女子網球閉鎖式與開放式站姿雙手反拍加速期之研究

The study of square and open stance for women's tennis two-handed backhand stroke during acceleration phase

目的：比較閉鎖式與開放式站姿雙手反拍在向前加速階段的擊球動作特徵。方法：以八位國家代表隊層級女子網球選手為受試對象，利用兩部Redlake高速攝影機（250Hz）同步拍攝閉鎖式與開放式站姿雙手反拍的三維擊球動作，並藉Kwon3D 3.1與Peak Motus 7.0動作分析系統進行數位化處理，以相依樣本t test檢驗不同站姿參數之差異。結果：閉鎖式與開放式站姿雙手反拍在球速上並未達顯著差異。其次，在向前加速階段閉鎖式站姿身體重心前後位移（18.9±5.4cm）顯著大於開放式站姿（10.4±8.5cm），而開放式站姿身體重心垂直位移（14.3±3.5cm）則顯著大於閉鎖式站姿（7.6±2.7cm）。在向前加速瞬間與擊球瞬間，開放式站姿髖軸角度（86.5±6.2°,　32.5±9.5°）顯著小於閉鎖式站姿（97.6±5.0°,　48.3±9.0°）；但在整個向前加速階段，開放式站姿髖軸最大旋轉角度（58.5±6.9°）顯著大於閉鎖式站姿（51.7±4.9°）。結論：不同站姿僅在髖軸最大旋轉角度、身體重心的前後位移與垂直位移及拍頭擺動斜率達顯著差異。改變站姿雖不影響肩—髖軸最大扭轉角度，但卻對髖部動作產生影響；相較於閉鎖式站姿，開放式站姿雙手反拍則須更著重在髖部的旋轉。

Purpose: The purpose of the study was to compare the kinematics of the square and open stance two-handed backhand stroke during acceleration phase. Methods: Eight female tennis players belonging to the national team of Taiwan participated in this study. Two Redlake high-speed cameras (250 Hz) were synchronized to record the three-dimensional two-handed backhand. The images were digitized by Kwon3D and Peak Performance motion analysis systems. Differences between two stances were analyzed by t-test for paired samples. Results: There was no significant difference on the ball velocity between square and open stance. In addition, the displacement of center of gravity in hitting direction was significantly larger in square stance (18.9±5.4 cm) than in open stance (10.4±8.5 cm), but the displacement of center of gravity in vertical direction was significantly larger in open stance (14.3±3.5 cm) than in square stance (7.6±2.7 cm). The hip-axis angle was significantly smaller at instant of acceleration and impact in open stance (86.5±6.2°, 32.5±9.5°) than in square stance (97.6±5.0°, 48.3±9.0°). The maximum hip rotation angle was significantly larger in square stance (58.5±6.9°) than in open stance (51.7±4.9°) during acceleration. Conclusion: There existed significant differences on the maximum hip rotation angle, the displacement for center of gravity and the slope of the racket path between two stances. In addition, there was no significant effect on the shoulder-hip twist angle, but the movement of hip rotation. Furthermore, the open stance two-handed backhand stroke relied on more hip rotation compared to the square stance one.