Whether you’re an avid runner or a dedicated weight lifter, you’ve probably cobbled together a training routine based on a few less-than-scientific factors: the distance or weight that athletic magazines and websites suggest you run or lift, the amount of exercise you can squeeze into your schedule, and whatever habits or tricks — incline on the treadmill, bicep curls on one foot — you notice among fellow joggers or gym-goers.

Epstein offers a fascinating look at how genetic research is already transforming sports science

In the future, however, you might be able to develop a training plan that has nothing to do with external edicts, generalized principles, or even trial and error. Instead, you’d train according to your own genetic athletic profile — an array of genes that determine what kind of exercise, done for how long and how often, your body will best respond to.

That’s only one of the tantalizing suggestions that David Epstein, a senior writer at Sports Illustrated, offers up in his new book The Sports Gene (Penguin). In a wide-ranging exploration of the links between genetics and athleticism — many of which are still being unraveled by scientists around the world — Epstein offers a fascinating look at how genetic research is already transforming sports science. Along the way, he digs into controversial questions about gender and race, examines the latest in genetic testing that purports to spot athletic traits, and unravels how some of the world’s best athletes — from Usain Bolt to Michael Jordan — attained the pinnacle of sporting success.

Your book is called The Sports Gene, but even a few pages in, it becomes apparent that the relationship between genetics and athletic ability is way more complex than a single gene. Were you surprised by just how complicated things get?

When I went into writing the book, I did think it would be somewhat simpler — and I wasn’t alone. If you look at article headlines from 10 years ago, when scientists finished mapping the human genome, a lot of them were saying that we’d soon know exactly what was in our individual genome, that we’d be carrying our genomes on cards in our wallets and handing those cards over to doctors during physical exams. There was a strong sense that we’d be able to link single genes to various illnesses, or abilities, or traits. But to a great extent, and this is certainly true in athletics, that’s proven to be untrue.

"There was a strong sense that we’d be able to link single genes to various illnesses, or abilities, or traits."

So no, there is no "sports gene." Instead, I think about that phrase as more of a saying that refers to an array of genetic traits — and even with all of those traits, athletic success still depends a lot on environment and a lot on practice. We can see that even more so when we look to the elite level: by the time we weed through the general population to select for athletes with elite potential, we’ve whittled down the genetic variability to a big degree. So there, you’re really seeing the power of practice and training, and training the right way, making a bigger difference.

You don’t shy away from controversial topics in the book, including gender and ethnic differences where athletic ability is concerned. You also mention how scientific progress has been hindered because of concerns about sexism or racism creeping into cultural discussions about findings. To what extent, do you think, have those fears held back research on genetics and athleticism?

You know, when I went into the book I figured that scientists worked in bubbles to some extent, and that they didn’t decide what to publish based on any external force. In a sense, that they published their data so long as they maintained academic rigor. But in this field, that hasn’t been the case at all: scientists have literally told me that they have data, really great data, that they won’t publish because of how it might be perceived or construed by the public.

The primary instance of this is related to race. Namely, scientists are concerned that data suggesting that black people are predisposed to some athletic superiority will get wound up into this bigoted misconception that athletic ability means someone lacks intellect. That might sound ridiculous, but it’s been a prejudice for some time, and it has really reached deeply into the psyches of some scientists. Where gender is concerned, I had one researcher who has published a huge amount on sex and gender differences tell me that he didn’t publish any findings until he got tenure, because it just threatened to be too controversial. From my perspective, the best way to move the field forward and to help athletes is to collect sound data and then publish it — I was disappointed to see that this hasn’t happened.

As you point out, the relationship between athletics and genetics is really complicated. But where do you see research going in the future, and what will it mean for athletes — elite or otherwise?

"We’re already seeing genetic tests trickling out that can hint at different aspects of someone’s athletic ability."

It is complicated, but we’re already seeing genetic tests trickling out that can hint at different aspects of someone’s athletic ability. Namely we’re seeing gene tests that relate to injury risk — one example is a test for the ApoE gene, which helps determine your vulnerability to brain damage from the hits you take during boxing or playing football, for example. That test is already out there, and it might really make a difference for athletes, how they compete, and what kind of medical treatment they get.

Where research is concerned, the most progress we’re seeing now is in studies that look at genes related to responses to endurance training — genetic pathways that determine who responds well to cardiovascular exercise, and who doesn’t. That has obvious appeal for athletes, or even people who wish they were athletes: the takeaway is that just because you don’t seem to have this innate, amazing talent, you might have an underlying predisposition to respond much better than you’d expect. The idea of figuring out someone’s training routine based on what they do and don’t respond to is really appealing, and I’d say we’re maybe five or ten years away from getting into that.

And it might also play an important role in personalized medicine: if someone with heart problems can respond well to aerobic activity, then maybe we can prescribe an exercise program instead of medicating them.

All of which brings me to the issue of gene doping or gene therapy — athletes actually adding or modifying genes to enhance performance. When do you anticipate that this will become a significant issue in elite sports?

Actually, I’ve done a lot of reporting on gene doping, and there is some evidence out there that athletes are already toying around with it. When I was traveling to the Beijing Olympics in 2008, I had one clinic overseas actually offer me gene therapy. And there was another incident, this one a trial of a German track coach, where it was suggested that he’d been looking for a method of delivering a gene that pushes the body to produce more red blood cells. My sense, overall, is that athletes are trying it in at least two ways right now: they’re doping with EPO receptor genes, which push the body to make red blood cells, and with human growth hormone-releasing genes. To be honest, though, these methods are risky, and some existing doping methods are so, so good and so hard to detect that athletes are probably better off sticking with the tried-and-true, at least for now.

The book introduces us to so many different genetic predispositions for different athletic talents. If you could pick one of those, and wake up tomorrow and have it, which one would it be?

Oh, this is a hard one. I grew up a pretty rabid baseball fan, and great baseball players often have incredibly stiff tendons — which relates to genes that code for the proteins that determine collagen production — and that allows them to throw really fast balls. If I had the ability to throw a ball incredibly fast, it’d make a pretty great party trick.

"They’re exercise junkies, basically."

But now that I’m thinking about it, the one that appeals the most is probably the dopamine system. Basically, genes that seem to determine the extent to which we get a sense of reward — a hit of dopamine — from a certain behavior. There are some athletes, including an ultramarathon runner named Pam Reed who I interviewed in the book, who genuinely become uncomfortable when they sit too long. They tend to run enormous, enormous distances and feel this sense of calm and happiness when they’re running, even going on 70 miles at one time. They’re exercise junkies, basically. I would love to be an ultrarunner, because each event is this epic accomplishment — I just wish I had the internal drive that these runners do.

I think anyone reading this is well-aware that they don’t have the innate talents of Usain Bolt. But what can the everyday gym rats get out of the research into genetics that informed your book?

I have one recommendation for them: stop slavishly following the latest Zumba or spinning trend, and start figuring out what your own body seems to respond to. If you look around and feel like the people next to you are reacting to a given activity, but you aren’t, then you’re probably onto something. And the fault is with you — in the very deepest sense, right down to your genes. Everyone is so different, genetically speaking, that a given method of training that works wonders for one person might not work at all for the next.

Take a scientific approach: measure some metric, whether it's how your weight changes or how much faster you’re getting, that indicates whether you’re improving or not. As far as I’m concerned, that’s really the only way to figure it out. And Usain Bolt is actually a great example, because his training is unconventional: for him, it seems like less training — but more explosive, high-intensity training — is ideal. So, in some cases, a certain genetic profile might mean that less exercise is going to have greater results.