Shoulder injuries are one of the most common injuries in athletics, especially the athletes who use overhead motions like volleyball hitters, quarterbacks in football, and baseball pitchers. Approximately 20% of all game and practice injuries were sustained in the shoulder; shoulder muscle strains (11%), shoulder tendinitis (7%), and shoulder subluxation (4%). Those shoulder muscle strain, tendinitis, and subluxation are caused by the glenohumeral joint multidirectional instability; the humeral head moves on the glenoid fossa excessively during the overhead motion due to the weakness of the shoulder and scapular muscles. The purpose of the study was to determine the shoulder internal rotation peak torque (PT) difference between the normal shoulder range of motion (ROM) and hyper-ROM group with 90° of shoulder abduction and 90° of elbow flexion. Twenty-one highly trained women volleyball athletes who were around Edmond and Oklahoma City area voluntary participated in the study and measured their active shoulder external rotation using the goniometer, as well as their shoulder internal concentric rotation peak torque by using the Biodex isokinetic dynamometer. There was no significant difference in shoulder internal rotation peak torque between the normal ROM and hyper-ROM with 90° of shoulder abduction and 90° of elbow flexion in this thesis study that indicated there was no shoulder dynamic stability difference in the both groups (F = 2.763, t (15) = .741, p = .115). Keywords: shoulder, stability, peak torque, range of motion, volleyball