A new study published today in Nature Communications of the daily-recorded exercise patterns of over 1 million runners over five years shows that exercise is socially contagious. According to the study, your knowledge of what your friends are doing can and will motivate you to do more.

“Knowing the running behaviors of your friends as shared on social networks can cause you to run farther, faster and longer,” said Sinan Aral, David Austin Professor of Management at MIT Sloan School of Management.

Aral and colleague Christos Nicolaides of MIT used a data set that recorded the geographic location, social network ties and daily running patterns of over 1 million individuals who ran 359 million combined kilometers and logged those runs digitally in a global social network of runners over five years. The data contain the daily distance, duration, pace and calories burned during runs undertaken by these individuals, as recorded by a suite of digital fitness tracking devices. The results, says Aral, revealed “strong contagion effects.”

According to the study: “On the same day, on average, an additional kilometer run by friends can inspire someone to run an additional 3/10th of a kilometer and an additional ten minutes run by friends can inspire someone to run three minutes longer.”

Historically, in the context of exercise, a debate exists about whether we make upward comparisons to those performing better than ourselves or downward comparisons to those performing worse than ourselves. Comparisons to those ahead of us may motivate our own self-improvement, while comparisons to those behind us may create “competitive behavior to protect one’s superiority.” According to Aral, there is evidence for both trajectories in the study, but comparisons to those better than us are more powerful.

Gender matters too. The contagion is most pronounced among men, with men influencing other men to run farther and faster. In this regard, men may be more competitive and, specifically, more competitive with each other. Influence among same-sex pairs is strong while influence among mixed-sex pairs is weaker. Both men and women influence men. However, only women influence women who have reported, in earlier studies, being more influenced by self-regulation and individual planning than by their peers.

See the full study here.