MMG Signals Research Articles

The effect of epoch length on time and frequency domain parameters of electromyographic and mechanomyographic signals

The selection of epoch lengths affects the time and frequency resolution of electromyographic (EMG) and mechanomyographic (MMG) signals, as well as decisions regarding the signal processing techniques to use for determining the power density spectrum. No previous studies, however, have examined the effects of epoch length on parameters of the MMG signal. The purpose of this study was to examine the differences between epoch lengths for EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, and MMG MPF from the VL and VM muscles during MVIC muscle actions as well as at each 10% of the time to exhaustion (TTE) during a continuous isometric muscle action of the leg extensors at 50% of MVIC. During the MVIC trial, there were no significant (p > 0.05) differences between epoch lengths (0.25, 0.50, 1.00, and 2.00-s) for mean absolute values for any of the EMG or MMG parameters. During the submaximal, sustained muscle action, however, absolute MMG amplitude and MMG MPF were affected by the length of epoch. All epoch related differences were eliminated by normalizing the absolute values to MVIC. These findings supported normalizing EMG and MMG parameter values to MVIC and utilizing epoch lengths that ranged from 0.25 to 2.00-s.

Investigation of the Relationship Between Electrical Stimulation Frequency and Muscle Frequency Response Under Submaximal Contractions.

Neuromuscular electrical stimulation (NMES) is a common tool that is used in clinical and laboratory experiments and can be combined with mechanomyography (MMG) for biofeedback in neuroprostheses. However, it is not clear if the electrical current applied to neuromuscular tissues influences the MMG signal in submaximal contractions. The objective of this study is to investigate whether the electrical stimulation frequency influences the mechanomyographic frequency response of the rectus femoris muscle during submaximal contractions. Thirteen male participants performed three maximal voluntary isometric contractions (MVIC) recorded in isometric conditions to determine the maximal force of knee extensors. This was followed by the application of nine modulated NMES frequencies (20, 25, 30, 35, 40, 45, 50, 75, and 100 Hz) to evoke 5% MVIC. Muscle behavior was monitored by the analysis of MMG signals, which were decomposed into frequency bands by using a Cauchy wavelet transform. For each applied electrical stimulus frequency, the mean MMG spectral/frequency response was estimated for each axis (X, Y, and Z axes) of the MMG sensor with the values of the frequency bands used as weights (weighted mean). Only with respect to the Z (perpendicular) axis of the MMG signal, the stimulus frequency of 20 Hz did not exhibit any difference with the weighted mean (P = 0.666). For the frequencies of 20 and 25 Hz, the MMG signal displayed the bands between 12 and 16 Hz in the three axes (P < 0.050). In the frequencies from 30 to 100 Hz, the muscle presented a higher concentration of the MMG signal between the 22 and 29 Hz bands for the X and Z axes, and between 16 and 34 Hz bands for the Y axis (P < 0.050 for all cases). We observed that MMG signals are not dependent on the applied NMES frequency, because their frequency contents tend to mainly remain between the 20- and 25-Hz bands. Hence, NMES does not interfere with the use of MMG in neuroprosthesis.

Mechanomyographic responses for the biceps brachii are associated with failure times during isometric force tasks.

In order to characterize the physiological adjustments within the neuromuscular system that contribute to task failure, this study examined the surface mechanomyographic (MMG) response during maximal and submaximal isometric force tasks of the elbow flexors sustained to failure. The time and frequency components of the MMG signal have shown to be influenced by motor unit activation patterns as well as tetanus. Therefore, it was hypothesized that the rate of change for the MMG response would associate with failure times and would be reduced to a similar degree between the two tasks. The isometric force tasks were performed by the dominant elbow flexors of twenty healthy males (age: 25 ± 4 years) and MMG was collected from the biceps brachii. Regression analyses were used to model the relationships between the rates of change for MMG versus failure times. There were high levels of interindividual variability in the response patterns, yet the models demonstrated significant negative associations between the rate of change for the MMG responses and failure times during both tasks (R 2 = 0.41–0.72, P < 0.05). Similarly, the mean MMG amplitude and frequency values were reduced to comparable levels at the failure point of the two tasks. The results of this study demonstrated that force failure is associated with the rate of diminution in the properties of the muscle force twitch.

Real-time continuous recognition of knee motion using multi-channel mechanomyography signals detected on clothes

Mechanomyography (MMG) signal has been recently investigated for pattern recognition of human motion. In theory, it is no need of direct skin contact to be detected and unaffected by changes in skin impedance. So, it is hopeful for developing wearable sensing device with clothes. However, there have been no studies so far to detect MMG signal on clothes and verify the feasibility of pattern recognition. For this study, 4-channel MMG signals were detected on clothes from the thigh muscles of 8 able-bodied participants. The support vector machines (SVM) classifier with 4 common features was used to recognize 6 knee motions and the average accuracy of nearly 88% was achieved. The accuracy can be further improved up to 91% by introducing a new proposed feature of the difference of mean absolute value (DMAV), but not by root mean square (RMS) or mean absolute value (MAV). Furthermore, the first-order Markov chain model was combined with the SVM classifier and it can avoid the misclassifications in some cases. For application to wearable power-assisted devices, this study would promote the developments of more flexible, more comfortable, and minimally obtrusive wearable sensing devices with clothes and recognition techniques of human motion intention.

Reliability of mechanomyographic amplitude measurements for trunk muscles during maximal voluntary isometric contraction

Mechanomyography (MMG) has been used to investigate mechanical characteristics of muscle contraction in clinical and experimental settings. The aim of this study was to determine the test-retest reliability of mechanomyographic amplitude (MMGRMS) measurements as a tool for measuring the maximal voluntary isometric contractions (MVICs) of trunk muscles in healthy participants. There were ten young adults participating in this study. Accelerometers were used to detect surface MMG signals from three trials of 5-s MVICs of the rectus abdominis, external obliques, erector spinae, and multifidus in the vertical, transverse, and longitudinal directions. Intraclass correlation coefficient (ICC), standard error of measurement (SEM), and minimum detectable change were calculated. Good to excellent test-retest reliability of mechanomyographic amplitude (MMGRMS) measurements was achieved for all MVICs of trunk muscles in healthy participants, as indicated by ICCs ranging from 0.99 to 0.64 for MMGRMS of the trunk muscles during MVIC. This study demonstrates that MMG is a reliable measurement to detect the activation amplitudes of trunk muscles during MVIC.

Acute effects of direct inhibitory pressure over the biceps brachii myotendinous junction on skeletal muscle activation and force output

Force (F) reduction is reported with myotendinous junction (MTJ) manipulation. Autogenic inhibition reflex (AIR) activation is supposed to be the main mechanism. Still, its role remains unclear. The study aimed at assessing the effects of MTJ direct inhibitory pressure (DIP) on neuromuscular activation and F in the elbow flexor (agonist) and extensor (antagonist) muscles. After maximum voluntary contraction (MVC) assessment, thirty-five participants randomly performed submaximal contractions at 20, 40, 60, and 80% MVC. Electromyographic (EMG), mechanomyographic (MMG), and F signals were recorded. Protocol was repeated under (i) DIP (10-s pressure on the biceps brachii MTJ) with the elbow at 120° (DIP120), (ii) DIP with the elbow at 180° (DIP180), and (iii) without DIP (Ctrl). Electromechanical delay (EMD) components, EMG and MMG root mean square (RMS), and rate of force development (RFD) were calculated. Independently from the angle, DIP induced decrements in MVC, RFD, and RMS of EMG and MMG signals and lengthened the EMD components in agonist muscles (P<0.05). The DIP-induced decrease in F output of the agonist muscles seems to be possibly due to a concomitant impairment of the neuromuscular activation and a transient decrease in stiffness. After DIP, the antagonist muscle displayed no changes; therefore, the intervention of AIR remains questionable.

Quantitative assessment of swallowing activity by MMG measurement with PVDF film.

Difficulty of swallowing, called dysphagia, leads to aspiration pneumonia which is particularly a big health concern in aging societies. Therefore, prevention and treatment of dysphagia would contribute to extending healthy-life and QOL of elderly people and decreasing healthcare cost. Robotics technologies are expected as one of the effective methods to solve the problem in terms of detecting malfunction in swallowing and recovering swallowing function. The aim of this study is to investigate muscle activity during normal swallowing using mechanomyography (MMG) with PolyVinylidene DiFluoride (PVDF) film which is a ferroelectrics polymer. Measurement of MMG signal during voluntary isometric contraction of the biceps brachii muscle was conducted to confirm whether PVDF film can detect MMG signal. In the experiment, surface electromyography (sEMG) was also measured as a reference to estimate muscle activity for comparison. Then, activities of swallowing muscles during normal swallowing with different volume of bolus were measured using MMG signal. As the result, it was confirmed that swallowing activity can be quantified by the detected MMG signal from different region of neck.

Assessment of elbow spasticity with surface electromyography and mechanomyography based on support vector machine.

The Modified Ashworth Scale (MAS) is the gold standard in clinical for grading spasticity. However, its results greatly depend on the physician evaluations and are subjective. In this study, we investigated the feasibility of using support vector machine (SVM) to objectively assess elbow spasticity based on both surface electromyography (sEMG) and mechanomyography (MMG). sEMG signals and tri-axial accelerometer mechanomyography (ACC-MMG) signals were recorded simultaneously on patients' biceps and triceps when they extended or bended elbow passively. 39 post-stroke patients participated in the study, and were divided into four groups regarding MAS level (MAS=0, 1, 1+ or 2). The three types of features, root mean square (RMS), mean power frequency (MPF), and median frequency (MF), were calculated from sEMG and MMG signal recordings. Spearman correlation analysis was used to investigate the relationship between the features and spasticity grades. The results showed that the correlation between MAS and each of the five features (MMG-RMS of the biceps, MMG-RMS of the triceps, the EMG-RMS of the biceps, EMG-RMS of the triceps, EMG-MPF of the triceps) was significant (p<;0.05). The four spasticity grades were identified with SVM, and the classification accuracy of SVM with sEMG, MMG, sEMG-MMG were 70.9%, 83.3%, 91.7%, respectively. Our results suggest that using the SVM-based method with sEMG and MMG to assess elbow spasticity would be suitable for clinical management of spasticity.

Electromechanical delays during a fatiguing exercise and recovery in patients with myotonic dystrophy type 1.

The partitioning of the electromechanical delay by an electromyographic (EMG), mechanomyographic (MMG) and force combined approach can provide further insight into the electrochemical and mechanical processes involved with skeletal muscle contraction and relaxation. The aim of the study was to monitor by this combined approach the changes in delays' electrochemical and mechanical components throughout a fatiguing task and during recovery in patients with myotonic dystrophy type 1 (DM1), who present at the skeletal muscle level fibres rearrangement, muscle weakness and myotonia, especially in the distal muscles. After assessing maximum voluntary contraction (MVC), 14 male patients with DM1 and 14 healthy controls (HC) performed a fatiguing exercise at 50% MVC until exhaustion. EMG, MMG, and force signals were recorded from tibialis anterior and vastus lateralis muscles. The electromechanical delay during contraction (DelayTOT) and relaxation (R-DelayTOT) components, EMG and MMG root mean square (RMS) and mean frequency (MF) were calculated off-line. The fatiguing exercise duration was similar in both groups. In patients with DM1, delays components were significantly longer compared to HC, especially in the distal muscle during relaxation. Delays components recovered quickly from the fatiguing exercise in HC than in patients with DM1 in both muscles. The alterations in delays observed in DM1 during the fatiguing exercise may indicate that also the lengthening of the electrochemical and mechanical processes during contraction and relaxation could play a role in explaining exercise intolerance in this pathology.

Influence of subcutaneous fat on mechanomyographic signals at three levels of voluntary effort

Introduction This study aims to assess the influence of different skinfold thicknesses (ST) and their relation to the attenuation of the mechanomyographic (MMG) signal at different force levels (maximal voluntary contraction – MVC, 40% of MVC and 70% of MVC) of the rectus femoris muscle. Methods Fifteen volunteers were divided in two groups: ST lower than 10mm (G 35) (7 participants). Student t tests were employed to investigate differences between G 35 regarding MMG analysis parameters (acceleration root mean square – aRMS, zero crossing – ZC, and median frequency – MDF), for the X, Y and Z axes, as well as for the modulus of these three axes. Results We found that thicker layers of body fat act as attenuator filters for the MMG signal [MDFMVC: X (p = 0.005), Z (p = 0.003); MDF70%MVC: X (p = 0.034); ZCMVC: Z (p = 0.037), modulus (p = 0.005); ZC70%MVC: Z (p = 0.047)]. We found significant correlation between ST values and aRMS in three levels, in the Yaxis (p = 0.591), for the group G 35 in 40%MVC (R2 = 0.610), and 70%MVC (R2 = 0.592). The MDF parameter showed correlation with ST values only in the Yaxis in 70%MVC (R2 = 0.700) for G>35. Conclusions We observed MMG signal attenuation in at least one of the parameters analyzed for each level of the rectus femoris muscle force, indicating that MMG signals are significantly attenuated with increasing thickness of the subcutaneous fat layer.

The effect of accelerometer mass in mechanomyography measurements

Mechanomyography (MMG) signals record and quantify low-frequency lateral oscillations of active skeletal muscles. These oscillations reflect the ‘‘mechanical counterpart’’ of the motor unit activity measured by electromyography (EMG). Accelerometers have been commonly used to measure MMG. However, the accelerometer mass can affect the MMG signal. The purpose of this paper was to investigate the relationship of the accelerometer mass and the MMG signal. Thirty-two normal volunteers conducted the maximum voluntary contraction of leg extension. MMG signals were obtained from the rectus femoris muscle using an accelerometer. For each subject, the accelerometer mass was varied from 3, 8, 13, 18, 23 and 28 g. The signals were measured for three seconds with a sampling rate of 1kHz. Results showed that the MMG signal amplitude increased as the accelerometer mass increased. However, the median frequency (MF) of the MMG signal decreased with the increased accelerometer mass. When the accelerometer mass increased from 8 g to 13 g, the amplitude of the MMG signal increased the most, and the MF of the MMG signal decreased the most. However, for accelerometers heavier than 13 g, no significant change was observed in both the amplitude and MF. Based on the present study, the mass of the accelerometer is recommended to not exceed 13 g to properly measure MMG signals.

Time Course of Changes in Neuromuscular Parameters During Sustained Isometric Muscle Actions

Smith, CM, Housh, TJ, Herda, TJ, Zuniga, JM, Camic, CL, Bergstrom, HC, Smith, DB, Weir, JP, Hill, EC, Cochrane, KC, Jenkins, NDM, Schmidt, RJ, and Johnson, GO. Time course of changes in neuromuscular parameters during sustained isometric muscle actions. J Strength Cond Res 30(10): 2697-2702, 2016-The objective of the present study was to identify the time course of changes in electromyographic (EMG) and mechanomyographic (MMG) time and frequency domain parameters during a sustained isometric muscle action of the leg extensors at 50% maximal voluntary isometric contraction. The EMG and MMG signals were measured from the vastus lateralis of 11 subjects to identify when motor unit activation strategies changed throughout the sustained isometric muscle action. The EMG amplitude (muscle activation) had a positive linear relationship (p = 0.018, r = 0.77) that began to increase at the initiation of the muscle action and continued until task failure. Electromyographic frequency (motor unit action potential conduction velocity) and MMG frequency (global motor unit firing rate) had negative quadratic relationships (p = 0.002, R = 0.99; p = 0.015, R = 0.94) that began to decrease at 30% of the time to exhaustion. The MMG amplitude (motor unit activation) had a cubic relationship (p = 0.001, R = 0.94) that increased from 10 to 30% of the time to exhaustion, then decreased from 40 to 70% of the time to exhaustion, and then markedly increased from 70% to task failure. The time course of changes in the neuromuscular parameters suggested that motor unit activation strategies changed at approximately 30 and 70% of the time to exhaustion during the sustained isometric muscle action. These findings indicate that the time course of changes in neuromuscular responses provide insight into the strategies used to delay the effects of fatigue and are valuable tools for quantifying changes in the fatiguing process during training programs or supplementation research.

Muscle- and Mode-Specific Responses of the Forearm Flexors to Fatiguing, Concentric Muscle Actions.

Background: Electromyographic (EMG) and mechanomyographic (MMG) studies of fatigue have generally utilized maximal isometric or dynamic muscle actions, but sport- and work-related activities involve predominately submaximal movements. Therefore, the purpose of the present investigation was to examine the torque, EMG, and MMG responses as a result of submaximal, concentric, isokinetic, forearm flexion muscle actions. Methods: Twelve men performed concentric peak torque (PT) and isometric PT trials before (pretest) and after (posttest) performing 50 submaximal (65% of concentric PT), concentric, isokinetic (60°·s−1), forearm flexion muscle actions. Surface EMG and MMG signals were simultaneously recorded from the biceps brachii and brachioradialis muscles. Results: The results of the present study indicated similar decreases during both the concentric PT and isometric PT measurements for torque, EMG mean power frequency (MPF), and MMG MPF following the fatiguing workbout, but no changes in EMG amplitude (AMP) or MMG AMP. Conclusions: These findings suggest that decreases in torque as a result of fatiguing, dynamic muscle actions may have been due to the effects of metabolic byproducts on excitation–contraction coupling as indicated by the decreases in EMG MPF and MMG MPF, but lack of changes in EMG AMP and MMG AMP from both the biceps brachii and brachioradialis muscles.

Fast, Intelligent and Secure an Embedded Health-care Supervisory System

&lt;p class="IEEEAbtract"&gt;The world of medical supervisory system should remotely monitor various parameters of patients with help of electronics. This work aims at monitoring parameters in fast, intelligent and secure way. The work emphasizes on designing an embedded system which handles critical parameters of patients in hospital/nursing units. The data samples are processed using an ARM based CPU’s and to achieve performance metrics TI RTOS is used and validated. The system generates interrupts based on the priority of each of critical parameters with a threshold in it and enables alarming/warning system. The data is then transferred to IoT layer using a CC3100 TI based SoC for further reference and processing.&lt;/p&gt;In this paper, 4 parameters has been monitored for designing system such as measuring Respiratory rate for human breath, MMG signal for muscle movement, Blood pressure rate as well as Temperature. RTOS helps with scheduling as well as with interrupts also helps Wi-Fi module to work with it. Wi-Fi module provides many security options as WEP, WAP, and WAP2.

Acute effects of static stretching on skeletal muscle relaxation at different ankle joint angles

By combining electromyographic (EMG), mechanomyographic (MMG) and force analysis, the electromechanical delay during muscle relaxation (R-DelayTOT) was partitioned into electrochemical and mechanical components. The study aimed to evaluate the effects of changes in joint angle on R-DelayTOT components during relaxation after electrically evoked contractions before and after static stretching (SS) administration. Nineteen male participants (age 24 ± 3 years; body mass 76.4 ± 8.9 kg; stature 1.78 ± 0.09 m; mean ± SD) were evaluated. Passive torque (T pass) of the plantarflexor muscles was measured at 0°, 10°, and 20° of dorsiflexion to determine joint stiffness. The maximum electrically evoked torque (pT) was also recorded at each angle. During pT, force, EMG and MMG signals were detected for offline calculations of R-DelayTOT and its electrochemical and mechanical components. The same procedures were repeated after SS. With increase in dorsiflexion angle, joint stiffness increased while R-DelayTOT and its mainly mechanical components decreased (from −8 to 20 %, P < 0.05). After SS, joint stiffness decreased (from 16 to 20 %, P < 0.05), while R-DelayTOT and its mainly mechanical components lengthened (from 8 to 28.5 %, P < 0.05). Moreover, post-SS R-DelayTOT and its components decreased with the increase in joint angle (from −13 to 31 %, P < 0.05). The reduction in R-DelayTOT with increase in joint angle could be ascribed to the increase in joint stiffness, and not to alterations of the electrochemical processes during relaxation. SS lengthened R-DelayTOT and its components with a concomitant decrease in joint stiffness. Nevertheless, the reduction of the R-DelayTOT mainly mechanical components seen with dorsiflexion was similar to that before SS.

Mechanomyography signals in spastic muscle and the correlation with the modified Ashworth scale.

The modified Ashworth scale (MAS) is the most widely used measurement technique to assess levels of spasticity. In MAS, the evaluator graduates spasticity considering his/her subjective analysis of the muscular endurance during passive stretching. Therefore, it is a subjective scale. Mechanomyography (MMG) allows registering the vibrations generated by muscle contraction and stretching events that propagate through the tissue until the surface of the skin. With this in mind, this study aimed to investigate possible correlations between MMG signal and muscle spasticity levels determined by MAS. We evaluated 34 limbs considered spastic by MAS, including upper and lower limbs of 22 individuals of both sexes. Simultaneously, the MMG signals of the spastic muscle group (agonists) were acquired. The features investigated involved, in the time domain, the median energy (MMGME) of the MMG Z-axis (perpendicular to the muscle fibers) and, in the frequency domain, the median frequency (MMGmf). The Kruskal-Wallis test (p<;0.001) determined that there were significant differences between intergroup MAS spasticity levels for MMGme. There was a high linear correlation between the MMGme and MAS (R2=0.9557) and also a high correlation as indicated by Spearman test (ρ=0.9856; p<;0.001). In spectral analysis, the Kruskal-Wallis test (p = 0.0059) showed that MMGmf did not present significant differences between MAS spasticity levels. There was moderate linear correlation between MAS and MMGmf (R2=0.4883 and Spearman test [ρ = 0.4590; p <; 0.001]). Between the two investigated features, we conclude that the median energy is the most viable feature to evaluate spasticity due to strong correlations with the MAS.

The influence of myosin heavy chain isoform content on mechanical behavior of the vastus lateralis in vivo

This study examined correlations between type I percent myosin heavy chain isoform content (%MHC) and mechanomyographic amplitude (MMGRMS) during isometric muscle actions. Fifteen (age=21.63±2.39) participants performed 40% and 70% maximal voluntary contractions (MVC) of the leg extensors that included increasing, steady force, and decreasing segments. Muscle biopsies were collected and MMG was recorded from the vastus lateralis. Linear regressions were fit to the natural-log transformed MMGRMS–force relationships (increasing and decreasing segments) and MMGRMS was selected at the targeted force level during the steady force segment. Correlations were calculated among type I%MHC and the b (slopes) terms from the MMGRMS–force relationships and MMGRMS at the targeted force. For the 40% MVC, correlations were significant (P<0.02) between type I%MHC and the b terms from the increasing (r=−0.804) and decreasing (r=−0.568) segments, and MMGRMS from the steady force segment (r=−0.606). Type I%MHC was only correlated with MMGRMS during the steady force segment (P=0.044, r=−0.525) during the 70% MVC. Higher type I%MHC reduced acceleration in MMGRMS (b terms) during the 40% MVC and the amplitude during the steady force segments. The surface MMG signal recorded during a moderate intensity contraction provided insight on the contractile properties of the VL in vivo.

Correlation between spectral and temporal mechanomyography features during functional electrical stimulation

Introduction: Signal analysis involves time and/or frequency domains, and correlations are described in the literature for voluntary contractions. However, there are few studies about those correlations using mechanomyography (MMG) response during functional electrical stimulation (FES) elicited contractions in spinal cord injured subjects. This study aimed to determine the correlation between spectral and temporal MMG features during FES application to healthy (HV) and spinal cord injured volunteers (SCIV). Methods: Twenty volunteers participated in the research divided in two groups: HV (N=10) and SCIV (N=10). The protocol consisted of four FES profiles transcutaneously applied to quadriceps femoris muscle via femoral nerve. Each application produced a sustained knee extension greater than 65o up to 2 min without adjusting FES intensity. The investigation involved the correlation between MMG signal root mean square (RMS) and mean frequency (MF). Results: HV and SCIV indicated that MMGRMS and MMGMF variations were inversely related with -0.12 ≥ r ≥ -0.82. The dispersion between MMGMF and MMGRMS reached 0.50 ≤ r2 ≤ 0.64. Conclusion The increase in MMGRMS and the decrease in MMGMF may be explained by the motor units coherence during fatigue state or by motor neuron adaptation (habituation) along FES application (without modification on parameters).

Fatigue analysis of the quadriceps femoris muscle based on mechanomyography

The aim of this study was to assess quantitative muscle fatigue during isometric and isotonic contractions using a mechanomyography (MMG) and a computational geometry technique known as a convex hull algorithm. Twenty-five male volunteers participated in the experiment. The subjects performed knee flexion and extension exercises on an isokinetic dynamometer. A 3-axis accelerometer (x: longitudinal; y: medial-lateral; z: superior-inferior) was placed on the right rectus femoris muscle. The MMG signal was recorded at a sampling rate of 1 kHz. Each subject performed the maximal knee extension 10 times to determine the 10-repetition maximum torque and maximal isometric contraction at a knee angle of 90°. The results showed that positive correlations were observed between normalized torque and x-direction MMG (linear, r2=0.44), z-direction MMG (linear, r2=0.58), and signal vector magnitude (linear, r2=0.44). The decreases in hull area or volume of MMG signal may result from fatigue due to reductions in motor unit firing rate and increase in muscle thickness. This study evaluated muscular function during fatigue exercises by analyzing the electrical activities of activated skeletal muscle fibers and low-frequency lateral oscillations using accelerometer-based MMG.

Triaxial MMG investigation during FES-induced cycle movements

Spinal cord injury is damage to the spinal cord that results in loss of functions, causes muscle, joint and bone deficits, moreover it increases the muscle tone level. FEScycling is an alternative rehabilitation process to conserve the musculoskeletal system affected by the injury in the functional state. The aim of this study is to get the legs bilaterally synchronized by FES and compare MMG signal responses. The preliminary protocol consists of five consecutive contractions. The first and the last contractions were discarded and the three intermediate contractions were analyzed. A ratio between MMG values of muscle responses during propulsion and return of pedalling phases was calculated for each cycle and each leg. The applied FES profile consisted of pulse and burst on time of 250 us and 5 ms and frequencies of 1000 Hz and 20 Hz, respectively. Results showed that greater MMG RMS values tend to occur during the propulsion phase than in the return phase. MMG Z axis of RLL and MMG X axis of LLL were the axes that presented the greatest ratios. The MMG RMS signal showed that greater values tend to occur during the propulsion phase than in the return phase of the same thigh.