Jer-Junn Luh

Isokinetic elbow joint torques estimation from surface EMG and joint kinematic data: using an artificial neural network model

Because the relations between electromyographic signal (EMG) and anisometric joint torque remain unpredictable, the aim of this study was to determine the relations between the EMG activity and the isokinetic elbow joint torque via an artificial neural network (ANN) model. This 3-layer feed-forward network was constructed using an error back-propagation algorithm with an adaptive learning rate. The experimental validation was achieved by rectified, low-pass filtered EMG signals from the representative muscles, joint angle and joint angular velocity and measured torque. Learning with a limited set of examples allowed accurate prediction of isokinetic joint torque from novel EMG activities, joint position, joint angular velocity. Sensitivity analysis of the hidden node numbers during the learning and testing phases demonstrated that the choice of numbers of hidden node was not critical except at extreme values of those parameters. Model predictions were well correlated with the experimental data (the mean root-mean-square-difference and correlation coefficient gamma in learning were 0.0290 and 0.998, respectively, and in three different speed testings were 0.1413 and 0.900, respectively). These results suggested that an ANN model can represent the relations between EMG and joint torque/moment in human isokinetic movements. The effect of different adjacent electrode sites was also evaluated and showed the location of electrodes was very important to produce errors in the ANN model.

Real-time implementation of electromyogram pattern recognition as a control command of man-machine interface

The purpose of this study was to develop a real-time electromyogram (EMG) discrimination system to provide control commands for man-machine interface applications. A host computer with a plug-in data acquisition and processing board containing a TMS320 C31 floating-point digital signal processor was used to attain real-time EMG classification. Two-channel EMG signals were collected by two pairs of surface electrodes located bilaterally between the sternocleidomastoid and the upper trapezius. Five motions of the neck and shoulders were discriminated for each subject. The zero-crossing rate was employed to detect the onset of muscle contraction. The cepstral coefficients, derived from autoregressive coefficients and estimated by a recursive least square algorithm, were used as the recognition features. These features were then discriminated using a modified maximum likelihood distance classifier. The total response time of this EMG discrimination system was achieved about within 0.17 s. Four able bodied and two C5/6 quadriplegic subjects took part in the experiment, and achieved 95% mean recognition rate in discrimination between the five specific motions. The response time and the reliability of recognition indicate that this system has the potential to discriminate body motions for man-machine interface applications.

In vivo imaging of blood flow in the mouse Achilles tendon using high-frequency ultrasound.

OBJECTIVE Achilles tendinitis is a common clinical problem with many treatment modalities, including physical therapy, exercise and therapeutic ultrasound. However, evaluating the effects of current therapeutic modalities and studying the therapeutic mechanism(s) in vivo remains problematic. In this study, we attempted to observe the morphology and microcirculation changes in mouse Achilles tendons between pre- and post-treatment using high-frequency (25 MHz) ultrasound imaging. A secondary aim was to assess the potential of high-frequency ultrasound in exploring therapeutic mechanisms in small-animal models in vivo. METHODS A collagenase-induced mouse model of Achilles tendinitis was adopted, and 5 min treatment of continuous-mode low-frequency (45 kHz) ultrasound with 47 mW/cm(2) maximum intensity and 16.3 cm(2) effective beam radiating area was applied. The B-mode images showed no focal hypoechoic regions in normal Achilles tendons either pre- or post-treatment. The Doppler power energy and blood flow rate were measured within the peritendinous space of the Achilles tendon. CONCLUSION An increase in the microcirculation was observed soon after the low-frequency ultrasound treatment, which was due to immediate induction of vascular dilatation. The results suggest that applying high-frequency Doppler imaging to small-animal models will be an invaluable aid in explorations of the therapeutic mechanism(s). Our future work includes using imaging to assess microcirculation changes in tendinitis between before and after treatment over a long time period, which is expected to yield useful physiological data for future human studies.

A novel STFT-ranking feature of multi-channel EMG for motion pattern recognition

STFT-ranking feature is efficient for multi-channel EMG signal analysis.STFT-ranking feature can characterize relationships between multi-channel signals.Recognition accuracy over 90% was achieved applying the STFT-ranking feature.The performance of STFT-ranking feature is superior to conventional features.STFT-ranking feature can be applied to other multi-channel signals applications. Electromyography (EMG) is widely applied for neural engineering. For motion pattern recognition, many features of multi-channel EMG signals were investigated, but the relationships between muscles were not considered. In this study, a novel STFT-ranking feature based on short-time Fourier transform (STFT) is proposed. The novelty of STFT-ranking features is considering and covering the relationship information between EMG signals and multiple muscles in a motion pattern. With an exoskeleton robot arm, two series of motion patterns corresponding to the shoulder and elbow in the sagittal plane were investigated. EMG signals from six muscles were acquired in arm motion patterns when participants worn the robot arm. Four types of feature combinations, including seven conventional features, were compared with the STFT-ranking feature. The principal component analysis (PCA) and support vector machine (SVM) were used to build the motion recognition model. With the STFT-ranking feature, the recognition performance (93.9%) is superior to the conventional features (33.3-90.8%). The recognition variation is smaller (SD=4.3%) than the other features tested (SD=5.9-13.8%). These achievements will contribute to the advancement of control method of exoskeleton robots or power orthoses based on multi-channel EMG signals in the future. Based on the principle of STFT-ranking feature, the method also has potential for other multi-channel signal applications, such as electroencephalography (EEG) signal processing, speech recognition, and acoustic analysis.

Development of a monitoring system for keyboard users' performance.

To precisely evaluate the typing performance of a VDT user, a program named KBlog was developed to record the typing activity under the Microsoft Windows operating system. This program is small and simply framed in order to avoid overloading of the operating system. Without interfering with the typing task, this program can record the time of every pressing and releasing movement of each keystroke at the millisecond level. The accuracy and reliability of KBlog was tested by comparing time intervals recorded by KBlog to time intervals of keyboard output electrical signals recorded by an oscilloscope. In the regression analysis on these two indicators, results of high correlation coefficients of almost 1.000 and intercepts within acceptable levels of around 1 ms indicated sufficient accuracy and reliability of this program. Further applications are discussed in this paper concerning both laboratory and field researches.

Clinical effects of combined bilateral arm training with functional electrical stimulation in patients with stroke

Cerebral vascular disease (or stroke) is the main cause of disabilities in adults. Upper-limb dysfunction after stroke usually exists, leading to severe limits of motor capabilities as well as daily activities. Therefore, effective treatment interventions for upper-limb rehabilitation after stroke are needed. Based on the neurophysiological evidence and clinical measures, combined bilateral arm training (BAT) with functional electric stimulation (FES) could improve hand function in stroke patients. In this study, we attempt to combine BAT with FES applying to the post-stroke paretic arm. A linear guide platform with FES feedback control was developed to execute the training of bilateral reaching movements. 35 stroke subjects were recruited and divided into two groups (BAT with FES and BAT alone). 23 participants completed this experiment with 3-week intervention. According to our preliminary results, a favorable trend toward improvement in experimental group (BAT with FES) existed after treatment and at follow-up. Further analysis would be conducted to investigate the kinematic change on motor performance. Moreover, various treatment doses as well as more functional approaches would also be considered for better effects of upper limb rehabilitation after stroke.

Patient-driven loop control for hand function restoration in a non-invasive functional electrical stimulation system.

Purpose. In this study, a patient-driven loop control in a non-invasive functional electrical stimulation (FES) system was designed to restore hand function of stroke patients with their residual capabilities. Method. With this patient-driven loop control, patients use the electromyographic (EMG) signals from their voluntary controlled muscles in affected limbs to adjust stimulus parameters of the system. A special designed FES system generated electrical stimuli to excite the paralyzed muscles through surface electrodes on the basis of the control command from the residual myoelectric signals. EMG signals were also served as the trigger and the adjustment of stimulus parameters and thereby adding versatility of the FES system. Four stroke patients were recruited in the experiment to validate our system. Results. The experimental results showed that hemiplegics could successfully control the system to restore their lost hand functions with the strategy of patient-driven loop control (the average estimated success rate was 77.5% with the tasks of cylindrical grasp and lateral pinch); and further, they would benefit by using the residual capabilities to regain their hand functions from the viewpoints of rehabilitation and psychology. Conclusion. According to the experiment results, this patient-driven loop control can be beneficial for hemiplegics to restore their hand functions such as cylindrical grasp and lateral pinch. The control strategy of this study has the potential to be employed not only in the FES system but also in other assistive devices.

H-Reflex, Muscle Voluntary Activation Level, and Fatigue Index of Flexor Carpi Radialis in Individuals With Incomplete Cervical Cord Injury

Background. Individuals with incomplete spinal cord injury (SCI) are predisposed to muscle fatigue during voluntary exercise. However, the origin of fatigue is unclear. Objective. The authors examined the motoneuron excitability, muscle activation level, and fatigue properties of the flexor carpi radialis muscle, just below the level of injury. Methods. Nine individuals with chronic, incomplete cervical cord injury and 9 age-matched healthy individuals were recruited. The authors tested maximum voluntary contraction (MVC), motoneuron excitability by the maximum amplitude of the H-reflex (Hmax at C-7), and muscle voluntary activation level measured by the interpolated twitch technique. Subjects were fatigued by repetitive maximal voluntary isometric wrist flexion. General fatigue index (GFI), central fatigue index (CFI), and peripheral fatigue index (PFI) of flexor carpi radialis were examined before, during, and immediately after exercise. Results. The Hmax in the SCI group was significantly higher (P = .0028) than in controls. The MVC (P < .001) and voluntary activation level (P = .016) in the SCI group were significantly lower. The GFI and CFI decreased in both the SCI and the non-SCI groups. The PFI in the SCI group was significantly higher (ie, less fatigue) than that in controls at 30 repetitive contractions. Conclusions. In individuals with incomplete SCI, the deficit in central drive is an important source of muscle weakness and fatigue in the muscle below the level of injury.

ELECTROPHYSIOLOGICAL AND FUNCTIONAL EFFECTS OF SHOCK WAVES ON THE SCIATIC NERVE OF RATS

Extracorporeal shockwave therapy (ESWT) has been applied in lithotripsy and treatments of musculoskeletal disorders over the past decade, but its effects on peripheral nerves remain unclear. This study investigated the short-term effects of shockwaves on the sciatic nerve of rats. The nerves were surgically exposed and then stimulated with shockwaves at three intensities. We evaluated the motor nerve conduction velocity (MNCV) of treated sciatic nerves before, immediately after (day 0) and at 1, 4, 7 and 14 d after shockwave treatment. Two functional tests-the sciatic functional index and the withdrawal reflex latency-were evaluated before and at 1, 4, 7 and 14 d after shockwave application. The rats were sacrificed on days 0, 1, 4, 7 and 14 for morphologic observation. The degassed treatment group received high-intensity shockwave treatment using degassed normal saline as the contact medium, and MNCV was measured before and on days 0, 1, 4, 7 and 14. The sham group received the same procedure as the treatment groups (i.e., the surgical operation to expose the sciatic nerve) but with no shockwave treatment. The control group received no surgical operation or shockwave treatment. The results showed moderate decrease in the MNCV after shockwave treatment and damage to the myelin sheath of large-diameter myelinated fibers. The effect was largest (reduction to 60.9% of baseline MNCV) and of longest duration (7 to 14 d) in the high-intensity group. There were no significant changes in functional tests. These results indicated that direct application of shockwaves can induce reversible segmental demyelination in large-diameter fibers, with the electrophysiological changes being positively correlated with the intensity of the shockwaves.

DOSAgE OF NEUROMUSCULAR ELECTRICAL STIMULATION: IS IT A DETERMINANT OF UPPER LIMb FUNCTIONAL IMPROvEMENT IN STROkE PATIENTS?

OBJECTIVE To investigate the predictors related to upper extremity functional recovery, with special emphasis on neuromuscular electrical stimulation dose-response in patients after stroke. SUBJECTS Ninety-five patients with stroke who received a 4-week neuromuscular electrical stimulation intervention. DESIGN Prospective predictive analysis. METHODS The change score of the Action Research Arm Test (ARAT) was used as the main outcome. Baseline subject characteristics, stroke-related data, and intervention-related data were collected. Multiple linear regression analysis was applied to identify the potential predictors related to main outcome. RESULTS The regression model revealed that the initial Fugl-Meyer upper limb score was the most important predictor for ARAT change score post-test, followed by time since stroke onset and location of stroke lesion. At 2-month follow-up, the neuromuscular electrical stimulation dosage became a significant determinant in addition to the above predictors. CONCLUSION Initial motor severity and lesion location were the main predictors for upper limb functional improvement in stroke patients. Neuromuscular electrical stimulation dosage became a significant determinant for upper limb functional recovery after stroke at 2-month follow-up. More intensive neuromuscular electrical stimulation therapy during early rehabilitation is associated with better upper limb motor function recovery after stroke.