## 1 Introduction  
The global prevalence of overweight and obesity has surged dramatically. From 1975 to 2016, the prevalence of overweight/obesity among children and adolescents aged 5-19 years escalated from 4% to 18% [1]. According to the National Korean School Health Examination Survey, in which participants self-reported their height and weight, childhood (6-18 years) obesity in South Korea increased from 8.7% in 2007 to 15.0% in 2017 [2]. Males exhibited a higher overweight and obesity prevalence, adolescents aged 13-15 years had the highest severe obesity prevalence, and positive linear trends were significant for both sexes and all ages for overweight, class 1 obesity, and class 2 obesity [3].  
Obesogenic behaviors often begin at a young age and may have a lasting impact on adult weight status and health [4]. Obesity prevention efforts help patients and families establish healthy home habits and model, teach, and reinforce healthy habits in youth [5]. In 40 Korean adolescent girls with obesity (BMI \(\geq\) 30 kg/m\({}^{2}\)), prehypertension, hyperinsulinemia, and abdominal obesity, 12 weeks of resistance and aerobic exercise training significantly improved body composition and other hemodynamic parameters [6]. Thesefindings suggest that combined resistance and aerobic exercise may be a useful treatment for obesity comorbidities [6]. A positive association between moderate-to-vigorous physical activity (MVPA) and fitness was observed in males (\(\beta\) = 0.013, 95% CI: 0.005; 0.021) and females (\(\beta\) = 0.014, 95% CI: 0.006; 0.022), indicating that public health recommendations to promote physical fitness in youth should target MVPA and should also consider reducing sedentary time [7]. Various studies have corroborated the influence of physical activity or exercise on weight-to-height, bone, and muscle tissue growth in children and adolescents [8].  
Household and individual physical activity habits have become even more crucial since the COVID-19 pandemic. Physical activity decreased significantly during the COVID-19 pandemic, ranging from \(-\)10.8 to \(-\)91 min/day. These statistics urge governments to consider the negative impact of restrictive measures on physical activity among children and adolescents and ensure high levels of physical activity [9]. Physical activity is essential for a healthy childhood and adolescence, and the WHO recommends 60 min of MVPA a day, such as walking, biking, recreational sports, and active play, for children and adolescents aged 5-17 [10].  
In Korea, the Public Health Center Mobile Healthcare Project was implemented in 2016. This project employed Information and Communications Technologies (ICT) and big data to establish a foundation for health-related services and a healthcare service operation system (this project allows intelligence agencies to monitor participants' physical activity information using wireless wearable devices). Previous studies reported that females in urban areas were significantly taller and had lower BMIs than females in rural areas, and males in urban areas also had lower BMIs than males in rural areas [11]. Obesity is more common in rural children compared with urban children [12]. These technologies break down the boundaries between urban and rural areas and ensure that all Korean adolescents have equal opportunities.  
In 2021, the Korea Health Promotion Institute began providing mobile-based healthcare services using ICT to overcome in-person healthcare service limitations from the COVID-19 pandemic [13]. Therefore, this study aimed to assess physical fitness and activity health promotion through an ICT-based health promotion service approach for public health surveillance among adolescents in South Korea.