New research has found that exercise is contagious – the more your friends exercise, the more you will. Scientists have long known that various behaviours are affected by those of our peers, and now it seems that fitness is no exception.

Researchers from the MIT Sloan School of Management decided to test whether a person’s network of friends across the world would affect how far they ran. To do this, they analysed fitness tracker data that was posted to a social site by around 1.1 million people across five years.

Nice day for a run
In designing the study, the research team recognised that identifying cause and effect is particularly difficult in the field of social influence, due in part to many behavioural factors being unobservable and surveys being unreliable. For this reason, they decided to exploit a variable that occurs naturally, namely, the weather.

The team reasoned that good weather would encourage longer runs, and bad weather shorter runs. They hypothesised that when people in one location experienced good weather, and extended their runs, their friends in a different location, and who had different weather, would see this and also extend their runs.

Everyone’s different
While they found this to be true, there were differences in how strongly people were influenced by their friends. Men appeared to be more easily influenced than women – and particularly influenced by their male friends. Women were moderately influenced by other women, and unaffected by men. Runners who were typically lazier had a stronger influence on their more active friends, while the opposite was not true.

The researchers believe that since prior studies have typically relied on imprecise and frequently inaccurate self-reporting methods, the current study has a far greater potential to extend our understanding of social behaviour. They noted the importance of observing natural behaviours in real-world settings, as opposed to a laboratory.

They also noted that the results demonstrate the extent to which different types of people react to social influence. Such differences, they said, suggest that policies that are tailored for different types of people in different subpopulations will be more effective than those that only take average effects into consideration.

* Aral, S & Nicolaides, C. Exercise contagion in a global social network. Nature Communications 8, 2017