Acute effects of an individually timed lower-limb post-activation performance enhancement protocol on 50 m front crawl performance and race kinematics in national-level swimmers.

Post-activation performance enhancement (PAPE) has been proposed as an acute strategy to improve explosive performance, yet its effects on sprint-swimming performance remain unclear, particularly when individualized recovery timing is considered. This study examined the acute effects of a lower-limb PAPE protocol, applied using an individually determined recovery time (IRT), on 50 m front crawl performance and selected start-, race-, and turn-related kinematic variables in national-level male swimmers. Fourteen male national-level swimmers completed a randomized repeated-measures cross-over design comprising control (CON) and PAPE conditions. In the PAPE condition, swimmers performed a lower-limb conditioning protocol consisting of loaded lunge-position squats on a Keiser Squat machine, followed by a maximal 50 m front crawl trial at the end of the IRT. In the CON condition, swimmers completed the same swimming trial without the conditioning stimulus. Lower-limb power output increased significantly after the conditioning activity and reached its highest mean value at 6 min post-exercise (F4,52 = 97.14, p < 0.001). However, the PAPE protocol did not significantly improve overall 50 m performance (25.508 ± 0.856 s vs. 25.529 ± 0.773 s; mean difference = - 0.021 s, 95% CI: -0.148 to 0.107; p = 0.731) or most start-related variables. The only significant effect was observed for turn time, which was lower in the PAPE condition than in CON (7.707 ± 0.251 s vs. 7.771 ± 0.261 s; mean difference = - 0.064 s, 95% CI: -0.126 to - 0.001; p = 0.046). Responder analysis revealed substantial inter-individual variability across outcomes. In conclusion, a lower-limb PAPE protocol applied using the IRT did not improve overall 50 m front crawl performance in national-level male swimmers, although it produced a small improvement in turn time. These findings suggest that the effects of lower-limb PAPE in sprint swimming may be segment-specific rather than global, and that practical implementation should be individualized rather than applied uniformly across swimmers.