## 4 Discussion  
The aim of the present study was to describe and compare the trunk muscle endurance in children and adolescents in relation to the CA, MAT, and sex. The main results showed differences in all trunk endurance tests according to the CA and MAT, with greater performance being found in the tests at an older CA or higher MAT. Differences were also found by sex; boys presented higher performance in the SB and DEE tests, while girls performed better in the BS test. Regarding interactions, boys performed better than girls in the DEE test (14 and 15 years old). In addition, interactions were also found between sex and MAT, where boys performed better than girls in all tests (with the only exception being the BS test) in the circa-PHV group, as well as in the post-PHV group for the SB-R, SB-L, and DEE tests. However, no interaction with sex was found for the pre-PHV group (except for the DEE test, where boys performed better than girls). The current findings are consistent with the results of previous studies evaluating trunk muscle endurance [15; 16; 30; 42] and other physical demands related to performance (strength, power, speed, etc.) [24; 25; 30; 43; 44] in youths, where an increase with advances in CA was observed. These findings are also in line with our MAT results, as well as those provided by [PERSON] et al. [31] in their study assessing trunk muscle endurance through the ventral Bourban test in youth athletes, in which an increase with MAT was found. The changes in individual structures at the whole-body level (e.g., size, weight, proportion, and architecture of muscles and specific patterns of muscle activation) as well as at a system level (e.g., skeletal, muscular, and endocrine systems) that occur during puberty may improve the ability to generate strength with age and maturation, explaining the better scores obtained by older and more mature youths in physical tests that require this capacity [34; 45]. By contrast, and unlike to what we found in this study, some researchersdid not report age-related differences in trunk muscle performance for the BS [16], BTC [23], and SB [16; 26] tests. In these studies, [PERSON] et al. [16] involved a sample of male and female adolescents between 15 and 18 years old, [PERSON] et al. [23] evaluated a sample of male and female adolescents with a mean age of 16.26 \(\pm\) 1.13 (14-18 years), and [PERSON] et al. [26] evaluated a sample of female volleyball players with a mean age of 13.9 \(\pm\) 1.9. Considering that the early onset of puberty occurs at age 12 in females and around age 14 in males [27] and that the largest differences in performance tend to appear at circa-PHV (as shown in our MAT analyses), it is plausible that these authors did not find age-related differences in performance, in part because most of their participants were at the post-pubertal stage. Regarding the effect of sex on trunk endurance performance, boys demonstrated, in general, a higher performance than girls for all field-based tests (with the exception of the BS test). Likewise, when the endurance of the trunk muscles is assessed in the adolescent population, boys tend to obtain higher scores than girls (i.e., the SB test, BTC test, ventral Bourban test, and FLEX-EXT dynamometer test) [16; 23; 24; 25; 30; 31], except in the BS test [15]. This difference can be partially attributed to sex-based morphological and neuromuscular characteristics. On average, males have larger and higher-density trunk muscles than females, which likely contributes to their superior performance [46; 47]. However, sex differences in performance may not depend solely on anthropometric measures, as intrinsic differences in muscle contractile properties, adaptations to training, and responses to clinical treatments may also play a role.