Runtastic has all sorts of apps (many of which have absolutely nothing to do with running) – everything from cycling, to heart rate monitoring, to abs, and so much more. Its newest app, however, really wants to help users get their ass in shape... literally. It's called Butt Trainer, and well, the name speaks for itself. (For the record, I suggested "RuntASStic," but they didn't go for it.)
If you've used any of Runtastic's other training apps – like Six Pack Abs, for example – then you're already familiar with how Butt Trainer works.