## 4 Discussion  
The aims of the study were to determine the intrasession and intersession reliability of isometric force by using a FEMD of three different starting block positions. The main finding of our study shows that intrasession and intersession reliability was moderate to extremely high in terms of the average and peak isometric strength of the three positions of the starting blocks. Therefore, the use of devices that measure the horizontal force exerted is transcendental, given the correlation between performance and this type of device, even superior to squat performance, which has been extensively studied [13]. Firstly, the first hypothesis indicated that intrasession and intersession reliability would be high with the device used. In this sense, in the bilateral position and with the non-dominant leg, we observed that the intrasession peak force measurements did not obtain high reliability, where the results in the first measurements T1-T2 and T3-T4 (first and second session) were much more accurate than in the last ones. This could be justified given that authors such as [PERSON] et al. [21] found a high variability when two measurements are taken in one session (T1-T2), recommending a third measurement to reduce this error due to the lower variability between T2 and T3. Figure 4: Comparison of the inter- and intra-session reliability of peak and average force results between the three different starting block positions (left panel **A,C**) and comparison of the inter- and intra-session reliability of the results of the three different starting block positions between peak and average force (right panel **B,D**). * Meaningful differences in reliability were identified by a CVratio higher than 1.15. However, it should be noted that in the position with the dominant leg, there was a more favorable trend towards familiarization comparing T1-T2 and T7-T8 for both peak strength (\(p\) = 0.07 vs. \(p\) = 0.24) and mean strength (\(p\) = 0.03 vs. \(p\) = 0.09). This finding is likely attributable to the athlete's condition, particularly given the importance of familiarization with specific movements to ensure adequate reliability between measurements. Most studies perform analyses that consider the most ergonomic position of the sprinters, which remains consistent across measurements [25; 26]. Additionally, in the cueing gesture, the force exerted in the horizontal direction is a critical factor requiring maximum ergonomic efficiency [3]. In the case of the mean force for the other two positions, no clear trend is found, since both the \(p\)-value and the ICC did not change positively or negatively. In turn, describing the average strength in the non-dominant leg, it occurred similarly to the dominant leg, finding differences from T1 to T2 and T7 to T8 (sessions one and four) with an ICC that went from 0.67 to 0.91 (position dominant) and from 0.70 to 0.81 (non-dominant position). This finding can be justified due to the nature of FEMD, where muscle involvement is evaluated in a much more specific position and environment than with other devices, for example, using linear velocity transducers [27]. It can be modified, especially when looking for a maximum peak strength. Finally, it should be noted that the ICC values were higher than 0.80 for the last of the sessions in the three positions for the average force and for the peak force (except in this case, for the non-dominant leg), which indicates the importance of the familiarization with the instrument to ensure adequate reliability. Discussing the results with the dominant leg as most studies are carried out, it should be noted that this reliability was high as for other authors with measurement devices in the starting blocks such as that of [PERSON] et al. [28] with a CV \(<\) 15%, values even higher than our data with the dominant leg (CV = 5.6-11.58%), or the study by [PERSON] et al. [3] also finding a high relationship between stud output power measured with a stud measurement device and sprint performance.