Gyms work by selling more memberships, and it's not surprising to know that gyms have more members that they can accommodate. So they're always assuming that most of its members won't show up. A new kind of concept gym charges you less the more you work out. The opposite!

That's kind of the concept behind Fitmob, a website and iOS app that launched Thursday. Anyone can sign up to run a class.

The first time you work out with Fitmob in a given week, you pay $15. The second time you workout, both classes is reduced to $10. If you to go three classes, you'll pay $5 each. Every time you go, there will be a financial incentive to keep coming back. What better way to motivate people than to use money?

Trainers will have access to the whole Fitmob dataset, with the idea being that the most popular classes will rise to the top and be imitated.

Fitmob's entire 13-person team aims to participate in as many classes as possible; the company's HQ in San Francisco is one of the listed workout locations.

Will this concept finally help people get fit and healthy?