## 4 Discussion  
The aim of this study was to examine the effect of simultaneous Smith machine back squats with EMS application on 10 m and 30 m sprint performance. Statistical analysis revealed no statistically significant differences between the preload protocols. In addition, according to the results at the individual level, the sprint performances of most of the participants did not change after the preloads, but a decrease in sprint performance was observed in some athletes. Although there is no other study in the literature that applies combined pre-loading as we did, there are a few studies examining the effect of EMS as a PAP protocol on sport performance. However, these studies did not examine the effect of EMS on sprint performance. [PERSON] et al. [25] examined the acute effect of EMS on vertical jumps and isokinetic strength. In the 90\({}^{\circ}\) static squat position, 16 s (4 s contraction, 4 s rest) of EMS was performed on the quadriceps and calf muscle groups at different frequency levels (30 Hz and 100 Hz). Significant increases in vertical jump heights and 180 and 300\({}^{\circ}\)/s knee flexion isokinetic power performances were reported after 90 s [25]. In another study, EMS and leg extension, as PAP protocols, were compared. Vertical jump heights at 30 s and 1 and 3 min after preloads improved in both protocols [5]. The results of these studies contradict ours in terms of PAP effect. Fast twitch muscle fiber plays an important role at high concentric speeds [11]. It has been reported that small and large motor units are recruited simultaneously during EMS [19; 26]. The fact that EMS applications can activate fast twitch fibers at a lower action potential threshold than voluntary contractions suggests that EMS can reveal the PAP effect. However, voluntary contractions were reported to be more effective than EMS [27; 28; 29; 30]. Therefore, in the current study, although we aimed to obtain a strong PAP effect by using EMS contractions, which can easily activate high-threshold motor units together with voluntary contractions, performance improvements were not observed. Our participants could not train regularly due to the restrictions imposed during the COVID-19 pandemic. Since this causes a decrease in maximal strength levels, it can be speculated that the simultaneous application of two contraction methods in preloads may create excessive fatigue. In a meta-analysis by [PERSON] and [PERSON] [31], male participants were classified as \"strong\" if the ratio of 1 RM back squat value to body mass was \(\geq\)1.75, or \"weak\" if they were \(<\)1.75. As a result, the effect size of PAP was determined as 0.41 in strong participants and 0.32 in weak participants [31]. In another meta-analysis, the effect size of PAP was reported as 0.81 in athletes, 0.29 in trained individuals, and 0.14 in untrained individuals [32]. When considering the average body mass (79.98 \(\pm\) 13.37 kg) and 1 RM average value (120.5 \(\pm\) 17.39 kg) of our participants (relative strength = 1.50), it is seen that they are classified as being in the \"weak\" category. Therefore, we can say that the PAP effect did not occur due to the weakness of our participants. Other studies with weak participant groups that found no PAP effect support our results [33; 34]. More research on trained and \"strong\" participants is needed to reveal definitive results of simultaneous back squat preloading with EMS. Studies [31; 34; 35; 36] have reported that the duration of recovery times given after preload may affect the PAP response and those optimal resting times may depend on the strength level of individuals. It was stated that \"strong\" individuals achieved the greatest PAP effect at 5-7 min after preload, whereas \"weak\" individuals obtained maximum PAP response after at least 8 min of recovery [31]. Another study reported that \"strong\" individuals had the best PAP response at the sixth minute after the back squat, and the \"weak\" individuals reached the best PAP response at the ninth minute [34].