研究目的在於了解不同守備位置的大學棒球選手在肩關節旋轉肌群等速肌力的表現是否有所不同，以27位大專男子棒球選手為研究對象，依守備位置區分為投手組(9位)、內野手組(10位)與外野手(8位)，以Biodex等速肌力測量儀來測試受試者慣用手肩關節內旋與外旋的最大力矩及爆發力矩，並以單因子變異數分析來考驗其差異。研究結果如下：(一)投手組、內野手組和外野手組在肩關節的內旋最大力矩和爆發力矩表現上並無顯著差異，而外野手組的肩關節外旋最大力矩和爆發力矩皆明顯大於投手組。(二)在外旋與內旋最大力矩的比值方面，分別為投手71.6%、內野手72.3%、外野手88.2%，雖未呈現顯著差異，但可看出外野手有較高的外旋/內旋比值的現象。本研究得出以下結論，投手組的內旋與外旋力矩相對較低，也反映出較低的外旋與內旋力矩的比值，顯示其肩關節肌力不足，尤其是外旋的肌力，需要安排更有效的肌力訓練來提升旋轉肌群的力量，除了可增加球速，更能提高肩關節的穩定以降低受傷的風險，而透過彈力繩或彈力帶進行離心收縮訓練來提升外旋肌群的肌力，是相當有效且安全性高的方法。

The purpose of this study was to investigate the different of dominant arm shoulder rotators performances between the baseball pitchers, infielders, and outfielders. Participants were 27 first-level collegiate baseball players, including 9 pitchers, 10 infielders, 8 outfielders. A Biodex Isokinetic Dynamometer was used to evaluate the peak torque and power of shoulder internal and external rotation. The results indicated that there was no significant different in peak torque and power of internal rotation. The outfielders showed greater peak torque and power of external rotation than pitchers. The ER/IR ratio of pitchers, infielders, and outfielders were 71.6%, 72.3%, and 88.2%. There was no significant different between these groups, but it indicated outfielders had higher ER/IR ratio. The conclusion of this study were that these pitchers showed the lower muscle strength of shoulder, espacially in external rotators. They need to design more muscular training to enhance their shoulder muscle strength, We suggest that eccentric isokinetic training for the external rotators will be effective to enhance the muscle strenght. Such consequence will improve the effciency of pitching, and further reduce the risk of shoulder injoury. It is a good way to use elastic cord or elastic belt.