## 4 Discussion
In accordance with the previously mentioned study, the results recorded in the present study show changes in the ability to maintain apnea, which increased on average by 0.6-1.2 s in the category of 9-14 years. In agreement with our study, another study concluded that long-term apneic breathing training can yield positive results by increasing tolerance to hypoxia [27]. After performing an analysis of the current study between the minimum average time achieved and the maximum average time recorded by age category, we derived the following values: in the 7-8-year-old group, the minimum starting time was 9.320 s and the maximum was 11.702 in free apnea tests without a nose clip; for those with nose clips the minimum was 9.338 s and the maximum was 12.623; in the category of 9-10 years, in the tests without nose clip, the minimum was10.330 s and the maximum was 12.777 s, and in the tests with the nose clip accessory, the minimum was11.206 s and the maximum was 12.195 s. In the 11-12 year group without the accessory, the minimum was 15.958 s recorded at the initial test and the maximum was 17.800 s recorded at the final test, and in the tests with the nose clip, the minimum was 16.684 s and the maximum was 18.619 s. In the 13-14-year-old group, in the initial tests without the accessory, a minimum of 27.953 was recorded and a maximum of 32.352 s was found; in the tests with a nose clip, a minimum of 31.035 s and a maximum of 33.908 s were found in the final test. Taking as a benchmark the statistical significance of the arithmetic averages from the tests, in the 7-8-year-old and 9-10-year-old groups, no statistically significant results were recorded, and the recorded results are in agreement with the level of development of the subjects by age category. Referring to the highlighted results, the recommendation given to synchronized swimming specialists regarding the average time to maintain the apnea for beginners should be 25.5 \(\pm\) 6.2 s [18]. The recorded results offer benchmarks of functional respiratory capacity related to synchronized swimming practice time intervals. In order to explain the differences recorded in the present study, we should consider how, in the 7-10-year-old group, in accordance with the particularities of anatomical-functional development, a series of changes in respiratory capacity occur: the differentiation of lung sizes ends at the age of 7, and their growth continues; one moves from predominantly abdominal to thoracic breathing. The breathing rate decreases from 20-22 at the age of 7 years to 18-20 at the age of 10 years, and it becomes more rhythmic and deeper [28; 29; 30]. Also, gradual increases were identified in the respiratory minute volume and the vital capacity of the lungs, which constitute 1800-2000 cm3 at 10 years. The vital capacity increases almost parallel to the anatomical capacity of the lungs, making an important leap between 6 and 8 years [31; 32]. In the age category 11-14 years, the possibilities of respiratory capacity are as follows: the amplitude of respiratory movements increases on average from 230 mL of air current volume at the age of 11 years up to 300 mL of air at the age of 13 years and up to 350 mL of air at age 15 [33]; the respiratory rate decreases from 22 breaths/min at the age of 11 years to 20 breaths/min at the age of 13 years, and to 18 breaths/min at the age of 15 years; the vital capacity at 11 years is between 2000 and 2200 mL of air, a value that increases on average by 250 mL of air for girls, which occurs at the age of 14-15 years [34]. In the first stage of puberty (10-13 years), the annual increase in vital capacity is up to 250 mL of air for girls and up to 300 mL of air for boys. In the second stage of puberty, the vital capacity develops rapidly, and the annual increase of this parameter reaches values of 3500 mL of air [25; 35; 36].