Methodology Based on the Continuous Wavelet Transform for Estimation of the Drop Jump Gesture

Abstract

One of the main objectives of sports biomechanics is the improvement of sports performance. The Drop Jump (DJ) is a vertical jump that seeks to evaluate reactive strength capacity, which can also be expressed as the ability to perform the muscle Stretch Shortening Cycle (SSC) quickly [1]. Thus, the interest in studying the EMG signals of some of the main muscles of the lower extremity was born. Different methods of surface Electromyography (sEMG) signal processing have been studied, some of them are focused on amplitude analysis. Nevertheless, this kind of methodology does not provide information about the frequency content of the signal. Therefore, analysis methods focused on spectral analysis has been introduced, for instance the Continuous Wavelet Transform (CWT) [4]. Considering the foregoing, the aim in the present pilot study is the application of CWT as a methodology for sEMG signals processing of high-performance athletes during the contact phase of DJ maneuver. First and foremost, the instants that define the contact phase were identified. Then, the processing of sEMG signals was carried out using the CWT with the Morlet wavelet as mother wavelet. Finally, the scalograms were segmented using Otsu’s method and followed of a post-processing stage to obtain information of the frequency content of the signals. From this methodology, information is obtained on the kinematic behavior of the Center of Mass (CoM) and the knee joint during the contact phase, as well as the muscular behavior in the time and frequency domains. In summary, it is possible to appreciate the benefits of the CWT as a processing methodology for sEMG signals. Also, this methodology has allowed a better understanding of the muscle activity and the kinematic variables during the contact phase of the Drop Jump maneuver. Nevertheless, observing the total contact phase makes it difficult to appreciate details in the muscle activity during the eccentric phase.