Diet pills? No way: Losing weight is about working out and eating right. But new research shows there might be a way to increase your motivation to work out in the first place.

Swiss researchers found that mice with elevated levels of the hormone erythropoietin were more inclined to exercise—something they think relates to the hormone’s positive effect on mood. Trouble getting your butt off the couch? This hormone might be your ticket to a toned physique and a smaller waistline.

MORE: Easy Exercises