## 1 Introduction  
Shoulder injuries are the most frequent in throwing sports such as handball (HB). The elite HB athletes make around 48.000 throwing actions in over 16.000 different shoulder positions during a season [1; 2; 3] which overloads the shoulder complex and may provoke several injuries such as impingement, labral and rotator cuff tears, and anterior instability, among others [4; 5; 6; 7; 8]. Studies in elite HB athletes have reported 3.7 injuries per 1000 h of training and 20.3 injuries per 1000 matches [9], and the prevalence of acute shoulder pain has been stated to be between 36% to 44.2% [10; 11; 12].  
The repetitive throwing actions have shown several adaptations in the shoulder complex. The most frequent adaptation is the reduction of the glenohumeral internal rotation (IR) range of motion (ROM) commonly known as glenohumeral internal rotation deficit (GIRD), and the decrease of the total rotation ROM (tROM) [8; 13; 14; 15; 16]. Athletes with GIRD have shown a two- to four-fold increased risk of suffering injuries in the shoulder complex [5].  
Adaptations in the soft tissues have been also described, such as external rotation (ER) weakness [17], strength imbalance between the ER and IR muscles [18], and shortening or lack of extensibility of the posterior muscles [8; 13; 14; 19].  
GIRD is currently considered the primary risk factor for shoulder pain [4; 20] and has been associated with the stiffness and weakness of the posterior shoulder muscles by several authors [6; 7; 8; 13; 14; 19]. The stiffness of the posterior muscles seems to shift the humeral head upward during the shoulder flexion, increasing the compression forces in the joint and the stress in the anterior part of the capsule and ligaments [6; 7; 21; 22]. Previous clinical trials have applied different interventions to the posterior shoulder muscles (upper trapezius, infrarespinatus [23], or shoulder external rotator muscles [24]) to decrease the posterior stiffness in overhead athletes, but the teres major muscle has never been taken into consideration.  
A cadaveric study hypothesized that the teres major muscle may play an important role in the glenohumeral stability and function [25]. The teres major muscle is a monoarticular scapulohumeral muscle that is inserted in the same plane as the subscapularis muscle but is not part of the conjoined tendon of the rotator cuff. When the arm is elevated, the inferior surface of the humeral head rests against the teres major muscle. This direct support of the humeral head may contribute to maintaining glenohumeral joint stability [25]. This muscle has been described to be more active in instable shoulders [26]. Therefore, in this way, an increment in the mechanical properties of tone and stiffness in this muscle may be related to GIRD. However, to the best of our knowledge, no study has assessed the mechanical properties of the teres major muscle in elite HB athletes.  
Thus, the assessment of the mechanical properties of the teres major muscle such as tone and stiffness, the internal and external rotators muscle strength, and extensibility of the posterior soft tissues could be relevant in elite HB athletes with GIRD. We hypothesize that the TS of the elite HB athletes with GIRD present a higher tone and stiffness in the teres major muscle, a muscle imbalance between internal and external rotators, and a decreased extensibility compared to the non-TS and non-HB athletes. Therefore, the aim of the study was to determine whether the elite HB athletes with GIRD present differences in the mechanical properties in the teres major muscle of the throwing shoulder (TS) compared to the non-throwing (non-TS) and non-HB athletes, and to verify if HB athletes present asymmetry in muscle strength and extensibility compared to the non-TS shoulder and differences compared to non-HB athletes.