前言：
棒球投手在投擲過程中，前導腳著地瞬間的前後，同時也是軀幹扭轉達到最高角度的同時，這瞬間可能會對肩、肘關節造成極大的壓力，並進一步影響到肱骨關節旋轉。本研究將記錄投手投球過程，於前導腳著地瞬間，量測其慣用手之肩關節旋轉角度(shoulder external rotation angle)，將小於45度以下的投手歸納為一個族群，大於45度以上的歸納為一個族群，於Cortex程式或是高速影片中表現不明顯的選手的則不納入實驗之中。
目的：
本研究宗旨在透過3-D動作分析針對前導腳著地瞬間，肩關節旋轉角度(shoulder internal rotation angle)小於45度以及大於45度兩族群投手投擲直球所造成的影響，並進一步探討兩族群之間的投擲直球之運動學、動力學和做功差異。
方法：
本研究將受測者分為兩族群，分別為前導腳著地瞬間，肩關節旋轉角度(shoulder internal rotation angle)小於45度(Group 1)以及大於45度(Group 2)兩族群。本實驗於戶外棒球投手丘上使用頻率300fps的三維動作分析系統，擷取投球動作過程，投球內容皆為直球。統計方法用重複測量變異數分析，比較兩族群間生物力學差異。設p<0.05為顯著差異。
結果：
球速表現方面，Group 1族群平均較Group 2族群來得快些，但並未達統計上差異。靜態關節活動度比較下，兩族群的肩關節活動度比較下，皆未達統計上差異，然而Group 2族群在肩關節外旋角度上，在投完球之後有增加的趨勢，在這方面相對於Group 1族群結果顯示有統計上的差異。
兩族群投擲直球的運動學分析中，81項運動學參數中，有40項達到統計上的差異。33項動力學參數中，有20項達到統計上的差異，標準化之後有17項達到統計上的差異。16項作功參數中，有6項參數達到統計上的差異。
在投球前後肌力比較結果下，兩族群皆未有肌力衰退的現象，所有肌力衰退參數皆未達統計上差異。
討論與結論：
結果顯示在許多動力學作用力上，Group 1族群的肩肘關節受力都較Group 2族群來的多，從這樣的受力來推測，本研究認為Group 1族群在投球上面較依賴手部力量。而在許多的運動學、時刻點分析下，Group 2族群在最大肩關節外旋角度(MER)之前的投球動作較快、重要時刻點發生區間較短暫，本研究認為這樣的投球機制可以減少能量在每個環節的散失、累積，較有利於能量的傳遞。
對於長久的投擲生涯來衡量，本研究較建議於跨步時期即開始進行投擲的先前準備，包括骨盆旋轉、肩關節外旋等動作，在前導腳著地之後的投球動作可以有較低肩肘受力。

SUMMARY

Literatures showed that the range of motion (ROM) of the dominant shoulder are common injury factor in overhand throwing athletes. Instant of foot contact timing was defined the star of pitching cycle, and ball release was defined the end of pitching cycle. Twenty three pitchers with shoulder external rotation under 45 degree and nineteen pitchers with shoulder external rotation over 45 degree, they were recruited in this study. All subjects pitched off an outdoor mound. Three dimensional motion analysis system with 8 CCD cameras were used to measure whole body kinematics at 300 Hz. Pitchers were defined as Group1 (under45°group) if their throwing shoulders displayed a 45° or more external rotation angle (ER) at instant of foot contact, and pitchers were defined as Group2 (over45°group) if their throwing shoulders displayed a less 45° external rotation angle (ER). This study show that shoulder abduction angle, shoulder external rotation angle, forearm pronation angle, trunk rotation angle and pelvis rotation angle were significantly different at the instant of foot contact (FC) between Group1 and Group2. These results indicated that shoulder external rotation angle at FC timing changed the pitching mechanism, affecting the shoulder kinetics and kinematics at the instant of foot contact. Furthermore this study found that the Group1 pitchers could not efficiently utilize the body rotation during the pitching motion, leading to restraint of the pitching performance. From the result of kinetics, Group1 displayed a greater shoulder force/moment in their dominant arm as compared with Group2. The greater force/moment in the Group1 will increase the loading on biceps, rotator cuff and para-scapular muscle which may further increase the risk of shoulder injuries. Group1 pitchers and Group2 have similarity in pitching speed. However, Group1 pitchers presented a little fast ball speed. Group1 with a great elbow total work in the arm acceleration phase which can also increase the risk of elbow injuries. These findings are useful for pitchers and coaches to have a better understanding of pitching biomechanics in pitchers shoulder external rotation at foot contact. Further training program may be necessary to improve pitching motion and decrease the risk of injury.

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