## 4 Discussion  
The aim of this study was to investigate functional and/or morphological parameters that might predict responsiveness to CMJ PAPE. It was found that a frequently adopted pre-activation protocol did not result in enhancements in CMJ height in a large sample (\(n=66\)) of untrained men, with 20 of them responding positively, 18 responding negatively, and 28 not presenting any worthwhile change. Correlation analyses resulted in no significant associations between responsiveness to PAPE (i.e., \(\Delta\)CMJ)) and baseline neuromuscular performance (IPT, \(\mathrm{CMJ}_{\mathrm{CON}}\), and \(\mathrm{PO}_{\mathrm{CON}}\)) or muscle morphology (\(\mathrm{VL}_{\mathrm{MT}}\)). Furthermore, linear stepwise multiple regression models revealed that no combination of these variables was able to predict improvements in CMJ height following pre-activation. Therefore, our hypothesis that it is not possible to predict responsiveness to PAPE based on performance and morphological parameters was confirmed. A common feature of pre-activation protocols designed to induce PAPE is the performance of heavy-load resistance exercise a few minutes prior to the activity to be potentiated [19; 20; 21; 22; 23]. However, set configuration, loads, and the interval between pre-activation and the targeted activity vary greatly among studies [12; 23]. In a meta-analysis, ref. [12] showed that trained individuals respond better to multiple-set pre-activation protocols followed by relatively short rest intervals, whereas untrained populations benefit the most from single-set protocols and longer rest intervals. The pre-activation protocol adopted in the present study was shown to be effective in improving CMJ height in both trained [19; 24] and untrained [16] individuals. However, it should be noted that non-responders (\(n=11\)) were excluded from the sample (\(n=22\)) of our recent study using this protocol [16] for methodological reasons. In the present study, 30% of the untrained men included in the sample responded positively to the pre-activation protocol with the remaining 70% either responding negatively (27%) or not showing any worthwhile change in CMJ height (43%). It is therefore reasonable to state that responsiveness to PAPE is heterogeneous in untrained individuals. Superior responsiveness to PAPE has been frequently reported for trained populations compared to untrained individuals [25; 26]. Nonetheless, athletes have also been shown to be better PAPE responders compared to resistance trained individuals [27]. Based on these observations, it can be speculated that training-induced adaptations in muscle performance and/or morphology might be associated with responsiveness to PAPE. Based on this rationale, we analyzed a cohort of previous PAPE studies from our group [15; 16] in conjunction with another experiment that has not yet been published) which used the same pre-activation protocol and population to screen for possible strength training-modifiable parameters that might explain responsiveness to PAPE. Although we agree that PAPE is an ergogenic phenomenon that is more ecologically valid for trained and athletic populations, the heterogeneity in responsiveness to PAPE observed in untrained populations--as is the case in the present study--is an interesting feature for correlational analyses. Our results show that changes in CMJ height following pre-activation are not associated with the manifestation of maximal strength (IPT), muscle power (\(\mathrm{PO}_{\mathrm{CON}}\)), and jump performance (\(\mathrm{CMJ}_{\mathrm{CON}}\)) assessed in an unpotentiated state. These markers are different manifestations of neuromuscular performance that have abundantly been shown to improve following strength training [28; 29; 30] and to be superior in athletic populations compared to untrained people [31; 32; 33]. They are also frequently associated with the expression of type II muscle fibers, which are the most responsive to PAPE [11; 14].