Target Site of Prepulse Inhibition of the Trigeminal Blink Reflex in Humans.

Despite the clinical significance of prepulse inhibition (PPI), the mechanisms are not well understood. Herein, we present our investigation of PPI in the R1 component of electrically induced blink reflexes. The effect of a prepulse was explored with varying prepulse test intervals (PTIs) of 20-600 ms in 4 females and 12 males. Prepulse-test combinations included the following: stimulation of the supraorbital nerve (SON)-SON [Experiment (Exp) 1], sound-sound (Exp 2), the axon of the facial nerve-SON (Exp 3), sound-SON (Exp 4), and SON-SON with a long trial-trial interval (Exp 5). Results showed that (1) leading weak SON stimulation reduced SON-induced ipsilateral R1 with a maximum effect at a PTI of 140 ms, (2) the sound-sound paradigm resulted in a U-shaped inhibition time course of the auditory startle reflex (ASR) peaking at 140 ms PTI, (3) facial nerve stimulation showed only a weak effect on R1, (4) a weak sound prepulse facilitated R1 but strongly inhibited SON-induced late blink reflexes (LateRs) with a similar U-shaped curve, and (5) LateR in Exp 5 was almost completely absent at PTIs >80 ms. These results indicate that the principal sensory nucleus is responsible for R1 PPI. Inhibition of ASR or LateR occurs at a point in the startle reflex circuit where auditory and somatosensory signals converge. Although the two inhibitions are different in location, their similar time courses suggest similar neural mechanisms. As R1 has a simple circuit and is stable, R1 PPI helps to clarify PPI mechanisms.SIGNIFICANCE STATEMENT Prepulse inhibition (PPI) is a phenomenon in which the startle response induced by a startle stimulus is suppressed by a preceding nonstartle stimulus. This study demonstrated that the R1 component of the trigeminal blink reflex shows clear PPI despite R1 generation within a circuit consisting of the trigeminal and facial nuclei, without startle reflex circuit involvement. Thus, PPI is not specific to the startle reflex. In addition, PPI of R1, the auditory startle reflex, and the trigeminal late blink reflex showed similar time courses in response to the prepulse test interval, suggesting similar mechanisms regardless of inhibition site. R1 PPI, in conjunction with other paradigms with different prepulse-test combinations, would increase understanding of the underlying mechanisms.

Estimating Rotational Acceleration in Shoulder and Elbow Joints Using a Transformer Algorithm and a Fusion of Biosignals.

In the present study, we used a transformer model and a fusion of biosignals to estimate rotational acceleration in elbow and shoulder joints. To achieve our study objectives, we proposed a mechanomyography (MMG) signal isolation technique based on a variational mode decomposition (VMD) algorithm. Our results show that the VMD algorithm delivered excellent performance in MMG signal extraction compared to the commonly used technique of empirical mode decomposition (EMD). In addition, we found that transformer models delivered estimates of joint acceleration that were more precise than those produced by mainstream time series forecasting models. The average R2 values of transformer are 0.967, 0.968, and 0.935, respectively. Finally, we found that using a fusion of signals resulted in more precise estimation performance compared to using MMG signals alone. The differences between the average R2 values are 0.041, 0.053, and 0.043, respectively. Taken together, the VMD isolation method, the transformer algorithm and the signal fusion technique described in this paper can be seen as supplying a robust framework for estimating rotational acceleration in upper-limb joints. Further study is warranted to examine the effectiveness of this framework in other musculoskeletal contexts.

Mechanomyography-Based Metric Scale for Spasticity: A Pilot Descriptive Observational Study.

(1) Background: The Modified Ashworth Scale (MAS) is commonly used clinically to evaluate spasticity, but its qualitative nature introduces subjectivity. We propose a novel metric scale to quantitatively measure spasticity using mechanomyography (MMG) to mitigate these subjective effects. (2) Methods: The flexor and extensor muscles of knee and elbow joints were assessed with the Modified Ashworth Scale (MAS) during the acquisition of mechanomyography (MMG) data. The median absolute amplitude of the MMG signals was utilized as a key descriptor. An algorithm was developed to normalize the MMG signals to a universal gravitational (G) acceleration scale, aligning them with the limits and range of MAS. (3) Results: We evaluated 34 lower and upper limbs from 22 volunteers (average age 39.91 ± 13.77 years) of both genders. Polynomial regression provided the best fit (R2 = 0.987), with negligible differences (mean of 0.001 G) between the MAS and MMG. We established three numerical sets for the median, minimum, and maximum MMG(G) values corresponding to each MAS range, ensuring consistent alignment of the Modified Ashworth levels with our proposed scale. (4) Conclusions: Muscle spasticity can now be quantitatively and semi-automatically evaluated using our algorithm and instrumentation, enhancing the objectivity and reliability of spasticity assessments.

Targeting Transcutaneous Spinal Cord Stimulation Using a Supervised Machine Learning Approach Based on Mechanomyography.

Transcutaneous spinal cord stimulation (tSCS) provides a promising therapy option for individuals with injured spinal cords and multiple sclerosis patients with spasticity and gait deficits. Before the therapy, the examiner determines a suitable electrode position and stimulation current for a controlled application. For that, amplitude characteristics of posterior root muscle (PRM) responses in the electromyography (EMG) of the legs to double pulses are examined. This laborious procedure holds potential for simplification due to time-consuming skin preparation, sensor placement, and required expert knowledge. Here, we investigate mechanomyography (MMG) that employs accelerometers instead of EMGs to assess muscle activity. A supervised machine-learning classification approach was implemented to classify the acceleration data into no activity and muscular/reflex responses, considering the EMG responses as ground truth. The acceleration-based calibration procedure achieved a mean accuracy of up to 87% relative to the classical EMG approach as ground truth on a combined cohort of 11 healthy subjects and 11 patients. Based on this classification, the identified current amplitude for the tSCS therapy was in 85%, comparable to the EMG-based ground truth. In healthy subjects, where both therapy current and position have been identified, 91% of the outcome matched well with the EMG approach. We conclude that MMG has the potential to make the tuning of tSCS feasible in clinical practice and even in home use.

Train-of-four ratio, counts and post tetanic counts with the Tetragraph electromyograph in comparison to mechanomyography.

Automated EMG devices to detect compound muscle action potentials from the adductor pollicis muscle in response to ulnar nerve stimulation, regardless of hand and thumb position, may serve as a better reference ("gold standard") for clinical assessment of neuromuscular function than traditional mechanomyography (MMG) systems that need custom design and validation in lab settings. This evaluation compared the TetraGraph EMG system against a validated MMG device to investigate the accuracy and repeatability of this quantitative EMG monitor for detecting onset, offset and deep neuromuscular block. Simultaneous muscle action potential recordings from the EMG neuromuscular monitor and muscle contractions from an in-house developed MMG monitor in response to ulnar nerve stimulation were obtained from patients having elective surgery requiring neuromuscular block. Train-of-four (TOF) ratios, TOF counts, and post-tetanic counts (PTCs) were recorded simultaneously from the same hand muscle and compared. In total, 685 pairs of simultaneous TOF ratios were evaluated. The mean difference (bias) of TOF ratios between devices was small (- 2.1%). TOF counts from 285 data pairs were within a count of 2 or less 96% of the time. During deep block, PTC comparisons from 215 data pairs were within a count of 2 or less 95% of the time. These findings, along with prior EMG device evaluations, indicate that real-time EMG neuromuscular monitoring technology to detect muscle action potentials from the adductor pollicis in the clinical setting is closely aligned with the force of thumb contraction determined from MMG. The accuracy of quantitative EMG technology of the TetraGraph EMG system lends strong support for this monitor, along with other similarly validated EMG monitors, to become a clinical standard for all phases (onset, depth and reversal) of neuromuscular block in clinical practice.

Evolution of a laboratory mechanomyograph.

Mechanomyography is currently the accepted laboratory reference standard for quantitative neuromuscular blockade monitoring. Mechanomyographs are not commercially available. Previously, a mechanomyograph was built by our laboratory and used in several clinical studies. It was subsequently redesigned to improve its usability and functionality and to accommodate a wider range of hand sizes and shapes using an iterative design process. Each version of the redesigned device was initially tested for usability and functionality in the lab with the investigators as subjects without electrical stimulation. The redesigned devices were then assessed on patients undergoing elective surgery under general anesthesia without neuromuscular blocking drugs. Since the patients were not paralyzed, the expected train-of-four ratio was 1.0. The device accuracy and precision were represented by the train-of-four ratio mean and standard deviation. If issues with the device's useability or functionality were discovered, changes were made, and the redesign processes repeated. The final mechanomyograph design was used to collect 2,362 train-of-four ratios from 21 patients. The mean and standard deviation of the train-of-four ratios were 0.99 ± 0.030. Additionally, the final mechanomyograph design was easier to use and adjust than the original design and fit a wider range of hand sizes. The final design also reduced the frequency of adjustments and the time needed for adjustments, facilitating data collection during a surgical procedure.

Comparative performance of stimpod electromyography with mechanomyography for quantitative neuromuscular blockade monitoring.

PURPOSE: The purpose of this study was to compare the Stimpod electromyograph neuromuscular blockade monitor to mechanomyography, which is widely considered to be the reference standard. METHODS: The Stimpod electromyograph was used with its designated electrode array on the same hand as the mechanomyograph. Pairs of train-of-four measurements were recorded every 0.5-2 min. When the train-of-four count was zero on the electromyograph monitor, pairs of post tetanic count measurements were recorded every 2.5 min, instead of train-of-four measurements. Measurements were recorded from immediately after induction of anesthesia until just before emergence. Stimulation current was set to 60 mA with a duration of 200 microsec. The mechanomyography recording system recorded each twitch waveform for analysis. High resolution electromyograph waveforms were also recorded using a datalogger accessory provided by the manufacturer, facilitating inspection of individual waveforms. The administration of neuromuscular blocking drugs was left up to the discretion of the anesthesia care team. RESULTS: Twenty-three patients contributed 1,088 data pairs suitable for analysis. Bland-Altman analysis of 415 pairs of train-of-four ratios showed a bias of 0.028 and limits of agreement of -0.18 and 0.24. Two hundred seventy-three train-of-four count data pairs were compared by Cohen's quadratically weighted kappa which was calculated to be 0.44, indicating moderate agreement. Three hundred thirty-eight post tetanic count data pairs were compared by Cohen's quadradically weighted kappa which was calculated to be 0.80, indicating substantial agreement. CONCLUSION: The electromyograph produced results that were comparable to the mechanomyograph.

Performance Fatigability and Neuromuscular Responses Are Not Joint Angle Specific Following a Sustained Isometric Forearm Flexion Task Anchored to a High Perceptual Intensity in Women.

OBJECTIVES: To examine the effects of joint angle (JA) on maximal voluntary isometric contractions (MVIC) and neuromuscular responses following a sustained, isometric forearm flexion task anchored to a rating of perceived exertion (RPE) of 8 (RPE=8). METHODS: Nine women (age: 20.7±2.9 yrs; height: 168.8±7.2 cm; body mass: 66.3±6.8 kg) performed 2,3s forearm flexion MVICs at JAs of 75°, 100°, and 125° prior to and following a sustained, isometric forearm flexion task anchored to RPE=8 to task failure (torque reduced to zero) at JA100. Electromyographic (EMG) and mechanomyographic (MMG) signals were recorded from the biceps brachii. RESULTS: The MVIC at JA100 (collapsed across Time) was significantly greater (p<0.05) than JA75 and JA125. The pre-test MVIC was significantly greater (p<0.001) than the post-test. For EMG amplitude (AMP) and EMG mean power frequency (MPF), pre-test values were significantly greater (p<0.05) than the post-test values, with no differences between JAs. For MMG AMP and MMG MPF, there were no significant (p>0.05) differences between Time or JAs. Pre-test neuromuscular efficiency (normalized MVIC/normalized EMG AMP) was significantly greater (p=0.005) than post-test. CONCLUSION: Following a sustained, isometric forearm flexion task anchored to RPE=8 at JA100, the fatigue-induced MVIC and neuromuscular responses were not affected by JA.

Assessing Quadriceps Muscle Contraction Using a Novel Surface Mechanomyography Sensor during Two Neuromuscular Control Screening Tasks.

Electromyography (EMG) is the clinical standard for capturing muscle activation data to gain insight into neuromuscular control, yet challenges surrounding data analysis limit its use during dynamic tasks. Surface mechanomyography (sMMG) sensors are novel wearable devices that measure the physical output of muscle excursion during contraction, which may offer potential easy application to assess neuromuscular control. This study aimed to investigate sMMG detection of the timing patterns of muscle contraction compared to EMG. Fifteen healthy participants (mean age = 31.7 ± 9.1 y; eight males and seven females) were donned with EMG and sMMG sensors on their right quadriceps for simultaneous data capture during bilateral deep squats, and a subset performed three sets of repeated unilateral partial squats. No significant difference in the total duration of contraction was detected by EMG and sMMG during bilateral (p = 0.822) and partial (p = 0.246) squats. sMMG and EMG timing did not differ significantly for eccentric (p = 0.414) and concentric (p = 0.462) phases of muscle contraction during bilateral squats. The sMMG magnitude of quadriceps excursion demonstrated excellent intra-session retest reliability for bilateral (ICC3,1 = 0.962 mm) and partial (ICC3,1 = 0.936 mm, n = 10) squats. The sMMG sensors accurately and consistently provided key quadriceps muscle performance metrics during two physical activities commonly used to assess neuromuscular control for injury prevention, rehabilitation, and exercise training.

Effect of Forearm Postures and Elbow Joint Angles on Elbow Flexion Torque and Mechanomyography in Neuromuscular Electrical Stimulation of the Biceps Brachii.

Neuromuscular electrical stimulation plays a pivotal role in rehabilitating muscle function among individuals with neurological impairment. However, there remains uncertainty regarding whether the muscle's response to electrical excitation is affected by forearm posture, joint angle, or a combination of both factors. This study aimed to investigate the effects of forearm postures and elbow joint angles on the muscle torque and MMG signals. Measurements of the torque around the elbow and MMG of the biceps brachii (BB) muscle were conducted in 36 healthy subjects (age, 22.24 ± 2.94 years; height, 172 ± 0.5 cm; and weight, 67.01 ± 7.22 kg) using an in-house elbow flexion testbed and neuromuscular electrical stimulation (NMES) of the BB muscle. The BB muscle was stimulated while the forearm was positioned in the neutral, pronation, or supination positions. The elbow was flexed at angles of 10°, 30°, 60°, and 90°. The study analyzed the impact of the forearm posture(s) and elbow joint angle(s) on the root-mean-square value of the torque (TQRMS). Subsequently, various MMG parameters, such as the root-mean-square value (MMGRMS), the mean power frequency (MMGMPF), and the median frequency (MMGMDF), were analyzed along the longitudinal, lateral, and transverse axes of the BB muscle fibers. The test-retest interclass correlation coefficient (ICC21) for the torque and MMG ranged from 0.522 to 0.828. Repeated-measure ANOVAs showed that the forearm posture and elbow flexion angle significantly influenced the TQRMS (p < 0.05). Similarly, the MMGRMS, MMGMPF, and MMGMDF showed significant differences among all the postures and angles (p < 0.05). However, the combined main effect of the forearm posture and elbow joint angle was insignificant along the longitudinal axis (p > 0.05). The study also found that the MMGRMS and TQRMS increased with increases in the joint angle from 10° to 60° and decreased at greater angles. However, during this investigation, the MMGMPF and MMGMDF exhibited a consistent decrease in response to increases in the joint angle for the lateral and transverse axes of the BB muscle. These findings suggest that the muscle contraction evoked by NMES may be influenced by the interplay between actin and myosin filaments, which are responsible for muscle contraction and are, in turn, influenced by the muscle length. Because restoring the function of limbs is a common goal in rehabilitation services, the use of MMG in the development of methods that may enable the real-time tracking of exact muscle dimensional changes and activation levels is imperative.

A Wireless Multi-Layered EMG/MMG/NIRS Sensor for Muscular Activity Evaluation.

A wireless multi-layered sensor that allows electromyography (EMG), mechanomyography (MMG) and near-infrared spectroscopy (NIRS) measurements to be carried out simultaneously is presented. The multi-layered sensor comprises a thin silver electrode, transparent piezo-film and photosensor. EMG and MMG measurements are performed using the electrode and piezo-film, respectively. NIRS measurements are performed using the photosensor. Muscular activity is then analyzed in detail using the three types of data obtained. In experiments, the EMG, MMG and NIRS signals were measured for isometric ramp contraction at the forearm and cycling exercise of the lateral vastus muscle with stepped increments of the load using the layered sensor. The results showed that it was possible to perform simultaneous EMG, MMG and NIRS measurements at a local position using the proposed sensor. It is suggested that the proposed sensor has the potential to evaluate muscular activity during exercise, although the detection of the anaerobic threshold has not been clearly addressed.

Mechanomyographic Analysis for Muscle Activity Assessment during a Load-Lifting Task.

The purpose of this study was to compare electromyographic (EMG) with mechanomyographic (MMG) recordings during isometric conditions, and during a simulated load-lifting task. Twenty-two males (age: 25.5 ± 5.3 years) first performed maximal voluntary contractions (MVC) and submaximal isometric contractions of upper limb muscles at 25%, 50% and 75% MVC. Participants then executed repetitions of a functional activity simulating a load-lifting task above shoulder level, at 25%, 50% and 75% of their maximum activity (based on MVC). The low-frequency part of the accelerometer signal (<5 Hz) was used to segment the six phases of the motion. EMG and MMG were both recorded during the entire experimental procedure. Root mean square (RMS) and mean power frequency (MPF) were selected as signal extraction features. During isometric contractions, EMG and MMG exhibited similar repeatability scores. They also shared similar RMS vs. force relationship, with RMS increasing to 75% MVC and plateauing to 100%. MPF decreased with increasing force to 75% MVC. In dynamic condition, RMSMMG exhibited higher sensitivity to changes in load than RMSEMG. These results confirm the feasibility of MMG measurements to be used during functional activities outside the laboratory. It opens new perspectives for future applications in sports science, ergonomics and human-machine interface conception.

Mechanomyography Signal Pattern Recognition of Knee and Ankle Movements Using Swarm Intelligence Algorithm-Based Feature Selection Methods.

Pattern recognition of lower-limb movements based on mechanomyography (MMG) signals has a certain application value in the study of wearable rehabilitation-training devices. In this paper, MMG feature selection methods based on a chameleon swarm algorithm (CSA) and a grasshopper optimization algorithm (GOA) are proposed for the pattern recognition of knee and ankle movements in the sitting and standing positions. Wireless multichannel MMG acquisition systems were designed and used to collect MMG movements from four sites on the subjects thighs. The relationship between the threshold values and classification accuracy was analyzed, and comparatively high recognition rates were obtained after redundant information was eliminated. When the threshold value rose, the recognition rates from the CSA fluctuated within a small range: up to 88.17% (sitting position) and 90.07% (standing position). However, the recognition rates from the GOA drop dramatically when increasing the threshold value. The comparison results demonstrated that using a GOA consumes less time and selects fewer features, while a CSA gives higher recognition rates of knee and ankle movements.

Time course of changes in torque and neuromuscular parameters during a sustained isometric forearm flexion task to fatigue anchored to a constant rating of perceived exertion.

OBJECTIVE: This study examined the time course of changes in torque and electromyographic (EMG) and mechanomyographic (MMG) responses during a sustained isometric task anchored to a constant perception of exertion (RPE). METHODS: Twelve college-aged men performed an isometric forearm flexion task to failure anchored to RPE=7 (OMNI-RES scale). The amplitude (AMP) and frequency (MPF) of the EMG and MMG signals from the biceps brachii were recorded. Repeated measures ANOVAs were used to examine differences for the normalized (%MVIC) torque and neuromuscular parameters. RESULTS: The time to task failure (TTF) was 678.0±468.1s. Torque decreased significantly (p<0.001, ηp2=0.774) across time and all subjects reduced torque to zero. Post-hoc comparisons indicated that the torque values from 20-100% TTF were less than the value at 10% TTF. There were no significant (p>0.05) changes from 10-100% TTF for the EMG and MMG parameters. CONCLUSION: We hypothesize that RPE was maintained by various mechanisms throughout the task: group III/IV afferent neurons, adequate blood flow, and a combination of reduced contractile efficiency, collective afferent feedback (group III/IV afferents) from muscles involved with forearm flexion, and motivation that resulted in an initial decrease, plateau, and final decline in torque to zero, respectively.

The influence of chronic training status on the mechanical behavior of the vastus lateralis during repetitive trapezoidal contractions.

OBJECTIVES: To examine maximal strength and fatigability of the knee extensors, and mechanomyographic amplitude (MMGRMS)-force relationships of the vastus lateralis (VL) during repetitive muscle actions for 5 aerobically-(AT), 5 resistance-trained-(RT), and 5 sedentary (SED) individuals. METHODS: Participants performed maximal voluntary contractions before (MVCPRE) and after (MVCPOST) attempting 20 isometric trapezoidal muscle actions at 50% MVCPRE. MMG was recorded from the VL. b terms (slopes) were calculated from the natural log-transformed MMGRMS-force relationships for each participant (increasing and decreasing segments). MMGRMS was averaged during steady force. RESULTS: RT had greater MVCPRE (P<0.001) and MVCPOST (P=0.001-0.004) than AT and SED. Only AT completed 20 muscle actions and exhibited no decrease in MVCPOST (P=0.149). The b terms were greater for RT than AT during the increasing segment of the first contraction (P=0.001) and decreasing segment of the last contraction (P=0.033). The b terms were also greater for RT (P=0.006) during the increasing than decreasing segment for the first contraction. MMGRMS during steady force was greater during the last contraction when collapsed across training status (P=0.021). CONCLUSION: Knee extensor MVC and fatigability, and motor unit control strategies for the VL during a series of repetitive contractions were influenced by chronic training status.

Short-term effects of two different recovery strategies on muscle contractile properties in healthy active men: A randomised cross-over study.

The aim of this study was to compare the immediate effects of cold-water immersion (CWI) and hot-water immersion (HWI) versus passive resting after a fatigue-induced bout of exercise on the muscle contractile properties of the Vastus Medialis (VM). We conducted a randomised cross-over study involving 28 healthy active men where muscle contractile properties of the VM wer recorded using Tensiomyography (TMG) before and after CWI, HWI or passive resting and up to one-hour post-application. The main outcomes obtained were muscle displacement and velocity of deformation according to limb size (Dmr and Vdr). Our results showed a significant effect of time (F(3.9,405) =32.439; p <0.001; η2p =0.29) and the interaction between time and temperature (F(7.9,405) =5.814; p <0.001; η2p=0.13) on Dmr but no for temperature alone (F(2,81) =2.013; p =0.14; η2p=0.04) while for Vdr, both time (F(5.2,486) =23.068; p <0.001 η2p = 0.22) and temperature (F(2,81) =4.219; p = 0.018; η2p= 0.09) as well as the interaction (F(10.4,486) =7.784; p <0.001; η2p =0.16) were found significant. Compared to CWI, HWI increased Dmr post-application and Vdr both post-application as well as 15 and 45' thereafter. These findings suggest that applying HWI could be a valid alternative to CWI to promote muscle recovery.

The interest of 100 versus 200 Hz tetanic stimulations to quantify low levels of residual neuromuscular blockade with mechanomyography: a pilot study.

A more sensitive method than the train-of-four ratio seems required to detect low levels of residual neuromuscular blockade before tracheal extubation. The goal of the study was to determine the potential benefit of 5 s of 100 versus 200 Hz tetanic stimulation to quantify the residual block with mechanomyography in anesthetised patients. Twenty informed and consenting 18- to 80-year-old patients undergoing nose surgery were included. On the left hand, neuromuscular transmission was continuously monitored by acceleromyography. On the right side, a new mecanomyographic device (Isometric Thumb Force©) recorded the force of thumb adduction (N) developed during 5 s of 100- and 200 Hz tetanic stimulations of the ulnar nerve at three consecutive times: baseline before inducing the neuromuscular blockade, at the time of contralateral train-of-four ratio 0.9 recovery, and 3 min after additional sugammadex reversal. Tetanic Fade Ratios (TFR = F residual/F max) were compared between 100 and 200 Hz stimulations using Student's t test. At the time of TOF ratio 0.9 recovery, both 100 and 200 Hz TFR were significantly decreased compared to baseline (0.61 and 0.16 on average, respectively, p < 0.0001). The 200 Hz TFR was significantly lower than the 100 Hz TFR (p < 0.0001). There were no differences between baseline and post-reversal TFR. The 200 Hz TFR has the potential to better describe low levels of residual neuromuscular blockade than the TOF ratio and 100 Hz TFR and would benefit from further investigations. Retrospectively registered in the Australian and New Zealand Clinical Trials Registry ACTRN12619000273189.

Assessment of muscle activity using electrical stimulation and mechanomyography: a systematic review.

This research has proved that mechanomyographic (MMG) signals can be used for evaluating muscle performance. Stimulation of the lost physiological functions of a muscle using an electrical signal has been determined crucial in clinical and experimental settings in which voluntary contraction fails in stimulating specific muscles. Previous studies have already indicated that characterizing contractile properties of muscles using MMG through neuromuscular electrical stimulation (NMES) showed excellent reliability. Thus, this review highlights the use of MMG signals on evaluating skeletal muscles under electrical stimulation. In total, 336 original articles were identified from the Scopus and SpringerLink electronic databases using search keywords for studies published between 2000 and 2020, and their eligibility for inclusion in this review has been screened using various inclusion criteria. After screening, 62 studies remained for analysis, with two additional articles from the bibliography, were categorized into the following: (1) fatigue, (2) torque, (3) force, (4) stiffness, (5) electrode development, (6) reliability of MMG and NMES approaches, and (7) validation of these techniques in clinical monitoring. This review has found that MMG through NMES provides feature factors for muscle activity assessment, highlighting standardized electromyostimulation and MMG parameters from different experimental protocols. Despite the evidence of mathematical computations in quantifying MMG along with NMES, the requirement of the processing speed, and fluctuation of MMG signals influence the technique to be prone to errors. Interestingly, although this review does not focus on machine learning, there are only few studies that have adopted it as an alternative to statistical analysis in the assessment of muscle fatigue, torque, and force. The results confirm the need for further investigation on the use of sophisticated computations of features of MMG signals from electrically stimulated muscles in muscle function assessment and assistive technology such as prosthetics control.

Task-specific performance fatigability and the bilateral deficit during isokinetic leg extensions.

OBJECTIVES: The purpose of the present study was to compare the fatigue-induced changes in performance fatigability, bilateral deficit, and patterns of responses for the electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF), during unilateral and bilateral maximal, fatiguing leg extensions. METHODS: Nine men (Mean±SD; age =21.9±2.4 yrs; height =181.8±11.9 cm; body mass =85.8±6.2 kg) volunteered to perform 50 consecutive maximal, bilateral (BL), unilateral dominant (DL), and unilateral non-dominant (NL) isokinetic leg extensions at 180°·s-1, on 3 separate days. Electromyographic and MMG signals from both vastus lateralis (VL) muscles were recorded. Repeated measures ANOVAs were utilized to examine mean differences in normalized force, EMG AMP, EMG MPF, MMG AMP, MMG MPF and the bilateral deficit. RESULTS: The results demonstrated a Condition × Repetition interaction for normalized force (p=0.004, η2p=0.222) and EMG MPF (p=0.034, η2p=0.214) and main effects for Repetition for EMG AMP (p=0.019, η2p=0.231), MMG AMP (p<0.001, η2p=0.8550), MMG MPF (p=0.009, η2p=0.252), and the bilateral deficit (p<0.001, η2p=0.366). CONCLUSIONS: The findings demonstrated less performance fatigability during the BL than the unilateral tasks, likely due to a reduced relative intensity via interhemispheric inhibition that attenuated the development of excitation-contraction coupling failure during the BL task.

Fatigue effect on cross-talk in mechanomyography signals of extensor and flexor forearm muscles during maximal voluntary isometric contractions.

OBJECTIVE: This paper presents the analyses of the fatigue effect on the cross-talk in mechanomyography (MMG) signals of extensor and flexor forearm muscles during pre- and post-fatigue maximum voluntary isometric contraction (MVIC). METHODS: Twenty male participants performed repetitive submaximal (60% MVIC) grip muscle contractions to induce muscle fatigue and the results were analyzed during the pre- and post-fatigue MVIC. MMG signals were recorded on the extensor digitorum (ED), extensor carpi radialis longus (ECRL), flexor digitorum superficialis (FDS) and flexor carpi radialis (FCR) muscles. The cross-correlation coefficient was used to quantify the cross-talk values in forearm muscle pairs (MP1, MP2, MP3, MP4, MP5 and MP6). In addition, the MMG RMS and MMG MPF were calculated to determine force production and muscle fatigue level, respectively. RESULTS: The fatigue effect significantly increased the cross-talk values in forearm muscle pairs except for MP2 and MP6. While the MMG RMS and MMG MPF significantly decreased (p<0.05) based on the examination of the mean differences from pre- and post-fatigue MVIC. CONCLUSION: The presented results can be used as a reference for further investigation of cross-talk on the fatigue assessment of extensor and flexor muscles' mechanic.