Signal-To-Noise Ratio Calculations to Validate Sensor Positioning for Facial Muscle Assessment Using Noninvasive Facial Electromyography

Abstract

The evaluation of neuromodulator treatment outcomes can be performed by noninvasive surface-derived facial electromyography (fEMG) which can detect cumulative muscle fiber activity deep to the skin. The objective of the present study is to identify the most reliable facial locations where the motor unit action potentials (MUAPs) of various facial muscles can be quantified during fEMG measurements. The study population consisted of five males and seven females (31.0 [12.9] years, body mass index of 22.15 [1.6] kg/m2). Facial muscle activity was assessed in several facial regions in each patient for their respective muscle activity utilizing noninvasive surface-derived fEMG. Variables of interest were the average root mean square of three performed muscle contractions (= signal) (µV), mean root mean square between those contraction with the face in a relaxed facial expression (= baseline noise) (µV), and the signal to noise ratio (SNR). A total of 1,709 processed fEMG signals revealed one specific reliable location in each investigated region based on each muscle's anatomy, on the highest value of the SNR, on the lowest value for the baseline noise, and on the practicability to position the sensor while performing a facial expression. The results of this exploratory study may help guiding future researchers and practitioners in designing study protocols and measuring individual facial MUAP when utilizing fEMG. The locations presented herein were selected based on the measured parameters (SNR, signal, baseline noise) and on the practicability and reproducibility of sensor placement.

Test-retest reliability of high-resolution surface electromyographic activities of facial muscles during facial expressions in healthy adults: A prospective observational study

“…Any repeated electrode application has also influences on inter-electrode distances and therefore electrode crosstalk variability. The EMG signal is highly sensitive to changes of the electrode positions with respect to the facial muscles ( Frank et al, 2021 ). Therefore, it appears plausible that the test-retest reliability was better for the Kuramoto scheme.…”

Stability of the distal radioulnar joint with and without activation of forearm muscles

“…Electrode placement was chosen anatomically and verified by ultrasound. After identifying the muscle, three distinct locations on the muscle surface were assessed in terms of the best signal strength ( Frank et al., 2021 ; Zaheer et al., 2012 ). sEMG recording was done using Ag/AgCl surface EMG electrodes (Ambu® BlueSensor NF, Columbia, MD, USA) with an interelectrode spacing of 20 mm ( Hermens et al., 2000 ).…”

High Levels of Physical Activity Reduce the Esthetic Durability of Botulinum Toxin Type A: A Controlled Single-Blind Clinical Trial

“…Bipolar surface electrodes, size 3.2 × 2.8 cm (Ag-AgCl disks, Covidien llc, Quebec, Canada), were fixed in the assessed muscles after the skin was cleaned with 70% alcohol, and the reference electrode was placed on the manubrium of the sternum. In the frontalis muscle, the electrodes were attached on the pupillary line, 2 cm above the eyebrow, in the procerus muscle at the cranial end of the nasal bones, and the corrugator supercili muscles at the midpoint of the cranial border of the eyebrow [ 36 ]. Then, participants were asked to perform the following facial expressions in front of a mirror to train their maximum voluntary contraction (MVC) for each facial expression: Forehead frowning (surprised facial expression).…”