## 4 Discussion
Thus, it is likely that the lack of a positive effect of the eccentric half-squat might be due to the short rest period. One possible explanation for the inefficiency of the short rest period is the longer \"time under tension\" of the knee extensors. It has been previously proposed that the participants tend to decrease their velocity during squats, increasing the time under tension in the muscle and leading to low-frequency fatigue [29; 39]. The short rest period likely did not allow the enhancing mechanism to outweigh the inhibitory one, leading to fatigue dominance in this stage. Regarding the two jumping tasks, our results showed no significant effects after the conditioning stimulus. Our results are in agreement with the previous report, which demonstrated that both eccentric and concentric squats do not affect jumping performance after a short rest period [29]. Even though previous studies [27; 40] have shown the efficiency of the high-load stimulus to induce PAPE during the subsequent vertical jump, it seems that our eccentric half-squat stimulus failed to cause any improvements. The specificity of the conditioning stimulus is a determined factor in these contradicting results [27]. Despite the effects of eccentric muscle actions on neural and muscle-tendon systems, they could not improve jumping height when used as a preconditioning stimulus. During SJs, the muscle groups are isometrically activated before the propulsion phase. The differences in muscle activation between the isometric contraction and eccentric action during the jumping test and the conditioning stimulus, respectively, could result in no alteration of the jumping performance. Moreover, the biomechanical differences between the conditioning activity and the jumping test did not affect the SJ jumping height. During the initiation of SJs, participants maintained a 90\({}^{\circ}\) knee joint position. In contrast, slightly greater knee flexion was observed during the conditioning activity. Previous research has shown that the depth of the squat can lead to increased activation of the glutel muscles, while knee extensor activity remains constant [28]. Consequently, the prescribed knee flexion during the SJ test procedure was restrictive, in line with the principle of specificity and the potential for increased glutel activation. Despite maintaining the same range of motion before and after the stimulus, the conditioning activity did not improve force production. Our data support this notion, as both work and power during the propulsion phase of SJ were stable after the conditioning. The force production during this phase was the same, with the same range of motion leading to the same level of produced work and power after the conditioning activity. Furthermore, the controlled stretching velocity during the eccentric half-squat, compared with the velocity of the eccentric phase during CMJs, could also negatively affect jumping performance. As previously reported, dynamic contractions show joint- and velocity-specific PAPE effects [23]. It is noteworthy that eccentric velocity alone does not seem to influence PAPE. However, the combination of a low level of eccentric load with a slow eccentric velocity may contribute to the lack of changes observed. It is important to consider that the stretch velocity during eccentric half-squats is lower than that experienced during the eccentric phase of the CMJ. This difference in velocity could potentially account for the lack of discernible effects. Further research is warranted to elucidate the relationship between stretching velocity and PAPE effects. While this study presents valuable insights into the acute effects of eccentric half-squats on jump performance within a specific population of male athletes specialized in jumping events, certain limitations should be acknowledged. This study's small sample size and exclusive focus on male athletes specializing in jumping events constitute important considerations regarding the generalization of the findings.