Parkour — once synonymous with an outlaw, fence-hopping subculture — became one of the fastest-growing fitness trends in the U.S. last year, Axios' Carly Mallenbaum writes from data by the fitness platform ClassPass.

• Why it matters: The sport, all about moving freely through space, has gone mainstream.

🤸 I tried it, and it's thrilling.

Catch up quick: Parkour was created in the '90s by a Parisian teenager who ran on rooftops and scaled walls with his friends. In the 2000s, it became more visible in the U.S. as videos circulated online.

• Then freerunning — a more expressive style that added tricks — branched off.

The popularity of obstacle-course TV shows like "American Ninja Warrior" helped fuel broader interest in movement-based workouts, and training gyms that incorporate parkour-style skills.

• The sport went viral after "The Office" Season 6 made "Parkour!" a punchline.

🧗 How it works: At Fr3running Society in L.A., I started by wiping my shoes on a sticky mat, then stepping into a vast, industrial space — a maze of wooden platforms, metal pipes, black mats and rock-climbing walls.

• The equipment was arranged into stations for drilling specific movements.
• I had to leap from a block to catch a bar, swing through the air, then release and land on a raised platform that looked very, very far away.

😮 I was scared. And said as much.

• As the gym's owner put it, my "central nervous system was taking over and saying 'don't get hurt' and preventing damage."

He recommended breathing through it and continuing to expose myself to more challenging scenarios — like higher jumps and swings — in a controlled environment.

• 🧠 That helps "sharpen the blade in your brain" and expand your comfort zone, he said.

My nerves didn't go away. But after swinging and not jumping, I finally did let go. I barely made it.

💬 Parkour is "everything I used to do as a kid that I was told not to do," says Christian Elijah Mayo, owner and operator of Fr3running Society.

• Mayo, a former gymnast turned off by rigid rules and scoring, quit the sport as a teen to "keep flipping." He channeled his playground rebellion into stunt work and eventually business ownership.

The bottom line: It feels good to do any kind of workout, but this was different. I was euphoric.

• I felt myself pushing physical limits — and tapping into a kind of play I hadn't experienced in years. It ended in a game of tag, for goodness' sake. (Being chased has a way of quieting second thoughts.)

And there was a camaraderie you don't usually get in Pilates.

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Britain's Phebe Bekker and James Hernandez compete in ice dance today at the Winter Olympics in Milan.