The same gene makes runners fast… and inflexible

This is a really neat study (tweeted about by @stevemagness). I’ve been writing a bunch lately about the fact that being inflexible seems to be associated with higher running economy (i.e. better “gas mileage,” so it takes less energy to run at a given pace). A new study from the guys at the University of Cape Town adds a very interesting wrinkle to this discussion: the same gene that makes people inflexible also makes them run fast.

The study focuses on a gene called COL5A1, which has recently been shown to be linked to your hereditary level of flexibility (about 64-72% of your flexibility is determined by genes, with the rest by environment, the paper says). One version of the gene means you’re quite flexible (and stay more flexible as you age), the other means you’re stiff.

So, in light of all these studies linking inflexibility and running economy, the UCT researchers decided to see if this same gene is also linked to endurance running performance. They analyzed results from the 2006 and 2007 South African Ironman triathlon for 313 athletes who agreed to genetic testing. Sure enough, those with the inflexible gene ran significantly faster than those with the flexible version (4:54 versus 5:07 for the marathon). But the two groups were indistinguishable in the swim and the bike — so this gene doesn’t make you a better endurance athlete, or improve your oxygen transport or anything like that. It just seems to make you run more efficiently.

Now, a study like this leaves a lot of dots to be connected. It’s possible that the effect on running performance is mediated by some completely different pathway other than flexibility that we don’t even expect. Genetic studies don’t lend themselves to simple conclusions.

But it’s certainly very suggestive, and it offers a convincing explanation for one of the enduring mysteries of running: why so many runners are so remarkably inflexible despite decades of indoctrination about the benefits of flexibility. We’ve always assumed that lots of running makes you inflexible — but maybe we’ve (once again) mistaken correlation for causation.