Concentric-ring electrode systems for noninvasive detection of single motor unit activity

Abstract

New recording techniques for detecting surface electromyographic (EMG) signals based on concentric-ring electrodes are proposed in this paper. A theoretical study of the two-dimensional (2-D) spatial transfer function of these recording systems is developed both in case of rings with a physical dimension and in case of line rings. Design criteria for the proposed systems are presented in relation to spatial selectivity. It is shown that, given the radii of the rings, the weights of the spatial filter can be selected in order to improve the rejection of low spatial frequencies, thus increasing spatial selectivity. The theoretical transfer functions of concentric systems are obtained and compared with those of other detection systems. Signals detected with the ring electrodes and with traditional one-dimensional and 2-D systems are compared. The concentric-ring systems show higher spatial selectivity with respect to the traditional detection systems and reduce the problem of electrode location since they are invariant to rotations. The results shown are very promising for the noninvasive detection of single motor unit (MU) activities and decomposition of the surface EMG signal into the constituent MU action potential trains.

Classification of the Systems Used in Surface Electromyographic Signal Detection according to the Degree of Isotropy

“…The behaviors of the isotropic detection systems as a function of the ber orientation were also examined [13]. However, the sensitivity of the BiTDD [14] and the MKF [15] systems to the muscle ber orientation has never been examined.…”

“…It has been shown that highly anisotropic, approximately isotropic [11,12] and isotropic systems [13] are very sensitive [12], less sensitive [11,12] and not sensitive [13], respectively, to the muscle ber direction. A comparative study showed that amplitude and spectral variables of surface EMG signals are less affected by the ber direction if almost isotropic detection systems are used than if anisotropic ones are used [1].…”

Nonlinear surface EMG analysis to detect changes of motor unit conduction velocity and synchronization

“…For this reason, past research efforts in the surface EMG field were mainly devoted to the development of processing techniques in time and frequency domain, which gave indications about the global EMG activity, without aiming at an analysis at the single MU level. Although, recently, techniques for noninvasive assessment of single MU properties have been proposed and refined (4,6,8), their applicability is still limited by the need of complex detection systems, to low-contraction levels, and controlled laboratory conditions for signal recording. Thus the extraction of global information from the surface EMG signal remains of paramount importance in many applications, such as sport and occupational medicine, rehabilitation, and basic and applied physiology.…”

Evaluation of Laplacian Diaphragm Electromyographic Recordings in a Static Inspiratory Maneuver

“…In the present study during both BHM and SIM, power spectrum of Laplacian EMGdi signal was more distributed in frequency, contained in a broader frequency range compared to bipolar EMGdi power spectrum. Because of their physical design, Laplacian electrode presents enhanced spatial selectivity, features which are reflected in its spatial transfer function [12]. The use of a Laplacian electrode in sEMG recordings can improve the study of motor unit action potential trains [12,13] and reduce the problem of location and orientation of the fibers related to the use of bipolar disc electrode configuration [12].…”