What started as a way to honor one fallen Marine has turned into a nationwide tradition.

Since 2016, the annual “Manion WOD” — a brutal CrossFit-style workout in memory of 1st Lt. Travis Manion — has steadily grown, drawing more than 6,000 participants to nearly 400 gyms across the country this year alone.

The workout is seven rounds of a 400-meter run and 29 back squats. Simple, but certainly not easy. And that’s the point.

CLICK HERE FOR MORE COVERAGE FROM OUTKICK

The ‘Manion WOD’ has been an annual tradition since 2016. (Travis Manion Foundaton)

“When people are like, ‘This is a hard workout,’ I’m like, ‘As it should be, right?’” Travis’ sister, Ryan Manion, told OutKick. “That’s the point. It should be a hard workout, because you think about the sacrifices that the men and women that have given their lives in defense of our freedoms have made for us. The least we can do is go out and challenge ourselves a little bit.”

Travis Manion, a former wrestler at the United States Naval Academy, was killed by an enemy sniper in Iraq on April 29, 2007, while saving his wounded teammates. The structure of the workout itself reflects that legacy. It was built around both the date of his death and the kind of physical toughness he was known for.

“It was designed by CrossFit to be a super hard leg workout because, as a wrestler, my brother was kind of known for his leg strength,” Ryan explained.

‘AMERICA’S GAME’: GOLD STAR SISTER EXPLAINS WHY ARMY-NAVY TRANSCENDS FOOTBALL

Now a nationwide event, the Manion WOD brings together veterans, families and plenty of people with no military connection at all, too.

Marine 1st Lt. Travis Manion was killed by enemy sniper on April 29, 2007, in Iraq. (Travis Manion Foundation)

And for those stepping into the gym without that personal connection, Ryan hopes they walk away with shaky legs and a new perspective.

“It’s seven rounds, and you’re doing this repetitive motion of squats and running. And once you hit that fourth, fifth, sixth round, it starts to hurt a little bit,” she said. “And I would say that’s the time to dig deep and think about those sacrifices and reflect on them.”

This year’s workout came with an extra personal touch. Participants across the country all worked out to the same music Travis listened to during his final deployment, pulled from an iPod that was returned to his family after his death.

“He had an iPod in Iraq, and it came back in his foot locker,” Ryan said. 

“A few years ago, I tried to turn it on, and it didn’t work. I actually took it to a friend who owns a tech shop, and he was able to pull all the songs off of it. And I was like, ‘How cool would it be that people could do this workout and actually listen to the songs he was listening to?’”

Ryan Manion Borek, sister of fallen Marine Travis Manion, speaks to participants during a ceremony before the 9/11 Heroes Run at Ellington Airport in Houston on Sept. 10, 2016. The event benefits wounded veterans, injured police officers and firefighters, and families of fallen heroes and veterans. (Annie Mulligan/Houston Chronicle/Getty Images)

If you’re wondering what that playlist sounds like, it’s got AC/DC, Creedence Clearwater Revival, Led Zeppelin, Rage Against the Machine and Metallica, to name a few. And, of course, “Stranglehold” by Ted Nugent — Travis’ old wrestling walk-out song.

But beyond the reps and the music, Ryan says the real impact is something much bigger, especially for veterans and military families navigating life after service.

“​​When you look at the bigger issues that are facing our service members when they take off the uniform, like mental health and depression. And, unfortunately, the suicide epidemic is pretty high amongst veterans,” Ryan said. 

CLICK HERE TO DOWNLOAD THE FOX NEWS APP

“What is that next step they’re going to take to serve outside of uniform, and what’s that community that they’re going to go to?”

The Travis Manion Foundation, she says, helps to bridge that gap.

The ‘Manion WOD’ consists of seven rounds of a 400-meter run and 29 back squats. (Travis Manion Foundation)

“We’ve found these simple approaches to creating this community have massive effects on really serious outcomes that our service members are facing,” Ryan said.

And, over the weekend, that community showed up in the simplest way possible — side by side in a gym, grinding through a workout, and remembering the ones who didn’t make it home.