Everyone knows we’re supposed to work out, because it’s good for our health and overall, general well being. But does anyone know why?

Well…um, no. We’re just over here dying on the treadmill because we’re pretty sure it’s good for us.

Now, you can jump on that stairmaster with purpose: because new research says the answer to this baffling may be in our DNA.

A new study found that exercise changes the shape and functioning in our genes, which is kind of a big deal on the way to improving our health and fitness. While the human genome is pretty complicated, scientists already know that certain genes become active or quieter because of exercise — but what they didn’t know was how those genes know how to respond to exercise.

So scientists at the Karolinska Institute in Stockholm decided to investigate. They recruited 23 young and healthy men and women, and had them exercise on a stationary bike, using just one leg, leaving the other dormant (and lazy). That way, each person became their own control group.

The volunteers pedaled, with just one leg, at a moderate pace for 45 minutes, four times per week for three months. I would be concerned that my pants would become disproportionate, but this study group pedaled on. Not only did the volunteers experience physical improvements in their more active leg, they also experienced interesting changes in their muscle cells’ DNA.

By using super savvy genomic analysis, researchers were able to determine that more than 5,000 sites on the genome of muscle cells from the exercised leg now had new methylation patterns — and the unexercised leg went unchanged. Which, in uncomplicated speak, means, well, I have NO idea. But if I’m understanding semi-correctly, it seems that exercise is still good for us.

According to Malene Lindhom, a graduate student at the Karolinska Institute who led the study, the overall findings of the study are confusing.

“Through endurance training — a lifestyle change that is easily available for most people and doesn’t cost much money we can induce changes that affect how we use our genes and, through that, get healthier and more functional muscles that ultimately improve our quality of life.”