Mat Fraser is now Fittest Man on Earth, besting 39 other insanely fit competitors to win the 2016 Reebok CrossFit Games.

It all came down to his consistently killer scores in workouts like Murph—a pullup, pushup, squat, and 2-mile run gauntlet where competitors wear 20lb weight vests—and Double DT, a workout where you race through 10 rounds of 12 deadlifts, 9 hang power cleans, and 6 push jerks with a 155 pound barbell.

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You might think that Fraser’s secret was simply doing more muscleups, snatches, and deadlifts in training than the other guys. But it’s actually what Fraser did before he stepped in the gym each day that made the most profound difference in his training: He smiled.

We interviewed Frasier for the story 6 Insanely Fit Guys Reveal One Thing They Do Each Day. When we asked Fraser the question—“what’s one thing you do every day that improves your fitness?”—he fumbled, perhaps trying to drum up some unique exercise he’s fond of.

Then he stopped searching for words, paused, and said, “Honestly, I just make sure that I have a smile on my face when I walk in the gym. I never train unhappy.”

Here’s why: A few years ago, Fraser, now 26, lived at the U.S. Olympic Training Center in Colorado Spring. He was a promising young talent for Team USA Olympic Lifting, and he hoped to compete in the 2016 games in Rio.

But then one bad lift caused Frasier to injure his back. “I needed to have back surgery, and it was a long road to recovery,” says Fraser. On that road he realized that some of the people in his life weren’t there for the right reasons.

“As soon as I got injured and thought my career was over, I realized that all of the sudden I had a few fewer friends. It created some resentment inside me,” says Fraser. “After I rehabbed, I found myself training with more of a ‘I’ll show them’ attitude instead of a ‘I’m excited to get in the gym and see what I’m capable of’ attitude. I trained like that for quite a while. But it eventually just burnt me out. I lost love for the sport. And I wasn’t even happy outside of the gym anymore.”

Related: The CrossFit Workout You Have to Try

Even though he was hitting PRs and was on track to make the Olympic team, Fraser decided to leave the sport of Olympic lifting.

He moved back to his home state of Vermont, eventually joining a local CrossFit box just so he could do some Olympic lifting. But soon he joined the group workouts and got hooked—and that’s when he declared that happiness was a requirement for training.

“I just don’t find that I’m able to push myself as hard if I’m at all unhappy, upset, or angry,” he says. "When I go into a workout happy, with a smile on my face, I’m willing to suffer a bit more, I’m willing to dig a little deeper, push a little harder.” That extra effort each workout amplifies the evolution of his fitness.

Related: How to Do 50 Perfect Pushups

Fraser might be onto something. When you smile, your brain shoots out chemicals like endorphins, dopamine, and serotonin. And those chemicals can help you relax, lower your heart rate, and even blunt the effect of pain, according to scientists at The University of Arizona.

A study in the Journal of Sport & Exercise found that people who were in a good mood exercised at a higher intensity. What’s more, that study also discovered that being in a good mood makes you more likely to exercise, while exercising boosts your mood—a happy disposition might create a positive fitness feedback loop.

Related: 5 Guys Who Wake Up at 4 a.m. to Work Out Tell You How They Do It

Fraser is so adamant about his rule that on days he wakes up in a bad mood (“some days it just happens,” he says), he’ll take steps to change it. “I’ll do something before training to cheer myself up, like go for a motorcycle ride or treat myself to a good lunch,” he says.

So what about you? Maybe your boss chewed you out right before your lunchtime workout, or some jackass cut you off on the way to the gym. Take a second to elevate your temperament. Listen to your favorite upbeat song—research conducted at the University of Missouri says that can make you happier.

Or consider working out at a CrossFit box. “It’s easier to be happy at a CrossFit box compared to a big box gym, because you’re all working out together, doing the same workout,” says Fraser. “That builds camaraderie and everyone becomes friends.”

Whatever you do, just make sure you train happy. “The most dangerous competitor is a happy competitor,” says Fraser.

Michael Easter Michael Easter is a health and fitness writer and a visiting lecturer at UNLV.

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