## 4 Discussion
This could be due to the fact that performance in both physical fitness tests is related to muscle mass [48, 49], and in the female population, the increase in muscle mass during adolescence occurs more gradually due to the sustained increase over time of the hormones responsible for its increase [45]. In fact, the results of the present research are in line with previous studies carried out in a female adolescent population, which found that age was a key factor when changes that occurred in sports performance variables at this stage were analyzed [16, 17], especially in physical condition variables that were dependent on muscular strength or agility [12, 56, 57]. Another objective of the present research was to determine if age, maturity offset or kinanthropometric variables could predict better performance in physical fitness tests. It was found that variables related to adiposity, \(\sum\)8 skinfolds, BMI and body mass predicted worse sports performance in the jump, sprint, agility and upper limb flexibility tests. This may be due to the fact that in most sports disciplines, low adiposity and weight favor performance, since added weight in the form of adipose tissue can weigh down performance in sports involving constant movement by requiring a greater effort for movement [58, 59]. Age was also shown to be a predictor of better performance in the long jump, medicine ball throw and CMJ. As has been found in previous research, age is a key factor in adolescent performance [60]. With advancing age, there is a significant increase in muscle and bone tissue, and it is more marked when there is a systematic practice of physical exercise due to the hormonal changes induced by it, but this also occurs in the absence of exercise, which could explain its influence on the models [12, 61]. In addition, it has been observed that the greatest influence of biological maturation on differences in physical performance is found around the APHV [12, 60]. The present study included a homogeneous sample that had mostly passed the APHV, which, together with the influence of age on the between-group differences found in the fitness tests, could be the reason why age is better than maturation in predicting physical performance in this sample. In addition, variables related to bone structure in both longitudinal and transverse planes were found to be key to performance in both flexibility tests and strength tests of both the upper and lower limbs. Previous studies have already pointed out the importance of bone structure in sports performance due to its relationship with the biomechanical parameters of force execution [62, 63] and in providing the appropriate environment for better muscle development [64]. In volleyball players, it was observed that there were differences in bone structure when comparing subjects of different competitive levels, with elite players showing higher values in height, upper limb length and bone diameters [65]. Therefore, factors related to bone structure in adolescent athletes could be key in talent identification and the prediction of future performance. On the other hand, one of the predictors of the power in the CMJ and medicine ball throw was muscle mass. Muscle strength and power production are initially related to neural factors but are later highly correlated with muscle mass gain [66, 67]. Muscle mass is a key factor in the improvement of performance in sports where body mass shifts in the horizontal or vertical plane, such as volleyball [59]. However, despite the fact that the present study found that physical performance was dependent on adiposity, muscle development and bone structure, there is a considerable lack of information in the scientific literature on this subject, which is why further research is needed to continue to expand knowledge on the relationship between plastic and structural components and sports performance, both in general physical fitness tests and in sport-specific actions.