This explosive exercise works the big, powerful muscles around your glutes and quads, and sends your heart into overdrive, according to research from the University of Wisconsin. In the study, participants burned 20.2 calories a minute and their average heart was 93% of its max for the course of a 20-minute workout. The kettlebell swing works you so hard because it’s not a movement you’re used to. You’re not super efficient at it, which is taxing to your body.