Root Mean Square Of Electromyogram Research Articles

Deceptive intensities: An exploratory strategy for overcoming early central fatigue in resistance training

Neuropsychological stress induced by misleading information can limit human performance, possibly by early central fatigue mechanisms. In this study, we investigated the impact caused by prescribing misleading intensities of resistance exercise on acute electroencephalogram (EEG) and electromyogram (EMG) responses and the total number of repetitions to exhaustion. Collegiate female students performed three sets of biceps curls to exhaustion. The actual intensity for all sets was set at 65% 1-Repetition Maximum (1-RM). However, participants were deceptively informed that the intensities were 60%, 65%, or 70% 1-RM. The number of repetitions to fatigue and the magnitude of EEG and EMG signals were analyzed. The number of repetitions to exhaustion was significantly lower in greater announced intensities (18.11 ± 8.44) compared to lower (29.76 ± 16.28; p = 0.017) and correctly (27.82 ± 11.01; p = 0.001) announced intensity. The correlation between frontal and motor-cortex signals was significant in lower (r = 0.72, p = 0.001) and higher (r = 0.64, p = 0.005) announced intensities. The median and mean frequencies of EMG signal and Root Mean Square (RMS) did not show any significant difference between sets, but the peak-to-peak range (PPR) of biceps EMG signals was significantly higher in lower intensity (0.145 ± 0.042) when compared with higher (0.104 ± 0.044; p = 0.028) or correctly (0.126 ± 0.048; p = 0.037) announced intensity. It seems that deceptive information regarding the mass of an object could affect the number of repetitions to exhaustion and PPR to cover muscle capacity in endurance-type strength training.

Standardization of rehabilitation program for post-apoplectic limb spasm treated by Tongjing Tiaoxing tuina and scalp acupuncture with physical therapy.

Background:Tong Jing Tiao Xing tuina (TJTX) is a Chinese massage method. Excising with scalp acupuncture (ESA) is a treatment combining scalp electroacupuncture with physical therapy (PT), and yinao fujian formula (YNFJ) is a Chinese oral herbal granule medicine. The combination of the 3 methods is called the “Zhishen Tiaoxing” (ZSTX) rehabilitation program, which is used as an alternative of limb spasm after stroke. There is little available evidence demonstrating its safety and efficacy.Methods:This will be a subject-blind, randomized controlled trial conducted in 3 medical centers. It will strictly follow the Standards for Reporting Interventions in Clinical Trials of Acupuncture, 2010. We will recruit 316 patients with limb spasm after stroke, 200 from the Affiliated Hospital of Changchun University of Chinese Medicine, Changchun, China, 80 from the Second Affiliated Hospital of Heilongjiang University of Chinese medicine, Harbin, China, and 36 from Huashan Hospital of Fudan University, Shanghai, China. A block randomization sequence stratified by centers will be generated using SAS Version 9.2 software (SAS Institute, Cary, NC, USA), which was performed at the Guangdong Provincial Hospital of Chinese Medicine's Key Unit of Methodology in Clinical Research. The treatment group is treated with TJTX (once a day), ESA (once a day), and oral YNFJ (twice a day). The control group will be treated with PT. Two groups of patients will be treated 5 sessions a week for 4 weeks, and there will be 6-month follow-up. The outcome evaluators will be blinded to patient grouping. The primary outcome will be modified Ashworth scales. The secondary outcome indexes will be the simplified Fugl–Meyer assessment scale, surface electromyogram root mean square value, modified Barthel index, stroke-specific quality of life scale, health scale of traditional Chinese medicine, visual analogue scale (VAS), and the Hamilton depression scale.Discussion:The Randomized Controlled Trial (RCT) mainly aim to evaluate the effectiveness and safety of traditional Chinese medicine rehabilitation program, by comparing the treatment of ZSTX with the PT for the treatment of limb spasm after stroke.Trial registration:Chinese Clinical Trial Registry: ChiCTR 1900024255. Registered on July 3, 2019.

Optimal Estimation of EMG Standard Deviation (EMG σ ) in Additive Measurement Noise: Model-Based Derivations and Their Implications.

Typical electromyogram (EMG) processors estimate EMG signal standard deviation (EMG σ ) via moving average root mean square (RMS) or mean absolute value (MAV) filters, whose outputs are used in force estimation, prosthesis/orthosis control, etc. In the inevitable presence of additive measurement noise, some processors subtract the noise standard deviation from EMG RMS (or MAV). Others compute a root difference of squares (RDS)-subtract the noise variance from the square of EMG RMS (or MAV), all followed by taking the square root. Herein, we model EMG as an amplitude-modulated random process in additive measurement noise. Assuming a Gaussian (or, separately, Laplacian) distribution, we derive analytically that the maximum likelihood estimate of EMG σ requires RDS processing. Whenever that subtraction would provide a negative-valued result, we show that EMG σ should be set to zero. Our theoretical models further show that during rest, approximately 50% of EMG σ estimates are non-zero. This result is problematic when EMG σ is used for real-time control, explaining the common use of additional thresholding. We tested our model results experimentally using biceps and triceps EMG from 64 subjects. Experimental results closely followed the Gaussian model. We conclude that EMG processors should use RDS processing and not noise standard deviation subtraction.

Normalizing cVEMPs: Which Method Is the Most Effective?

To determine the most effective method for normalizing cervical vestibular evoked myogenic potentials (cVEMPs). cVEMP data from 20 subjects with normal hearing and vestibular function were normalized using 16 combinations of methods, each using one of the 4 modes of electromyogram (EMG) quantification described below. All methods used the peak to peak value of an averaged cVEMP waveform (VEMPpp) and obtained a normalized cVEMP by dividing VEMPpp by a measure of the EMG amplitude. EMG metrics were obtained from the EMG within short- and long-duration time windows. EMG amplitude was quantified by its root-mean-square (RMS) or average full-wave-rectified (RECT) value. The EMG amplitude was used by (a) dividing each individual trace by the EMG of this specific trace, (b) dividing VEMPpp by the average RMS or RECT of the individual trace EMG, (c) dividing the VEMPpp by an EMG metric obtained from the average cVEMP waveform, or (d) dividing the VEMPpp by an EMG metric obtained from an average cVEMP "noise" waveform. Normalization methods were compared by the normalized cVEMP coefficient of variation across subjects and by the area under the curve from a receiver-operating-characteristic analysis. A separate analysis of the effect of EMG-window duration was done. There were large disparities in the results from different normalization methods. The best methods used EMG metrics from individual-trace EMG measurements, not from part of the average cVEMP waveform. EMG quantification by RMS or RECT produced similar results. For most EMG quantifications, longer window durations were better in producing receiver-operating-characteristic with high areas under the curve. However, even short window durations worked well when the EMG metric was calculated from the average RMS or RECT of the individual-trace EMGs. Calculating the EMG from a long-duration window of a cVEMP "noise" average waveform was almost as good as the individual-trace-EMG methods. The best cVEMP normalizations use EMG quantification from individual-trace EMGs. To have the normalized cVEMPs accurately reflect the vestibular activation, a good normalization method needs to be used.

Spatial Analysis of Multichannel Surface EMG in Hemiplegic Stroke.

We investigated spatial activation patterns of upper extremity muscles during isometric force generation in both intact persons and in hemispheric stroke survivors. We used a 128-channel surface electromyogram (EMG) grid to record the electrical activity of biceps brachii muscles during these contractions. EMG data were processed to develop 2-D root mean square (RMS) maps of muscle activity. Our objective was to determine whether motor impairments following stroke were associated with changes in the muscle activity maps and in the spatial distribution of muscular activation. We found that, for a given subject, spatial patterns in muscle activity maps were consistent across all measured contraction levels differing only the RMS EMG. However, the maps from opposite arms (stroke-affected versus non-affected) of stroke survivors were significantly different from each other, especially when compared with the differences observed intact participants. Our analyses revealed that chronic stroke altered the size and location of the active region in these maps. The former is potentially related to disruption of fiber and tissue structure, possibly linked to factors such as extracellular fat accumulation, connective tissue infiltration, muscle fiber atrophy, fiber shortening, and fiber loss. Changes in spatial patterns in muscle activity maps may also be linked to a shift in the location of the innervation zone or the endplate region of muscles. Furthermore, the textural analysis of EMG activity maps showed a larger pixel-to-pixel variability in stroke-affected muscles. Alterations in the muscle activity maps were also related to functional impairment (estimated using Fugl-Meyer score) and to the degree of spasticity (estimated using the modified Ashworth scale). Overall, our investigation revealed that the muscle architecture and morphology were significantly altered in the chronic stroke.

Concordance et dissociation des seuils de fatigue électromyographiques et des seuils ventilatoires chez le patient en réadaptation cardiaque

Exercise prescription was generally based on the determination of ventilatory thresholds (VT1, VT2) during cardiopulmonary exercise testing (CPX). Changes in surface electromyographic activity (EMGth1, EMGth2) were also related to VT1 and VT2 in healthy subjects. ObjectiveTo observe the occurrence of EMGth1 and EMGth2 and whether these events accompany VT1 and VT2 during CPX in cardiac patients (CP). MethodThirty-four CP (62.1±7.3years, 172.1±6.3cm, 81.3±15.3kg, BMI: 27.3±4.1) performed a cycle CPX at a 60-rpm cadence. VT1 was determined as the breakpoint in the curve of carbon dioxide output against oxygen uptake plot (V-slope method). VT2 was defined as the point at which the ratio of minute ventilation to carbon dioxide output starts to increase. The root mean square of electromyogram (rms-EMG) was on-line calculated from the real time bipolar surface electromyographic signals recorded from the vastus lateralis. EMGth1 and EMGth2 were defined as the first and the second breakpoints in the rms-EMG–power output relationship. ResultsPeak values of oxygen uptake (16.3±4.6mL·min−1·kg−1) and heart rate (106.7±13.8bpm) were reached at 112.9±38.5w (PMT). VT1 and VT2 occurred at 71.1±25.9w (62.5±5.5% PMT) and 87.9±28.6w (78.0±5.1% PMT). All subjects presented two breakpoints in the rms-EMG curve, EMGth1 at 68.0±24.7w and EMGth2 at 88.5±30.1w, i.e. 60.0±7.6 and 78.6±5.0% of PMT. EMGth1 occurred significantly before VT1 (P=0.004, small effect size). No significant difference was observed between EMGth2 and VT2 (P=0.13, small effect size). ConclusionThe EMGth1 occurrence before VT1 suggested a role of skeletal muscle conditioning on ventilatory responses, which should be taken into account in cardiac rehabilitation program prescription.

Effects of a 12-week neck muscles training on muscle function and perceived level of muscle soreness in amateur rugby players

Neck injuries are the most frequent traumatism in rugby at all levels of the game. Strengthening and mobilizing the neck musculature has often been indicated as a possible strategy to reduce the perceived level of muscle soreness and number of neck injuries. Still, the efficacy of such intervention is under debate. This study assessed the efficacy of a 12-week training for neck muscle strength and mobility in reducing the level of perceived soreness in amateur rugby players. The perceived soreness of the neck muscles was recorded before, immediately and 24 h after 12 rugby matches in amateur rugby players (NT, n = 12) and controls (Ctrl, n = 11). The neck range of motion (ROM), the maximum voluntary force (MVC), and surface electromyogram (EMG) of the neck muscles were evaluated before and after 12-week neck muscle training (3 sessions per week, 35 min each). Training consisted of isometric and concentric contractions, and passive stretching of the neck muscles. From EMG, the root mean square (RMS) was calculated. After 4 weeks, the perceived soreness of neck muscles was lower in NT than in Ctrl (P < 0.05), and decreased further during the next 8 weeks (P < 0.05). After training, MVC, EMG RMS and ROM increased in NT but not in Ctrl (P < 0.05). The introduction of a specific training program focusing on neck muscle strength and mobility improved the perceived soreness and muscle function of neck muscles in amateur rugby players. Its inclusion within the normal training routine of amateur rugby players should, therefore, be strongly recommended.

지압과 온열의 조합마사지가 인체의 스트레스 완화에 미치는 영향 평가

This study was designed to investigate the effect of a combined stimulus which was composed of chiropractic massage and thermotherapy on the relief of mental and physical stress. Fifteen healthy male subjects were treated with three type of stimuli; control (without any stimulus), a single stimulus (only chiropractic) and a combined stimulus. To evaluate the effects of stimuli, visual analogue scale (VAS), trunk extension, electromyogram (EMG) on erector spinae muscle and electrocardiogram (ECG) were measured and analyzed before and after stimuli. In the control group, there were no significant changes in EMG root mean square (RMS) value and low Frequency/high Frequency (LF/HF) ratio (p > 0.05, p > 0.05). However, both stimulus groups showed significant increases in trunk extension and EMG RMS values (p < 0.05, p < 0.05), but significant decreases in LF/HF ratios (p < 0.05). Particularly the decrement rate in LF/HF ratio was significantly higher in the combined stimulus group than that in the single stimulus group (p < 0.05). Also, a significantly lower VAS was recorded after combined stimulus. Our findings indicate that the combined stimulus might not only improve flexibility and strength of muscle, but also active parasympathetic nerve activity. The combined stimulus may thus contribute to relieve the stress and to enhance the muscle function.

Combined effects of fatigue and temperature manipulation on skeletal muscle electrical and mechanical characteristics during isometric contraction

Peripheral fatigue and muscle cooling induce similar effects on sarcolemmal propagation properties. The aim of the study was to assess the combined effects of muscle temperature (Tm) manipulation and fatigue on skeletal muscle electrical and mechanical characteristics during isometric contraction. After maximum voluntary contraction (MVC) assessment, 16 participants performed brief and sustained isometric tasks of different intensities in low (TmL), high (TmH) and neutral (TmN) temperature conditions, before and after a fatiguing exercise (6s on/4s off at 50% MVC, to the point of fatigue). During contraction, the surface electromyogram (EMG) and force were recorded from the biceps brachii muscle. The root mean square (RMS) and conduction velocity (CV) were calculated off-line. After the fatiguing exercise: (i) MVC decreased similarly in all Tm conditions (P<0.05), while EMG RMS did not change; and (ii) CV decreased to a further extent in TmL compared to TmN and TmH in all brief and sustained contractions (P<0.05). The larger CV drop in TmL after fatigue suggests that TmL and fatigue have a combined and additional effect on sarcolemmal propagation properties. Despite these changes, force generating capacity was not affected by Tm manipulation. A compensatory mechanism has been proposed to explain this phenomenon.

Neural Respiratory Drive in Patients with COPD during Exercise Tests

Background: It is unknown whether neural drive is comparable in constant rate and incremental exercise tests. Few data have previously been available to address this question because of the lack of reliable methods to assess neural respiratory drive in patients with chronic obstructive pulmonary disease (COPD). Objectives: The aims of this study are to determine whether neural respiratory drive during constant rate exercise differs from that during incremental exercise and to determine whether neural respiratory drive was maximal at the end of exhaustive exercise tests. Methods: We studied sixteen patients with moderate-severe COPD (mean ± SD FEV₁ 29 ± 10%). Both diaphragmatic electro-myogram (EMG) and transdiaphragmatic pressure were recorded with a combined multipair electrode balloon catheter during incremental and constant (80% of maximal oxygen consumption derived from a prior incremental exercise test) treadmill exercise. Minute ventilation and oxygen uptake were also measured. Results: Root mean square (RMS) of the diaphragmatic EMG increased gradually without a plateau during incremental exercise, whereas the RMS increased initially and reached a plateau during constant work rate exercise. The RMS of the diaphragmatic EMG at the end of exercise was similar for both incremental and constant work rate exercise (176 ± 42 µV vs. 184 ± 39 µV); these values were 70 and 73% of maximal values recorded over the study. Conclusions: The pattern of increase in neural respiratory drive during incremental exercise is different to that observed during constant work rate exercise, but both exercise protocols are terminated when the patients achieve a similar but submaximal drive.

Increase of Muscle Activities in Hemiplegic Lower Extremity During Driving a Cycling Wheelchair

For the patients with severe hemiplegia, long-time wheelchair sitting is unavoidable, which however increases a risk of secondary impairments due to non-use of the affected leg. A cycling wheelchair (C-W/C) has a possibility to activate paretic muscle through self-locomotion with bilateral pedaling. We therefore measured driving speed of C-W/C and electromyogram (EMG) in both legs during driving in the healthy adults and severe hemiplegic patients. Ten healthy volunteers (mean age 32.8, 26-45 years) and ten non-ambulatory post-stroke patients (mean age 69.0, 55-81 years) with complete or semi-complete hemiplegia participated in this study. EMG was recorded from the key muscles for cycling during isometric movement as baseline and during driving a C-W/C straightforward. All of the patients could drive a C-W/C with mean maximum driving speed of 46.6 (31.7-61.7) m/min, which was about half of that in the healthy subjects and within practical level. Root mean square of EMG (R-EMG) as a parameter reflecting muscle activity was compared between baseline and C-W/C driving. There was no increase in most of the values of R-EMG during driving in the healthy subjects and in the intact side of the hemiplegic patients. In contrast, significant increase was found during driving in several paretic muscles, despite that EMG of the paretic leg showed almost silent at baseline. These results suggest C-W/C can induce muscle activities of the paretic leg and provide a chance of practical locomotion even for the severe hemiplegics. Daily use of a C-W/C may contribute to restore paretic leg function.

Electrical and mechanical response of finger flexor muscles during voluntary isometric contractions in elite rock-climbers

To determine the differences between rock-climbers and controls in finger flexor (FF) motor units (MUs) features and activation strategy, eleven climbers and ten controls volunteered for the study. After maximal voluntary contraction (MVC) assessment, five levels of isometric contractions at 20, 40, 60, 80 and 100% MVC were performed. During contractions, electromyogram (EMG) and mechanomyogram (MMG) were recorded, from which the root mean square (RMS) and mean frequency (MF) were calculated. Climbers showed significantly higher MVC. EMG RMS was statistically higher in climbers than in controls from 60 to 100% MVC. In climbers MMG RMS increased up to 80% MVC, whereas in controls it increased only up to 60% MVC. MMG MF was higher in climbers than in controls from 60 to 100% MVC (P < 0.05). EMG-MMG combined analysis revealed significant differences in MU activation strategy between the two groups. The results are compatible with a shift of climbers' muscles toward faster MUs.

The Effects of an Acute Bout of Plyometrics on Muscle Fatigue in Female Athletes

It is often presumed that after performing plyometric exercises muscle fatigue and delayed onset muscle soreness occur resulting in an overall decline in athletic performance. For this reason many coaches do not employ plyometric training within 24 hours of competition, however, very little of the plyometric research has been performed on plyometrically trained athletes. PURPOSE: To evaluate muscle fatigue in female athletes accustomed to plyometric training immediately after and 24 hours after an acute bout of plyometric exercises. METHODS: Twenty-three females aged 18-22 years (165± 2.59 cm; 65.9± 10.53 kg) from the Syracuse University soccer and field hockey teams participated in this study. The subjects completed 10 plyometric exercises consisting of various forms of squat jumps, lateral jumps, box jumps and skipping with one minute rest periods between exercises. Force production of the knee extensors (KE) and knee flexors (KF), vertical jump height, and the Illinois Agility Test were used to assess muscle fatigue and athletic performance. Additionally, surface electromyogram (EMG) signals were collected from the thigh muscles and analyzed for root mean square (RMS) alterations during maximal and submaximal contractions. These tests were completed prior to, immediately after and 24 hours after the plyometric exercises. RESULTS: KE and KF force production decreased 14 and 10% respectively immediately after the exercise (p=0.000 and p=0.001) and KE force remained 7% lower than pre-exercise at 24-hours post exercise (p=0.032). During the submaximal contractions, RMS EMG was significantly elevated immediately after the exercise in the rectus femoris (p=0.026) and vastus medialis (p=0.001)muscles only. Immediately after the exercise the time to complete the Illinois Agility Test increased 3% (p=0.006) and vertical jump ability declined 6% (p=0.18). CONCLUSIONS: Decrements in performance were seen immediately after exercise indicating that fatigue had occurred, but most measurements (with the exception of KE strength) returned to pre-exercise values at 24-hours after exercise. An intense bout of plyometrics should not be performed the day before competition because muscle strength may not be fully recovered the following day.

Fatigue in repeated-sprint exercise is related to muscle power factors and reduced neuromuscular activity

The purpose of this study was (1) to determine the relationship between each individual's anaerobic power reserve (APR) [i.e., the difference between the maximum anaerobic (Pana) and aerobic power (Paer)] and fatigability during repeated-sprint exercise and (2) to examine the acute effects of repeated sprints on neuromuscular activity, as evidenced by changes in the surface electromyogram (EMG) signals. Eight healthy males carried out tests to determine Pana (defined as the highest power output attained during a 6-s cycling sprint), Paer (defined as the highest power output achieved during a progressive, discontinuous cycling test to failure) and a repeated cycling sprint test (10 x 6-s max sprints with 30 s rest). Peak power output (PPO) and mean power output (MPO) were calculated for each maximal 6-s cycling bout. Root mean square (RMS) was utilized to quantify EMG activity from the vastus lateralis (VL) muscle of the right leg. Over the ten sprints, PPO and MPO decreased by 24.6 and 28.3% from the maximal value (i.e., sprint 1), respectively. Fatigue index during repeated sprints was significantly correlated with APR (R = 0.87; P < 0.05). RMS values decreased over the ten sprints by 14.6% (+/-6.3%). There was a strong linear relationship (R2 = 0.97; P < 0.05) between the changes in MPO and EMG RMS from the vastus lateralis muscle during the ten sprints. The individual advantage in fatigue-resistance when performing a repeated sprint task was related with a lower anaerobic power reserve. Additionally, a suboptimal net motor unit activity might also impair the ability to repeatedly generate maximum power outputs.

The interpretation of abdominal wall muscle recruitment strategies change when the electrocardiogram (ECG) is removed from the electromyogram (EMG)

The purpose of this study was to determine the effect of the ECG artifact on low-level trunk muscle activation amplitudes and assess the effectiveness of two methods used to remove the ECG. Simulations were performed and percent error in root mean square (RMS) amplitudes were calculated from uncontaminated and contaminated EMG signals at various ECG to EMG ratios. Two methods were used to remove the ECG: (1) filtering by adaptive sampling (FAS) and (2) Butterworth high pass filter at 30 Hz (BW-30 Hz HPF). The percent error was also calculated between the ECG removed and the uncontaminated EMG RMS amplitudes. Next, the BW-30 Hz HPF method was used to remove the ECG from 3-bilateral external oblique (EO) muscle sites collected from 30 healthy subjects performing a one handed lift and replace task. Two separate ANOVA models assessed the effects of ECG on the statistical interpretation of EO recruitment strategies. One model included EMG data that contained the ECG and the other model included EMG data after the ECG was removed. Large percent errors were observed when the ECG was not removed. These errors increased with larger ECG to EMG ratios. Both removal methods reduced the errors to below 10%, but the BW-30 Hz HPF method was more time efficient in removing the ECG artifact. Different statistical findings were observed among the muscle sites for the ECG contaminated model compared to the ECG removed model, which resulted in different conclusions concerning neuromuscular control.

Effects of electrode dislocation on electromyographic activity and relative rest time: effectiveness of compensation by a normalisation procedure.

Myofeedback seems a promising technique to treat myalgia related to computer work. A garment with embedded electrodes allows independent use by the subject. However, this inevitably results in electrode dislocations that can cause such variability in the electromyogram (EMG) parameters that the treatment fails. The objective was to investigate the variability introduced by electrode displacement on EMG root mean square (RMS) and relative rest time (RRT) and the effect of a normalisation procedure using a reference contraction to compensate for this. Dislocation was simulated using simultaneous recordings of pairs of electrodes situated 15mm apart on the trapezius muscle, surrounding a central electrode pair at the standard position. To assess sensitivity for electrode displacement, intra-subject variability was used. To assess the effects of normalisation, both intra and inter-subject variability were used. Results indicated a large sensitivity of RMS to electrode displacements, with no differences between typing (42%) and the reference task (43%). No systematic changes were found relative to a specific electrode dislocation. Normalisation of RMS resulted in a decrease in the sensitivity for electrode displacement (33%), but did not decrease inter-subject variability (27%). The median value of the intra-subject variability of RRT, using a fixed threshold, was 4.9%, whereas the normalised threshold did not decrease the intra-subject variability (7%). The results suggest that RRT is suitable for individual follow-up measurements and applications such as myofeedback, without the need for a normalisation procedure. The use of RMS requires considerably more care, owing to its large sensitivity to electrode displacement and lack of substantial effects of normalisation.

The effect of subcutaneous fat on myoelectric signal amplitude and cross-talk.

The effect of subcutaneous fat on myoelectric signal amplitude and cross-talk was studied using finite element (FE) models of electromyogram (EMG) signal propagation. A FE model of the upper arm consisted of skin, fat, muscle and bone tissues in concentric layers. Single muscle fibre action potentials were simulated for muscle fibres at a variety of depths and combined to simulate surface EMG interference patterns. As fat layers of 3, 9 and 18 mm were added to the model, the RMS (root mean square) amplitude of the surface EMG signal directly above the centre of the active muscle decreased by 31.3, 80.2 and 90.0%, respectively. Similarly, surface EMG cross-talk above the region of inactive muscle increased as the fat layer thickness increased. The surface EMG RMS amplitude fell below 5% of its value above the centre of the muscle at 14 degrees, 17 degrees, 34 degrees and 47 degrees from the edge of the active muscle with fat layers of 0, 3, 9 and 18 mm, respectively. An additional model was developed with the subcutaneous fat layer thinned from 9 mm to 3 mm in a small, focal region under a pair of recording electrodes. Reducing the fat layer in this manner caused the surface EMG amplitude at the electrodes to increase by 241% and decreased the EMG cross-talk by 68%; this was near the values for the 3 mm uniform fat layer. This demonstrates that fat reduction surgery can increase surface EMG signal amplitude and signal independence for improved prosthesis control.

Mechanomyogram and electromyogram responses of upper limb during sustained isometric fatigue with varying shoulder and elbow postures.

To investigate the behavior of mechanomyogram (MMG) and electromyogram (EMG) signals in the time and frequency domains during sustained isometric contraction, MMG and surface EMG were obtained simultaneously from four muscles: upper trapezius (TP), anterior deltoid (DL), biceps brachii (BB), and brachioradialis (BR) of 10 healthy male subjects. Experimental conditions consisted of 27 combinations of 9 postures [3 shoulder angles (SA): 0 degree, 30 degrees, 60 degrees and 3 elbow angles (EA): 120 degrees, 90 degrees, 60 degrees] and 3 contraction levels: 20%, 40%, and 60% of maximum voluntary contraction (MVC). Subjective evaluations of fatigue were also assessed using the Borg scale at intervals of 60, 30, and 10 sec at 20%, 40%, and 60% MVC tests, respectively. The mean power frequency (MPF) and root mean square (RMS) of both signals were calculated. The current study found clear and significant relationships among physiological and psychological parameters on the one hand and SA and EA on the other. EA's effect on MVC was found to be significant. SA had a highly significant effect on both endurance time and Borg scale. In all experimental conditions, significant correlations were found between the changes in MPF and RMS of EMG in BB with SA and EA (or muscle length). In all four muscles, MMG frequency content was two or three times lower than EMG frequency content. During sustained isometric contraction, the EMG signal showed the well-known shift to lower frequencies (a continuous decrease from onset to completion of the contraction). In contrast, the MMG spectra did not show any shift, although its form changed (generally remaining about constant). Throughout the contraction, increased RMS of EMG was found for all tests, whereas in the MMG signal, a significant progressive increase in RMS was observed only at 20% MVC in all four muscles. This supports the hypothesis that the RMS amplitude of the MMG signal produced during contraction is highly correlated with force production. Possible explanations for this behavioral difference between the MMG and EMG signals are discussed.

Changes in surface EMG and acoustic myogram parameters during static fatiguing contractions until exhaustion: influence of elbow joint angles.

The purpose of this study was to evaluate muscle fatigue using electromyogram (EMG) and acoustic myogram (AMG) signals of the shoulder and arm muscles during sustained holding tasks, with the elbow at different angles and at different levels of maximum voluntary contraction (MVC). The EMG and AMG of four muscles, including the upper trapezius (TP), anterior deltoid (DL), biceps brachii (BB), and brachioradialis (BR), were recorded during experiments using 10 healthy young males. The experiments were conducted under 9 pairs of conditions: 3 elbow angles (120 degrees, 90 degrees, and 60 degrees) and *3 levels of %MVC (20%, 40%, and 60%). Subjects were instructed to hold a weight equal to the designated %MVC at designated joint angles and asked to maintain that condition for as long as possible until exhaustion. Joint angles were also recorded by the electrogoniometers. The analysis of variance revealed that there was no significant effect of elbow angle on the mean MVC or on the endurance time. Elbow angle showed a significant effect on mean power frequency (MPF) of EMG in DL, BB, and BR, and a significant effect on root mean square (RMS) of EMG in four muscles. In BB and BR, MPF of EMG at 120 degrees was found to be significantly lower than 90 degrees and 60 degrees, respectively. There was a significant main effect of elbow angle on MPF of AMG for TP at 20% MVC; for DL at 20% and 40% MVC; for BB at 40% and 60% MVC; and for BR at the three levels of %MVC. The results showed that the range MPF of AMG for DL, BB, and BR was between 32 to 46 Hz, whereas that for TP was from 49 to 83 Hz. There was a significant effect of elbow angle on RMS of AMG in all four muscles in all experiments. At 20% MVC, a progressive increase in RMS of AMG was observed with time. In contrast, at 40% and 60% MVC, RMS showed very different behavior; specifically, it was found that RMS of AMG at 20% MVC significantly increased with increase of elbow angle. We conclude that RMS of AMG has a good and clear correlation with elbow angle at a low level of contraction.

Electromyographic changes in work-related myalgia of the trapezius muscle.

In 11 patients, all women, 21-55 years of age, with unilateral work-related myalgia of the trapezius muscle, the right and left trapezius muscles were examined simultaneously for electromyogram (EMG) signs of localized muscle fatigue. All patients were tested with 0-kg hand load for 5 min, holding the arms straight at 90 degrees of elevation in the scapular plane. Only 4 of the patients tolerated exposure to higher load levels. They were tested with 1 kg hand load for 3 min and 2 kg hand load for 2 min, with a period of rest of 30 min between the trials. The EMG mean power frequency (MPF) and root mean square (rms) were calculated. Data were normalized with the initial value as a reference and regression analyses were performed. On both sides a decrease of MPF and an increase of rms were found with increasing time and load, i.e. classical EMG signs of localized muscle fatigue. Compared with the nonaffected side smaller changes were found on the affected side, possibly due to pain inhibition, impaired microcirculation and biochemical changes along the muscle fibres. At 0-kg hand load we found no change of MPF on either side despite subjective feelings of fatigue and pain. We interpreted these findings as an indication of reduced capacity of the affected trapezius muscle to sustain static load with early development of pain-associated local fatigue.