New research suggests that social networks can motivate people to execise more.

Researchers from the University of Pennsylvania found that compared to promotional ads or motivational messaging, the social influence of online peers proved more effective in improving exercise habits.

"While promotional messaging remains one of the standard ways of encouraging healthy behavior, it is also quite expensive," Damon Centola, who led the study, said in a statement. "What our results show is that you don't necessarily need to generate new media content in order to reach people. You just have to put people into the right kind of social environment where they can interact with each other, and even anonymous social interaction will create behavior change."

For the study, researchers collected and analyzed data from more than 200 graduate students enrolled in free exercise classes at the University of Pennsylvania gym.

Part of the group also received promotional messages from the University, including highly engaging motivational videos and infographics emphasizing fitness tips and the importance of exercise. The remainder saw no advertising messages. Instead, they were placed into social networks with six of their peers. While these peer groups remained anonymous to one another, participants were regularly updated on each other's fitness achievements. They could monitor each other's progress on the website, and when one signed up for a weightlifting or yoga class, for example, the others were notified by email.

As a control group for the two interventions, a final group of participants received no further follow-up through the study.

By the end of the 13 week study, the findings were clear. Promotional messages caused an initial bump in class attendance, but the motivational effects quickly wore off. The promotional messages had almost no long term effect on class participation.

Program-assigned "buddies," on the other hand, were much more effective at motivating people to exercise. As the weeks went by, the motivating effects increased, producing a substantial growth in enrollment levels among people in peer networks.

The participants in the social media group, in fact, knew remarkably little about one another, yet the results indicate that even minimal exposure to social cues can have strong effects. Simply knowing that your peers are going to yoga class is effective motivation to get you into your workout clothes -- and the technology required to share that information is incredibly cost-effective.

The findings are detailed in the journal Preventive Medicine Reports.