本研究之主要目的是要藉由地面反作用力以及淨關節間作用力、力矩與功率來了解疊球投手投擲快速球時跨步腳在著地期間下肢關節承受的負荷及各肢段肌群參與活動的情形。 以四名國家級女子快速壘球投手為施測對象。 將一塊測力板（ 600Hz ）與一部 Peak高速攝影機（ 120Hz ）同步擷取跨步腳著地期間各運動學與動力學參數, 並以動力學逆過程算得跨步腳著地期間其踝、膝、髖關節之淨關節間作用力與力矩。實驗結果發現，地面反作用力第一峰值出現在人體骨骼神經系統產生緩衝反應之前，劇烈的地面反作用力值在下肢緩衝動作不足的情況下形成強大的壓力與剪力值作用在各關節上，長期訓練的累積可能會使關節、韌帶與軟骨組織承受不容輕忽的負荷。此外，在運動技術上建議加強膝關節伸肌的離心肌力可促進著地時的制動技術，讓能量有效的傳導到軀幹，以達高效能的投球表現。

　　　　　The purpose of this study was to investigate the ground reaction forces, joint reaction forces, net muscle joint moments and powers of the ankle, kneeand hip during the softball pitch with windmill style threw the fastball. Fourelite softball pitchers served as the subjects for this study. A Peak high-speedcamera (120Hz) and synthesized with a force plate (600Hz) was used to collectthe relative parameters of landing leg during pitching. The joint reactionforces and moments were calculated by using inverse dynamics process. Theresults indicated that the peak ground reaction forces appeared before the humanneuromuscular system responded to modify these forces. The greater compressiveand shear stresses which around the joint created during the landing phase wouldput a heavy load on soft tissue, ligament and tendon. In addition, theextensors' eccentric muscle powers of knee and the flexors' concentric musclepowers of hip were the important ability for the softball pitching performance.