RÉSUMÉ
BACKGROUND: There have been many efforts to rectify lifestyles that contribute to obesity using a variety of methodologies in heterogeneous settings, but effective and sustainable interventions that are suitable for children are still needed. We developed a smartphone application called "HAPPY ME" for guiding health behavior decisions, which employs gamification and self-monitoring strategies. The aim of this paper is to outline the rationale and methods for the development and feasibility test of "HAPPY ME". METHODS: The study consisted of two phases: 1) description of theory-based conceptual framework and rationales for smartphone application development and 2) outline of a pre- and post-test design in 4th-6th grade of healthy elementary school students for 4 weeks. The students will be delivered missions or messages on a daily basis, which is to stretch the knowledge and skills for action. They will simultaneously be engaged in self-monitoring their eating and physical activities to clear daily quests. To measure acceptability and feasibility we will monitor usability, compliance, and satisfaction for a 4-week study period and evaluate the intervention effects on self-efficacy, readiness, and intention to engage in healthy behavior. CONCLUSIONS: The results of the feasibility study will show whether the smartphone application "HAPPY ME" for children is acceptable, as well as if it is usable and feasible for self-directed health management. The results will provide preliminary evidence of the effectiveness of smartphone application-supported child behavioral modification for child obesity prevention and management.