Background: Volleyball is a sport characterized by short, intensive and explosive actions. In the performance of these repetitive movements, the shoulder joint receives the largest load. Therefore, a detailed assessment of biomechanics and muscle performance is fundamental in the evaluation, treatment and in prevention of shoulder injuries in volleyball athletes. Methods and Findings:Information from a database concerning the isokinetic evaluation of the shoulder's external and internal rotator muscles at the 60°/s and 180°/s angular velocities from 20 adolescent male volleyball athletes under 17 years of age was assessed. At a velocity of 60°/s the average values for internal rotators on the nondominant limb were significantly smaller than those of the dominant limb, and at a velocity of 180°/s both the internal and external rotators average values for the non-dominant limb were significantly smaller than those for the dominant limb. For the external-internal rotator ratio analyses, there was no significant difference between the limbs. Conclusions:In conclusion, the unilateral demands during typical movements in volleyball resulted in higher peak torque values for the dominant limb in comparison to that of the non-dominant limb. For the external-internal rotators ratio, no relevant differences were found between limbs, and the average values were within the parameters of normality.