## 4 Discussion
According to the World Health Organization growth charts, z-scores for boys aged 5 to 19 years old show that the height and mass norms change every three months [10]. In our study, significant changes occurred within 8 weeks. Height is the simplest parameter for growth and affects almost all orthopedic conditions during a child's growth [42]. An increase in body height was found to increase trunk asymmetry [43]. Consequently, in the current study, the significant increase in standing and sitting height observed within 8 weeks might have negatively affected the programs' effectiveness in correcting thoracic kyphosis and lumbar lordosis. An alternative reason could be that the frequency of the intervention program application and the 8-week duration of the training intervention was not adequate to contribute to significantly improving thoracic kyphosis and lumbar lordosis. A combination of both above mentioned reasons could have caused the lack of improvement in thoracic kyphosis and lumbar lordosis following the intervention program. Hamstring flexibility was significantly improved bilaterally, with a large effect size, following the application of CEP, a result which is supported by several previous studies [32; 44]. The frequency of our proposed hamstering stretching program was twice a week, 2.5 to 12.5 min, for 8 weeks. It is essential to preserve flexibility in young athletes, through stretching programs from an early age [12]. It was found that the inclusion of stretching programs on tight hamstrings in 6- to 11-year-old school children can improve their performances in straight-leg-raise and sit-and-reach tests. In order for such a program to be effective, it was suggested that stretching exercises should be included during both the warm-up and cool-down periods [44]. It was also found that studies with two to four sessions per week, 4 to 7 min per session, 20 s holding per stretching, and between 8 and 32 weeks duration, may effectively improve hamstering flexibility [44]. [PERSON] and [PERSON] (2020) tested the efficacy of the hamstering stretching program in 13-15-year-old students. They found significant improvements in the intervention group who performed a 3 min stretching program, holding each stretch for 20 s, twice a week for nine weeks [45]. Consequently, the results of the current study are in line with these previous reports and further support the significance and inclusion of stretching exercises in the individual CEPs of young soccer players. Both hip external and internal rotation ROM demonstrated statistically significant improvements following the application of the current individual intervention exercise programs. Similarly to our study, a previous study showed that stretching exercises used for lower-body muscle tightness and decreased ROM, combined with strengthening exercises targeting weak muscles, results in an improved muscle balance and postural asymmetries [3]. [PERSON] et al. (2014) found that the combined program, which included joint mobilization exercises, elicited improvement in the left hip flexion ROM. Improvements in the rectus femoris, tensor fasciae latae, knee flexors, and triceps surae bilateral muscles shortening were also found. Additionally, improvements in the left liiopsoas, right rectus femoris, bilateral tensor fasciae latae, bilateral knee flexors, and right triceps surae were found [3]. In our study, the [PERSON] test score included testing liiopsoas, rectus femoris, and tensor fasciae latae muscle tightness. Similar to the study of [PERSON] et al. (2014), the results from our study showed that both sides demonstrated statistically significant bilateral improvements in the [PERSON] test score, with a strong association of the Gamma value. Regarding ankle dorsiflexion, [PERSON] et al. (2014) found no modification in the ROM; only ankle plantar flexion ROM was improved [3]. In our study, the ankle prone passive dorsiflexion was passively assessed in positions with extended and flexed knees in order to test gastrocnemius and soleus shortening, respectively.