Social network intervention to promote physical activity in adolescents by using vlogs.

This study tests the effectiveness of vlogs that promote physical activity among adolescents between 9 and 15 years old. In addition, it will test whether a social network intervention is more effective than a mass media campaign. The study uses smartphones to send out questionnaires, determine the social network and expose the adolescents to the intervention vlogs. Physical activity is measured by accelerometer (Fitbit flex). In the intervention groups, the adolescents are exposed to persuasive vlogs that promote physical activity. In the social network intervention, these vlogs are created by a small number of influential children per class (i.e., ’social influence agents’). In the mass media intervention, the adolescents are exposed to vlogs created by children from other schools.

Hypothesis 1: Adolescents who are exposed to a vlog intervention to promote physical activity will be more physically active compared to adolescents who are not exposed to a vlog intervention.



Hypothesis 2: Adolescents who are exposed to a social network vlog intervention to promote physical activity will be more physically active compared to adolescents who are exposed to a mass media vlog intervention.

There are 3 measurement periods (baseline, intervention and post intervention) and each period will consist out of seven days (5 days of physical activity data): 5 school days and 2 weekend days.



Because cooperation of schools is needed, the time points might vary slightly. The aim is to keep the amount of time between time points the same between schools.



The baseline measure will be conducted in February and March2018. The intervention will take place in and around April 2018. The post-intervention will be measured 5 weeks after the intervention week.

There will be two intervention conditions: [A] The social network intervention and [B] the mass media intervention. The control condition will not receive an intervention, but will have the opportunity to watch unrelated videos.



[A] The social network intervention:



At baseline, peers will nominate each other on a number of sociometric questions (e.g., friendship). Based on these nominations, a small subsample per classroom will be approached to become an influence agent on the last day of the baseline measures. The influence agents will create 6 vlogs (short video clips) to promote physical activity. Based on the self-determination theory, the influence agents are free to think of the content of the vlogs, however suggestions and ideas are provided during the instructions. After the influence agents filmed the content of the vlogs, a professional YouTube company will edit the content to make it appealing. During the intervention week, all the participants receive a vlog per day of the influence agents of their particular class.



[B] The mass media intervention:

Adolescents who are in the mass media intervention condition will receive the vlogs that are created in the social network intervention. For these participants, the vloggers are not classmates but someone who they have not seen before. The intervention vlogs of the classrooms are matched so that every vlog used in the social network intervention is used once in the mass media intervention