前言：
過去有許多文獻已經證實投手慣用側的盂肱關節外旋活動度大於非慣用側外旋活動度，但慣用側的盂肱關節內旋活動度卻會小於非慣用側。本研究將慣用手的盂肱關節內旋活動度小於非慣用手盂肱關節內旋活動度達20度以上的現象定義為盂肱關節內旋活動度缺損 (Glenohumerl internal rotation deficit, GIRD)，此種症狀可能改變投球運動模式的動力鏈能量傳遞，進而增加棒球選手肘關節疼痛與受傷的機會。
目的：
探討台灣患有GIRD之症狀的投手與正常的投手，在投擲直球過程中的運動學、動力學和功參數差異，進一步了解盂肱關節內旋活動度缺損對於過肩運動選手所造成的影響，並同步建立台灣戶外棒球投手投球生物力學資料庫。
研究方法：
本研究受測者為兩個族群，分別為十位患有GIRD之症狀的投手，十位Normal族群的投手。於戶外真實投手丘，使用頻率300fps的三維動作分析系統擷取過肩投球動作過程，分析其運動、動力學和功參數。投球內容為直球。統計方法用重複測量變異數分析，比較兩族群間同球種差異。設定p<0.05為顯著差異。
結果：
在關節角度的比較上，GIRD族群和Normal族群族內的肩關節內旋角度和肩關節外旋角度皆達統計上的顯著差異。
GIRD族群與Normal族群投擲直球的分析結果，81項運動學參數中，有7項達到統計上的顯著差異。33項動力學參數中，有5項達到統計上的顯著差異。16項功參數中，有2項達到統計上的顯著差異。
肌力方面，GIRD族群慣用手與非慣用手的肌力衰退率比較結果皆未達統計上的顯著差異。兩族群在投球前後的肌力衰退率比較結果也未達統計上的顯著差異。
結論：
GIRD族群在投球機制的表現上，在球離手時肩關節的三個運動學參數中有兩個達統計上的差異，進而影響了投手的控球表現。另外，GIRD族群呈現較少利用上軀幹的轉動，造成過大的負荷施加於肩、肘關節中。
GIRD族群在傷害機轉的表現上，幾項與傷害有關的關節受力參數都大於Normal族群，讓GIRD族群發生運動傷害的風險增大許多。
GIRD族群在投擲運動表現上，球速是有較快的趨勢，在手臂後拉時期和手臂加速時期所做的功也大於Normal族群，但也因為這些高強度能量的產生，會讓GIRD族群的選手更容易造成投擲上的傷害。
因此，建議GIRD族群需多加強肩、肘關節的肌群，並伴隨著核心肌群的訓練，減少投擲時手臂的負擔，以避免投球後造成傷害。

SUMMARY

Previous studies have documented changes in range of motion in the dominant shoulder of the overhand throwing athlete, and this change may increase the risk of injury. This study conducted medical examinations and motion analyses of throwing movements. To investigate the relationship between GIRD and throwing motion, and compare the difference between GIRD and without GIRD pitchers from biomechanical perspective. Twenty baseball pitchers from the university and high school were recruited pitched off an outdoor mound during 3-dimensional motion analysis to measure whole body kinematics at 300 Hz.
Pitchers were defined as GIRD group if their throwing shoulders displayed a 200 or more loss of IR compared with their nonthrowing shoulders. The examinations showed that the shoulder horizontal abduction angle and shoulder external rotation angle were significantly different at the instant of ball release between two groups. This phenomenon changed the pitching mechanism, affecting the shoulder positon at the instant of ball release. Moreover, this study revealed that GIRD groups presented the smaller torso rotation angle in the pitching process. Not properly using the transfer of momentum within the kinetic chain let the upper arm bear excessive load. On the other hand, shoulder inferior force, shoulder internal rotation torque, elbow medial force, and elbow varus torque were significantly different between the two groups. Pitchers with a deficit had an increased risk for shoulder and elbow injury.

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