In life, there are people who run marathons for fun and people who’d rather die than put on a sports bra. Experts are starting to think that the difference has something to do with genetics, according to new research presented at an American Physiological Society meeting held last week in Phoenix.

When researchers from University of Georgia looked at 3,000 adults’ exercise habits and observed their brains’ response to exercise, they found that people who have trouble sticking to an exercise routine (or don’t even bother) have a genetic variation that affects the way their brain cells bind with dopamine, the neurotransmitter responsible for making you feel pleasure and reward.

Because your body is supposed to reward you for exercising by releasing dopamine, thus making your extra efforts seem worthwhile, the results suggest people who don’t experience this response are effectively wired to appreciate exercise less.

“Combined with personality measures, we think these genes may help explain why some people have a natural urge to be active, while others never do,” wrote lead researcher Rodney Dishman, PhD, a professor of kinesiology at the University of Georgia, in an email.

While this genetic disposition might make it tougher for you to stay fit, it doesn’t doom you to a life of inactivity. After all, you can still adult up and break a sweat every now and then simply because it’s good for you (like it or not). And paired with a stellar playlist, a competitive exercise partner, or a new gym buddy, all of which make exercise feel a little less painful, you might even learn to like it.

If all else fails, this new science provides the perfect way to respond to your mom when she asks whether you’re getting any exercise: Just explain that it’s her gene pool that’s led you to the couch.