What’s the hottest work-out class today? An online one. A growing number of fitness companies are streaming online exercise classes. In fact, experts say that online sweat sessions will be the norm soon, and going to the gym will be ancient history.

Why? Because taking an online work-out class is exactly like taking one in person – but a heck of a lot more convenient. You can log on with your computer or smartphone anytime and anywhere - whether you’re at home, at work, or even on vacation.

All you have to do is click on a class you want, from Pilates to “Jersey Kick” and then mimic the instructor’s moves. And most online fitness companies upload new videos every day.  So you won’t get bored with the same work-out, like you would watching the same exercise DVD over and over. Are you interested in becoming a digital gym rat? Here are some top “online gyms”:

First: EMGLiveFitness.com: They stream hundreds of classes a month, like kick-boxing, yoga, and spinning. And you can watch a quick preview clip of the class before deciding whether or not to buy it. Each class costs $5.

And if you want to get in shape, but don’t have a clue as to what type of online class you should take, check out DailyBurn.com. You complete a questionnaire that asks you about your current diet and fitness goals, then it uses software to choose matching classes. The classes cost a flat rate of $10 a month.