## 4 Discussion
While the literature presents conflicting evidence regarding the influence of sex [25; 26; 27] on the magnitude of PAPE [24], factors such as training background and sport specificity [28] and relative strength [15; 29] may significantly impact PAPE responses. The CA protocol utilized by [PERSON] et al. [24] differed from that applied in the present study. The current protocol consisted of two sets of 10 s of Bulgarian split squat holds with an external load of 15% body mass, followed by 10 vertical hops. It is plausible that the CA stimulus in this study was weaker compared to that employed by [PERSON] et al. [24]. However, despite this difference, the improvements observed were of a comparable magnitude. Similarly, studies evaluating exclusively isometric CAs have demonstrated that short-duration maximal or near-maximal isometric contractions can effectively enhance performance [10; 12; 19]. Notably, the magnitude of the improvements in CMJ performance reported in this study closely aligns with those of [PERSON] et al. [10], where a single set of 4 s of submaximal isometric back squat at 75% of one repetition maximum was sufficient to elicit a PAPE response. This aligns with our findings, with a significant increase in CMJ height of \(\sim\)2.8%. Furthermore, these findings emphasize the importance of identifying the optimal CA dosage to maximize performance benefits while minimizing unnecessary fatigue accumulation. Although the observed improvements in athletic performance were modest, it is noteworthy that the participants were highly trained athletes for whom even small performance gains can be meaningful. These findings highlight the need for further research on combined isometric-plyometric CAs, as they demonstrate potential as a simple and effective training stimulus. The activation exercises targeted the quadriceps and gluteal muscles, both of which play a crucial role in the start and acceleration phases of sprinting. As hypothesized, the greatest performance improvements were observed in the first 20 m of the sprint distance. The activation of these muscle groups also contributed to a significant improvement in CMJ performance [8]. Both higher RSI and CMJ height have been shown to be related to starting speed and acceleration [30; 31]. Although there was a trend toward improved performance over longer distances (40 and 50 m), these changes were of low magnitude. Given that contact time and flight time remained unchanged following the CA, it is likely that only the force output of the lower limb extensors influenced acceleration and starting speed within the first 20 m. Isometric holds in key sprinting positions might increase ankle and knee stiffness, which is essential for effective force transmission to the ground [32]. However, while these exercises engage the primary muscles, they lack the dynamic explosiveness and reactivity necessary for sprint acceleration [11; 33]. Conversely, pyometric exercises emphasize rapid, high-intensity movements that leverage the SSC, stimulating fast-twitch muscle fibers and closely replicating the explosive demands of sprinting. [PERSON] et al. [16] showed improvements in 30 m sprint times 2 and 4 min post CA and following three sets of five CMJs. Similarly, [PERSON] et al. [13] demonstrated that performing 10 consecutive reactive hops led to an enhanced drop jump performance, suggesting that pyometric training influences the muscle-tendon unit behavior during SSC movements. Furthermore, pyometric exercises can elicit a stretch reflex response, increasing excitation potential transmittance via Ia afferents, thereby enhancing neuromuscular activation [21]. Given their distinct physiological effects, combining isometric and pyometric CAs may provide a unique stimulus, potentially enhancing sprint performance via the PAPE effect. However,it remains uncertain whether this specific combination of isometric and glyometric CA is more effective than other activation protocols, as no direct comparisons were performed in this study.