緒論：高臺著地反彈跳是最常見的下肢增強式訓練動作，訓練中常同時涵蓋有著地後向上跳與向前跳兩種跳躍型態。過去研究指出，此類的高強度運動訓練對下肢具有潛在性的傷害風險；然而改變反彈跳躍方向對下肢著地負荷產生之影響仍屬未知。本研究旨在探討進行高臺著地反彈跳訓練時，著地後銜接垂直跳與水平跳兩種反彈跳躍方向對下肢著地負荷產生之影響。方法：以12位健康的大學體育系男生為受試對象，利用七台光學攝影機(200Hz)與兩塊測力板(1000Hz)同步蒐集運動學與動力學資料。每位受試者從40公分高臺著地後須進行高臺著地垂直跳與高臺著地水平跳動作。以Motion Monitor軟體進行所有資料處理。利用SPSS14.0統計軟體進行相依樣本t檢定，顯著水準訂為α = .05。結果：相較於高臺著地水平跳，高臺著地垂直跳動作在觸地瞬間髖關節與踝關節屈曲角度較小，著地期間髖關節與膝關節的角位移量亦較小。其次，高臺著地垂直跳在垂直地面反作用力峰值、朝後的水平地面反作用力峰值與膝關節近脛骨前剪力峰值上皆顯著高於高臺著地水平跳動作。在勁度調節上，高臺著地垂直跳動作有較大的腿部勁度與膝關節角勁度。結論：進行高臺著地反彈跳躍訓練時，著地後銜接垂直上跳的跳躍型態有較高的下肢傷害風險，尤其是前十字韌帶。 Introduction: Drop jump (DJ) is the most common plyometric training for the lower extremity. The training often includes two types, one is jumping vertically after drop, the other is jumping horizontally after drop. Previous studies have indicated that such high intensity training might increase the potential of injuring lower extremity. However, it was unproven whether changing the directions after first drop would effect on the lower extremity injury. The purpose of this study was to investigate the influence of jumping direction on the lower extremity regarding vertical and horizontal jump. Methods: Twelve healthy male students from the department of Physical Education were subjects for this study. The motion capture system with seven infrared cameras (200 Hz) and two force plates (1000 Hz) were synchronized and used to collect the kinematic and kinetic data. Each subject performed both vertical DJ and horizontal DJ from 40-cm height. All data were analyzed with the MotionMonitor software. Statistical analysis was performed with SPSS 14.0 for Windows. The dependent t-test was used to test the differences variables between the vertical DJ and horizontal DJ. The significance level was set at α = .05. Results: The vertical DJ exhibited smaller hip and ankle flexion at initial foot contact with the ground, and a smaller hip and knee angular displacement during landing in comparison to the horizontal DJ. The vertical DJ showed a greater peak vertical ground reaction force, peak posterior ground reaction force and peak knee proximal tibia anterior shear force during landing than the horizontal DJ. The vertical DJ tended to increase leg stiffness and knee joint stiffness. Conclusion: The vertical DJ has a higher risk of lower extremity injury, especially in anterior cruciate ligament.