Vicky Hallett / The Washington Post

At home, anyone with a DVD player can start a workout with the push of a button. Tamara Zemlo would rather have a trainer push her buttons.

“I was trying to cheat a little bit, but she was telling me, ‘Keep those abs in.’ It motivated me to keep going,” says Zemlo, 44, who recently sweated through a one-on-one workout session under the watchful eye of Julie Bobek — even though Zemlo was in her Bethesda, Md., living room and Bobek was in New York City.

Their “Core and More” appointment was set up through Expertory, a site that promises to help visitors “learn, teach and consult practically anything online via video chat.” Founder and CEO Tony Jarboe came up with the idea after he read a newspaper article about a piano teacher using Skype with clients. In the article, the teacher mentioned some hurdles, such as setting up scheduling and processing online payments. Reading that, Jarboe realized he could establish a site that would deal with the logistics for a cut of the fee.

His next thought? This format is ideal for fitness. “You just have to get up and change clothes,” Jarboe says.

The site is just one of a series of startups giving more people access to exercise whenever and wherever they want it. There’s FitnessGlo, which offers a catalog of videos taught by top instructors available on demand for a monthly fee. There’s FitBlok, which bills itself as the iTunes of fitness classes. And there are a few options like Flirty Girl Fitness Live, which lets people peek into classes streamed directly from a Toronto studio.

What’s missing in those programs is the ability to form relationships, says Viva Chu, co-founder of Powhow. Like Expertory, his site aims to give instructors an online platform to interact directly with students. Videos can be helpful — they’re available on his site as well — but nothing beats real-time feedback, Chu says.

When instructors sign on with Powhow, they open up a virtual studio to showcase their expertise, whether that’s yoga in sign language or belly dance, and get the tools to offer classes ranging in size from one to 100 students.

For busy parents, the online set-up can make all the difference, says Zemlo, who has three kids in elementary school and runs a honey business out of her backyard. On the rare occasion she can find time to get to the gym, “I need to have someone tell me what to do,” Zemlo says.