Oh the holidays — a bit more drinking than usual, second helpings at dinner, one too many extra slices of pie. Maybe it’s time to get into some serious training at the gym.

Enter boot camp classes — intensive instructor-led gym sessions designed to kick your workout into high gear.

POWER WORKOUTS

At a recent morning session at Fit Body in Huntington, about 20 men and women jump, climb ropes and steps, crawl, squat and lunge, as owner Kathleen Eaton barks out orders.

“Go, Mommy, go!” Charlotte Ullrich, 3, of Huntington yells, cheering her mom on as she climbs the rope.

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A regular at Fit Body since September, Don LaGreco, 77, of Huntington Station is determined to stay in shape so he can dance at his granddaughter’s wedding.” I have to get all the old things that have been sitting around moving again,” he says.

Eaton puts the group through their paces as they roll an enormous truck tire they’ve named Bessie, do backward lunges holding sandbags and crawl under the military net holding a fire hose. There are jumping jacks (while weighed down by kettle balls) and attempts to jump over large boxes, as if climbing over a wall.

The room erupts with cheers as Franny Palacio of Huntington, 52, and Laurene Gilbert, 47, of Greenlawn cycle through the complete set of monkey bars for the first time since they’ve been training here.

But it’s not all fun and games, and Eaton warns the group if anyone takes more than 10 seconds to get to the next station, they’ll all pay the price.

Sure enough, there were some slackers. So come the dreaded burbees: jump up, legs shot out in back; a push-up, repeat, and repeat again.

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GROUP MINDSET

Each 35-minute session is different, but always ends with a team-building group activity.

Today, everyone grabs onto a very long rope and simultaneously does sets of jumping jacks, knee-ups, squats, sit-ups and “Superman poses” — keeping arms and legs up in the air while lying on their backs.

“I want to do something inspiring,” says Tara Howard-Saunders, 53, of Huntington after her second boot camp class. “So far, so good: I came back.”

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Newbies may feel pretty sore after one session, says Debbie Green, a boot camp trainer at Fit Body’s Deer Park location. But if you hang in there, by about the fourth session, you’ll notice an improvement in strength, endurance and stamina.

After a few classes, John Magin, 48, of Huntington Station was hooked. Early on, he wasn’t able to climb the rope or complete the monkey bars. Now, he’s aced both challenges.

“It’s a confidence booster,” Magin says.

And it shows.

Meanwhile, weekends are not for relaxation at Better Body Boot Camp.

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The techno beat blares at the “Saturday Sweat” class, where about two dozen folks have their game faces on as they do jump squats, suicide sprints, side planks, variations on jumping jacks and countless other cardio exercises for the better part of an hour.

“We’re like having a personal trainer, but in a group environment,” explains gym owner Kaiser Serajuddin.

Angona Tran, 27, makes the trek at least twice a week from Brooklyn to work out here. “It’s very intense,” she says. “At the end of the class, I say, ‘It’s crazy and I did it.’ ”

Five-year boot camp veteran Jennifer Levinson, 45, of Great Neck works out four times a week, for good reason: “Just the energy, every day,” she says. “It’s amazing.”