54D is NYC’s ‘hardest and most expensive’ workout

On a recent Saturday morning, the newly minted 54D fitness studio on West 25th Street was a hive of nervous and excited energy.

Adults of all physiques packed onto the rubber-turf floor, jockeying for space, stretching their hamstrings and mentally preparing for their sixth consecutive daily workout of the week.

Latin music pumped through the 6,041-square-foot state-of-the-art studio in the Flatiron District as coaches Luis Calderon, 32, and Kevin Piedrahita, 31, salsa’d around the room, high-fiving their trainees.

Stationary bikes, weights, punching bags, a running ramp and stairs fill out the space.

“I appreciate the intensity [of] having to commit to this for six days a week, every week — there was no room for slacking if I wanted real results,” Liz Striapko, 31, told The Post during her fifth week of training.

The corporate banker from Queens heard about the workout program through a friend in Miami, where the class has a waitlist and fans in celebrities such as Adriana Lima and Alex Rodriguez.

Striapko decided to see what all the hype was about and try to drop a few pounds, but the program has become about much more to her.

“For one hour, I am able to fully disconnect from the outside world,” she said. “It’s such a challenging workout, I can’t focus on anything that might be stressing me out in my day-to-day life because I’m too focused on breathing and doing the exercises properly.”

Advertised as “New York’s hardest and most expensive workout class,” 54D — named for its 54-day length — made its Big Apple debut in January, charging $5,400 for the grueling ordeal.

Created by former professional soccer player Rodrigo Garduño, 44, the immersive experience is strictly regimented — you’re even told when to sip water.

Workouts are never the same, but participants can count on a mix of high-intensity interval training and cardio, with lots of squats, jumps and sprints.

Not only are the hourlong circuit classes intense, but the program includes strict diet guidelines and recovery plans.

But the most surprising thing about the hottest new workout in town might be that it’s getting New Yorkers to commit — and stick to a schedule too.

Participants must attend class at the same time every Monday through Friday for nine weeks (Saturday’s schedule is more flexible).

If you are three minutes late, you’re locked out of class.

Miss three classes, or show up with a bad attitude, and you are kicked out of the program. (A pro-rated amount will be refunded.)

“You have to train like an athlete, eat like an athlete and recover like an athlete,” Omar Yunes, the CEO of 54D, told The Post, comparing the program to an athlete’s preseason training. All the instructors are former professional athletes.

“The whole concept is much more similar to a school than the usual fitness concept,” Yunes said. “It’s understanding how your body works and having somebody there with you to talk about it, which is very important.”

Each workout is explained, demonstrated and guided by the coaches. The trainees are all provided with heart monitors that allow the coaches to track how hard everyone is working — and who needs pushing. Trainees are sent a performance report after the workout is complete.

A registered dietician sits down with each trainee to guide them through one week of a detox diet (eating mostly whole and natural foods) and help them plan healthy meals going forward.

Trainees are also encouraged to use one of the two recovery methods — a cold compression leg machine or a full-body massage chair — at the studio at least twice a week.

While the latest craze might have Manhattan fitness buffs clamoring to get in, some research suggests that too much high-intensity exercise may be an ineffective and possibly harmful workout for some.

“When it comes to physical activity, it’s possible to have too much of a good thing,” Sara Gottfried, a Harvard-educated doctor, told The Post.

However, Yunes insists that “what matters is that you push yourself as hard as you can for your level.”

“We don’t really care who’s the fastest … or the strongest. We only care about people who come in and give their 100%,” he said.

And while entering a city already well-served by expensive gyms and workout classes with cult-like followings might have initially been a challenge, Yunes said that 54D’s emphasis on learning, commitment and tailored training makes it unique.

So far, the hefty commitment of time and money that’s required for 54D participants appears to be paying off. They spoke of a rise in motivation supplied by seeing real results.

“It’s a bit addictive,” Kate Backhouse, 39, told The Post.

Backhouse began the program in January, when she saw the studio opening up near her home.

The biotech company director has tried all types of workout classes and programs but decided to jump into the “big commitment” to whip herself into shape ahead of her 40th birthday.

“It was the same people every day at 6 a.m. — everybody made that commitment,” she said. “Everybody turned up, showed up, tried their best, and there was a real sense of camaraderie.”