In patients suffering from facial nerve paresis, functional deficits of facial muscles are usually evaluated by clinical tests, scores and by means of electromyography. Currently the needle-EMG technique is the Golden Standard, but it is an invasive technique. Different muscle locations can only be examined successively. However, for research in facial nerve paresis therapy an overall view to the facial muscles is necessary to investigate gradual deficits or improvements. Therefore, multi-channel surface EMG technique was developed, measuring EMG activities of different facial muscles simultaneously. Using 48 small Ag/AgCl disc surface electrodes, EMGs were monopolarly recorded by means of a multi-channel EMG system (Biovision, Wehrheim, Germany) with frequency range of 10–700 Hz and 3000 samples/s (resolution 2.44 mV/bit). Surface electrodes were symmetrically placed on the skin above of the M. orbicularis oculi, M. frontalis, M. levator labii, M. zygomaticus, M. orbicularis oris, M. depressor anguli oris, M. depressor labii and M. mentalis according to the topography demonstrated in anatomical textbooks and international recommendations. The M. temporalis and M. masseter were examined too. 30 healthy male healthy volunteers (mean age of 26.0 years, SD 3.2) were involved. They were instructed to perform 30 specific motor tasks. For example, they had to articulate the vowels A, E, I, O, U and perform facial poses like smiling, pressing lips together, frowning. For data processing, the EMGs were visually checked for artefacts and quantified by power spectral analysis. The normalised mean EMG-amplitude was demonstrated in symmetrically arranged bar charts. To evaluate interindividual differences the median of the Spearman's rank correlation coefficient of each test movement was calculated between all volunteers. The results showed characteristic EMG activity patterns during different facial poses and articulation of vowels. Motor tasks which were able to isolate specific muscle regions, to achieve high EMG amplitudes and to show high interindividual correlations were, e. g., puckering lips for the M. orbicularis oris (r=0.94), smiling for the M. zygomaticus (r=0.70), wrinkling the nose for the M. levator labii (r=0.58), moving the lower lip forward for the M. depressor anguli oris (r=0.88) and closing the eyes tightly for the M. orbicularis oculi (r=0.85). Re-examinations of volunteers showed a high retest-reliability. The Spearman coefficient in two re-examinations were r=0.99 and r=0.90 for pressing the lips together and r=0.92 and r=0.95 for smiling.

The presented EMG data are objective and statistically representative EMG characteristics of the facial muscle function and indicate the total range of facial muscle activation which can be used for reference purposes. Thus, an objective evaluation of activation deficits in paretic facial muscles and the characterization of the course of the disease could be possible in the future.