## 3 Results
### Second Hypothesis
\begin{table}
\begin{tabular}{c c c c} \hline  & \(\Delta\)**RSA (s)** & \(\Delta\)**Sprint (s)** & \(\Delta\)**CMJ (cm)** \\ \hline \(\Delta\) RSA & 1.000 & & \\ \(\Delta\) sprint & 0.648 & 1.000 & \\ \(\Delta\) CMJ & \(-\)0.509 & \(-\)0.676 & 1.000 \\ \(\Delta\) body mass & \(-\)0.516 & \(-\)0.373 & 0.546 \\ \(\Delta\) stature & \(-\)0.374 & \(-\)0.394 & 0.591 \\ \(\Delta\) low limb & 0.061 & \(-\)0.157 & 0.320 \\ \(\Delta\) trunk height & \(-\)0.552 & \(-\)0.423 & 0.574 \\ \(\Delta\) BMI & \(-\)0.479 & \(-\)0.292 & 0.289 \\ \(\Delta\) APHV & 0.530 & 0.400 & \(-\)0.597 \\ \(\Delta\) waist c & \(-\)0.172 & \(-\)0.022 & 0.257 \\ \(\Delta\) hip c & \(-\)0.413 & \(-\)0.221 & 0.391 \\ \(\Delta\) arm red c & \(-\)0.277 & \(-\)0.177 & 0.441 \\ \(\Delta\) arm con c & \(-\)0.271 & \(-\)0.094 & 0.377 \\ \(\Delta\) calf c & \(-\)0.319 & \(-\)0.311 & 0.292 \\ \(\Delta\) thigh c & \(-\)0.209 & \(-\)0.128 & 0.242 \\ \(\Delta\) humeral d & \(-\)0.432 & \(-\)0.324 & 0.672 \\ \(\Delta\) femoral d & \(-\)0.459 & \(-\)0.277 & 0.288 \\ \(\Delta\) tric SK & 0.429 & 0.593 & \(-\)0.604 \\ \(\Delta\) bic SK & 0.534 & 0.431 & \(-\)0.422 \\ \(\Delta\) subs SK & 0.199 & 0.194 & 0.156 \\ \(\Delta\) spinal SK & 0.589 & 0.535 & \(-\)0.615 \\ \(\Delta\) iliac SK & 0.579 & 0.557 & \(-\)0.518 \\ \(\Delta\) thigh SK & 0.470 & 0.448 & \(-\)0.255 \\ \(\Delta\) mL calf SK & 0.461 & 0.580 & \(-\)0.533 \\ \(\Delta\) l calf SK & 0.358 & 0.439 & \(-\)0.466 \\ \(\Delta\) TUA & \(-\)0.342 & \(-\)0.218 & 0.453 \\ \(\Delta\) UMA & \(-\)0.438 & \(-\)0.398 & 0.590 \\ \(\Delta\) UFA & 0.393 & 0.580 & \(-\)0.546 \\ \(\Delta\) UFI & 0.416 & 0.572 & \(-\)0.625 \\ \(\Delta\) TCA & \(-\)0.327 & \(-\)0.305 & 0.276 \\ \(\Delta\) CMA & \(-\)0.375 & \(-\)0.355 & 0.317 \\ \(\Delta\) CFA & \(-\)0.011 & 0.010 & 0.009 \\ \(\Delta\) CFI & 0.579 & 0.551 & \(-\)0.472 \\ \(\Delta\) TTA & \(-\)0.224 & \(-\)0.123 & 0.237 \\ \(\Delta\) TMA & \(-\)0.371 & \(-\)0.259 & 0.323 \\ \(\Delta\) TFA & 0.425 & 0.402 & \(-\)0.235 \\ \(\Delta\) TFI & 0.492 & 0.483 & \(-\)0.269 \\ \(\Delta\) BF & 0.511 & 0.582 & \(-\)0.535 \\ \(\Delta\) FM & 0.321 & 0.497 & \(-\)0.410 \\ \(\Delta\) FFM & \(-\)0.583 & \(-\)0.472 & 0.596 \\ \(\Delta\) endo & 0.548 & 0.643 & \(-\)0.520 \\ \(\Delta\) meso & \(-\)0.048 & 0.106 & \(-\)0.133 \\ \(\Delta\) ecto & 0.189 & 0.004 & 0.030 \\ \(\Delta\) R & 0.666 & 0.488 & \(-\)0.469 \\ \(\Delta\) Xc & 0.443 & 0.197 & \(-\)0.306 \\ \(\Delta\) PhA & \(-\)0.078 & \(-\)0.223 & 0.095 \\ \hline \end{tabular} Note: BMI, body mass index; PHY, peak height velocity; APHV, age at peak height velocity; c, circumference; d, diameter; tric, tricteps; bic, biceps; subs, subsexular; spinal, supraspinal; iliac, supra-iliac; m, medial, l, lateral; SK, skinkold thickness; endo, endomorphic; meso, mesomorphic; ecto, ectomorphic; R, resistance; Xc, reactance; PhA, phase angle; CMJ, countermovement jump; RSA, repeated sprint ability.  
\end{table} 
Table 2: Pearson product–moment’s correlation matrix of physical performance and body composition variations. performance and anthropometrical parameters, and we provided three new regression models to justify players' power and speed variabilities. In line with our hypotheses, we highlighted that growth induced many morphological changes that need to be accounted for in juvenile development because they have a noticeable relationship with physical performance. Power, agility, and speed are conditioning abilities vital for football success, and specific body shape proportions could enhance them. We found that many parameters, such as lengths, circumferences and areas, diameters, and body composition (fat and fat-free mass), change with age. [PERSON] et al. [25] suggested that body size could be an important factor for progression in a football career between 10 and 14 years of age. As regards stature and body mass, the longitudinal increments we observed were comparable to what was found by [PERSON] et al. [26] in their study on Basque football players aged 10-15 years.