EMG onset detection and upper limb movements identification algorithm

Electromyography (EMG) consists of the measurement and recording of the electrical potential generated by the activation of muscle fibers when performing voluntary or involuntary movements. Therefore, electromyography signals (EMGs) are directly linked to the movement performed by a person. Hence, the study of surface EMGs to determine the movement a person is performing to control exoskeletons for post-stroke rehabilitation has become increasingly popular in recent years; particularly towards bilateral rehabilitation (BLR). Bilateral rehabilitation provides the patient the opportunity to control the intensity and frequency of the rehabilitation exercises. This paper introduces an onset detection method and a movement identification algorithm to differentiate (identify) among five different movements of the upper limb; abduction (AB), adduction (AD), flexion of the upper limb (FUL), extension of the upper limb (EUL) and AB followed by arm to the front (ABF). The movement identification algorithm focuses on the activation of muscle fibers within a single muscle when performing different movements; rather than a comparison between flexor and extensor muscles. This algorithm was evaluated using surface EMG recordings measured on healthy subjects at the Deltoid Muscle. Prior to the movement identification, the proper EMG preprocessing, feature extraction and onset detection of each EMGs recording was performed using Matlab. Two features were extracted from each channel, the root mean square (RMS) and the contractility characteristic of the muscle. An algorithm is then followed to identify the movement performed by a person. Results have shown a highly percentage of accuracy for both, the onset detection and movement identification algorithms.     

Electromyographical study on surgeons in urology. II. Determination of muscular fatigue

Abstract

An electromyographical fatigue analysis was performed in the operating theatre on four surgeons during 14 urological operations in which ‘direct endoscopy’ (cf. Luttmann el al. 1996, Part I) was applied. Surface electromyograms (EMG) were derived from the m. trapezius on both sides of the body, the right m. deltoideus, and the left m. erector spinae. The surgeons’ activities were documented by simultaneously recording an electrical activity code signal parallel to the EMGs. The electrical activity (EA) was formed from the raw EMG by rectification and continuous averaging. For purposes of spectral analysis, the EMGs were digitized and converted to the frequency domain by Fast Fourier Transformation. During the performance of endoscopic surgery, an increase in EA, as well as a spectral shift towards lower frequencies, are observed for at least one of the muscles under test in all of the operations. This indicates the development of muscular fatigue in the course of the operations. The finding is confirmed by applying a newly developed method for the joint analysis of the spectrum and the amplitude of EMGs (JASA) which permits discrimination between fatigue-induced and force-related changes in the EMG. Utilizing this method, the development of fatigue was confirmed for 11 of the 14 operations in the case of the right m. trapezius. The right trapezius muscle therefore constitutes a bottleneck for the performance of the operations. The endurance time was estimated from the increase in EA and compared with the actual duration of the operations. Since both are of the same order of magnitude, it is concluded that the final part of an operation has to be performed when the muscles are already fatigued. Application of the newly available method known as ‘monitor endoscopy’ (cf. Part I) can lead to a reduction in muscular strain and fatigue. This, in turn, will enable operations to be performed at less risk to the patient.     

Dynamic modeling and CPG-based trajectory generation for a masticatory rehab robot

Human mastication is a complex and rhythmic biomechanical process which is regulated by a brain stem central pattern generator (CPG). Masticatory patterns, frequency and amplitude of mastication are different from person to person and significantly depend on food properties. The central nervous system controls the activity of muscles to produce smooth transitions between different movements. Therefore, to rehab human mandibular system, there is a real need to use the concept of CPG for development of a new methodology in jaw exercises and to help jaw movements recovery. This paper proposes a novel method for real-time trajectory generation of a mastication rehab robot. The proposed method combines several methods and concepts including kinematics, dynamics, trajectory generation and CPG. The purpose of this article is to provide a methodology to enable physiotherapists to perform the human jaw rehabilitation. In this paper, the robotic setup includes two Gough–Stewart platforms. The first platform is used as the rehab robot, while the second one is used to model the human jaw system. Once the modeling is completed, the second robot will be replaced by an actual patient for the selected physiotherapy. Gibbs–Appell’s formulation is used to obtain the dynamics equations of the rehab robot. Then, a method based on the Fourier series is employed to tune parameters of the CPG. It is shown that changes in leg lengths, due to the online changes of the mastication parameters, occur in a smooth and continuous manner. The key feature of the proposed method, when applied to human mastication, is its ability to adapt to the environment and change the chewing pattern in real-time parameters, such as amplitudes as well as jaw movements velocity during mastication.     

Temporal Discrepancies in the Electromyographic Study of Rapid Movement

Elbow flexor and extensor contraction and relaxation delays, relative to muscle action potentials are evaluated as 30-60 msec for contraction and 30-70 msec for relaxation, but with significant differences between subjects and between different muscles in the same subject. The contention that proper temporal interpretation of rapid movement EMGs is impossible without prior evaluation of the delays specific to the subject and muscles involved is supported by applying such evaluations to explain anomolies in rapid elbow movement EMGs. It is shown that apparent cocontraction of antagonist muscles may be an artifact explicable by these (subject and muscle specific) delay differences. The need for extensive study of muscle action delays is stressed.     

A microcomputer system for collecting and processing physiological information about the masticatory system.

A software system has been written for IBM PC, XT, AT and compatible computers to be used for data collection, analysis and display. The system supports the sampling and processing of data for jaw movement tracks, myoelectrical activities of masticatory muscles, the temporomandibular joint (TMJ) and occlusal sounds and bite force, etc. The package includes the following functions: calculating displacement, velocity, curvature, and curvature center of jaw movement trace, analyzing myoelectrical signals in amplitude integration, root mean square and power spectrum, processing TMJ sounds and occlusal sounds and bite force, analysing jaw movement traces and myoelectrical activities during mastication simultaneously, determining the maxillomandibular relations, etc. The program also provides versatile formatting capability for video, printing and plotting of data, and graph creation. The most of the above programs have flexibility and adaptability to other physiological signal processes.     

Choosing new ways to chew: a robotic model of the human masticatory system for reproducing chewing behaviors

This paper discusses the efforts to design a robotic device that can be used to reproduce the mastication process in a mechanically controllable way while the masticatory efficiency and/or food dynamics are assessed quantitatively. While being aimed at a robotic device that is able to fully reproduce human chewing behaviors, this paper is about building and simulating its robotic model. Following an examination into the biological muscles of mastication, the muscles responsible for the chewing movements are represented by a set of linear actuators and are placed between the mandible and the skull via spherical joints, resulting in a robotic mechanism. Simulations for the mandible movements with respect to the given muscular actuations, and for the muscular actuations required for a real human chewing pattern, are conducted using the Solidworks and COSMOS/Motion.     

A study by EMG stick diagrams of the muscular activities in the trunk flexion and extension movement

The activity of the leg and abdominal muscles in trunk flexion and extension was investigated with reference to the sudden decreases and increases of the erectores spinae activity. The movement was performed under conditions with and without an additional load, and with and without fatigue. Surface EMGs were recorded from the erectores spinae, the gluteus maximus, the semitendinosus, the rectus abdominis and the external oblique. The pattern of activity was analysed using EMG stick diagrams. Under the condition without fatigue, the semitendinosus activity increased during the sudden changes of the erectores spinae activity, but the abdominal muscles were not activated during the movement. However, the rectus abdominis was activated whenever the semitendinosus activity did not increase during the changes of the erectores spinae activity. Under the condition of fatigue, the leg muscle was vigorously active during the movement, and the abdominal muscles were activated before and after the erectores spinae activity changed suddenly. The results suggest that the leg muscle plays some important part during the sudden changes of the erectores spinae activity.     

Sub-pixel precision image matching for measuring surface displacements on mass movements using normalized cross-correlation

This study evaluates the performance of two fundamentally different approaches to achieve sub-pixel precision of normalised cross-correlation when measuring surface displacements on mass movements from repeat optical images. In the first approach, image intensities are interpolated to a desired sub-pixel resolution using a bi-cubic interpolation scheme prior to the actual displacement matching. In the second approach, the image pairs are correlated at the original image resolution and the peaks of the correlation coefficient surface are then located at the desired sub-pixel resolution using three techniques, namely bi-cubic interpolation, parabola fitting and Gaussian fitting. Both principal approaches are applied to three typical mass movement types: rockglacier creep, glacier flow and land sliding. In addition, the influence of pixel resolution on the accuracies of displacement measurement using image matching is evaluated using repeat images resampled to different spatial resolutions. Our results show that bi-cubic interpolation of image intensity performs best followed by bi-cubic interpolation of the correlation surface. Both Gaussian and parabolic peak locating turn out less accurate. By increasing the spatial resolution (i.e. reducing the ground pixel size) of the matched images by 2 to 16 times using intensity interpolation, 40% to 80% reduction in mean error in reference to the same resolution original image could be achieved. The study also quantifies how the mean error, the random error, the proportion of mismatches and the proportion of undetected movements increase with increasing pixel size (i.e. decreasing spatial resolution) for all of the three mass movement examples investigated.     

Identification of EMG signals using discriminant analysis and SVM classifier

The electromyography (EMG) signal is a bioelectrical signal variation, generated in muscles during voluntary or involuntary muscle activities. The muscle activities such as contraction or relaxation are always controlled by the nervous system. The EMG signal is a complicated biomedical signal due to anatomical/physiological properties of the muscles and its noisy environment. In this paper, a classification technique is proposed to classify signals required for a prosperous arm prosthesis control by using surface EMG signals. This work uses recorded EMG signals generated by biceps and triceps muscles for four different movements. Each signal has one single pattern and it is essential to separate and classify these patterns properly. Discriminant analysis and support vector machine (SVM) classifier have been used to classify four different arm movement signals. Prior to classification, proper feature vectors are derived from the signal. The feature vectors are generated by using mean absolute value (MAV). These feature vectors are provided as inputs to the identification/classification system. Discriminant analysis using five different approaches, classification accuracy rates achieved from very good (98%) to poor (96%) by using 10-fold cross validation. SVM classifier gives a very good average accuracy rate (99%) for four movements with the classification error rate 1%. Correct classification rates of the applied techniques are very high which can be used to classify EMG signals for prosperous arm prosthesis control studies.     

ART2 Neural Network for Surface EMG Decomposition

Extraction of individual Motor Unit Action Potentials (MUAPs) from a surface ElectroMyoGram (EMG) is an essential but challenging task for clinical study and physiological investigation. This paper presents an automatic decomposition of surface EMGs using a self-organised ART2 neural network. In our approach, MUAP peaks are first detected using a Weighted Low-Pass Differential (WLPD) filter. A modified ART2 network is then utilised to classify MUAPs based on MUAP waveforms and firing time information. Individual MUAP trains are identified from real surface EMG signals recorded during weak contraction, and also from simulated surface EMGs. The firing statistics and the waveforms of individual MUAPs are then extracted. A number of computer tests on 50 simulated and real surface EMGs of limb muscles show that up to five MUAP trains can be effectively extracted, with their waveforms and firing parameters estimated. Being able to decompose real surface EMGs has essentially demonstrated the potential applications of our approach to the non-invasive diagnosis of neuromuscular disorders.       

Effects of load and speed on lumbar vertebral kinematics during lifting motions

This experimental study investigated the effects of load magnitude and movement speed on lumbar vertebral kinematics during lifting task performance. Ten participants performed sagittally symmetric lifting movements with systematically varied load using either a normal or a faster-than-normal speed. Skin-surface markers were strategically placed over the participants' spinous processes and other landmarks representing major body joints and were recorded during the movements by a motion capture system. The center of rotation (COR) locations and segmental movement profiles for lumbar vertebrae L2 to L5 were derived and analyzed. Results suggested that (a) the COR locations and vertebral angular displacement were not significantly affected by the speed or load variation; (b) a faster speed tended to shorten the time to complete the acceleration for all the lumbar vertebrae considered; and (c) the load increase incurred a tendency for the L5 to complete the primary displacement in a briefer time while enduring greater peak acceleration and velocity. The findings lead to a better understanding of the relation between lifting dynamics and spinal motion. Potential applications of this research include the development of more accurate biomechanical models and software tools for depicting spinal motions and quantifying low-back stress.     

Peak activation of lower limb musculature during high flexion kneeling and transitional movements

Few studies have measured lower limb muscle activation during high knee flexion or investigated the effects of occupational safety footwear. Therefore, our understanding of injury and disease mechanisms, such as knee osteoarthritis, is limited for these high-risk postures. Peak activation was assessed in eight bilateral lower limb muscles for twelve male participants, while shod or barefoot. Transitions between standing and kneeling had peak quadriceps and tibialis anterior (TA) activations above 50% MVC. Static kneeling and simulated tasks performed when kneeling had peak TA activity above 15% MVC but below 10% MVC for remaining muscles. In three cases, peak muscle activity was significantly higher (mean 8.9% MVC) when shod. However, net compressive knee joint forces may not be significantly increased when shod. EMG should be used as a modelling input when estimating joint contact forces for these postures, considering the activation levels in the hamstrings and quadriceps muscles during transitions.

Practitioner Summary: Kneeling transitional movements are used in activities of daily living and work but are linked to increased knee osteoarthritis risk. We found peak EMG activity of some lower limb muscles to be over 70% MVC during transitions and minimal influence of wearing safety footwear.     

Muscle responses to simulated torque reactions of hand-held power tools

The aim of this work was to investigate physiological responses to torque reaction forces produced by hand-held power tools used to tighten threaded fasteners. Such tools are used repetitively by workers in many industries and are often associated with upper limb musculoskeletal complaints. The tools considered for stimulation in this study had straight handles and required from 100 to 400 ms to tighten fasteners to a peak torque of 1.0 to 2.5 Nm and from 50 to 150 ms for the torque to decay to zero. A tool stimulator was constructed to apply a programmed torque profile to a handle similar to that of a straight in-line power screwdriver. Wrist flexor and extensor surface EMGs and handle position were recorded as subjects held handles subjected to controlled torque loads that tended to flex the wrist. It was found that: (1) very high EMG values occurred even though torques were of short duration (50 to 600 ms) and the peak torques were low (7–28% of maximum strength); (2) high EMGs in anticipation of torque are directly related to torque build-up rate and peak torque; (3) high peak flexor and extensor EMGs during and following torque onset are related to torque build-up rate and peak torque; (4) minimum time of peak EMGs of 72–87 ms following the onset of torques with 50 ms build-up suggests the contribution of an extensor muscle stretch reflex component; delayed peak for longer build-ups suggests a central control of muscle force in response to torque; (5) angular excursions of handles increase with decreasing torque build-up time and increasing torque magnitude causes increasing eccentric work; (6) the results show that the slow torque build-up times (450 ms) correspond to minimum peak EMGs; and (7) accumulated EMGs increase with increasing torque and torque build-up times. Further studies are needed to evaluate fatigue and musculoskeletal injuries associated with prolonged periods of tool use.     

Vision for Performance in Virtual Environments: The Role of Feedback Timing

This work explores how people use visual feedback when performing simple reach-to-grasp movements in a tabletop virtual environment. In particular we investigated whether visual feedback is required for the entire reach or whether minimal feedback can be effectively used. Twelve participants performed reach-to-grasp movements toward targets at two locations. Visual feedback about the index finger and thumb was provided in four conditions: vision available throughout the movement, vision available up to peak wrist velocity, vision available until movement initiation, or vision absent throughout the movement. It was hypothesized that vision available until movement onset would be an advantage over a no vision situation yet not attain the performance observed when vision was available up to peak velocity. Results indicated that movement time was longest in the no vision condition but similar for the three conditions where vision was available. However, deceleration time and peak aperture measures suggest grasping is more difficult when vision is not available for at least the first third of the movement. These results suggest that designers of virtual environments can manipulate the availability of visual feedback of one's hand without compromising interactivity. This may be applied, for example, when detailed rendering of other aspects of the environmental layout is more important, when motion lag is a problem or when hand/object concealment is an issue.     

基于隐马尔科夫模型的中文发音动作参数预测方法研究

发音动作参数描述发音过程中唇、舌、颚等发音器官的位置与运动。本文对给定文本与语音情况下中文发音动作参数的预测方法进行研究。首先,设计了基于电磁发音仪的发音动作参数采集与预处理方法,通过头部运动规整与咬合面规整保证了发音动作参数的可靠性;其次,将隐马尔科夫模型应用于中文发音动作参数预测,采用包含声学参数与发音动作参数的双流模型结构实现从声学参数到发音动作参数的映射,并且分析对比了建模过程中不同上下文属性、模型聚类方式以及流间相关性假设对于中文发音动作参数预测性能的影响。实验结果表明,当采用三音素模型、双流独立聚类并且考虑流间相关性的情况下,可以获得最优的预测性能。     

ELECTROMYOGRAPHIC INVESTIGATIONS DURING TYPEWRITING

By recording electrical impulses from muscles during movements, it is possible to find the number of muscles taking part in the movement and when they are in activity and to estimate the force of contraction. The different factors which influence typewriting can therefore be studied by electromyography.

From these experiments it would appear that the most important factor is thorough practice on the typewriter. The person tested must also use favourable equipment (e.g. chair and table) and a satisfactory working position. The environment must be well lighted, not too cold, nor too noisy. The typist must use the highest preferred working speed, and take a short rest when tired.     

An optimal control model of a neuromuscular system in human arm movements and its control characteristics

The joint torque which sets human limbs into motion is generated by a separate group of muscles provided for each joint. As the activation of each muscle is determined by a neural input, a neuromuscular system controlling all muscles has to be considered in order to understand human movements. In this study, an optimal control model of a neuromuscular system is investigated, and its control characteristics are examined. First, the dynamic and mechanical properties of a muscle are examined, and a neuromuscular system is formulated mathematically. Second, a performance criterion for the optimal control model is defined in order to characterize the dynamic behavior of the neuromuscular system, and a mathematical procedure for producing optimal trajectories is represented. Third, optimal trajectories in human arm movements are produced under various conditions of movement, and these trajectories are compared with experimentally observed ones. It is then verified that the optimal trajectories demonstrate human arm movements well. Finally, the behavior of individual muscles in various movements is examined quantitatively by means of simulation results, and the control characteristics of the human neuromuscular system are investigated. This work was presented in part at the Sixth International Symposium on Artificial Life and Robotics, Tokyo, January 15–17, 2001.     

Electromyography applied to sport ergonomics

Abstract

The improvement of electromyographic (EMG) devices for the detection of electric potentials produced in voluntary complex movements and the evolution of methodological approaches to data acquisition and computerized analysis of patterns, are responsible for the increased applications of EMG in bioengineering, rehabilitation, sport and occupational biomechanics, physiology and zoology and to a lesser extent in ergonomics. This paper describes three different EMG applications related to a sport environment using three different EMG registration and data acquisition approaches.

The first study examined the relation between the swimming action in water and its simulation using training equipment on land. It was found that with respect to the mechanical aspects of dry-land equipment and to the biomechanical differences in the execution of the front crawl action on dry land and in water, based on EMG activity of the propulsion muscles, the best results were found when using devices with accommodating resistance. Recovery muscles were best imitated using isokinetics, but despite the greater effort on land, lower EMG activity was recorded than in water. It was generally observed that whenever the swimmer acted against a mechanical resistance an important pattern deviation was noted.

Second, a study to determine the influence of ski materials on the EMG muscle activity of skiers showed systematic differences between the use of racing, soft and compact skis. The results supported the idea that the soft ski should be more highly recommended than the compact or racing ski for both general and competive use.

Finally, in a third study we found that there was a very high degree of similarity in the pattern and intensity of muscle activity in both free swimming and swimming against a mechanical resistance (MAD swimming), even though the kinesiological aspects of the movement trajectory were proved different beforehand.     

Spatial updating of objects after rotational and translational body movements in virtual environments

Spatial reasoning in architectural design can be better understood by considering the factors that affect the spatial updating process of the individual in an environment. This study focuses on the issue of spatial updating of viewed and imagined objects after rotational and translational body movements in a virtual environment (VE). Rotational and translational movements based on an egocentric frame of reference where there is no control of the user are compared in a desktop VE. Moreover, preference in architectural drawing medium and gender are analyzed as the factors that affect the spatial updating of objects in each body movement type. The results indicated that translational movement was more efficient than the rotational movement in judgment of relative directions in viewed objects. Furthermore, the viewed objects were more correctly spatially updated than the imagined ones both in translational and rotational body movements. In comparison of hand, computer and both as the drawing media, findings indicated that preference in computer medium in architectural design drawings was an effective one in spatial updating process in a VE. Contrary to the previous studies, it is found that there was no significant difference between gender and movement types.     

CONSTANT VELOCITY IN LIFTING AS A CRITERION OF MUSCULAR SKILL*

The derivation of a measure of skill from changes in velocity throughout a lifting movement was studied. The distances traversed by the wrists in lifting n 10 kg weight to the height of 1-67 in were recorded photographically with the aid of neon lights flashing at 0.1 sec intervals. The values of velocity, acceleration and force were computed at successive stages throughout each movement.

A shift from constant acceleration to constant velocity in movement was significant after training. The estimates of this trend were made by comparing within movement: (a) the mean acceleration with the mean acceleration in the central phase of movement, (b) the kinetic energy developed with the square of mean velocity, (c) the maximum with the mean velocity.

The following effects were shown: as lifting became faster during training the peak velocity approached a constant; the peak velocity was not appreciably increased but the velocity in the initial and final phases of movement was progressively raised towards the peak; this was most pronounced for the mean velocity of lifting 1 -6 m/see and coincided with the greatest work output per litre of expired air. With even faster lifting the constant acceleration reappeared together with a sharp decline of the work output per litre of expired air.

With constant velocity in lifting which involved a vast number of muscles, a reduced force, used with the maximal velocity, reflects the characteristic relation between velocity of contraction and force. With constant acceleration great force coincides with great velocity, suggesting that the elastic element of the muscle engages the contractile mechanism and that a time lag between the motor discharge and its sensory feedback occurs which takes the velocity of the limbs out of control.

On the behavioural level the correspondence, approaching one to one, between the maximum and the mean velocity in movement was statistically a sensitive measure of progress in acquisition of skill.