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Abstract

The fast Fourier transforms (FFT) is commonly applied in transformation of electromyography (EMG) signals from the time domain to the frequency domain. However, this technique has a limitation to provide the time-frequency information for EMG signals. This paper presents the analysis of EMG signal for contraction of muscle activity by using spectrogram. Spectrogram is one of the time-frequency representations (TFR) that represents the three-dimensional of the signal with respect to time and frequency in magnitude presentations. The contraction of muscle activity was based on manual lifting of a 5 kg load performed by the right biceps brachii at lifting height of 75 cm and 140 cm. Ten healthy volunteers in fresh condition participated as subjects to acquire raw data of EMG signals. The raw data of EMG signals were then analysed using MATLAB 2011 to obtain the TFR. Based on the TFR, this study obtained the instantaneous RMS Voltage (Vrms(t)) to visualize the trend of the EMG signals performance in window size of 1024. Results of this study evince that the lifting height of 140 cm obtained higher Vrms than 75 cm. It concluded that the application of spectrogram is able to counter the limitation of FFT in providing the time-frequency information for EMG signals.