Exercise May Be Contagious

Megan Brooks

April 24, 2017

An in-depth look at the daily-recorded exercise patterns of more than 1 million runners suggests exercise can be contagious.

Knowing how far, fast, and long fellow runners run, as shared on a global social network, can influence a person's running habits, moreso for men than women, the investigators found.

"The results suggest that social intervention strategies, which account for peer effects, may spread behavior change in networks more effectively than policies that ignore social spillovers," they write.

The study was published online April 18 in Nature Communications.

Calorie Burning a Competitive Sport?

Sinan Aral, PhD, the David Austin Professor of Management, MIT Sloan School of Management, Massachusetts Institute of Technology, Boston, and colleague Christos Nicolaides, PhD, a postdoctoral fellow at MIT Sloan, utilized a dataset that included data on the geographic location, social network ties, and daily running habits of 1.1 million people who ran 359 million combined km (223 million miles) and who logged those runs digitally in a global social network of runners during a 5-year period. The dataset included daily distance, duration, pace, and calories burned by the runners. The data were recorded by digital fitness trackers.

There was "strong evidence of the possibility of social contagion in running behaviors," the researchers report.

It was found that on average, an additional kilometer run by friends on the same day can inspire someone to run an additional 0.3 km. An additional 10 min spent running by friends can motivate someone to run 3 min longer. An additional 10 calories burned by friends can influence a peer to burn 3.5 additional calories.

Less active runners influence more active runners, but not the reverse, the researchers note. A person's sex also matters; contagion was most pronounced among men. It was found that men influence other men to run farther and faster.

"This may be due to gender differences in the motivations for exercise and competition," Dr Aral told Medscape Medical News. "For example, in previous studies, men report receiving and being more influenced by social support in their decision to adopt exercise behaviors, while women report being more motivated by self-regulation and individual planning. Moreover, men may be more competitive and specifically more competitive with each other," he said.

The results support the idea that social networks can influence behavior.

"Today we are inundated with digital social signals from our peers on platforms like Facebook, Twitter, Instagram, Snapchat, and others," said Dr Aral. "These technologies are amplifying the interdependence of our heath behaviors, our consumption patterns, and voting patterns, among others.

"Just 10 to 15 years ago, none of these technologies even existed. These platforms may be having a very significant impact on human evolution, and we need more research to investigate how, as we are barely scratching the surface of the topic," he added.

Real-World Research

Commenting on the findings for Medscape Medical News, Judy Van Raalte, PhD, professor of psychology, Springfield College, Massachusetts, noted that "anything that we can do to promote or increase exercise in a healthy way is an appealing, interesting, valuable finding for Americans. One of the fascinating things about this study is the use of real-world information about people exercising, not lab information."

She cautioned that there could be "a whole number of other variables to explain the findings, aside from contagion, like competitiveness. And these are people who are already exercising. Do these findings suggest that all we need to do is hook people up with a fitness website and tell them what their friends are doing and they will exercise more? Maybe, but maybe not. If it were that easy, we'd all be running."

The study was partly funded by the company that provided the running data. The authors say confidentiality agreements prevent them from revealing the name of that company. The authors have disclosed no relevant financial relationships.

Nat Comm. Published online April 18, 2017. Full text

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