## 4 Discussion  
### Results Discussion  
The main findings of this study can be summarized as follows: (1) The direction and velocity change: The joints of the non-throwing arm changed their displacement direction prior to shot put release, and the shoulder exhibits a trend of first increasing and then decreasing with decreasing velocity of elbow and wrist regarding non-throwing side, indicating a complex coordination pattern; (2) Angular changes: While the shoulder and elbow angles generally showed a flexion trend, the elbow angle exhibited brief periods  
Figure 5: The angular change regarding the elbow and shoulder of non-throwing arm. Figure 6: The correlation results between joints of non-throwing arm and throwing side joints, center of mass and shot put. \({}^{*}\), \(p\) < 0.05.  
of extension, suggesting a nuanced joint control strategy; (3) Velocity correlations: The resultant velocity of the non-throwing arm joints showed significant correlations with the throwing arm joints and shot put velocity, but notably, not with the hip joint of the throwing side. Specifically: Shoulder velocity was positively correlated with center of gravity velocity. Elbow and hand velocities were negatively correlated with throwing arm joint velocities and shot put velocity. These findings highlight the complex and nuanced role of the non-throwing arm in shot put performance, suggesting that the non-throwing arm is not merely a passive component but plays an active role in throw mechanics, potentially influencing balance, energy transfer, and overall throwing effectiveness. The following discussion will examine these results in detail, exploring their implications for shot put technique and training strategies. Shot put performance demands high mechanical power output, generated by the movement of the center of mass and all body segments within a confined space. Therefore, all the muscles needed by the shot put must work for great performance. Previous studies confirm that the right arm and trunk play a significant role in higher performance and better energy transformation [12]. Thus, the functions of the non-throwing arm are crucial as they influence the rotation and translation of the trunk and throwing arm from the back to the front. In addition to its impact on the center of mass movement, the non-throwing arm plays a significant role in the prestretch and the stretch-shortening cycle. The study observed the increasing resultant velocity regarding the shoulder of the non-throwing arm in the first half of the completion phase. While this displacement initiates the movement of the throwing side, [PERSON] suggests that it also increases the release velocity of the shot put, a phenomenon explained by the stretch-shortening cycle [14]. The non-throwing arm's swinging motion stretches antagonistic muscles, activating the stretch-shortening cycle, which enhances energy efficiency and velocity output. This mechanism aligns with the force-velocity relationship in muscle physiology, allowing for greater power output during the throw [19]. Therefore, the prestretch was one of the important functions of the non-throwing arm and this was a reason to explain the shoulder of the non-throwing arm's increasing velocity. The direction and velocity of the non-throwing arm's swing are significant because it moves forward on the left side before the throwing side, influencing the movement direction and rotation radius of the throwing arm. Thus, the non-throwing arm increasing resultant velocity in the first half of the completion phase can accelerate the velocity of the center of mass for preparing better shot putting by stretch-shortening cycle and decreasing rotation radius. The non-throwing arm decelerated the resultant velocity prior to the release. The non-throwing arm moved downward, coinciding with the deceleration of the athlete's overall velocity. Lowering the non-throwing arm can be associated with lateral flexion of the left trunk. [PERSON] et al.