Human biological development usually proceeds according to the norms. This enables the comparison of percentiles and the decision of whether the changes comply with the physiological norm or not. When assessing body composition, all parameters in the study group are consistent with the physiological norm. This indicates the correct selection of the examined adolescents and the proper training process, which does not disturb the proper development of the organism in terms of tissue and biochemical composition. The problem of body composition in young footballers was studied by Santos-Silva et al. The 16-week futsal training program contributed to the improvement of body composition and cardiovascular capacity in a group of boys before puberty (7–10 years). There was a significant increase in total body weight (4%), height (3%), lean body mass (8%) and a significant 6% decrease in body fat percentage [
21]. The research presented in this study also shows that in older boys (14–16 years old) there was a greater percentage of boys who were below the norm than in the other groups. Similar results were obtained by Ørntoft et al. [
22] found that Danish children aged 10–12 engaged in club football (FC) and other ball games (OBGs) had more muscle mass and a lower body fat percentage than children who did not play sports in their free time (NSC). Children participating in club ball games had a higher (
p < 0.05) lean body weight than NSC and OBG: participation in soccer classes also affects the percentage of body fat. Significant scientific reports indicate the improvement of the body’s ability to maintain balance until the age of 10–12. The differences in the limits of the ability maximization are determined by the measurement method, or rather the conditions for showing the body’s ability to balance. Different limits are indicated by the authors for measurements under static conditions, others under dynamic conditions. In our own study, it was observed that the body balance was better with the increasing duration of the training rigor. The oldest group of the boys under study showed the lowest balance disturbances during the stabilometric test. The research conducted by Lebiedowska M. and Syczewska M. [
23] showed that despite changes in the body dimensions of children between 7 and 18 years of age in balance tests, the invariability of the swing amplitude is noticeable, which confirms the view that the same patterns of muscle activation are used in children and adolescents. Different results, but adequate to the authors of this study, were obtained by Riach C.L. and Starkes J.L. [
24] who in studies of children (4–13 years old) and adults showed an age-related change in the velocity of the center of gravity and in the position of the feet. The problem of the influence of regular football training on balance was investigated by Olchowiak G. and Czwalik A. [
25]. The authors carried out research on women training in football (
n = 25) and a control group (
n = 50). In the tests used, statistically significant differences between the groups were obtained. Women training in football showed better postural stability and balance. The study showed that regular training can improve the balance system. The authors’ conclusions are consistent with the results obtained by the authors of this study, as they showed statistically significant differences between the groups in terms of body posture stability. Kumala M.S. et al. [
26] also dealt with balance in athletes, comparing the balance between normal and flat feet. None of the tests performed showed statistically significant differences between the groups (
p > 0.05) in the balance of the body. Jaszczur-Nowicki J. et al. [
27,
28,
29] in their works analyze changes in the balance and distribution of pressure forces on the plantar side of the foot under the influence of various factors. In children, under the influence of an external load (backpack), the results of body balance were statistically significant. They concerned measurements of the area of the center of gravity of the body, the area of the center of gravity of the left foot and the parameter comparing the distance to area ratio. In all these parameters tested,
p < 0.05 was obtained. The authors obtained statistically significant results in all parameters of the body balance by analyzing the influence of exercise (Harvard Step Test) on the examined parameters in students. The authors of the above studies also analyzed the distribution of pressure forces on the plantar side of the foot; in children, the results indicated that after putting on the backpack for the entire study group, statistically significant differences (
p < 0,05) were found in the distribution of the foot pressure on the ground in the left foot, forefoot, and heel area. However, in the right foot, this difference was noted for the forefoot and the metatarsus. The
p-value in these parameters was also below 0.05. On the other hand, among students, when comparing the mean results of measurements at rest and after exercises for the forefoot, the value of the rest vs. the post-training values for the left foot were comparable, as for the right foot. The image of the metatarsal area, being a reference to the correct longitudinal cavity of the foot. It was different for both feet when measured at rest compared to after exercise. For the heel area, the mean differences in the values between the measurements for the right and left foot was also noted. Additionally, in the author’s study, differences in the pressure on the ground of individual parts of the foot between the right and left foot were noted. Systematic football training, as well as external load and physical effort, affects changes in body balance and the distribution of pressure forces on the sole of the foot. Further studies confirming the results obtained by the authors of this study are the analyses of Bibro M. et al. [
29]. They took up the problem of the analysis of the arching and pressure distribution of the plantar side of the feet of young men under the influence of strength training of the lower limbs. The surveyed men were divided into two groups of 30. Group I, subjected to training, completed training in the gym including lower limb exercises within 60 minutes, and group II spent the same period of time passively, in a sitting position. In the group subjected to strength training, in the measurements before and after exercise, the lateral and medial side of the hindfoot were symmetrically loaded, while the load on the forefoot increased significantly, especially on the medial part. One hour of effort also had a slight effect on the height of the arches of both feet. Bogut I. et al. [
30] conducted research on the occurrence of foot deformities in city children, as well as on possible generation and sex differences. The results of the research showed that the highest percentage of children did not have a noticeable foot deformity, so more than three-quarters of children in 2005 and 2011 had healthy feet. The only noticeable percentage of children with foot deformities relates to the first-degree flatfoot category, from 9.39% in 2005 and 14.69% in 2011. There were no significant differences in the occurrence of foot deformities between the 2005 and 2011 generations or by gender and age between and within each subgroup. The results of these studies indicate that the largest number of children aged 7–11 years did not have noticeable foot deformities, so in children studied in 2005 and 2011, so most of the children did not have deformities. The only noticeable percentage of children with foot deformity relates to the first-degree flat foot category; however, their percentage was in the range of 9–15%. The boys studied for the purposes of this study were also city dwellers. The results obtained by the authors were not compatible with the studies cited above. The author’s study noted that the total length of the longitudinal arch of both feet of the examined boys showed a tendency to flatten in direct proportion to the age of the examined boys. The arches of the foot differ, however, between the right and left roof. Zdunek M.K. et al. [
17] confirmed that people practicing the above disciplines have hollow long arches of the foot. Additionally, the results of the research carried out by the authors showed differences in the distribution of forces on the sole of the foot depending on the sports discipline practiced. In the throwing group, in the right and left feet, the front part of the foot was loaded more frequently, while in the jumping group, the back of the foot was more loaded in the right and left feet. The authors concluded that the observed differences probably resulted from the fact that, due to the specificity of the sports discipline, players have different morphological profiles. The authors of this study also noticed that the studied footballers were mostly characterized by a hollow longitudinal arch. Due to the specifics of their discipline, players are more likely to put stress on the rear of the left foot and the front of the right foot.