Effectiveness of a High‐Intensity Interval Games Program in Extra‐Curricular Context (MOVI‐daFIT!) on Gross Motor Competence and Health‐Related Quality of Life in Primary Schoolchildren: Cluster‐Randomized Trial

High-intensity interval training (HIIT) has emerged as a time-efficient approach to improve aerobic capacity, cardiovascular health, and cognitive functioning in children and adolescents. However, evidence regarding the impact of school-based HIIT programs on motor competence and health-related quality of life in children is limited. This study evaluated the effectiveness of a HIIT intervention, based on playground games on gross motor competence and health-related quality of life in schoolchildren aged 9-11 years. A cluster-randomized controlled trial was conducted with 562 participants. The intervention involved four weekly 60 min sessions of extracurricular physical activity using traditional games adapted to a HIIT protocol. Gross motor competence and health-related quality of life were assessed using the Movement Assessment Battery for Children-Second Edition (MABC-2) and the KIDSCREEN-27 questionnaire, respectively. Analyzes were conducted on an intention-to-treat basis using mixed linear regression models to compare changes from baseline to postintervention between the intervention and control groups. No significant improvements in gross motor competence or health-related quality of life were observed after adjusting for baseline variables, age, sex, and school. The results suggest that this HIIT-based program was not effective in enhancing gross motor competence or in improving health-related quality of life. Future programs could improve effectiveness by optimizing the balance between movement intensity and quality, aligning activities with gross motor competence assessment tools, emphasizing health-related quality of life components, training educators to enhance quality of life, extending intervention duration to impact self-esteem and psychological well-being, and improving adherence rates.