Humeral retrotorsion will be measured with the T3300 ultrasound system (BenQ, Taipei, Taiwan). Participants lay supine with 90° shoulder abduction and elbow flexion. The main assessor places the transducer on the participant's anterior shoulder for a short-axis view of the lesser and greater tubercles. The two-person technique is adopted. The first assessor adjusts the probe perpendicular to the floor and rotates the participant's humerus with a line connecting the greater and lesser tubercles parallel to the horizontal plane. Then, the second assessor places a digital inclinometer on the ulnar side of the forearm to record the rotation angle, which is defined as the humeral retroversion.23 The ICC3,k of intra-rater reliability is 0.995. Each measurement will be performed 3 times, and averaged data will be used for analysis.

Acromiohumeral distance will be measured with the ultrasound transducer placed on the lateral aspect of the acromion in line with the longitudinal axis of the humerus to visualize the shortest distance between the humerus and the acromion.58 Three consecutive ultrasound images of the acromiohumeral distance are captured. The investigator captures 3 more consecutive ultrasound images at rest while the participant sit with the shoulder in the neutral position. The shortest distance will be measured with built-in calipers. The ICC3,k for intra-rater reliability is 0.963. Each measurement will be performed 3 times and averaged data will be used for analysis.

The probe will be positioned on the bicipital grove horizontally to measure subscapularis tendon thickness in a short axis of view. The participant's forearm is placed with the elbow flexed to 90° in slight internal rotation, with the palm facing upward and medially. This position allows the bicipital groove to be brought to an anterior position, allowing clear visualization of the tendon within the grove. .

For measurement of the posterior capsule thickness, the participants sit upright in a chair with both forearms resting on the thighs and upper arms by the participant's sides. The examiner positions a transducer on the posterior shoulder and visualizes the glenoid labrum, humeral head, rotator cuff, and posterior capsule. The posterior capsule is defined as the tissue immediately lateral to the tip of the labrum between the humeral head and rotator cuff. When the capsule is identified in the image, posterior capsule thickness will be measured with built-in calipers. The ICC3,k for intra-rater reliability is 0.951. Each measurement will be performed 3 times, and averaged data will be used for analysis.

The KJOC is the most common questionnaire for overhead athletes, and it was conducted in several studies.66 Recently, the Major League Baseball (MLB) organization adopted this evaluation tool as the standard for recovering injuries in MLB players.67 The questionnaire is commonly used to assess shoulder function and performance. It is valid, reliable in its pilot form, and responsive to the tested population of adult overhead athletes.66 KJOC questionnaire ranges from 0 to 100, and the lower score represents a limited function.

To measure the posterior capsule elasticity, the participants sit upright in a chair with both forearms resting on the thighs and upper arms by the participant's sides. The examiner positions a transducer on the posterior shoulder and visualizes the glenoid labrum, humeral head, rotator cuff, and posterior capsule. The posterior capsule is defined as the tissue immediately lateral to the tip of the labrum between the humeral head and rotator cuff. When the capsule is identified in the image, posterior capsule elasticity will be recorded. Each measurement will be performed 3 times and averaged data will be used for analysis.