現代競技排球朝向求快、求變、求準的趨勢邁進，進而提升了比賽的強度以及速度，想擁有傑出的防守表現，「準確判斷」及「快速移動」已為關鍵的技術目標。而防守屬於被動技術，需隨著攻擊手的變化調整接球動作以應付瞬間移位，以目前競技水準而言，球在空中飛行時間大約在0.3~0.5秒之間，一般選手的反應時間約為0.29~0.33秒，因此，防守選手必須要能準確判斷及獲取爆發力量才能達到迅速移動的效果。本研究主要目的在比較不同層級選手騰空開跳動作型態之差異性，並討論對防守表現的影響。受試對象為受過訓練並且擁有報名參加大專排球聯賽特優級資格之台灣師大優秀甲組排球選手(共計7名)，另外一組則為台灣師大乙組排球選手(共計7名)，甲組平均年齡20.25歲，身高168.25±4.1公分、平均球齡9.25年；乙組選手平均年齡21.25歲、身高170.75±5公分、平均球齡3年。實驗儀器以兩部JVC高速攝影機(250HZ)同步擷取攻擊手與受試者同時進行中的攻防動作之運動學參數，影片以Kwon3D動作分析軟體進行2D直接線性轉換(2D-DLT)，所得參數以t-test檢定結果之差異性，顯著水準為α= .05，再以時間、角度、角速度之參數以描述統計方式說明其差異性。所得結果中發現，甲組7名選手騰空動作出現時間點分佈範圍較為集中，表示甲組選手動作出現時機相當接近，約在0~0.5區間內，另外，甲組選手平均騰空高度約0.10~0.14之間，下壓角度約21.3~30.9之間與所得關節角速度約在169.5~231.4之間，皆明顯大於乙組選手且達顯著差異p< .05。因此提出以下結論，動作出現時機接近則表示接球動作較有節奏感與規律性，能隨著攻擊手動作變化來調整動作時機；而騰空高度高、下壓角度大、速度快，依地面反作用力理論及牽張反射原理得知，除可穩定身體重心接球外，下肢肌群也可獲得有效的爆發力量。

The “accurate judgment” and “swift movement” have become key skills for achieving outstanding defense performance. Defense is a passive skill; it requires a player to adjust his/her serve-receiving in compliance with the attacker’s movements so as to deal with instantaneous shift. Volleyball flies in the air for about 0.3 to 0.5 seconds while a player spends 0.29 to 0.33 seconds in responding. Hence, a defense player must be able to judge accurately and gain explosive force to move swiftly. The purpose of this study is to contrast the motions of hop step of players of different levels and discuss the influences on the defense performance.The subjects of this study is consisted of seven trained players from volleyball Team A of National Taiwan Normal University. The other group includes seven players from volleyball Team B of National Taiwan Normal University. The average age of Team A is 20.25 years old, the average height is 168.25±4.1cm, and the average playing years are 9.25 years. The average age of Team B is 21.25 years old, the average height is 170.75±5cm, and the average playing years are 3 years. Two JVC high speed videom camera (250HZ) simultaneously record the kinematic parameters of offense and defense motions of the attackers and the subjects respectively. The video clips are analyzed with Kwon3D for 2D direct linear transformation (2D-DLT). The parameters retrieved from the analysis are examined with t-test for difference. The result indicates a significance of α= .05. Then, parameters of time, angles, and angle speeds are utilized to explain the difference by means of the descriptive statistics method. The results indicate that the distribution of hop step timing of the players in Team A is more concentrated, meaning that the hop step timing, which ranges between 0 and 0.5, of each Team A player is close to that of each other. Besides, the average height of hop step of Team A is between 0.10 and 0.14, the pushdown angle is between 21.3 and 30.9, and the joint angle speed is between 169.5 and 231.4. All of these figures are significantly larger than those of Team B and achieve significant difference (p< .05). Therefore, this study generates the following conclusions. When the hop step timing of every player is close to that of each other in a team, it means the motions of serve-receiving of the team are rhythmic and regular, and the players can adjust the timing of their motions according to the movements of the attackers. Additionally, when the hop step is high, the pushdown angle is large, and the speed is swift, based the theories of ground reaction force and stretch reflex, a player is able to stabilize his/her body for serve-receiving and gains effective explosive force.

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