The Triple E project: a factorial randomised controlled trial to enhance engagement with eHealth approaches to improve health risk behaviours among adolescents

Digital, or eHealth, interventions are highly promising approaches to help adolescents improve their health behaviours and reduce their risk of chronic disease. However, they often have low uptake and retention. There is also a paucity of high-quality research into the predictors of eHealth engagement, and a lack of studies that have systematically evaluated existing engagement strategies in adolescent populations. This paper describes the protocol for a randomised controlled trial which primarily aims to assess the effectiveness of different strategies in increasing engagement with a healthy lifestyles app, Health4Life. Associations between the engagement strategies and improvements in adolescent health behaviours (healthy eating, physical activity, sleep, recreational screen time, smoking, alcohol use) will also be examined, along with potential predictors of adolescents' intentions to use health apps and their use of the Health4Life app.