## 1 Introduction  
There has been a significant increase in the number of overweight children [1], with as many as 100 million young people now being overweight [2]. One cause is the decrease or lack of physical activity, which, in turn, generates other diseases such as type 2 diabetes mellitus, and overweight and/or obesity in childhood has been associated with possible early death in adulthood [3]. Long-term physical inactivity is transformed into a sedentary lifestyle, generating osterectacular diseases such as osteoporosis, which has grown into a public health problem with economic repercussions associated with treatment and rehabilitation [4]. This osteogenic disease is quite common in women and the elderly because of low bone density [5]. Although many factors influence the risk of developing osteoporosis [6], adequate bone mass acquisition in childhood reduces the risk of osteoporosis in adulthood or old age. The beneficial effects of physical activity can counteract the negative influence of a sedentary lifestyle on body composition and physical condition in children [7].  
Currently, international guidelines recommend that young people should engage in 60 min or more of moderate to vigorous physical activity, along with muscle and bone strengthening activities or exercises at least 3 times a week [8]. Regular physical activity is a key factor in the prevention, development, and treatment of childhood diseases such as obesity and osteoporosis, as recurrent physical activity has positive effects on body composition, osteogenic development, cardiorespiratory fitness, and psychological state [9].  
Football is a widely played game around the globe, and due to its high aerobic component, it produces a high energy expenditure, which is why it can be considered an effective tool to reduce and prevent obesity, overweight, and thus cardiovascular diseases [10]. Previous research has shown that 70-80% of maximal heart rate, indicating a high level of physical exertion, results in greater fat oxidation and fat loss during exercise compared to other activities of lower physical intensity [11]. Football is considered an impact sport, and as such, it produces benefits in bone development [12]. These high intensity levels may lead to an improvement in bone health through increased BMC and BMD during a child's growth period [13]. Previous studies of 12 weeks of football training in an untrained adult population [14], children with obesity [15], or older people [16] have shown benefits in body composition, bone quality, and physical condition variables. Therefore, it is important to know the adaptations in a healthy child population, together with the physical demands that children have in football training and matches, and thus design training programmes appropriate to their stage of growth and development in order to ensure healthy parameters in children [17].  
The Global Positioning System (GPS) is the appropriate device to determine and analyse these physical demands. It provides data on the external load experienced by players [18; 19; 20]. Utilising this technology in football training and contests enables coaches to comprehend the specific physical demands of different positions and tailor conditioning for each player's specific role on the team [21; 22]. In youth soccer, GPS is frequently employed to evaluate match performance, primarily for players aged 11 to 16 years [23; 24; 25]. However, to date, there is a paucity of data on the external load experienced by U10 and U12 football players in training and matches, which is needed to determine whether these physical demands are sufficient to improve body composition and enhance bone development in children. Therefore, the aim of this study was to describe and analyse the effects of a 12-week football programme on body composition (fat mass, muscle mass, and bone mass) in male children compared to a sedentary lifestyle, as well as the physical demands and loads required in training and matches in young football players.