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Simulation of surface EMG for the analysis of muscle activity during whole body vibratory stimulation
Abstract
This study aims to reproduce the effect of motor-unit synchronization on surface EMG recordings during vibratory stimulation to highlight vibration evoked muscle activity. The authors intended to evaluate, through numerical simulations, the changes in surface EMG spectrum in muscles undergoing whole body vibration stimulation. In some specific bands, in fact, vibration induced motion artifacts are also typically present. In addition, authors meant to compare the simulated EMGs with respect to real recordings in order to discriminate the effect of synchronization of motor units discharges with vibration frequencies from motion artifacts. Computations were performed using a model derived from previous studies and modified to consider the effect of vibratory stimulus, the motor unit synchronization and the endplates-electrodes relative position on the EMG signal. Results revealed that, in particular conditions, synchronization of MUs' discharge generates visible peaks at stimulation frequency and its harmonics. However, only a part of the total power of surface EMGs might be enclosed within artifacts related bands (±1Hz centered at the stimulation frequency and its superior harmonics) even in case of strong synchronization of motor units discharges with the vibratory stimulus.
... In order to extract valuable attributes, they randomly select 5 s from an ECG recording and estimate the normalized autocorrelation (AC) over a window of m lags (see Eq. 2). AC embeds information about ECG's peculiar characteristics: it is shift invariant and highlights non-random patterns [82]. The QRS complex, in particular, maintains a strong invariance in shape and time width. ...
... Following this first study, Agrafioti [83][84][85][86], Wang [87,88] and other researchers [81][82][83] also proposed the use of normalized autocorrelation coefficients. ...
During last decade the use of ECG recordings in biometric recognition studies has increased. ECG characteristics made it suitable for subject identification: it is unique, present in all living individuals, and hard to forge. However, in spite of the great number of approaches found in literature, no agreement exists on the most appropriate methodology. This study aimed at providing a survey of the techniques used so far in ECG-based human identification. Specifically, a pattern recognition perspective is here proposed providing a unifying framework to appreciate previous studies and, hopefully, guide future research.
We searched for papers on the subject from the earliest available date using relevant electronic databases (Medline, IEEEXplore, Scopus, and Web of Knowledge). The following terms were used in different combinations: electrocardiogram, ECG, human identification, biometric, authentication and individual variability. The electronic sources were last searched on 1st March 2015. In our selection we included published research on peer-reviewed journals, books chapters and conferences proceedings. The search was performed for English language documents.
100 pertinent papers were found. Number of subjects involved in the journal studies ranges from 10 to 502, age from 16 to 86, male and female subjects are generally present. Number of analysed leads varies as well as the recording conditions. Identification performance differs widely as well as verification rate. Many studies refer to publicly available databases (Physionet ECG databases repository) while others rely on proprietary recordings making difficult them to compare. As a measure of overall accuracy we computed a weighted average of the identification rate and equal error rate in authentication scenarios. Identification rate resulted equal to 94.95 % while the equal error rate equal to 0.92 %.
Biometric recognition is a mature field of research. Nevertheless, the use of physiological signals features, such as the ECG traits, needs further improvements. ECG features have the potential to be used in daily activities such as access control and patient handling as well as in wearable electronics applications. However, some barriers still limit its growth. Further analysis should be addressed on the use of single lead recordings and the study of features which are not dependent on the recording sites (e.g. fingers, hand palms). Moreover, it is expected that new techniques will be developed using fiducials and non-fiducial based features in order to catch the best of both approaches. ECG recognition in pathological subjects is also worth of additional investigations.
... It is shift-invariant and applies patterns that are not random. It is evident that the QRS complex, in shape and time, keeps a strong invariance [72]. By using this method, samples are combined into a sequence of sums of products. ...
In recent years, security systems based on biometric features have become a promising solution to identify humans, and it is preferred over traditional methods working based on what we know. With the rapid growth of such identification methods, ECG authentication approaches as an emerging biometric recognition scheme is developed. It can be efficiently used to identify individuals, specifically for continuous authentication to allow particular access privileges for users. In comparison with other biometric features even in abnormal conditions, it gives more valid and better results. Although there are several works that have offered some techniques in order to overcome the various issues affecting the ECG authentication schemes’ outputs, there are still many concerns to be considered. How can we see, there are not many studies that deal with all aspects of ECG authentication techniques? The objective this paper is to evaluate some surveys related to ECG authentication domain since 2010. We have done a comprehensive taxonomy including existing methods and techniques in ECG based authentication domain. With the aim of providing a classical taxonomy form, this study presents a Systematic Literature Review (SLR) on ECG-based authentication schemes to introduce the state-of-the-art approaches in this domain. We have done the selection of journals and conference proceedings using the standard systematic literature review methodology in order to find and assess the studies related to ECG authentication. Finally, the paper is concluded with a summary of the content of the paper, and open issues and future research challenges are discussed.
... To confirm that WBVs stimulated the targeted muscles (GL, SOL and TA), the root mean square (RMS) value of their EMG signals was analysed. Trials before and after the stimulation were compared to rule out any potential confounding factor given by motion artefacts during WBVs [45][46][47][48] . The median frequency (MF) of the EMG power spectrum was also analysed to exclude muscle fatigue 49 . ...
Efficient postural control results from an effective interplay between sensory feedbacks integration and muscle modulation and can be affected by ageing and neuromuscular injuries. With this study, we investigated the effect of whole-body vibratory stimulation on postural control strategies employed to maintain an upright posture. We explored both physiological and posturography metrics, through corticomuscular and intramuscular coherence, and muscle networks analyses. The stimulation disrupts balance in the short term, but leads to a greater contribution of cortical activity, necessary to modulate muscle activation via the formation of (new) synergies. We also observed a reconfiguration of muscle recruitment patterns that returned to pre-stimulation levels after few minutes, accompanied by a slight improvement of balance in the anterior–posterior direction. Our results suggest that, in the context of postural control, appropriate mechanical stimulation is capable of triggering a recalibration of the sensorimotor set and might offer new perspectives for motor re-education.
... The analysis of the physiological response of muscles to WBVs did instead highlighted specific combinations of posture/frequency able to produce maximal results. Recordings have been appropriately filtered for vibration-induced motion artefacts and therefore WBV-induced muscle activations were not overestimated (Fratini et al., 2014(Fratini et al., , 2009aRomano et al., 2018). As expected, muscles behaved differently: GL activity was significantly enhanced in all WBV combinations, supporting the previously-demonstrated beneficial effects of WBV (Cardinale and Lim, 2003;Di Giminiani et al., 2013;Krol et al., 2011;Marin et al., 2009;Roelants et al., 2006), while for the SOL and the TA only specific combinations were able to significantly increase muscle activation. ...
Purpose
To characterise the mechanical and neuromuscular response of lower limb muscles in subjects undergoing Whole Body Vibration (WBV) at different frequencies while holding two static postures.
Methods
Twenty-five participants underwent WBV at 15, 20, 25 and 30 Hz while holding a static ‘hack squat’ and on ‘fore feet’ posture. Surface electromyography (sEMG) and soft tissue accelerations were collected from Gastrocnemius Lateralis (GL), Soleus (SOL) and Tibialis Anterior (TA) muscles.
Results
Only specific WBV settings led to a significant increase in muscle contraction. Specifically, the WBV-induced activation of SOL and GL was maximal in fore-feet and in response to higher frequencies. Estimated displacement at muscle bellies revealed a resonant pattern never highlighted before. After stimulation starts, muscle oscillation reaches a peak followed by a drop and a further stabilisation (few seconds after the peak) that suggests the occurrence of a neuromuscular activation to reduce the vibration-induced oscillation.
Conclusion
Lower leg muscles need a response time to tune to a vibratory stimulation, which discourages the use of dynamic exercises on vibrating platforms. To maximize calf muscle response to WBVs, a stimulation frequency in the range of 25-30 Hz and an ‘on fore feet’ posture are recommended.
... Whereas m(t) represents the MUAP waveform in time domain (obtained differentiating a Gaussian pulse p(t)) and M(ω) its spectrum (ω = 2πf), λ determines the time duration of the MUAP. Equation 1 provides a simple, yet realistic representation of a MUAP and its Fourier transform, the reader can found more accurate simulations and sophisticated MUAP descriptions in [30] and [31]. Fig. 1 shows an example of biphasic MUAP (panel a, solid line) and its spectrum (panel b, solid line) obtained using equation 1: in this example λ is set to 1.5 ms that correspond to a MUAP duration of about 12 ms (in accordance to [32]- [38]). ...
Objective: Provide a definitive analysis of the spectrum of a motor unit action potential train elicited by mechanical vibratory stimulation via a detailed and concise mathematical formulation. Experimental studies demonstrated that motor unit action potentials are not exactly synchronized with the vibratory stimulus but show a variable latency jitter, whose effects have not been investigated yet. Methods: Synchronized action potential train was represented as a quasi-periodic sequence of a given motor unit waveform. The latency jitter of action potentials was modeled as a Gaussian stochastic process, in accordance to previous experimental studies. Results: A mathematical expression for power spectrum of a synchronized motor unit action potential train has been derived. The spectrum comprises a significant continuous component and discrete components at the vibratory frequency and its harmonics. Their relevance is correlated to the level of synchronization: the weaker the synchronization, the more relevant the continuous spectrum. EMG rectification enhances the discrete components. Conclusion: The derived equations have general validity and well describe the power spectrum of actual EMG recordings during vibratory stimulation. Results are obtained by appropriately setting the level of synchronization and vibration frequency. Significance: This study definitively clarifies the nature of changes in spectrum of raw EMG recordings from muscles undergoing vibratory stimulation. Results confirm the need of motion artifact filtering for raw EMG recordings during stimulation and strongly suggests to avoid EMG rectification that significantly alters the spectrum characteristics.
... Recently, many low-cost prosthetic devices have been proposed, they can also be produced with 3D printers [6][7][8] and off-the-shelf motors. Given the limitations in EMG recording [9][10][11][12][13], we thought to use the muscle volume change during contraction as an alternative control signal. This volumetric change can be detected by a stretchable, rubber cord sensors (appropriately positioned on the arm via an armband), which modify its internal resistance in function of the stretching to which they are subjected. ...
Recently, many type of prosthetic hands have been proposed. Nonetheless, any active prosthesis needs patient's physiological signals to be controlled. Electromyography is one of the most used signals to control prostheses. However, EMG needs electrodes in contact with patient's skin. This study aims to test an alternative, easy to wear sensor able to detect muscle contraction and to control hand prosthesis as well. The new sensor consists of a conductive rubber cord that changes its electrical resistance when stretched. The rubber cord was enclosed in a soft fabric cuff that can be easily worn by the patient. No electrical contact between the cord and the patient is needed. Simultaneous recordings of EMG and the correspondent rubber cord resistance were carried out in order to test the relationship between the two signals and to assess the effectiveness of proportional control of the prosthesis motor. A simple 3D printed, under-actuated prosthetic hand was connected to the new sensor. Results show that the new sensor offers a control signal very similar to the EMG envelope and it is able to provide both on-off and proportional control of the prosthesis.
... We used equation (9) and the parameters given in Table 1 to simulate the temporal signal that represents the sEMG of different muscles [10,11]. In our case, we distinguish four different muscles [12,13]. Each of them is caracterized by a specific number of fibers assigned to each motor unit (see Table 2) [14]. ...
... WBV is a stimulus that involves the combination of various mechanical variables. Vibrations are transmitted through the kinematic chain of the body; the combination of frequency, amplitude of the stimulus, subject posture and vibration delivery design can dramatically change the actual stimulus at the target site [10,11]. ...
Whole body vibration treatment is a non-pharmacological intervention intended to stimulate muscular response and increase bone mineral density, particularly for postmenopausal women. The literature related to this topic is controversial, heterogeneous, and unclear despite the prospect of a major clinical effect.The aim of this study was to identify and systematically review the literature to assess the effect of whole body vibration treatments on bone mineral density (BMD) in postmenopausal women with a specific focus on the experimental factors that influence the stimulus. Nine studies fulfilled the inclusion criteria, including 527 postmenopausal women and different vibration delivery designs. Cumulative dose, amplitudes and frequency of treatments as well as subject posture during treatment vary widely among studies. Some of the studies included an associated exercise training regime. Both randomized and controlled clinical trials were included. Whole body vibration was shown to produce significant BMD improvements on the hip and spine when compared to no intervention. Conversely, treatment associated with exercise training resulted in negligible outcomes when compared to exercise training or to placebo. Moreover, side-alternating platforms were more effective in improving BMD values than synchronous platforms and mechanical oscillations of magnitude higher than 3 g and/or frequency lower than 25 Hz were also found to be effective. Treatments with a cumulative dose over 1000 minutes in the follow-up period were correlated to positive outcomes.Our conclusion is that whole body vibration treatments in elderly women can reduce BMD decline.However, many factors (e.g., amplitude, frequency and subject posture) affect the capacity of the vibrations to propagate to the target site; the adequate level of stimulation required to produce these effects has not yet been defined. Further biomechanical analyses to predict the propagation of the vibration waves along the body and assess the stimulation levels are required.
... The analysis of surface EMG (sEMG) and its concise parameters is a common method of analysis of muscle activity (6). ...
Whole-body vibration (WBV) has shown positive results increasing electromyographic (EMG) activity and strength in a healthy population when applied to upper and lower limbs. The aim of this study was to verify if WBV increases the EMG signal of the upper limb muscles in patients with spinal cord injury (SCI). For this study, 15 patients with SCI were selected and one single session of WBV was applied to the upper limb. Five sessions of 30 s at 30 Hz were applied and EMG of anterior deltoid and forearm muscles was measured. The results show that EMG activity had a significant increase during WBV session compared with baseline muscle activity. These results support WBV as an efficient tool to increase the upper body EMG in individuals with SCI.
... Surface electromyography (sEMG) is the sum of the action potentials generated by the active motor units recorded by electrodes placed on the skin overlying the muscles [3]. It is dependent on numerous factors such as the rate of stimulation of the muscle, size of motor units recruited, morphology of the motor units, electrical properties of the tissues and the presence of any synchronization of the activity of different motor units. ...
More and more people suffer from lumbar muscle strain due to lack of exercise. Cycling serves as both a stylish model of fitness and a training method in exercise and rehabilitation. A few of previous studies have examined the changes in lower extremity muscle activities during indoor cycling, but fewer data pertain to the low back muscles. This study aims to analyze the functional status of erector spinae during cycling by learning the regularity and characteristics of changes in sEMG frequency domain index-mean frequency (MF) within ten minutes. The statistical results showed that the values of 70% subjects fluctuated within the range of (0.04688±0.00125) Hz within the first 30 s and the values raised rapidly to the (150±10) Hz range after the 30 s. Moreover, the values trended to decline slowly in a fluctuating way after a while. However, no obvious regularity was observed among the remaining 30% of the subjects. Results of this study demonstrated that the muscle fatigue with a smaller level of low back began to emerge gradually after 30 s. Moreover, it is evident that cycling can be an incentive to the low back muscles in most people.
... While performing these functions, muscular tissue changes its characteristics, composition and architecture. It has been demonstrated that these characteristics modify also in presence of some pathologies, in response to rehabilitation treatments, and as consequence of electrical or mechanical stimulations [1][2][3][4]; so that a comprehensive under-standing of muscular modifications could be helpful in clinical environments. Among the most used methodologies to study muscle activity, there is the electromyography (EMG) [5]. ...
Performing physiological functions, muscular tissue changes its characteristics. The study of these changes, through assessment of impedance modification, has proven useful both in research and clinical fields. Electrical impedance spectroscopy is a relatively new technique and very promising in which the tissue impedance is calculated at different frequency values. This work aimed to study the muscular tissue changes in correspondence of different subjects' characteristics and different muscle conditions, rest, contraction and phase after contraction, with a concise index related to the position of Nyquist plots in the complex plane. The study was carried out by applying EIS to the group of the forearm flexor muscles in vivo in 33 subjects. Obtained results show that Nyquist plots are arranged in different ways in correspondence of various measurement conditions and subjects' characteristics.
Upper limb amputation can severely restrict the
mobility and ability of amputees to perform daily activities. In
addressing this issue, deep learning algorithms and
electromyography pattern recognition have emerged as
promising clinical solutions for functional upper-limb
prosthetics. This article presents the use of EMG sensors to
capture muscle movement signals and applies the pattern
recognition function of a 1D convolutional neural network to
identify these signals and control the movement of prosthetics.
Experimental results demonstrate that the convolutional neural
network exhibits fast training and high-precision recognition
capabilities enabling it to accurately identify muscle signals and
effectively control prosthetic movements.
L’électrostimulation (EMS) est l’envoi d’impulsion électrique par le biais d’électrodes. Ces électrodes de surface sont posées sur la zone musculaire à stimuler. Cette technique est de plus en plus utilisée dans la rééducation musculaire lors de blessures, de pertes de mouvement ou d’atrophie. Ces EMS sont généralement combinées avec l’électromyogramme (EMG) qui enregistre l’activité électrique du muscle. Le but de la thèse est d’optimiser les paramètres de stimulation en temps réel lors d’une EMS. Pour ce faire, de nouvelles stratégies de contrôle robustes sont à développer. Nous avons convenu durant la thèse de travailler sur un modèle spécifique.
Feature extraction plays a major role in the pattern recognition process, and this paper presents a novel feature extraction approach,
adaptive local binary pattern (aLBP). aLBP is built on the local binary pattern (LBP), which is an image processing method, and one-dimensional local binary pattern (1D-LBP). In LBP, each pixel is compared with its neighbors. Similarly, in 1D-LBP, each data in the raw is judged against its neighbors. 1D-LBP extracts feature based on local changes in the signal. Therefore, it has high a potential to be employed in medical purposes. Since, each action or abnormality, which is recorded in SEMG signals, has its own pattern, and via the 1D-LBP these (hidden) patterns may be detected. But, the positions of the neighbors in 1D-LBP are constant depending on the position of the data in the raw. Also, both LBP and 1D-LBP are very sensitive to noise. Therefore, its capacity in detecting hidden patterns is limited. To overcome these drawbacks, aLBP was proposed. In aLBP, the positions of the neighbors and their values can be assigned adaptively via the down-sampling and the smoothing coefficients. Therefore, the potential to detect (hidden) patterns, which may express an illness or an action, is really increased. To validate the proposed feature extraction approach, two different datasets were employed. Achieved accuracies by the proposed approach were higher than obtained results by employed popular feature extraction approaches and the reported results in the literature. Obtained accuracy results were brought out that the proposed method can be employed to investigate SEMG signals. In summary, this work attempts to develop an adaptive feature extraction scheme that can be utilized for extracting features from local changes in different categories of time-varying signals.
The aim of this study is to evaluate the application of ensemble averaging to the analysis of electromyography recordings under whole body vibratory stimulation. Recordings from Rectus Femoris, collected during vibratory stimulation at different frequencies, are used. Each signal is subdivided in intervals, which time duration is related to the vibration frequency. Finally the average of the segmented intervals is performed. By using this method for the majority of the recordings the periodic components emerge. The autocorrelation of few seconds of signals confirms the presence of a pseudosinusoidal components strictly related to the soft tissues oscillations caused by the mechanical waves.
The authors developed PDMS (polydimethylsiloxane)-based dry type surface electromyography (SEMG) electrodes for myoelectric prosthetic hands. The SEMG electrodes were strongly recommended to be fabricated on a flexible substrate to be compatible with the surface of skin. In this study, the authors designed a bar-shaped dry-type flexible SEMG electrodes comprised of two input electrodes and a reference electrode on a flexible PDMS substrate to measure EMG signals. The space distance between each electrode with a size of 10 mm × 2 mm was chosen to 18 mm to get optimal result according to the simulation result with taking into consideration the conduction velocity and the median frequency of EMG signals. Raw EMG signals were measured from Brachioradialis, Biceps brachii, deltoideus, and pectoralis major muscles, to drive the application of the myoelectric hand prosthesis. Measured raw EMG signals were transformed to root mean square (RMS) EMG signals using Acqknowledge4.2. The experimental peak voltage values of RMS EMG signals from Brachioradialis, Biceps brachii, deltoideus, and pectoralis major muscles were 2.96 V, 4.45 V, 1.74 V, and 2.62 V, respectively. Values from the dry type flexible SEMG electrodes showed higher peak values than a commercially available wet type Ag-AgCl electrode. The study shows that the PDMS-based flexible electrode devised for measuring myoelectric signals from the surface of skin is more useful for prosthetic hands because of its greater sensitivity and flexibility.
During medical emergencies, the ability to communicate the state and position of injured individuals is essential. In critical situations or crowd aggregations, this may result difficult or even impossible due to the inaccuracy of verbal communication, the lack of precise localization for the medical events, and/or the failure/congestion of infrastructure-based communication networks. In such a scenario, a temporary (ad hoc) wireless network for disseminating medical alarms to the closest hospital, or medical field personnel, can be usefully employed to overcome the mentioned limitations. This is particularly true if the ad hoc network relies on the mobile phones that people normally carry, since they are automatically distributed where the communication needs are. Nevertheless, the feasibility and possible implications of such a network for medical alarm dissemination need to be analysed.
To this aim, this paper presents a preliminary study on the feasibility of medical alarm dissemination through mobile phones in an urban environment, based on realistic people mobility. The results showed the dependence between the medical alarm delivery rates and both people and hospitals density. With reference to the considered urban scenario, the time needed to delivery medical alarms to the neighbour hospital with high reliability is in the order of minutes, thus revealing the practicability of the reported network for medical alarm dissemination.
The impact of whole body vibrations (vibration stimulus mechanically transferred to the body) on muscular activity and neuromuscular response has been widely studied but without standard protocol and by using different kinds of exercises and parameters. In this study, we investigated how whole body vibration treatments affect electromyographic signal of rectus femoris during static and dynamic squat exercises. The aim was the identification of squat exercise characteristics useful to maximize neuromuscular activation and hence progress in training efficacy. Fourteen healthy volunteers performed both static and dynamic squat exercises without and with vibration treatments. Surface electromyographic signals of rectus femoris were recorded during the whole exercise and processed to reduce artifacts and to extract root mean square values. Paired t-test results demonstrated an increase of the root mean square values (p
The aim of the study is to characterize the local muscles motion in individuals undergoing whole body mechanical stimulation. In this study we aim also to evaluate how subject positioning modifies vibration dumping, altering local mechanical stimulus. Vibrations were delivered to subjects by the use of a vibrating platform, while stimulation frequency was increased linearly from 15 to 60 Hz. Two different subject postures were here analysed. Platform and muscles motion were monitored using tiny MEMS accelerometers; a contra lateral analysis was also presented. Muscle motion analysis revealed typical displacement trajectories: motion components were found not to be purely sinusoidal neither in phase to each other. Results also revealed a mechanical resonant-like behaviour at some muscles, similar to a second-order system response. Resonance frequencies and dumping factors depended on subject and his positioning. Proper mechanical stimulation can maximize muscle spindle solicitation, which may produce a more effective muscle activation.
We present a bio-potential front-end capable of recording unipolar ECG leads without making use of the Wilson central terminal (WCT). The information contained in the new unipolar recordings may yield unique diagnostic information as it avoids the need to essentially subtract data or make use of the averaging effect imposed by the WCT. The system also allows a direct, real-time software calculation of signals corresponding to standard ECG leads for standard diagnosis. These calculated standard ECG leads have a correlation in excess of 92% with a gold standard ECG recorded in parallel. The circuit is wideband, compatible with both the standard and the dry electrodes, and of low power (requiring less than 20 mW powered at 12 V). It is therefore well suited for long-term applications.
This paper describes a multi-frequency single-channel electrical implantable bioimpedance monitor (35 mm × 35 mm × 10 mm, weight 52 g) powered by a NiMH battery. By using the tetrapolar method and injecting 10 µA(peak), the monitor is capable of measuring at 14 different frequencies, from 100 Hz to 200 kHz. It contains a ZigBee transceiver to monitor the measurements performed, and has an embedded memory for backing up the data. RC networks and in-situ heart excised tissues were used to test the system. When measuring a full spectrum every 5 min, 35 days of autonomy are possible due to the low power consumption of the monitor. Temperature drift was estimated by short-term and long-term measurements. Temperature cycling was used to measure modulus and phase angle stability. The result was a very low effect on a modulus decrease of 2.34 Ω, with respect to an impedance of 322 Ω, at 100 Hz and a phase angle increase of 1.1°, at 200 kHz. In addition, measurement errors were bigger at low frequencies because of the high impedance of the electrodes used, which was higher than 10 kΩ at frequencies below 1 kHz.
Long term recording of biomedical signals such as ECG, EMG, respiration and other information (e.g. body motion) can improve diagnosis and potentially monitor the evolution of many widespread diseases. However, long term monitoring requires specific solutions, portable and wearable equipment that should be particularly comfortable for patients. The key-issues of portable biomedical instrumentation are: power consumption, long-term sensor stability, comfortable wearing and wireless connectivity. In this scenario, it would be valuable to realize prototypes using available technologies to assess long-term personal monitoring and foster new ways to provide healthcare services. The aim of this work is to discuss the advantages and the drawbacks in long term monitoring of biopotentials and body movements using textile electrodes embedded in clothes. The textile electrodes were embedded into garments; tiny shirt and short were used to acquire electrocardiographic and electromyographic signals. The garment was equipped with low power electronics for signal acquisition and data wireless transmission via Bluetooth. A small, battery powered, biopotential amplifier and three-axes acceleration body monitor was realized. Patient monitor incorporates a microcontroller, analog-to-digital signal conversion at programmable sampling frequencies. The system was able to acquire and to transmit real- time signals, within 10 m range, to any Bluetooth device (including PDA or cellular phone). The electronics were embedded in the shirt resulting comfortable to wear for patients. Small size MEMS 3-axes accelerometers were also integrated. Keywords-component; Biomedical sensor, MEMS accelerometers, wearable device
We present a new, low-power electrocardiogram (ECG) recording system with an ultra-high input impedance that enables the use of long-lasting, dry electrodes. The system incorporates a low-power Bluetooth module for wireless connectivity and is designed to be suitable for long-term monitoring during daily activities. The new system using dry electrodes was compared with a clinically approved ECG reference system using gelled Ag/AgCl electrodes and performance was found to be equivalent. In addition, the system was used to monitor an athlete during several physical tasks, and a good quality ECG was obtained in all cases, including when the athlete was totally submerged in fresh water.
The aim of this study was to investigate the effects of whole-body vibrations (WBV) on the mechanical behaviour of human skeletal muscle. For this purpose, six female volleyball players at national level were recruited voluntarily. They were tested with maximal dynamic leg press exercise on a slide machine with extra loads of 70, 90, 110 and 130 kg. After the testing, one leg was randomly assigned to the control treatment (C) and the other to the experimental treatment (E) consisting of vibrations. The subjects were then retested at the end of the treatment using the leg press. Results showed remarkable and statistically signi®cant enhancement of the experimental treatment in average velocity (AV), average force (AF) and average power (AP) (P<0á05±0á005). Consequently , the velocity±force and power±force relationship shifted to the right after the treatment. In conclusion, it was af®rmed that the enhancement could be caused by neural factors, as athletes were well accustomed to the leg press exercise and the learning effect was minimized.
Muscle fiber conduction velocity (MFCV) gives critical information on neuromuscular control and can be considered a size principle parameter, being suggestive of motor unit recruitment strategies. MFCV has been recently measured during constant-load sub-maximal cycling exercise and was found to correlate positively with percentage of type I myosin heavy chain. The aim of this study was to test the hypothesis that MFCV measured during an incremental cycling test using surface electromyography (sEMG), can be sensitive to the different metabolic requests elicited by the exercise. In particular, the relationship between ventilatory threshold (T-vent), V(')O(2max) and MFCV was explored. Eleven male physically active subjects (age 30+/-9 years) undertook a 1-min incremental cycling test to exhaustion. T-vent and V(')O(2max) were measured using an open circuit breath by breath gas analyzer. The sEMG was recorded from the vastus lateralis muscle with an adhesive 4-electrodes array, and the MFCV was computed on each sEMG burst over the last 30-s of each step. The mean V(')O(2max) obtained during the maximal test was 53.32+/-2.33 ml kg(-1) min(-1), and the T-vent was reached at 80.77+/-3.49% of V(')O(2max). In all subjects reliable measures of MFCV were obtained at every exercise intensity (cross correlation values >0.8). MFCV increased linearly with the mechanical load, reaching a maximum value of 4.28+/-0.67 ms(-1) at an intensity corresponding to the T-vent. Thereafter, MFCV declined until maximal work intensities. This study demonstrates that MFCV can be used as non-invasive tool to infer MUs recruitment/derecruitment strategies even during dynamic exercise from low to maximal intensities.
The distribution of innervation zones was investigated in 3 subjects for 17 muscles and 8 muscle groups in the upper and lower limb, by detecting bi-directional propagation of motor unit action potentials (MUAPs) with the multichannel surface electrode array. Clarification of the distribution of innervation zones depended on the ease in detecting the propagation of MUAPs and the actual scattering of innervation zones, which were closely related with muscle morphology with respect to the arrangements of muscle fibers. In muscles having fibers running parallel to each other, such as the biceps brachii, intrinsic hand muscles, vastus lateralis and medialis, tensor fasciae latae, peronei, soleus, tibialis anterior, and hypothenar muscles in the foot, it was relatively easy to detect the propagating MUAPs, and the innervation zones were distributed in a relatively narrow band around muscle belly. On the other hand, in muscles with a complicated structure including pinnation of muscle fibers, in-series muscle fibers and aponeurotic tissues, such as the deltoid, flexors and extensors in the forearm, rectus femoris, sartorius, hamstrings and gastrocnemius, it was more difficult to detect the propagating MUAPs and to identify the innervation zones, which were widely scattered or distributed in complex configurations. The distribution of the innervation zones clarified in the present study can be used to find the optimal location of electrodes in surface EMG recordings and of stimulus electrodes in the functional and therapeutic electrical stimulations. It may also be useful in motor point biopsy for diagnosis of neuromuscular diseases as well as in the botulinum toxin injection for the treatment of spasticity.
The aim of this work is to provide information about the degree of inter-subject uniformity of location of innervation zone (IZ) in 13 superficial muscles of the lower limb. The availability of such information will allow researchers to standardize and optimize their electrode positioning procedure and to obtain accurate and repeatable estimates of surface electromyography (sEMG) signal amplitude, spectral variables and muscle fiber conduction velocity.
Surface EMG signals from gluteus maximus, gluteus medius, tensor faciae latae, biceps femoris, semitendinosus, vastus medialis obliquus, vastus lateralis, rectus femoris, tibialis anterior, peroneus longus, soleus, gastrocnemius medialis and lateralis muscles of ten healthy male subjects aged between 25 and 34 years (average = 29.2 years, S.D. = 2.5 years) were recorded to assess individual IZ location and signal quality.
Tensor faciae latae, biceps femoris, semitendinosus, vastus lateralis, gastrocnemius medialis and lateralis showed a high level of both signal quality and IZ location uniformity. In contrast, rectus femoris, gluteus medius and peroneus longus were found to show poor results for both indexes. Gluteus maximus, vastus medialis obliquus and tibialis anterior were found to show high signal quality but low IZ location uniformity. Finally, soleus muscle was found to show low signal quality but high IZ location uniformity.
This study identifies optimal electrode sites for muscles in the lower extremity by providing a standard landmarking technique for the localization of the IZ of each muscle so that surface EMG electrodes can be properly positioned between the IZ and a tendon.
Whole body vibration has been recently proposed as an exercise intervention because of its potential for increasing force generating capacity in the lower limbs. Its recent popularity is due to the combined effects on the neuromuscular and neuroendocrine systems. Preliminary results seem to recommend vibration exercise as a therapeutic approach for sarcopenia and possibly osteoporosis. This review analyses state of the art whole body vibration exercise techniques, suggesting reasons why vibration may be an effective stimulus for human muscles and providing the rationale for future studies.
Excessive, chronic whole-body vibration (WBV) has a number of negative side effects on the human body, including disorders of the skeletal, digestive, reproductive, visual, and vestibular systems. Whole-body vibration training (WBVT) is intentional exposure to WBV to increase leg muscle strength, bone mineral density, health-related quality of life, and decrease back pain. The purpose of this study was to quantitatively evaluate vibration exposure and biodynamic responses during typical WBVT regimens.
Healthy men and women (N = 16) were recruited to perform slow, unloaded squats during WBVT (30 Hz; 4 mm(p-p)), during which knee flexion angle (KA), mechanical impedance, head acceleration (Ha(rms)), and estimated vibration dose value (eVDV) were measured. WBVT was repeated using two forms of vibration: 1) vertical forces to both feet simultaneously (VV), and 2) upward forces to only one foot at a time (RV).
Mechanical impedance varied inversely with KA during RV (effect size, eta(p)(2): 0.668, P < 0.01) and VV (eta(p)(2): 0.533, P < 0.05). Ha(rms) varied with KA (eta(p)(2): 0.686, P < 0.01) and is greater during VV than during RV at all KA (P < 0.01). The effect of KA on Ha(rms) is different for RV and VV (eta(p)(2): 0.567, P < 0.05). The eVDV associated with typical RV and VV training regimens (30 Hz, 4 mm(p-p), 10 min.d(-1)) exceeds the recommended daily vibration exposure as defined by ISO 2631-1 (P < 0.01).
ISO standards indicate that 10 min.d(-1) WBVT is potentially harmful to the human body; the risk of adverse health effects may be lower during RV than VV and at half-squats rather than full-squats or upright stance. More research is needed to explore the long-term health hazards of WBVT.
The outside of the skin of the. forearm is typically 15 mV more negative than the inside. Stretching the skin causes a reduction in the magnitude of this skin potential V, which we observe as a motion artifact Delta V. We seek to determine the origin of this motion artifact by successively stripping 12 layers of the skin using Scotch Tape, Between each stripping we measure artifact Delta V, 13 Hz impedance Z, and change in impedance Delta Z. On the interior surface of the forearm, Z decreases with number of strippings. Delta Z can be first either positive or negative, then is always negative and decreases linearly with Z. Delta V first remains constant and then decreases with Z and Delta Z. Delta V and Delta Z increase with stretch force following a logarithmic relationship. Delta Z has a rectangular shape waveform, whereas the rising edge of Delta V shows a fast followed by a slow component and its falling edge decays exponentially with a large time constant. We have expanded the model of Thakor and Webster to best fit the waveform of Delta V and Delta Z caused by stretch.
Whole Body
Vibrations consist of a vibration stimulus mechanically transferred to
the body. The impact of vibration treatment on specific muscular
activity, neuromuscular, and postural control has been widely
studied. We investigated whole body vibration (WBV) effect on
oxygen uptake and electromyographic signal of the rectus femoris
muscle during static and dynamic squat. Fourteen healthy subjects
performed a static and dynamic squat with and without vibration.
During the vibration exercises, a significant increase was found in
oxygen uptake (P=0.05), which increased by 44% during the static
squat and 29.4% during the dynamic squat. Vibration increased heart
rate by 11.1 ± 9.1 beats·min-1 during the static squat and 7.9 ± 8.3
beats·min-1 during the dynamic squat. No significant changes were
observed in rate of perceived exertion between the exercises with
and without vibration. The results indicate that the static squat with
WBV produced higher neuromuscular and cardiorespiratory system
activation for exercise duration ?60 sec. Otherwise, if the single bout
duration was higher than 60 sec, the greater cardiorespiratory
system activation was achieved during the dynamic squat with WBV
while higher neuromuscular activation was still obtained with the
static exercise.
Power line interference is one of the main problems in surface electromyogram signals (EMG) analysis. In this work, a new method based on the stationary wavelet packet transform is proposed to estimate and remove this kind of noise from EMG data records. The performance has been quantitatively evaluated with synthetic noisy signals, obtaining good results independently from the signal to noise ratio (SNR). For the analyzed cases, the obtained results show that the correlation coefficient is around 0.99, the energy respecting to the pure EMG signal is 98-104%, the SNR is between 16.64 and 20.40dB and the mean absolute error (MAE) is in the range of -69.02 and -65.31dB. It has been also applied on 18 real EMG signals, evaluating the percentage of energy respecting to the noisy signals. The proposed method adjusts the reduction level to the amplitude of each harmonic present in the analyzed noisy signals (synthetic and real), reducing the harmonics with no alteration of the desired signal.
In this paper, a human-machine interface with the concept of "blink control" is proposed. The human-machine interface is applied to an assistive device, namely "blink scanning keyboard", which is designed specifically for the severely physical disabled and people suffering from motor neuron diseases or severe cerebral palsy. The pseudo electromyography (EMG) signal of blinking eyes could be acquired by wearing a Bluetooth headset with one sensor on the forehead and the other three on the left ear of the user. Through a conscious blink, a clear and immediate variation will be formed in the pseudo EMG signal from the users' forehead. The occurrence of this variation in pseudo EMG signal could be detected and filtered by the algorithms proposed in this paper, acting like a trigger to activate the functions integrated in the scanning keyboard. The severely physical and visual disabled then can operate the proposed design by simply blinking their eyes, thus communicating with outside world.
Driver distraction is regarded as a significant contributor to motor-vehicle crashes. One of the important factors contributing to driver distraction was reported to be the handling and reaching of in-car electronic equipment and controls that usually requires taking the drivers' hands off the wheel and eyes off the road. To minimize the amount of such distraction, we present a new control scheme that senses and decodes the human muscles signals, denoted as Electromyogram (EMG), associated with different fingers postures/pressures, and map that to different commands to control external equipment, without taking hands off the wheel. To facilitate such a scheme, the most significant step is the extraction of a set of highly discriminative feature set that can well separate between the different EMG-based actions and to do so in a computationally efficient manner. In this paper, an accurate and efficient method based on Fuzzy Neighborhood Discriminant Analysis (FNDA), is proposed for discriminant feature extraction and then extended to the channel selection problem. Unlike existing methods, the objective of the proposed FNDA is to preserve the local geometrical and discriminant structures, while taking into account the contribution of the samples to the different classes. The method also aims to efficiently overcome the singularity problems of classical LDA by employing the QR-decomposition. Practical real-time experiments with eight EMG sensors attached on the human forearm of eight subjects indicated that up to fourteen classes of fingers postures/pressures can be classified with <7% error on average, proving the significance of the proposed method.
Stress is a major growing concern in our day and age adversely impacting both individuals and society. Stress research has a wide range of benefits from improving personal operations, learning, and increasing work productivity to benefiting society - making it an interesting and socially beneficial area of research. This survey reviews sensors that have been used to measure stress and investigates techniques for modelling stress. It discusses non-invasive and unobtrusive sensors for measuring computed stress, a term we coin in the paper. Sensors that do not impede everyday activities that could be used by those who would like to monitor stress levels on a regular basis (e.g. vehicle drivers, patients with illnesses linked to stress) is the focus of the discussion. Computational techniques have the capacity to determine optimal sensor fusion and automate data analysis for stress recognition and classification. Several computational techniques have been developed to model stress based on techniques such as Bayesian networks, artificial neural networks, and support vector machines, which this survey investigates. The survey concludes with a summary and provides possible directions for further computational stress research.
M.rectus femoris motor unit potentials were picked up by a bipolar needle electrode during voluntary isometric contraction. The tension varied from 0 to 4–14 kg (17–47% of maximal strength). When the contraction was increased, not only more motoneurones were recruited but their frequency was also increased. Low threshold motoneurones reached the highest frequency (up to 18–21/sec). The majority of motoneurones discharged with frequencies exceeding 11/sec. Fluctuations of strength were accompanied by corresponding fluctuations of frequency. During a long contraction at constant strength the frequency decreased during the first 1–2 min to the level of not more than 10–13/sec. A voluntary increase of tension was accompanied by a new increase in frequency. During a long contraction at constant strength new motoneurones were gradually recruited.
When vibration is applied to a muscle, the discharges of its motor units (MUs) become correlated with vibratory pulses. This effect has been extensively studied by single MU recording techniques. We suggested the surface EMG to be useful in this context to reveal a generalized pattern of MU firing. The surface EMG of human soleus muscle subjected to vibration during a voluntary contraction was recorded with precautions to suppress vibratory artifacts. Spectral analysis of the EMG and of the rectified EMG (REMG) revealed characteristic peaks, present in the power spectra at the vibration frequency (VF) and its harmonics. Vibratory artifacts were negligible, since during the ischemic block of the muscle, the peaks disappeared similar to the T-reflex extinction. If the VF was low compared with the major frequency domain of the EMG, the peaks were better expressed in the spectra of the REMG, while at higher VFs they were more pronounced in the EMG spectra. With the increase in the force of muscle contraction, the peaks, normalized to the total power of the spectrum, diminished. During a prolonged contraction in the presence of vibration, the peaks augmented, probably due to synaptic potentiation. Mathematical modeling of the surface EMG was performed to interpret the experimental data. The simulated patterns were consistent with the experimental results. Since the model predicted an increase in the normalized peaks with increasing number of MUs, it was suggested that at larger forces of contraction the correlation of MU discharges with the vibratory stimuli, on average, deteriorated.
The firing of 97 soleus motor units (MUs) and 52 triceps brachii MUs of eight volunteers has been studied in the tonic vibration reflex. The vibration frequency was varied from 30 to 150 Hz. Interspike interval histograms of single MUs as well as cross-correlograms between their spikes and vibration mechanograms were obtained to reveal the correlation between MU discharges and vibration stimuli. In all of the MUs studied, both methods revealed the correlation. More detailed study of the discharge pattern of soleus MUs revealed the dependence of the correlation on the vibration frequency: the highest degree of correlation was observed at low vibration frequencies (30-50 Hz); the correlation gradually decreased with the increase in vibration frequency and disappeared with frequencies higher than 85 Hz. However, the correlation was observed when high frequency vibration was applied to a voluntarily contracted muscle. The muscle contraction also removed the vibration-induced depression of the soleus H reflex. At low frequency vibration, the correlation may be caused by the group II afferent EPSPs. A voluntary muscle contraction seems to be accompanied by removal of the vibration-induced presynaptic inhibition of the monosynaptic input to motoneurons from Ia afferents that leads to the correlation at high vibration frequencies.
The purpose of this study was to compare the accuracy of the estimated innervation zone (IZ) locations obtained from cross-correlation, the minimum amplitude, and maximum center frequency criteria. Eight healthy men (mean±SD age=23.0±4.3 yrs) performed isometric muscle actions of the leg extensors, and 15 separate bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis. A custom software program was used to estimate the location of the IZ based on: (1) the EMG channel that demonstrated the lowest amplitude, (2) the EMG channel that showed the highest mean frequency, and (3) the EMG channel that demonstrated the lowest peak cross-correlation between the signals from adjacent channels. The IZ location estimates from the lowest amplitude and highest mean frequency criteria were accurate in only 43.75% and 7.5% of the cases, respectively. The accuracy of the cross-correlation-based method was 90%. The cross-correlation-based method was much more accurate for estimating IZ location than were the lowest amplitude and highest mean frequency criteria. Cross-correlation could potentially be used for estimating the location of the IZ without the need for visual inspection of EMG signals.
The aim of this study is to highlight the relationship between muscle motion, generated by whole body vibration, and the correspondent electromyographic (EMG) activity and to suggest a new method to customize the stimulation frequency. Simultaneous recordings of EMG and tri-axial accelerations of quadriceps rectus femoris from fifteen subjects undergoing vibration treatments were collected. Vibrations were delivered via a sinusoidal oscillating platform at different frequencies (10-45 Hz). Muscle motion was estimated by processing the accelerometer data. Large EMG motion artifacts were removed using sharp notch filters centred at the vibration frequency and its superior harmonics. EMG-RMS values were computed and analyzed before and after artifact suppression to assess muscular activity. Muscles acceleration amplitude increased with frequency. Muscle displacements revealed a mechanical resonant-like behaviour of the muscle. Resonance frequencies and dumping factors depended on subject. Moreover, RMS of artifact-free EMG was found well correlated (R(2)=0.82) to the actual muscle displacement, while the maximum of the EMG response was found related to the mechanical resonance frequency of muscle. Results showed that maximum muscular activity was found in correspondence to the mechanical resonance of the muscle itself. Assuming the hypothesis that muscle activation is proportional to muscle displacement, treatment optimization (i.e. to choose the best stimulation frequency) could be obtained by simply monitoring local acceleration (resonance), leading to a more effective muscle stimulation. Motion artifact produced an overestimation of muscle activity, therefore its removal was essential.
Using a single fibre EMG electrode the firing pattern of 46 motor units in the triceps surae has been studied during vibration of the Achilles tendon at frequencies of 25--200 Hz. Potentials activated in the tonic vibration reflex (TVR) were phase-locked to the vibration cycle but tended to become somewhat less so with continued vibration. The firing pattern of voluntarily activated motor units became locked to the waveform by the application of the vibrator. The discharges of 21 motor units were studied during low threshold (sub-M wave) tetanic stimulation of the tibial nerve at 25--100 Hz. No evidence was found of synchronization of potentials activated in the resulting tonic contraction. During weak voluntary contractions, stimulation also failed to regularize voluntarily activated motor units. The findings can be reconciled by postulating that, in normal man, vibration activates monosynaptic and polysynaptic pathways, the latter circuit being adequate to generate reflex contraction, while the former merely affects the temporal patterning of the motor outflow.
1. We observed in a previous study on the human foot dorsiflexor muscles that the fatigue-induced decline in motor output during sustained maximal voluntary contractions (MVCs) was temporarily counteracted during the initial phase of superimposed high-frequency (150 Hz) muscle vibration, whereas prolonged muscle vibration seemed to accentuate the fatigue-induced decline in gross EMG activity and motor unit firing rates. A more extensive investigation of this late effect of muscle vibration on MVCs was performed in the present study. 2. Prolonged periods of superimposed muscle vibration caused a reduction of EMG activity, motor unit firing rates and contraction force in both intermittent and sustained MVCs. This vibration-induced effect had the following main characteristics: (i) it developed slowly during the course of about 1 min of sustained vibration and subsided within 10-20 s after the end of vibration; (ii) it was much more pronounced in some subjects than in others (not age-dependent) and it was accentuated by preceding muscle exercise; (iii) it affected primarily the subject's ability to generate and/or maintain high firing rates in high-threshold motor units. 3. Since the effect developed while vibration at the same time exerted a tonic excitatory influence on the alpha-motoneurone pool (as evidenced by the presence of a tonic vibration reflex) it is argued that the vibration-induced suppression of motor output in MVCs probably does not depend on alpha-motoneurone inhibition, but on a reduced accessibility of these neurones to the voluntary commands. It is suggested that contributing mechanisms might be vibration-induced presynaptic inhibition and/or 'transmitter depletion' in the group Ia excitatory pathways which constitute the afferent link of the gamma-loop.
We compared single motor unit and surface EMG responses in the active right tibialis anterior following anodal electrical or magnetic stimulation of the motor cortex over the vertex. Magnetic stimulation used a monophasic current pulse through a circular coil centred 3 cm anterior to the vertex. Lowest threshold magnetic stimulation occurred when the current in the coil flowed from the left to the right side at the posterior rim of the coil. Such stimulation produced single unit and surface EMG responses which had the same latency as those produced by anodal electric stimulation. If the direction of the magnetic stimulating current was reversed, response latencies became more variable from unit to unit, and on average they occurred 1.0 +/- 0.5 msec later. In single motor units anodal and magnetic post-stimulus time histogram (PSTH) peaks had the same duration. This was similar to the duration of the PSTH peaks produced by a single low intensity stimulus given to the common peroneal nerve. We conclude that magnetic stimulation can produce direct activation of corticospinal neurones to the tibialis anterior if the direction of induced current flow is optimal. This projection is likely to be either monosynaptic or oligosynaptic.
The outside of the skin of the forearm is typically 15 mV more negative than the inside. Stretching the skin causes a reduction in the magnitude of this skin potential V, which we observe as a motion artifact . We seek to determine the origin of this motion artifact by successively stripping 12 layers of the skin using Scotch Tape. Between each stripping we measure artifact , 13 Hz impedance Z, and change in impedance . On the interior surface of the forearm, Z decreases with number of strippings. can be first either positive or negative, then is always negative and decreases linearly with Z. first remains constant and then decreases with Z and . and increase with stretch force following a logarithmic relationship. has a rectangular shape waveform, whereas the rising edge of shows a fast followed by a slow component and its falling edge decays exponentially with a large time constant. We have expanded the model of Thakor and Webster to best fit the waveform of and caused by stretch.
Keywords: skin, electrode, motion artifact, skin potential, skin impedance, skin model
The influence of vibration frequency (40, 80, 100, 120, 150, or 200 Hz) at selected displacement amplitudes (0.2, 0.3 mm) on tonic vibration reflex (TVR) characteristics was investigated. The degree of synchronization of motor unit activity with vibratory stimuli in ten humans was determined using the electromyographic (EMG) activity of the finger and wrist flexor muscles when vibration was applied to the distal tendons of the hand flexor muscles. The EMG spectral analysis indicates that harmonic and subharmonic motor unit synchronization mechanisms contribute to the modulation of the amplitude of the TVR as the vibration frequency increases. Harmonic synchronization decreases while subharmonic synchronization increases as vibration frequency increases. It is suggested that the synchronization process influences muscle fatigue, since it forces the driving of motor units, leading to a decrease in contraction efficiency. This phenomenon most probably results from an impairment of excitation-contraction coupling. High-frequency vibration (> 150 Hz) tends to induce less motor unit synchronization in a frequency range beyond the known mechanical resonance of biological tissues. The findings of this study may be applied to the design of hand-held power tools, since their vibration triggers the TVR in active muscles.
To reduce the time of computation of a motor unit potential (MUP), the shape of intracellular action potential (IAP) and (or) MU anatomy are generally simplified. A method of MUP presentation is suggested. It provides accuracy of the MUPs calculated for any distance and size of rectangular electrodes together with considerably reduced computational load and time. No simplification of the IAP shape or location of muscle fibres of different diameters and lengths is required. The MUP generated by N temporally and spatially dispersed single fibre action potentials is considered to be the output signal of a linear time-shift invariant system for potential generation. The input signal is the first temporal derivative of the IAP. The common impulse response (CIR) is the sum of potentials produced at the electrode by N pairs of dipoles propagating from the motor end-plates to the ends of the corresponding fibres. The potentials of each dipole at the rectangular plate electrode are determined analytically. Thus, the MUP is calculated as a single convolution between the input signal and CIR for a rectangular electrode of any size.
The aim of this study was to investigate the effects of whole-body vibrations (WBV) on the mechanical behaviour of human skeletal muscle. For this purpose, six female volleyball players at national level were recruited voluntarily. They were tested with maximal dynamic leg press exercise on a slide machine with extra loads of 70, 90, 110 and 130 kg. After the testing, one leg was randomly assigned to the control treatment (C) and the other to the experimental treatment (E) consisting of vibrations. The subjects were then retested at the end of the treatment using the leg press. Results showed remarkable and statistically significant enhancement of the experimental treatment in average velocity (AV), average force (AF) and average power (AP) (P < 0.05-0.005). Consequently, the velocity-force and power-force relationship shifted to the right after the treatment. In conclusion, it was affirmed that the enhancement could be caused by neural factors, as athletes were well accustomed to the leg press exercise and the learning effect was minimized.
The aim of this paper is to study the femoral quadriceps muscles activation in patients suffering from anterior knee pain (AKP) during an isokinetic exercise. AKP is a common pathological condition, associated to an abnormal motion of the patella. It possibly depends on a muscular or structural imbalance. A lack of synergy in the quadriceps muscles results in a dynamic misalignment of the patella, which in turn produces pain. A quantitative analysis of the muscle activation strategy is important for an objective measurement of the knee functionality in that it helps to diagnose and monitor the rehabilitative treatment. Surface electromyography (EMG) from the three superficial muscles of the femoral quadriceps during a concentric isokinetic exercise has been analysed. A group of AKP patients has been compared with a control group of healthy subjects. Ensemble average of the EMG linear envelopes reveals significant modifications in Vastus Medialis activity in AKP patients. In order to quantify the synergy of the muscles, different parameters have been associated to EMG linear envelopes significant features. A decomposition in gaussian pulses and an asymmetry coefficient have been utilised. The results relative to these concise parameters highlight an appreciable delay and a modification in the activation of the Vastus Medialis in AKP patients.
In many situations of everyday life, vibration load occurs. Here whole body vibration in vehicles, such as boats, cars, helicopters and others as well as hand-transmitted vibration (motor saws etc.) can be named. As vibration is assumed liable to cause various threats to human health, a great number of studies in work science focussed on dose-effect relations and concepts for prevention. Although in many sports remarkable vibration load also occurs, there is very little research on the potential dangers and benefits of vibration stimuli, e.g. on whole body vibration and the implications for muscular activity and neuromuscular control in sport. In personal studies the damping behaviour and training effects under whole body vibration were investigated. Various research areas have been studied in order to approach the relevant topics: neuromuscular and posture control, energy metabolism in terms of oxygen uptake under whole body vibration and local concentration of phosphates by means of 31P-MRS. Furthermore the effects of a strength training under whole body vibration were analysed. The results underline that vibration is a neglected research topic in sport science from the preventive point of view as well as from the one focussing on the improvement of sport performance.
Anterior knee pain (AKP) is a common pathological condition, particularly among young people and athletes, associated to an abnormal motion of the patella during the bending of the knee and possibly dependent on a muscular or structural imbalance. A lack of synergy in the quadriceps muscles results in a dynamic misalignment of the patella, which in turn produces pain. AKP rehabilitative therapy consists of conservative treatment whose main objective is to strengthen the Vastus Medialis. The aim of this article is to study the quadriceps muscle control strategy in AKP patients during an isokinetic exercise. Analysis of the muscle activation strategy is important for an objective measurement of the knee functionality in that it helps to diagnose and monitor the rehabilitative treatment. Surface electromyography (EMG) from the three superficial muscles of the femoral quadriceps during a concentric isokinetic exercise has been analyzed along with the signals of knee joint position and torque. A group of 12 AKP patients has been compared with a group of 30 normal subjects. Analysis of the grand ensemble average of the EMG linear envelopes in AKP patients reveals significant modifications in Vastus Medialis activity compared to the other quadriceps muscles. In order to study the synergy of the muscles, temporal identifiers have been associated to the EMG linear envelopes. To this end, EMG linear envelope decomposition in Gaussian pulses turned out to be effective and the results highlight an appreciable delay in the activation of the Vastus Medialis in AKP patients. This muscular unbalance can explain the abnormal motion of the patella.
The main results of our recent several studies, i.e. the measurements of vibration training results for single case and group studies as well as the cardiovascular parameter measurements during vibrations and the corresponding hydrodynamic analysis, are summarized. Our studies and previous work all confirm that vibration training is an effective training method in order to improve maximal strength and flexibility as well as various other factors if the training is properly designed. Some recommendations regarding the proper ranges of frequencies, amplitudes and exposure duration of vibration training are made based on the existing vibration training practice and mechanism analysis, although much work remains to be carried out in order to set up clear rules for various groups of people so that maximal training results could be expected and in the meantime potential dangerous effects could be avoided. Cardiovascular parameter measurements confirm that total peripheral resistance (TPR) to the blood flow is increased during body vibration. Hydrodynamic analysis offers the mechanism for the increase of TPR through the deformation of vessels. As a reaction of compensation, more capillaries are probably opened in order to keep a necessary level of cardiac output needed for the body, resulting in more efficient gas and material metabolism between the blood and muscle fibres. This might be one of the reasons for the various potential beneficial effects of vibration training.
The purpose of this investigation was to examine the influence of electrode placement over the estimated innervation zone (IZ) for the vastus lateralis, as well as proximal and distal to the estimated IZ, on the torque-related patterns for electromyographic (EMG) amplitude and mean power frequency (MPF) during concentric and eccentric isokinetic muscle actions of the leg extensors. Eleven men performed randomly ordered, submaximal to maximal concentric and eccentric isokinetic muscle actions of the dominant leg extensors in 10% increments from 10 to 90% peak torque (PT). Surface EMG signals were recorded simultaneously from the vastus lateralis muscle with bipolar electrode arrangements placed over the estimated IZ, as well as proximal and distal to the estimated IZ. The results indicated that there were no consistent differences among the proximal, IZ, and distal electrode placement sites for the patterns of responses for absolute and normalized EMG amplitude and MPF versus torque, or the mean absolute and normalized EMG amplitude and MPF values. Thus, these findings suggested that during concentric and eccentric isokinetic muscle actions of the leg extensors, electrode placement over the estimated IZ for the vastus lateralis had no effect on the patterns of responses or mean values for absolute and normalized EMG amplitude and MPF versus torque.
The aim of this study was to analyze electromyography (EMG) responses of vastus lateralis muscle to different whole-body vibration frequencies. For this purpose, 16 professional women volleyball players (age, 23.9 +/- 3.6 years; height, 182.5 +/- 11.1 cm; weight, 78.4 +/- 5.6 kg) voluntarily participated in the study. Vibration treatment was administered while standing on a vibrating platform with knees bent at 100 degrees (Nemes Bosco-system, Rome, Italy). EMG root mean square (rms) and was recorded for 60 seconds while standing on the vibrating plate in the following conditions: no vibrations and 30-, 40-, and 50-Hz vibration frequencies in random order. The position was kept for 60 seconds in each treatment condition. EMGrms was collected from the vastus lateralis muscle of the dominant leg. Statistical analysis showed that, in all vibration conditions, average EMGrms activity of vastus lateralis was higher than in the no-vibration condition. The highest EMGrms was found at 30 Hz, suggesting this frequency as the one eliciting the highest reflex response in vastus lateralis muscle during whole-body vibrations in half-squat position. An extension of these studies to a larger population appears worthwhile to further elucidate the responsiveness of the neuromuscular system to whole-body vibrations administered through vibrating platforms and to be able to develop individual treatment protocols.
The evaluation of postural stability using posturography could be both a valuable functional diagnostic and treatment outcome monitoring tool in rehabilitation practice of patients with chronic low back pain (cLBP). No evidence, however, seems to exist, whether or not such posturographic measures are reliable in these patients and therefore clinically and scientifically useful. The aims of this study were manifold and aimed at investigating (1) differences of posturographic measures between cLBP patients and healthy controls (HCs), (2) short- (intrasession-) and long-term (intersession-) reliability of these measurements, and (3) the relationship between both pain intensity and test-related feelings and significant learning effects of the posturographic measures in cLBP.
Identification of the innervation zone is widely used to optimize the accuracy and precision of noninvasive surface electromyography (EMG) signals because the EMG signal is strongly influenced by innervation zones. However, simply structured fusiform muscle, such as biceps brachii muscle, has been employed mainly due to the simplicity with which the propagation from raw EMG signals can be observed. In this study, the optimum electrode location (OEL), free from innervational influence, was investigated by the propagation pattern of action potentials for brachii muscles and more complicated deltoid muscle structures using an automatized signal analysis technique. The technique employed newly developed computer software with additional clinical uses and minimized subjective differences. EMG signals were recorded using surface array electrodes during voluntary isometric contractions obtained from 12 healthy male subjects. Peaks in EMG signals were detected and averaged for each muscle. The propagation patterns and OEL were examined from biceps brachii muscles for all subjects and from deltoid muscles for seven subjects. The estimated locations were partially confirmed by comparing the root mean squares of the EMG signals. These results show that propagation patterns and OEL could be estimated simply and automatically even from the surface EMG signals of deltoid muscles.
Electromyography readings (EMGs) from quadriceps of fifteen subjects were recorded during whole body vibration treatment at different frequencies (10-50 Hz). Additional electrodes were placed on the patella to monitor the occurrence of motion artifact, triaxial accelerometers were placed onto quadriceps to monitor motion. Signal spectra revealed sharp peaks corresponding to vibration frequency and its harmonics, in accordance with the accelerometer data. EMG total power was compared to that associated with vibration harmonics narrow bands, before and during vibration. On average, vibration associated power resulted in only 3% (+/-0.9%) of the total power prior to vibration and 29% (+/-13.4%) during vibration. Often, studies employ surface EMG to quantitatively evaluate vibration evoked muscular activity and to set stimulation frequency. However, previous research has not accounted for motion artifacts. The data presented in this study emphasize the need for the removal of motion artifacts, as they consistently affect RMS estimation, which is often used as a concise muscle activity index during vibrations. Such artifacts, rather unpredictable in amplitude, might be the cause of large inter-study differences and must be eliminated before analysis. Motion artifact filtering will contribute to thorough and precise interpretation of neuromuscular response to vibration treatment.
In order to use the volitional electromyography (EMG) as a control
signal for the stimulation of the same muscle, it is necessary to
eliminate the stimulation artifacts and the muscle responses caused by
the stimulation. The stimulation artifacts, caused by the electric field
in skin and tissue generated by the stimulation current, are relatively
easy to eliminate by shutting down the EMG-amplifier at the onset of the
stimulation pulses. The muscle response is a nonstationary signal,
therefore, an adaptive linear prediction filter is proposed. The filter
is implemented and for three filter lengths tested on both simulated and
real data. The filter performance is compared with a conventional fixed
comb filter. The simulations indicate that the adaptive filter is
relatively insensitive to variations in amplitude of the muscle
responses, and for all filter lengths produces a good filtering. For
variations in shape of the muscle responses and for real data, an
increased filter performance can be achieved by increasing the filter
length. Using a filter length of up to seven stimulation periods, it is
possible to reduce real muscle responses to a level comparable with the
background noise. Using the shut-down circuit and the adaptive filter
both the stimulation artifacts and the muscle responses can be
effectively eliminated from the EMG signal from a stimulated muscle. It
is therefore possible to extract the volitional EMG from a partly
paralyzed muscle and use it for controlling the stimulation of the same
muscle
The EMG-force relationships of electrically stimulated muscle under a wide range of firing rate and recruitment control strategies were studied in a predominantly slow (soleus) and fast (m. gastrocnemius) twitch muscles with the objective of applying the results in rehabilitative systems where the EMG serves as a force feedback parameter. The method of least squares was used to obtain best fit linear regression polynomials to the pooled plots of normalized mean absolute value of the EMG versus normalized force at each control strategy of each muscle. For the soleus, it was shown that control strategies in which all the motor units were fully recruited by the time the initial 30–40 percent of the maximal force was obtained and firing rate increase complemented the remaining force segment, the EMG force curves were linear, while increasing the recruitment generated initial force segment from 50 to 70 percent of the maximal resulted in progressively increasing nonlinear relationships. No statistically significant differences were observed in the relationships for strategies in which recruitment generated 70 percent and up to 100 percent of the maximal force. For the m. gastrocnemius, linear EMG versus force model was apparent when all the motor units were recruited to obtain 50 percent of the initial force, while progressive increase in nonlinearity was evident for strategies in which full recruitment was employed to obtain 60–80 percent of the initial force. Modifications of the firing rate stimulus pattern from linear increase in rate over time, to piecewise linear pattern in which pulse rate increased at an accelerated fashion once recruitment was terminated resulted in linear force output as well as linear EMG versus force model. A control system was constructed in which the input-output were linearly related as well as a linear force feedback which employed the EMG as a parameter representing force.
Muscles Alive Williams and Wilkins
- J Basmajian
- C De
J. Basmajian, C. De Luca, Muscles Alive Williams and Wilkins, Williams & Wilkins, Baltimore, USA, 1985, pp. 1–561.
European Recommendations for Surface Electromyography, Chap. 5, Roessingh Research and Development, The Netherlands
- C Rau
- C Disselhorst-Klug
- Hägg
Rau, C. Disselhorst-Klug, C. Hägg, European Recommendations for Surface Electromyography, Chap. 5, Roessingh Research and Development, The Netherlands, 1999.
Analysis and modelling of muscles motion during whole body vibration Electromyography activity of vastus lateralis muscle during whole-body vibrations of different frequencies
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