研究背景與目的：肩上投擲為大角度且快速的動作，除了平衡的肌肉、軟組織具有適當柔軟度，更需要良好的本體感覺來提供關節的穩定，以預防重複動作造成肩部傷害。過去的研究發現測量關節主動復位的準確度最能代表本體感覺缺損程度，然而此類研究最大限制在於只測量單一關節單一平面上的動作，無法應用在功能性動作上。雖然有學者提出改良的實驗方法，但仍未有組織受傷後與肩痛症狀對本體感覺影響的相關研究。因此本篇研究目的是探討具有肩痛症狀與無症狀的壘球選手之肩關節位置覺的差異，藉此瞭解肩痛症狀與本體感覺缺損之間的關係，方法：我們選取兩位大學壘球隊隊員，一位具有肩痛症狀，另一位無肩痛症狀。針對肩上投擲動作中的預備位置和球出手位置，使用電磁場追蹤儀收集空間座標，藉由計算絕對誤差和三維變異誤差來比較受試者之間各肩部關節動作的主動復位能力。結果與討論：結果顯示肩痛者比無肩痛者在肩胛胸廓、肩盂、以及胸鎖三個關節都有著較高的三維變異誤差，代表受傷組織使得肩部各關節在整體動作中的準確性皆下降，尤其在肩盂關節兩者的差異最大。且預備位置這種極端角度和球出手位置相比，可能牽扯較多非收縮性組織，並且肩峰下空間更為狹窄，使得關節位置覺傳遞能力降低。而各關節內動作，以肩盂關節的內轉及水平外展在兩者之間差異最大，可能原因在於肩上投擲常造成維持靜態穩定的前盂肱韌帶鬆弛，而幫助動態穩定的旋轉肌有可能是肩痛者的疼痛來源。結論：在肩上投擲時，肩痛症狀會影響肩部關節位置覺，造成主動復位時準確度下降，尤其是肩盂關節的內轉及水平外展，且關節在末端角度受到的影響更為明顯。這可能會降低肩部穩定度及影響運動表現。

Background & Purpose: Overhead throwing is a fast movement which requires extreme range of motion at shoulder complex. Proprioception plays an important role to maintain joint stability and to prevent further injury. Recent studies suggested that the active reposition acuity reflects the degree of joint position sense deficit. However, they are limited in measuring single joint motion in single plane. Additionally, few studies examined the association between shoulder symptoms and active reposition acuity in overhead throwing athletes. The purpose of this study was to investigate the shoulder joint position sense in softball players with and without shoulder pain. Method: Two softball players (1 with and 1 without shoulder pain) were recruited from our school team. We used electromagnetic tracking device to collect data in arm-cock and ball-release positions. We compared the active reposition acuity between two participants by calculating absolute error and three dimensional variable error. Result and Discussion: Participant with shoulder pain had significantly decreased acuity than that in participant without shoulder pain, especially internal rotation and horizontal abduction in glenohumeral joint. Compared with ball-release position, it is possible that arm-cock position involved more soft tissue in end range and compressed subacromial space. Therefore, possible causes of shoulder pain might influence the input of proprioception. Conclusion: Shoulder joint position sense decreased in the softball player with shoulder pain. This might decrease the stability of shoulder complex and affect the performance of the athlete.