At Orangetheory Fitness in Fairfax, which opened in December, the walls are orange, and so is the suspension training equipment. Ditto with the rowing machines, the lighting and the balloons tied up by the entrance.

Soon, Reggie Williams promises me, I’ll turn orange, too.

The names of the dozen people in our “Orange 60” session, including mine, appear on a TV screen mounted above a row of treadmills. The color of the box around each name changes depending on the individual’s heart rate. In this and every hour-long class, the goal is to spend 12 to 20 minutes in the “orange zone.”

That color represents 84 percent or more of your maximum heart rate, explains Williams, regional general manager of the rapidly growing Florida-based franchise that has plans to open another 40 locations between Northern Virginia and Baltimore. (“We’re bleeding orange everywhere,” he says.)

Orangetheory’s high-intensity workouts, which shuffle students among treadmills (or low-impact cardio equipment), rowing machines and a strength-training area, would be effective even if no one wore heart rate monitors, he says. But when students have them strapped beneath their breastbones, they can gauge exactly how their bodies are responding and use that information to get the most out of a day’s routine.

Rolando Lopez, left, grimaces as he and David Ballow take part in an Orange 60 class at Orangetheory Fitness in Fairfax. (Matt McClain/The Washington Post)

“People are learning they don’t have to go all out for an hour for results,” Williams says. “There’s a time to work hard and a time to recover.”

And the fitness industry is learning a lesson of its own: Embracing this kind of technology can be beneficial for both waistlines and the bottom line.

Activity trackers that calculate every step you take, every stair you climb and every minute you’ve moved are now in the hands — or more likely, around the wrists — of thousands of consumers. As people get hooked on data, health clubs have recognized an opportunity to educate their clients on how to make sense of the numbers.

That premise is the very DNA of Koko FitClub, says co-founder Mike Lannon. The technology that powers his “digital gym” franchise, with 130 locations and counting is the Koko Smartraining System: Members plug a Koko Key that stores their workout history into the strength or cardio equipment, and the machines use that information and various sensors to offer a custom routine.

If someone wants to see results beyond what’s in the mirror, he or she can log into the MyKoko Web site. The dashboard displays gym activity, strength gains, changes in lean muscle and something called a “Q” score that makes it easy to compare your fitness level with others’.

“The secret sauce of Koko is that it’s not just about data and tracking. Data is a big deal. But data alone doesn’t complete the circle,” Lannon says. “It is a means to an end for us.”

That goal? “Dramatically different engagement,” says Lannon, who is continuing to develop new technologies. Four company-owned (non-franchise) locations in Northern Virginia — which all opened in 2012 — serve as Koko’s laboratory. And he hopes to use them to find even better methods for harnessing the digital health revolution, so members can track their exercise both in and out of the gym.

At Orangetheory, the color-coded TV screen helps people understand the heart-rate data. The only other number up there is a tally of calories burned, which doesn’t require much explanation. But even those two stats demand a quick lecture or two.

First-timers like me have to learn how to put on a heart rate strap and then pay attention to which zone we’re supposed to be in throughout the cardio portion of class. (Because it’s interval training, it’s always changing.) During the strength segment, Williams asks that we ignore the screen and instead focus on proper form as we pump out push-ups, lunges on a Bosu balance trainer and bench hops.

After the cooldown and stretch, Williams invites everyone to gather by the screen, which now shows a heart rate graph for each exerciser.

“We want to see a nice slope,” he explains, noting that the majority of our time should be in the green zone in the middle of the graph. A peak on either side is a sign that something went wrong. But we’ll work on that , Williams says: “My power walkers will eventually become joggers. Joggers will become runners.”

And many of them could become Orangetheory addicts like Fairfax resident Carol Eshleman, 52.

“When I go to the gym I belong to, it’s easy not to have an optimal workout. It’s easy not to push yourself,” admits Eshleman, who says she’s shown up here five times in eight days. Seeing the numbers — both on the television and in the e-mail that’s automatically delivered as soon as class ends — keeps her honest.

Numbers can also rev up some healthy competition. That’s what I discovered when I hopped on a bike at Ride DC, a new cycling studio just north of U Street on 14th Street NW. Folks who show up there for class get a bottle of water, a towel to wipe off their sweat and the chance to see how hard they’re working projected on the front wall above the instructor.

There are no names on the leader board, which lists the bike numbers in order of their total power output (speed plus resistance). So all I knew was that I wanted to out-pedal whoever was on the bike ahead of me. As we climbed hills, sprinted and lifted our rear ends out of our seats, I was transfixed by the idea of inching a spot higher.

So, apparently, was the guy on Bike 15, who edged me out in the final minute of class. “My goal was to keep it in the top five,” said Barry Poechmann, 33, who lives in Logan Circle and is training for a triathlon.

Cyclists looking for a similar set-up can also visit Wired Cycling, which opened in the Northeast neighborhood of Eckington last week. The name is a nod to the technology-based approach that owner Leticia Long believes will shape the industry. “Exercise should be more like training,” she adds. “Not just empty workouts.”

At Ride DC, which has been using the system for the past month, anyone who’s feeling shy can opt out of publicizing the info on the leader board. All students still get their numbers e-mailed to them after class, so they can compare workouts and see an estimated calorie burn. That latter number is more accurate if you’re wearing a heart-rate monitor, which folks are welcome to do. (The studio’s sensors are on the bikes, so they can’t tell when you’re sweating through a series of push-ups on the handlebars or lifting weights while pedaling. “Those are bonus calories,” says co-owner Zac Smith.)

For Herly Rosemond, 38, tracking her fitness has always seemed like too much hassle. But after that cycling class, she raved about how painless the Ride DC method is — until she got her results e-mail and saw that her power output had dropped from her previous class.

“The machine doesn’t lie,” she says. “I’ve got to keep at it.”

@postmisfits on Twitter

Hallett edits the Fit section of Express.

Read past columns by Hallett and Lenny Bernstein at washingtonpost.com/wellness . There, you can subscribe to the Lean & Fit newsletter to get health news e-mailed to you every Wednesday.