Effect of Plyometric Training on Vertical Jump Height in Pre-Peak Height Velocity Boys and Girls Aged 9-11 Years

This study aimed to compare changes in countermovement jump (CMJ) height and take-off velocity, force and power in pre-peak height velocity (pre-PHV) boys and girls aged 9-11 years following 6 weeks of lower body plyometric training (PT). Forty pre-PHV children (20 boys and 20 girls) were allocated to a plyometric training group (PG; n = 20) or a control group (CG; n = 20). The PG completed a progressive plyometric training programme twice weekly for 6 weeks, whereas the CG maintained usual physical activity. CMJ height and kinetic variables were assessed pre- and post-intervention, and training effects were analysed using repeated-measures ANOVA. Results demonstrated a significant between-group difference in CMJ height (p = 0.018) driven by an increase in PG (5.8%; p = 0.013) and no change in CG (-0.5%; p = 0.083). No significant sex differences were observed within PG (p ≥ 0.359); however, CMJ height increased significantly in girls (7.0%; p = 0.030) but not boys (4.7%; p = 0.211). For kinetic variables, only take-off velocity increased in PG (3.2%; p = 0.002), with comparable responses in boys (3.0%; p = 0.038) and girls (3.4%; p = 0.029), whereas force and power showed no significant changes (p ≥ 0.202). No significant changes were observed in CG for CMJ or kinetic variables (p ≥ 0.083). In conclusion, plyometric training improved CMJ performance in pre-PHV children, with no significant sex differences observed. Training adaptations at this stage should be interpreted considering biological maturation status.