## 3 Results
### Correlations
The results of that study should, however, be interpreted with caution because of the limited number of typically developing male participants (n = 16) and the comprehensive measures provided for all the participants. Notably, a recent meta-regression study demonstrated a non-significant relationship between gastrocnemius medialis FL and age [40]. However, the authors noted that it was difficult to compare studies across different ages due to the small number of participants in each study and the dependence of FL on joint position [40]. Specifically, in the studies included in that meta-regression analysis, architectural characteristics were measured at various degrees of plantar- or dorsiflexion, making direct comparisons difficult. Thus, the authors suggested that further research was required across ages using larger samples and standardized joint positions. In the present study, 89 female athletes divided into 5 age groups were assessed in a standard joint position (at rest) to examine differences in gastrocnemius medialis FL. The results indicated that FL increases significantly from the age of 8 until 14 years of age and remains unaltered from 14 to 18 years. In line with these results, [PERSON] et al. [41] suggested that adults possess muscle FLs not significantly longer than that of 15-year-old adolescents, although the 15-year-old had significantly longer muscle FLs than children, possibly implying that FL reaches adult levels at around 15 years of age [41]. Additionally, a recent study comparing adult volleyball athletes with rhythmic gymnasts showed similar FL values to those reported in the present study for the 14-16 y group (4.74 \(\pm\) 0.33 cm vs. 4.54 \(\pm\) 0.61, respectively), suggesting that FL may reach adult values during adolescence [42]. This pattern of FL development throughout maturation might be due to the muscle catching up with bone growth [43]. Studies examining gastrocnemius ACSA in typically developing children and adolescents are limited. The present study found a 31% increase in gastrocnemius medialis ACSA from the age of 8-10 until the age of 12-14 (Table 3), while small, non-significant increases were observed from 14 until 18 years of age (\(d\) = 0.28 to 0.37, respectively). Notably, ACSA increased by 14% (\(d\) = 0.61; \(p\) = 0.352) from the age of 12 to 18 years. Previous studies reported increases in muscle ACSA during maturation, with some suggesting that the greatest changes in boys occur around the age of 13-15 years [44]. However, to date, no other study has focused on female participants despite the continuously increasing number of child and adolescent female athletes in sports. In the present study, large increases in gastrocnemius medialis muscle ACSA were observed until the age of 12-14, while, after this age, changes in ACSA were non-significant. Girls mature earlier than boys, which is evident from the earlier growth spurt in girls than boys [45; 46]. Skeletal muscles' morphological adaptation to loading during adolescence might change also in response to endocrine signaling. Thus, it is plausible that muscle morphology changes occur earlier in females than in males during growth, but this warrants further investigation. The small non-significant increases found in ACSA in female athletes after the age of 12 years (\(d\) = 0.61) may suggest that ACSA does not reach adult levels at this age but continues to increase until late adolescence or early adulthood. The twofold greater increase in ACSA (49%) compared with FL (24%) during this time frame (8-18 years) indicates that growth in gastrocnemius medialis muscle fascicles may be primarily transverse rather than longitudinal, at least in these developing athletes. Significant correlations were found between gastrocnemius medialis FL and athletes' body height, calf and leg length (\(r\) = 0.263 to 0.617), while an almost similar pattern of percent changes in muscle FL and body height was observed (24 and 19%, respectively).