In sports, “peak age” is always looming, and it can come as quickly as the early 20s. But it doesn’t have to be this way — and we’re likely to see more and more older athletes, says journalist Jeff Bercovici, San Francisco bureau chief for Inc. Magazine and author of Play On: The New Science of Elite Performance at Any Age.

Five years ago, Bercovici noticed that, increasingly, the best athletes in the world weren’t necessarily the youngest. To figure out why, he interviewed hundreds of athletes and coaches to unravel the mystery of athletic longevity. The Verge spoke with Bercovici about what happens to our bodies when we age, the influence of genetics, and the technology helping us improve performance.

This interview has been lightly edited for clarity.

What made you interested in writing this book? You mention that in your 30s you began to play soccer again and discovered that you weren’t so good, was that the genesis?

The good news is that I wasn’t good at soccer to begin with, I didn’t have any skill to lose. In my mid-30s I got obsessed with soccer and, really, for the first time my age caught up with me physically. I had all these injuries and an emergency surgery that left me with a downtime that I filled by watching sports on TV.

And I really began to pay attention to this phenomenon where the world’s top players were people that were over 30, even older than me, and they’re having their career-best performances well past what would have been considered the peak age of their sports. That was five years ago — before Roger Federer and Rafael Nadal had their career resurgences, before Tom Brady and Peyton Manning’s wins — and it’s only become harder to ignore.

How long has the phenomenon of “older peak players” been happening?

That’s really hard to answer. There’s a lot of statistical noise, it’s going to vary a lot by sport, there are trends and countertrends. I’m focusing on the past 15 to 20 years, after around 2000. It was really around the turn of the century, for example, that American runners started doing altitude training, experimenting with building in rest, and having huge effects.

So we age, what exactly is happening to the body? There are so many different processes, but what exactly are the big-picture changes holding us back?

I would highlight two things. One, the body gets worse at rejuvenating and repairing itself, which obviously affects every system. The other issue is about power and getting weaker. That’s why endurance athletes have later career peaks than athletes who need to generate a lot of power, like sprinters or long-jumpers or NFL running backs.

Genetics is a hot area right now. What do we know about what genetics tells us about athleticism and how long we’ll be able to keep improving?

This is a really tantalizing question because we’re starting to know some things, but the answers that I really want are still a ways off. There’s a guy I talk to, Stuart Kim, a geneticist at Stanford, who is one of the very few people looking at both the genetics of longevity and genetics of athleticism and trying to find the connection. But we don’t know much yet.

We do know a bit about the genetics of sports injury. More than anything else, it’s injury that limits the length of athletes’ careers. People end up retiring because they have trouble staying healthy and have too many accumulated injuries. So he has done research into genetic risk factors for certain common sports injuries, like stress fractures. There’s already a long and growing list of gene associations with different sports and in the future it may inform how athletes train and also contract negotiation between athletes and teams.

How would this genetic data come into play in contract negotiations?

This is an incredibly fraught question. As we are able to measure things they didn’t measure before, this information is both potentially empowering, but also potentially disheartening. If you know you’re at elevated risk for an ACL tear and teams know, too, that’s going to affect the market value. This is likely going to be in collective bargaining agreements and an increasingly large issue.

Genetics aside, how are training and technological advances going to push back peak age?

There’s two big ways I see training technology having promise. One is helping athletes and coaches take a more sophisticated approach to the accumulation of fatigue — basically, balancing fatigue with freshness and understanding that athletes that are highly fit but accumulating a lot of fatigue are going to perform worse and sustain more injuries. We’re seeing athlete performance programs being structured much better in sports like basketball and soccer. And there are a number of technologies that are used to monitor athlete training loads and look for signs they might need more rest.

The other big trend in technology I saw was technologies that separate desirable stresses from undesirable. Your body needs to be stressed in order to have an adaptive response to training. Your muscles need to be broken down, you need to progressively overload the system. But with a lot of types of training, that sort of progressive overload brings stresses that you don’t want or amounts that might be excessive.

So a really straightforward example is the AlterG treadmill that can be programmed to subtract weight from your body. Basically, you can dial up or down the gravity so you can hit the ground with different amounts. The main use is to rehab athletes, but it can be used in training programs.

There’s also the Kaatsu. This is blood-flow restriction training technology. It’s these pressurized, programmable bands that capture blood in your muscles while you’re exercising. For reasons that are not obvious to someone who is not a physiologist, which includes me, it basically tricks your body into responding to exercise as though you had exercised much more vigorously than you had. I did bicep curls with two little water bottles and it felt like I was curling 40-pound barbells.

It’s got really obvious uses in rehab that it’s already widely being used for, but the company that has brought it from Japan to America thinks that it’s going to have much wider application in sports because a lot of athletes need to get that training volume, but don’t want to stress down their bodies to the point where they’re breaking down prematurely.

So what’s next? Are we going to see more and more older, expert athletes?

We’re living at a really interesting moment. We’re seeing the Tom Bradys and Serena Williamses and we’re saying how amazing it is that they’re doing what they’re doing.

Of course it makes sense that older athletes are better. The advantages that accrue from experience and maturity are so great that if you can subtract physical decline from the equation — or push back that horizon — it makes sense that the best players are going to be 35 or 40. And I think that’s going to be more widespread, and we’re in for lots more 35- and 40-year-old world champions.