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Difference between revisions of "Electromyography"
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The signal-to-noise ratio and distortion are two problems that, by altering the recorded signal representation, can modify or hide the information the sEMG signal is meant to convey. | The signal-to-noise ratio and distortion are two problems that, by altering the recorded signal representation, can modify or hide the information the sEMG signal is meant to convey. | ||
'''Noise Characteristics of sEMG''' | '''Noise Characteristics of sEMG:''' Electromagnetic Interference: Noise sources include electromagnetic environmental noise, such as 50 Hz power line interference, often exceeding the sEMG signal amplitude by several magnitudes. Proper differential amplifier design and shielding are crucial to reducing this interference. | ||
Electromagnetic Interference: Noise sources include electromagnetic environmental noise, such as 50 Hz power line interference, often exceeding the sEMG signal amplitude by several magnitudes. Proper differential amplifier design and shielding are crucial to reducing this interference. | |||
Movement Artifacts: Artifacts arise from electrode movement or cable displacement during recording. Flexible electrodes and shielded cables minimize these disturbances, which typically affect frequencies below 20 Hz and can be filtered out without impacting the useful signal band (20–500 Hz). | Movement Artifacts: Artifacts arise from electrode movement or cable displacement during recording. Flexible electrodes and shielded cables minimize these disturbances, which typically affect frequencies below 20 Hz and can be filtered out without impacting the useful signal band (20–500 Hz). | ||
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Intrinsic Randomness: The sEMG signal's quasi-random nature, attributed to motor unit discharge variability, adds complexity. While low-frequency components (0–20 Hz) often reflect noise, high-frequency analysis provides clinically meaningful insights. | Intrinsic Randomness: The sEMG signal's quasi-random nature, attributed to motor unit discharge variability, adds complexity. While low-frequency components (0–20 Hz) often reflect noise, high-frequency analysis provides clinically meaningful insights. | ||
'''Electrodes''' | '''Electrodes:''' Electrodes serve as an interface, converting ionic currents in tissues into electronic signals. Commonly used Ag/AgCl electrodes are reversible and consumable, enabling consistent measurements while avoiding polarization. Proper placement and maintenance are essential for minimizing liquid junction potentials and ensuring signal fidelity. | ||
Electrodes serve as an interface, converting ionic currents in tissues into electronic signals. Commonly used Ag/AgCl electrodes are reversible and consumable, enabling consistent measurements while avoiding polarization. Proper placement and maintenance are essential for minimizing liquid junction potentials and ensuring signal fidelity. | |||
Differential Amplification and CMRR: Differential amplifiers enhance the difference between two electrode inputs while suppressing common-mode noise, such as power line interference. The Common-Mode Rejection Ratio (CMRR) quantifies this efficiency, with optimal designs achieving values of 90–120 dB. | '''Amplifier Design:''' Differential Amplification and CMRR: Differential amplifiers enhance the difference between two electrode inputs while suppressing common-mode noise, such as power line interference. The Common-Mode Rejection Ratio (CMRR) quantifies this efficiency, with optimal designs achieving values of 90–120 dB. | ||
'''Input Impedance:''' High input impedance minimizes signal loss and distortion, ensuring accurate recording. Modern amplifiers achieve input impedances of up to 10<sup>15</sup> ohms, reducing electrode load and preserving signal integrity. | '''Input Impedance:''' High input impedance minimizes signal loss and distortion, ensuring accurate recording. Modern amplifiers achieve input impedances of up to 10<sup>15</sup> ohms, reducing electrode load and preserving signal integrity. | ||
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==Conclusions== | ==Conclusions== | ||
This chapter underscores the critical factors affecting sEMG fidelity, from electrode design to amplifier characteristics and signal processing methods. While challenges such as noise and distortion persist, advancements in technology and methodology enable precise muscle activity analysis, fostering enhanced diagnostic and research applications. | This chapter underscores the critical factors affecting sEMG fidelity, from electrode design to amplifier characteristics and signal processing methods. While challenges such as noise and distortion persist, advancements in technology and methodology enable precise muscle activity analysis, fostering enhanced diagnostic and research applications. | ||
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