目的：過去研究認為從事肩上運動的運動員，慣用手側盂肱關節內旋活動度缺損的現象，肇因可能來自軟組織或骨質的適應，然而訓練球齡可能也對慣用手側盂肱關節旋轉活動度會有影響。因此，本研究旨在調查不同訓練球齡層，棒球投手兩側盂肱關節活動度變化是否存在有顯著差異。方法：本研究共徵召160位男性投手（平均年齡14.5±2.9歲），球齡介於2－9年之間。評估內容包括兩側盂肱關節內旋與外旋活動度。以正規化定義內旋或外旋角度占總內、外旋活動度的百分比代表本研究角度差異。利用單因子變異數分析（One-way ANOVA）探討不同球齡層在正規化後，兩側盂肱關節內旋與外旋角度百分比及整體旋轉活動度（內旋＋外旋）的差異性，並以Tukey法進行事後檢定比較不同球齡層在旋轉活動度百分比的差異。結果：顯著差異在訓練球齡第二年的投手其慣用手內旋活動度百分比小於第九年的投手活動度百分比（31.57% vs 25.96%）。而整體旋轉活動度在第六年開始有顯著減少（P<.05）。並且慣用側盂肱關節外旋活動度百分比在球齡第9年74.25%多於第2年68.43%亦達顯著差異（P<.05）。結論：棒球投手慣用手側盂肱關節內旋活動度百分比與整體旋轉活動度會隨著訓練球齡增加而逐漸減少，並且外旋活動度百分比亦會隨著球齡增長而改變。

Purpose: Previous studies have been reported that overhead throwing athletes demonstrate glenohumeral internal rotation deficit in the dominant shoulder. The reason may result from soft tissue or bony adaptation. Little is known about the relationship between years of play and glenohumeral range of motion (ROM) at dominant arm in baseball pitchers. The purpose of this study was to investigate glenohumeral rotation motion changes in baseball pitchers and correlates these measurements with years of play, and the difference between dominant and non-dominant shoulders. Methods: One hundred and sixty baseball pitchers (Mean age=14.5±2.9 years; years of play=2-9 years) participated in this study. Bilateral glenohumeral internal and external ROM were measured. To normalize the definition of the rotation, internal or external rotation ROM percentage of total rotation ROM was used. One-Way ANOVA was used to compare the difference in glenohumeral internal and external rotation, and total arc of motion between bilateral shoulder ROM of each subject. Tukey post hoc analyses were performed to determine significant differences in shoulder rotation among the years of play. Result: Significant difference was found in internal rotation ROM percentage between 2-year of play and 9-year of play in the dominant shoulder (31.57% vs 25.96%). Significant decrease in shoulder total arc of motion was found at 6-year of play (p＜.05). Besides, significant differences was in external rotation ROM percentage between 9-year of play and 2-year of play (74.25% vs 68.43%). Conclusion: In the dominant shoulder, internal rotation and total arc of motion decrease as the years of play increased. In addition, external rotation changes as the years of play increases.