Surface electromyogram (EMG) has a relatively large pick-up volume, reflecting the activity of muscle tissue placed quite far from the electrodes. This could be beneficial when the global muscle activity is of interest, but it is a limitation when selective information is needed. The EMG from muscles that are neighbors of the one of interest is called crosstalk. Its interpretation, identification, quantification and removal have been the objectives of many works in the literature. However, it is still considered as an open problem, with effects that are difficult to predict. In this paper, the problem of crosstalk is discussed and the main literature is reviewed. Finally, a few recent techniques are introduced that are potentially relevant to quantify or reduce it.

Crosstalk in surface electromyogram: literature review and some insights

Muscle oximetry based on near-infrared spectroscopy (NIRS) and electromyography (EMG) techniques in adherent clothing might be used to monitor the muscular activity of selected muscle groups while exercising. The fusion of these wearable technologies in sporting garments can allow the objective assessment of the quality and the quantity of the muscle activity as well as the continuous monitoring of exercise programs. Several prototypes integrating EMG and NIRS have been developed previously; however, most devices presented the limitations of not measuring regional muscle oxyhemoglobin saturation and did not embed textile sensors for EMG. The purpose of this study was to compare regional muscle oxyhemoglobin saturation and surface EMG data, measured under resting and dynamic conditions (treadmill run and strength exercises) by a recently developed wearable integrated quadriceps muscle oximetry/EMG system adopting smart textiles for EMG, with those obtained by using two “gold standard” commercial instrumentations for EMG and muscle oximetry. The validity and agreement between the wearable integrated muscle oximetry/EMG system and the “gold standard” instrumentations were assessed by using the Bland-Altman agreement plots to determine the bias. The results support the validity of the data provided by the wearable electronic garment developed purposely for the quadriceps muscle group and suggest the potential of using such device to measure strength and endurance exercises in vivo in various populations.

https://www.mdpi.com/1424-8220/20/17/4664/pdf

Validation of Fabric-Based Thigh-Wearable EMG Sensors and Oximetry for Monitoring Quadriceps Activity during Strength and Endurance Exercises.

Objective.Surface electromyography (EMG) decomposition techniques can be used to establish human-machine interfacing (HMI), but most investigations are implemented offline due to the computational load of the approach. Here, we generalize the offline decomposition algorithm to identify the motor unit (MU) activities in real time, and we propose a MU-based approach for online simultaneous and proportional control of multiple motor tasks.Approach.High-density surface EMG signals recorded from forearm muscles were decomposed into motor unit spike trains (MUST) with the proposed decomposition method. The MUSTs were first pooled into clusters in the calibration phase and the cumulative discharges of active MUs in each group were extracted as the control signal for each motor task. Then the subjects were instructed to control a virtual cursor with multiple motor tasks involving grasp and wrist movements. Fifteen able-bodied subjects and two patients with limb deficiency participated in the experiments to validate the proposed control scheme.Main results.On average, over 20 MUSTs were identified in real time with an estimated decomposition accuracy > 85%. The cumulative discharge in each pool was highly correlated with the activation of the specific motion (R=0.93±0.05). Moreover, the proposed MU-based method had superior performance in online tests than conventional myo-control methods based on global EMG features.Significance.These results indicate the feasibility of real-time neural decoding in a non-invasive way. Moreover, the superior performance in online tests proves the potential of the MU-based approach for the simultaneous and proportional control, promoting the application of EMG decomposition for HMI systems.

Simultaneous and proportional control of wrist and hand movements by decoding motor unit discharges in real time.

Skeletal muscle is considered as a near-constant volume system, and the contractions of the muscle are related to the changes in tissue thickness Assessment of the skeletal muscle contractile parameters such as maximum contraction thickness ( T h ), contraction time ( T c ), contraction velocity ( V c ), sustain time ( T s ), and half-relaxation ( T r ) provides valuable information for various medical applications This paper presents a single-element wearable ultrasonic sensor (WUS) and a method to measure the skeletal muscle contractile parameters in A-mode ultrasonic data acquisition The developed WUS was made of double-layer polyvinylidene fluoride (PVDF) piezoelectric polymer films with a simple and low-cost fabrication process A flexible, lightweight, thin, and small size WUS would provide a secure attachment to the skin surface without affecting the muscle contraction dynamics of interest The developed WUS was employed to monitor the contractions of gastrocnemius (GC) muscle of a human subject The GC muscle contractions were evoked by the electrical muscle stimulation (EMS) at varying EMS frequencies from 2 Hz up to 30 Hz The tissue thickness changes due to the muscle contractions were measured by utilizing a time-of-flight method in the ultrasonic through-transmission mode The developed WUS demonstrated the capability to monitor the tissue thickness changes during the unfused and fused tetanic contractions The tetanic progression level was quantitatively assessed using the parameter of the fusion index (FI) obtained In addition, the contractile parameters ( T h , T c , V c , T s , and T r ) were successfully extracted from the measured tissue thickness changes In addition, the unfused and fused tetanus frequencies were estimated from the obtained FI-EMS frequency curve The WUS and ultrasonic method proposed in this study could be a valuable tool for inexpensive, non-invasive, and continuous monitoring of the skeletal muscle contractile properties

Ultrasound Measurement of Skeletal Muscle Contractile Parameters Using Flexible and Wearable Single-Element Ultrasonic Sensor.

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 sig...

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

Crosstalk in myographic signals is a major hindrance to the understanding of local information related to individual muscle function. This review aims to analyse the problem of crosstalk in electromyography and mechanomyography. An initial search of the SCOPUS database using an appropriate set of keywords yielded 290 studies, and 59 potential studies were selected after all the records were screened using the eligibility criteria. This review on crosstalk revealed that signal contamination due to crosstalk remains a major challenge in the application of surface myography techniques. Various methods have been employed in previous studies to identify, quantify and reduce crosstalk in surface myographic signals. Although correlation-based methods for crosstalk quantification are easy to use, there is a possibility that co-contraction could be interpreted as crosstalk. High-definition EMG has emerged as a new technique that has been successfully applied to reduce crosstalk. The phenomenon of crosstalk needs to be investigated carefully because it depends on many factors related to muscle task and physiology. This review article not only provides a good summary of the literature on crosstalk in myographic signals but also discusses new directions related to techniques for crosstalk identification, quantification and reduction. The review also provides insights into muscle-related issues that impact crosstalk in myographic signals.

A review on crosstalk in myographic signals

Skeletal muscles contribute to the movement produced in the human body. They are therefore of vital importance for the study of muscles in various applications of movement including exercise, sports, prosthesis, rehabilitation, etc. The movement produced by skeletal muscles can be analyzed through various techniques like mechanomyography (MMG) and electromyography (EMG). MMG is a novel technique to assess skeletal muscle function through the oscillations produced during muscle contractions. MMG advocates well for its reliability, performance, and ease in application to other presently used techniques. MMG employs several types of sensors to observe vibrations in skeletal muscles. These sensors vary widely from application to type of movement and muscle. This review provides a comprehensive chunk of information on MMG sensor selection according to its placement, muscle function and condition, and limb movement and application. Recommendations for the choice of MMG sensor are given through extensive literature search over here.

Choice Of Mechanomyography Sensors For Diverse Types Of Muscle Activities

This systematic review aims to categorically analyses the literature on the assessment of biceps brachii (BB) muscle activity through mechanomyography (MMG). The application of our search criteria to five different databases identified 319 studies. A critical review of the 48 finally selected records, revealed the diversity of protocols and parameters that are employed in MMG-based assessments of BB muscle activity. The observations were categorized into the following: muscle torque, fatigue, strength and physiology. The available information on the muscle contraction protocol, sensor(s), MMG signal parameters and obtained results were then tabulated based on these categories for further analysis. The review affirms that - 1) MMG is suitable for skeletal muscle activity assessment and can be employed potentially for further investigation of the BB muscle activity and condition (e.g., force, torque, fatigue, and contractile properties), 2) a majority of the records focused on static contractions of the BB, and the analysis of dynamic muscle contractions using MMG is thus a research gap, and 3) very few studies have focused on the analysis of BB muscle activity under externally stimulated contractions. Taken together, the findings of this review on BB activity assessment using MMG affirm the potential of MMG as an alternative tool.

A systematic review of muscle activity assessment of the biceps brachii muscle using mechanomyography.

Mechanomyography (MMG) signals can be used to study and analyze skeletal muscles. It retains its potential application in various fields including athletics, sports, medicine and prosthetic control. MMG signals do exhibit crosstalk from adjacent muscles. The measurement of crosstalk in MMG signals could be beneficial for the study of muscle mechanics. Hence, this research contributes to the development of a standalone application (APP) to measure crosstalk in MMG signals coming from human forearm muscles during various wrist postures. The application has been developed on National Instruments LabVIEW software version 14.0. Peak cross correlations have been used as a measure of crosstalk between neighboring muscles. The results produced by APP while measuring crosstalk in MMG signals are very close to literature. Hence the results for APP have been validated by previous studies. The APP can be used for both forms of MMG data either stored in the form of tdms files or real-time signals. MMG signals are acquired, displayed, processed and finally used for measurement of crosstalk. All the steps are done automatically in the APP. Hence APP cannot only save time to measure crosstalk through other tedious methods but it also provides a source of MMG data validation in a real-time environment.

Development of a Standalone Application to Measure Crosstalk in MMG Signals from Forearm Muscles during Wrist Postures

OBJECTIVE To analyse the influence of muscle fibre axis on the degree of crosstalk in mechanomyographic (MMG) signals during sustained isometric forearm flexion, pronation and supination exercises performed at 80% maximum voluntary contraction (MVC) at an elbow joint angle of 90°. METHODS MMG signals in longitudinal, lateral and transverse directions of muscle fibres were recorded from the elbow flexors of twenty-five male subjects using triaxial accelerometers. Cross-correlation coefficients were used to quantify the degree of crosstalk in all nine possible pairs of fibre axes, all muscle pairs and all exercises. RESULTS MMG root mean square (RMS) was statistically significant among the fibre axes (p<0.05, η2=0.17- 0.34) except for biceps brachii and brachioradialis in supination and brachialis in flexion. Overall mean crosstalk values in the three muscle pairs (biceps brachii & brachialis, brachialis & brachioradialis and brachioradialis & biceps brachii) were found to be 6.09-52.17%, 4.01-61.42% and 2.16-51.85%, respectively. Crosstalk values showed statistical significance among all nine axes pairs (p<0.05, η2=0.16-0.51) except for biceps brachii & brachialis during pronation. The transverse axes pair generated the lowest mean crosstalk values (2.16-9.14%). CONCLUSION MMG signals recorded using accelerometers from the transverse axes of muscle fibres in the elbow flexors are unique and yield the least amount of crosstalk.

Analysis of the crosstalk in mechanomyographic signals along the longitudinal, lateral and transverse axes of elbow flexor muscles during sustained isometric forearm flexion, supination and pronation exercises.

Irsa Talib

Papers

A review on crosstalk in myographic signals

Choice Of Mechanomyography Sensors For Diverse Types Of Muscle Activities

A systematic review of muscle activity assessment of the biceps brachii muscle using mechanomyography.

Development of a Standalone Application to Measure Crosstalk in MMG Signals from Forearm Muscles during Wrist Postures

Analysis of the crosstalk in mechanomyographic signals along the longitudinal, lateral and transverse axes of elbow flexor muscles during sustained isometric forearm flexion, supination and pronation exercises.