MIT researchers looked at a fitness-related social network—the researchers wouldn't say which—to reveal whether or not our exercise regimens affect others. In short, they do. The study looked specifically at about 1.1 million runners worldwide and found that the social contagion of their routines went past correlation to causation. That is, you don't just befriend people who exercise as much as you do—you're actually influenced by the quality and quantity of their posted workouts.

As Gretchen Reynolds of the New York Times elaborates, "if one person ran for about 10 minutes more than usual on any given day, that runner's friends would lengthen their workout by approximately three minutes, even if the weather was discouraging." According to their research, if Ashley runs faster than usual, her friends will likely boost their running that same day. But that's not all—runners are also motivated by a slower friend's sudden improvement. The threat of falling behind alone can drive them to pick up the pace.

Interestingly enough, the study states that "both men and women influence men, while only women influence other women." Of course, this study only applies to people who have already adopted an exercise routine. In the future, the MIT team plans to explore whether or not other types of exercise are similarly contagious, and what ways we can use this information to help those who have trouble starting a workout habit. Still, their findings add to a mountain of evidence that behaviors may in fact be contagious among friends. Take note, runners.

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