(CNN) — It’s miserable outside. The whole world is a depressing gray color that just makes you want to lie on the couch and watch reruns of “Sex and the City.”

You don’t have time to pack your gym bag, drop off the kids, drive to the fitness studio, shower and change, pick up the kids and get back home before dinner.

Plus, you’re really tired of floor mats that reek and that woman in the back row who always steps left instead of right, effectively knocking you down on your out-of-shape gluteus maximus.

Whatever your reason is for not wanting to hit the gym, Kristin Knee of Flirty Girl Fitness understands.

“I don’t even want to go to my own studio when it’s raining,” she said with a laugh.

That’s why late last year, she and her sister, Kerry, launched Flirty Girl Fitness LIVE, a Web service that streams three or four of their franchise’s group classes every day.

A Flirty Girl Fitness instructor teaches a class that’s streaming live online to subscribers.

Subscribers can log in at home and participate in classes like “Bikini Bootcamp” or “Hottie Body Boxing” from their living room. The classes stay online for 24 hours and then are replaced with the next day’s workouts. Unlimited subscription passes are $15 a month.

Online video streaming is just starting to blossom in the fitness industry, IDEA Health and Fitness Association editor Sandy Todd Webster says. Several sites offer similar programs, including Yogis Anonymous, Connect Online Fitness,EMG Live Fitness and DailyBurn.

“It seems like the next natural progression to home fitness DVDs,” Webster said. “It’s another way of making fitness more convenient for yourself.”

Knee was shocked by how quickly the LIVE service caught on with her regular members. People were doing classes on their lunch break at work or logging in while on vacation.

“You know you have a [workout] DVD, and it’s an awesome DVD, but the girl tells the same joke every day,” Knee said. “This is always live, always fresh, and you feel like you’re there.”

Variety is one of the reasons Joyce Wells loves group fitness classes. But when Wells moved to the suburbs from New York, she was disappointed with the caliber of local studios.

The businesswoman remembered how much her colleagues at Microsoft had loved video conferencing during meetings. Her subsequent research on online paid content revealed astonishing numbers: In 2010, the National Football League raked in $500 million in revenue from its streaming services; Major League Baseball earned $450 million. Netflix’s digital revenue totaled more than $1.5 billion.

Joyce Wells founded EMG Live Fitness after finding her local suburban fitness studios lacking.

So Wells launched EMG Live Fitness, an Internet-based fitness studio that streams classes from instructors across the country. There’s no subscription for Wells’ site; classes are bought for $5 apiece.

In Wells’ opinion, the fitness industry is dragging its feet in making the transition online. The brick-and-mortar gyms are afraid of catalyzing their current market, she says.

“It’s going to be like Netflix was to Blockbuster. Blockbuster refused to let go of that model, and look at what happened to them.” (Blockbuster filed for bankruptcy in September 2010).

Wells’ target market is stay-at-home mothers and people who are obese. But online classes appeal to anyone who’s uncomfortable in a gym setting, Webster says.

“You hear, ‘I can’t go to the gym until I get in shape,’ ” Webster said. “This gives them privacy … to experience it on their own without feeling self-conscious. This could go a long way to promoting compliance because it’s convenient and portable.”

Webster says personal trainers also use online video libraries to encourage clients to keep up with their workouts.

While on-demand fitness video libraries are nothing new, they’re becoming more elaborate. Fitness company Daily Burn recently introduced HD-quality, customized video workouts on DailyBurn.com. The workouts are led by the “DB6,” a team of six instructors who have a variety of areas of expertise.

DailyBurn asks new users questions about their ability levels and goals. It then uses the site’s “IntelliBurn” technology to analyze and stream a personalized workout.

By adding the video service, CEO Andy Smith and his producers have turned the site into one giant personal trainer.

“It doesn’t put you in a certain bucket,” Smith said. “It learns about you as you go, constantly monitoring what workout you did yesterday, are you hitting a plateau. … People really want to stay motivated and be told what to do.”

Nearly 20% of all TVs worldwide will be connected to the Internet by 2016, according to Digital TV Research, which will make it even easier for online fitness videos to infiltrate America’s living rooms.

Put bluntly, there are no more excuses.

“People are realizing more and more that there’s not a magic pill for [weight loss],” Smith said. “You just need to get started.”