Personal trainers used to be reserved for the rich or the famous. The phrase conjured images of Hollywood celebs with chiseled shoulders or posh housewives striving to impress.

With the rise of fitness culture over the past couple decades, trainers became much more commonplace. How many times have you been to the gym and not seen a session taking place somewhere on the floor? And yes, those are usually because someone decided losing weight or prepping for a specific event was worth the pricey investment in one-on-one attention — the cost barrier is high.

But in the sharing economy, personal trainers are for everyone. At least, they are in Philadelphia, thanks to a local startup called WeTrain.

If you’re within a 20-mile radius of the city, you can sign onto WeTrain’s website or open the app and book a half-hour session at the date, time and place of your choice for $30 or less (an hour session goes for $50). A personal trainer will show up at the proper location and time, and, after asking about your fitness goals, lead you through a series of exercises that’ll leave you sore for days.

I know because I tried it — and immediately wanted to book again.

On a sunny summer afternoon, trainer Danny Charles Jr. met me in Washington Square and subsequently whupped my butt with nothing but a stopwatch and a resistance band. He said he’d double my heart rate by the end of our 30-minute session, and he very nearly succeeded. The combination of aerobic activity and strength training — I could hardly walk down my stairs the next morning — was way beyond what I would have pushed myself to do in half an hour. Plus, I didn’t need to sign a year contract at a gym.

WeTrain, which launched in late 2015, says it now has a user base of more than 600 people. Nearly 90 percent like the service enough to become monthly members, paying an upfront monthly fee (usually $50, currently $39) that cuts session rates in half. With that membership, you can still schedule a session online at any time, as your schedule allows. You can even request a trainer to show up ASAP.

That last feature — getting a trainer to your door within 15 minutes — is what led WeTrain to be labeled “the Uber of personal training” by Shark Tank-enamored reporters. But it turns out on-call training is much less popular than expected.

“Originally, we were hearing excitement about on-demand,” says 29-year-old WeTrain co-founder Zach Hertzel, a Kansas native who joined the military to escape life on a farm, did two tours in Iraq and Afghanistan and this fall will graduate from the physician’s assistant graduate program at Jefferson. “But it turns out people like having predictability.”

The company declined to release demographic figures, but Hertzel says that while many WeTrain customers are students, there are also way more elderly people than he expected. “They’re maybe intimidated by the gym, where lots of people are looking at them. This gives them the chance for a personalized in-home experience.” An algorithm assigns sessions by optimizing proximity, among other things, although sometimes staff overrides this if they know a specific trainer specializes in a specific need — sending someone with hip rehab experience to work with a customer who has arthritis of the hip, for example.

Sessions at traditional fitness centers usually cost at least 50 percent more than WeTrain, if not beyond that. There are various other on-demand personal training companies out there, but they’re mostly concentrated on the West Coast and generally tout much higher prices: A quick online search showed sessions from $69 an hour to $115 and up.

Those pricey rates are what inspired the company.

Not long ago, Hertzel’s business partner Jon Sockol was at least 60 lbs. overweight. By the time the pair met at a Wharton incubator, Sockol had gotten into shape, but when Hertzel asked why he’d never considered a personal trainer, the answer was price. “He was living in NYC and couldn’t afford to drop $100 or $150 an hour on it at the gyms there.” Together, they had a revelation: The massive personal training industry was ripe for disruption.

Charles, who destroyed my quads in the park the other day, was one of the first trainers to sign with WeTrain. When he joined there were just a handful of others; WeTrain now has around 100 vetted freelancers who fill slots on any given day. Some, like Charles, devote all their time to WeTrain, but most do it as a side gig. For them, the benefits are similar to those enjoyed by the customer: flexible schedules and locations.

But trainers also like the money. According to Hertzel — and corroborated by Charles — WeTrain freelancers make double the rate they’d usually get for one-on-one sessions booked through a gym.

How can WeTrain afford to offer both low prices and good rates? It comes down to overhead — WeTrain maintains a small, nine-person office at Curtis Building coworking space Benjamin’s Desk, but rent and maintenance costs are nothing like a full fitness center. Plus, there’s no precedent for a lower price.

“Gyms are making $50 profit [off each session] just because it’s always been that way,” Hertzel says.

To the question of why other on-demand personal trainer apps don’t offer this kind of pricing, Hertzel has no real answer, other than being frustrated.

“They see it as a cash cow, we’re trying to democratize personal training. That’s fine for them, but money is not our endgame.”

That’s not to say the business isn’t profitable. In its first year, the company brought in around $750,000 in revenue, Hertzel says. In addition to philanthropy — the company has hosted free workout nights for veterans and sponsored Special Olympics events — most of the funds will be reinvested to add features to the app, plus expand WeTrain’s reach.

“Our five-year plan is to be in multiple cities throughout the East Coast,” Hertzel says, pegging D.C. as the first expansion city with target launch of fall 2016.

“At the end of the day, we love being in shape, feeling good and having lots of energy. We want to share that feeling with as many people as possible.”

Danya Henninger is director and editor of Billy Penn at WHYY, where she oversees the team, all editorial decisions, and all revenue generation, including the membership program. She is a former food and...