Spatial localization of electromyographic amplitude distributions associated to the activation of dorsal forearm muscles

Abstract

In this study we investigated whether the spatial distribution of surface electromyographic (EMG) amplitude can be used to describe the activation of muscle portions with different biomechanical actions. Ten healthy subjects performed isometric contractions aimed to selectively activate a number of forearm muscles or muscle subportions. Monopolar electromyographic signals were collected with an electrode grid of 128 electrodes placed on the proximal, dorsal portion of the forearm. The monopolar EMG amplitude [root mean square (RMS) value] distribution was calculated for each contraction, and high-amplitude channels were identified through an automatic procedure; the position of the EMG source was estimated with the barycenter of these channels. Each of the contractions tested was associated to a specific EMG amplitude distribution, whose location in space was consistent with the expected anatomical position of the main agonist muscle (or subportion). The position of each source was significantly different from the others in at least one direction (ANOVA; transversally to the forearm: P < 0.01, F = 125.92; longitudinally: P < 0.01, F = 35.83). With such an approach, we could distinguish the spatial position of EMG distributions related to the activation of contiguous muscles [e.g., extensor carpi ulnaris (ECU) and extensor digitorum communis (EDC)], different heads of the same muscle (i.e., extensor carpi radialis (ECR) brevis and longus) and different functional compartments (i.e., EDC, middle, and ring fingers). These findings are discussed in terms of how forces along a given direction can be produced by recruiting population of motor units clustered not only in specific muscles, but also in muscle sub-portions. In addition, this study supports the use of high-density EMG systems to characterize the activation of muscle subportions with different biomechanical actions.

Selectivity of conventional electrodes for recording motor evoked potentials: An investigation with high‐density surface electromyography

“…High‐density surface electromyography (HDsEMG) is a technique that utilizes several small electrodes placed closely over 1 or more muscles. When applied to the forearm, HDsEMG can be used to distinguish EMG amplitude distributions associated with activation of individual wrist extensor muscles . This enables differentiation of MEPs from the extensor carpi radialis (ECR) muscle from those of the extensor digitorum communis (EDC) muscle .…”

Filtered Virtual Reference: A New Method for the Reduction of Power Line Interference With Minimal Distortion of Monopolar Surface EMG

“…For example, largest EMGs were observed over different forearm regions when subjects were asked to isometrically extend their different finger extensor muscles [14]. Regardless of whether contracting any of the finger extensors, EMGs with largest amplitudes were detected by ~20 out of 128 electrodes [14]. As predicted by our theoretical analysis and simulation results, and as suggested experimentally (Fig.…”

“…For large electrode arrays, covering muscles with pinnate geometry or a group of small muscles, EMGs with large amplitude may be detected from different, localised skin regions [14], [27], [30]. For example, largest EMGs were observed over different forearm regions when subjects were asked to isometrically extend their different finger extensor muscles [14].…”

“…Indeed, uneven distribution of standing waves' amplitude has been observed experimentally for muscles with long fibres (e.g. biceps brachii: [25]; forearm muscles: [14]), for muscles whose fibres attach to a broad bone region (e.g. trapezius: [26]) and for muscles with pennate geometry (e.g.…”

“…EMG signals were detected from dorsal, forearm muscles with 96 electrodes arranged in a grid of 12 rows and 8 columns with 10 mm inter-electrode distance (LISiN, Politecnico di Torino, Torino, Italy). Signals were recorded during isometric wrist extension at 10% of the maximum voluntary contraction (see [14] for details). Images were created from the root mean square (RMS) values computed for raw monopolar EMGs and for EMGs conditioned with both VR and FVR methods.…”