Biomedical subjects

Roberto Merletti

Publications and source records attributed to Roberto Merletti.

At least 19 recordsLinked to original sources

PubMed2006

Sensitivity of the cross-correlation between simulated surface EMGs for two muscles to detect motor unit synchronization.

The purpose of the study was to evaluate the use of cross-correlation analysis between simulated surface electromyograms (EMGs) of two muscles to quantify motor unit synchronization. The volume conductor simulated a cylindrical limb with two muscles and bone, fat, and skin tissues. Models of two motor neuron pools were used to simulate 120 s of surface EMG that were detected over both muscles. Short-term synchrony was established using a phenomenological model that aligned the discharge times of selected motor units within and across muscles to simulate physiological levels of motor unit synchrony. The correlation between pairs of surface EMGs was estimated as the maximum of the normalized cross-correlation function. After imposing four levels of motor unit synchrony across muscles, five parameters were varied concurrently in the two muscles to examine their influence on the correlation between the surface EMGs: 1) excitation level (5, 10, 15, and 50% of maximum); 2) muscle size (350 and 500 motor units); 3) fat thickness (1 and 4 mm); 4) skin conductivity (0.1 and 1 S/m); and 5) mean motor unit conduction velocity (2.5 and 4 m/s). Despite a constant and high level of motor unit synchronization among pairs of motor units across the two muscles, the cross-correlation index ranged from 0.08 to 0.56, with variation in the five parameters. For example, cross-correlation of EMGs from pairs of hand muscles, each having thin layers of subcutaneous fat and mean motor unit conduction velocities of 4 m/s, may be relatively insensitive to the level of synchronization across muscles. In contrast, cross-correlation of EMGs from pairs of leg muscles, with larger fat thickness, may exhibit a different sensitivity. These results indicate that cross correlation of the surface EMGs from two muscles provides a limited measure of the level of synchronization between motor units in the two muscles.

Computer Simulation↗

PubMed2006

Two-dimensional spatial distribution of surface mechanomyographical response to single motor unit activity.

In order to better understand the mechanisms of generation of mechanomyography (MMG) signals, the two-dimensional distribution of surface MMG produced by the activity of single motor units was analyzed by a novel two-dimensional recording method. Motor unit action potentials were identified from intramuscular electromyographic (EMG) signals and used to trigger the averaging of MMG signals detected over the tibialis anterior muscle of 11 volunteers with a grid of 5x3 accelerometers (20-mm inter-accelerometer distance). The intramuscular wires were inserted between the first and second accelerometer in the middle column of the grid, proximal to the innervation zone. The subjects performed three contractions with visual feedback of the intramuscular EMG signals. In each contraction, a new motor unit was recruited at the minimum stable discharge rate (mean+/-S.D., N = 11 subjects, 7.3+/-2.3 pulse/s), resulting in torque of 2.4+/-2.8% of the maximal voluntary contraction (MVC), 4.6+/-2.7% MVC, and 6.3+/-3.1% MVC (all different, P < 0.01). For 23 out of 33 detected motor units, it was possible to extract the motor unit surface acceleration map (MUAM). A negative MUAM peak (-2.7+/-2.2 mm/s2) was detected laterally and a positive MUAM peak (4.1+/-2.4 mm/s2) medially (P < 0.001). The time-to-peak was shorter in the medial part of the muscle (2.9+/-0.4 ms) than in the other locations (3.4+/-0.5 ms, P < 0.001). The double integrated signals (muscle displacement) indicated negative deflection in the lateral part and inflation close to the tibia bone. The maps of acceleration showed spatial dependency in single motor unit MMG activities. The technique provides a new insight into motor unit contractile properties.

Acceleration↗

PubMed2006

Compression of surface EMG signals with algebraic code excited linear prediction.

Despite the interest in long timescale recordings of surface electromyographic (EMG) signals, only a few studies have focused on EMG compression. In this paper we investigate a lossy coding technique for surface EMG signals that is based on the algebraic code excited linear prediction (ACELP) paradigm, widely used for speech signal coding. The algorithm was adapted to the EMG characteristics and tested on both simulated and experimental signals. The coding parameters selected led to a compression ratio of 87.3%. For simulated signals, the mean square error in signal reconstruction and the percentage error in average rectified value after compression were 11.2% and 4.90%, respectively. For experimental signals, they were 6.74% and 3.11%. The mean power spectral frequency and third-order power spectral moment were estimated with relative errors smaller than 1.23% and 8.50% for simulated signals, and 3.74% and 5.95% for experimental signals. It was concluded that the proposed coding scheme could be effectively used for high rate and low distortion compression of surface EMG signals. Moreover, the method is characterized by moderate complexity (approximately 20 million instructions/s) and an algorithmic delay smaller than 160 samples (approximately 160ms).

Adult↗

PubMed2006

Amplitude cancellation reduces the size of motor unit potentials averaged from the surface EMG.

The purpose of the study was to evaluate the influence of selected physiological parameters on amplitude cancellation in the simulated surface electromyogram (EMG) and the consequences for spike-triggered averages of motor unit potentials derived from the interference and rectified EMG signals. The surface EMG was simulated from prescribed recruitment and rate coding characteristics of a motor unit population. The potentials of the motor units were detected on the skin over a hand muscle with a bipolar electrode configuration. Averages derived from the EMG signal were generated using the discharge times for each of the 24 motor units with lowest recruitment thresholds from a population of 120 across three conditions: 1) excitation level; 2) motor unit conduction velocity; and 3) motor unit synchronization. The area of the surface-detected potential was compared with potentials averaged from the interference, rectified, and no-cancellation EMGs. The no-cancellation EMG comprised motor unit potentials that were rectified before they were summed, thereby preventing cancellation between the opposite phases of the potentials. The percent decrease in area of potentials extracted from the rectified EMG was linearly related to the amount of amplitude cancellation in the interference EMG signal, with the amount of cancellation influenced by variation in excitation level and motor unit conduction velocity. Motor unit synchronization increased potentials derived from both the rectified and interference EMG signals, although cancellation limited the increase in area for both potentials. These findings document the influence of amplitude cancellation on motor unit potentials averaged from the surface EMG and the consequences for using the procedure to characterize motor unit properties.

Action Potentials↗

PubMed2006

A finite element model for describing the effect of muscle shortening on surface EMG.

A finite-element model for the generation of single fiber action potentials in a muscle undergoing various degrees of fiber shortening is developed. The muscle is assumed fusiform with muscle fibers following a curvilinear path described by a Gaussian function. Different degrees of fiber shortening are simulated by changing the parameters of the fiber path and maintaining the volume of the muscle constant. The conductivity tensor is adapted to the muscle fiber orientation. In each point of the volume conductor, the conductivity of the muscle tissue in the direction of the fiber is larger than that in the transversal direction. Thus, the conductivity tensor changes point-by-point with fiber shortening, adapting to the fiber paths. An analytical derivation of the conductivity tensor is provided. The volume conductor is then studied with a finite-element approach using the analytically derived conductivity tensor. Representative simulations of single fiber action potentials with the muscle at different degrees of shortening are presented. It is shown that the geometrical changes in the muscle, which imply changes in the conductivity tensor, determine important variations in action potential shape, thus affecting its amplitude and frequency content. The model provides a new tool for interpreting surface EMG signal features with changes in muscle geometry, as it happens during dynamic contractions.

Action Potentials↗

PubMed2005

Influence of motor unit properties on the size of the simulated evoked surface EMG potential.

The purpose of the study was to quantify the influence of selected motor unit properties on the simulated amplitude and area of evoked muscle potentials detected at the skin surface. The study was restricted to a motor unit population simulating a hand muscle whose potentials were recorded on the skin over the muscle. Peak-to-peak amplitude and area of the evoked potential were calculated from the summed motor unit potentials and compared across conditions that simulated variation in different motor unit properties. The simulations involved varying the number of activated motor units, muscle fiber conduction velocities, axonal conduction velocities, neuronal activation times, the shape of the intracellular action potential, and recording configurations commonly used over hand muscles. The results obtained for the default condition simulated in this study indicated that ~7% of the motor unit potentials were responsible for 50% of the size of the evoked potential. Variation in the amplitude and area of the evoked muscle potential was directly related to the number of active motor units only when the stimulus activated motor units randomly, and not when activation was based on a parameter such as motor unit size. Independent adjustments in motor unit properties had variable effects on the size of the evoked muscle potential, including when the stimulus activated only a subpopulation of motor units. These results provide reference information that can be used to assist in the interpretation of experimentally observed changes in the size of evoked muscle potentials.

Action Potentials↗

PubMed2005

Non-invasive characterization of single motor unit electromyographic and mechanomyographic activities in the biceps brachii muscle.

The aim of the study was to investigate amplitude and frequency content of single motor unit (MU) electromyographic (EMG) and mechanomyographic (MMG) responses. Multi-channel surface EMG and MMG signals were detected from the dominant biceps brachii muscle of 10 volunteers during isometric voluntary contractions at 20%, 50%, and 80% of the maximal voluntary contraction (MVC) force. Each contraction was performed three times in the experimental session which was repeated in three non-consecutive days. Single MU action potentials were identified from the surface EMG signals and their times of occurrence used to trigger the averaging of the MMG signal. At each contraction level, the MUs with action potentials of highest amplitude were identified. Single MU EMG and MMG amplitude and mean frequency were estimated with normalized standard error of the mean within subjects (due to repetition of the measure in different trials and experimental sessions) smaller than 15% and 7%, respectively, in all conditions. The amplitude of the action potentials of the detected MUs increased with increasing force (mean +/- SD, 244 +/- 116 microV at 20% MVC, and 1426 +/- 638 microV at 80% MVC; P < 0.001) while MU MMG amplitude increased from 20% to 50% MVC (40.5 +/- 20.9 and 150 +/- 88.4 mm/s(2), respectively; P<0.001) and did not change significantly between 50% and 80% MVC (129 +/ -82.7 mm/s(2) at 80% MVC). MU EMG mean frequency decreased with contraction level (20% MVC: 97.2 +/- 13.9 Hz; 80% MVC: 86.2 +/- 11.4 Hz; P < 0.001) while MU MMG mean frequency increased (20% MVC: 33.2 +/- 6.8 Hz; 80% MVC: 40.1 +/- 6.1 Hz; P < 0.001). EMG peak-to-peak amplitude and mean frequency of individual MUs were not correlated with the corresponding variables of MMG at any contraction level.

Action Potentials↗

PubMed2005

Time-frequency analysis and estimation of muscle fiber conduction velocity from surface EMG signals during explosive dynamic contractions.

Time-frequency analysis of the surface electromyographic (EMG) signal is used to assess muscle fiber membrane properties during dynamic contractions. The aim of this study was to compare the direct estimation of average muscle fiber conduction velocity (CV) with instantaneous mean frequency (iMNF) of surface EMG signals in isometric and explosive dynamic contractions. The muscles investigated were the vastus lateralis and medialis of both thighs in 12 male subjects. The isometric contractions were at linearly increasing force (0-100% of the maximal voluntary contraction in 10s). The explosive contractions were performed on a multipurpose ergometer-dynamometer (MED). The subject, sitting on the MED, performed six explosive contractions, separated by 2 min rest, by pushing against two force platforms and thrusting himself backwards with the maximum possible speed, while completely extending his legs. The estimated CV significantly increased with force in both the isometric (mean+/-S.D., from 3.24+/-0.34 to 5.12+/-0.31 m/s for vastus lateralis and from 3.17+/-0.26 to 5.11+/-0.34 m/s for vastus medialis, with force in the range 10-100% of the maximal voluntary contraction level) and explosive contractions (from 4.36+/-0.49 to 5.00+/-0.47 m/s for vastus lateralis, and from 4.32+/-0.46 to 4.94+/-0.44 m/s for vastus medialis, with force in the range 17.5-100% of maximal thrusting force). Moreover, estimated CV was not significantly different at the maximal force in the two exercises. On the contrary, iMNF, computed from the Choi-Williams time-frequency transform, was significantly lower in the explosive (57.7+/-8.2 and 66.5+/-10.3 Hz for vastus laterialis and medialis, respectively) than in the isometric exercises (73.7+/-9.2 and 75.0+/-8.5 Hz for vastus laterialis and medialis, respectively) and did not change with force in any of the conditions. It was concluded that EMG spectral features provide different information with respect to average muscle fiber CV in dynamic contractions. Thus, in general, they cannot be used to infer CV changes during the exertion of a dynamic task. A joint analysis of CV and EMG spectral features is necessary in this type of contractions.

Adult↗

PubMed2005

Reinnervation of motor units in intrinsic muscles of a transplanted hand.

Functional recovery of transplanted hand can be evaluated clinically but until now there has been no direct assessment of muscle control. In October 2000 we transplanted the right hand of a brain-dead man aged 43 onto a man aged 35 who had lost his right dominant hand 22 years before. Starting from day 205 after the transplant, multi-channel surface electromyographic (EMG) signals were recorded from intrinsic muscles of the transplanted hand in order to assess their degree of reinnervation. Eleven months post-operatively, the first motor unit action potential train was detected from the abductor digiti minimi. One month later, also the abductor pollicis brevis and the opponens pollicis muscles showed motor unit activity, while, after 15 and 24 months, the first dorsal interosseous and the first lumbricalis muscles, respectively, showed activation of their first motor units. An increase in the number of active motor units was observed after the first signs of reinnervation, although the process was rather slow. In sustained maximal contractions, the motor unit discharge rate decreased from (mean +/- S.D.) 34.0+/-6.7 pps to 23.4+/-5.1 pps in 60 s for the abductor digiti minimi, although the subject was verbally encouraged to maintain a maximal activation. Moreover, the subject was able to perform basic control tasks involving voluntary modulation of motor unit discharge rate. With a visual feedback, he could increase discharge rate of the abductor digiti minimi approximately linearly over time, from 13.4+/-6.7 pps to 32.5+/-11.2 pps in 60 s. In conclusion, we showed reinnervation of single motor units in a transplanted hand after 22 years of denervation. Moreover, voluntary modulation of discharge rates of these motor units could be performed since the first sign of reinnervation.

Adult↗

PubMed2004

Single motor unit and spectral surface EMG analysis during low-force, sustained contractions of the upper trapezius muscle.

Intramuscular and surface electromyographic (EMG) activities were recorded from the left and right upper trapezius muscle of eight healthy male subjects during 5-min long static contractions at 2% and 5% of the maximal voluntary contraction (MVC) force. Intramuscular signals were detected by wire electrodes while surface EMG signals were recorded with linear adhesive electrode arrays. The surface EMG signals were averaged using the potentials extracted from the intramuscular EMG decomposition as triggers. The conduction velocity of single motor units (MUs) was estimated over time from the averaged surface potentials while average rectified value and mean power spectral frequency were computed over time from 0.5 s epochs of surface EMG signal. It was found that (1) MUs were progressively recruited after the beginning of sustained contractions of the upper trapezius muscle at 2% and 5% MVC, (2) the conduction velocity of the MUs active since the beginning of the contraction significantly decreased over time, and (3) although the CV of single MUs significantly decreased, the mean power spectral frequency of the surface EMG did not show a consistent trend over time. It was concluded that spectral surface EMG analysis, being affected by many physiological mechanisms, may show limitations for the objective assessment of localized muscle fatigue during low force, sustained contractions. On the contrary, single motor unit conduction velocity may provide an early indication of changes in muscle fiber membrane properties with sustained activity.

Action Potentials↗

PubMed2004

Cross-comparison of time- and frequency-domain methods for monitoring the myoelectric signal during a cyclic, force-varying, fatiguing hand-grip task.

Various conventional methods to estimate the mean and median power spectral frequencies, and amplitude of the surface electromyogram during 30-90 min, cyclic, force-varying, constant-posture contractions were cross-compared in an experimental trial. The aim was to determine the most appropriate algorithm implementations and reduce the total number of algorithms that need to be considered when monitoring time trends. Subjects produced hand-grip contractions in a repeated intermittent pattern until exhaustion. For all estimated parameters: analysis of contraction levels below 25% maximum voluntary contraction produced poor estimates due to high relative measurement noise; parameter reproducibility was best when comparisons were aligned to the actual force produced rather than the target force and when the biomechanics of the contraction were more consistent; and estimates were not greatly influenced by the rate of change of the force trajectory. For frequency parameters: estimates based on the short-time Fourier transform were similar to those based on time-varying autoregressive methods; longer duration analysis windows exhibited better repeatability; and simple frequency-domain noise filters were not effective in reducing the impact of measurement noise. For amplitude estimates: whitening reduced the variance of the amplitude estimate; and the best analysis window duration was a trade-off between bias (decreased with a short duration window) and variance (decreased with a long duration window).

Adult↗

PubMed2004

Influence of amplitude cancellation on the simulated surface electromyogram.

The purpose of the study was to quantify the influence of selected motor unit properties and patterns of activity on amplitude cancellation in the simulated surface electromyogram (EMG). The study involved computer simulations of a motor unit population with physiologically defined recruitment and rate coding characteristics that activated muscle fibers whose potentials were recorded on the skin over the muscle. Amplitude cancellation was quantified as the percent difference in signal amplitude when motor unit potentials were summed before and after rectification. The simulations involved varying the level of activation for the motor unit population, the recording configuration, the upper limit of motor unit recruitment, peak discharge rates, the amount of motor unit synchronization, muscle fiber length, the thickness of the subcutaneous tissue, and the motor unit properties that change with advancing age. The results confirmed a previous experimental report (Day SJ and Hulliger M, J Neurophysiol 86: 2144-2158, 2001) that amplitude cancellation in the surface EMG can reach 62% at maximal activation. A decrease in the range of amplitudes of the motor unit potentials, as can occur during fatiguing contractions, increased amplitude cancellation up to approximately 85%. Differences in the amount of amplitude cancellation were observed across all simulated conditions, and resulted in substantial changes in the absolute magnitude of the EMG signal. The most profound factors influencing amplitude cancellation were the number of active motor units and the duration of the action potentials. The effects of amplitude cancellation were minimal (<5%) when the EMG amplitude was normalized to maximal values, with the exception of variations in peak discharge rate and recruitment range, which resulted in differences up to 17% in the normalized EMG signal across conditions. These results indicate the amount of amplitude cancellation that can occur in various experimental conditions and its influence on absolute and relative measures of EMG amplitude.

Action Potentials↗

PubMed2004

A new method for the extraction and classification of single motor unit action potentials from surface EMG signals.

It has been shown that multi-channel surface EMG allows assessment of anatomical and physiological single motor unit (MU) properties. To get this information, the action potentials of single MUs should be extracted from the interference EMG signals. This study describes an automatic system for the detection and classification of MU action potentials from multi-channel surface EMG signals. The methods for the identification and extraction of action potentials from the raw signals and for their clustering into the MUs to which they belong are described. The segmentation phase is based on the matched Continuous Wavelet Transform (CWT) while the classification is performed by a multi-channel neural network that is a modified version of the multi-channel Adaptive Resonance Theory networks. The neural network can adapt to slow changes in the shape of the MU action potentials. The method does not require any interaction of the operator. The technique proposed was validated on simulated signals, at different levels of force, generated by a structure based surface EMG model. The MUs identified from the simulated signals covered almost the entire recruitment curve. Thus, the proposed algorithm was able to identify a MU sample representative of the muscle. Results on experimental signals recorded from different muscles and conditions are reported, showing the possibility of investigating anatomical and physiological properties of the detected MUs in a variety of practical cases. The main limitation of the approach is that complete firing patterns can be obtained only in specific cases due to MU action potential superpositions.

Action Potentials↗

PubMed2004

Estimation of average muscle fiber conduction velocity from two-dimensional surface EMG recordings.

We propose a novel method for the estimation of muscle fiber conduction velocity (CV) from surface EMG recordings. The approach is based on the analysis of signals detected along a number of linear electrode arrays parallel to the fiber direction, thus collected by a bi-dimensional (2-D) array (matrix) of electrodes. The information provided by the 2-D array is used to derive a maximum likelihood estimator which can be applied to any number of signals and which may account for missing channels in the matrix. An iterative technique in the frequency domain for the estimation of the propagation delay is proposed to reduce the computational time and avoid the limit of resolution due to signal sampling. The method proposed is applied to signals collected from the biceps brachii muscle of eight healthy subjects during isometric, constant force contractions at 50% of the maximal voluntary contraction torque. It is shown that CV estimation standard deviation and sensitivity to electrode displacements significantly decrease by the application of the method proposed with respect to classic CV estimation techniques. The method promises to be a useful tool when average CV is estimated for muscle assessment and diagnostic purposes.

Action Potentials↗

PubMed2004

M-wave properties during progressive motor unit activation by transcutaneous stimulation.

The aim of this study was to interpret changes in experimentally recorded M waves with progressive motor unit (MU) activation based on simulation of the surface electromyogram. Activation order during transcutaneous electrical stimulation was analyzed by investigating M-wave average rectified value, spectral properties, and conduction velocity (CV) during electrically elicited contractions. M-waves were detected from the biceps brachii muscle of 10 healthy male subjects by a linear adhesive array of eight electrodes. Electrical stimulation was delivered to the motor point at either constant current intensity (40, 60, 80, and 100% of the supramaximal stimulation current) or with linearly increasing current. A model of surface electromyogram generation that varied activation order based on MU size and location was used to interpret the experimental results. From the experimental and model analysis, it was found that 1) MUs tended to be activated from low to high CV and from the superficial to the deep muscle layers with increasing transcutaneous electrical stimulation of the biceps brachii muscle, and 2) characteristic spectral frequencies of the M-wave were affected by many factors other than average CV (such as the activation order by MU location or the spread of the MU innervation zones and CVs), thus decreasing with a concomitant increase in CV during progressive MU activation.

Adult↗

PubMed2004

Reproducibility of muscle-fiber conduction velocity estimates using multichannel surface EMG techniques.

The aim of this study was to assess the reproducibility of muscle-fiber conduction velocity (MFCV) estimates obtained from multichannel surface electromyographic (EMG) recordings. Surface EMG signals were collected with a matrix of 61 electrodes during isometric, submaximal (50% of the maximal voluntary contraction torque) contractions of the biceps brachii muscle. Conduction velocity was estimated using multichannel maximum likelihood techniques. Reproducibility of MFCV estimates was assessed varying the number of signals (two to seven) used for the estimate and the distance between detection points (5-30 mm). Intraclass correlation coefficient (ICC) of both initial MFCV values and their rates of change with fatigue increased when increasing number of signals and distance between detection points. ICC of initial MFCV was negative using two signals for MFCV estimate, and it increased to approximately 75% with six to seven signals. Thus, reproducibility of MFCV estimates may be improved significantly using advanced multichannel estimation methods with respect to classic two-channel techniques.

Analysis of Variance↗

PubMed2004

Myoelectric manifestations of fatigue during exposure to hypobaric hypoxia for 12 days.

Lack of oxygen, as occurs at high altitude (HA), leads to a number of adaptive processes in muscle, but their precise nature is unclear. To better understand mechanisms of adaptations of the neuromuscular system to HA, we collected surface electromyographic (EMG) signals during a 12-day stay at 5,050 m above sea level (SL). The aim was to investigate the effect of hypobaric hypoxia on muscle-fiber membrane and motor-unit control properties. Surface EMG signals were recorded from the dominant biceps brachii muscle of six subjects at HA and 3 months after their return to SL. Supramaximal electrical stimuli (25 HZ) were delivered and voluntary isometric contractions at 40 and 80% of maximal voluntary torque were performed in 10 experimental sessions at HA and in 3 at SL. Maximal isometric torque was not altered at HA. Surface EMG spectral frequencies at the beginning of the voluntary contractions were greater at HA than SL. The rates of change of spectral frequencies and conduction velocity during the voluntary contractions were significantly larger at HA than SL. No differences in EMG variables were observed in the electrically elicited contractions. The maximal torque and surface EMG variables did not depend on the day of measure at HA. It was concluded that acute exposure to hypobaric hypoxia does not significantly affect the muscle-fiber membrane properties but does impact motor-unit control properties. This provides new insights in the understanding of motor control in extreme conditions of oxygen reduction, with relevance for sport and rehabilitation medicine, and may also explain the pathophysiological adaptations of the neuromuscular system occurring in such disorders as chronic obstructive pulmonary disease.

Acclimatization↗

PubMed2004

Neck flexor muscle fatigue is side specific in patients with unilateral neck pain.

Despite the evidence of greater fatigability of the cervical flexor muscles in neck pain patients, the effect of unilaterality of neck pain on muscle fatigue has not been investigated. This study compared myoelectric manifestations of sternocleidomastoid (SCM) and anterior scalene (AS) muscle fatigue between the painful and non-painful sides in patients with chronic unilateral neck pain. Myoelectric signals were recorded from the sternal head of SCM and the AS muscles bilaterally during sub-maximal isometric cervical flexion contractions at 25% and 50% of the maximum voluntary contraction (MVC). The time course of the mean power frequency, average rectified value and conduction velocity of the electromyographic signals were calculated to quantify myoelectric manifestations of muscle fatigue. Results revealed greater estimates of the initial value and slope of the mean frequency for both the SCM and AS muscles on the side of the patient's neck pain at 25% and 50% of MVC. These results indicate greater myoelectric manifestations of muscle fatigue of the superficial cervical flexor muscles ipsilateral to the side of pain. This suggests a specificity of the effect of pain on muscle function and hence the need for specificity of therapeutic exercise in the management of neck pain patients.

Adult↗