Background The effectiveness of preventive training programs (PTP) aiming at changing the biomechanical behaviour related to anterior cruciate ligament injuries is subject to pre-existing risk. However, these assumptions are based on studies in females. Moreover, it is unclear what influence this training has on performance of young male athletes.

Objective To examine the influence of a PTP on changes in kinematics during landings and in maximum vertical jump height (VJH) in males.

Design 6 weeks prospective exercise intervention.

Setting Young male volleyball athletes.

Participants 15 male volleyball athletes (13±0.7 years, 1.70±0.12 m, 60±12 kg).

Interventions PTP consisting of plyometric, balance and core stability exercises three times per week for 6 weeks. Bilateral vertical jumps with double leg (DL) and single leg (SL) landings were performed to measure the effects of training.

Main outcome measurements Kinematics of knee and hip before and after training and VJH attained during both tasks after training. The hypothesis was that the PTP would produce improvements in VJH, but would not generate great changes in biomechanical behaviour.

Results The only change revealed for the SL was the longest duration of landing (p=0.0273), while in the DL was the largest angular displacement of the knee (p=0.0371). The training did not significantly alter the VJH in the SL (diff: 2.7 cm, p=0.3054) or DL condition (diff: 3.5 cm, p=0.3635).

Conclusion Despite the alterations in the kinematics behaviour, the changes observed are specific for each landing task, which highlights the importance of the principle of specificity. Despite the absence of significant increases in the VJH after training, the absolute differences pre to post training showed an increase consistent with other studies that compared the results with control groups. The present study showed that short time PTP in low-risk populations, although generating little influence on the kinematics, are capable of enhancing performance.