Browsing by Author "Mora Tola, Esteban Javier"

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Assessing the SNR influence in the estimation of the mean frequency of lower limbs sEMG signals
(2018) Rojas Bustos, Andrés Bolívar; Mora Tola, Esteban Javier; Minchala Ávila, Luis Ismael; Wong de balzan , Sara Null; Farfán Bernal, Ángel Bolívar
The mean frequency of the power spectrum (MNF) is commonly used to describe the frequency content of an electromyographic (EMG) signal. The objective of this study is to determine the minimum/desirable signal to noise ratio (SNR) value to achieve a reliable measurement of the MNF in superficial EMG (sEMG) signals of lower limbs during gait. To this end, measurements of MNF and SNR were taken in nine muscles of 21 subjects, and recorded signals were contaminated with different noise levels. The minimum threshold of a desirable SNR was determined using the K-means algorithm. A lower bound of 5.51 dB was determined as the SNR value for sEMG acquisition, while 12.28 dB is the desirable SNR value for recording sEMG signals. The methodology presented throughout this paper helps in the determination of the minimum SNR value necessary to validate the sEMG acquisition process that can be used, for example, as a control signal for identifying motion intention in the development of control systems devoted for a lower limb exoskeleton.
Mean frequency and noise from patients with pathologies in lower limbs
(Institute of Electrical and Electronics Engineers Inc., 2020) Minchala Ávila, Luis Ismael; Mora Tola, Esteban Javier; Wong de balzan , Sara Null; Astudillo Salinas, Darwin Fabián; Vázquez Rodas, Andrés Marcelo; Cárdenas León, Verónica Vanessa; Ayavaca Tapia, Luz María
Raw electromyography (EMG) signals are useful for several purposes in the analysis of muscles in both clinical and engineering applications. For instance, muscles fatigue is, typically, assessed by the mean frequency (MNF) of the EMG signal. Previous research works have shown that there is a positive correlation between the signal to noise ratio (SNR) of the EMG signal and its MNF value. The aim of this work is to determine and compare MNF in subjects with impairments in the lower limbs. Measurements of the MNF and the SNR were performed in nine muscles of six pathologic subjects, which were compared with a similar database of subjects without apparent pathologies. The MNF value was estimated using the power spectral density. The SNR for pathologic patients database was higher (17.28±1.67 dB) with respect to the database of subjects without apparent pathologies (12.86±1.71 dB). Subjects with pathologies in the lower limbs presented a decrease in the average value of the MNF.