Surface EMG cross talk quantified at the motor unit population level for muscles of the hand, thigh, and calf

Author(s)

Germer, Carina M. ^{[1, 2]} ; Farina, Dario ^[3] ; Elias, Leonardo A. ^{[1, 4]} ; Nuccio, Stefano ^[5] ; Hug, Francois ^{[6, 7, 8]} ; Del Vecchio, Alessandro ^[9]

Affiliation

^[1] Univ Estadual Campinas, Ctr Biomed Engn, Neural Engn Res Lab, Campinas - Brazil

^[2] Univ Fed Pernambuco, Dept Bioengn, Recife, PE - Brazil

^[3] Imperial Coll London, Fac Engn, Dept Bioengn, London - England

^[4] Univ Estadual Campinas, Sch Elect & Comp Engn, Dept Elect & Biomed Engn, Campinas - Brazil

^[5] Univ Rome Foro Italico, Dept Movement Human & Hlth Sci, Rome - Italy

^[6] Inst Univ France, Paris - France

^[7] Nantes Univ, Lab Movement Interact Performance, Nantes - France

^[8] Univ Queensland, Sch Biomed Sci, Brisbane, Qld - Australia

^[9] Friedrich Alexander Univ, Fac Engn, Dept Artificial Intelligence Biomed Engn, Erlangen - Germany

• Document type: Journal article
• Source: Journal of Applied Physiology; v. 131, n. 2, p. 808-820, AUG 2021.
• Web of Science Citations: 0

Abstract

Cross talk is an important source of error in interpreting surface electromyography (EMG) signals. Here, we aimed at characterizing cross talk for three groups of synergistic muscles by the identification of individual motor unit action potentials. Moreover, we explored whether spatial filtering (single and double differential) of the EMG signals influences the level of cross talk. Three experiments were conducted. Participants (total 25) performed isometric contractions at 10% of the maximal voluntary contraction (MVC) with digit muscles and knee extensors and at 30% MVC with plantar flexors. High-density surface EMG signals were recorded and decomposed into motor unit spike trains. For each muscle, we quantified the cross talk induced to neighboring muscles and the level of contamination by the nearby muscle activity. We also estimated the influence of cross talk on the EMG power spectrum and intermuscular correlation. Most motor units (80%) generated significant cross-talk signals to neighboring muscle EMG in monopolar recording mode, but this proportion decreased with spatial filtering (50% and 42% for single and double differential, respectively). Cross talk induced overestimations of intermuscular correlation and has a small effect on the EMG power spectrum, which indicates that cross talk is not reduced with high-pass temporal filtering. Conversely, spatial filtering reduced the cross-talk magnitude and the overestimations of intermuscular correlation, confirming to be an effective and simple technique to reduce cross talk. This paper presents a new method for the identification and quantification of cross talk at the motor unit level and clarifies the influence of cross talk on EMG interpretation for muscles with different anatomy. NEW \& NOTEWORTHY We proposed a new method for the identification and quantification of cross talk at the motor unit level. We show that surface EMG cross talk can lead to physiological misinterpretations of EMG signals such as overestimations in the muscle activity and intermuscular correlation. Cross talk had little influence on the EMG power spectrum, which indicates that conventional temporal filtering cannot minimize cross talk. Spatial filter (single and double differential) effectively reduces but not abolish cross talk. (AU)

• FAPESP's process: 17/22191-3 - Effects of sensory and biomechanical manipulations on the neurophysiological control of muscle force: experiments and computer simulations
• Grantee: Leonardo Abdala Elias
• Support Opportunities: Regular Research Grants