Time-frequency coherence of categorized sEMG data during dynamic contractions of biceps, triceps, and brachioradialis as an approach for spasticity detection.

The assessment of muscular interactions between biceps, triceps, and brachioradialis can be used as an approach for the detection of spasticity in the upper limbs. A crucial prerequisite for the aforementioned validation of muscular interactions is the calculation of time frequencies due to the non-stationary characteristics of electromyographic (EMG) signals and thus the estimation of coherences. Adding biomechanical parameters increases the validity of the assessment process and simplifies the comparison of EMG data as a result of categorization. In this numerical-experimental study, a method will be introduced by using the smoothed pseudo Wigner-Ville distribution and a categorization algorithm to estimate and categorize coherences between biceps, triceps, and brachioradialis during dynamic contractions. The categorization will be performed according to the type of contraction, external load, joint angle, and angular velocity and will be used to assess 10 healthy subjects and 6 patients with spasticity. Generally, the introduced method shows the velocity dependence of coherence during spasticity in extension movements as well as much stronger muscular co-activation between triceps, biceps, and brachioradialis in spastic patients in comparison to healthy subjects. Furthermore, the influence of variables e.g. as joint angle, angular velocities, and type of contraction on the coherence is quantified.

[Influence of sex and side dominance on the results of quantitative, three-dimensional motion analysis of the upper extremities]. / Einfluss des Geschlechts und der Seitendominanz auf die Ergebnisse der quantitativen, dreidimensionalen Bewegungsanalyse der oberen Extremitäten.

AIM: Clinical assessment does not provide objective and quantitative evaluation of the shoulder function. Based on instrumental gait analysis a system for three-dimensional motion analysis of the upper extremities has been developed. The aim of this study is to evaluate the results of instrumental upper extremity motion analysis with respect to dependence on sex and side dominance. METHOD: 16 healthy subjects (8 male, 8 female, mean age 26 years) were included. Three-dimensional motion analysis was carried out with a video-based system and passive markers. All subjects performed two movement tasks representing activities of daily living (task A: reaching the neck, task B: removing a parking token). All joint angles of the upper extremity were recorded and graphically displayed. Additionally, a calculation of quantitative parameters was performed. RESULTS: Contrary to expectations the task "reaching the neck" was not combined with external shoulder rotation. Females performed most of the tasks quicker and with higher reproduction accuracy. Movement reproduction accuracy was rarely dependent on dominance. CONCLUSION: Three-dimensional upper extremity motion analysis of activities of daily living allows a precise and quantitative evaluation of movement patterns. The differences with respect to sex and side in a healthy group have to be respected in studies dealing with comparative shoulder function.

Movement analysis in the early detection of newborns at risk for developing spasticity due to infantile cerebral palsy.

In order to limit the consequences of infantile cerebral palsy (ICP), physiotherapy should start as early as possible. This requires that infants at risk are detected at the earliest age possible. Today, diagnosis is based on visual observation by physicians and as such is influenced by subjective impressions. Objective methods, quantifying the pathological deviation from normal spontaneous motor activity would be preferable as they, for example, allow an inter- and intra-individual comparison of movement. In this paper we have developed a methodology that allows the 3-dimensional acquisition of unconstrained movement in newborn babies, using a motion analysis system. From the recorded movement data we have extracted 53 quantitative parameters that describe the differences between healthy and affected participants. Considered individually, each of these parameters does not permit a conclusive statement to be made as to whether or not the patient is at risk. Cluster analysis based on Euclidian distances therefore has been used to find an optimal combination of eight parameters. The optimal combination has been subsequently applied to organize the participants' movement into preferably homogeneous classes labelled "healthy" or "at risk". Classification was performed utilising quadratic discriminant analysis. The methodology presented allows a reliable discrimination between healthy and affected participants. Overall detection rate reached 73%. This value is expected to rise with increasing patient and norm collective database size.

Upper trapezius muscle conduction velocity during fatigue in subjects with and without work-related muscular disorders: a non-invasive high spatial resolution approach.

The development of fatigue at the muscle fibre level can be assessed in terms of a decrease in conduction velocity (CV). The present study aimed to investigate if work-related muscular disorders in occupations characterised by static loads of long duration affect fatigue resistance in the painful muscle. A group of eight secretaries suffering from bilateral chronic muscle pain in the shoulder/neck region was compared to a group of healthy subjects. The upper trapezius muscle was studied under isometric contractions, holding the arm in the horizontal plane up to the endurance point. Changes in CV estimated at the motor unit level were investigated using a non-invasive high spatial resolution electromyographic (EMG) approach. In addition, the number of motor unit potentials per second (PPS), and the root mean square (RMS) of bipolar signals were assessed, and the results reported as the mean and standard error for each value. Subjects with work-related disorders showed less pronounced changes in CV with respect to healthy subjects. No differences between subjects with and without work-related disorders were encountered for the PPS and RMS. The present findings on CV indicate an increased fatigue-related recruitment of MUs in the painful muscle with respect to a healthy muscle. The fact that this recruitment is not reflected in the PPS and RMS estimates might be due to a fatigue-induced decrease in the firing rate and/or the de-recruitment of fatigued MUs. Furthermore, methodological limitations of the adopted method in the estimation of 'global' parameters such as the PPS and RMS have to be considered.

Comparison of the electromyographic activity in the upper trapezius and biceps brachii muscle in subjects with muscular disorders: a pilot study.

The aim of the present study was to investigate the extent to which work-related muscular disorders of the upper trapezius affect the activity of other pain-free muscles, in particular in the biceps brachii. Two groups of female subjects (age >43 years) participated in the study: seven affected subjects with self-reported disorders in the shoulder/neck region (cases) and nine healthy subjects (control group). Multi-channel electromyography (EMG) and force were recorded during maximum voluntary contractions (MVC) and during 6 min sustained contractions (at 30% MVC) of the upper trapezius and biceps brachii on the dominant side. From the EMG signals, the root mean square (RMS), median frequency (MDF) and single motor unit (MU) conduction velocity (CV) were estimated. From the force signal, the coefficient of variation was calculated. All data are presented as mean values and standard deviation. Differences between the cases and controls were found in the MVC force of the upper trapezius, which was lower in cases [253 (70) N] than in controls [357 (75) N], while the coefficient of variation of force during the sustained contraction was increased [cases 5.5 (2.2); controls 4.1 (1.9)]. The RMS (normalized to the RMS at MVC) during the 6 min sustained contractions was significantly lower in the cases than in the controls for both the upper trapezius and the biceps brachii. A tendency towards a smaller increase in the RMS with fatigue was only found in the trapezius muscle [slope: cases 6.5 (14.1) %/min, controls 10.2 (12.9) %/min]. No differences were found between the two subject groups with respect to the MDF and single MU CV in both muscles. While the lower RMS for the trapezius muscles of the cases may reflect changes at the local level, as well as in motor control, the lower biceps activity indicates a change in the central control strategies of the primarily unaffected muscle. Indications for a changed fatigability of the muscle were only found in the trapezius.

Estimation of the muscle fibre semi-length under varying joint positions on the basis of non-invasively extracted motor unit action potentials.

Changes in muscle fibre length and surface electrode position with respect to the muscle fibres affect the amplitude and frequency characteristics of surface electromyography (SEMG) in different ways. Knowledge of changes in muscle fibre length would help towards a better interpretation of the signals. The possibility of estimating the length through SEMG during voluntary contractions was checked in this study. The fibres' semi-length was estimated from the product of the conduction velocity and conduction time during which the wave of excitation propagated from the end-plate region to the ends of the fibres. Short (10 s), moderate (30% of maximum voluntary contraction) isometric contractions were performed by 10 subjects at different elbow joint angles (80-140 degrees in steps of 20 degrees ). Monopolar signals were detected non-invasively, using a two-dimensional electrode array. High spatial resolution EMG and a decomposition technique were utilised to extract single motor unit activities for triggered averaging and to estimate conduction velocity. A significant increase with joint angle was found in conduction time and estimated fibre semi-length. Changes in conduction velocity with joint angle were found to be not significant. The methodology described allows the relative changes in fibres' semi-length to be estimated from SEMG data.

From cell to movement: to what answers does EMG really contribute?

This paper aims to address some of the possibilities and limitations of EMG technologies available to date. Considerable progress has been achieved in this field during the last 30 years and EMG signals can be easily obtained on different levels beginning at the cell membrane and ending with the global EMG associated with the movement itself. Different aspects from cell to movement have been considered in this paper. Highly selective needle EMG for the detection of the processes at the membrane is discussed as well as high spatial resolution EMG which gives non-invasive access to the acquisition of the single motor unit activity. On the highest level of muscles, an expert system is introduced as a novel approach to support the interpretation of muscular co-ordination as detected by conventional surface EMG. While there is a high potential in the newly developed EMG methodologies, it is a big challenge to utilize these methodologies in order to obtain detailed, repeatable, reliable--and meaningful--results. However, the risk of over- and misinterpretation has to be carefully considered. In this paper, this risk is exemplified in situations dealing with muscle fatigue, conduction velocity and cross-talk. Despite all the new possibilities available, the authors recommend that EMG with its inherent strengths and limitations should still be diligently, but carefully, used.

Influence of muscle fibre shortening on estimates of conduction velocity and spectral frequencies from surface electromyographic signals.

The study of surface electromyographic (EMG) signals under dynamic contractions is becoming increasingly important. However, knowledge of the methodological issues that may affect such analysis is still limited. The aim of the study was to analyse the effect of fibre shortening on estimates of conduction velocity (CV) and mean power spectral frequency (MNF) from surface EMG signals. Single fibre action potentials were simulated, as detected by commonly used spatial filters, for different fibre lengths. No physiological modifications were included with changes in fibre length, and thus only geometrical artifacts related to fibre shortening were investigated. The simulation results showed that the dependence of CV and MNF on fibre shortening is affected by the fibre location, electrode position and the spatial filter applied. With shortening of up to 50% for a fibre of 50 mm semi-length, the variations in CV and MNF estimates with shortening in bipolar recordings were 0.5% (CV) and 0.7% (MNF) for superficial fibres, and 3.6% and 5.1% for deeper fibres. Using the longitudinal double differential filter, under the same conditions, the percent variation was 0% and 0.2%, and 24.7% and 15.8%, respectively. The main conclusions were, first, muscle fibre shortening can significantly affect estimates of CV and MNF, especially for short fibre lengths. However, for long (semi-length >50 mm) and superficial fibres, this effect is limited for shortenings of up to 50% of the initial fibre length. Secondly, CV and MNF are almost equally affected by changes in muscle length; and, thirdly, sensitivity to fibre shortening depends on the spatial filter applied for signal detection.

Experimental muscle pain increases trapezius muscle activity during sustained isometric contractions of arm muscles.

OBJECTIVE: In the present study, the influence of experimental muscle pain on muscle co-ordination and fatigue development during sustained isometric elbow flexion was investigated. METHODS: Conventional surface electromyography (EMG) was recorded from the biceps brachii, brachioradialis, deltoideus and trapezius muscle during isometric elbow flexion at 40% maximum force. Single motor unit (MU) conduction velocity in the biceps brachii was assessed using a high spatial resolution surface EMG technique. Measurements were performed on 15 healthy subjects before, during and after (1) injection of hypertonic (pain condition) and (2) isotonic saline (control) into the biceps brachii. The pain intensity was assessed on a 10 cm visual analogue scale. RESULTS: The experimental results showed in both experimental sessions a fatigue-related increase of the root mean square value of EMG (222+/-164% of the baseline), and a decrease of the median frequency (118+/-16% of the baseline) in all investigated muscles. A maximum pain level of in average 3.2 cm on the visual analogue scale was reached after injection of hypertonic saline during contraction. Differences between painful and control condition were seen in an increased trapezius activity (230+/-141%) during pain. The global EMG activity of the brachioradialis and biceps brachii was unaffected by experimental muscle pain in line with unaffected single MU conduction velocity in the biceps brachii. Differences in endurance time (mean 89.3 and 102.3 s, pain and control, respectively) were not significant. CONCLUSIONS/SIGNIFICANCE: The findings suggest that upper extremity pain could be a possible source for overloading the trapezius muscle and as such is an important factor in occupational settings.

Single motor unit analysis from spatially filtered surface electromyogram signals. Part I: spatial selectivity.

The aim of the study was to compare experimentally, on the basis of single motor unit (MU) activities, the selectivity of different spatial filters commonly used to detect surface electromyogram (EMG) signals. Surface EMG signals were recorded from the biceps brachii and the upper trapezius muscle of five subjects using a two-dimensional (2D) electrode array consisting of 16 pin electrodes. The subjects performed isometric contractions at different elbow angles and shoulder abduction and flexion. The same monopolar surface EMG signals were filtered using longitudinal single and double differential, transverse single and double differential and normal double differential filters. From the single MU action potentials, extracted by automatic EMG decomposition, indexes of transverse (perpendicular with respect to the fibre direction) and longitudinal (along the fibre direction) selectivity were computed. The number of detected MUs was 46 for the upper trapezius, with the arms held in the sagittal plane, and 52 when the arms were held in the frontal plane; 85 MUs were identified from the biceps brachii contractions. The results showed that transverse selectivity was significantly higher for the 2D and transverse one-dimensional (1D) filters with respect to the 1D longitudinal filters, whereas longitudinal selectivity was higher (i.e. MU action potentials were shorter) for the 2D filter and the longitudinal double differential filter. In particular, the relative attenuation of potential amplitude moving 5 mm from the source was, on average (for the two muscles), 16.5% for the least selective filter in the transverse direction (longitudinal single differential) and 35.7% for the most selective one in the same direction (transverse double differential). The MU action potential duration was, on average, 13.8 ms for the most selective filter in the longitudinal direction (longitudinal double differential) and 18.7 ms for the least selective one (transverse double differential). The normal double differential filter resulted in spatial selectivity indexes that ware not statistically different in the two directions from those of the best filters in each direction.

Single motor unit analysis from spatially filtered surface electromyogram signals. Part 2: conduction velocity estimation.

The aim of the study was to compare experimentally conduction velocity (CV) estimates obtained with different estimation methods based on surface electromyogram (EMG) signals detected using five spatial filters. The filters investigated were the longitudinal single and double differential, transverse single and double differential, and normal double differential. The same surface EMG signals detected as described in Part 1 were used in this work. CV was estimated with four commonly used delay estimation techniques, i.e. from the distance between the peak values of two waveforms (with and without polynomial interpolation around the peak), and by the maximum likelihood estimate (MLE) based on two or more surface EMG channels. The average standard deviation of CV estimation (for all the MUs and the two muscles together) was 0.61 m s(-1) and 0.79 m s(-1) for the peak method, with and without interpolation, respectively, and 0.50 m s(-1) and 0.31 m s(-1) for the MLE method, from two and more surface EMG channels, respectively. Moreover, the mean of CV estimates varied by as much as 1 m s(-1) depending on the spatial filter used and the method adopted for CV estimation. Considering the dependence on the spatial filter only, the average (over all estimation methods) CV estimates obtained with the five spatial filters were 4.32 m s(-1) (normal double differential), 4.23 m s(-1) (longitudinal double differential), 4.61 m s(-1) (transverse double differential), 4.64 m s(-1) (transverse single differential) and 4.03 m s(-1) (longitudinal single differential). It was concluded that the comparison of single MU CV values obtained in different studies is critical if different spatial filters and processing techniques are used for their estimation. Higher estimates of CV were attributed to a smaller reduction in non-travelling signal components and thus were assumed to be positively biased.

[Arm motion analysis: a new method and its clinical application]. / 3D-Analyse der Armbewegung: eine neue Methode und erste klinische Anwendung.

AIM: An investigation into the objective criteria of shoulder mobility possesses special meaning for diagnostic documentation, the evaluation of therapy and the effects of rehabilitation in the treatment of diseases of the shoulder. In order to ascertain the criteria which characterise shoulder mobility, it is necessary to have a tool available that is objective, comparable and allows the complexity, variability and range of motion to be recorded. Motion analysis represents one such standard procedure used to measure joint movement. METHOD: Accordingly, a marker- based motion analysis of the wrist and elbow, a marker-based three-dimensional motion analysis system for the upper extremities was developed. We evaluated 10 healthy subjects without shoulder conditions and 8 patients with impingement syndrome (7 operative, 1 conservative therapy). RESULTS: The healthy subjects revealed a reproducible motion curve for the specific motion tested. The curves were defined as the normal standard and we used them for comparative purposes. In the treatment group, an improvement of the 3D range of motion could be documented for the affected shoulder following rehabilitation. CONCLUSION: It can be stated that this newly developed marker-based procedure for the three-dimensional motion analysis is suitable for recording complex unconstrained movements. This was found to be more relevant for the assessment of the ability of patients to manage the physical demands of daily living than traditional clinical tests. Furthermore, the information gained from motion analysis of the upper extremities will play a valuable role in the future for quality control during diagnosis and treatment, as well as for the design of shoulder rehabilitation programs.

Area-to-amplitude ratio of the terminal phase of the belly-tendon detected motor unit potentials could be used to recognize reinnervated motor units.

Besides the increased number of fibres, the reinnervated motor units (MUs) are characterised by an increased scattering the end-plates, greater desynchronization in the fibres' activation, greater dispersion in the diameters of the MU fibres and thus in propagation velocities along them. As a result, desynchronization in the moments, at which the excitation waves reach the fibres' ends, increases in reinnervated MUs. The possibility to recognize reinnervated MUs in short (hand) muscles on the basis of changes in duration of the terminal (second) phase of the belly-tendon detected motor unit potentials (MUPs) was examined by numerical experiments. A convolution model that took into account the finite fibre length, was used to calculate MUPs for distances typical of surface detection. It was shown that the ratio between the area of the terminal phase and its amplitude, as a measure of duration of the terminal phase, was sensitive to desynchronisation of the waves of excitation. The ratio was independent of the distance from the MU axis and of the volume conductor properties. Basing on the results obtained, we can conclude that the ratio reflects main functional compensations in reinnervated MUs and could be used for discrimination between reinnervated and normal MUs.

Surface detected potentials of normal and reinnervated motor units: a simulation study for muscles consisted of short fibres.

We aimed to check whether the characteristics used up to now in macro EMG to distinguish between normal and reinnervated motor unit potentials (MUPs), were suitable for surface detected MUPs. MUPs produced by normal and reinnervated MUs were simulated with a fast and precise convolution model. An increased number of fibres in the MU territory enhanced the amplitude, area and RMS of the MUP proportionally irrespective of the MU-electrode distance. An increased scatter of the end-plates and greater desynchronization in the fibres' activation decreased the MUP amplitude and affected the temporal characteristics of the MUP (duration of the negative phase and its area to amplitude ratio). The effects were more pronounced at shorter distances. At larger distances, the effect of the MU-electrode distance on temporal and amplitude characteristics of MUPs was much stronger than that of the parameters changed with reinnervation. We conclude that reinnervated MUs consisting of short fibres can not be distinguished from the normal ones by means of characteristics of MUP used in macro EMG. To discriminate reinnervated MUs non-invasively, the MUP amplitude should be normalized in respect of the MU-electrode distance or other MUP characteristics (independent of MU-electrode distance and sensitive to reinnervation) should be used.

The presence of unknown layer of skin and fat is an obstacle to a correct estimation of the motor unit size from surface detected potentials.

To overcome problems with a strong distance-dependence of the motor unit potentials (MUPs), different methods to estimate the MU location and size have been proposed. Distance-independence of the exponent of the power function, that describes the MUP distance decline, and homogeneity of the volume conductor, are assumed in all methods. Some of them consider the exponent value as unique, irrespective of persons, muscles and their functional state. One method estimates the current exponent value. We evaluate this method by computer simulation of MUPs in infinite and semi-infinite volume conductor. Our results show that although the first assumption is not fulfilled, it does not affect considerably the estimate of the MU location and size obtained for infinite or semi-infinite homogeneous volume conductor. The errors of the MU location can be insignificant even in inhomogeneous volume conductor with a layer of lower conductivity (skin and fat) between the muscle tissue and electrode. The accurate location of the MU electrical axis is, however, not a sufficient condition for a correct MU size estimation that depends considerably on actual parameters of the layer. Thus, the surface EMG could hardly be considered as non-invasive alternative to macro EMG for detection of the enlarged MUs.

[Muscle strength and functional results after surgical repair of Achilles tendon rupture with fibrin gluing]. / Kraftverhältnisse und funktionelle Ergebnisse nach operativer Therapie der Achillessehnenrupturmittels Fibrinklebung.

Treatment of Achilles tendon rupture is discussed controversially. Some trauma centers prefer a conservative therapy. Because of the tendency to a higher rate of reruptures and worse functional results following conservative treatment, operation is the standard therapy of fresh ruptures of the Achilles tendon in Germany. Concerning the functional postoperative outcome, only few studies with uncomparable results were published. To evaluate the functional outcome after Achilles tendon ruptures treated by fibrin gluing, we realized reactive force measurements and motion analysis of 30 patients and 25 healthy test persons. We could observe significant limitations of active range of motion in the ankle joint and a significant deficiency of maximum- and rapid-force. Force deficiency was only detected by the sensitive technical examinations. In daily routine 26 of 30 patients had no limitations. The detected force- and motion-deficiencies were completely compensated. Therefore fibrin gluing of fresh ruptures of the Achilles tendon usually allows postoperatively the same leisure sports activity level as preoperatively. In competitive sporting athletes postoperative loss of performance must be expected.