Don’t like to exercise? You may be able to blame your genes.

A new study done on lab rats and published in The Journal of Physiology suggests that whether or not people feel motivated to exercise may be at least partially inherited. In the study, scientists observed a group of rats to see which rats voluntarily spent the most time running on a wheel. They bred those rats together. They then did the same with rats who spent the least amount of time running. They continued this process until they had two sets of rats – one that was descended from the running rats and another descended from the more sedentary rats.

What they found was that the offspring of the rats who liked to run were willing to spend hours running on the wheel, while the descendants of the sedentary rats tended to avoid the wheel. The researchers also identified some unusual differences in the brains of each group of rats. Specifically, certain genes that help neurons mature didn’t function properly in an area of the brain called the nucleus accumbens, which participates in processing rewards. Even if they hadn’t done very much running, the offspring of the pro-running rats had many more mature neurons in this area of the brain, compared to rats who were more sedentary. The researchers hypothesize that running may activate reward areas more strongly in rats bred to run, setting up a positive feedback loop that motivates them to stay active.

This could help explain why so many people avoid exercise even when they know it’s so good for them, while others can’t wait to get to the gym. According to The New York Times, a prior study done in twins showed that fraternal and identical twins had activity levels that were similar and likely not attributable to the influence of a shared upbringing alone.

But if you fear that you might be in the exercise-averse category, it’s not all bad news. When scientists made the sedentary rats run, they only ran about a tenth as far as the pro-running rats, but over time their brains started to change. Compared to their exercise-averse relatives, they had more mature neurons in their nucleus accumbens, perhaps suggesting that they might be able to learn to enjoy exercise more by being more active.

Whether these results translate to humans is unclear and requires further study. However, researchers are hopeful that all people might be able to enjoy exercising more just by pushing themselves to be active.