前言:在棒球選手肩、肘關節損傷因子當中，投球的負荷量是造成青少年運動員受 傷危險的主要因素，原因在反覆投擲的情況下逐漸累積肩、肘關節的負荷與產生細微創 傷進而增加傷害的風險，而過量的投球負荷是否會對青少年族群在投球動作造成影響是 值得去深入的。目的:探討青少年棒球投手在投球數累積過程中，投球動作的生物力學 變化包括檢測運動學、關節受力以及下肢在地面反作用力與身體質心偏移量上的差異， 以瞭解投球負荷量所造成的相關影響。方法:實驗參與者為 36 名青少年 (14.1 ± 0.6 歲) 男性棒球投手，慣用手為右手、投擲方式為過肩投法。投球實驗開始前會收取 5 筆投球 資料作為基準，之後以模擬比賽形式進行 5 局的投球，每局有 5 球試投與 20 球正式 投擲，休息 8 分鐘進入下一局投球，動作擷取每局最後 5 筆動作資料。實驗使用六台 紅外線高速攝影機 (Motion analysis corp., 250 Hz)、一塊測力板 (Kistler, 2500 Hz) 收取 運動學與動力學資料，並使用雷達測速器收取球速數值。動作分期主要針對前導腳著地 到球投出手之間的投球動作的運動學與動力學參數進行分析。統計方式使用單因子重複 量數變異數分析，比較前測與各局之間各項參數之差異，若統計結果達顯著差異則再以 LSD 檢定進行事後比較，統計考驗顯著水準之 α 值定義為.05。結果:發現青少年投手 在模擬比賽中投擲 100 球後，為中到中高程度疲勞，並且球速顯著下降 (p<.001)。下 肢膝關節變化從 FC 到 BR 過程中屈曲角度顯著減少。骨盆軀幹與上肢關節動作的運 動學變化，集中出現在手臂加速期。在肩關節最大外旋時，肩水平內收、肘屈曲角度減 少，骨盆軀幹旋轉、軀幹屈曲角度增加。球投出手時，骨盆旋轉、軀幹屈曲角度增加。 動力學則是在球出手時前導腳的垂直力量減少、伴隨前後方向衝量以及膝關節伸展力矩 增加。結論:青少年棒球投手在投球數量累積後，會產生疲勞的現象，除了球速下降外，也會出現代償動作使投球機制改變，從而增加上肢傷害的潛在風險。基於保護選手的立 場，青少年棒球投手投球量的限制與監控是必要的。未來可再進一步探討其下肢肌力的 影響，可以更完整的了解投球機制變化趨勢與可能損傷風險進行後續討論。

Introduction: Baseball pitchers' workloads are a significant risk factor for injury in adolescent players. Pitching volume is a simple way to quantify pitching loads. These pitching-related injuries occurred and were caused by repetitive mechanical strains and repeated microtrauma to the soft tissues during throwing. The purpose of this study is to analyze the variation of pitching mechanisms during the accumulation of pitches and understand the effects of pitching volume on biomechanical changes in adolescent players. Methods: There will be 36 male teenage baseball pitchers who are right-handed and pitch with an overhand delivery recruited in this study. Before the experiment, each subject will ask to throw 5 pitches as the baseline data collection. Then followed the simulated game consists of 5 innings of pitching. Subjects will throw 20 pitches in each inning, and will have 8-minute rest between innings. A motion analysis system with 6 cameras (Motion analysis corp., 250 Hz) is used to collect 3D reflective marker trajectories, and then calculate for joint angles. A force plate (Kistler, 2500 Hz) is used to collect the ground reaction force of the stride leg and further calculate for joint moments. The biomechanical data of the last 5 pitches in each inning will be analyzed. One-way ANOVA with repeated measures and LSD post-hoc is used to compare the variation of the biomechanical throwing motion in baseline and each innings. Results: After 100 balls of pitching, pitching velocity was significantly reduced (p < .001), and RPE and VAS were significantly increased (p<.001). Knee flexion angle significantly decreased in the pitching cycle. In the acceleration phase of the pitching cycle, kinematic changes primarily occurred in the pelvic, trunk, and upper arms. The stride leg vertical GRF was significantly reduced at ball release, while anterior-posterior momentum and knee extension moment was significantly increased. Conclusion: Teenage baseball pitchers became fatigued after repetitive pitching, and their pitching velocity decreased as the volume accumulated. Furthermore, compensatory movements of the pitching mechanism to fatigue may raise the risk of upper arm injuries. However, teenage pitchers’ pitching volumes should be monitored in games and daily training. Pitchers' lower limb strength should be combined in future studies to discuss the related injury risk effectively.

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