不同結構網球線自然退磅之探討

Decline of Tension in the Tennis Strings with Different Design

網球拍網線的網壓對於網球選手在控球與回擊力的表現是一項相當重要的因素之一，但是許多網球初學者對不同的網線的認識較少，部分網球選手也並不容易感知到網線網壓的變化。本研究的目的在於了解在不同的網球拍網線結構在不同網壓張力下的變化情形，利用四種基本結構的網線來做實驗。實驗將目前市面上較常被使用的有心線（Wilson Performance）、無心線（Wilson Sensation）、實心線（Kirschbanum Polymax II）及Kevlar材質的四種不同結構的網線，穿與四種不同磅數的網壓網線於相同型式的網球拍上。利用網壓測磅器來收取這些線於兩星期內的自然退磅情形。所得的資料經由處理分析得出一個測量結果趨勢圖和一個退磅百分比趨勢圖。從測量結果的趨勢圖中我們可以很清楚的看出四種不同網線的變化情形。這四種線在穿好線後24小時內很迅速的產生退磅效應，但退磅的程度卻有不同，在從穿好線第50小時後，網球拍網壓的退磅情形就減緩許多。而在退磅百分比的圖表中也得到一些結果：有心線的退磅百分比是最高的，但是隨著網壓的增高，退磅率卻逐漸下降。無心線的退磅百分比是最低的，也代表著這種線的穩定性高，隨著網壓的增高，退磅率卻逐漸上升。實心線的退磅百分比並沒有因網壓的高底而產生較大的變化，其網壓變化都維持在一定的範圍內。Kevlar材質的退磅百分比並不是很高，但實驗結果看出，這種網線是退磅最不明顯的線，在高磅數下，其網壓退磅率也隨之變低，這也就是代表這種線並不具有較佳的延展性。這些結果顯示無論何種結構的網線都有明顯的退磅，然而不同結構的網線，在承受不同的網壓下，其退磅的特性也有明顯的不同。所以建議網球選手針對想要的擊球特性，選擇適合的網壓，搭配該網壓下表現較好的網線。

The tension in the string is one of the importance factors, which affect the performance of a tennis player in the control and power of striking. However, many novice players have little information regarding to the material properties of different strings. In addition, few advanced players have the sharp sensitivity to notice the differences of the string tension. Therefore, the purpose of this study is to investigate the natural declination of the tension in different strings. It is hope that the information can be a reference for choosing a proper sting for the tennis players. Four kinds of the popular strings in the market: Wilson Sensation, Wilson Performance, Kirschbanum Polymax II and Kevlar were investigated for this study. They were strung with four different tensions of 50, 55, 60, and 65 pounds into sixteen brand new rackets with same model. The tensions of these rackets were measured and recorded in the two weeks after strung. The results indicated that four kinds of the strings had the rapidest declination happened in the first day, and then the declination of the tension became decreased afterwards. The relative declinations in tension for Performance decreased with the strung tension increased, and the declinations were the largest in these four kinds of strings. The relative declinations for Kevlar also decreased with the stung tension increased, and the declinations were the smallest in these four kinds of strings. For Sensation, the declinations in tension became more significant with the tension increased. Strings with different material and constructions inhibit different characteristics in tension declinations. The results of this study provided valuable information for choosing proper string and tension of the racket for all tennis players.