## 4 Discussion
### Resisted Sprint Performance and Mechanical Variables
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **CMJ** \\ **Variables** \\ \end{tabular} } & \multirow{2}{*}{**Group**} & \multirow{2}{*}{**Pre**} & \multirow{2}{*}{**Post**} & \multirow{2}{*}{**Post-Pre**} & \multirow{2}{*}{**SE**} & \multicolumn{3}{c}{**Post-Pre**} \\ \cline{5-10}  & & & & & & **10** & **10** & **10** & **10** \\ \hline \multirow{3}{*}{\begin{tabular}{c} Height \\ (cm) \\ \end{tabular} } & RST2M & 40.63 \(\pm\) 4.21 & 38.68 \(\pm\) 3.44 & \(-\)1.95 \(\pm\) 2.09 & 0.541 & & \multirow{3}{*}{\(-\)3.407} & \multirow{3}{*}{0.127} & \multirow{3}{*}{0.068} & \multirow{3}{*}{0.71} \\ \cline{2-2} \cline{5-10}  & RST40S & 39.86 \(\pm\) 4.23 & 39.54 \(\pm\) 3.89 & \(-\)0.31 \(\pm\) 2.60 & & & & \\ \hline \multirow{3}{*}{\begin{tabular}{c} Take-off \\ Velocity \\ (m/s) \\ \end{tabular} } & RST2M & 2.82 \(\pm\) 0.14 & 2.75 \(\pm\) 0.12 & \(-\)0.06 \(\pm\) 0.7 & 0.019 & & & & \\ \cline{2-2} \cline{5-10}  & RST40S & 2.79 \(\pm\) 0.14 & 2.78 \(\pm\) 0.13 & \(-\)0.01 \(\pm\) 0.09 & 0.023 & & & \\ \hline \multirow{3}{*}{\
\begin{tabular}{c} CMJ \\ Depth (cm) \\ \end{tabular} } & RST2M & \(-\)29.44 \(\pm\) 6.62 & \(-\)30.43 \(\pm\) 6.18 & \(-\)0.98 \(\pm\) 5.41 & 1.397 & & & & \\ \cline{2-2} \cline{5-10}  & RST40S & \(-\)30.26 \(\pm\) 5.77 & \(-\)30.98 \(\pm\) 5.86 & \(-\)0.72 \(\pm\) 2.03 & 0.526 & & & \\ \hline \end{tabular}
\begin{tabular}{c} SE = standard error; CI = confidence interval; LL = 95\% confidence interval lower limit; UL = 95\% confidence interval upper limit; CMJ, countermovement jump. \\ \end{tabular}
\end{table} 
Table 7: Group differences in CMJ characteristics. Peak force and peak power showed no significant differences between RST2M and RST40S across the entire 20 m distance. The results of this study contrast with previous research on repeated sprint training performed with unresisted sprints. Prior studies have shown that during repeated sprints, fatigue leads to greater decreases in force and power output in the first and later phases of sprinting [24; 33; 72; 73; 74]. Sustaining sprints with reduced force and power applied by the neuromuscular system makes it difficult to achieve positive adaptations on maximal and repeated sprint ability for soccer players [75]. The principle of resisted sprint training is to apply greater force to the ground compared to unresisted sprints [55; 64; 65]. The neuromuscular system adapts by generating more force to overcome the resistance, thereby improving acceleration sprint performance [55; 61; 65; 76]. AvgStep length and frequency did not differ significantly between RST2M and RST40S across the entire 20 m distance. The findings of this study differ from previous research that observed changes in step length and step frequency during repeated sprints [21; 77; 78]. Earlier studies typically involved sprint distances exceeding 30 m with rest intervals of less than 30 s, with participants performing between 6 and 12 sprints. Alterations in step length and frequency during repeated sprints are thought to result from decreased vertical leg stiffness [14; 77]. Vertical leg stiffness, which describes how rigidly the body behaves like a spring, absorbing and releasing energy efficiently, diminishes with repeated sprints and is linked to alterations in neuromuscular activation and muscle oxygenation rates. Moreover, fatigue from repeated sprints is generally known to cause changes in knee and hip momentum at the beginning of acceleration sprints, as well as in the coordination of posterior chain muscles such as the glutes and hamstrings [28; 44; 45]. This study presented results that contrasted with those of typical repeated sprint training protocols. To understand these phenomena, further research is needed to elucidate the underlying mechanisms.