Exploring Mediators of Accelerometer Assessed Physical Activity in Young Adolescents in the HEIA Study – A Randomized Controlled Trial

Introduction School-based interventions which include efforts to increase physical activity (PA) may promote a healthy weight development in adolescents, but results are inconsistent (Brown et al., 2009). One possible explanation for low efficacy or effectiveness is limited evidence as to how interventions induce behaviour change (Baranowski et al., 2005). The purpose of this study was to examine whether personal, social and physical-environmental factors mediated intervention effect on PA and whether gender and weight status moderated mediated effects in the HEIA study – a school-based, randomized controlled trial to promote healthy weight development among young adolescents.

Methods Accelerometer assessed PA (mean count per minute) and six potential mediators based on the social/ecological framework were assessed at baseline and post-intervention after 20 months. The product-of coefficient test was used to assess mediating effects.

Results No mediating effect of any of the hypothesized mediators was identified. Gender and weight status did not moderate any mediated effects with the exception of weight status that moderated the mediated effect of enjoyment. Few intervention effects were seen on the mediators, except for a positive change in social support from teachers among girls.

Discussion Even though no mediating effect on PA change could be observed, personal, social and physical-environmental factors were identified as potential mediators. Future studies should continue to examine mediating and moderation mechanisms in PA change in adolescents using a broad set of mediators.

References Baranowski T, Jago R. (2005). Understanding the mechanisms of change in children’s physical activity program. Exerc Sport Sci Rev, 33,163-168. Brown T, Summerbell C. (2009). Systematic review of school-based interventions that focus on change in dietary intake and physical activity levels to prevent childhood obesity: and update to the obesity guidance produced by the National Institute for Health and Clinical Excellence. Obesity reviews, 10, 110-141.

Link to Abstract: http://www.biomedcentral.com/1471-2458/12/814/abstract