## 4 Discussion  
### The Effects of EMS on Athletic Performance  
Among the 10 studies included, 6 focused on the use of EMS to improve athletic performance in soccer players [14, 17, 19, 20, 21, 23]. The findings suggest that EMS has potential in enhancing physical conditioning in this population. However, the effectiveness of EMS appears to vary considerably depending on the specific stimulation protocol, application setting, and training objectives. This heterogeneity includes differences in stimulation intensity, frequency, pulse duration, electrode placement, timing relative to exercise, and intervention duration, which significantly limit the comparability of study outcomes and undermine the generalizability of findings across contexts. Some studies have reported improvements in localized muscle strength and functional outcomes when EMS was applied to specific muscle groups [24]. The underlying mechanism involves the recruitment of large, high-threshold Type II muscle fibers, which are important for generating explosive strength. This recruitment occurs through supramaximal impulses, even at moderate intensities. Unlike voluntary contractions--which follow the Henneman size principle and activate smaller Type I fibers before larger Type II fibers--EMS directly stimulates Type II fibers from the outset [19]. This results in rapid mechanical loading and metabolic stress, which may promote hypertrophy and improved neuromuscular performance. In particular, [PERSON] et al. (2010) [14] reported significant gains in knee extensor strength and shooting velocity following EMS application to the quadriceps, suggesting its effectiveness in enhancing specific motor patterns. Similarly, [PERSON] et al. (2022) [21] revealed moderate improvements in muscle strength and sprint performance among soccer players who underwent neuromuscular EMS combined with traditional strength and pylemetric training, although the effect size was limited compared with traditional training alone. In contrast, [PERSON] and [PERSON] (2019) [20] found that EMS applied during the competitive season did not result in significant improvements in muscle strength. It was suggested that concurrent EMS use may have disrupted the natural adaptations induced by regular training, thereby diminishing overall effectiveness [25]. These mixed findings underscore the importance of carefully planning EMS interventions, especially during high training loads or competitive periods. WB-EMS, which stimulates multiple large muscle groups simultaneously, has been associated with broader improvements in overall athletic performance. [PERSON] et al. (2016, 2019) [17, 19] consistently demonstrated that WB-EMS positively affects muscle strength, \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Randomization** & \begin{tabular}{c} **Deviations** \\ **from Intended** \\ **Interventions** \\ \end{tabular} & \begin{tabular}{c} **Missing** \\ **Outcome Data** \\ \end{tabular} & \
\begin{tabular}{c} **Measurement** \\ **of the Outcome** \\ \end{tabular} &
\begin{tabular}{c} **Selection of the** \\ **Reported** \\ **Result** \\ \end{tabular} & **Overall** \\ \hline [PERSON] et al., 2019 [18] & Low risk & Some concerns & Low risk & Low risk & Low risk & Some concerns \\ \hline [PERSON] et al., 2019 [19] & Low risk & High risk & Low risk & Low risk & Low risk & High risk \\ \hline [PERSON] and [PERSON], 2019 [20] & Low risk & Some concerns & Low risk & Some concerns & Low risk & Some concerns \\ \hline [PERSON] et al., 2022 [21] & Low risk & Low risk & Low risk & Low risk & Low risk & Low risk \\ \hline [PERSON] and [PERSON], 2024 [22] & Low risk & Some concerns & Low risk & Low risk & Low risk & Some concerns \\ \hline [PERSON] et al., 2024 [23] & Low risk & Low risk & Low risk & Low risk & Low risk & Low risk \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._explosive power, sprint performance, and kicking ability.