## 1 Introduction  
Handball, baseball, volleyball, and water polo are sports that place large demands on the shoulder complex because of the repetitive throwing actions. Studies suggested that elite athletes could perform approximately 48,000 throwing actions during a single session in more than 18,000 different shoulder positions [1, 2]. These throwing actions are commonly performed in extreme positions of the glenohumeral joint and at high velocities, leading to overuse injuries [3, 4].  
Several studies have investigated risk factors for shoulder injuries in overhead athletes, paying special attention to the glenohumeral range of motion (ROM) and shoulder muscle imbalances [5, 6]. Athletes with a glenohumeral internal rotation deficit (GIRD) higher than 15\({}^{\circ}\) and a total shoulder ROM reduction higher than 10\({}^{\circ}\) have shown a two-to-four-fold increase in the risk of injury [7, 8]. External rotator-muscle weakness [6] and a decrease in the external rotation and internal rotation ratio may double the risk of injury [9, 10].  
Despite the fact that shoulder pathobiomechanic is not fully understood, [PERSON] et al. [11; 12] hypothesized that these changes in glenohumeral ROM and muscle function occur due to the restriction of the posteroinferior part of the shoulder-joint capsule and the inferior part of the glenohumeral ligament, as well as to the shortening or stiffness of the muscles of the posterior part of the shoulder. [PERSON] et al. [13; 14] found that the throwing shoulder of overhead athletes presented a greater posterior capsule thickness and was negatively correlated to internal rotation shoulder ROM. In addition, [PERSON] et al. [15] showed that some muscles of the posterior part of the shoulder presented an increased tone and stiffness.  
In this sense, diverse clinical trials have applied different interventions to improve the restriction of the shoulder capsule and ligaments, such as glenohumeral dorsal gliding [16; 17; 18] or other soft-tissues-targeted techniques, to decrease the stiffness of the muscles of the posterior part of the shoulder, such as dry needing [19], diacutaneous fibrolisis [20], manual therapy [21; 22] or stretching [23; 24]. Among these conservative interventions, static stretching and proprieptive neuromuscular facilitation (PNF) stretching are the most studied techniques, either in isolation or combined with other manual therapy techniques, to treat glenohumeral deficits in overhead athletes. Two previous systematic reviews have investigated the effects of stretching on overhead athletes [23; 24]. However, none of them selected as an inclusion criterion the presence of GIRD. So, to the best of our knowledge, there is no systematic review and meta-analysis evaluating the effectiveness of stretching in isolation or combined with other manual therapy interventions in overhead athletes with GIRD.  
Therefore, the primary aim of this study was to assess the effectiveness of stretching in overhead athletes with GIRD. The secondary aim was to investigate if the addition of other manual therapy techniques to a stretching protocol produces better benefits than stretching in isolation. The third aim was to evaluate which stretching technique produces better benefits in athletes with GIRD.