On November 10, 2012, Jess Underhill ran the Richmond, VA, Marathon. It did not go well. She’d planned to run the New York City Marathon, which was cancelled in the wake of Hurricane Sandy, and instead registered for Richmond, finishing 18 minutes short of her expectations.

That night, she wrote about the experience on her blog, FitChickintheCity. “Everyone was like, ‘Ugh, you’re doing your blog again,’ but I was just waiting for the time where I could sit and write about it,” she said. “I needed to write about it to feel better about it.”

Underhill has been pouring her heart out on her blog since 2009. That year she became one of a growing number of female fitness writers who share online the details of their everyday existence, everything from meals to workouts to family vacations. Fitness communities have increasingly found niche communities on the web and Underhill is one of the leaders of this growing movement. Through short posts on her health-related struggles, goals, and achievements, she’s created a loyal following of thousands of fans who see her energetic grin and know that, whether they’re running, lifting, or playing chef, she’s cheering them on. I arranged to meet Underhill to find out if she was the real deal, and to see what a member of this always-peppy, always-on-the-go movement looked like in real life.

The Write Kind of Workout: Fitness On the Web

Over the last few years, the blogosphere has become a home for 20- and 30-something women writing about their personal fitness routines and inspiring others to get active. There’s Monica of RunEatRepeat; Carla of MizFitOnline; and Janae of Hungry Runner Girl. Though every site has its own quirks, there are common threads running between them: colorful photos of home-cooked health food, almost-TMI detail about how much sweat was produced during spin classes, and lots of exclamation points. It’s not uncommon for a single post to generate more than 50 comments, from a perfunctory “yum!” to full paragraphs on learning to step out of your comfort zone.

To be honest, I’d never met any fitness bloggers in real life, at least not ones who had more than a few hundred fans. So I was curious to see whether the FitChick was anywhere near as cheery as her photos made her seem, or if she was really an overconfident fitness fanatic who’d let blogger fame go to her head.

We arranged to meet at a café in midtown on an unusually cold day in early November. I got there early and, though I’d thoroughly stalked Underhill’s blog, I hesitated when I saw a bundled-up figure scurry through the door. Tall and thin, her brown hair tied up in a tight, high pony, she flashed a big grin. I knew it was her.

Underhill, 36, moved to New York City from Nashville, TN, in 2002 and launched FitChickintheCity seven years later. Today she lives with her husband on the Upper East Side; both are personal trainers. Jess works mostly with women who have some kind of running goal.

Since 2009, FitChickintheCity has accrued more than 11,500 Twitter followers and 3,200 Facebook fans. (In comparison, RunEatRepeat has about 10,000 Twitter followers and MizFitOnline has about 16,000.) But when I asked Underhill how many visitors her blog gets on a monthly basis, she said she didn’t know. “I haven’t looked in a long time,” she told me. “I was like, ‘I don’t care anymore.’”

In a way it’s hard to understand how FCITC has quickly become one of the most popular fitness blogs out there. Perhaps the site’s simplicity is what makes it so successful. Underhill’s posts are short and easy to read; if you miss a week of updates, it’s fine to go back and review five in one sitting. The pages are filled with photos of sweaty, Lululemon-clad women posing after their run. (“Post 20-miler means smiles and endorphins for everyone!”)

For Underhill, the whole purpose of blogging is to make new friends and meet her fans, whether virtually or in real life. She almost always ends her posts by asking for tips and advice. “On Twitter, I’m really anal,” she says. “I try to reply back to every tweet I get.”

Running Away: Underhill’s Journey to Fitness

Running for Underhill is less an excuse to eat all the vegetarian rice ’n curry she wants and more an emotional escape from everything else that’s going on in her life. She started running around age 13 and as a teenager, she told me, “If I had some sort of emotion to deal with I would run. Like if I was angry, I would run. If a boyfriend broke up with me, I would go for a run.”

In college, Underhill said, she didn’t know anyone else who ran for fun, and she was glad to be part of a “fringe” trend, even one that was gaining in popularity. “I liked doing what other people weren’t doing.”

Today, her favorite spot is the bridle path in Central Park. “You feel a bit more of the elements, I feel like, on the bridle path, like you’re running through trees in the fall and in the winter there’s a lot of snow and in the summer you’re kind of shaded because of all the trees and it’s almost like you can pretend like for a second you’re not in Manhattan.”

The problem is that a lot of Underhill’s clients don’t see running that way. Some start training in the months leading up to their weddings, hoping to squeeze into one-size-too-small dresses and bikinis. “It is a constant challenge,” Underhill told me. “There’s more to working out than being skinny.” And while Underhill once ran to stand out, today, she said, clients come because they see all their friends running and want to join in.

I asked Underhill if her blog had ever received any negative feedback and she said not really. She flashed a big grin, the same one I’d seen dozens of times in the last half hour, and shook her head.

“I just want people to get something out of it and feel like inspired or happy or something.” I jotted down the words in my notebook and smiled back.

For more from Underhill, read her blog and follow her on Facebook and Twitter.

Do you follow any fitness bloggers? Who are your favorites? Let us know in the comments below or tweet the author directly @ShanaDLebowitz.