## 4 Discussion  
The purpose of this study was to analyze the absolute and relative test-retest reliabilities of peak muscle strength in knee flexion-extension controlled using a FEMD in a group of young female soccer players. This study reported consistent to acceptable reliability in all strength evaluations, with no significant variation found between the two sessions measuring peak muscle strength. The results of our study confirm that the assessment of peak muscle strength in knee flexion and extension, both concentrically and eccentrically with FEMD is reliable. For many decades, knee flexion and extension strength have been evaluated using isokinetic devices, which are considered the gold standard for strength assessment [30; 31]. However, multi-joint isokinetic devices have emerged, and these devices can be used to reliably and effectively evaluate and train specific muscle activation patterns through various stimuli, as demonstrated by the use of the FEMD [32]. In previous studies, FEMDs have proven to be reliable for assessing trunk strength in flexion-extension and rotation [33; 34; 35], as well as shoulder [36] and hip strength [17]. Similar results were found in all studies that examined the reliability of the FEMD for the assessment of strength; however, in our study, we found higher absolute reliability values than those found in the trunk and shoulder flexion and extension studies [35; 36]. The assessment of peak muscle strength in knee flexion and extension is an assessment that has been performed with a FEMD, and the population evaluated is female soccer players, a population that has not been studied with FEMDs, since most of the research previously conducted with FEMDs was in young university students. Similar results to those of our study were obtained in the level of reliability in the study by [PERSON] et al. [22], which analyzed the peak muscle strength for the hamstring exercise protocol with eccentric swing at a displacement velocity of 0.4 m\(\cdot\)s\({}^{-1}\), equal to that of this study. In the scientific literature, speed in isokinetic tests has been examined [37; 38]. Research indicates that when evaluating strength in the various isokinetic tests, velocities less than 0.6 m\(\cdot\)s\({}^{-1}\) are often the most accurate [38]. Although it is possible that the concentric phase of movements is not practiced as frequently as the concentric phase, which could explain the greater impact of learning in the eccentric phase [39]. These new functional electromechanical devices need an appropriate and detailed familiarization process to ensure the repeatability of measurements in the assessment of different manifestations of strength, especially with variable movements [22]. In a study  
Figure 4: Relationship between peak muscle strength in right knee extension (RKE), peak muscle strength in left knee extension (LKE), peak muscle strength in right knee flexion (RKF), and peak muscle strength in left knee flexion (LKF) in the concentric and eccentric phases in both test sessions during FEMD-controlled peak muscle strength assessment. The small circles are the analyzed muscle force loads, the central line is the graph of the Pearson correlation model, the blue dashed lines are the 95% confidence interval of the model provided by the JASP statistical package. by [PERSON] et al. [40], carried out on young handball players, handball throwing skills showed poor reliability when no familiarization process was carried out to ensure the learning of the athletic movement to be assessed. The peak strength, speed, and power of the musculature may be better understood through the study of a trustworthy evaluation methodology using FEMDs. The previously assessed procedures exhibited dependable values, enabling the utilization of the evaluation circumstances that corresponded to each study across all of them. While this study proved the good reliability of the FEMD, future research should take into consideration some limitations.