This piece was adapted from David Epstein’s new book The Sports Gene: Inside the Science of Extraordinary Athletic Performance.
It was January 2002, my senior indoor track season at Columbia University. I was having a good start to the year, and on this particular day I was looking forward to testing myself against my training partner, Scott. But in the final moments before our 800-meter race, Scott told me he wasn’t going to finish—that he would run the first 600 meters and then drop out. It was a strange choice, but one I understood.
Two years earlier, when I was a college sophomore and he was a high school senior, I hosted Scott on his recruiting trip. I knew he was a hot prospect because one of our assistant coaches gave me the “be very, very nice to this kid” talk. In 1997, the year I took up track as a high school junior, Scott set a 14-to-15-year-old age group record for the 400 meters in his home county of Canada. Not only did he appear talented, but he was competitive, smart, and experienced. By contrast, I was a walk-on who had yet to make the varsity traveling team. Scott was already running a good five seconds faster in the half-mile than my two minutes flat.
Over the next two years, though, our fortunes changed. By my senior season, Scott was struggling mentally. His times weren’t improving, and dropping out was a safety valve. If you stop at 600, no one can say you failed, again, to improve your 800 time. No one can say you have talent, but that you must be a head case because you’re not getting faster. I, meanwhile, had improved relatively rapidly. I came to track late in high school, so I was less experienced than my recruited training partners. And I was certainly no natural. Each fall, I would report to school having done the same prescribed light summer training as all the other half-milers. And yet, I would invariably be in worse shape than the rest of the guys. But when the arduous training began, I would catch up, quickly.
Coaches and teammates who saw me—a walk-on—gaining on a coveted recruit praised me for my toughness and work ethic. Our head coach even once used me in a pep talk about the power of hard work, saying that I appeared to have so little innate ability that he felt pity watching me race during my freshman year. My coach was right: I was a hard worker. But he couldn’t see the genes that were also driving this feel-good tale, the ones that made the hard work matter—that made my body respond to training more rapidly than many of my teammates.
This pattern plays out on every track in America—similar boys and girls experiencing spectacularly dissimilar results despite training similarly—and is now well known to scientists. In the most famous exercise genetics study ever conducted, the Heritage (Health, Risk Factors, Exercise Training and Genetics) Family Study, a consortium of five universities in the United States and Canada subjected 98 two-generation families to identical stationary-bicycle training regimens, three workouts per week of increasing intensity that would be strictly controlled in the lab. The researchers collected DNA from all 481 participants and tracked their aerobic capacity—the amount of oxygen their bodies could use during exercise—a powerful predictor of endurance. After five months of training, the variation was astonishing, ranging from about 15 percent of participants who showed little or no aerobic capacity gain all the way up to 15 percent of participants who improved dramatically, increasing the amount of oxygen their bodies could use by 50 percent or more.
Amazingly, the improvement that any one person experienced had nothing to do with how good she was to start. In some cases, the poor got relatively poorer (people who started with a low aerobic capacity and improved little); in others, the oxygen rich got richer (people who started with higher aerobic capacity and improved rapidly); with all manner of variation between—exercisers with a high baseline aerobic capacity and little improvement and others with a meager starting aerobic capacity whose bodies transformed drastically. But along the curve of improvement, families stuck together, and in 2011 the Heritage research group reported a breakthrough in exercise genetics. They identified 21 gene variants—slightly different versions of genes between people—that predict a substantial portion of an individual subject’s aerobic improvement. Heritage subjects who had at least 19 of the “favorable” versions of the genes improved their aerobic capacity nearly three times as much as subjects who had fewer than 10. The fortunate few with the beneficial gene variants became known as “high responders.”
Looking back at my time training with Scott, I believe that I was like a set of the Heritage subjects, a high responder to training who started with a low aerobic baseline. When I first started running track in high school, I had so much trouble keeping up on longer runs that I went to a pulmonologist who tested my breathing and found that I was only expelling about 60 percent as much air as my peers with each breath. Despite my youth, one of the doctor’s follow-up reports notes that my results were consistent with very early stage emphysema. When I’m in bad shape, I’m in really bad shape. As in, I get winded walking up stairs. But when I visited the pulmonologist in the winter, with serious training having just begun, I had been transformed into a young man with the power to exhale as forcefully as my peers. Though every member of my training group seemed to have a higher baseline aerobic capacity, we all responded to training to varying degrees.