以慣性感測器分析擊球時機對於網球選手運動表現之影響

Abstract

目的：在網球比賽中，優秀選手的腳步移位較快，能夠準確地掌握擊球的時機，而贏得比賽的勝利。目前還沒有一個客觀量化分析擊球時機的方法，通常以教練主觀的方式判斷。因此本研究透過慣性感測器分析網球選手在移位擊球過程中的擊球時機，並研究擊球時機對運動表現的影響。方法：實驗參與者為16名大專網球校隊的男選手，分別在持拍手及雙腳配戴慣性感測器，接者以16球/分、18球/分及20球/分的頻率送球，進行網球專項測驗，以球速和準確度評估選手的運動表現。其中6位實驗參與者各進行一場單打模擬比賽，總共收集三場比賽的數據分析擊球時機與球速及得分之間的關係。結果：透過慣性感測器可以量化分析網球選手的擊球時機，網球專項測驗的結果顯示，擊球頻率從16球/分增加到20球/分，擊球時機從788毫秒顯著下降至702毫秒 (p<.05)，準確度則從3.36分顯著降低到2.10分 (p<.05)，但球速則沒有明顯變化，擊球頻率與擊球時機有高度相關 (r=-.800)，擊球時機與準確度有高度相關性 (r=.660)。在比賽的過程中，勝負選手之間的擊球時機並無明顯差異，但是得分 (770毫秒) 與失分 (754毫秒) 之間的擊球時機有顯著的差異 (p<.001)，擊球時機與球速有高度相關性 (r=.788)、與得分呈現中度相關性 (r=.351)，球速與得分呈現中度相關性 (r=.430)。討論：本研究成功地利用慣性感測器量化網球選手的擊球時機，擊球時機的變化確實與擊球頻率的改變有關，選手的運動表現也會因為擊球時機的改變而受影響，而最先受到影響的是擊球準確度。在比賽過程中，選手在腳步到位的情況下擊球時機較高，能夠打出速度較快的球，球速越快愈容易得分。選手的身高、握拍方式及打球習慣都可能影響擊球時機的長短，未來需要進一步釐清這些因素的影響。未來擊球時機可以用於選手狀態評估、疲勞偵測及戰術分析等不同層面的應用，提高選手的運動表現。結論：透過慣性感測器能夠量化分析網球選手的擊球時機，當擊球頻率增加時，擊球時機會減少，準確度也會降低。在比賽的過程中，勝負選手之間的擊球時機並無明顯差異，但是得分與失分之間的擊球時機有顯著的差異，顯示擊球時機會影響網球選手的運動表現，因此，擊球時機可當作評估網球選手運動表現的指標。

Purpose: In tennis, the elite players have faster footwork and are able to accurately time their shots to win the game. Currently, there is no objective method to quantify the timing of shots, and it is usually judged subjectively by the coach. Therefore, this study was conducted to analyze the stroke timing of tennis players in the process of moving to hit the ball through inertial sensors and to study the effect of stroke timing on sports performance. Methods: The participants were 16 male players from the college tennis team, who wore inertial sensors on their racket hand and both feet. They then underwent tennis-specific tests with ball speeds of 16, 18, and 20 balls per minute to evaluate their sports performance in terms of ball speed and accuracy. Six of the participants also played three singles matches to collect data on the relationship between shot timing , ball speed and scores. Results: The inertial sensor was used to quantify the stroke timing of the tennis players. The results showed that the stroke frequency increased from 16 to 20 balls/min, the stroke timing decreased significantly from 788 ms to 702 ms (p<.05), and the accuracy decreased significantly from 3.36 to 2.10 (p<.05), but the ball speed did not change significantly. There was a high correlation between stroke frequency and stroke timing (r=-.800) and between stroke timing and accuracy (r=.660). During the matches, there was no significant difference in stroke timing between winners and losers, but there was a significant difference in stroke timing between scored (770 ms) and unearned runs (754 ms, p<.001). There was a high correlation between stroke timing and ball speed (r=.788), a moderate correlation between ball speed and runs scored (r=.351), and a moderate correlation between stroke timing and score (r=.430). The ball speed showed moderate correlation with the score (r=.430). Discussion: This study successfully used inertial sensors to quantify the stroke timing of tennis players. The change in stroke timing was indeed related to the change in hitting frequency, and the athletic performance of players was also affected by the change in stroke timing, and the first to be affected was the accuracy of the stroke. During a match, players with better footwork have a higher chance of hitting the ball faster, and the faster the ball is hit, the easier it is to score. A player's height, grip and playing habits may affect the length of the stroke, and these factors need to be further clarified in the future. In the future, stroke timing can be used for different applications such as condition assessment, fatigue detection and tactical analysis to improve athletic performance of tennis players. Conclusion: The inertial sensor can quantify a tennis player's stroke timing. As the frequency of shots increases, the stroke timing and accuracy decreases. There is no significant difference in stroke timing between winners and losers during the match, but there is a significant difference in stroke timing between points scored and points allowed, indicating that stroke timing affects a tennis player's athletic performance, and therefore, stroke timing can be used as an indicator to assess a tennis player's athletic performance.