Relationship between electrical and vibratory output of muscle during voluntary contraction and fatigue

Measurements were done on the biceps muscles of 6 healthy volunteers to record simultaneously the surface electromyogram (EMG) and vibromyogram (VMG) by means of a piezoelectric device (accelerometer). The VMG is generated by mechanical waves due to the contraction mechanism and often measured as sound. The frequency spectrum and integrated value (IEMG and IVMG) of both signals were calculated. Both IEMG and IVMG showed a clear linear correlation with force, although at high forces, the variability of the VMG became rather high. Two series of experiments were performed to study the EMG and VMG changes in relation to changes induced by fatigue: (1) during constant force at 50% of the maximal voluntary contraction (MVC) and recovery; (2) for one 1 minute during declining force at MVC. The main finding was that the IVMG was related to the absolute force, irrespective of the fatigue state of the muscle. In contrast, the IEMG showed the well-known changes during fatigue, such as an increase during endurance. The spectral changes of the two measurements also showed a divergence. The spectra of the EMG shifted to lower frequencies in both fatigue protocols. In contrast, the spectra of the vibratory signal did not shift, except for several measurements at MVC. However, the shape did change to a somewhat flatter spectrum with less pronounced peaks. Possible explanations for this different behavior are discussed. It is concluded that the vibratory energy generated by the contraction mechanism is linearly related to force. Changes induced by fatigue do not alter this relationship: this contrasts with the behavior of the EMG.(ABSTRACT TRUNCATED AT 250 WORDS)     

Utility of electromyographic fatigue threshold during treadmill running

Introduction: We investigated 2 different methods for determining muscle fatigue threshold by electromyography (EMG). Methods: Thirteen subjects completed an incremental treadmill running protocol for EMG fatigue threshold (EMG_FT) determination based on the critical power concept (EMG_FT1) and the breakpoint in the linear relationship between EMG amplitude and exercise intensity (EMG_FT2). Then, both the EMG_FT1 and EMG_FT2 were tested in a continuous treadmill running protocol. EMG was recorded from the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and lateral gastrocnemius (LG) muscles. Results: For BF, EMG_FT2 was higher than EMG_FT1, and EMG_FT1 for BF was lower than EMG_FT1 for LG. EMG of RF was higher at EMG_FT2 than at EMG_FT1, and LG EMG was lower at EMG_FT2. Conclusions: EMG_FT can be determined during a single treadmill running test, and EMG_FT1 may be the most appropriate method to estimate the muscle fatigue threshold during running. Muscle Nerve 52 : 1030–1039, 2015     

EMG spectral differences among the quadriceps femoris during the stretch reflex

Introduction: The purpose of this study was to examine the electromyographic (EMG) spectral characteristics of the quadriceps femoris muscles during tendon tap stretch reflexes. Methods: Sixteen healthy subjects (mean ± SD age = 21.2 ± 2.8 years) performed tendon tap reflexes of the leg extensors as surface EMG signals were detected from the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles of the dominant thigh. All EMG signals were processed with a wavelet analysis, and the resulting spectra were decomposed with nonparametric spectral decomposition. Results: The results showed that the spectra for the VL had significantly more high‐frequency power than those for the RF and VM, with similar spectral shapes for the RF and VM. Conclusions: These findings could be due to differences in the width of the innervation zone, or the fiber type composition of the muscles, although the latter seems to be more likely. Muscle Nerve 52 : 826–831, 2015     

Activation linearity and parallelism of the superficial quadriceps across the isometric intensity spectrum

The purpose of this study was to assess neuromuscular activation of the three superficial portions of the quadriceps femoris muscles during linearly increasing isometric contraction intensities. Thirty healthy volunteers were assessed for isometric electromyographic (EMG) activity of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscles with the knee at 60 degrees of flexion. For 5 s, subjects performed isometric contractions equivalent to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% of the average of three maximal voluntary contractions (MVC), in random order. Full-wave rectified and integrated EMG signals over the middle 3 s of each contraction were expressed as a percentage of the activity recorded during the three averaged MVCs. One sample t-tests and 95% confidence intervals were calculated at each relative torque level. A two-factor analysis of variance (muscle by intensity) with repeated measures was performed to evaluate parallel activation across the intensity levels. Activation linearity was assessed via regression analysis for each muscle. VM activation was shown to be significantly lower than expected at 20-70% MVC. VL and RF activations were significantly higher than expected at 10% MVC, and RF EMG was less than expected at 40-70% MVC. EMG of VM was shown to increase significantly more than VL and RF from 80% to 90% MVC. Significant linear and quadratic relations were also demonstrated for all three muscles. Parallel activation of the superficial quadriceps muscles occurred from low to moderate intensities, whereas convergence was noted at near maximal intensities.     

Comparison of electromyographic responses for the superficial quadriceps muscles: Cycle versus knee‐extensor ergometry

The purpose of this study was to compare the electromyographic (EMG) amplitude and mean power frequency (MPF) versus power output relationships for the three superficial quadriceps muscles during incremental cycle (CE) and knee‐extensor (KE) ergometry in the same subjects. Eight men performed incremental CE and KE tests to exhaustion. Surface EMG signals were recorded simultaneously from the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). Polynomial regression analyses on a subject‐by‐subject basis indicated that the relationship between EMG amplitude versus power output was best‐fit with either a linear, quadratic, or cubic model for CE, whereas the relationship was best‐fit with a linear model for all subjects for the KE test. No consistent relationship was found for EMG MPF within subjects and between muscle groups for CE or KE. Compared with CE, however, the EMG amplitude during KE exercise was, on average, approximately 87% and 30% higher for the RF and VM muscles, respectively. These results suggest that KE exercise may be a better mode of examining EMG amplitude in the quadriceps muscle during incremental exercise than traditional CE. Muscle Nerve, 2009     

Electromyography and mechanomyography of elbow agonists and antagonists in Parkinson disease

The purpose of this study was to assess the electromyographic (EMG) and mechanomyographic (MMG) activities of agonist and antagonist muscles in Parkinson disease patients during maximal isometric elbow contraction in flexion and extension. Ten elderly females with Parkinson disease (average age 75 years) and 10 age‐matched healthy females were tested. The torque and the EMG and MMG signals from biceps brachii and triceps brachii were recorded during sustained maximal voluntary isometric contraction of the elbow flexors and extensors. There were no intergroup differences in the EMG and MMG activities of agonist and antagonist muscles or in torque. This might be because the Parkinson subjects were tested during their medication “ON” phase, or perhaps maximal isometric contraction (MVC) induced greater active muscle stiffness that affected the MMG signal. Muscle Nerve 40: 240–248, 2009     

High-frequency oscillations in human respiratory electromyograms during voluntary breathing

Electromyograms (EMGs) from respiratory muscles were obtained from human subjects during voluntarily controlled breathing. In 10 studies on 6 subjects EMGs were recorded from right and left lower ventrolateral surface of the rib cage while the subject emphasized the use of his diaphragm for breathing. Simultaneous samples of the 2 EMG signals of 256-ms duration were obtained once per inspiration (in either the first or second half of inspiration) from each of 30 consecutive breaths using a laboratory minicomputer. Individual power spectra for the 2 EMG signals, and the squared coherence spectrum between them, were calculated. From the coherence spectrum common high-frequency oscillations could be identified within two frequency ranges: 70–100 Hz and 20–50 Hz. Peaks at similar frequencies were identified in both early-inspiratory and late-inspiratory EMG signals. Similar experiments were done on 3 subjects from whom an esophageal diaphragm EMG was obtained as well. The coherence spectrum between the esophageal EMG and the right rib cage surface EMG again demonstrated the presence of common high-frequency oscillations in the same frequency ranges as above. Evidence of these oscillations was not usually apparent in the power spectra. When ECG signal components were allowed of contaminate some of the EMG data samples, the coherence spectrum could be altered considerably, leading to inappropriate conclusions regarding the presence or absence of high-frequency oscillations.It is hypothesized that these high-frequency oscillations are similar to those described in nerve recordings from previous studies on anesthetized and decerebrate cats and dogs and a mechanism for their expression in EMG signals is proposed.The coherence spectrum is a very sensitive method for detecting related signal components in two signals. That high-frequency oscillations can be detected using the less sensitive techniques of autocorrelation and power spectral analysis in some animal preparations may reflect an enhancement of these oscillations in those preparations.     

Mechanomyographic amplitude and mean power output during maximal, concentric, isokinetic muscle actions

The purpose of this study was to determine the velocity-related patterns for mechanomyographic (MMG) amplitude, electromyographic (EMG) amplitude, mean power output (MP), and peak torque (PT) of the superficial muscles of the quadriceps femoris (vastus lateralis [VL], rectus femoris [RF], and vastus medialis [VM]) during maximal, concentric, isokinetic leg extensions. Twelve adult women (mean +/- SD: 22 +/- 3 years of age) performed such leg extensions at velocities of 60 degrees, 120 degrees, 180 degrees, 240 degrees, and 300 degrees /s on a Cybex 6000 dynamometer. PT decreased (P < 0.05) across velocity to 240 degrees /s. MP and MMG amplitude for each muscle (VL, RF, and VM) increased (P < 0.05) with velocity to 240 degrees /s and then plateaued. EMG amplitude increased (P < 0.05) to 240°/s for the VL, remained unchanged across velocity (P > 0.05) for the RF, and increased (P < 0.05) to 300 degrees /s for the VM. The results indicated close similarities between the velocity-related patterns for MMG amplitude and MP, but dissociations among EMG amplitude, MMG amplitude, and PT. These findings support the recent hypothesis that MMG amplitude is more closely related to MP than PT during maximal, concentric, isokinetic muscle actions and, therefore, may be useful for monitoring training-induced changes in muscle power.     

Knee extensor torque,work, and EMG during subjectively graded dynamic contractions

We examined knee extensor peak torque, work, and electromyogram (EMG) during dynamic contractions to perceived exertion levels in men and women. Thirty subjects performed three maximal effort isokinetic knee extensions (60 deg x s(-1)), followed by three contractions to each of nine separate levels of perceived exertion. Surface EMG of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF), and knee extensor peak torque and work were normalized to a percent of each respective value obtained during the maximal effort contractions. The results demonstrated a significant linear increase in voluntary knee extensor peak torque and work across perceived exertion levels. Knee extensor peak torque and work were less than 70%, 80%, and 90% maximal voluntary contraction (MVC) at perceived exertion levels 7, 8, and 9, respectively. A significant increase in VM, VL, and RF muscle EMG was observed across perceived exertion levels 1 through 9, with EMG increase highest for the VL. The findings demonstrate that dynamic contractions guided by perceived exertion are underproduced at relatively high perceptual intensities, and that reliance on VL activation occurs across submaximal torque levels. The overestimation of knee extensor peak torque and work at relatively high perceptual intensities may suggest the presence of a subconscious mechanism aiming to reduce high muscle and joint forces.     

Monitoring of free calcium in the neuronal endoplasmic reticulum: an overview of modern approaches

This paper describes an improved spike triggered averaging technique for the assessment of control properties and conduction velocity (CV) of single motor units (MUs) of the tibialis anterior muscle during voluntary muscle contractions. The method is based on the detection of multi-channel surface EMG signals (with linear electrode arrays) and intramuscularly recorded single MU action potentials (MUAPs). Intramuscular electrodes were inserted in the muscle taking into account the MU structural properties (innervation zone, tendon locations, length of the fibers), assessed by the linear array surface EMG detection technique. An algorithm for intramuscular EMG signal decomposition is used to identify single MUAP trains. The MUAPs detected by the intramuscular EMG decomposition algorithm were used to trigger and average the multi-channel EMG signals. CV of single averaged surface MUAPs was estimated by the use of advanced signal processing methods based on multi-channel recordings which allow to consistently reduce the variance of CV estimates compared with traditional two channel delay estimators. The number of averaged potentials can thus be limited, resulting in high temporal resolution CV estimates. The developed technique was tested on recordings from the tibialis anterior muscle in 11 volunteers during fatigue. It was shown that the method allows the assessment of single MU CV changes (fatigue) as small as 0.1 m/s with less than 2 s data epochs. The method allows reliable assessment of firing rate and conduction properties of single MUs with applications for the investigation of central and peripheral fatigue mechanisms.     

Fatigue modulates synchronous but not asynchronous soleus activation during stimulation of paralyzed muscle

ObjectiveElectrical stimulation over a motor nerve yields muscle force via a combination of direct and reflex-mediated activation. We determined the influence of fatigue on reflex-mediated responses induced during supra-maximal electrical stimulation in humans with complete paralysis.MethodsWe analyzed soleus electromyographic (EMG) activity during repetitive stimulation (15 Hz, 125 contractions) in 22 individuals with complete paralysis. The bout of stimulation caused significant soleus muscle fatigue (53.1% torque decline).ResultsBefore fatigue, EMG at all latencies after the M-wave was less than 1% of the maximal M-wave amplitude (% MaxM). After fatigue there was a fourfold (p < 0.05) increase in EMG at the H-reflex latency; however, the overall magnitude remained low (<2% change in % MaxM). There was no increase in “asynchronous” EMG ～ 1 s after the stimulus train.ConclusionsFatigue enhanced the activation to the paralyzed soleus muscle, but primarily at the H-reflex latency. The overall influence of this reflex modulation was small. Soleus EMG was not elevated during fatigue at latencies consistent with asynchronous activation.SignificanceThese findings support synchronous reflex responses increase while random asynchronous reflex activation does not change during repetitive supra-maximal stimulation, offering a clinical strategy to consistently dose stress to paralyzed tissues.     

Involvement of the sensorimotor cortex in physiological force and action tremor.

Whole scalp magnetoencephalography (MEG) signals were recorded in 10 healthy subjects simultaneously with the surface electromyogram (EMG) of the contralateral forearm extensor muscles during isometric contraction and phasic movement of the wrist. In eight subjects, coherence and time domain analyses demonstrated correspondence between the MEG signal, originating near or in the hand region of the motor cortex, and the 6-12 Hz EMG recorded during isometric postural contractions. In contrast, we found little evidence for correspondence between the contralateral EMG and the MEG recorded over the Rolandic region during phasic movements. We conclude that the sensorimotor cortex is differentially involved in physiological force and action tremor at the wrist.     

MMG and EMG responses during fatiguing isokinetic muscle contractions at different velocities

The purpose of this study was to determine mechanomyographic (MMG) and electromyographic (EMG) responses of the superficial quadriceps muscles during repeated isokinetic contractions in order to provide information about motor control strategies during such activity, and to assess uniformity in mechanical activity (MMG) between the investigated muscles. Ten adults performed 50 maximal concentric muscle contractions at three randomly selected contraction velocities (60, 180, and 300 degrees.s(-1)) on different days. Surface electrodes and an MMG sensor were placed on the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). EMG and MMG amplitude and peak torque (PT) were calculated for each contraction, normalized, and averaged across all subjects. The results demonstrated that MMG amplitude more closely tracked the fatigue-induced decline in torque production at each velocity than did EMG amplitude. This indicates that MMG amplitude may be useful for estimating force production during fatiguing dynamic contractions when a direct measure is not available, such as during certain rehabilitative exercises. MMG amplitude responses of the VL, RF, and VM were not uniform for each velocity or across velocities, indicating that it may be possible to detect the individual contribution of each muscle to force production during repeated dynamic contractions. Therefore, MMG amplitude may be clinically useful for detecting abnormal force contributions of individual muscles during dynamic contractions, and determining whether various treatments are successful at correcting such abnormalities.     

Pitfalls and errors in measuring jitter

The safety factor of neuromuscular transmission can be assessed by measuring the neuromuscular jitter, which reflects the time variability of processes in the motor end-plate. Jitter is increased in any condition with disturbed end-plate function, such as myasthenic conditions and ongoing reinnervation. Jitter is increasingly being measured with concentric needle (CN) electrodes, which are more prone to artefacts than single fiber EMG recordings.The objective of this review is to identify and demonstrate pitfalls that can be seen with CN jitter measurements, made with both voluntary activation and electrical stimulation.With voluntary activation, errors are caused by poor signal quality; inappropriate time reference points on the signal; an irregular firing rate; and signals with dual latencies, i.e., “flip-flop.” With electrical stimulation, additional errors result from insufficient stimulation intensity; from abrupt change in firing rate; and from axon reflexes.Many pitfalls cannot be avoided during recording and can only be detected during post-processing.It is critical to be aware of these artefacts when measuring jitter with CN electrodes.     

Acoustic myography: A noninvasive monitor of motor unit fatigue

Acoustic myography is the recording of sounds produced by contracting muscle. These sounds become louder with increasing force of contraction. We have compared muscle sounds with surface EMG to monitor the dissociation of electrical from mechanical events (presumably, the loss of excitation–contraction coupling) which occur with motor unit fatigue. Acoustic signals were amplified using a standard phonocardiograph, recorded on FM magnetic tape, and digitally analyzed. Muscles were examined at rest, with intermittent contractions, and with sustained contractions. We found that with fatigue, the acoustic amplitude decayed, but the surface EMG amplitude did not. With decreased effort, however, the acoustic and the surface EMG amplitudes declined simultaneously. By simultaneously recording acoustic signals and needle EMG, individual motor units were resolved acoustically in two muscles with decreased numbers of motor units and increased motor unit size. Fasciculations also produced acoustic signals, although no acoustic signal has yet been found that correlates with fibrillations. Analysis of acoustic signals from muscle provides a noninvasive method for monitoring motor unit fatigue in vivo. It may also be useful in distinguishing muscle fatigue from decreased volition.     

Linearity and reliability of the mechanomyographic amplitude versus dynamic torque relationships for the superficial quadriceps femoris muscles

The purpose of this investigation was to examine the linearity and reliability of the mechanomyographic (MMG) amplitude versus dynamic torque relationships for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Nine healthy men and 11 healthy women performed submaximal to maximal, concentric, isokinetic muscle actions of the leg extensors at 30° s^?1 on two occasions. Surface MMG signals were detected from the VL, RF, and VM of the dominant thigh during both trials. The ranges of the coefficients of determination for the MMG amplitude versus dynamic torque relationships were 0.01–0.94 for the VL, 0.01–0.84 for the RF, and 0.19–0.96 for the VM. The intraclass correlation coefficients for the linear MMG amplitude versus torque slope coefficients were 0.823 (VL), 0.792 (RF), and 0.927 (VM). These results indicate that, when analyzed for individual subjects, the MMG amplitude versus dynamic torque relationships demonstrated inconsistent linearity. When using MMG in the clinical setting, dynamic muscle actions of the superficial quadriceps femoris muscles do not appear to be appropriate for assessing changes in muscle function during strength training. Muscle Nerve, 2009     

A surface EMG multi-electrode technique for characterizing muscle activation patterns in mice during treadmill locomotion

In mice a new method for 2x4-channel surface electromyography (EMG) recordings of the vastus lateralis and biceps femoris muscles during locomotion on a treadmill with varying speed is presented. The approach involves high-speed-videography (sampling interval 2.5 ms) in concert with the application of chronically implanted surface EMG multi-electrodes (EMG sampling rate 4000 Hz, frequency range 10-700 Hz). The recordings are started 2 days after surgery and finished 2 weeks after surgery. During the whole investigation period EMG recordings of both muscles have been possible. The monopolar EMG activities recorded by the electrode-arrays and the bipolar EMG signals derived from the monopolar activities permit an evaluation of the extent of myo-electrical activation in larger regions of both muscles and co-ordination between the flexor and extensor muscles. Bipolar EMG signals indicate propagation of activities along the muscle fibers and a slight effect of non-propagating signal components. Thus, the cross talk between these muscles is small and does not influence the evaluation of the EMG results. The resolution of the simultaneously recorded synchronized data allows a precise temporal correlation of kinematic and EMG parameters.     

The relationship between mean power frequency of the EMG spectrum and muscle fibre conduction velocity

Models of the behaviour of the surface EMG signal during fatigue have assumed that there is a linear relationship between the mean power frequency of the EMG spectrum and muscle fibre conduction velocity. They attribute the fall in mean power frequency during fatigue to a proportionate fall in fibre velocity. Experiments have been performed on human vastus lateralis in which forces ranging from 10% to 90% of the maximum force were sustained for times such that the product of the target force and the time was constant. Muscle fibre conduction velocity was estimated using a cross-correlation technique to determine the lag between two EMG signals. The results confirmed the linearity between mean power frequency and fibre velocity. It is still possible, however, that other factors such as de- and recruitment of fibres and change in motor unit firing rates contribute to the fall in mean power frequency during fatigue. Even if these factors are important, the primary assumption of current EMG models relating mean power frequency and muscle fibre velocity has been confirmed.     

书写痉挛患者丘脑腹外侧核团细胞电活动特点

目的 探讨书写痉挛(WC)患者丘脑腹外侧核团(VL)细胞电活动特点,为临床治疗提供可靠的依据.方法 10例WC患者在行立体定向VL毁损术的同时,应用微电极和肌电记录技术采集VL细胞和手术对侧肢体肌电活动.分析不同细胞的放电模式和平均自发放电频率(MSFR),并探讨VL细胞放电活动与肢体肌电的关系.结果 在10个针道中共甄别出85个VL神经元,61.2%的神经元呈不规则放电活动,MSFR为(20.3±14.9)Hz,变异系数(CV)为1.38±0.40;38.8%的神经元为紧张性放电活动,MSFR为(44.4±21.5)Hz,CV为0.84±0.11.功率谱相关性分析发现VL细胞放电活动的改变与WC相关(P＜0.05,n=12).结论 VL参与WC的病理生理过程.     

Role of valued living and associations with functional outcome following traumatic brain injury

Valued living (VL) is associated with improved enjoyment and engagement with daily activities despite negative emotional state or ongoing pain. However, the role of VL in recovery following traumatic brain injury (TBI) has yet to be investigated. This study aimed to examine changes in VL over the course of recovery and variables associated with VL. Participants with moderate-to-severe TBI were recruited from a rehabilitation hospital in three cohorts: “Early” (n?=?25), “Mid” (n?=?9) and “Late” (n?=?36) post-TBI. All participants were assessed at time of recruitment and 12 months later. The main measure was the Valued Living Questionnaire. Compared to pre-injury estimates, VL was significantly reduced at 12 months post-injury. Levels of VL remained reduced between 2 and 3 years and increased between 3 and 6 years post-injury. VL was strongly associated with improved functional and psychosocial outcomes. Changes in VL occur over at least 3–5 years post-injury, with 12 months post-TBI a suitable time for intervention given VL remains low over the next 24 to 36 months post injury. Targeted intervention to modify values and/or valued activities to be consistent with post-injury capacity could improve rates of return to pre-injury levels of VL.