Posts Tagged Electromyography

[ARTICLE] Variation of Finger Activation Patterns Post-stroke Through Non-invasive Nerve Stimulation – Full Text

Purpose: A transcutaneous proximal nerve stimulation technique utilizing an electrode grid along the nerve bundles has previously shown flexible activation of multiple fingers. This case study aimed to further demonstrate the ability of this novel stimulation technique to induce various finger grasp patterns in a stroke survivor.

Methods: An individual with chronic hemiplegia and severe hand impairment was recruited. Electrical stimulation was delivered to different pairs of an electrode grid along the ulnar and median nerves to selectively activate different finger flexor muscles, with an automated electrode switching method. The resultant individual isometric flexion forces and forearm flexor high-density electromyography (HDEMG) were acquired to evaluate the finger activation patterns. A medium and low level of overall activation were chosen to gauge the available finger patterns for both the contralateral and paretic hands. All the flexion forces were then clustered to categorize the different types of grasp patterns.

Results: Both the contralateral and paretic sides demonstrated various force clusters including single and multi-finger activation patterns. The contralateral hand showed finger activation patterns mainly centered on median nerve activation of the index, middle, and ring fingers. The paretic hand exhibited fewer total activation patterns, but still showed activation of all four fingers in some combination.

Conclusion: Our results show that electrical stimulation at multiple positions along the proximal nerve bundles can elicit a select variety of finger activation patterns even in a stroke survivor with minimal hand function. This system could be further implemented for better rehabilitative training to help induce functional grasp patterns or to help regain muscle mass.


Following a stroke, a majority of individuals have paresis due to a loss of excitatory input and subsequent complications, such as disuse atrophy (1) and altered spinal organization (24). This loss of voluntary control of muscle activation often limits activities of daily living. Neuromuscular electrical stimulation (NMES) has been widely utilized both in the clinic and in research settings to help restore atrophied muscle and lost functions (57). Electrical stimulation has been particularly successful with post-stroke survivors for functional recovery (810). Research in NMES also aims to restore functional activation of muscles, such as the restoration of hand grasps (11).

Traditionally, NMES uses large electrode pads, targeting the distal branches of the nerve, known as the motor point stimulation (12). Although stimulation of the motor point is straightforward methodologically, NMES is limited to localized muscle activation, which limits its functional efficacy and also leads to rapid muscle fatigue (13). Advances in NMES techniques to alleviate these issues involve various multi-electrode techniques, which can stimulate multiple small regions of the muscle to help distribute the current and potentially activate more muscle fibers (1415). Crema et al. has also demonstrated flexible activation of multiple fingers using a multi-electrode array across the forearm and hand (16). Other approaches to NMES involve stimulation of the nerve bundle prior to branching and innervating a muscle, which has shown to allow for a larger area of muscle activation and potentially reduce long-term fatigue effects (1719).

Recent developments have demonstrated the capabilities of an alternative non-invasive transcutaneous electrical nerve stimulation method targeting the ulnar and median nerves proximal to the elbow to flexibly activate individual and multiple fingers (2021). In addition, this technique shows the ability to delay the force decline (2223). A stimulation electrode grid placed along the two nerves allows us to activate different muscles or muscle portions to elicit varied desired movements, but manually switching between different electrode pairs is time-consuming. To shorten this process, an automated electrode pair searching method has been developed and tested on intact control subjects (24). This new method can further categorize the total available sets of finger activation patterns across the entire electrode grid, providing valuable information on electrode selection and the force generation capacity of stroke muscles. However, the efficiency of this method has not been tested on stroke survivors. Therefore, this case study recruited a control subject and a stroke survivor with severe weakness of the right arm, and evaluated the available finger activation patterns of the subjects. Our results showed varied activation of multiple fingers from both subjects. Further development of this stimulation technique can provide valuable alternatives to current rehabilitation for the restoration of hand movements.[…]


Continue —> Frontiers | Variation of Finger Activation Patterns Post-stroke Through Non-invasive Nerve Stimulation | Neurology

Figure 1. Experimental Setup and Data Samples. (A) Stimulation Electrode Array and Force/HDEMG Setup. Processed Data samples are displayed adjacent to the setup figure. (B) The EMG map is the spatial map of calculated AUC values from each EMG channel’s CMAP and (C) the Force Profile is the smoothed force of each finger. (D) Sample Depiction of Automated Stimulation Procedure. Each stimulation pair can be paired with an EMG activity map and a force profile, which is the repetition of 3 stimulations.

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[Abstract] EMG Feature Extractions for Upper-Limb Functional Movement During Rehabilitation


Rehabilitation is important treatment for post stroke patient to regain their muscle strength and motor coordination as well as to retrain their nervous system. Electromyography (EMG) has been used by researcher to enhance conventional rehabilitation method as a tool to monitor muscle electrical activity however EMG signal is very stochastic in nature and contains some noise. Special technique is yet to be researched in processing EMG signal to make it useful and effective both to researcher and to patient in general. Feature extraction is among the signal processing technique involved and the best method for specific EMG study needs to be applied. In this works, nine feature extractions techniques are applied to EMG signals recorder from subjects performing upper limb rehabilitation activity based on suggested movement sequence pattern. Three healthy subjects perform the experiment with three trials each and EMG data were recorded from their bicep and deltoid muscle. The applied features for every trials of each subject were analyzed statistically using student T-Test their significant of p-value. The results were then totaled up and compared between the nine features applied and Auto Regressive coefficient (AR) present the best result and consistent with each subjects’ data. This feature will be used later in our future research work of Upper-limb Virtual Reality Rehabilitation.

via EMG Feature Extractions for Upper-Limb Functional Movement During Rehabilitation – IEEE Conference Publication

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[Thesis] Recovery of arm-hand function after stroke: developing neuromechanical biomarkers to optimize rehabilitation strategies. – Leiden University


The aim of this thesis was to explore the neuromechanics of recovery of arm-hand function after stroke. A literature review revealed six articles that measured biomechanical and electromyographical outcome measures simultaneously, while applying active and passive tasks and multiple movement velocities to separate neural and non-neural contributors to movement disorders after stroke. Therefore, a neuromechanic assessment protocol was developed. Parameters were responsive to clinical status and had good to excellent test-retest reliability. Selective muscle activation was assessed with high measurement reliability and was significantly lower in chronic stroke patients compared to healthy participants. Longitudinally, neuromechanical parameters were combined with data on arm-hand function at six months after stroke. Paresis and diminished modulation of reflexes were associated with poor functional outcome. Changes in tissue properties were represented by a shift in wrist rest angle towards flexion and decline in passive range of motion. Increase in active range of motion and steady rest angle contributed most to prediction of functional outcome. The precision diagnostics provided by a neuromechanical assessment protocol could support clinical decision making and should be used in prediction models and as biomarkers in recovery of arm-hand function after stroke, for example by improving the selection of time-window and patients.

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via Recovery of arm-hand function after stroke: developing neuromechanical biomarkers to optimize rehabilitation strategies.

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[ARTICLE] Speed-adaptive control of functional electrical stimulation for dropfoot correction – Full Text



Functional electrical stimulation is an important therapy technique for dropfoot correction. In order to achieve natural control, the parameter setting of FES should be associated with the activation of the tibialis anterior.


This study recruited nine healthy subjects and investigated the relations of walking speed with the onset timing and duration of tibialis anterior activation. Linear models were built for the walking speed with respect to these two parameters. Based on these models, the speed-adaptive onset timing and duration were applied in FES-assisted walking for nine healthy subjects and ten subjects with dropfoot. The kinematic performance of FES-assisted walking triggered by speed-adaptive stimulation were compared with those triggered by the heel-off event, and no-stimulation walking at different walking speeds.


Higher ankle dorsiflexion angle was observed in heel-off stimulation and speed-adaptive stimulation conditions than that in no-stimulation walking condition at all the speeds. For subjects with stroke, the ankle plantarflexion angle in speed-adaptive stimulation condition was similar to that in no-stimulation walking condition, and it was significant larger than that in heel-off stimulation condition at all speeds.


The improvement in ankle dorsiflexion without worsening ankle plantarflexion in speed-adaptive stimulation condition could be attributed to the appropriate stimulation timing and duration. These results provide evidence that the proposed stimulation system with speed-related parameters is more physiologically appropriate in dropfoot correction, and it may have great potential value in future clinical applications.



About three quarters of stroke survivors experience different levels of brain dysfunction and movement disorder [1], which result in lower living quality and limited ability in social activities [2]. Of these subjects, 20% suffer from impaired motor function in the lower extremities. One of such impairments is dropfoot, which is characterized by poor ankle dorsiflexion during the swing phase and an inability to achieve heel strike at the initial contact [34]. Abnormal gaits such as circumduction gait and abnormal foot clearance on the affected side are often found as a method of compensating for excessive hip abduction and pelvis elevation on the unaffected side [5]. This results in gait asymmetry and slow walking speed [6].

Functional electrical stimulation was a representative intervention to correct dropfoot and Liberson et al. first introduced functional electrical stimulation (FES) to correct dropfoot for chronic hemiplegic subjects in the 1960s [7]. An electrical charge is delivered via a pair of electrodes to activate the tibialis anterior (TA), which results in ankle dorsiflexion. Yan et al. applied two dual-channel stimulators to the quadriceps, hamstring, gastrocnemius, and TA to recover motor function of the lower extremities in an early stage after stroke [8]. The stimulation was followed by a predetermined sequence of muscle activations that mimic a healthy gait cycle [9]. The duration of stimulation was five seconds in Yan et al.’s study. However, subjects with different severities of impairment might have different walking speeds [10], which means that a fixed stimulation duration might not be able to account for different walking patterns.

Liberson et al. used the heel-off event detected by a footswitch to trigger the stimulation [7]. However, the reliability of the footswitch controller was significantly reduced when subjects who dragged their feet during walking encountered a slope or an obstacle [11]. Bhadra et al. proposed a manual switch to trigger stimulation as a walking aid for subjects with spinal cord injury (SCI) [12]. However, manual control may distract subjects from maintaining balance and lead to an increased risk of falls [1314]. Furthermore, the cable between the control sensor and stimulator was inconvenient for walking [15].

Instead of a footswitch, Mansfield et al. [16] and Monaghan et al. [17] detected the heel event of the gait cycle in FES-assisted walking using an accelerometer and a uniaxial gyroscope, respectively. The commercially available product WalkAide also uses an accelerometer for this purpose [18]. Electromyography (EMG) signal is also applied as a control source in FES-assisted walking for the detection of volitional intent of muscle [19]. Yeom et al. amplified the EMG signal of the TA and modulated the stimulation intensity in proportion to the integrated EMG envelope. The electrical pulses are then sent to the common peroneal nerve for dropfoot correction [20].

In these studies, FES applied to the TA was mainly triggered by the heel-off event. However, this event occurs during the push-off phase and before TA activation [17]. An earlier start of TA stimulation results in reduced ankle plantarflexion [21]. Spaich et al. suggested implementing a constant time interval before the onset timing of TA stimulation to extend the push-off phase before the ankle dorsiflexion [21]. Some studies have found that walking speed can affect the activation of TA [2223]. Shiavi et al. found that the duration of EMG activity decreased as speed increased [22]. In Winter et al.’s study, the shape of the EMG patterns generally remained similar at the different walking speeds and the duration of EMG activity was closely related to the normalized stride time [23]. Although the duration of TA activation changes with the walking speeds has been reported [24], the selection of speed-adaptive FES parameters for TA has not been investigated.

The objective of this study is to find a more physiologically appropriate FES design for dropfoot correction. Firstly, speed-related changes in onset timing and the duration of TA activation were examined. Next, linear models were built for the walking speed and time interval from the heel-off event to the onset timing of TA activation, as well as for the walking speed and the duration of the TA activation. The speed-adaptive stimulation (SAS) timing and duration were then calculated based on the two models and applied for FES-assisted walking. Finally, the performance of stimulation triggered by SAS, heel-off event (HOS) and no stimulation (NS) were compared during FES-assisted walking on both subjects with stroke and healthy subjects at different walking speeds.[…]


Continue —->  Speed-adaptive control of functional electrical stimulation for dropfoot correction | Journal of NeuroEngineering and Rehabilitation | Full Text


Fig. 1a The experiment setup of SAS condition; b one healthy subject on the treadmill for system evaluation; c the position of five markers on the right leg

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[Abstract] An attempt to explain the Vojta therapy mechanism of action using the surface polyelectromyography in healthy subjects: A pilot study



Rehabilitation according to Vojta is a neurophysiological method used to obtain reflex responses in muscles following stimulation of particular activation zones.


This study aims to objectively evaluate the muscular responses following stimulation according to Vojta’s method. The possible routes of spinal transmission responsible for the phenomenon of muscle activation in upper and lower extremities are considered.


Polyelectromyographic (pEMG) recordings in the upper and lower extremities in healthy volunteers (N = 25; aged 24 ± 1 year) were performed to find out the possible routes of spinal transmission, responsible for muscle activation. The left acromion and right femoral epicondyle were stimulated by a Vojta therapist; pEMG recordings were made including the bilateral deltoid and rectus femoris muscles.

Results and discussion

Following acromion stimulation, muscle activation was mostly expressed in the contralateral rectus femoris, rather than the contralateral deltoid and the ipsilateral rectus femoris muscles. After stimulation of the lower femoral epicondyle, the following order was observed: contra lateral deltoid, ipsilateral deltoid and the contra lateral rectus femoris muscle.

One of the candidates responsible for the main crossed neural transmission involved in the Vojta therapy mechanism would be the long propriospinal tract neurons.

via An attempt to explain the Vojta therapy mechanism of action using the surface polyelectromyography in healthy subjects: A pilot study – Journal of Bodywork and Movement Therapies

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[Abstract] Electromyography Based Orthotic Arm and Finger Rehabilitation System


Electromyography (EMG), a technique used to analyze and record electric current produced by skeletal muscles, has been used to control replacement limbs, and diagnose muscle irregularities. In this work, an EMG based system comprising of an orthotic arm and finger device to aid in muscle rehabilitation, is presented. As the user attempts to contract their bicep or forearm muscles, the system senses the change in the EMG signals and in turn triggers the motors to assist with flexion and extension of the arm and fingers. As brain is a major factor for muscle growth, mental training using motor imagery was incorporated into the system. Subjects underwent mental training to show the capability of muscle growth. The measured data reveals that the subjects were able to compensate for the loss of muscle growth, due to shorter physical training sessions, with mental training. Subjects were then tested using the orthotic arm and finger rehabilitation device with motor imagery. The findings also showed a positive increase in muscle growth using the rehabilitation system. Based on the experimental results, the EMG rehabilitation system presented in this paper has the potential to increase muscle strength and improve the recovery rate for muscle injuries, partial paralysis, or muscle irregularities.

via Electromyography Based Orthotic Arm and Finger Rehabilitation System – IEEE Conference Publication

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[Abstract] How effective is physical therapy for gait muscle activity in hemiparetic patients who receive botulinum toxin injections?

BACKGROUND: Administration of botulinum neurotoxin A (BoNT-A) to the ankle plantar flexors in patients with hemiplegia reduces the strength of knee extension, which may decrease their walking ability. Studies have reported improvements in walking ability with physical therapy following BoNT-A administration. However, no previous studies have evaluated from an exercise physiology perspective the efficacy of physical therapy after BoNT-A administration for adult patients with hemiplegia.

AIM: To investigate the effects of physical therapy following BoNT-A administration on gait electromyography for patients with hemiparesis secondary to stroke.

DESIGN: Non-randomized controlled trial.

SETTING: Single center.

POPULATION: Thirty-five patients with chronic stroke with spasticity were assigned to BoNT-A monotherapy (n=18) or BoNT-A plus physical therapy (PT) (n=17).
METHODS: On the paralyzed side of the body, 300 single doses of BoNT-A were administered intramuscularly to the ankle plantar flexors. Physical therapy was performed for 2 weeks, starting from the day after administration. Gait electromyography was performed and gait parameters were measured immediately before and 2 weeks after BoNT- A administration. Relative muscle activity, co-activation indices, and walking time/distance were calculated for each phase.

RESULTS: For patients who received BoNT-A monotherapy, soleus activity during the loading response decreased 2 weeks after the intervention (p<0.01). For those who received BoNT-A+PT, biceps femoris activity and knee co-activation index during the loading response and tibialis anterior activity during the pre-swing phases increased, whereas soleus and rectus femoris activities during the swing phase decreased 2 weeks after the intervention (p<0.05). These rates of change were significantly greater than those for patients who received BoNT-A monotherapy (p<0.05).

CONCLUSIONS: Following BoNT-A monotherapy, soleus activity during the stance phase decreased and walking ability either remained unchanged or deteriorated. Following BoNT-A+PT, muscle activity and knee joint stability increased during the stance phase, and abnormal muscle activity during the swing phase was suppressed.

CLINICAL REHABILITATION IMPACT: If botulinum treatment of the ankle plantar flexors in stroke patients is targeted to those with low knee extension strength, or if it aims to improve leg swing on the paralyzed side of the body, then physical therapy following BoNT-A administration could be an essential part of the treatment strategy.


via How effective is physical therapy for gait muscle activity in hemiparetic patients who receive botulinum toxin injections? – European Journal of Physical and Rehabilitation Medicine 2018 Jun 11 – Minerva Medica – Journals

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[Abstract] sEMG Bias-driven Functional Electrical Stimulation System for Upper Limb Stroke Rehabilitation


It is evident that the dominant therapy of functional electrical stimulation (FES) for stroke rehabilitation suffers from heavy dependency on therapists experience and lack of feedback from patients status, which decrease the patients’ voluntary participation, reducing the rehabilitation efficacy. This paper proposes a closed loop FES system using surface electromyography (sEMG) bias feedback from bilateral arms for enhancing upper-limb stroke rehabilitation. This wireless portable system consists of sEMG data acquisition and FES modules, the former is used to measure and analyze the subject’s bilateral arm motion intention and neuromuscular states in terms of their sEMG, the latter of multi-channel FES output is controlled via the sEMG bias of the bilateral arms. The system has been evaluated with experiments proving that the system can achieve 39.9 dB signal-to-noise ratio (SNR) in the lab environment, outperforming existing similar systems. The results also show that voluntary and active participation can be effectively employed to achieve different FES intensity for FES-assisted hand motions, demonstrating the potential for active stroke rehabilitation.
Published in: IEEE Sensors Journal ( Early Access ) Date of Publication: 18 June 2018

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via sEMG Bias-driven Functional Electrical Stimulation System for Upper-Limb Stroke Rehabilitation – IEEE Journals & Magazine

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[Abstract] Hand strengthening exercises in chronic stroke patients: Dose-response evaluation using electromyography


STUDY DESIGN: Cross-sectional.

PURPOSE OF THE STUDY: This study evaluates finger flexion and extension strengthening exercises using elastic resistance in chronic stroke patients.

METHODS: Eighteen stroke patients (mean age: 56.8 ± 7.6 years) with hemiparesis performed 3 consecutive repetitions of finger flexion and extension, using 3 different elastic resistance levels (easy, moderate, and hard). Surface electromyography was recorded from the flexor digitorum superficialis (FDS) and extensor digitorum (ED) muscles and normalized to the maximal electromyography of the non-paretic arm.

RESULTS: Maximal grip strength was 39.2 (standard deviation: 12.5) and 7.8 kg (standard deviation: 9.4) in the nonparetic and paretic hand, respectively. For the paretic hand, muscle activity was higher during finger flexion exercise than during finger extension exercise for both ED (30% [95% confidence interval {CI}: 19-40] vs 15% [95% CI: 5-25] and FDS (37% [95% CI: 27-48] vs 24% [95% CI: 13-35]). For the musculature of both the FDS and ED, no dose-response association was observed for resistance and muscle activity during the flexion exercise (P > .05).

CONCLUSION: The finger flexion exercise showed higher muscle activity in both the flexor and extensor musculature of the forearm than the finger extension exercise. Furthermore, greater resistance did not result in higher muscle activity during the finger flexion exercise. The present results suggest that the finger flexion exercise should be the preferred strengthening exercise to achieve high levels of muscle activity in both flexor and extensor forearm muscles in chronic stroke patients. The finger extension exercise may be performed with emphasis on improving neuromuscular control.


via Hand strengthening exercises in chronic stroke patients: Dose-response evaluation using electromyography. – PubMed – NCBI

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[ARTICLE] Using Corticomuscular Coherence to Reflect Function Recovery of Paretic Upper Limb after Stroke: A Case Study – Full Text

Purpose: Motor deficits after stroke are supposed to arise from the reduced neural drive from the brain to muscles. This study aimed to demonstrate the feasibility of reflecting the motor function improvement after stroke with the measurement of corticomuscular coherence (CMC) in an individual subject.

Method: A stroke patient was recruited to participate in an experiment before and after the function recovery of his paretic upper limb, respectively. An elbow flexion task with a constant muscle contraction level was involved in the experiment. Electromyography and electroencephalography signals were recorded simultaneously to estimate the CMC. The non-parameter statistical analysis was used to test the significance of CMC differences between the first and second times of experiments.

Result: The strongest corticomuscular coupling emerged at the motor cortex contralateral to the contracting muscles for both the affected and unaffected limbs. The strength of the corticomuscular coupling between activities from the paretic limb muscles and the contralateral motor cortex for the second time of experiment increased significantly compared with that for the first time. However, the CMC of the unaffected limb had no significant changes between two times of experiments.

Conclusion: The results demonstrated that the increased corticomuscular coupling strength resulted from the motor function restoration of the paretic limb. The measure of CMC can reflect the recovery of motor function after stroke by quantifying interactions between activities from the motor cortex and controlled muscles.


Stroke is one of the major diseases that cause long-term motor deficits of adults (1). However, our poor understanding of the mechanisms underlying motor impairments after stroke limits greatly the development of effective intervention and evaluation methods. In general, motor impairments after stroke are deemed to arise from changes in both neural and muscle properties. Poststroke changes in the neural system have been studied from different points of view such as the decreased excitability of the affected cortex (23) and the increased inhibitory effect from the unaffected hemisphere on the affected hemisphere (4). Spasm and flaccid paresis of muscles are believed to result from the loss of control input from the brain at different phases after stroke. Even though stroke survivors have been demonstrated to have significant descending information flow in the affected side during the chronic period (5), there is evidence that poststroke impairments reflect the reduced central neural drive to muscles. Mima et al. and Fang et al. found that the functional coupling between cortical commands and consequent muscle activities of stroke subjects were weaker than that of healthy controls (67). The conduction time from the central cortical rhythm to peripheral oscillations in the affected side was significantly prolonged compared with that of the unaffected side after stroke (8).

It is believed that stroke interrupts the motor-related neural network and then reduces the neural drive to the muscles. The coherent activities between the motor cortex and the muscles are believed to reflect the synchronized discharge of corticospinal cells (9). It can be estimated by analyzing the frequency domain coherence (10) between electromyography (EMG) and electroencephalography (EEG) signals termed as corticomuscular coherence (CMC). Although previous studies have demonstrated that the CMC strength of poststroke subjects was weaker than that of healthy controls, it is still not clear whether the corticomuscular coupling will enhance along with the motor function recovery to directly reflect the motor function state of paretic limbs after stroke. In the current study, a poststroke patient was recruited to participate in two times of experiments involving an elbow flexion task. The time interval between two times of experiments was determined to guarantee that the patient had obtained an obvious motor function recovery of the affected upper extremity. CMC from two times of experiments was estimated and compared to verify whether motor function recovery can be reflected by the change of corticomuscular coupling strength.


Experiment and Subject

An elbow flexion task was designed for the stroke patient because only poor rehabilitation outcomes can be generally obtained for hand. The force applied by the elbow flexion was monitored by a strain gage and fed back to the patient visually to help him finish the task with moderate and constant muscle contractions (11), because coherence analyses (1213) have demonstrated that the coupling is most pronounced in the beta-band range during steady muscle contractions and the beta-band CMC is assumed to be associated with strategies for controlling submaximal muscle forces (121415). The designed motion task and the visual feedback information on screen are illustrated in Figures 1A,B, respectively. A trial was initiated when a circle and a target ring showed on screen and was over when they disappeared. Each trial lasted 11 s and there was a 2-s long interval between adjacent trials. Each run contained 20 trials and each side of upper limbs performed two runs, respectively. The subject practiced before data recording until the target force could be reached within the first 2 s of each trial.

Figure 1. The motion task of elbow flexion (A) and the visual feedback information on screen (B). When the biceps brachii contracts, the wrist will press the strain gage and the force level can be detected. The circle can be shifted vertically by applying force to the strain gage and the position of the ring is fixed. The subject was requested to move the circle into the ring as soon as possible when a trial started and maintain the force until the end of a trial when the circle and the ring both disappeared. The force needed to shift the circle into the ring was 3 N.

Continue —> Frontiers | Using Corticomuscular Coherence to Reflect Function Recovery of Paretic Upper Limb after Stroke: A Case Study | Neurology

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