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.