Study: Better Runners Are … Inflexible?

According to one study, better runners are less flexible than others.

Matt Fitzgerald— Since the days of the original Olympics in ancient Greece, we have known that training and talent are the two key ingredients to maximum athletic performance. Until very recently, however, we understood training much better than we did talent. That’s because training is easily observed, measured, and controlled, whereas talent is nested in our microscopic genetic code.

That code is no longer invisible. Human beings now possess the capacity to link physical traits back to their underlying genetic substrates. This allows scientists to identify the genetic underpinnings of athletic talent, and they’ve gotten a good start on the project.

In 2011, researchers at the University of Cape Town, South Africa studied the association between the COL5A1 gene, flexibility, and performance in participants in the 56K Two Oceans ultramarathon. Previous work had shown that the COL5A1 gene was associated with running economy — specifically, those who had the gene tended to be more economical than those who did not. Separate work had shown that people possessing the COL5A1 gene were less flexible, as measured by a sit-and-reach test. The authors of this study sought to determine whether they could link these two traits — in other words, whether the COL5A1 gene makes people better runners because it makes them inflexible.

Seventy-two runners agreed to participate in the event. Before the race, each submitted to genetic testing to determine whether the COL5A1 gene was present. In addition, flexibility was measured with a sit-and-reach test. After the event, race times were collected and correlated with the other data.

On average, runners who possessed the COL5A1 gene finished the race 24 minutes, or 6.5 percent, faster than those who lacked the gene. Those with the COL5A1 gene were also less flexible. When the researchers divided the 72 runners into four quadrants: fast and flexible, fast and inflexible, slow and flexible, and slow and inflexible, they found that the COL5A1 gene was significantly overrepresented in the fast and inflexible quadrant.

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What is the connection between running speed and inflexibility? It’s really a connection between running economy and the elastic properties of muscle fibers. Muscle fibers are like rubber bands. Some are tight and others are loose. The loose ones stretch more, but they can’t store and discharge a lot of force. The tight ones can’t stretch very well but they can store and discharge a lot of force. That’s why you would rather be “snapped” on the forearm by a schoolyard bully using a loose rubber band instead of a tight one that’s been stretched to its limit.

Neither tight nor loose muscle fibers are inherently preferable; each is best for certain purposes. A gymnast wants looser fibers so he or she can do the splits. A runner wants tighter muscle fibers. Why? Because when a runner’s foot hits the ground, muscle fibers on the back of the lower leg and the front of the thigh stretch as the ankle and knee bend. As these muscle fibers stretch, they capture and store energy from ground impact forces, much as a rubber band stores elastic energy when you stretch it. As the runner extends the ankle and knee to push off the ground, this stored energy is released back into the ground, helping to “spring” the runner forward. This “free energy” enables the runner to maintain any given pace with a lower energy cost. In other words, it improves running economy, hence running performance.

Now, either you have the COL5A1 gene or you don’t. There’s nothing you can do about that. But you’ve probably noticed that the more you run, the harder it is to touch your toes. This loss of flexibility is a natural adaptation to training that makes you more economical. It may seem like a negative effect, but it’s actually a positive one, and you don’t want to interfere with it by doing too much stretching.

That said, it’s important to point out that inflexibility in itself is not a virtue for runners. It’s the muscle fiber elasticity associated with inflexibility that’s a virtue. There are plenty of runners whose performance is inhibited, not so by specific flexibility and mobility issues.

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About The Author: Matt Fitzgerald is the author of numerous books, including Racing Weight: How To Get Lean For Peak Performance (VeloPress, 2012) and The New Rules of Marathon & Half-Marathon Nutrition (Lifelong Books, 2013). He is also a Training Intelligence Specialist for PEAR Sports. To learn more about Matt