Purpose: To examine the effect of a 10-week plyometric training (PT) on the kinematic and kinetic properties of prepubescent girls during squat jump, countermovement jump, and drop jumps.
Methods: Twenty-four untrained girls (aged 9-11 y) were assigned to a training group (TG) and a control group. The TG followed twice a week PT for 10 weeks. Squat jump, countermovement jump, and drop jumps performed from heights of 20, 35, and 50 cm were tested before and after PT. Jump height, kinematic, and kinetic parameters were evaluated using a motion analysis system and a force plate.
Results: Jumping height in all jump types increased significantly after PT for the TG (P < .001). After training, the TG presented increased power (P < .001) and knee angular velocity (P < .001), higher knee flexion at the deepest point during the braking phase (P < .001), longer contact time (P < .001), and unchanged stiffness and reaction strength index (P > .05). No differences were observed in the control group (P > .05).
Conclusion: These findings indicate that a 10-week PT positively affected jumping performance in prepubescent girls who improved their drop jump performance after training not by adopting a stiff/bouncing jumping style of short contact time and increased stiffness, but a compliant/absorbing style of prolonged contact time.
Keywords: child; contact time; drop jump; exercise; female; reactive strength.