Everyone has the fitness-crazed friend who constantly posts about his runs—or at least lets a fitness tracker app do it for him.

Whether you find it inspiring or annoying to see updates of others’ physical feats in your newsfeed, these posts (likely read while in a stationary position) may motivate you to lace up your own sneakers. Researchers from MIT analyzed five years of global data from fitness trackers and found that runners who use trackers linked to their social media accounts generate new paths of runners behind them. Their work was published in Nature Communications on April 18.

Sinan Aral, a management professor at MIT, and his colleague Christos Nicolaides collected data from fitness trackers including Fitbit and Garmin from users in North America, Europe, and Asia over five years. These apps store data on websites connected to different forms of social media; every run was posted online for friends to see. In total, the data include roughly 1.1 million runners who logged 350 million km (217 million miles) during that time, and their 3.4 million connections on Twitter and Facebook.

Aral and Nicolaides did some serious number crunching and found that people were more influenced by their connections who shared mutual friends. If two friends have several mutual connections and one is an avid runner, the other will likely pick up the habit—and probably end up running a bit farther or faster than his or her friend, possibly to stay ahead of the pack. Men also tended to run more when they saw both their male and female friends running, but women ran more only at the influence of other women.

The work suggests that running is contagious—at least, in an online social network setting.

This is the first time that scientists have collected such a massive amount of data that show a health habit can seep through our social media alone. Previous research on gaining weight or quitting smoking linked to Facebook activity have been smaller studies or haven’t looked exclusively at social media’s effect.

You can thank your fellow runners for their inspiration, but take it with a grain of salt. On the one hand, running (like any exercise), comes with physical and mental benefits that may make you feel better overall. On the other, you can definitely overdo it—marathons and anything beyond are often considered excessive from a health standpoint.