## 3 Results  
The anthropometric measurements for the youth and pro soccer players are presented in Table 1. Independent \(t\)-tests demonstrated that the professional players were significantly taller [\(t_{(94)}\) = 2.94, \(p<0.05\), CI = 1.23-6.39] and heavier [\(t_{(94)}\) = 7.76, \(p<0.05\), CI = 7.55-12.74] than the youth players. Body composition analysis demonstrated that youth players had a similar body fat percentage (BF%) compared to professional players (Table 1). Furthermore, the analysis demonstrated that the youth players had a significantly higher \(V\)O\({}_{2}\) max (59.89 \(\pm\) 5.6 mL\(\cdot\)kg\({}^{-1}\cdot\)min\({}^{-1}\)) compared to the professional players (56.43 \(\pm\) 4.81 mL\(\cdot\)kg\({}^{-1}\cdot\)min\({}^{-1}\)) [\(t_{(94)}\) = \(-\)3.24, \(p<0.05\), CI = \(-\)5.55--1.33]. However, the professional players had significantly better running performance (18:08 \(\pm\) 1.83 min) than the youth players (17:19 \(\pm\) 1.86 min) [\(t_{(94)}\) = 2.36, \(p<0.05\), CI = 0.14-1.64]. Similarly, the professional players had significantly better RE (43.95 \(\pm\) 3.59 mL\(\cdot\)kg\({}^{-1}\cdot\)min\({}^{-1}\)) than the youth players (46.86 \(\pm\) 3.33 mL\(\cdot\)kg\({}^{-1}\cdot\)min\({}^{-1}\)) [\(t_{(94)}\) = \(-\)2.92, \(p<0.05\), CI = \(-\)4.33--1.50]. The effect sizes measured by [PERSON]'s \(d\) were \(d\) = 0.66 and \(d\) = 0.48, indicating medium effects for \(V\)O\({}_{2}\) max and running performance, with a large effect for RE at \(d\) = 0.86. For the same purposes, the \(\eta^{2}\) values for multivariate analysis (\(\eta^{2}\geq\) 0.01, \(\geq\)0.06, \(\geq\)0.14) indicated small, medium, and large effects. A two-way ANOVA analysis indicated a main effect of playing standards (pro vs. youth) for the FBLA LT method, with the professional players having significantly higher FBLA LT than the youth (Table 2) [\(F(1,94)\) = 9.40, \(p<0.01\), \(\eta^{2}=0.10\)]. The analysis indicated no main effect of playing position or an interaction between playing standards and playing position (Table 3). Furthermore, the analysis indicated no main effect of playing standards (pro vs. youth) and playing position and no interaction for the rest of the LT methods. For this part of the analysis, one youth athlete was removed from the group as coaches utilized the athlete in multiple playing positions. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Playing Standards** & **n** & **M \(\pm\) SD (km/h)** \\ \hline \multirow{2}{*}{Age (years)} & pro & 52 & 27.37 * \(\pm\) 5.67 \\ \cline{2-4}  & youth & 44 & 16.20 \(\pm\) 0.8 \\ \hline \multirow{2}{*}{Height (cm)} & pro & 52 & 179.78 * \(\pm\) 6.72 \\ \cline{2-4}  & youth & 44 & 175.97 \(\pm\) 5.84 \\ \hline \multirow{2}{*}{Body Mass (kg)} & pro & 52 & 77.12 * \(\pm\) 6.54 \\ \cline{2-4}  & youth & 44 & 66.98 \(\pm\) 6.19 \\ \hline \multirow{2}{*}{Body Mass Index (BMI)} & pro & 52 & 23.83 * \(\pm\) 1.26 \\ \cline{2-4}  & youth & 44 & 21.59 \(\pm\) 1.84 \\ \hline \multirow{2}{*}{Body Fat Percentage (7-site)} & pro & 52 & 10.50 \(\pm\) 3.83 \\ \cline{2-4}  & youth & 44 & 9.24 \(\pm\) 3.28 \\ \hline \end{tabular} Note * = \(p\) \(<\) 0.05.  
\end{table} 
Table 1: The anthropometric characteristic differences between the pro and youth players. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Methods for LT Detection** & **Playing Standards** & **n** & **M \(\pm\) SD (km/h)** \\ \hline \multirow{2}{*}{Visual Inspection} & pro & 52 & 13.51 \(\pm\) 1.33 \\ \cline{2-4}  & youth & 44 & 13.45 \(\pm\) 1.78 \\ \hline \multirow{2}{*}{Log–Log} & pro & 52 & 12.32 \(\pm\) 1.61 \\ \cline{2-4}  & youth & 44 & 12.67 \(\pm\) 1.83 \\ \hline \multirow{2}{*}{Dmax} & pro & 52 & 13.55 \(\pm\) 0.89 \\ \cline{2-4}  & youth & 44 & 13.79 \(\pm\) 1.01 \\ \hline \multirow{2}{*}{FELA (4 mmol/L)} & pro & 52 & 13.54 * \(\pm\) 1.13 \\ \cline{2-4}  & youth & 44 & 12.71 \(\pm\) 1.63 \\ \hline \end{tabular} Note * = \(p\) \(<\) 0.05.  
\end{table} 
Table 2: The LT running velocity differences between the pro and youth players for each LT detection method.