Physical activity and adolescents: An exploratory randomized controlled trial investigating the influence of affective and instrumental text messages

Objective. The present study attempts to develop and pilot the feasibility and efficacy of a novel intervention using affective messages as a strategy to increase physical activity (PA) levels in adolescents. Design. An exploratory pilot randomized control trial was used to compare behaviour change over 2 weeks. A modified form of the International Physical Activity Questionnaire was used to assess PA behaviour. A total of 120 adolescents (16-19 years) from 4 sixth forms in West Yorkshire completed the field-based study. Method. Participants were randomly assigned to one of three experimental conditions, or the control condition (N = 28). Participants in experimental conditions received 1 short messaging service (SMS) text message per day over the 2 weeks, which included manipulations of either affective beliefs (enjoyable/unenjoyable; N = 31), instrumental beliefs (beneficial/harmful; N = 30), or a combination of these (N = 31). Control participants received one SMS text message per week. Outcomes were measured at baseline and at the end of the 2 week intervention. Results. PA levels increased by the equivalent of 31.5 minutes of moderate (four metabolic equivalent) activity per week during the study. Main effects of condition (p = .049), and current physical activity level (p = .002) were identified, along with a significant interaction between condition and current activity level (p = .006). However, when the sample was split at baseline into active and inactive participants, a main effect of condition remained for inactive participants only (p = .001). Post hoc analysis revealed that inactive participants who received messages targeting affective beliefs increased their activity levels significantly more than the instrumental (p = .012), combined (p = .002), and control groups (p = .018). Conclusion. Strategies based on affective associations may be more effective for increasing PA levels in inactive individuals.