Among tennis coaches and players, the standard volley and drop volley are considered basically similar, but muscles need to be relaxed (deactivation) just at the moment of impact when hitting the drop volley. However, this is not evidence-based. The aim of this study was to clarify racket head trajectory and muscle activity during the drop volley and to compare them with those of the standard volley. We hypothesized that 1) the racket head would move less forward for the drop volley than for the standard volley and 2) the wrist and elbow muscles be relaxed for the drop volley at the time of ball impact. Eleven male college students with sufficient tennis experience volunteered to participate in this study. Wireless EMG sensors recorded activation of the four arm muscles. Each subject performed the standard volley or the drop volley with both a forehand and a backhand from a position near the net. Four high speed video cameras (300 Hz) were set up on the court to measure ball speed and racket head trajectory. Returned ball speed of the drop volley was significantly lower than that of the standard volley (p < 0.05). The racket head moved less forward than in the standard volley, supporting the first hypothesis. Muscle activity of the drop volley, just before and after ball impact for both the forehand and backhand, was lower than that of the standard volley. However, the activity was in the form of a gradual increase as impact time approached, rather than a sudden deactivation (relaxation), which did not support the second hypothesis. For the drop volley, lower muscle activity in the forearm enabled a softer grip and thus allowed a "flip" movement of the racket to diminish the speed of the returned ball.

中文翻译：

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网球标准截击和下垂截击的拍头轨迹和肌肉活动的差异。

在网球教练员和球员中，标准截击和截击截击被认为基本相似，但在击打截击截击时，肌肉需要在撞击瞬间放松（失活）。然而，这不是基于证据的。这项研究的目的是澄清在下落截击过程中的球拍头轨迹和肌肉活动，并将它们与标准截击进行比较。我们假设 1) 与标准截击相比，下垂截击的球拍头向前移动得更少，2) 在击球时手腕和肘部肌肉在下垂截击时会放松。11 名具有足够网球经验的男大学生自愿参加了这项研究。无线 EMG 传感器记录了四个手臂肌肉的激活情况。每个受试者从靠近网的位置用正手和反手进行标准截击或截击。球场上设置了四台高速摄像机（300Hz），用于测量球速和拍头轨迹。落地截击的回球速度明显低于标准截击（p < 0.05）。球拍头向前移动的幅度小于标准截击，支持第一个假设。在正手和反手击球前后，空投截击的肌肉活动低于标准截击的肌肉活动。然而，随着撞击时间的临近，该活动呈逐渐增加的形式，而不是突然停用（松弛），这不支持第二个假设。对于空投截击，