The aim of this research was to assess the effect of a single set of contrast preloading on peak vertical displacement (PD) during a loaded countermovement jump (LCMJ) training session. Nine strength-trained males participated in 2 randomly assigned, crossover design testing sessions consisting of 5 sets of 6 repetitions of 20-kg LCMJs with 3-minute rest intervals between sets. The preloading intervention was performed 3 minutes after the first set and 4 minutes before the second set of 20-kg LCMJs. The control (CON) group performed 1 set of 20-kg LCMJs, whereas the jump squat (JS) group performed 1 set of 40-kg LCMJs. The number of repetitions performed during each preloading condition was varied to match total concentric work between the 2 sessions. A significant (p < 0.05) preload × set interaction for PD was observed, with the JS group jumping significantly higher during the third set performed after the preload in comparison with the CON group. Analysis of peak power output and mean power output during the concentric movement for this set revealed that as the knee flexion angle increased, the effect of the preload was augmented. These results suggest that a single set of preloading exercises enhances performance during a lower-body explosive power training session; however, the effects of a single preloading set may not peak until midway through the training session.
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