## 2 Materials and Methods  
### Participants and Procedure  
We conducted a longitudinal observational study to analyze the role of a structured prevention program of exercises in improving the scapular girdle biomechanics. We enrolled 2 groups of subjects: healthy students of \"Magna Gracia University\" with an active lifestyle (Group A) and male athletes of a water polo team of the Italian Major League (Group B). The inclusion criteria were as follows: no previous history of shoulder or elbow injury or disease in the last year; a Neer and Hawkins test to exclude the clinical diagnosis of subacromial impingement syndrome; and no cervical pain or limitations. Informed consent was acquired from each of the participants and the Regional Ethics Committee approved the methodological approach proposed (Prot. N. 115/2022 Calabria Centrale). All participants underwent a kinematic analysis of both shoulders consecutively using a stereophotogrammetry system and an sEMG wireless system. Data collected on Group A were utilized to test the intrasubject, inter-rater, and intra-rater reliability of the kinematic analysis protocol and to collect a series of normative data. Conversely, Group B underwent a kinematic analysis before (T0) and after (T1) the exercise protocol. At the start and at the end of this study, each athlete completed a Kerlan-Jobe Orthopaedic Clinic Shoulder & Elbow (KJOCSE) questionnaire to assess the performance and function of the upper limb [23; 24]. KJOCSE is intended for use with overhead athletes and aims to determine if there is pain during throwing, with a good-excellent reliability and a minimal detectable change of 6.7. The stereophotogrammetry system was composed of two infrared cameras (Smart-DX, BTS bioengineering-Garbagnate Milanese, Italy), BTS-Emilia-Romagna, Italy), with its sampling frequency set to 200 Hz. The optoelectronic system represents the gold standard for kinematic analysis, with reported errors of < 4.0\({}^{\circ}\) for movement in the sagittal plane and < 2.0\({}^{\circ}\) in the coronal plane [25]. The system was calibrated according to the instructions of the manufacturer. As shown in Figure 1, 17 reflective markers (9.5 mm diameter) were positioned at reference points on each participant's body, detailed as follows: the processus spinosus of the seventh cervical (C7) and eighth thoracic vertebra (T8), the acromion process (AC), the center of the humerus diaphysis (Hm), the lateral epicondyle (EL), the ulnar styloid (US), the trigonom scapulae (TS), the inferior angle of the scapula (AI), and the anterior superior iliac spine (Clsup) [21]. Each participant also wore five sEMG wireless electrodes (freeemg 1000, BTS bioengineering-Garbagnate Milanese, Italy) on the following muscles: the pectoralis major, the deltoid, the trapezius, the latissimus dorsi, and the teres minor. The kinematic protocol was adapted from previous studies [11; 21; 26]. Before performing the analysis, the electrode sites on the skin surface were shared and abraded, and alcohol was used to reduce the skin's impedance. Surface electrodes were placed according to the recommendations of sEMG for Not-Invasive Assessment of Muscles (SENIAM) [27]. We compared the abduction, flexion, extension, and internal and external rotation ROM of both shoulders to calculate any difference between the scapular movement and the electromyographic data for the main muscles involved in the shoulder movement during throwing, as shown in Figure 2[10; 28; 29]. All participants performed the maximum movement of flexion, extension, abduction, and internal and external rotations three times, firstly with the dominant limb and then with the non-dominant limb. Three trials from each participant were analyzed in one session to assess the intra-subject reliability with 4 min of rest between tests. Each participant was rated by the same examiner over two days of testing with an average test-to-test interval of 10 days (\(\pm\)0.5 days) [30].