Just as no amount of cooking prowess can turn rotten ingredients into a gourmet meal, a world-class training regimen can't turn just anyone into Olympic gold. Elite athletes are the final product of decades of hard work, to be sure, but for many, their DNA spells out a list of superior raw ingredients.
So what's the recipe for an Olympian, exactly?
Ability in running, swimming, weightlifting and the other so-called "nonskill sports" comes down to raw power, strength, speed or endurance (depending on the sport), rather than training. Bob Girandola, a kinesiologist at the University of Southern California, said these forms of athleticism "ultimately are determined by genetics. You don't increase the number or type of muscle fibers by training."
Whereas most people sport a fairly even split between fast- and slow-twitch muscle fibers — the former delivering explosive power, the latter, slow-burning endurance — genetic tests show elite marathon runners' fibers are 80 percent to 90 percent of the slow-twitch variety. If you lack such a skewed set, you'll never run a 2-hour, 15-minute marathon. Sprinters, meanwhile, harbor more than their fair share of fast-twitch fibers for raw power and speed — "not something you can train," Girandola said.
Studies show that the body's muscle-fiber production depends on which variant of the gene ACTN3 one possesses. Two copies of the X variant of the gene produces a bounty of slow fibers and a predisposition for endurance sports, while two copies of the R variant lead to an overproduction of fast fibers and, consequently, a capacity for activities requiring strength or speed. So as not to waste kids' time training for events they'll never conquer, companies have even sprung up offering saliva tests to determine children's ACTN3 makeup.
On top of muscle type, there's also quantity. Two people following exactly the same training regimen can gain strength at very different rates. "In a few weeks, one person will be almost doubling the amount of weight they can lift. They simply had more muscle fibers that could respond to the training stimulus," Girandola told Life's Little Mysteries.
Basketball players are almost always tall; gymnasts are generally short; weightlifters usually are stocky. In short, body type matters in most sports. But even within these general profiles, subtle differences often give Olympic gold medalists a leg up over their competitors. [Why Rivalries Make Us Better]
For sprinters, some scientists think there's a reason why every world-record holder in the 100-meter dash for the past 50 years has been ethnically West African: black people generally have higher centers of gravity.
"Blacks tend to have longer limbs with smaller circumferences, meaning that their centers of gravity are higher compared to whites of the same height," said Adrian Bejan, a professor at Duke University who co-authored a 2010 study on ethnic differences between athletes. "Asians and whites tend to have longer torsos, so their centers of gravity are lower." Because legs do the work of running while the torso of the body is mostly just extra weight that the legs must carry, a higher leg-to-torso-length ratio gives blacks who are elite runners an advantage in a race lasting under 10 seconds.
Meanwhile, whites and Asians tend to dominate in swimming, where a longer torso helps. "Swimming actually generates a wave. The sport is the art of surfacing on that wave. When the wave is bigger — because the torso is longer — they go faster," Bejan said.
More pain, more gain
When it comes to sports like sailing, gymnastics and soccer, one must be naturally fit and have the right body type, but ultimately, practice makes perfect. As Girandola put it, "With soccer players in Brazil, of course they're good; you see kids playing out there morning, noon and night."
And yet, even in such sports, some athletes may be, by nature, more motivated to keep practicing after others have lost interest, and better able to ignore pain that would send others to the sidelines.
"You see some athletes pushing their pain thresholds and having the mental capacity to push themselves to their full potential. Maybe they're processing information differently," said Jon Williamson, a professor at the University of Texas Southwestern Medical Center who studies the brain's role in exercise and physical activity.
Elite athletes' brains may simply ignore pain signals from their muscles, allowing them to push through injuries and tolerate a greater buildup of lactic acid in their working muscles, he said. (Lactic acid is a muscle fuel that gets produced from the breakdown of glucose during strenuous exercise; its accumulation causes the burning sensation that makes you want to take a break.) However, no one yet knows whether a higher pain tolerance is inborn or learned. [How Powerful Is Willpower?]
One step ahead
Recent research shows top athletes exhibit greater activity in a region of the brain called the insular cortex, or insula, which takes part in such diverse deeds as perception, self-awareness, motor control, emotion and regulating homeostasis. "It's one of these regions that allows you to process external information and generate an internal response," Williamson said.
By anticipating their bodies' future needs, athletes' insulas generate a physical response in advance, thereby preventing a lag time. For example, "if you're running and you see a hill in front of you, some people see the hill before the body begins to respond to the hill," he said. "If you're experienced or trained, your body responds sooner, pumping blood through your muscles faster, making adjustments in advance that will make running up the hill easier."
In one study, Williamson examined athletes riding exercise bikes under hypnosis. "We told them they were about to go up a hill, and their heart rate increased even though their work load hadn't changed. When that happened, we saw activation in the insular cortex," he said. Other studies have shown athletes can even prepare their bodies to perform well despite a decrease in ambient oxygen levels if they know the drop is coming in advance.
It isn't yet clear whether insular cortex activity gets honed by training, or simply works better, in some people, by nature. "It's an interesting question," Williamson said. Either way, a lively insula might just be the ultimate ticket to the Olympics.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.
Natalie Wolchover was a staff writer for Live Science from 2010 to 2012 and is currently a senior physics writer and editor for Quanta Magazine. She holds a bachelor's degree in physics from Tufts University and has studied physics at the University of California, Berkeley. Along with the staff of Quanta, Wolchover won the 2022 Pulitzer Prize for explanatory writing for her work on the building of the James Webb Space Telescope. Her work has also appeared in the The Best American Science and Nature Writing and The Best Writing on Mathematics, Nature, The New Yorker and Popular Science. She was the 2016 winner of the Evert Clark/Seth Payne Award, an annual prize for young science journalists, as well as the winner of the 2017 Science Communication Award for the American Institute of Physics.