ABSECON— It begins calmly enough, with people standing in two rows in a gym, barbells resting on the ground in front of them.

Then you hear, "Go!"

Suddenly, men, women and teens are lifting the barbells above their heads. Others are doing push-ups and sit-ups beside them. Another group runs out of the building to take a 200-meter lap.

The whole time, the participants are encouraging each other: "Don't stop" isn't just advice; it's a mantra.

For some people, stretching out on a yoga mat or pedaling through a spin class just isn't intense enough. That's why there's CrossFit.

CrossFit is a strength and conditioning workout that focuses on body-weight exercises, gymnastics and some Olympic weightlifting. It has become one of the most popular fitness regimens in the country — and in South Jersey.

CrossFit uses pull-up bars, kettle bells, barbells, tire flips, dead lifts and squats — lots of squats.

The program, founded by former gymnast Greg Glassman in 1995, has expanded to over 12,000 affiliate gyms around the globe.

Gym owners pay an annual fee for the CrossFit name and a two day, 16-hour "Level One Trainer Course."

The typical workout lasts one hour in the "box" or the workout area.

With band-restricted bench presses, dead lifts and push presses above the head, the workout isn't for the faint of heart. In fact, you could actually faint.

But on this recent Friday morning, people of all ages were in the gym, pushing one another for one more rep.

Murray Rapoport didn't need a push.

The 73-year-old was doing his push presses right into pushups and sit ups. He's been doing CrossFit for five years, with the goal of getting in shape and living longer.

"I do this almost every day each week," said Rapoport, of Brigantine.

"Most (people my age) spend their time sitting on the sofa and walking on the boardwalk. I end up coming in and doing this for an hour. And after, I feel like I can fly. It's great."

Rapoport's son, Andy, brought his daughter Alyssa to visit from Oklahoma. The three generations of family members spent their morning working out together, with maybe a little bit of family competition.

"We follow his progress on Facebook so we couldn't be outdone when we came to visit," Andy Rapoport said of his father.

Ryan Palmucci, co-owner of the CrossFit Absecon gym, said there's a wide array of people training in his gym, but they all come in for the same reason.

"The person who comes in here is bored with the usual gym regimen," Palmucci said. "Self-motivation is good, but you can get bored. But seeing a group this dynamic and seeing someone suffering right next to you, it makes you driven to keep going."

And Amanda Bittle, of Mays Landing, has to stay driven. The 18-year-old will be heading off to Coast Guard boot camp in October. She said she wanted a workout that most closely resembled a boot camp.

"You can go to the gym and sit on the bike for 45 minutes and not really break a sweat, but here you get pushed to the limits," Bittle said.

Tim Janicki, 34, of Galloway Township, said he thinks most people enjoy classes rather than working out alone. He even convinced his wife to come to a class.

The sign of a job well done comes the next morning.

"When they feel it tomorrow, they'll know they had a good workout," Janicki said.

Mike O'Hala, 48, of Egg Harbor Township, joined CrossFit Absecon when it opened in 2013. He said the most important thing to know is that people should not be intimidated by the workout.

"A lot of people think you have to be a pro athlete, but 90 percent of people coming here are not top-notch athletes. They're just normal people looking for some intensity in their lives,"