"Have you guys been training at home?" Omenson shouted over the music. "Awesome."
And they were - girls who'd like to lose a few and skinny boys, all doing things they couldn't have done a month before.
They're charter members of the HiFive Club, Triton Regional High School's month-old after-school activity aimed at winning students, including the formerly sedentary, over to a healthier lifestyle.
The need is no secret. Childhood obesity is at epidemic proportions. For the last year, Michelle Obama has been exhorting young people to eat healthier and get active through her Let's Move! campaign.
The idea seems to be catching on. In the last year, growing numbers of initiatives have been launched to bring healthier foods into school lunches, take junk food out of machines, and get kids exercising more. On Feb. 1, for instance, Let's Move in School, sponsored by the 20,000-member American Alliance for Health, Physical Education, Recreation and Dance, announced an effort to spur physical activity before, during, and after school.
Omenson and history teacher Candace Vrooman saw the problem in their students, teenagers who got winded walking up a flight of stairs of their Runnemede school.
"I'm 44, and I beat them all up the steps," said Omenson, who teaches photography and computer graphics.
But the teachers were concerned, not judgmental.
"Basically, I was a shy, fat kid in high school," said Omenson, a Cherry Hill East graduate. "I hated gym, and it hated me."
At 25, she signed up for Jenny Craig and joined a gym. "I thought kids should be able to experience personal fitness sooner than that," she said.
Vrooman, 26, a Triton alumna, had been a high school athlete but petered out in college. After the death of an overweight aunt, she began running with Omenson.
The two teachers came up with the idea for HiFive, for Health, Intensity, Fitness, Inspiration, Vision, Energy. They liked the boot-camp approach of TV's The Biggest Loser, mixing up exercise styles to keep things interesting.
The students would compete for points based on effort rather than pounds lost. The teachers spent about $200 of their own money on prizes, such as yoga mats and exercise balls.
They guessed that only girls would apply. But, some boys were interested, too.
They were "the emo kids," Omenson said - boys who weren't on athletic teams but wanted to build some muscle.
They started in January with eight students, few enough for the teachers to give a lot of personal attention.
School teams had dibs on the gym and cafeteria, so the club - which meets from 2 to 4 p.m. three days a week - was left with a second-floor hall and Omenson's computer lab, doing dips between computer tables. The Miami Sports Club in Runnemede, Vrooman's gym, came through with free one-month memberships, meaning access to weights, machines, and classes. The students started keeping food journals, and they got talking about healthier eating.
Exercise fever soon took hold.
"They want us to take them to the gym. They want to work out. They're getting the craving," said Vrooman, who with Omenson works out as hard as the students do.
"We're motivating them while they've motivating us," said Melisa Peck, 16, who signed up to lose weight and gain confidence.
Like Omenson, she was never big on gym class.
"I don't like the fact that we have to become nasty and sweaty during the school day, and I hate to change in front of everybody," she said. "I always hated it because I always was a bigger kid."
Peck remembered the day Omenson showed them her own high school photo: a chubby teenager in sweater vest and mullet hairdo.
"You'd never know it was her," Peck said.
Anna DeMarco, 16, signed up with boyfriend Emanuel Ferreira, 17, and both have cut back on junk food. They've noticed a change in mood.
"I'm a lot less negative," DeMarco said. "I am a lot nicer." Her guy's outlook is better, too.
"I really wasn't too optimistic," Ferreira said. "Now I'm set on setting goals for myself."
There seems to be a lot of that going on.
Kayla Varquez, 16, is working out to get in better shape for softball tryouts. Saraya Bethel, 18, and Gionna Naticchione, 16, joined to lose weight and ended up making friends. Naticchione has also taken pride in reaching incremental goals, such as 10 minutes on the elliptical.
At first, "I couldn't even do it for a minute," she said.
A.J. Aranes, 18, is one of the boys who joined to feel healthier. He runs about four times a week in the warmer months but not in winter, and he's not big on team sports.
"I did it for the health benefits and just to be more athletic," he said.
Aranes also likes learning about nutrition; a recent visiting speaker told them about the evils of high fructose syrup. He shares the information at home.
"My mom's been wanting to do this - eat healthy. I tell her what I've learned. She reads labels now," he said.
At the end of a recent session, soothing water tones had replaced the high-energy rock, and the students stood, eyes closed, breathing, relaxing, in the mountain yoga position.
"Stay balanced," Omenson said.
Then they adjourned in a manner most fitting - high-fives all around.
Contact staff writer Rita Giordano at 856-779-3841 or email@example.com.