## 4 Discussion
### Shoulder biomechanics during Overhead Sporting Motions  
Shoulder joint moments perform an important role in producing high joint angular velocities for any rapid overhead movement. As such, one common biomechanical predictor of faster overhead motions was identified (demonstrated by higher post-impact ball/shuttlecock speed, ball release speed, and racket head speed) in the badminton smash, baseball pitch, and volleyball spike, namely shoulder internal rotation angular velocities during acceleration phase to the instant of contact/release [10; 11; 40; 42; 43; 45; 50; 55]. Current literature (Table 3) shows consistent findings on shoulder biomechanics during overhead sporting motions across various sports with a larger external rotation along with sequential forward shoulder movement enabling faster extension from proximal to distal segments. Consensus was met among the authors wherein the pre-stretch of the upper body demonstrated by maximal shoulder ER and abduction angle during the backswing stores elastic energy that facilitates a greater shoulder internal rotation moment during the forward acceleration phase [71]. Inversely, the literature also shows that achieving greater peak shoulder ER at the end of backswing movement and abduction angles at ball release were associated with increased superior translation and distraction force at the shoulder joint [42]. Comparison based on gender, sports experience level, and presence of injury shows agreement in that significant differences exist in the biomechanical predictors men tioned and the speed of the particular overhead movement, with the male, elite/skilled, and injury-free individuals being more dominant than their respective counterparts. Adding to that, amateur performers consistently demonstrated higher compression and distraction force at the shoulder joint compared to professional players when performing overhead tasks [23]. Ref. [56] reported no kinematic difference detected between successful and unsuccessful tennis serves among 11 female elite players. Meanwhile, significantly different timing of segments or joint motions were reported between genders [40; 51; 52; 57; 58] and experience levels [11; 22; 45], indicating the employment of different optimal strategies, but overall exhibiting similar movement patterns. Overhead athletes with disabled throwing shoulder (DTS) often exhibit consistent alteration in glenohumeral rotation, which has been identified as the factor most strongly associated with shoulder pain and injury [72; 73]. Even though having greater shoulder flexibility and mobility allows the athletes to have advantages by performing overhead movements with greater range of motion, they are also carrying the risk of overuse injury due to the nature of having pathomechanics [74]. This repetitive movement can potentially cause increased load on anterior shoulder with corresponding internal impingement [74]. Glenohumeral internal rotation (GIR) has been identified critically as key to normal force development in overhead throwing motion and, when altered beyond certain level, it changes the glenohumeral kinematics and it is implicated in shoulder injury [72]. The need to scrutinize shoulder metrics as a basis for determining which athletes should undergo preventive measures warrants scrutiny. The primary objective of assessing shoulder parameters in sports involving overhead movements should focus on appraising the present condition of the shoulder, gauging enhancements in performance, or establishing normative benchmarks to achieve before resuming play post-injury [75]. In addition, the only study that analyzed the shoulder muscle activation patterns among the included papers, ref. [41] suggests that racket specifications are critical for coaches who train players with shoulder pain and upper limb injuries.