在棒球投球中，不適當的骨盆/軀幹旋轉機制，會增加投球手臂肩/肘關節的傷害風險，因此對投手和教練來說，識別不適當的骨盆/軀幹旋轉機制是很重要的。
目前而言，要偵測這些旋轉模式，通常還是得靠肉眼去識別，這種質性的區別方法，其實是比較不精確的。首先，本研究試圖從已經存在的質性方式出發，慢慢延伸到量性方式，進而發展出一套能夠評估骨盆/軀幹旋轉機制的全新量性方法。透過這個新方法，可以將骨盆/軀幹旋轉機制分成四型(Type 1: proper mechanics, Type 2: early trunk rotation, Type 3: delayed pelvic rotation, Type 4: delayed pelvic rotation with trunk turning-back)。第一型相較於其他三型，能夠達到明顯較快的球速，所以也被認為是較適當的能量傳遞機制。第二、三、四型則被認為是不適當的機制，擁有較慢的球速，也意味著較低效能的能量傳遞。傳統由專家來識別的質性方式，也許能分辨出適當的骨盆/軀幹旋轉機制，但是若要分辨出不適當的三型骨盆/軀幹旋轉機制，還是得靠動態分析的全新量性方式，才能得到比較精確的結果。
接下來，本研究運用這個全新量性方法來了解第一型(proper mechanics, PM)和第二型(early trunk rotation, ETR)機制的差異，藉此，也能夠比較清楚在骨盆旋轉被控制之下，軀幹旋轉對於投擲肩/肘關節的真實影響效應。在這部分，收錄了57位菁英棒球投手，並將他們分成PM和ETR兩組，以室外動態分析，收集兩組多種運動學及動力學參數，並加以分析比較，結果發現PM組的球速(127km/h)比ETR組的球速(120km/h)快。在ETR組的肩關節呈現了「水平內收延遲」(horizontal adduction lag)及「垂肘」(dropped elbow)的不正常運動學表現。此外，在肩關節的動力學發現，ETR組的最大posterior force、inferior force、horizontal abduction torque及vertical adduction torque比PM組上升了9.2%、13.6%、21.3%及24.3%。至於肘關節的動力學發現，ETR組的最大anterior force、medial force、flexion torque及varus torque比PM組上升了20.3%、22.7%、18%及24.5%。這些結果顯示了ETR對於投擲肩/肘關節是有風險的，不但球速變慢，肩/肘關節負荷還增加，代表ETR確實不是適當的骨盆/軀幹旋轉機制。當治療一位有肩/肘關節傷害的棒球選手時，不僅需要了解其肩/肘關節構造及病態變化，同時也要清楚可能由ETR造成的肩/肘關節不正常機制及致病過程，如此才能有效制定針對軀幹柔軟度及核心肌群強化的訓練，來避免ETR，並降低肩/肘關節的受傷風險。本篇研究所發展出的全新評估方法，將能夠幫助棒球選手們早期偵測、篩檢出不適當的骨盆/軀幹旋轉機制，進而減少傷害並提升表現。

In baseball pitching, inadequate rotational mechanics of pelvis/trunk increase risks of throwing shoulder and elbow injuries. Therefore, it is critical to recognize those improper rotational mechanics for pitchers and coaches.
Currently, it is common practice to detect rotational patterns with use of human eyes in a qualitative, less precise way. First, this study intended to build on existing qualitative to quantitative approaches to develop a new quantitative method for evaluating pelvis/trunk axial rotational pitching mechanics. Based on the new evaluating method, pelvis and trunk rotational mechanics were classified into four types, Type 1: proper mechanics, Type 2: early trunk rotation, Type 3: delayed pelvic rotation, Type 4: delayed pelvic rotation with trunk turning-back. Type 1 enabled significantly higher ball speed than the other three types and was thought to involve proper energy transfer from the stride foot to the throwing upper limb. Types 2, 3, and 4, however, were regarded as improper mechanics, which could result in slower ball speeds and less efficient energy transfer. A qualitative approach, based on ‘expert opinion’, can specify optimal pelvis/trunk rotational mechanics. However, quantitative motion analysis is more precise in identifying three improper types of pelvis/trunk rotational mechanics.
Next, this newly developed method was applied to understand the differences between Type 1 (proper mechanics, PM) and Type 2 (early trunk rotation, ETR) mechanics. Thus, the “pure” effects of trunk rotation on throwing shoulder/elbow biomechanics were realized clearly with pelvic rotation under control. In this part, fifty-seven elite throwers were enrolled and divided into two groups, PM and ETR, using an outdoor motion analysis system. Several kinematics and kinetics parameters of the throwing shoulder/elbow were analyzed and compared between the two groups. Ball velocity was faster in the PM group (127 km/h) compared with the ETR group (120 km/h). The shoulders of throwers in the ETR group showed patho-kinematics of “horizontal adduction lag” and “dropped elbow”. The increases in maximal posterior force, inferior force, horizontal abduction torque, and vertical adduction torque were 9.2%, 13.6%, 21.3%, and 24.3%, respectively, in the shoulders of throwers in the ETR group. The increases in maximal anterior force, medial force, flexion torque, and varus torque were 20.3%, 22.7%, 18%, and 24.5%, respectively, in the elbows of throwers in the ETR group. These results indicate that ETR may be hazardous for the throwing shoulder/elbow. With lower ball velocity and higher shoulder/elbow joint loading, ETR is not a proper pitching pattern for kinetic energy transfer. When treating throwers with shoulder/elbow injuries, it is important not only to address shoulder/elbow anatomy and pathology, but also to understand the possible pathomechanics and pathogenesis of the shoulder/elbow caused by ETR. Furthermore, special training programs focusing on trunk flexibility and core muscle strengthening should be implemented to prevent ETR and decrease the risk of shoulder/elbow injuries. The new evaluating method with use of motion analysis is helpful for the screening and early detection of improper pitching mechanics in throwers.

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