Effect of Glenohumeral Internal Rotation Deficit on Shoulder Endurance and Stability in Adolescent Male Volleyball Players

This study aims to investigate whether glenohumeral internal rotation deficit (GIRD) is associated with shoulder endurance and functional stability in male adolescent volleyball players aged 14 to 18 years who do not have shoulder pain. GIRD refers to a reduction in internal rotation range of motion of the dominant (spiking) shoulder compared with the non-dominant shoulder and is commonly observed in young athletes participating in overhead sports such as volleyball. Participants will be divided into two groups based on shoulder range of motion measurements. Athletes with a loss of at least 10 degrees of internal rotation in the dominant shoulder compared to the non-dominant shoulder will be classified as having GIRD, while those without this difference will be classified as not having GIRD. Shoulder internal and external rotation range of motion will be measured using standardized clinical assessment methods. Shoulder endurance and upper extremity functional stability will then be evaluated using clinically applicable performance-based tests, including the Shoulder Endurance Test, the Posterior Shoulder Endurance Test, and the Modified Closed Kinetic Chain Upper Extremity Stability Test. The results of these tests will be compared between athletes with and without GIRD. The main research question of this study is whether the presence of GIRD in asymptomatic adolescent volleyball players is associated with reduced shoulder muscle endurance and decreased functional stability of the upper extremity. The study hypothesizes that athletes with GIRD will demonstrate lower posterior shoulder endurance and poorer upper extremity stability compared to athletes without GIRD.