Cross-country skier Teresa Stadlober of Austria competes in Pyeongchang, South Korea. (Image: Al Bello/Getty Images)

The shelves of drug-testing laboratories in dozens of countries are stocked with biological samples from the best athletes in the world, who deliver blood and urine for investigators to test for banned performance-enhancing substances. They’re a veritable gold mine for scientists looking to figure out what, exactly, makes an athlete at the highest level tick.

In one of the first-ever broad looks at the metabolic profiles of elite athletes, researchers at the Anti-Doping Laboratory in Qatar took advantage of that sample set. They wanted to tease out the differences between the biochemistry of power athletes, like weightlifters, and endurance athletes, like cross-country skiers. They published their results in the journal Sports Medicine in January.

Dozens of factors, both environmental and biological, go into the makeup of an elite athlete. “It’s such a complicated phenotype,” said Mohamed El-Rayess, lead author on the study. That’s why the team turned to metabolic analysis, which takes an in-depth look at the hundreds of substances that are formed as byproducts of reactions in the body. Metabolic profiles are impacted both by someone’s genetics, and by their activity and environment. That makes it a useful intermediary tool to learn about these athletes, El-Rayess said.

Metabolic panels are sometimes used as part of routine medical screenings, and can help test for conditions like diabetes, liver disease, or hypertension. The most robust screening done in your average doctor’s office, though, only looks at the levels of 14 compounds, while this study included hundreds.

El-Rayess and the study team analyzed 743 metabolites in the blood serum samples of each of 191 elite athletes (all of which initially tested negative for illegal substances). They found stark differences between the two groups: endurance athletes, for example, had higher levels of endogenous steroids hormones. Power athletes, on the other hand, had higher levels of creatine, which helps muscles recycle the energy molecule ATP—useful for explosive bursts of muscle strength.

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Some of the variation may come from the differences in body composition between the two types of athlete. Apart from the outward, physical differences (it’s not hard to tell a powerlifter from a marathoner), endurance and power athletes rely on different types of muscle, which work under different metabolic conditions. Endurance athletes tend to have a higher proportion of slow-twitch muscle fiber, which use oxygen to produce slow and steady energy, while power athletes have a higher proportion of fast-twitch muscles, which generate spikes of energy without oxygen. Muscle fiber type is partly driven by genetics, and the rest of the gap comes from sport-specific training.

“What surprised us,” El-Rayess said, “is that despite the fact that these athletes are quite heterogeneous, with different ethnicities, and competing in different sporting events, we still managed to see a very significant metabolic signature associated with elite performance in endurance and power.”

Most previous research on metabolites and sports involved carefully monitoring the diet and exercise of athletes, and taking a close look at a limited number of metabolites. This study was nearly the opposite—loosely controlled, and tracking hundreds of metabolites. The team only had information about sex and sport for each athlete, and nothing about their age, sex, diet, or body type. They had no control over the time the samples were gathered, because athletes at elite competitions are pulled by drug testers randomly.

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That’s why it was striking, El-Rayess said, that they still managed to see a significant difference between the two groups of athletes. But, he stressed, it was still just a pilot study, and later research will need to be more targeted.

Liam Heaney, a researcher at the University of Leicester who studies metabolics, said the limitations of the analysis make it difficult to interpret the results. For example, the high levels of creatine seen in the power athletes could be in response to the power and explosiveness their sport demands. Or, he noted, it could just be because many of the exercise supplements taken by athletes contain creatine.

These issues aren’t unique to this particular study, Heaney said. “It’s a great example of the problems we face in this type of work. There’s so much information and so many things that drive that information, that it’s difficult to be clear-cut.”

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But the step toward wide-ranging metabolic analysis is still important, Heaney said. “Moving towards the the wide range metabolomics allow us to generate more information, and generate new experiments and analysis,” he said.

The next steps, El-Rayess suggested, are to study the way metabolic profiles respond to exercise or diet, and compare the results from athletes to those from non-athletes. The information generated by this type of research might help improve athlete performance in different types of sports, he said, or help prevent injury. “By understanding what’s happening, we might be able to give them better advice on how to exercise, or control their diet,” he said.

Looking to the future, a complete understanding of the metabolics of elite athletes might one day be useful for talent identification, Heaney said. Or, El-Rayess suggested, it might help us understand the role genetics play in building an Olympian, compared with the power of intense training.

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A magic bullet to find the next gold medal winners is still a long way off, but the field is moving in the right direction.

“The premise of this type of analysis has now been around for a reasonable amount of time, but the sort of applications to sport is starting to blossom,” Heaney said. “Now, people are starting to think about it more pragmatically, and thinking about what answers we actually want.”

Nicole Wetsman is a health and science reporter based in New York. She tweets @NicoleWetsman.

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