Effects of Plyometric Training on Jump Biomechanics, Explosive Strength, and Jump Endurance in Adolescent Volleyball Players Aged 13–14 Years

Background/Objectives: This study examined the effects of an eight-week plyometric training programme on jump biomechanics, field-based jump performance, and repeated-jump endurance in 13–14-year-old volleyball players, and explored training-induced changes. Methods: A pre–post controlled experimental design was used. Thirty male volleyball players aged 13–14 years were assigned to an experimental group (EG, n = 15) or a control group (CG, n = 15). The EG completed a structured plyometric programme three times per week for eight weeks in addition to regular volleyball training, whereas the CG continued usual practice. Biomechanical variables were assessed during the Repeated Countermovement Jump test using the BTS Bioengineering G-Walk inertial measurement system, together with field-based jump and repeated-jump endurance tests. Outcomes were analysed using two-way mixed ANOVA (Group × Time). Δ-based correlations were examined using Pearson and Spearman coefficients with false discovery rate correction. Results: Significant Group × Time interaction effects were found for all analysed RCMJ variables (all p < 0.001). Significant interaction effects were also observed for all field-based jump and repeated-jump endurance outcomes (all p ≤ 0.025). The EG showed greater improvements over time than the CG across the principal biomechanical, practical, and endurance-related indicators. Correlation analysis revealed strong associations among the principal RCMJ variables and selected links with field-based and endurance measures. Conclusions: A structured plyometric programme may improve jump biomechanics, jump performance, and repeated-jump endurance in adolescent volleyball players. These findings should be interpreted cautiously because of baseline differences, the modest sample size, and the IMU-derived nature of force- and power-related estimates.