What it is: A workout that involves using a special indoor “surfboard” in order to do a number of different movements that surfers do when they're out on the water.

Why it became popular: Surfing is great exercise because it involves the use of a number of different muscle groups. In order to surf, you need to use your arms to paddle, your legs to stand up on the board, and your core to balance yourself and to stay put. The problem, of course, is that not everyone can surf, and not everyone has the time or the money to invest in surfing everyday. So Surfset was designed to provide people with all the benefits of surfing without the hassle of going to the beach and actually getting into the water. And it's a lot of fun, too, which is why it's growing in popularity right now and why it was such a hit when the founders of it appeared on ABC's Shark Tank back in 2012.