Motor unit properties in the biceps brachii of stroke patients assessed with surface array EMG

As a consequence of a stroke, both motor control as well as motor unit (MU) characteristics may change, e.g. MU size has been reported to increase due to reinnervation. The aim of the present study was to investigate how differences between the affected and unaffected side of hemiparetic stroke patients are reflected in surface array electomyography parameters

Reliability of MUAP properties in multi-channel array EMG recordings of trapezius and SCM

Muscle activity can be assessed non-invasively by means of surface electrodes places at the skin overlyin a muscle. When multiy-channel array electrodes are used, it is possible to extract motor unit action potentials (MUAP's) from the EMG signals with a segmentation approach based on the Continuous Wavelet Transform... The objective of the present study was to determine the test-retest reliability of the mentioned parameters during different tasks of the shoulder and neck muscles

The effect of electrode dislocation on lower back surface electromyography amplitude

Surface Electromyography (SEMG) plays an important role in the understanding of trunk muscle activity during various postures and movements. The Root Mean Square (RMS) is used to quantify the muscle activation amplitude and was shown to be a valuable parameter in research focusing on the etiology and maintenance of chronic lower back pain.\ud The aim of the current study was to determine the effect of electrode dislocation on the RMS of the low back muscles

MUAP rate and MUAP shape properties in subjects with work-related muscle pain

The objective of this study was to investigate differences in motor control of the trapezius muscle in cases with work-related chronic pain, compared to healthy controls. Ten cases with chronic pain and 13 controls participated in the study. Electromyographic (EMG) signals were recorded from the upper trapezius during five computer work-related tasks. Motor control was assessed using global root-mean-square value (RMSG), motor unit action potential (MUAP) rate (number of MUAPs per second, MR) and two MUAP shape parameters, i.e. root-mean-square (RMSMUAP) and median frequency (FMEDMUAP). MR and FMEDMUAP were higher for the cases than for the controls (P<0.05). RMSMUAP showed a trend for higher values in the chronic pain group (P<0.13), whereas RMSG did not show a significant difference between the groups. The higher MR, FMEDMUAP and the trend for higher RMSMUAP suggest that more high-threshold MUs contribute to low-level computer work-related tasks in chronic pain cases. Additionally, the results suggest that the input of the central nervous system to the muscle is higher in the cases with chronic pain

A Biomechanical Model for the Development of Myoelectric Hand Prosthesis Control Systems

Advanced myoelectric hand prostheses aim to reproduce as much of the human hand's functionality as possible. Development of the control system of such a prosthesis is strongly connected to its mechanical design; the control system requires accurate information on the prosthesis' structure and the surrounding environment, which can make development difficult without a finalized mechanical prototype. This paper presents a new framework for the development of electromyographic hand control systems, consisting of a prosthesis model based on the biomechanical structure of the human hand. The model's dynamic structure uses an ellipsoidal representation of the phalanges. Other features include underactuation in the fingers and thumb modeled with bond graphs, and a viscoelastic contact model. The model's functions are demonstrated by the execution of lateral and tripod grasps, and evaluated with regard to joint dynamics and applied forces. Finally, additions are suggested with which this model can be of use in mechanical design and patient training as well

A multichannel sEMG method for myoelectric control of a forearm prosthesis

A large number of amputee patients doesn't use their myoelectric prosthesis, mainly due to the limited functionality of the prosthesis.\ud The aim of this study was to investigate if it is possible to distinguish 8 different contractions by using multi-electrode sEMG. \ud We analysed sEMG signals of a grid of 40 and 30 electrodes from 10 healthy subjects and 1 amputee patient respectively during 8 different isometric movements of the wrist and fingers and classified them with a nearest neighbour classifier.\ud The results were very promising: over 99.5% of the movements were correctly classified and reducing the number of electrodes to 20 and 10 electrods only decreases the performance with 0.05 and 0.18%.\u

Influence of gravity compensation on muscle activity during reach and retrieval in healthy elderly.

INTRODUCTION: Arm support like gravity compensation may improve arm movements during stroke rehabilitation. It is unknown how gravity compensation affects muscle activation patterns during reach and retrieval movements. Since muscle activity during reach is represented by a component varying with movement velocity and a component supposedly counteracting gravity, we hypothesized that gravity compensation decreases the amplitude of muscle activity, but does not affect the pattern. To examine this, we compared muscle activity during well defined movements with and without gravity compensation in healthy elderly. METHODS: Ten subjects performed reach and retrieval movements with and without gravity compensation. Muscle activity of biceps, triceps, anterior, middle and posterior parts of deltoid and upper trapezius was compared between the two conditions. RESULTS: The level of muscle activity was lower with gravity compensation in all muscles, reaching significance in biceps, anterior deltoid and trapezius (p0.026). The muscle activation pattern did not differ between movements with and without gravity compensation (p0.662). DISCUSSION: Gravity compensation only influenced the level of muscle activity but not the muscle activation pattern in terms of timing. Future studies should examine if the influence of gravity compensation is comparable for stroke patients. This may stimulate early and intensive training during rehabilitation

A biomechanical model for the development of myoelectric hand prosthesis control systems

Advanced myoelectric hand prostheses aim to reproduce as much of the human hand's functionality as possible. Development of the control system of such a prosthesis is strongly connected to its mechanical design; the control system requires accurate information on the prosthesis' structure and the surrounding environment, which can make development difficult without a finalized mechanical prototype. This paper presents a new framework for the development of electromyographic hand control systems, consisting of a prosthesis model based on the biomechanical structure of the human hand. The model's dynamic structure uses an ellipsoidal representation of the phalanges. Other features include underactuation in the fingers and thumb modeled with bond graphs, and a viscoelastic contact model. The model's functions are demonstrated by the execution of lateral and tripod grasps, and evaluated with regard to joint dynamics and applied forces. Finally, additions are suggested with which this model can be of use in mechanical design and patient training as well

Multi-channel array EMG in chronic neck-shoulder pain

Chronic muscular pain has become an important problem, affecting a considerable part of the working population in the industrialised countries. Chronic muscular pain is a multifactorial problem and comprises a range of conditions that are not all clinically well-defined. Subjective symptoms include constant muscle pain, muscle fatigue and/or stiffness, and radiating pain. Identified risk factors for the development of chronic pain in the neck-shoulder region include exposure to awkward posture, repetitious movements, low level static contractions and high force demands. Beside these physical factors, psychosocial risk factors such as stress, high job demands and low vocational satisfaction play an important role. A variety of individual factors such as age, body mass index and perception of work load can contribute to the development of chronic pain as well. Several pathophysiological models, explaining the mechanisms that underlie the development of chronic pain, have been proposed. The vicious circle model predicts a positive feedback loop consisting of muscle pain that via nociceptors activates the γ-motoneuron system that projects to the α-motoneuron, thereby activating the muscle, which in turn leads to increased muscle pain. The pain adaptation model suggests a task-dependent increased antagonist activity and decreased agonist activity, thereby reducing painful movements. The Cinderella hypothesis suggests that muscle fibres of low-threshold motor units (MUs) are getting damaged in chronic pain cases because of continuous activation and lack of sufficient muscle relaxation. These models have in common that they predict changes in motor control. However, the models propose different working mechanisms and consensus on the nature of the changes in motor control is lacking. A better understanding of the underlying mechanisms is an important prerequisite for development of effective treatment methods. Model-based experimental studies assessing motor control in chronic pain cases may provide more insight into these mechanisms......

Calcium signalling in secretory cells

Stimulation of secretory cells with muscarinic agonists leads to an increase in the intracellular Ca2+ concentration ([Ca2+]i), which activates protein secretion through exocytosis and causes closure of gap junctions between adjacent cells. In addition, the increase in [Ca2+]i activates three different kinds of ion channels: large K+ channels, Cl- channels and non-specific cation channels. The opening of those channels leads to an increase of [Na+] and a decrease of [Cl-] and [K+] in the cell. The two components that contribute to the increase in [Ca2+]i are calcium release from intracellular stores, localised in the endoplasmic reticulum and calcium influx through the plasma membrane. Several models for the regulation of [Ca2+]i have been proposed, including a recently suggested model whereby a distinct pathway involving arachidonic acid is added to the well-established capacitative model. Different hypotheses concerning coupling between the intra-cellular calcium stores and membrane channels co-exist. In addition to a historical overview, recent developments and future challenges are discussed in this review