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Acquiring biopotentials with fidelity using low-cost circuits is a significant challenge in biomedical instrumentation. In this perspective, our goal is to investigate the characteristics of the widely applied AD8232®, an analog front-end for biopotential acquisition. We designed and evaluated circuits to acquire the most common biosignals: electrocardiogram (ECG), electromyogram (EMG), and electroencephalogram (EEG). Our findings show that the circuit is suitable for ECG and EMG instrumentation, although it has limitations for EEG signals, particularly concerning the gain. The entire project of the boards is also a contribution of this work as we intend to corroborate open-source do-it-yourself biomedical instrumentation.

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

Introduction Military police activity individuals performing operational activity remain 12 hours using mandatory safety equipment. This work aimed to verify the electromyographic response in operational military police officers before and after a cycle of two working days. Methods Forty-four male individuals were evaluated, with an average age of 34.59 ± 8.05. The used protocol consisted in the evaluation of paravertebral muscles and rectus abdominis muscles in a maximum isometric voluntary contraction test (MVC) during trunk extension movements, starting from the sitting position. Moreover, the Roland-Morris functional evaluation questionnaire and the Corlett and Manenica diagram for painful areas were used. An electromyograph with 16 pre-set channels was used. Signals were processed in time (EMGME) and spectral (EMGMF) domains, using the MatLab® program. The Shapiro-Wilk test and Wilcoxon Signed Ranks Test were applied. Statistical analyses were performed through the SPSS v21.0 software and Microsoft Office Excel 2010, considering p < 0.05 as significance level. Results Results showed statistical differences in the post-working day for time analysis, an EMGME decrease in the right rectus abdominis muscle (p = 0.016) and in the age-stratified sample, with individuals over 31 years old (p = 0.016); in the spectral analysis, EMGMF reduction in the right iliocostalis (p = 0.027) and right and left side in the stratified sample, in individuals over 31 years old and with more than 10 years of service. Conclusion The used protocol highlighted a decrease in the amplitude of the electromyographic signal, as well as possible muscle fatigue on the right side where officers usually carry their weapons.

The core muscles can be evaluated through functional tests, such as the prone bridge test (PBT) and supine unilateral bridge test (SUBT). However, there are differences in reliability and muscle fatigue related to these tests.The study evaluated 30 sedentary individuals and 30 individuals who practiced resistance exercises. Participants performed the PBT and SUBT in association with muscle recruitment, through surface electromyography of the upper and lower limbs and trunk muscles. The order of the tests was random and the participants performed one repetition of each test until fatigue. After a 30-min rest interval the participants repeated the tests. After one week, the participants returned and repeated the tests.The resistance group (RG) presented longer PBT holding time (RG 111.8 ± 9.4 and sedentary group (SG) 81 ± 7.7; p = 0.01), while the holding time in the SUBT was similar for both groups (RG = 100.7 ± 8.1 and SG = 79 ± 9.2; p = 0.09). Good to excellent reliability (ICC0.836; SEM 3.85) was established for the PBT and SUBT. Comparing the two groups there were no significant differences or interactions regarding muscle fatigue. The intragroup analysis on the PBT indicated greater gluteus maximus muscle fatigue, and for the SUBT the rectus abdominis presented greater fatigue, in both groups.The PBT and SUBT are reliable. Resistance exercise practitioners maintain the PBT for a longer time. The PBT led to greater gluteus maximus muscle fatigue, while the SUBT generated greater fatigue in the rectus abdominis and gluteus medius, in both groups.

Background The mechanisms underlying impaired balance in chronic obstructive pulmonary disease (COPD) are poorly understood, which makes it difficult to choose the best therapeutic approaches. Therefore, this study aimed to investigate patterns of muscular activation to maintain balance and its determinants in this population. Methods Thirty-three subjects with COPD and 33 controls were assessed by a force platform in four tasks: standing with eyes opened (FHEO) and closed (FHEC); standing on unstable surface (SUS) and one-legged stance (OLS). Electromyographic activity of lower limb, trunk and neck muscles was concomitantly recorded. To asses functional balance, Brief-balance evaluation systems and timed up & go (TUG) tests were applied. Lung function, exercise capacity and muscle force were also assessed. Results Subjects with COPD presented worse balance and higher scalene activation than controls in OLS (mean difference 23.0 [95%CI 1.7–44.3] %Δ μVRMS; P = 0.034), besides presenting also higher activation of gluteus medius during FHEC task (mean difference 1.5 [95%CI 0.2–2.8] %Δ μVRMS; P = 0.023) and taking longer to complete the TUG (mean difference 0.6 [95%CI 0.1–1.2] seconds; P = 0.042). Exercise capacity and peripheral muscle force were determinants of functional balance (r2 = 0.505), whereas age (OR = 1.24; 95%CI 1.02–1.52) and total lung capacity (OR = 2.42; 95%CI 1.05–5.56) were determinants of static balance. Conclusion Individuals with COPD have worse static and functional balance in comparison with controls, besides presenting higher activation of scalene and gluteus medius during static balance tasks. Exercise capacity and peripheral muscle force emerged as determinants of functional balance, whereas age and lung hyperinflation contributed to poor static balance.

The application of low-intensity electrical stimulation (LIES) to neural tissue increases neurochemical factors responsible for regeneration as nerve growth factor. Stem cell (SC) therapy for patients with Spinal cord injury (SCI) promote some increase functional improvement.ObjectiveInvestigate the electromyographic response in paraplegic dogs undergoing LIES and SC transplantation.Methods27 dogs paraplegics with SCI were divided into three groups with different types of therapy. GADSC: two SC transplants (n = 9); GLIES: LIES (n = 8); GCOMB: two SC transplants and LIES (n = 10). Adipose derived mesenchymal stem cells (ADSCs) were transplanted by lumbar puncture in the amount of 1.2 × 106 cells/50 μL. Acupuncture needles positioned in the interspinous space were used for stimulation. The electrical stimulation was applied with a mean voltage ∼30 mV and four consecutive modulated frequencies (5 Hz, 10 Hz, 15 Hz and 20 Hz) within 5 min each. The patients motor performance was evaluated before (Pre) the procedure and after 30 (Post30) and 60 (Post60) days, from electromyography root mean square (EMGRMS) registered with subcutaneous electrodes in the vastus lateralis muscle, while the animals were in quadrupedal position.ResultsAll three groups showed a significant intra-group increase of EMGRMS (Pre vs. Post30 or Pre vs. Post60). However, there were no statistically significant differences between Post30 and Post60. The inter-group test (GADSC X GLIES X GCOMB) did not present significance when compared the instants Pre (p = 0.34), Post30 (p = 0.78) and Post60 (p = 0.64).ConclusionSome dogs recovered motor activity, expressed by the EMGRMS, in all groups, in pre vs. post (30 or 60 days) comparisons. This is the peer-reviewed version of the article: Krueger, E., Magri, L.M.S., Botelho, A.S., Bach, F.S., Rebellato, C.L.K., Fracaro, L., Fragoso, F.Y.I., Villanova, J.A., Brofman, P.R.S., Popović-Maneski, L., 2019. Effects of low-intensity electrical stimulation and adipose derived stem cells transplantation on the time-domain analysis-based electromyographic signals in dogs with SCI. Neuroscience Letters 696, 38–45. [https://doi.org/10.1016/j.neulet.2018.12.004] Published version: [https://hdl.handle.net/21.15107/rcub_dais_4595]

The muscle-machine interface assists in the neuroplasticity of healthy with lesions during the combination of electromyography techniques and functional electrical stimulation (EMG-FES). This case report aimed to evaluate this interface for rehabilitation in a post-stroke participant. For the treatment, an EMG-FES interface was associated with functional exercises for wrist and finger extension. This case report aimed to evaluate this interface for rehabilitation in a post-stroke participant. The protocol was applied 3x/week during 12 sessions. Were applied eliminatory tests (Mini mental exam, active range of motion and Ashworth modified scale), functional tests (Fugl Meyer scale and 9 hole peg test) and electromyography evaluation in time (EMGRMS) and frequency (EMGMDF) domain. In the functional tests occurred increase in sensibility, mobility, oriented tasks and pain reduction (18/48 to 23/48) and the electromyography showed an increase 35.12 VRMS in EMGRMS and 123 Hz in EMGMDF. This interface is effective for improving voluntary movement of hand extension after stroke.

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.

A motor neural prosthesis based on surface functional electrical stimulation (sFES) can restore functional movement (e.g., standing, walking) in patients with a spinal cord injury (SCI). sFES generates muscle contractions in antigravity muscles and allows balance-assisted standing. This induced standing has several benefits, such as improved cardiovascular function, decreased incidence of urinary infections, reduced joint contractures, and muscle atrophy. The duration of sFES assisted standing is limited due to the quick onset of muscle fatigue. Currently, there is no method available to reliably estimate real-time muscle fatigue during sFES. Simply monitoring the M-wave changes is not suitable due to the high signal disturbances that arise during multi-channel electrical stimulation. Mechanomyography (MMG) is immune to electrical stimulation artifacts and can be used to detect subtle vibrations on the surface of the skin related to activation of the underlying muscle's motor units (MU). The aim of this study was to develop a method for detecting muscle fatigue brought on by sFES. The method was tested in three different heads of the quadriceps muscle in SCI patients during electrically elicited quasi-isometric contraction. Six spinal cord-injured male volunteers, with no voluntary control of the quadriceps muscle participated in the study. Electrical bursts of voltage-controlled monophasic square pulses at frequencies of 1 kHz (50% duty cycle) at 50 Hz (15% duty cycle) were used to generate thigh muscle contractions that controlled the knee joint in the sagittal plane. The pulse amplitudes were set to position the knee joint at a 5° angle from the horizontal plane and when the knee angle dropped to 20° (e.g., the quadriceps were unable to hold the lower leg in the desired position), the test was terminated. Two data segments lasting 10 s each, at the beginning and end of each test, were analyzed. The muscle contraction was assessed by MMG sensors positioned on the rectus femoris, vastus lateralis, and vastus medialis muscles. Data segments were decomposed into 11 frequency bands using a Cauchy wavelet transform. In the initial time interval (non-fatigued muscle), the power peak was concentrated in the 11.31 Hz frequency band. In the final interval (muscle fatigued) this peak shifted to lower frequencies (2 and 6 Hz frequency bands). The decreased frequency was most prominent during the last 4 s of the recordings. It was shown that MMG could be used as a real-time indicator of muscle fatigue during FES-induced isometric contraction of quadriceps; hence, MMG could be used in closed-loop control as a fatigue detector. Subsequent studies for non-isometric contractions could possibly lead to prediction of muscle fatigue before contractile failure during functional use of the muscle.

Spinal cord injury (SCI) is classified as neurological disorder that affects motor and sensory function below the injury level. Studies show that application of low-intensity electrical stimulation (LIES) to neural tissue increases neurochemical factors responsible for regeneration as nerve growth factor. Stem cell (SC) therapy for patients with SCI can result in the replacement of injured neurons after trauma. The electromechanical delay (EMD) is defined as time elapsed between the onset of muscle electrical activation and onset of force production. A dog diagnosed with incomplete thoracolumbar SCI followed by disc hernia between the vertebral segments LI and L2, was evaluated by electromyography and mechanomyography after surgical decompression procedure, one SC transplantation and LIES. We observed motor response and decrease in the EMD from 8.25ms to 5.75ms after the procedures. The wavelet decomposition of EMG signals showed reestablishment of vastus lateralis muscle activity 30 days after the procedure. In addition, the EMG RMS increased from 3.3 µV RMS to 157 µV RMS . The preliminary results of this case report indicate positive effects of the hybrid therapy involving stem cells and low-intensity electrical stimulation after surgical decompression.

Mechanomyography (MMG) acquires the oscillatory waves of contracting muscles. Electromyography (EMG) is a tool for monitoring muscle overall electrical activity. During muscle contractions, both techniques can investigate the changes that occur in the muscle properties. EMG and MMG parameters have been used for detecting muscle fatigue with diverse test protocols, sensors and filtering. Depending on the analysis window length (WLA), monitoring physiological events could be compromised due to imprecision in the determination of parameters. Therefore, this study investigated the influence of WLA variation on different MMG and EMG parameters during submaximal isometric contractions monitoring MMG and EMG parameters. Ten male volunteers performed isometric contractions of elbow joint. Triaxial accelerometer-based MMG sensor and EMG electrodes were positioned on the biceps brachii muscle belly. Torque was monitored with a load cell. Volunteers remained seated with hip and elbow joint at angles of 110˚ and 90˚, respectively. The protocol consisted in maintaining torque at 70% of maximum voluntary contraction as long as they could. Parameter data of EMG and the modulus of MMG were determined for four segments of the signal. Statistical analysis consisted of analyses of variance and Fisher’s least square differences post-hoc test. Also, Pearson’s correlation was calculated to determine whether parameters that monitor similar physiological events would have strong correlation. The modulus of MMG mean power frequency (MPF) and the number of crossings in the baseline could detect changes between fresh and fatigued muscle with 1.0 s WLA. MPF and the skewness of the spectrum (μ3), parameters related to the compression of the spectrum, behaved differently when monitored with a triaxial MMG sensor. The EMG results show that for the 1.0 s and 2.0 s WLAs have normalized RMS difference with fatigued muscle and that there was strong correlation between parameters of different domains.

The goal of this paper is to investigate the temporal-spectral decomposition content during a maximal electrically evoked contraction (MEEC) in two spinal cord injured participants using triaxial mechanomyography (MMG). Two male spinal cord injured volunteers performed the tests both injured at T7 neurologic level. The triaxial MMG signal of rectus femoris muscle was processed with Cauchy wavelet transform adjusted to third-order 5–50 Hz bandpass Butterworth filter. A custom electrical stimulator voltage-controlled was configured: pulse frequency set to 1 kHz (20% duty cycle) and burst (modulating) frequency set to 70 Hz (20% active period). The MEEC force was performed by increasing the electrical stimulating magnitude (∼3 V/s to avoid motoneuron adaptation/habituation) until the force started to level off. We conclude that the peak energy of MMG signal frequency did not occur simultaneously with the maximal electrically evoked contraction to rectus femoris muscle. Moreover, the vibration vector of muscle, expressed in three axes (X, Y and Z), presented different fired frequencies, mainly between X (transverse) and Z (perpendicular) axis, where the frequencies fired by Z axis were greater.

Mechanomyography (MMG) measures both muscular contraction and stretching activities and can be used as feedback in the control of neuroprostheses with Functional Electrical Stimulation (FES). In this study we evaluated the correlation between MMG features and passive knee angular movement of rectus femoris and vastus lateralis muscles acquired from healthy volunteers (HV) and spinal cord injured volunteers (SCIV). Twelve HV and thirteen SCIV were submitted to passive and FES elicited knee extensions and in each extension, eleven windows of analysis with 0.5s length were inspected. Temporal (RMS and INT) and frequency (MF and μ3) features were extracted. Spearman correlation coefficients (p) were computed in order to check correlations between the features obtained from both MMG sensors. The correlation between MMG(MF) and MMG temporal analysis (RMS and INT) to HV was classified as positive, moderate (p from 0.635 to 0.681) and high (p from 0.859 to 0.870), and weak (positive e negative) to SCIV. These results differ from those obtained in voluntary contraction or artificially evoked by functional electrical stimulation and may be relevant in applications with closed loop control systems.

Mechanomyography (MMG) registers lateral oscillations of contracting muscles. Functional electrical stimulation (FES) improves the rehabilitation of paraplegic subjects and can be used in neuroprosthesis control. During FES application, muscular contraction responses may vary, possibly due to fatigue or adaptation of nerve cells face to electrical stimuli. This study measured the differences in MMG RMS and median frequency (MF) features between healthy (HV) and spinal cord injury (SCI) volunteers. Ten HV and three SCI participated in the research. FES waveform consisted of a monophasic square wave, 1kHz pulse frequency, 100us active pulse period and 3ms active burst period with burst frequency of 70Hz. For each stimulation series, three analysis windows were inspected. RMS and MF variations were inversely related. The obtained results may help to create new strategies of muscular closed-loop control.

Mechanomyography (MMG) is a technique for measuring muscle oscillations and fatigue. Functional electrical stimulation (FES) has been applied to control movements mainly in people with spinal cord injury (SCI). The goal of this study is the application of the MMG signal as a tool to investigate muscle response during FES. Ten healthy individuals (HI) and three SCI were submitted to four FES profiles in the rectus femoris (RF) and vastus lateralis (VL) muscles. Four FES profiles were applied in different days. The FES profile set to 1 kHz pulse frequency, 200 us active pulse duration and burst frequency of 50 Hz presented the lowest MMG root mean square and spectral median frequency values, suggesting less muscle modification. The MMG signal was different between HI and SCI but there was no difference between the RF and VL muscles.

Functional electrical stimulation (FES) can artificially elicit movements in spinal cord injured (SCI) subjects. FES control strategies involve monitoring muscle features and setting FES profiles so as to postpone the installation of muscle fatigue or nerve cell adaptation. Mechanomyography (MMG) sensors register the lateral oscillations of contracting muscles. This paper presents an MMG efficiency index (EI) that may indicate most efficient FES electrical parameters to control functional movements. Ten healthy and three SCI volunteers participated in the study. Four FES profiles with two FES sessions were applied with in-between 15min rest interval. MMG RMS and median frequency were inserted into the EI equation. EI increased along the test. FES profile set to 1kHz pulse frequency, 200εs active pulse duration and burst frequency of 50Hz was the most efficient.