## 1 Introduction  
Water polo is a physically demanding sport, in particular for the upper limbs, with an intense snap in swimming, change in direction, passing, and repetitive shooting of the ball [1]. It is a contact sport with the highest incidence of injuries, in particular shoulder injuries, among the other aquatic sports [2; 3]. In competitive situations, shoulder injury is reported to have an estimated incidence of 56.2 per 1000 h of play [4]. In particular, shoulder pain has a prevalence of 24 to 80% and represents the most common water polo injury [4]. The throwing pattern is similar to that of other overhead sports, requiring repetitive upper limb movement involving high-grade elevation and external rotation. In particular, the throwing activity can be divided into a first acceleration phase, in which the scapula rotates upward externally and tilts posteriorly; afterwards, the deceleration phase occurs, in which the scapula performs a movement of downward and internal rotation and tilts anteriorly [5]. Moreover, the aquatic environment makes it difficult to generate a high throwing force without the contribution of a solid base of support and the conventional throwing proximal-distal kinematic chain sequence [2]. In particular, the scapula represents an internal link between the body and the kinetic chain of the upper limb, and any type of difference in the scapular alignment represents a risk factor for shoulder injuries. Correct scapular control and symmetry are essential for efficient shoulder biomechanics, providing a stable base for rotator cuff muscle activation, which is considered to be an important link in the kinetic chain of the shoulder [6]. The overhead nature of this sport causes functional alterations that could precede pathological changes and represent a risk factor for soft tissue injury and glenohumeral joint instability [7]. However, it is necessary to specify that a certain grade of asymmetry between the dominant and non-dominant is physiological in healthy athletes in unilateral sports, e.g., tennis, and the physician should be aware of the pathologic threshold for scapular posture asymmetry at which the asymmetry becomes problematic [8; 9]. The throwing motion forces the shoulder into its maximum flexion, abduction, and extra-rotation and may lead to shoulder pathologies, such as scapular dyskinesia, glenohumeral internal rotation deficit (GIRD), superior labral anterior-posterior (SLAP) tears, and rotator cuff tears [10; 11; 12]. This represents a serious concern for athletes considering the days spent out of competition, the risk of chronicity, and the detraining effect on their overall performance [2]. The therapeutic options for the treatment of shoulder injuries include, but are not limited to, intra-articular injections (e.g., hyaluronic acid, corticosteroids, and prp), physical therapy (e.g., laser and shockwave), and exercise therapy (e.g., strength training and visual feedback training) [13; 14; 15; 16; 17; 18]. In this context, prevention plays a key role in the management of injuries, with an increasing need for prevention strategies, daily athlete functional monitoring, and tailored exercise programs targeting the athlete's needs [2; 5]. Several approaches could be utilized for the functional analysis of the shoulder. The first and most important step is the physical examination of the patients, starting from the anamnesis, the revision of the medical records, and the examination of the shoulder's range of motion and muscle strength [19]. Moreover, it is common to make use of clinical scores, which are useful in clinical practice. However, technological advancements have provided the physician with new tools for a detailed and objective movement analysis [20]. There are different possibilities to choose from according to the ratio between the accuracy of the examination and the costs in terms of time and expensive equipment. However, 3D motion capture with optoelectronic systems represents the gold standard for the analysis of athletic gestures [21].