## 2 Material and Methods
### Cardirespiratory Endurance  
The assessment of VO\({}_{2\max}\) was performed on a motorized treadmill (HP Cosmos, Pulsar, Nussdorf-Traustein, Germany) using a continuous exercise testing protocol. The initial grade and speed were set at 0% at 8 km/h. Every two minutes, the speed increased by 2 km/h up to a speed of 12 km/h. Then, from a speed of 14 km/h, the gradient was set at 2%, and the speed increased every 1 min until exhaustion. The oxygen uptake, determined by means of absolute (mL/min) and relative values adjusted to body weight (mL/kg/min), as well as the cardiorespiratory indices, were measured via an ergospirometric device based \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Monday** & **Tuesday** & **Wednesday** & **Thursday** & **Friday** & **Saturday** & **Sunday** \\ \hline \multirow{4}{*}{Soccer} & \multirow{4}{*}{Recovery} & Aerobic training & Power & Specific endurance & \multirow{4}{*}{\begin{tabular}{} \end{tabular} } & \multirow{4}{*}{\begin{tabular}{} \end{tabular} } \\  & & Technical– & & & \\  & Tactical training & Speed & Tactical training & Tactical training & & \\  & & Strength & & & & \\ \hline \multirow{4}{*}{Basketball} & \multirow{4}{*}{Recovery} & Aerobic training & Strength & Power & \multirow{4}{*}{\begin{tabular}{} \end{tabular} } \\  & & Technical– & Technical– & & & \\  & Tactical training & Tactical training & Tactical training & Tactical training & & \\ \hline \multirow{4}{*}{Handball} & \multirow{4}{*}{Recovery} & Aerobic training & Technical– & \multirow{4}{*}{\
\begin{tabular}{} \end{tabular} } & \multirow{4}{*}{
\begin{tabular}{} \end{tabular} } \\  & & Technical– & & & \\ \cline{1-1}  & & Tactical training & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Basic training characteristics during the competitive season. \begin{table}
\begin{tabular}{l c c c} \hline \hline  & **Soccer** & **Basketball** & **Handball** \\ \hline \hline \multicolumn{1}{l}{Stature (cm)} & 164.9 \(\pm\) 6.0 *** & 175.4 \(\pm\) 5.7 \(\lx@sectionsign\) 585 & 167.3 \(\pm\) 4.7 \\ Body mass (kg) & 58.7 \(\pm\) 6.1 *** & 71.6 \(\pm\) 13.7 \(\lx@sectionsign\) 58 & 63.1 \(\pm\) 6.5 \\ Biceps (mm) & 4.9 \(\pm\) 2.2 \(\lx@sectionsign\) *** & 7.5 \(\pm\) 3.8 & 8.5 \(\pm\) 3.1 \\ Triceps (mm) & 9.4 \(\pm\) 4.9 \(\lx@sectionsign\) *** & 16.3 \(\pm\) 5.6 & 17.8 \(\pm\) 7.0 \\ Suprailiac (mm) & 7.8 \(\pm\) 2.9 \(\lx@sectionsign\) *** & 13.3 \(\pm\) 4.8 & 11.5 \(\pm\) 3.7 \\ Subscapular (mm) & 7.8 \(\pm\) 1.4 \(\lx@sectionsign\) * & 9.8 \(\pm\) 3.3 & 9.9 \(\pm\) 2.3 \\ Lean body mass (kg) & 46.7 \(\pm\) 3.7 \(\lx@sectionsign\) 52.0 \(\pm\) 7.6 \(\lx@sectionsign\) 585 & 46.2 \(\pm\) 3.2 \\ Body fat (\%) & 20.2 \(\pm\) 3.6 \(\lx@sectionsign\) *** & 26.4 \(\pm\) 4.4 & 26.6 \(\pm\) 4.7 \\ \hline \hline \end{tabular}  
* Soccer vs. Basketball: *: \(p<0.05\); **: \(p<0.01\); ***: \(p<0.001\); Soccer vs. Handball: #: \(p<0.05\); #: \(p<0.01\); ###: \(p<0.001\); Basketball vs. Handball: 58: \(p<0.01\); 585: \(p<0.001\).  
\end{table} 
Table 2: Anthropometric characteristics of participants by sport at baseline (Mean \(\pm\) SD). on a breath-by-breath automated pulmonary/metabolic gas exchange system (Oxycon Pro-Jaeger, Wurzburg, Germany) using a tight face mask specially designed for children. The HR was recorded continuously using a Polar HR monitor (Polar Electro, Oy, Kempele, Finland) connected to the ergospirometric device. VO\({}_{\rm 2 max}\) was assumed when three of the four following criteria were met: (a) the HR during the last minute exceeded 95% of the expected maximal HR predicted 220-age; (b) a respiratory exchange ratio (RER) (VCO\({}_{2}\)/VO\({}_{2}\)) at or higher than 1.1 was reached; (c) VO\({}_{2}\) reached a plateau and/or signs of subjective exhaustion were present and the subject was unable to continue running, despite verbal encouragement [29]. Blood samples were obtained from the hand-warmed fingertip and the concentration of blood lactate was determined in the 5 th minute of recovery using a lactate photometer analyzer (Accusport, Boegringer Manheim, Germany).