Obesity is a chronic disease characterized by the accumulation of body fat. School-age children obesity is one of the most serious public health challenges since it progressively becomes a risk factor in adulthood. Recent studies and technological innovations have demonstrated the feasibility of game-based interventions for promoting physical activity among children. Nevertheless, there is a gap in fitting the system specifications to specific user profiles. This paper aims to present the development of an adaptation component for a particular exergame based on wearable technology that measures heart rate to support a personalized tracking system of the physical activity. The employed methodology was the General Adaptivity Model (GAM) that provides guidelines for the designing process of adaptivity models, incorporating user modeling and personalization in existing or new interactive systems. For validation purposes, an experiment was conducted at a primary school with thirty subjects aged between five to seven years to test the effectiveness of a user adaptive system against a conventional interactive system for the promotion of physical activity. Results indicate that the developed system was able to change its behavior according to the variations of the heart rate and therefore encouraging users to perform higher/lower physical activity levels.