When Rich Vos tells you to pack sand, he’s not kidding.

It’s the kind of abuse that goes along with being part of his militaristic breed of athlete.

Vos, 29, a former Army soldier, is head coach of CrossFit Hustle, a Northern Kentucky strength and conditioning program. CrossFit gets people prepared for runs like the “Tough Mudder” (think mud, sweat and tears), and team events like the “GORUCK Challenge” (imagine doing an obstacle course with a weighted pack strapped on your back).

Vos and his friends begin workouts by packing their rucksacks with bricks or sand. They run. They carry kettlebells up hills. They do push-ups, crawls and lunges. They run some more. Sometimes they carry logs or heavy tires. They even carry each other. And they finish their missions together.

The camaraderie sets their training apart from other fitness programs, Vos says. “It’s a community.”

Misery loves company

It’s one thing to commit to a 5K race, or even a triathlon. The people who sign up for brutal training and obstacle courses are looking for more extreme ways to motivate themselves.

Since Jeff Brinkman teamed up with Vos in February, the 32-year-old graphic designer from Florence has lost 35 pounds.

“I played hockey a lot in school, and I kind of let myself go,” Brinkman says. “I needed an excuse to get back into shape. They always say the hardest part is signing up, so once you do it, it’s just a matter of grin and bear it. The GORUCK Challenge will introduce you to yourself. I’m capable of a lot more than I thought I was.”

But it’s not just lifelong athletes who are joining these ranks.

Two years ago, Michelle Bugel weighed almost 300 pounds. She lost 115 pounds last year on the Jenny Craig weight-loss program. Then she showed up at a cross-training program to try to build muscle.

“It’s intimidating walking through the front door,” says Bugel, 41, of Fort Wright. “There’s no way I could have done all of this stuff when I came in here, but I’m getting stronger.”

Today, “I have a lot more energy,” she says, “and I’m liking myself a lot more. I really wasn’t liking myself for a long time there.”

Ripple Effect

High-intensity workout trends like CrossFit are exploding, not just because of mud races and social media attention, but because participants are so driven by results, says Lucas Vega, owner and head coach at Underground Fitness NKY in Florence. His clients range from their 20s to their 60s, and members have grown close.

“The group atmosphere is really motivating,” he says. “And we put numbers up on the board and show your improvement. Some programs are based on aesthetics. We focus on performance.”

At Vos’s Monday night CrossFit Hustle training in Erlanger, Nick Nampalli explains the appeal: “It’s teaching me that I can push the limits I thought I had. And that’s an awesome feeling.

“You think you’ve reached your peak, and you push it one more,” says Nampalli, 27, of Burlington, a financial analyst for Citibank. “I think it has ripple effects across your personal and professional life.”

For Jonathan Lepisto, 34, of Independence, the addiction to extreme sports is in the unknown.

“You never know what they’re going to make you do,” says Lepisto, who recalls the morning he and two buddies carried rocks on a four-mile run and felt such a sense of accomplishment when they were finished.

In his job at dunnhumby, a marketing analytics company, Lepisto calls on the same skills he’s learning in his workouts.

“Not a day goes buy that I don’t think, ‘How can I use what I learned in GORUCK,’ seeing a project through to the very end rather than putting it off, or saying, ‘What would I do if this were a GORUCK Challenge?’ ” he says. “It’s been pretty cool.”