## 4 Discussion
Post-Activation Performance Enhancement on Sprinting Performance through Different Conditioning Activities  
The results of the meta-analysis indicate that the PAPE effects elicited by resistance exercise protocols appear to surpass those of pyometric and mixed exercises. This enhanced efficacy may not only be attributed to the physiological mechanisms discussed earlier but also to the biomechanical patterning of sprinting actions. Current standards for sprinting techniques prioritize the cultivation of \"front-side mechanics,\" which entail lower-limb movements primarily occurring in front of the body. The intention is to bolster the ability of the limbs to execute a \"whip-like\" downward thrust and a rapid \"hip drive.\" This focus ultimately aims to indirectly elevate the efficiency of force production in the vertical direction during the support phase of sprinting. An array of literature supports the notion that the vertical ground reaction forces exerted during this phase play a crucial role in enhancing speed [49; 50; 51; 52]. Athletes striving to achieve this \"whip-like\" thrust and augmented vertical force production necessarily demand higher lower-limb strength, particularly in the muscles of the posterior chain (such as the gluteus maximus and the hamstrings). When selecting resistance exercises for the CA of PAPE, the back squat and hip thrust are predominantly preferred in most studies. The hip thrust, in particular, proves to be highly effective in activating the muscles of the posterior chain, such as the gluteus maximus and hamstrings [53]. Although the back squat primarily targets the quadriceps, it still activates the gluteus maximus to a certain degree [54]. As such, through the enhanced activation of the posterior chain musculature with resistance exercises, there was an indirect improvement in the vertical ground reaction forces during the running process, which in turn enhanced subsequent sprint performance. Both pyometric exercises and sprinting rely on the Stretch-Shortening Cycle (SSC) mechanism of the lower-limb muscle groups. Theoretically, pyometric exercises should induce a more potent PAPE effect for sprint performance. Nonetheless, the studies included in the present research did not corroborate this outcome. Possible explanations for this discrepancy are as follows. On the one hand, the inconsistency with the movement plane may be related. The CAs employed in previous research, such as depth jumps, hurdle hops, and tuck jumps, predominantly initiate vertical movement via explosive lower-limb extension, with minimal engagement in forward horizontal movement--essential for linear sprinting. Studies have shown that executing movements in distinct directions necessitates distinct intermuscular and intramuscular coordination mechanisms [55]. Thus, the rapid SSC benefits induced by athletes in the upward direction fail to effectively transfer to the horizontal sprinting motion pattern. On the other hand, the research under review mostly used bilateral actions for CAs, with limited attention to unilateral actions, which are more closely related to the sprinting movement pattern. If unilateral pyometric exercises(such as single-leg hops or bounding) were employed, a more favorable sprint PAPE might be produced. In the field of sprint performance PAPE methodologies, mixed exercises that integrate resistance with sprint exercises are gaining attention. Examples include utilizing elastic resistance combined with sprinting or incorporating sled resistance sprinting. These exercises blend sprint mechanics with resistance, ensuring that the movement is directed forwards. This approach addresses the vertical motion typically associated with pyometric exercises, which may not directly translate to sprinting mechanics. The designers of these training interventions posit that such hybrid exercises could mimic the same biomechanical properties of short sprints, thereby inducing PAPE [30; 56] Despite the initial design intentions, the experimental outcomes have not consistently aligned with expectations.