Comparison of EMG signal of the flexor hallucis longus recorded using surface and intramuscular electrodes during walking

The purpose of this study was to compare the use of intramuscular (iEMG) and surface (sEMG) electromyography electrodes to record flexor hallucis longus (FHL) muscle activity during walking, and describe the role of the FHL. Muscle activity was recorded in 12 participants using sEMG and iEMG during treadmill and overground walking. Inter-tester reliability for visual detection of onset and offset of muscle activity was high (ICC = 1.00). During the loading period, the number of bursts of muscle activity was statistically significantly greater using iEMG compared to sEMG when treadmill walking (p = 0.016), and the duration of muscle activity was significantly greater for iEMG (p = 0.01) on both walking surfaces. There were no differences for peak and mean root mean squared (p ≥ 0.07). The FHL activity observed during the loading period (heel strike to forefoot strike) supports the function of the FHL to act as a dynamic ankle stabiliser of the rearfoot, as well as contributing to propulsion during the latter part of stance. The choice of electrodes to detect FHL activity should be dependent on whether the loading and propulsive periods are of interest, and whether treadmill or overground walking will be examined.     

Surface EMG recorded by branched electrodes during sustained muscle activity.

The purpose of the present investigation is to use surface interference EMG recorded by branched electrodes for assessment of muscle fatigue during sustained voluntary isometric contractions at different levels. Level-trigger averaging and turn/amplitude analysis have been applied. The conduction velocity (CV) of excitation was calculated from the time shift of the negative peaks of the averaged potentials (AvPs) derived from the EMG recorded by two electrodes placed along the muscle fibers. The recruitment of new motor units affects the negative amplitude (NA) of AvPs, the number of turns per second and the mean amplitude of turns in a different way depending on the level of sustained contractions. In contrast, the CV declined at all levels of sustained contractions and was the most appropriate parameter for the muscle fatigue assessment. There was a good correlation between CV decrease and torque reduction during sustained maximal efforts. The level-trigger averaging technique of the interference EMG recorded by surface branched electrodes is easy and non-invasive, thus being very convenient for routine application.     

Use of surface electromyography to estimate neck muscle activity

This paper reviews the literature concerning the use of surface electromyography (sEMG) for the study of the neck musculature in response to work and workplace design during light work and semi-static tasks. The paper also draws upon basic research and biomechanical modeling in order to provide methodological recommendations for the use of surface electromyography in this region of the body and to identify areas which require further investigation. The paper includes review and discussion of electrode site location, methods of normalization, data reliability, and factors that can affect sEMG signals from this region, including noise, physiologic artifact, stress, visual deficiencies, and pain. General guidance for maximum exertions with the neck musculature, for sEMG normalization or other purposes, is also included.     

Comparison between line and surface mesh models to represent the rotator cuff muscle geometry in musculoskeletal models

Accurate muscle geometry (muscle length and moment arm) is required to estimate muscle function when using musculoskeletal modelling. In shoulder, muscles are often modelled as a collection of independent line segments, leading to non-physiological muscles trajectory, especially for the rotator cuff muscles. To prevent this, a surface mesh model was developed and validated against 7 MRI positions in one participant. Mean moment arm errors was 11.4% for the line vs. 8.8% for the mesh model. While the model with independent lines led to some non-physiological trajectories, the mesh model gave lower misestimations of muscle lengths and moment arms.     

Quantifying extensibility of rotator cuff muscle with tendon rupture using shear wave elastography: A cadaveric study

Surgical repair for large rotator cuff tear remains challenging due to tear size, altered muscle mechanical properties, and poor musculotendinous extensibility. Insufficient extensibility might lead to an incomplete reconstruction; moreover, excessive stresses after repair may result in repair failure without healing. Therefore, estimates of extensibility of cuff muscles can help in pre-surgical planning to prevent unexpected scenarios during surgery. The purpose of this study was to determine if quantified mechanical properties of the supraspinatus muscle using shear wave elastography (SWE) could be used to predict the extensibility of the musculotendinous unit on cadaveric specimens. Forty-five fresh-frozen cadaveric shoulders (25 intact and 20 with rotator cuff tear) were used for the study. Passive stiffness of 4 anatomical regions in the supraspinatus muscle was first measured using SWE. After detaching the distal edge of supraspinatus muscle from other cuff muscles, the detached muscle was axially pulled with the scapula fixed. The correlation between the SWE modulus and the extensibility of the muscle under 30 and 60 N loads was assessed. There was a significant negative correlation between SWE measurements and the experimental extensibility. SWE modulus for the anterior-deep region in the supraspinatus muscle showed the strongest correlation with extensibility under 30 N (r = 0.70, P < 0.001) and 60 N (r = 0.68, P < 0.001). Quantitative SWE assessment for the supraspinatus muscle was highly correlated with extensibility of musculotendinous unit on cadaveric shoulders. This technique may be used to predict the extensibility for rotator cuff tears for pre-surgical planning.     

Effects of rotator cuff ruptures on the cellular and intracellular composition of the human supraspinatus muscle

Ruptures of the rotator cuff tendons of the human shoulder are a common incidence and lead to functional impairment of the four muscles connected to the cuff, entailing profound changes of their cellular tissue composition. Most importantly, such tendon tears lead to atrophy, fatty degeneration and fibrosis of the corresponding muscles. The muscle most commonly affected with such changes is the M. supraspinatus. The present study uses biopsy samples from the supraspinatus muscle of 12 elderly patients and 6 controls to examine the rupture-induced muscle change at both the cellular and the intracellular (ultrastructural) levels. Amounts of fatty tissue, connective tissue and muscle were assessed by light microscopy-based morphometry and stereology. Stereology of electron micrographs was employed to determine volume densities of muscle fibre mitochondria, myofibrils and intracellular lipid. Results demonstrate that the supraspinatus muscles of patients with a massive rupture contain significantly higher amounts not only of fatty tissue but also of intracellular lipid than those of control subjects. These patients further exhibit a major decrease in relative amounts of myofibrils, thus confirming that change of intracellular composition is a major component of the observed muscle degeneration. The results contribute to establish the true spectrum of supraspinatus muscle damage in humans induced by tendon rupture.     

The use of the long head of triceps interposition muscle flap for treatment of massive rotator cuff tears

Massive rotator cuff tears present a difficult problem for orthopedic surgeons. To address this problem, a long head of triceps muscle interposition flap was proposed. Ten patients underwent repair of massive rotator cuff tears using the triceps muscle flap. The patients' strength and range of motion were tested preoperatively, and a University of California, Los Angeles, shoulder score was assigned. Similar testing was performed 1 year later. Postoperatively, the patients showed significant improvement in the overall shoulder score and in the pain and function components of the score. There was no significant improvement in shoulder range of motion, except for shoulder flexion. An important finding was that there was no loss of strength in elbow extension following the loss of the long head of triceps muscle. It was concluded that the long head of triceps interposition flap is useful in the reconstruction of the massive rotator cuff tear.     

Reduction of electrode polarization capacitance in low-frequency impedance spectroscopy by using mesh electrodes

Dielectric measurements of biological samples are obscured by electrode polarization, which at low frequencies dominates over the actual sample response. Reduction of this artifact is especially necessary in studying interactions of electric field with biological systems in the α-dispersion range. We developed a method to reduce the influence of electrode polarization by employing mesh instead of solid electrodes as sensing probes, thereby reducing the area of the double layer. The design decreases the electrode-electrolyte contact area by almost 40% while keeping the bulk sample capacitance the same. Interrogation electric fields away from the electrode surface and sensitivity are unaffected. Electrodes were microfabricated (600μm×50μm, spacing of 100μm) with and without mesh holes 7.5μm×7.5μm in size. Simulations of electric field performed using Comsol Multiphysics showed non-uniformity of the electric field within less than 1.5μm from the electrode surface, which encompasses the double layer region, but at greater distance the solid and mesh electrodes gave the same results. Mesh electrodes reduced capacitance measurements for water and KCl solutions of different concentrations at low frequencies (<10kHz), while higher frequency capacitance remained the same for both electrode types, confirming our hypothesis that this design leaves the electric field mainly unaffected. Impedance measurements at low frequencies for water and mice heart mitochondrial suspension were lower for mesh than for solid electrodes. Comsol simulations confirmed these results by showing that mesh electrodes have a greater charge density than solid electrodes, which affects conductance. These electrodes are being used for mitochondrial membrane potential studies.     

Determination of body surface area and formulas to estimate body surface area using the alginate method

The purpose of this study was to determine the body surface area (BSA) based on the alginate method, to derive formulae for estimating BSA, and to compare the error of the present formula to previous formulas obtained from other countries. We directly measured the entire body surface area of 34 males (20-60 years old, 158.5-187.5 cm in height, 48.5-103.1 kg in body weight) and 31 females (20-63 years old, 140.6-173.1 cm, 36.8-106.1 kg) using alginate. The measurements showed that the BSA had a mean of 18,339 cm(2) (15,416-22,753 cm(2)) for males, and 16,452 cm(2) (12,825-22,025 cm(2)) for females. Based on these measurements, a regression model to estimate BSA was derived: Estimated BSA (cm(2))=73.31 Height (cm)(0.725) x Weight (kg)(0.425) (r(2)=0.999). The mean error of the formula was -0.1%, and did not show any significant difference by gender or body shape. When applied to the datasets (n=506) composed of various races (Caucasians, Africans, and Asians), the mean error of the formula was 0.4% and was smaller than that of DuBois & DuBois's, Gehan & George's, and Mosteller's formulas when applied to the same datasets. The errors of the three previous formulas were also within 2%. Overall, formulas based on the DuBois exponent (Weight(0.425) Height (0.725)) did not show any tendency of overestimation or underestimation by body shape, but other BSA-formulae showed differences by body shape. The present BSA formula has shown good accuracy in Korean adults of all weight categories compared to traditional formulas.     

Determination of kinase activity by using an enzyme electrode

A method for determining the enzymatic activity of hexokinases, acetate kinase and pyruvate kinase using an enzyme electrode was developed. The assay time is 2-3 min. The lower limit of the activity determining is 0,054 U/ml. The proposed method was applied to investigation of pyruvate kinase and acetate kinase reactivation under the action of mercaptoethanol.     

Heterogeneous activity of the human genioglossus muscle assessed by multiple bipolar fine-wire electrodes.

Genioglossus (GG) electrical activity [measured by electromyogram (EMGgg)] is best measured by intramuscular electrodes; however, the homogeneity of EMGgg is undefined. We investigated the relationships between EMGgg and the site from which activity was measured to determine whether and to what extent inhomogeneity in activity occurred. Eight healthy human volunteers underwent ultrasound to determine GG depth and width. Four pairs of electrodes were then inserted percutaneously into the left and right GG muscle, anteriorly and posteriorly. Additional configurations were obtained by connecting electrodes across the midline and along each muscle belly. EMGgg activity was simultaneously recorded from these 10 configurations at rest and during various respiratory maneuvers. Heterogeneous behavior of the GG was evidenced by 1) the variable presence of phasic EMGgg at rest, which was undetectable in two subjects but evident in 65% of configurations in six subjects and present in all configurations in all subjects during voluntary hyperventilation; 2) a greater amplitude of EMGgg response to pharyngeal square-wave negative pressure in anterior than posterior configurations (14.1 +/- 7.1 vs. 8.5 +/- 5.1% of maximum, P < 0.05); and 3) variable (linear and alinear) relationships between EMGgg and lingual force within and between subjects. We hypothesize that regional differences in density and type of muscle fiber are the most likely sources of heterogeneity in these responses.     

Rotator cuff tendinopathy alters the muscle activity onset and kinematics of scapula

Athletes with rotator cuff (RC) tendinopathy demonstrate an aberrant pattern of scapular motion which might relate to deficits in the scapular muscles. This study aimed to determine whether alteration in scapular kinematics is associated with deficits in the activity onset of scapular muscles. Forty-three male volleyball players (17 asymptomatic and 26 with RC tendinopathy) joined the study. Three-dimensional scapular kinematics was quantified using an acromial marker cluster method. The activity onset of the upper (UT), middle (MT), and lower trapezius (LT), and serratus anterior (SA) during arm abduction was assessed with electromyography. Athletes with RC tendinopathy demonstrated less scapular upward rotation (6.6 ± 2.3 vs. 8.2 ± 1.1°, p = 0.021) in the early phase of shoulder abduction from 0° to 30° when compared to asymptomatic athletes. The tendinopathy group had delayed activity onset of LT (14.1 ± 31.4 ms vs. 74.4 ± 45.1 ms, p < 0.001) and SA (−44.9 ± 26.0 ms vs. 23.0 ± 25.2 ms, p < 0.001) relative to UT when compared to the asymptomatic group. In asymptomatic athletes, earlier activity onset of MT and LT relative to UT was associated with more scapular upward rotation during 0–30° of abduction (r = 0.665, p = 0.021) and 30–60° of abduction (r = 0.680, p = 0.015), respectively. Our findings showed the control of the scapular upward rotation is related to the activity onset of the scapular muscles in athletes.     

Comparison of proximal and distal placements of electrodes to assess body composition by bioelectrical impedance in obese adults

The purpose of this study was to compare the variability and accuracy of proximal and traditional distal electrode placement to estimate body composition in obese adults. Fifty-two obese men and women had a mean age of 37 years and an average body mass index (BMI) of 30.6 kg.m(-2). Body composition was measured using DEXA and an RJL bioelectric impedance analysis 101A bioelectric impedance analyzer. Impedance was measured using the traditional distal electrode placement (hand and foot) and a proximal electrode placement where the current detecting electrodes were placed in the antecubital and popliteal fossae. The distal resistance was 482.4 +/- 79 Omega, which was more than double the mean proximal values of 193.2 +/- 27 Omega. Multiple regression analysis derived the best-fitting equation to predict DEXA-derived fat-free mass. The combination of Ht(2)/R (height(2)/resistance) and mass were the only significant predictors for both the proximal and distal electrode placements. The resulting R(2) values were 0.86 and 0.88, whereas standard errors of the estimate (SEEs) were 4.0 and 3.6 kg for the distal and proximal placements, respectively. An independent sample of 40 obese women was used to cross-validate this new equation. Mean impedance predictions using the distal and proximal electrode placements (45.78 +/- 1.07 and 45.29 +/- 0.97 Omega, respectively) were similar to the reference values (45.29 +/- 0.64 Omega) determined by DEXA. Fat-free mass predicted with the distal and proximal electrode placements correlated significantly (p < 0.001) with the reference fat-free mass value (r = 0.72 and 0.75, respectively). These data suggest that using a proximal electrode placement and a fatness-specific equation helps to reduce the variability of the bioelectric impedance analysis technique in obese adults.     

Effect of electrode characteristics on electromyographic activity of the masseter muscle

ObjectivesThe study investigated effects of electrode material, inter-electrode distance (IED), and conductive gel on electromyographic (EMG) activity recorded from the masseter muscle.Materials and methodsEMG was recorded unilaterally, as ten volunteers performed standardized oral tasks. Ag/AgCl and Ag coated with Au were the gel-based; Ag alloy coated with graphene, pure Ag coated with graphene and silver nanowire embedded electrodes were the gel-free materials tested. Ag/AgCl electrodes were tested at three different IEDs (i.e. 15 mm, 20 mm, 25 mm). An electrode relative performance index (ERPI) was defined and calculated for each of the standardized oral tasks that the volunteers performed. ERPI values obtained for the different oral tasks with different electrode materials and IEDs were compared using two-way repeated-measures ANOVA.ResultsERPI values were not significantly influenced by IED. However, for the electrode materials statistically significant differences were found in ERPI values for all oral tasks. Of the gel-free electrode materials tested, pure silver electrodes coated with graphene had the highest ERPI values followed by Ag alloy electrodes coated with graphene and silver nanowire embedded electrodes.ConclusionsWithin the limitations of the study, IED between 15 and 25 mm has a negligible effect on masseter muscle EMG. Graphene coated and silver nanowire embedded electrodes show promise as gel-free alternatives.     

A study of the healing-over in the cardiac muscle using suction electrodes

Suction electrodes were used to investigate the phenomenon of the healing-over in preparations of rabbit, cat and dog ventricular muscles. At least two processes were shown to participate in the process of the healing-over: a rapid one (time constant approximately 1 min) and a slow one (time constant approximately 10 min). Procion Yellow dye was used to determine the size of the injured zone under the suction electrode tip. Larger tips resulted in larger zones injured. The specific resistance of the border formed during the healing over was estimated to be in the range of approx. 1 k omega X cm2, i.e. much smaller than that of the intact surface membrane.