Now here’s a contagion that might not be so bad to encounter. A new analysis of the running habits of about 1.1 million people reveals that exercise is indeed contagious — though its communicability depends on who’s spreading it.
The findings, published in the journal Nature Communications, also reveal that certain relationships are better at spreading the running bug than others — and could have implications for the study of other social contagions, such as obesity and smoking.
In recent years, researchers in a wide range of fields — from economics and politics to medicine and computer science — have begun to investigate the ways in which many of our individual decisions affect the decisions of our peers, and how behavioral changes may spread through a social network.
Creating health and other interventions that effectively could harness the social network to maximize their benefit would be a real game-changer, researchers say. But it’s been difficult to draw conclusions from studies based on self-reporting surveys (where participants may not be fully honest or aware of their own behaviors) or laboratory experiments (which may not fully capture the real-life complexities of causal relationships within social networks).
So for this paper, Sinan Aral and Christos Nicolaides of the Massachusetts Institute of Technology used fitness tracker data to study the running and activity habits of around 1.1 million people in an actual global social network. The runners had formed about 3.4 million social network ties; the researchers analyzed the 2.1 million or so ties for which they could pinpoint geographic location and weather information for both users. Over five years, these social media users ran a collective 350 million kilometers — and their runs were all automatically posted online for their friends to see, reducing the issues that come with self-reporting.
On the same day on average, an additional kilometer run by friends influences an individual to run an additional 0.3 kilometers. An additional kilometer per minute run by friends pushes a person to run an additional 0.3 kilometers per minute faster than usual. If those friends run an extra 10 minutes, that person is likely to run about three minutes longer than they would have. If those friends burn an extra 10 calories, that person will end up burning 3.5 more calories.
The effect is strongest on the same day and appears to diminish with time, the authors wrote.
But do we make upward comparisons to peers performing better than us, or downward comparisons to those performing worse? That’s been a subject of debate, the researchers said.
“Comparisons to those ahead of us may motivate our own self-improvement, while comparisons to those behind us may create ‘competitive behaviour to protect one’s superiority,’” they explained. “Our findings are consistent with both arguments, but the effects are much larger for downward comparisons than for upward comparisons.”
So people who we think are our closest fitness “peers” — particularly those who we think are slightly lower on the totem pole relative to ourselves — are most likely to get us to push our limits.