(1) Background: Post-activation performance enhancement (PAPE) protocols using heavy resistance preloading may improve RSA, yet optimal preloading intensity for amateur players is still unknown. This study investigated the effects of two PAPE protocols using different preloading intensities (85% and 90% of 1RM back squat) on RSA. (2) Methods: A double-blind, randomized, two-period crossover design was used, and 18 amateur male players were included in the study. RSA was assessed using a 6 x 35m sprint protocol with 10-second rest intervals (RAST). (3) Results: While the main effect of time significantly (p=0.01, η²=0.71) influenced performance decline across all groups, there was no significant (p=0.65, η²=0.01) interaction between time and condition. Individual responses to PAPE varied, highlighting the importance of individual differences. Interestingly, the BS85% group exhibited a less pronounced decline in performance compared to the control group, while the BS90% group only showed significant differences in three sprint levels. (4) Conclusions: Our findings suggest that a lower preload of 85% of 1RM may be as adequate as a higher preload of 90% of 1RM in enhancing RSA in amateur soccer players. These results may indicate a potential fatigue-delaying effect of PAPE protocols and emphasize the importance of individualized approaches for optimizing PAPE strategies.