• Y. Yamamoto
  • T. Nakamura
  • H. Tsuji
  • T. Yamamoto


The purpose of this work is to propose a skill evaluation of tennis movement based on forearm electrical impedance and its measurement method. We try to evaluate the pattern of movement using the pattern of impedance waveform and the stability of movement using the reproducibility of impedance waveform. It can be intuitively evaluated reproducibility and mobility of serve movement using waveform of forearm electrical impedance (Z). Consequently 4 parameters which show reproducibility and mobility using waveform of Z was defined. We made a trial about principal component analysis of Z during serve and got a scatter diagram of first second principal component about 9 subjects including skilful and beginner players. Then the principal component analysis devided subjects into skilful and beginner players. The measurement method of Z used the four electrodes technique based on constant current(50 k Hz,500 uA). Z changes with the changes of cross sectional area of muscle and blood volume caused by the change of joint angle and acceleration. Hence Z has information of movement. The results of this experiment was as follows. In waveforms of Z during serve with a ball and without a ball, each waveform of a skillful player was very similar to each other, but each waveform of a beginner player was not. Z of a skillful player varied more than that Z of a beginner player, because the movement of a skillful player is larger than that of a beginner player. The advantages of this method are as follows. There is no spatial and temporal limitation for measurement. The subject is scarcely restricted in movement. Although we must select appropriate locations of electrodes in each type of movement, this method can be expected to have applications for various sports.