Background Knee injuries are prevalent in elite volleyball and their preventive management is still discussed. Isokinetic assessment is largely use in sports injury prevention; however few studies investigate the differences in the isokinetic profile of injured knees. These studies analyses the agonist/antagonist ratio and do not consider other parameters as fatigue index.

Objective to investigate the differences between injured and non injured knee in the hamstring/quadriceps ratio and fatigue index in volleyball male athletes.

Setting all testing took place in the Sports Injury Prevention and Rehabilitation Laboratory- LAPREV in elite volleyball.

Participants 49 male (mean+SD age, 21.96+4.1; height, 196.5+0.06; body mass, 89.1+9.03) athletes were evaluated in this study, being 20 at injured group. Participants with lower-extremity surgery in the previous 6 months and pain during the isokinetic test were excluded.

Assessment of risk factor: hamstring/quadriceps ratio at 60°/s and 300°/s and fatigue at 300°/s at the dominant knee with 90° of hip flexion.

Main outcome measurements trauma and overuse knee injuries provided by questionnaire.

Results Differences between groups were found just in hamstring fatigue (p=0.002). The means of this parameter were 63.1 and 55.6 for injured and non-injured group respectively. For quadriceps fatigue the means were 48.4 and 47.3 respectively. No differences were found in the ratio analysis between groups (p=0.403 for 60°/s and p=0.289 for 360°/s). The means were 199.4 and 203.5 for injured and non-injured groups at 60°/s and 157.4 and 168.6 respectively at 300°/s.

Conclusion The results showed that the injured group has more hamstring fatigue compared to non-injured group. The ratio analysis does not reveal differences between groups. The fatigue analysis must be incorporated in the athlete's assessment, because seems to be more informative about injury risk.