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EMG signals detection and processing for on-line control of functional electrical stimulation
C Frigo1, M Ferrarin, W Frasson
1Centro di Bioingegneria, Fnd. Don Gnocchi I.R.C.C.S.-Politecnico di Milano, Milan, Italy. frigo@biomed.polimi.it
Summary
Optimizing surface EMG signal acquisition for functional neuromuscular electrical stimulation requires careful electrode placement and signal processing. Placing recording electrodes outside stimulation electrodes and using a comb filter with blanking windowing best reduced artifacts and improved signal quality.
Area of Science:
- Biomedical Engineering
- Neuroscience
- Rehabilitation Technology
Background:
- Surface electromyography (EMG) signals from voluntary muscle activation are crucial for controlling functional neuromuscular electrical stimulation (FNES).
- Effective FNES control necessitates minimizing stimulus artifacts and non-voluntary muscle contributions (M-waves) through optimal electrode configuration and signal processing.
- Accurate EMG signal detection is vital for reliable FNES system performance.
Purpose of the Study:
- To investigate the impact of recording electrode positioning and orientation relative to stimulation electrodes on surface EMG signal quality.
- To evaluate the effectiveness of a comb filter, with and without blanking windowing, in reducing stimulus artifacts and M-waves.
- To define and implement signal-to-noise ratio (SNR) and efficiency index metrics for assessing optimal configurations and filtering techniques.
Main Methods:
- Systematic evaluation of six recording electrode orientations and six locations relative to stimulation electrodes.
- Application of a comb filter, with and without a blanking window, to remove stimulus-correlated signal components.
- Quantification of signal quality using defined signal-to-noise ratio and efficiency index.
Main Results:
- Recording electrodes placed within stimulation electrodes yielded optimal results with a perpendicular orientation.
- The best overall signal-to-noise ratio and efficiency were achieved when recording electrodes were positioned externally to stimulation electrodes, with a longitudinal orientation.
- Employing a blanking window prior to comb filtering significantly enhanced performance in artifact reduction.
Conclusions:
- Electrode placement and orientation significantly influence the quality of surface EMG signals for FNES control.
- External electrode placement with longitudinal orientation, combined with comb filtering and blanking windowing, provides the most effective method for artifact reduction and signal enhancement.
- These findings offer practical guidelines for optimizing EMG-controlled FNES systems.