EMG Power Spectrum Research Articles

The use of a three-dimensional dynamic arm support prevents the development of muscle fatigue during repetitive manual tasks in healthy individuals.

Work-related upper extremity disorders are costly to society due to resulting medical costs, presenteeism and absenteeism. Although their aetiology is likely multifactorial, physical workplace factors are known to play an important role in their development. Promising options for preventing work-related upper extremity disorders include assistive technologies such as dynamic arm supports designed to follow the movement of the arm while compensating for its weight. The objective of this study was to assess the effects of a dynamic arm support on perceived exertion, muscle activity and movement patterns of the upper limb during repetitive manual tasks in healthy individuals. Thirty healthy right-handed individuals were allocated either a static or a dynamic task to perform with and without a dynamic arm support. During the task, surface electromyographic activity (anterior and middle deltoid, upper trapezius) and upper limb kinematics (elbow, shoulder, sternoclavicular) were measured using surface EMG and inertial sensors. Results showed that the dynamic arm support significantly reduced perceived exertion during the tasks and limited the development of muscular fatigue of the anterior and middle deltoid as demonstrated by EMG signal mean epoch amplitudes and median frequency of the EMG power spectrum. The dynamic arm support also prevented a decrease in shoulder elevation and an increase in total shoulder joint excursion during static and dynamic task, respectively. These results denote the potential benefits of dynamic arm supports in work environments. Further studies should focus on their efficacy, acceptability and implementability in work settings.

Impact of fatigue at the shoulder on the contralateral upper limb kinematics and performance.

BackgroundAltered movement patterns have been proposed as an etiological factor for the development of musculoskeletal pain. Fatigue influences upper limb kinematics and movement performance which could extend to the contralateral limb and potentially increasing risk of injury. The aim of this study was to investigate the impact of fatigue at the dominant arm on the contralateral upper limb movement.MethodsForty participants were randomly assigned to one of two groups: Control or Fatigue Group. All participants completed a reaching task at the baseline and post-experimental phase, during which they reached four targets with their non-dominant arm in a virtual reality environment. Following the baseline phase, the Fatigue Group completed a shoulder fatigue protocol with their dominant arm only, while the Control Group took a 10-minute break. Thereafter, the reaching task was repeated. Upper limb and trunk kinematics (joint angles and excursions), spatiotemporal (speed and accuracy) and surface electromyographic (sEMG) activity (sEMG signal mean epoch amplitude and median frequency of the EMG power spectrum) were collected. Two-way repeated-measures ANOVA were performed to determine the effects of Time, Group and of the interaction between these factors.ResultsThere was a significant Time x Group interaction for sternoclavicular elevation range of motion (p = 0.040), movement speed (p = 0.043) and accuracy (p = 0.033). The Fatigue group showed higher contralateral sternoclavicular elevation and increased movement error while experiencing fatigue in the dominant arm. Moreover, the Control group increased their speed during the Post-experimental phase compared to baseline (p = 0.043), while the Fatigue group did not show any speed improvement. There was no EMG sign of fatigue in any of the muscles evaluated.ConclusionThis study showed that fatigue at the dominant shoulder impacts movement at the contralateral upper limb. Such changes may be a risk factor for the development of shoulder pain in both the fatigued and non-fatigued limbs.

Surface EMG cross talk quantified at the motor unit population level for muscles of the hand, thigh, and calf.

Cross talk is an important source of error in interpreting surface electromyography (EMG) signals. Here, we aimed at characterizing cross talk for three groups of synergistic muscles by the identification of individual motor unit action potentials. Moreover, we explored whether spatial filtering (single and double differential) of the EMG signals influences the level of cross talk. Three experiments were conducted. Participants (total 25) performed isometric contractions at 10% of the maximal voluntary contraction (MVC) with digit muscles and knee extensors and at 30% MVC with plantar flexors. High-density surface EMG signals were recorded and decomposed into motor unit spike trains. For each muscle, we quantified the cross talk induced to neighboring muscles and the level of contamination by the nearby muscle activity. We also estimated the influence of cross talk on the EMG power spectrum and intermuscular correlation. Most motor units (80%) generated significant cross-talk signals to neighboring muscle EMG in monopolar recording mode, but this proportion decreased with spatial filtering (50% and 42% for single and double differential, respectively). Cross talk induced overestimations of intermuscular correlation and has a small effect on the EMG power spectrum, which indicates that cross talk is not reduced with high-pass temporal filtering. Conversely, spatial filtering reduced the cross-talk magnitude and the overestimations of intermuscular correlation, confirming to be an effective and simple technique to reduce cross talk. This paper presents a new method for the identification and quantification of cross talk at the motor unit level and clarifies the influence of cross talk on EMG interpretation for muscles with different anatomy.NEW & NOTEWORTHY We proposed a new method for the identification and quantification of cross talk at the motor unit level. We show that surface EMG cross talk can lead to physiological misinterpretations of EMG signals such as overestimations in the muscle activity and intermuscular correlation. Cross talk had little influence on the EMG power spectrum, which indicates that conventional temporal filtering cannot minimize cross talk. Spatial filter (single and double differential) effectively reduces but not abolish cross talk.

Control of oscillatory force tasks: Low-frequency oscillations in force and muscle activity

Force variability during steady force tasks is strongly related to low-frequency oscillations (<0.25 Hz) in force. However, it is unknown whether low-frequency oscillations also contribute to the variability of oscillatory force tasks. To address this, twelve healthy young participants (21.08 ± 2.99 years, 6 females) performed a sinusoidal force task at 15% MVC at two different frequencies (0.5 and 1 Hz) with isometric abduction of the index finger. We recorded the force from the index finger and surface EMG from the first dorsal interosseous muscle and quantified the following outcomes: 1) trajectory variability and accuracy; 2) power spectrum of force and EMG bursting below 2 Hz; 3) power spectrum of the interference EMG from 4 to 60 Hz. The trajectory variability and error significantly increased from 0.5 to 1 Hz task (P < 0.01). Increased force oscillations <0.25 Hz contributed to greater trajectory variability and error for both the 0.5 and 1 Hz oscillatory task (R2 > 0.33; P < 0.05). The <0.25 Hz oscillations in force were positively associated with greater power in the <0.25 Hz for EMG bursting (R2 > 0.52; P < 0.01). The modulation of the interference EMG from 35 to 60 Hz was a good predictor of the <0.25 Hz force oscillations for both the 0.5 Hz task and 1 Hz task (R2 > 0.66; P < 0.01). These results provide novel evidence that, similar to steady contractions, low-frequency oscillations of the motor neuron pool appear to be a significant mechanism that controls force during oscillatory force tasks.

Spectral analysis of peri-pharyngeal muscles’ EMG in patients with OSA and healthy subjects

IntroductionIn addition to dyscoordination of upper airway dilator muscles activity, sleep may also alter the pattern of intra-muscular activation of single motor units (SMUs). Such changes should be identifiable by a state dependent change in EMG power spectrum, i.e., a shift in centroid frequency (ƒc) during sleep. MethodsEMGs of the genioglossus and four other peri-pharyngeal muscles were recorded in OSA patients (n = 8), age-matched healthy subjects (n = 7), and 5 young healthy subjects, and ƒc was calculated for wakefulness and sleep periods. Resultsƒc decreased with the onset of sleep and returned to baseline levels after arousal. ƒc of all muscles decreased similarly and significantly during sleep in the OSA and the age-matched healthy subjects, but not in the young subjects. ConclusionsThe pattern of decrease in ƒc is compatible with altered synchronization of SMUs during sleep. We speculate that these changes may contribute to the failure of dilator muscles to improve flow limitation during sleep in older subjects.

A model computation of how synchronization and clustering of motor unit action potentials alter the power spectra of electromyograms

Abstract Introduction The duration of bursts of muscle activity e.g. while running or walking, is too short for long pulse trains of motor unit action potentials (MUAPs) to develop. A pool of motor units is likely activated simultaneously which generates clustered MUAPs. The hypothesis is that the EMG power spectra are modulated by the fact that MUAPs cluster. The purpose is to quantify this modulation analytically. Methods A model of an EMG signal is presented that includes clustered MUAPs. Results According to the model the influence of MUAPs clustering is shown to be largest at lower frequencies and increases when the width of the time window containing the clusters decreases. Discussion The power at frequencies below 60 Hz strongly reflects changes of the degree of clustering. The mean frequency of the EMG therefore decreases when MUAPs cluster more tightly. Thus, clustering of MUAPs competes with other physiological properties that influence the mean frequency. The EMG power is proportional to the number of active MUAPs at high frequencies but approaches a value proportional to the square of the number of active MUAPs at very low frequencies. To obtain a measure of amplitude that is proportional to the number of active motor units, one should focus on the higher frequency power components only, however, to monitor the effect of clustering of MUAP one should focus on the lower frequency power. That could become relevant for comparing pre- and post-operative clinical gait studies where changes in MUAPs clustering may play a significant role.

Evaluating abdominal core muscle fatigue: Assessment of the validity and reliability of the prone bridging test.

The aims of this study were to research the amplitude and median frequency characteristics of selected abdominal, back, and hip muscles of healthy subjects during a prone bridging endurance test, based on surface electromyography (sEMG), (a) to determine if the prone bridging test is a valid field test to measure abdominal muscle fatigue, and (b) to evaluate if the current method of administrating the prone bridging test is reliable. Thirty healthy subjects participated in this experiment. The sEMG activity of seven abdominal, back, and hip muscles was bilaterally measured. Normalized median frequencies were computed from the EMG power spectra. The prone bridging tests were repeated on separate days to evaluate inter and intratester reliability. Significant differences in normalized median frequency slope (NMFslope ) values between several abdominal, back, and hip muscles could be demonstrated. Moderate-to-high correlation coefficients were shown between NMFslope values and endurance time. Multiple backward linear regression revealed that the test endurance time could only be significantly predicted by the NMFslope of the rectus abdominis. Statistical analysis showed excellent reliability (ICC=0.87-0.89). The findings of this study support the validity and reliability of the prone bridging test for evaluating abdominal muscle fatigue.

Relationship of EMG and Subjective Discomfort Ratings for Repetitive Handling of Lightweight Loads

Objective: The aim of this study is to evaluate the effect of weight of load and time on the physical workload of repetitive upper-limb tasks with handling light weight loads using EMG and perceived discomfort, and to investigate the relationship between EMG and perceived discomfort for those repetitive tasks of moving light weight loads. Background: Repetitive upper-limb motion is known as one of the main risk factors of musculoskeletal disorders, and a lot of repetitive tasks are carried out while handling light weight loads in the industry. In evaluating the workload of repetitive tasks handling light weight loads, EMG and perceived discomfort can be used, though their relationship in those work conditions are not much investigated. Method: A laboratory experiment with 18 healthy males were conducted to record EMG signals from 5 muscle sites of the right arm and shoulder and rate perceived discomforts for the body parts and the whole body while carrying out repetitive materials-handling tasks for 52min. The subjects were divided into 3 groups which handled the loads of 1kg, 2kg and 3kg, respectively. ANOVAs were conducted to analyze the effects of the weight and time on RMS of EMG amplitude (normalized RMS: NRMS), median frequency of power spectrum of EMG (normalized MDF: NMDF) and perceived discomfort. The correlations between NRMS and NMDF and perceived discomfort were also analyzed. Results: Statistically significant muscular fatigue effects were not found from NRMS and NMDF in most muscles, while there were significant increases of discomfort as the task time elapsed. It was shown that there were an increasing trend of the muscular activity as the weight of load increased and a decreasing trend of median frequency of EMG of upper and lower arms as time elapsed. It was found that there were significant negative correlations between NMDFs from the lower arm and discomfort ratings, though the relationships were weak. Conclusion: It can be concluded that the working conditions adopted in this study were not enough to induce muscular fatigue, while there was significant increase in perceived discomfort. A further study is necessary to integrate the objective and subjective measures for more reliable and sensitive evaluation of workload of repetitive tasks of handling light weight loads. Application: This study can be used as a basic study for the evaluation of workload of repetitive tasks handling light weight loads.

Force control is related to low-frequency oscillations in force and surface EMG.

Force variability during constant force tasks is directly related to oscillations below 0.5 Hz in force. However, it is unknown whether such oscillations exist in muscle activity. The purpose of this paper, therefore, was to determine whether oscillations below 0.5 Hz in force are evident in the activation of muscle. Fourteen young adults (21.07±2.76 years, 7 women) performed constant isometric force tasks at 5% and 30% MVC by abducting the left index finger. We recorded the force output from the index finger and surface EMG from the first dorsal interosseous (FDI) muscle and quantified the following outcomes: 1) variability of force using the SD of force; 2) power spectrum of force below 2 Hz; 3) EMG bursts; 4) power spectrum of EMG bursts below 2 Hz; and 5) power spectrum of the interference EMG from 10–300 Hz. The SD of force increased significantly from 5 to 30% MVC and this increase was significantly related to the increase in force oscillations below 0.5 Hz (R 2 = 0.82). For both force levels, the power spectrum for force and EMG burst was similar and contained most of the power from 0–0.5 Hz. Force and EMG burst oscillations below 0.5 Hz were highly coherent (coherence = 0.68). The increase in force oscillations below 0.5 Hz from 5 to 30% MVC was related to an increase in EMG burst oscillations below 0.5 Hz (R 2 = 0.51). Finally, there was a strong association between the increase in EMG burst oscillations below 0.5 Hz and the interference EMG from 35–60 Hz (R 2 = 0.95). In conclusion, this finding demonstrates that bursting of the EMG signal contains low-frequency oscillations below 0.5 Hz, which are associated with oscillations in force below 0.5 Hz.

Inspiratory muscle resistance to fatigue during exercise and simulated airway obstruction

Respiratory muscle fatigue can develop during simulated airway obstruction. The aim of this study was to characterize the pattern of inspiratory muscle fatigue and to assess the resistance to fatigue of diaphragm (D), parasternal (PS), sternocleidomastoid (SM) and scalene (SC). 8 healthy untrained subjects participated in this study. To identify signs of inspiratory muscles fatigue development electromyographic activity of D, PS, SCM and SC was recorded during 5-min exercise with loaded breathing (40 cm H2O/L · s(-1)). The before-to-after exercise measurements of maximal inspiratory pressure (MIP) and EMG power spectrum changes were performed. Maximal inspiratory pressure declined about 12% after exercise test compared with control, whereas the peak magnitude of integrated electrical activity of D, PS, SCM and SC during post-exercise Muller's maneuver was significantly greater than in pre-exercise test in all subjects. The extent ofinspiratory muscles fatigue was evaluated by analysis of shift in centroid frequency (fc) of EMG power spectrum. All subjects demonstrated a significant reduction in fc of PS, SCM and SC.fc of D was not changed. Diaphragm is more resistantto fatigue during obstructive breathing compared with PS, SCM and SC. The data suggest that the reduction of maximum inspiratory pressure in chronic obstructive pulmonary disease also caused primarily by the weakening of the accessory muscles, while the weakness of the diaphragm may occur in the later stages of the disease. The functional failure of accessory muscles is an additional factor, which, along with the additional breathing resistance increases the load on the diaphragm, promoting its fatigue and reduced respiratory reserve.

Power spectrum of the rectified EMG: influence of motor unit action potential shapes.

The rectification of EMG signals is a preprocessing method widely used for inferring neural connectivity by coherence analysis. The assumption for the use of this non-linear operator is that it enhances the neural information in the signal, i.e. the motor unit spike trains. However, because of non-linearity, it is difficult to predict the effect of rectification on the EMG power spectrum. In this study, we analyze the influence of the motor unit action potential properties on spectral content of the rectified EMG. The results show that changes in the action potential waveforms have a strong influence on the rectified EMG power spectrum, with an effect on estimated coherence functions. Knowledge on the properties of action potentials may be necessary for properly comparing the rectified EMG power spectrum across conditions.

Effects of inspiratory muscle training on resistance to fatigue of respiratory muscles during exhaustive exercise.

The aim of this study was to assess the effect of inspiratory muscle training (IMT) on resistance to fatigue of the diaphragm (D), parasternal (PS), sternocleidomastoid (SCM) and scalene (SC) muscles in healthy humans during exhaustive exercise. Daily inspiratory muscle strength training was performed for 3 weeks in 10 male subjects (at a pressure threshold load of 60% of maximal inspiratory pressure (MIP) for the first week, 70% of MIP for the second week, and 80% of MIP for the third week). Before and after training, subjects performed an incremental cycle test to exhaustion. Maximal inspiratory pressure and EMG-analysis served as indices of inspiratory muscle fatigue assessment. The before-to-after exercise decreases in MIP and centroid frequency (fc) of the EMG (D, PS, SCM, and SC) power spectrum (P<0.05) were observed in all subjects before the IMT intervention. Such changes were absent after the IMT. The study found that in healthy subjects, IMT results in significant increase in MIP (+18%), a delay of inspiratory muscle fatigue during exhaustive exercise, and a significant improvement in maximal work performance. We conclude that the IMT elicits resistance to the development of inspiratory muscles fatigue during high-intensity exercise.

A Feasibility Study of Fatigue and Muscle Contraction Indices Based on EMG Time-dependent Spectral Analysis

Parameters derived from EMG power spectrum are beneficial methods for assessing muscle fatigue. Two important indices are median frequency and mean frequency (MDF and MNF). They have been established as the global muscle fatigue indices, particularly in static muscle contraction of biceps brachii muscle. However, a major problem of these parameters is a nonlinear relationship between muscle load/force and feature value, particularly in cyclic dynamic muscle contraction of forearm muscles. In this study, EMG feature indices that can simultaneously identify both fatigue and load are proposed. Instead of using an entire EMG signal fast Fourier transformation (FFT), a concept of using consecutive FFT has been proposed as known as the “Time-Dependent MDF and MNF” (TD-MDF and TDMNF). The success of TD-MDF and TD-MNF features used to determine muscle fatigue have been presented in a lot of research works, whereas the performance of TD-MDF and TD-MNF used to determine muscle load have been proposed in a few research works. Moreover, it has not previously been evaluated with the forearm muscles. Thus it has been investigated in this study. Four forearm muscles are evaluated including flexor pollicis longus, supinator longus, extensor carpi radialis longus and pronator radii teres. The results showed that the proposed methods have a linear relationship with muscle load in some selected range of TD-MNF for flexor pollicis longus muscle that were not found for traditional MDF and MNF. Moreover, a statistically significant difference between TD-MNF values for different loading conditions (p < 0.2) was observed. The optimal method of TD-MNF was successful when overlapping consecutive window was performed with 512-sample window size and 128-sample window increment.

Effect of Botulinum Toxin on Pressure Pain Threshold and EMG Power Spectrum of Masseter Muscle During Sustained Fatiguing Contraction

The aims of this study were to test the effect of botulinum toxin on a reversible, prolonged, experimental pain and on muscle fatigue in human masseter muscle, both caused by a sustained clench. The masseter muscles were injected with botulinum toxin in 19 subjects and with isotonic saline in 16 subjects. We measured electromyographic activity at maximum voluntary contraction, pressure pain threshold before and after a 70% maximum voluntary contraction clench sustained to pain tolerance, and the median frequency of the electromyographic power spectrum during that clench at baseline and at 1, 2, and 3 mos after botulinum toxin or saline injection. After botulinum toxin injection, the botulinum toxin group had a reduced maximum voluntary contraction for the ensuing 3 mos and smaller decreases in pressure pain threshold from before to after the sustained clench. Also, the change in median frequency from before to after the sustained clench did not significantly differ during the postinjection sessions. However, postinjection, preclench median frequency was lower in the group injected with botulinum toxin. We interpret the reduced change in pressure pain threshold with botulinum toxin as a clinically modest but statistically significant analgesic effect on this model of acute muscle pain.

Isometric back muscle endurance: An EMG study on the criterion validity of the Ito test

The validity of the Sorensen test as a measure for back muscle endurance is controversial due to a possible impact of hip extensor muscles. The aim of this study was to investigate the criterion validity of an alternative test (Ito test) compared to the Sorensen test. Both procedures were performed by 29 healthy subjects (11 women) for 5 s and until exhaustion (randomized order). EMG activity was measured from 3 lumbar back and 3 hip extensor muscles. Muscular involvement in test positions was calculated as percentage of maximal voluntary contraction (MVC). Muscle fatigue was determined by the normalized regression coefficient of the median frequencies of the EMG power spectrum (NMF slope). Prediction of holding time by NMF slope values was investigated using regression analysis. In the test positions, the hamstring muscles were activated to a higher MVC percentage in the Sorensen than in the Ito test, while the iliocostalis muscle was less activated. Similarly, the iliocostalis ( p = 0.006) and the multifidi muscles ( p = 0.03) significantly contributed to predict holding time in the Ito test, whereas the multifidi muscles ( p = 0.001) and the semitendinosus muscle ( p = 0.046) did so in the Sorensen test. The results of this study indicate that the Ito test might present a valuable alternative for testing back muscle endurance in LBP patients.

Robust EMG–fMRI artifact reduction for motion (FARM)

Current template-based artifact reduction methods are inadequate to reduce irregular volume- and slice-artifacts induced by limb motion in combined (surface) EMG-fMRI (electromyography-functional magnetic resonance imaging) studies. In addition, artifacts are not removed adequately for EMG frequencies above 50 Hz. We present a new fMRI artifact reduction algorithm for motion (FARM) and compare it with standard artifact correction as implemented in fMRI artifact slice-template removal (FASTR). One control subject generated motion artifacts during EMG-fMRI. Low-frequency motion artifacts and volume-artifacts were removed prior to slice-artifact correction. Slice-artifacts were phase-shifted and removed with motion adaptive templates (FARM). EMG data were also corrected applying FASTR. Time traces demonstrate that artifacts related to sudden changes in wire position are contained to shorter time periods. EMG power spectra from neck and arm muscles show that FARM has improved performance at higher frequencies. High-pass filtering, volume-artifact removal, phase-shifting and adaptation of slice-templates to motion improve the quality of artifact-corrected EMG recorded during limb motion. The improved accuracy at which EMG-fMRI data can be obtained opens up new ways to directly relate self-paced movements to brain activations and to study patients suffering from movement disorders.

EMG analysis of lumbar paraspinal muscles as a predictor of the risk of low-back pain

Studies of EMG power spectra have established associations between low-back pain (LBP) and median frequency (MF). This 2-year prospective study investigates the association of LBP with EMG variables over time. 120 health care workers underwent paraspinal EMG measurements and assessment of back pain disability. The EMG recordings were performed under isometric trunk extension at 2/3 maximum voluntary contraction and acquired from erector spinae muscles at the level of L4/L5. 108 (90%) subjects were reviewed at a minimum 2-year follow up. 16 out of 93 subjects with no history of chronic low-back pain became worse as measured by time off work, disability, reported pain and self-assessment rating. The value of the EMG variable half-width at inception demonstrated significant association with changes in subject's outcome measure and their own assessment of their LBP at follow up (p < 0.05). Based on self-assessment data, subjects with no history of chronic LBP with half-width of greater than 56 Hz were at threefold greater risk of developing back pain compared with the remainder of the population (p = 0.045). The value of the initial median frequency (IMF) and MF slope at inception were also associated with the subjects' own assessment of LBP at follow up. Subjects with an IMF greater than 49 Hz were at 5.8-fold greater risk of developing back pain compared with the remainder of the population (p = 0.014). EMG variables recorded from lumbar paraspinal muscles can identify a sub group of subjects at increased risk of developing low-back pain in the future.

Rectification of the EMG Signal Impairs the Identification of Oscillatory Input to the Muscle

Rectification of EMG signals is a common processing step used when performing electroencephalographic-electromyographic (EEG-EMG) coherence and EMG-EMG coherence. It is well known, however, that EMG rectification alters the power spectrum of the recorded EMG signal (interference EMG). The purpose of this study was to determine whether rectification of the EMG signal influences the capability of capturing the oscillatory input to a single EMG signal and the common oscillations between two EMG signals. Several EMG signals were reconstructed from experimentally recorded EMG signals from the surface of the first dorsal interosseus muscle and were manipulated to have an oscillatory input or common input (for pairs of reconstructed EMG signals) at various frequency bands (in Hz: 0-12, 12-30, 30-50, 50-100, 100-150, 150-200, 200-250, 250-300, and 300-400), one at a time. The absolute integral and normalized integral of power, peak power, and peak coherence (for pairs of EMG signals) were quantified from each frequency band. The power spectrum of the interference EMG accurately detected the changes to the oscillatory input to the reconstructed EMG signal, whereas the power spectrum of the rectified EMG did not. Similarly, the EMG-EMG coherence between two interference EMG signals accurately detected the common input to the pairs of reconstructed EMG signals, whereas the EMG-EMG coherence between two rectified EMG signals did not. The frequency band from 12 to 30 Hz in the power spectrum of the rectified EMG and the EMG-EMG coherence between two rectified signals was influenced by the input from 100 to 150 Hz but not from the input from 12 to 30 Hz. The study concludes that the power spectrum of the EMG and EMG-EMG coherence should be performed on interference EMG signals and not on rectified EMG signals because rectification impairs the identification of the oscillatory input to a single EMG signal and the common oscillatory input between two EMG signals.

시각장애청소년의 Cycle Ergometer 운동시 환기역치와 근피로도 분석

This study aims to investigate levels of physical strength, including ventilatory threshold and muscle fatigue, in an adolescent with blindness using cycle ergometer. The participants were composed of an adolescents with or without the blindness (n=15). 30 subjects performed grade maximal exercise tests(GXT) in cycle ergometer. Surface EMG data taken from quadriceps muscles during exercise on cycle ergometer. The frequency components of the surface EMG power spectrum were analyzed using MPF and IEMG. The statistical procedures used to the analysis were unpaired t-test. The results showed that exercise time, VO2max and ventilatory threshold were significantly decreased in the group with blindness compared to the normal group. Also there were significant differences to MPF (mean power frequency) and IEMG values of musculus vastus lateralis and musculus vastus medialis between two groups. In conclusion, our data suggest that increased physical fitness by aerobic exercise is one of the most effective methods to enhance quality of life in an adolescent with blindness.

Cortical correlates of the basic and first harmonic frequency of Parkinsonian tremor

It has been hypothesized that the basic and first harmonic frequency of Parkinsonian tremor are somewhat independent oscillations the biological basis of which remains unclear. We recorded 64-channel EEG in parallel with EMG of the forearm muscles most affected by rest tremor in 21 PD patients. EMG power spectrum, corticomuscular coherence spectra and EEG power spectra for each EEG electrode were calculated. The dynamics of the coherence and relative EMG and EEG power at the basic (tremor) frequency were calculated by a sliding, overlapping window analysis. Corticomuscular delays and direction of interaction were analysed by the maximizing coherence method for narrow band signals. The contralateral EEG electrodes with maximal coherence were different for the basic and first harmonic frequency. The dynamical coherence curves showed non-parallel time courses for the two frequencies. The mean EEG-EMG and EMG-EEG delays were all around 15-20ms but significantly longer for the first harmonic than for the basic frequency. Our data indicate different cortical representations and corticomuscular interaction of the basic and first harmonic frequencies of Parkinsonian tremor. Separate central generators seem to contribute to the tremor via different pathways. Further studies on this complex tremor network are warranted.