## 5 Discussion
[10], who demonstrated a positive effect of the same ICA duration within three sets of ICA on CMJ height. These discrepancies may stem from differences in experimental protocols, such as the number of sets and the distribution of ICA within individual sets. In our study, we compared two durations of ICA--9 s and 27 s--within one and three sets of ICA protocols, with each set comprising three repetitions of 3 s contractions. By contrast, [PERSON] et al. [12] analyzed a single contraction lasting 9 or 15 s within one set of ICA, while [PERSON] et al. [10] investigated single contractions lasting 3 s performed in three sets of ICA. Therefore, when analyzing the impact of ICA on the occurrence of the PAPE effect, it seems reasonable to examine not only the number of sets or the total duration of ICA but also the interdependence of these two parameters. The ratio of the number of sets to the distribution of ICA, as studies have shown, is of significant importance. However, it seems that it cannot be analyzed without assessing the duration of the rest interval between ICA sets. Our findings indicate that a 3 min rest interval between ICA sets is a significant factor contributing to the increase in CMJ height, consistent with the findings of [PERSON] et al. [1]. This suggests that longer rest intervals are particularly important in protocols involving a greater number of sets or extended ICA durations. Conversely, research by [PERSON] et al. [10] suggests that shorter 1 min rest intervals may be effective only in the context of fewer sets and shorter ICA durations. Physiological mechanisms such as phosphocreatine resynthesis and lactate clearance [22; 23] justify the need for longer rest intervals to sustain high performance during subsequent ICA sets. However, variations in the literature and methodological differences underscore the need for further research to precisely define the optimal rest interval parameters in ICA protocols for enhancing CMJ height. The level of training experience determines the occurrence of the PAPE effect [24]. Similarly, this may apply to the use of ICA, as although the parameters previously described indicate their significant impact, these studies confirm a relationship between training experience and the level of muscular strength [25]. As suggested by [PERSON] et al. [10] and [PERSON] et al. [26], both muscular strength and a higher percentage of fast-twitch fibers in highly trained athletes, resulting from the increased phosphorylation of myosin light chains [15], are positively correlated with improvements in CMJ height and PP, which may explain the positive responses observed under the ISO-3 condition in this study. Additionally, highly trained athletes exhibiting better resistance to fatigue, a greater buffering capacity, and improved motor unit synchronization [27, 28] may have been better prepared to capitalize on the benefits of the ISO-3 condition. The increased buffering capacity and enhanced resistance to skeletal muscle damage suggest that athletes with high training levels are better adapted to endure intense stimuli. As reported by [PERSON] [18], this translates to a prolonged PAPE effect, which is directly associated with higher firing frequencies and greater motor unit recruitment, possibly explaining the positive responses observed in this study. Therefore, it seems that highly trained participants require greater training stimulus and, thus, a higher number of sets and extended ICA duration with longer rest intervals between sets to improve both CMJ height and PP. One of the limitations of this study is the lack of fatigue monitoring. A potential assessment of physiological factors, such as biochemical blood analysis (including lactate, creatine kinase, and cortisol), as well as the use of methods like tensiomyography or electromyography could potentially confirm whether a relationship exists between PAPE and fatigue and provide new insights into the obtained results.