This study aimed to investigate the effects of knee flexion during the preparation phase of a serve on the tennis serve performance, using inertial sensors. Thirty-two junior tennis players were divided into two groups based on their maximum knee flexion during the preparation phase of serve: Smaller (SKF) and Greater (GKF) Knee Flexion. Their racket velocity, racket height, and knee extension velocity were compared during the tennis serve. Inertial sensors tracked participants’ shank, thigh, and racket motions while performing five first, flat, and valid serves. Knee flexion was analysed during the preparation phase of serve, knee extension velocity after this phase, racket velocity just before ball impact, and racket height at impact. Pre-impact racket velocity (mean difference [MD] = 3.33 km/h, p = 0.004) and the knee extension velocity (MD = 130.30 °/s, p = 0.012) were higher in the GKF than SKF; however, racket impact height was not different between groups (p = 0.236). This study’s findings support the importance of larger knee flexion during the preparation phase of serve-to-serve performance. This motion should be seen as a contributor to racket velocity.

中文翻译：

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膝关节屈曲对中级网球运动员网球发球能力的影响

本研究旨在使用惯性传感器研究发球准备阶段膝关节屈曲对网球发球性能的影响。32 名青少年网球运动员在发球准备阶段根据他们的最大膝关节屈曲度分为两组：小 (SKF) 和大 (GKF) 膝关节屈曲。在网球发球过程中比较了他们的球拍速度、球拍高度和膝盖伸展速度。惯性传感器跟踪参与者的小腿、大腿和球拍的动作，同时执行五次先发、平发和有效发球。分析了发球准备阶段的膝关节屈曲、此阶段后的膝伸速度、击球前的球拍速度和击球时的球拍高度。冲击前球拍速度（平均差 [MD] = 3.33 km/h，p= 0.004) 和膝关节伸展速度 (MD = 130.30 °/s, p = 0.012) 在 GKF 中高于 SKF；然而，各组之间的球拍撞击高度没有差异（p = 0.236）。这项研究的结果支持在发球比赛准备阶段更大的膝关节屈曲的重要性。这种运动应该被视为球拍速度的一个贡献者。