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

Overview

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.

Repetitive overhead sports activities are known to produce sport-specific adaptations in the glenohumeral joint. One of the most commonly observed adaptations is a reduction in glenohumeral internal rotation on the dominant side, referred to as glenohumeral internal rotation deficit (GIRD). Although GIRD has been widely investigated in adult athletes and in relation to shoulder pain and injury, less is known about its functional implications in asymptomatic adolescent athletes. This study is designed to explore the association between GIRD and shoulder-related functional performance parameters in adolescent volleyball players. The focus of the protocol is on muscle endurance and dynamic upper extremity stability, which are key components of shoulder function during repetitive overhead tasks. The study specifically examines whether alterations in glenohumeral rotation are reflected in measurable differences in performance-based clinical tests, even in the absence of pain or reported injury. Standardized physical assessment procedures are used to quantify shoulder rotation and functional performance. All measurements are performed by trained assessors using consistent testing protocols to minimize inter-rater and intra-rater variability. Testing is conducted under controlled laboratory conditions to ensure uniformity across participants. The analytical approach is based on between-group comparisons according to the presence or absence of GIRD. Statistical methods are selected to evaluate differences in endurance and stability outcomes and to quantify the magnitude of these differences. Sample size estimation is based on previously published data examining shoulder endurance and stability outcomes in overhead athletes. This protocol aims to contribute to the understanding of early functional changes associated with shoulder motion adaptations in adolescent volleyball players and to inform future injury prevention and training strategies in youth overhead sports.