damage groups produced similar results.
That’s kind of cool. But it’s a long way from the hype in the press release and some of the resulting news stories. Some sample headlines: “Maybe you just weren’t born to run a marathon, says science,” according to Metro. Or “That Explains It: Avid Runners Are Genetically Gifted to Feel Less Pain,” as Reader’s Digest put it. The sub-headline continues: “Does it take you twice as long to reach the finish line? Blame your genetics.”
There’s just one problem: the actual race results don’t support this conclusion. Both groups finished the marathon in times that averaged a little below 4:00, with no statistically significant difference between them.
Similarly, both groups saw a basically identical reduction in maximum jump height from pre- to post-marathon. The change in leg muscle power was the same, too; so was the rating of perceived exertion during the race. And even self-reported leg muscle soreness, which you’d think would track pretty closely with muscle damage, was the same. (If anything, the group with lower damage reported higher perceived soreness, averaging 6.34 on a 10-point scale compared to 6.14 for the high-damage group.)
So a better headline would have been “That Explains Nothing.” I don’t doubt that the genes identified are indeed linked to how much levels of CK increase, and that this increase is in some way related to muscle damage. But these subtle differences, in this study at least, have absolutely zero predictive power for how fast you run or how sore you feel.
In a sense, you can take this as a broader cautionary tale about the dubious practical value of many of the genetic tests that are currently being marketed to athletes and everyone else. Even when the effects are real, the resulting differences are subtle.
And, moreover, even if there were big differences – if the low-muscle-damage group was significantly faster, say – what would that change? Would knowing you have the high-damage genes deter you from trying a marathon? If so, that seems like a good argument not to get that particular genetic test.
There’s also a simpler, narrower lesson to take here: read the study, not the press release (or, worse, the news articles based on the press release). In this case, it’s in an open-access journal that’s freely available to read. It’s interesting, in my opinion, to learn more about the factors, including genes, that may help explain why I suffered so terribly during the last 10K of my marathon. But this particular study is not the alibi I was looking for.
