Christopher Johnson, right, from North Carolina leads a crowd of more than 200 paddlers during the Watermans Paddle for Humanity competition on the Potomac river in Georgetown. Johnson is followed by world-class paddler Slater Trout, who won the 10K race in which both men were competing. Johnson came in fourth. (Astrid Riecken/FOR THE WASHINGTON POST)

When the Watermans Paddle for Humanity race series announced it was coming to the District last year, event director Pete Stirling was nervous no one would show up. “We didn’t know if anyone paddled there. We just wanted to see if we could do it on the Potomac,” he says.

So Stirling was shocked when more than 100 folks flooded into Georgetown armed with stand-up paddleboards.

The sport (called SUP for short) was invented in Hawaii by surfers looking for a way to keep up their training on days with disappointing waves. Over the past decade, it’s won over a much wider following as word has spread that a wide, stable board and a paddle make it possible to traverse long distances while getting one heck of a core workout. Plus, unlike surfing, practically anybody can do it.

Washington’s lagging a bit behind beach communities, but we’ve gotten on board — on lots of boards. Not only do several area boathouses rent out SUP equipment, but businesses from here to the coast are going further, adding speed and fitness to the equation. At this year’s Paddle for Humanity race — held in Georgetown last weekend — more than 200 people competed, making it one of the largest SUP events on the East Coast.

“Racing is starting to explode. Everybody wants to train for distance,” says Kathy Summers, founder of Stand Up Paddle DC, who got into SUP for a popular reason: injury. After busting her ankle in 2009, the California native realized running wasn’t in the cards. But SUP, which she’d tried in Hermosa Beach, reminded her of the balance exercises she was performing in physical therapy.

Summers found she couldn’t go for a ride without people yelling questions at her from the Key Bridge, and she quickly recognized a business opportunity. Instead of simply renting SUP equipment, Summers offers small-group lessons in technique and fitness classes.

“If you can stand and walk, you can do it,” she says. So the fun comes from challenging yourself and exploring the versatility of the boards. There’s standard paddling for speed and distance, which is a popular cross-training option for runners and cyclists. You can also use the wobbly surface for yoga poses or moves you’d expect to see at a gym — burpees, squats, mountain climbers, etc.

Next season, she’s planning to add a PaddleFit boot camp, based on the rapidly growing exercise system devised by Brody Welte. The fitness instructor’s first SUP ride in Hawaii in 2007 left him exhausted but exhilarated. “And it just clicked,” says Welte, who’s developed programming for the boards in the water, on land and even indoors. You can buy SUP ergometers (imagine a rowing machine you stand on) and paddle attachments for rowing machines to mimic the stroke. “Usually when you’re sore from exercise it’s because you haven’t been to the gym in two months and you don’t want to go back. But you want to go paddling again.”

Since offering the first certification in 2010, PaddleFit has built up a roster of more than 300 instructors in North America and the Caribbean, including Camille Smith of Richmond’s Black Dog Paddle. “I used to love going to the gym, and I don’t anymore. I like to be outside. You’re out on the water, having a blast. There isn’t a better workout studio,” says Smith, who notes there also isn’t a better way to get fit. “Every exercise is more intense, and it increases your coordination and balance.”

PaddleFit is the largest training program to come out of the SUP trend, but Welte’s hardly the only person to recognize the fitness potential of the boards. Stirling’s company partnered with CrossFit to create a SUP WOD (workout of the day). SurfSET, a new indoor fitness format that’s slated to come to the District’s Mint Fitness in November, has a SUP class on its roster. And wherever there’s water, there are businesses popping up with exercise programming.

Flowga, Paddle Bootcamp and Core Paddle are all on the schedule at OC SUP Fitness, which Dawn Ehman Marohl opened in Ocean City last year. She expanded her class offerings for 2012 and expects to keep growing as more students take the plunge — though, remarkably, SUP doesn’t usually result in falling in the water. (Attempt to stand on one leg, however, and you’ll probably wind up quite wet.)

In nearby Fenwick Island, Del., DelMarVa Board Sport Adventures has offered SUP yoga since 2010. “I don’t even know how many women have found aqua Zen,” says owner Janis Markopoulos, who plans to add a full-time instructor to keep up with demand. Because many students already have yoga experience, it’s a comfortable way for them to get introduced to the boards.

Another option in Fenwick Island area: Lori Martin’s SUP Fitness classes at Coastal Kayak. She relies some on paddling — instead of running suicides, you’ll paddle them — as well as resistance bands and a dash of creativity. “We’ll have our feet on one board and hands on another board and do push-ups,” she says.

Closer to Washington, you can work up a SUP sweat at Ultimate Watersports, just outside Baltimore. There’s a huge difference between yoga on land and on water, says instructor Colleen Webster. “On the ground, if I’m cheating myself and have more weight in the front foot than the back foot, I may not know. A paddleboard forces me to distribute the weight evenly,” she explains.

Ultimate Watersports instructor Jessie Benson is also floored by what happens when she tries the exact same moves on the board that she’s done in the gym. “I feel like I’ve worked completely different muscles,” she says.

It’s this fitness side of SUP that Stirling expects to see help grow the community in Washington. “It’s like jogging. You start doing it to get in shape, and then you want to do more. You do SUP yoga because you love being on the water,” he says. “Eventually you want a goal, and something to train for.”

So you show up in Georgetown ready to race, and prove that people definitely do paddle here.

@postmisfits on Twitter

Hallett edits the Fit section of Express.