## 4 Discussion
We found that in the standard PA children, there was an increase in FM of 5.55 kg, and in the elevated PA children, there was a decrease of nearly 2.5 kg. This is in agreement with other studies involving obese children, which demonstrated a reduction of 2-3 kg in fat mass following PA intervention [39; 47; 48]. Our study did not consider possible changes in children's diets and PA outside the study protocols, which could have influenced the results. FFM depends on age and gender. Research confirms that regular PA leads to an increase in FFM, including SMM [16]. Our study also found that elevated PA children had higher FFM compared to standard PA ones (72.10% vs. 68.83%), and elevated PA children recorded a higher increase in FFM during the study. The results were similar to the studies of [PERSON] et al. (2017) and [PERSON] et al. (2007), which indicated that elevated PA increased FFM [43; 49]. [PERSON] et al. (2007) showed that obese teenagers practicing sports indicated that training longer than 14 weeks allows for a significant increase in FFM compared to children who did not participate in additional PA classes [50]. Our study reported an increase in FFM of approximately 11 kg in elevated PA children and a decrease of 9 kg in standard PA ones. Furthermore, other studies show that introducing regular PA to overweight children for a period of 5 to 10 months resulted in an increase in FFM ranging from 2.7 to 3.8 kg [51; 52]. [PERSON] et al. (2020) evaluated changes in TBW by BIA in children with excessive weight. In the age group 8-12, the average TBW in girls was 25.3 kg, and in boys, it was 26.5 kg [53]. In our study, average TBW was lower in girls (24.03 kg) and higher in boys (28.18 kg). From ages 10 to 12, TBW increased by nearly 6.55 kg in standard PA children and 7.21 kg in elevated PA ones. However, in terms of percentages, although TBW increased slightly in the elevated PA group from 53.26% to 53.59%, in the standard PA group, it decreased from 50.70% to 49.93%. This indicated that children with excessive weight were hypohydrated, which may increase their risk of dehydration, which is also supported by other authors [54]. It is estimated that less than 30% of children and adolescents meet the global PA recommendations of at least 60 min of moderate-to-vigorous PA per day. Schools are an ideal setting for PA interventions, given that children spend a significant amount of time at school under the supervision of teachers [55]. School-based PA intervention programs may be effective at preventing and treating obesity [56]. They can impact many children simultaneously, including hard-to-reach groups, since most children and adolescents go to school daily. These programs have the potential to play a pivotal role not only in preventing obesity but also in promoting growth, development, fitness, mental health, and cognitive performance in children [55; 56]. From a public health perspective, an increase in organized physical activity in the school curricula should be considered as a health policy option for decision-makers to reduce the risk of obesity among school-aged children and, thus, improve public health in the future. This work, however, is not without limitations. One of them is the small sample size. Furthermore, this study did not consider children's diet and PA outside of the study protocols, which could have influenced the results. Although DXA is considered the standard method for measuring FM, this method requires stationary tests. Therefore, since our tests are field-based, we decided to use the less precise BIA method. We did not assess the obesity phenotype. The study excluded children with normal weight obesity (NWO) with normal body weight and excessive FM. The body composition results obtained in this study were indicative only because the instrument used did not provide the parameters of resistance, reactance, impedance, and phase angle. Children's nutritional education and eating habits were not analyzed.