## 4 Discussion  
The main aim of the present study was to compare the non-localized PAPE of a lower body vs. an upper body resistance exercise session. Results confirmed that a small but significant non-localized PAPE was activated by a high intensity-low volume resistance exercise protocol. However, our findings show that significant differences may exist when different muscle groups were involved. In particular, a non-localized PAPE was registered following the HI protocol in the UB group, while no improvements were detected in the LB group. Although different resistance exercises were performed in the two protocols (bench press and squat, respectively, in UB and LB), both HI protocols included the same number of repetitions, relative intensity and recovery time between sets. Our results also show that a big interindividual variability exists in the non-localized PAPE. Previous investigations reported higher levels of perceived exertion and fatigue when the same exercise protocol was performed at squat compared to bench press [21]. Muscle fatigue is known to decrease the ability to completely activate the working muscle [22] and fatigue may also impair the performance of non-exercised muscles [23]. Furthermore, some muscles are more susceptible to non-local fatigue than other muscles [23]. In our study, central fatigue resulting from the HI squat protocol, consisting of 5 sets of 1 repetition at 90% of 1 RM with 3 min of rest between sets, may have impaired the ability to fully activate upper body muscles in the subsequent BPT assessment. On the contrary, the potentiation effect resulting from the HI bench press protocol may have exceed the non-local fatigue caused by the same exercise, inducing an elevation in lower body power. Fatigue may be also the reason for the lack of localized-PAPE following the HI protocol in both UB and LB groups (e.g., Pectorals in UL and knee extensors and glutes in LB). Conversely, significant local effects on BPT and lower body power were previously reported following high intensity or power exercises in resistance trained men [24,25]. In most of these investigations however, participants performed only one set of a resistance exercise. In the present study, participants were asked to perform 5 sets of 1 rep of squat or bench press in LB and UB, respectively. As suggested by [PERSON] and [PERSON] [26], the localized potentiation effect may be reduced following the second exercise set and multiple sets are known to produce fatigue without providing additional localized PAPE. No significant localized and non-localized PAPE were detected following the POW protocols. Despite significant localized PAPE being registered following a single set of ballistic contractions, such as ballistic push-ups or bench press throw [25,27], concentric-only exercises, are known to be less effective than eccentric contractions for this purpose [28]. Localized PAPE has been attributed to increased phosphorylation of myosin regulatory light chains and to increased firing synchronicity of motor neurons [4]. Other mechanisms, such as elevation in plasma adrenaline and noradrenaline may also contribute to PAPE and  
Figure 3: Individual changes in CMJP (in W) from prior to post the HI (high intensity) protocol in UB (upper body: (**a**) and LB (lower body: (**b**) group. Both groups were composed by 12 individuals. CMJP = countermovement jump power. produce a systemic effect on muscle performance [29]. Indeed, catecholamines are known to enhance force production in fast and slow muscle fibers [30; 31]. A possible explanation for the lack of non-localized PAPE registered following the POW protocols, may be that fast concentric contractions are less effective than HI protocols including the eccentric phase, in inducing strong adrenergic responses. However, limitations of the present study are that plasma catecholamine concentration and perceived exertion were not measured. In addition, findings of the present study may not be generalizable to female participants since no women were assessed in this investigation.