High-resolution surface electromyographic activities of facial muscles during mimic movements in healthy adults: A prospective observational study

Abstract

ObjectivesSurface electromyography (sEMG) is a standard tool in clinical routine and clinical or psychosocial experiments also including speech research and orthodontics to measure the activity of selected facial muscles to objectify facial movements during specific facial exercises or experiments with emotional expressions. Such muscle-specific approaches neglect that facial muscles act more as an interconnected network than as single facial muscles for specific movements. What is missing is an optimal sEMG setting allowing a synchronous measurement of the activity of all facial muscles as a whole.MethodsA total of 36 healthy adult participants (53% women, 18–67 years) were included. Electromyograms were recorded from both sides of the face using an arrangement of electrodes oriented by the underlying topography of the facial muscles (Fridlund scheme) and simultaneously by a geometric and symmetrical arrangement on the face (Kuramoto scheme). The participants performed a standard set of different facial movement tasks. Linear mixed-effects models and adjustment for multiple comparisons were used to evaluate differences between the facial movement tasks, separately for both applied schemes. Data analysis utilized sEMG amplitudes and also their maximum-normalized values to account for amplitude differences between the different facial movements.ResultsSurface electromyography activation characteristics showed systematic regional distribution patterns of facial muscle activation for both schemes with very low interindividual variability. The statistical significance to discriminate between the different sEMG patterns was good for both schemes (significant comparisons for sEMG amplitudes: 87.3%, both schemes, normalized values: 90.9%, Fridlund scheme, 94.5% Kuramoto scheme), but the Kuramoto scheme performed considerably superior.ConclusionFacial movement tasks evoke specific patterns in the complex network of facial muscles rather than activating single muscles. A geometric and symmetrical sEMG recording from the entire face seems to allow more specific detection of facial muscle activity patterns during facial movement tasks. Such sEMG patterns should be explored in more clinical and psychological experiments in the future.

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

“…On day t1 two sessions were performed with a time lag of about 20 min. The row data of t1 were already presented in the previous publication ( Mueller et al, 2022 ). The same two sessions with the same time lag were repeated on day t2 14 days later ( Figure 1 ).…”

“…The study included the same 36 healthy adult volunteers as published recently ( Mueller et al, 2022 ). Nineteen women and 17 men were included (age range: 18–67 years).…”

“…The sEMG protocol was published recently ( Mueller et al, 2022 ). Briefly, a multi-channel EMG system (gain: 100, frequency range 10–1,861 Hz; sampling rate 4,096/s; resolution: 5.96 nV/bit; DeMeTec, Langgöns, Germany) was used for the sEMG recordings using monopolarly connected reusable surface electrodes (Ag-AgCl discs, diameter of 4 mm, DESS052606, GVB-geliMED, Bad Segeberg Germany).…”

“…As an alternative, Kuramoto et al (2019) recommended to even cover the complete face by using 21 sEMG electrodes in an EEG-like arrangement. Recently, we showed that a geometric and symmetrical sEMG recording from the entire face like it is recommended by Kuramoto et al (2019) seems to allow a more specific distinction of facial muscle activity patterns during various facial expression tasks than the more frequently applied scheme by Fridlund and Cacioppo ( Mueller et al, 2022 ).…”

“…Therefore, we wanted to study the test-retest reliability of both the sEMG electrode schemes of Fridlund and Cacioppo and of Kuramoto et al (2019) in the same healthy probands as in the previous study ( Mueller et al, 2022 ). Both schemes were applied simultaneously during specific facial expressions.…”