## 4 Discussion
Collectively, these mechanisms lead to a substantial enhancement in explosive performance [13]. Plyometric exercises are closely associated with the recruitment of Type II muscle fibers [47], which are the biological foundation necessary for performing Stretch-Shortening Cycle (SSC) movements--a mechanism employed during jumping actions. Hence, in theory, employing pyjometric exercises as a CA to induce PAPE could enhance an athlete's jumping performance. However, the results of the present study imply that pyjometric exercises do not elicit superior PAPE effects compared to resistance exercises. Possible explanations for such findings include the following. (1) The stimulus intensity of the pyjometric exercises may be too low to prompt a significant involvement of fast-twitch muscle fibers in the jump execution process [48]. For instance, studies by [PERSON] et al. applied a constant drop height of 25 cm in depth jump exercises for participants of various athletic abilities without tailoring the drop height to each individual's fitness level [22], suggesting that, for more trained athletes, a 25 cm drop might not be sufficient to induce optimal PAPE. (2) The complexity of pyjometric exercises might pose challenges for inexperienced participants to execute correctly. [PERSON] and colleagues discovered that exercises such as ankle hops, hurdle jumps, and depth jumps were capable of inducing superior PAPE effects [21]. However, in contrast, [PERSON] et al. found that similar pyjometric exercises, including bilateral and unilateral depth jumps, did not lead to PAPE in their subjects [22]. The key difference may lie in the participants' proficiency levels: [PERSON]'s [21] subjects were highly trained adult rugby players who could reliably perform the high-intensity phases of 'ground contact buffering' and 'concentric drive' in depth jump exercises, while [PERSON]'s [22] subjects were less experienced adolescent athletes who might struggle with the complex movement patterns required for such exercises. The absence of PAPE following mixed exercises could be attributed to the cumulative effect of the exercise load, which combines resistance exercises with pyjometric exercises, potentially leading to an excessive fatigue state [27]. Following pyjometric exercise, the body experiences concurrent fatigue and potentiation effects. If the potentiating factors outweigh fatigue, PAPE will gradually develop and reach its peak. In contrast, if fatigue predominates, it will delay the onset of PAPE and diminish its duration of effectiveness [6]. Thus, the timing, peak, and duration of PAPE depend on the balance between the potentiating effects and fatigue [18]. The specific reasons for this are as follows. Performing pyometric exercises immediately after resistance exercises without an appropriate recovery interval may compound fatigue. In such cases, the athlete experiences dominant fatigue after resistance exercises, and the immediate transition to pyometric exercises can exacerbate this fatigue. The accumulation of dual fatigue necessitates an extended recovery period for the body. Further, pyometric exercises impose a high demand on neuromuscular excitability. When fatigue predominates, neuromuscular excitability decreases, resulting in prolonged ground contact times and reduced explosive force during activities like depth jumps. As such, this diminishes the stimulus intensity required for effective PAPE. On the other hand, while several studies integrated a rest interval between resistance and pyometric exercises, with reported rest durations as brief as 3 min, the widely recognized optimal timeframe for PAPE is between 4 and 12 min, indicating that the potentiation effects only start to predominate after the fourth minute. Engaging in pyometric exercises at the third minute clearly falls within the fatigue-dominant period. Thus, when selecting mixed exercises as CAs, it is essential to arrange an appropriate recovery time and manage the relationship between stimulus load and fatigue recovery effectively.