Intramuscular Electrodes Research Articles

A Comprehensive Review of Electromyography in Rehabilitation: Detecting Interrupted Wrist and Hand Movements with a Robotic Arm Approach

Electromyography (EMG) is a diagnostic technique that measures the electrical activity generated by skeletal muscles. Utilizing electrodes placed either on the skin (surface EMG) or inserted directly into the muscle(intramuscular EMG), it detects electrical signals produced during muscle contractions. EMG is widely employed in clinical and research settings to assess muscle function, diagnose neuromuscular disorders,and guide rehabilitation therapy. Over the years, EMG has evolved from a basic measurement tool into an essential technology within clinical and research environments, propelled by advances in recording techniques and digital innovations. The integration of wearable technology and artificial intelligence (AI) has significantly expanded its applications, particularly in rehabilitation and sports science. By capturing muscle electrical activity through surface or intramuscular electrodes, EMG benefits from enhanced signal processing that improves accuracy and data analysis. Despite challenges such as signal interference and the complexities of movement patterns—especially in wrist and hand rehabilitation—EMG combined with robotic systems offers real-time feedback for precise and personalized therapy. However, obstacles like cost, complexity, and variability among patients still remain. Future advancements aim to make EMG more accessible and to integrate AI for tailored rehabilitation strategies, alongside improvements in sensors and wireless communication to enhance reliability and performance. This review explores various facets of EMG,from its fundamental principles to its application in detecting disrupted wrist and hand movements through robotic approaches. It provides a comprehensive analysis of EMG’s historical and technological evolution, recent innovations like AI and wearable devices, and its extensive applications in rehabilitation and sports science. Detailed case studies illustrate its effectiveness in areas such as stroke recovery and spinal cord injury rehabilitation. Additionally, the review addresses challenges like technical limitations and patient variability while emphasizing the integration of EMG with robotic systems for personalized therapy. It also discusses the significance of real-time feedback, future enhancements in AI and sensor technology, and the pressing need for more affordable, user-friendly solutions to improve therapeutic outcomes.

Restoration of coherent reach-grasp-pull movement via sequential intraneural peripheral nerve stimulation in rats

Objective. Peripheral nerve stimulation (PNS) has been demonstrated as an effective way to selectively activate muscles and to produce fine hand movements. However, sequential multi-joint upper limb movements, which are critical for paralysis rehabilitation, has not been tested with PNS. Here, we aimed to restore multiple upper limb joint movements through an intraneural interface with a single electrode, achieving coherent reach-grasp-pull movement tasks through sequential stimulation. Approach. A transverse intrafascicular multichannel electrode was implanted under the axilla of the rat’s upper limb, traversing the musculocutaneous, radial, median, and ulnar nerves. Intramuscular electrodes were implanted into the biceps brachii (BB), triceps brachii (TB), flexor carpi radialis (FCR), and extensor carpi radialis (ECR) muscles to record electromyographic (EMG) activity and video recordings were used to capture the kinematics of elbow, wrist, and digit joints. Charge-balanced biphasic pulses were applied to different channels to recruit distinct upper limb muscles, with concurrent recording of EMG signals and joint kinematics to assess the efficacy of the stimulation. Finally, a sequential stimulation protocol was employed by generating coordinated pulses in different channels. Main results. BB, TB, FCR and ECR muscles were selectively activated and various upper limb movements, including elbow flexion, elbow extension, wrist flexion, wrist extension, digit flexion, and digit extension, were reliably generated. The modulation effects of stimulation parameters, including pulse width, amplitude, and frequency, on induced joint movements were investigated and reach-grasp-pull movement was elicited by sequential stimulation. Significance. Our results demonstrated the feasibility of sequential intraneural stimulation for functional multi-joint movement restoration, providing a new approach for clinical rehabilitation in paralyzed patients.

Development of a novel technique to insert intramuscular electromyography electrodes into the deep intrinsic foot muscles via the dorsum of the foot

This study aimed to develop an insertion technique for intramuscular EMG recording of the oblique head of adductor hallucis (AddH) and first dorsal interosseous (FDI) muscles in humans via the dorsum of the foot, and report feasibility of intramuscular EMG data acquisition during walking in shoes. In eight individuals without musculoskeletal pain or injury (5 males; 32 ± 8 years), intramuscular electrodes were inserted into AddH (oblique head) and FDI through the right foot’s dorsum (between metatarsals I-II) with ultrasound guidance. The ultrasound transducer was positioned on the plantar surface. Intramuscular EMG was also recorded from abductor hallucis, tibialis posterior, flexor digitorum longus and peroneus longus. Participants performed six overground walking trials wearing modified shoes, and rated pain associated with the intramuscular electrodes during walking (numerical rating scale, 0–10). High-quality EMG recordings were obtained from intrinsic and extrinsic foot muscles. Analyses of power spectral densities indicated that movement artefacts commonly observed during gait were removed by filtering. Pain associated with AddH/FDI electrodes during walking was low (median[IQR] 1[2]; range 0–4) and similar to other sites. Findings demonstrate that intramuscular EMG recording from AddH (oblique head) and FDI using this insertion technique is feasible and associated with minimal pain when walking in shoes.

Effects of Intramuscular Electrical Stimulation for Treatment of Non-Traumatic Shoulder Pain

Non-traumatic shoulder pain is the third most common cause of consultations for musculoskeletal pain in primary health care. It is one of the common musculoskeletal conditions of the shoulder which may develop sensory-motor and autonomic dysfunctions at the various level of the neuromuscular system. The objective of the study to find out the Effects of Intramuscular Electrical Stimulation for Treatment of Non-Traumatic Shoulder Pain. The pain and dysfunction caused by NSP were primarily treated with physical therapy and pharmacological agents in order to achieve pain free movements. However, in recent years intramuscular electrical stimulation (IMES) with conventional electrode placement was used by researchers to maximize therapeutic values. But, in this study an inverse electrode placement was used to deliver electrical impulses intramuscularly to achieve neuro-modulation at the various level of the nervous system. Nine patients with NSP were treated with intramuscular electrode stimulation using inversely placed electrodes for a period of three weeks. All nine subjects recovered from their shoulder pain and disability within the few weeks of intervention. So, this IMES may be more appropriate for treatment approach for Non traumatic shoulder pain management.

Tutorial on MUedit: An open-source software for identifying and analysing the discharge timing of motor units from electromyographic signals

We introduce the open-source software MUedit and we describe its use for identifying the discharge timing of motor units from all types of electromyographic (EMG) signals recorded with multi-channel systems. MUedit performs EMG decomposition using a blind-source separation approach. Following this, users can display the estimated motor unit pulse trains and inspect the accuracy of the automatic detection of discharge times. When necessary, users can correct the automatic detection of discharge times and recalculate the motor unit pulse train with an updated separation vector. Here, we provide an open-source software and a tutorial that guides the user through (i) the parameters and steps of the decomposition algorithm, and (ii) the manual editing of motor unit pulse trains. Further, we provide simulated and experimental EMG signals recorded with grids of surface electrodes and intramuscular electrode arrays to benchmark the performance of MUedit. Finally, we discuss advantages and limitations of the blind-source separation approach for the study of motor unit behaviour during tonic muscle contractions.

Short term effects of contralateral tendon vibration on motor unit discharge rate variability and force steadiness in people with Parkinson's disease.

Vibration of one limb affects motor performance of the contralateral limb, and this may have clinical implications for people with lateralized motor impairments through vibration-induced increase in cortical activation, descending neural drive, or spinal excitability. The objective of this study was to evaluate the effects of acute biceps brachii tendon vibration on force steadiness and motor unit activity in the contralateral limb of persons with Parkinson's disease. Ten participants with mild to moderate Parkinson's disease severity performed a ramp, hold and de-ramp isometric elbow flexion at 5% of maximum voluntary contraction with the more-affected arm while vibration was applied to the distal biceps brachii tendon on the contralateral, less-affected arm. Using intramuscular fine wire electrodes, 33 MUs in the biceps brachii were recorded across three conditions (baseline, vibration, and post-vibration). Motor unit recruitment & derecruitment thresholds, discharge rates & variability, and elbow flexion force steadiness were compared between conditions with and without vibration. Coefficient of variation of force and discharge rate variability decreased 37 and 17%, respectively in post-vibration compared with baseline and vibration conditions. Although the motor unit discharge rates did not differ between conditions the total number of motor units active at rest after de-ramp were fewer in the post-vibration condition. Contralateral tendon vibration reduces MU discharge rate variability and enhances force control on the more affected side in persons with Parkinson's disease.

Inferring position of motor units from high-density surface EMG

The spatial distribution of muscle fibre activity is of interest in guiding therapy and assessing recovery of motor function following injuries of the peripheral or central nervous system. This paper presents a new method for stable estimation of motor unit territory centres from high-density surface electromyography (HDsEMG). This completely automatic process applies principal component compression and a rotatable Gaussian surface fit to motor unit action potential (MUAP) distributions to map the spatial distribution of motor unit activity. Each estimated position corresponds to the signal centre of the motor unit territory. Two subjects were used to test the method on forearm muscles, using two different approaches. With the first dataset, motor units were identified by decomposition of intramuscular EMG and the centre position of each motor unit territory was estimated from synchronized HDsEMG data. These positions were compared to the positions of the intramuscular fine wire electrodes with depth measured using ultrasound. With the second dataset, decomposition and motor unit localization was done directly on HDsEMG data, during specific muscle contractions. From the first dataset, the mean estimated depth of the motor unit centres were 8.7, 11.6, and 9.1 mm, with standard deviations 0.5, 0.1, and 1.3 mm, and the respective depths of the fine wire electrodes were 8.4, 15.8, and 9.1 mm. The second dataset generated distinct spatial distributions of motor unit activity which were used to identify the regions of different muscles of the forearm, in a 3-dimensional and projected 2-dimensional view. In conclusion, a method is presented which estimates motor unit centre positions from HDsEMG. The study demonstrates the shifting spatial distribution of muscle fibre activity between different efforts, which could be used to assess individual muscles on a motor unit level.

The neural control of movement: a century of in vivo motor unit recordings is the legacy of Adrian and Bronk.

In two papers dated 1928 to 1929 in The Journal of Physiology, Edgar Adrian and Detlev Bronk described recordings from motor nerve and muscle fibres. The recordings from motor nerve fibres required progressive dissection of the nerve until a few fibres remained, from which isolated single fibre activity could be detected. The muscle fibre recordings were performed in humans during voluntary contractions with an intramuscular electrode - the concentric needle electrode - that they describe for the first time in the second paper. They recognised that muscle fibres would respond to each impulse sent by the innervating motor neurone and that therefore muscle fibre recordings provided information on the times of activation of the motor nerve fibres which were as accurate as a direct record from the nerve. These observations and the description of the concentric needle electrode opened the era of motor unit recordings in humans, which have continued for almost a century and have provided a comprehensive view of the neural control of movement at the motor unit level. Despite important advances in technology, many of the principles of motor unit behaviour that would be investigated in the subsequent decades were canvassed in the two papers by Adrian and Bronk. For example, they described the concomitant motor neurones' recruitment and rate coding for force modulation, synchronisation of motor unit discharges, and the dependence of discharge rate on motor unit recruitment threshold. Here, we summarise their observations and discuss the impact of their work. We highlight the advent of the concentric needle, and its subsequent influence on motor control research.

Low-load blood flow restriction reduces time-to-minimum single motor unit discharge rate.

Resistance training with low loads in combination with blood flow restriction (BFR) facilitates increases in muscle size and strength comparable with high-intensity exercise. We investigated the effects of BFR on single motor unit discharge behavior throughout a sustained low-intensity isometric contraction. Ten healthy individuals attended two experimental sessions: one with, the other without, BFR. Motor unit discharge rates from the tibialis anterior (TA) were recorded with intramuscular fine-wire electrodes throughout the duration of a sustained fatigue task. Three 5-s dorsiflexion maximal voluntary contractions (MVC) were performed before and after the fatigue task. Each participant held a target force of 20% MVC until endurance limit. A significant decrease in motor unit discharge rate was observed in both the non-BFR condition (from 13.13 ± 0.87Hz to 11.95 ± 0.43Hz, P = 0.03) and the BFR condition (from 12.95 ± 0.71Hz to 10.9 ± 0.75Hz, P = 0.03). BFR resulted in significantly shorter endurance time and time-to-minimum discharge rates and greater end-stage motor unit variability. Thus, low-load BFR causes an immediate steep decline in motor unit discharge rate that is greater than during contractions performed without BFR. This shortened neuromuscular response of time-to-minimum discharge rate likely contributes to the rapid rate of neuromuscular fatigue observed during BFR.

P039 Genioglossus motor control during mandibular advancement.

Abstract Introduction High genioglossus muscle activity is thought to prevent/resolve upper airway collapse. Overall genioglossal activity results from the simultaneous firing of many motor units (MUs) which typically have one of 5 firing patterns: active only (IP) or at higher frequency (IT) during inspiration; active only (EP) or at higher frequency during expiration (ET); and constantly active without respiratory modulation (TT). To date, most experimental manipulations tested (e.g. hypoxia, hypercapnia, resistive loading) have influenced IP and IT MUs, with minimal changes in ET, EP and TT MUs. We hypothesized that IT/IP MUs respond to respiratory drive, whereas TT/EP/ET MUs will change in response to airway anatomical manipulations. Methods The number and firing frequencies of genioglossal MUs were assessed with intramuscular electrodes in healthy individuals during wakefulness, before and during mandibular advancement (MAD) to 80% of maximum with an myTAP device, to change airway anatomy but minimally alter respiratory drive. Results 201 MUs were identified from 55 trials in 14 participants. Ventilation did not differ between baseline and MAD. At baseline, 175 MUs were active: EP=0.6%, ET=12.6%, IP=14.9%, IT=48%, TT=24%. During MAD, 35 MUs ceased firing, but an additional 26 MUs began firing, with the resulting MUs proportions not differing from baseline: EP=0%, ET=10.2%, IP=21.1%, IT=36.7%, TT=31.9%, χ2(9)=12.0, p=.213. The mean firing frequency of MUs did not change during MAD (baseline=20.9±4.7Hz, MAD=21.9±5.4Hz). Discussion Contrary to the hypothesis, the firing patterns of genioglossal MUs did not differ from baseline during mandibular advancement. What controls the non-respiratory/expiratory MUs of the genioglossus remains unclear.

Mechanisms underlying the prolonged activation of the genioglossus following arousal from sleep.

Transient arousal from sleep has been shown to elicit a prolonged increase in genioglossus muscle activity that persists following the return to sleep and which may protect against subsequent airway collapse. We hypothesized that this increased genioglossal activity following return to sleep after an arousal is due to persistent firing of inspiratory-modulated motor units (MUs) that are recruited during the arousal. Thirty-four healthy participants were studied overnight while wearing a nasal mask with pneumotachograph to measure ventilation and with 4 intramuscular genioglossus EMG electrodes. During stable N2 and N3 sleep, auditory tones were played to induce brief (3-15s) AASM arousals. Ventilation and genioglossus MUs were quantified before the tone, during the arousal and for 10 breaths after the return to sleep. A total of 1089 auditory tones were played and gave rise to 239 MUs recorded across arousal and the return to sleep in 20 participants (aged 23 ± 4.2 years and BMI 22.5 ± 2.2 kg/m2). Ventilation was elevated above baseline during arousal and the first post-arousal breath (p < .001). Genioglossal activity was elevated for five breaths following the return to sleep, due to increased firing rate and recruitment of inspiratory modulated MUs, as well as a small increase in tonic MU firing frequency. The sustained increase in genioglossal activity that occurs on return to sleep after arousal is primarily a result of persistent activity of inspiratory-modulated MUs, with a slight contribution from tonic units. Harnessing genioglossal activation following arousal may potentially be useful for preventing obstructive respiratory events.

Motor unit firing rates in young and very old adult males during an isokinetic fatiguing task and short-term recovery in the anconeus muscle.

Understanding motor unit (MU) properties with muscle fatigue in adult aging is limited to isometric tasks. The purpose was to investigate the effect of an isokinetic fatiguing task on MU firing rates between two adult age groups of males. Single MUs were recorded by intramuscular electrodes in the anconeus muscle of eight young (19-33 yr) and 11 very old adults (78-93 yr). Fatigue was induced by repeated isokinetic maximal voluntary contractions at 25% of maximum velocity (Vmax), until elbow extension power decreased by 35%. At baseline, the very old had lower maximal power (135 vs. 214 W, P = 0.002) and slower maximal velocity (177 vs. 196°/s, P < 0.001) compared with young. Despite a similar number of contractions (average 39 young and 44 very old) to task failure (P = 0.33), the older males were less fatigable as time under tension was ∼25% longer (P = 0.04). Maximum firing rates from ∼20 single MUs per age group were tracked continuously throughout the task and during 10 min of recovery. Similar rates were recorded (24.7 and 23.6 Hz, P = 0.18) at baseline 25% Vmax, and during the task (23.3 and 28.7% decrease, P = 0.21) between young and very old, respectively. Power and MU rates were recovered similarly by 2 min of rest in both groups (all P > 0.15). Despite differences in baseline capability, very old males in this relatively slow isokinetic task were more fatigue resistant, but the fatigue-related reduction and recovery in MU rates were similar between groups. Therefore, fatigue in this task between age groups is not differentially affected by alterations in firing rates.NEW & NOTEWORTHY Maximal motor unit firing rates were recorded during an isokinetic fatiguing protocol and short-term recovery in young and very old adult males. Prior studies were limited to isometric fatiguing tasks. Despite the old being ∼37% weaker and less fatigable, anconeus rates during elbow extension declined with fatigue and recovered similarly to young males. Therefore, it is unlikely that greater fatigue resistance of very old males during isokinetic contractions is related to differences in motor unit rates.

Volume conduction: Extracellular waveform generation in theory and practice.

The extracellular waveform manifestations of the intracellular action potential are the quintessential diagnostic foundation of electrodiagnostic medicine, and clinical neurophysiology in general. Volume conduction is the extracellular current flow and associated voltage distributions in an ionic conducting media, such as occurs in the human body. Both surface and intramuscular electrodes, in association with contemporary digital electromyographic systems, permit very sensitive detection and visualization of this extracellular spontaneous, voluntary, and evoked nerve/muscle electrical activity. Waveform configuration, with its associated discharge rate/rhythm, permits the identification of normal and abnormal waveforms, thereby assisting in the diagnosis of nerve and muscle pathology. This monograph utilizes a simple model to explain the various waveforms that may be encountered. There are a limited number of waveforms capable of being generated in excitable tissues which conform to well-known volume conductor concepts. Using these principles, such waveforms can be quickly identified in real time during clinical studies.

Contributions of flexor hallucis longus and brevis muscles to isometric toe flexor force production

Purpose Morphological differences between the two primary great toe flexors – flexor hallucis longus (FHL) and flexor hallucis brevis (FHB) – likely drive differences in how these muscles contribute to functional toe flexion torque production. The aim of the study was to investigate FHL and FHB activation in two isometric toe flexion tasks – one called a “toe-pushing” task with the metatarsophalangeal (MTP) joints extended and the interphalangeal (IP) joints in neutral and another called a “toe-gripping” task with the MTP joints in neutral and flexed IP joints. Methods Twenty participants’ FHL and FHB muscles were instrumented with intramuscular electromyography electrodes. Muscle activation was normalized to a maximum voluntary contraction and compared between the two isometric toe flexor force production tasks. Results Overall, participants utilized these two toe flexors completely differently in the two tasks. In the toe-gripping task, the FHL was activated to a much greater extent than the FHB. In fact, 18 our of 20 participants activated FHL at more than seventy percent maximum voluntary contraction and half of participants activated FHB at less than ten percent. In contrast, muscle activation during the toe-pushing task appeared more reliant on the FHB for most participants. Conclusions Different contributions from the FHL and FHB to toe flexor force production in these two tasks are potentially driven by differences in muscle functional length among other factors. These findings help to inform the selection of rehabilitation and training exercises meant to preferentially target intrinsic or extrinsic foot musculature.

Effects of Different Orthoses on Neuromuscular Activity of Superficial and Deep Shoulder Muscles during Activities of Daily Living and Physiotherapeutic Exercises in Healthy Participants.

This study aimed to investigate the effects of different shoulder orthoses on the neuromuscular activity of superficial and deep shoulder muscles during activities of daily living (ADL) and physiotherapeutic exercises. Ten participants with healthy shoulders (31 ± 3 years, 23.1 ± 3.8 kg/m2) were randomized to receive a "shoulder sling", an "abduction pillow" and a "variably adjustable orthosis" on the dominant side. With each orthosis, they completed seven ADL with and four physiotherapeutic exercises without wearing the orthoses. An electromyographic system was used to record the neuromuscular activity of three superficial (trapezius, deltoid, pectoralis major) and two deep shoulder muscles (infraspinatus, supraspinatus) using surface and intramuscular fine-wire electrodes. The neuromuscular activity differs between the orthoses during ADL (p ≤ 0.045), whereby the "variably adjustable orthosis" mostly showed the highest activation levels associated with the worst subjective wearing comfort rated on a visual analog scale. In addition, differences exist between the physiotherapeutic exercises (p ≤ 0.006) demonstrating the highest activations of the infra- and supraspinatus muscles for assistive elevation and wipe across a table, middle for pendulum and lowest for continuous passive motion exercises. The neuromuscular activity of superficial and deep shoulder muscles differs between the orthoses during ADL and also between the physiotherapeutic exercises.

Comparison between a targeted exercise program and a sham intervention on gluteal muscle activity in people with hip osteoarthritis: Analysis of secondary outcomes from a randomised clinical trial

BackgroundPeople with hip osteoarthritis (OA) typically display altered gluteus minimus (GMin) and gluteus medius (GMed) activity during gait, in addition to reduced walking speed and stride length. It is unknown if current rehabilitation programs address changes in gluteal muscle activity in people with hip OA. Research questionCan a targeted gluteal intervention restore normal gluteal muscle segment activity during gait in people with hip OA? MethodsThis study presents secondary outcomes from a multi-site, double-blinded clinical trial in which participants with radiologically confirmed mild-moderate hip OA were randomised into a targeted gluteal or sham intervention for 12-weeks following baseline testing. Electromyography (EMG) outcomes were only conducted at a single site and data were collected from 22 participants. Intramuscular electrodes were inserted into two segments of GMin (anterior, posterior) and three segments of GMed (anterior, middle, posterior) to record average amplitude, peak amplitude and time to peak (TTP) during the first 60 % of the gait cycle (stance phase) at baseline and post-intervention. ResultsFollowing the targeted gluteal intervention, posterior GMin displayed a decrease in average (P = 0.032, ES=1.04) and peak (P = 0.017, ES=1.17) muscle activity during late stance phase with a shift to an earlier TTP (P = 0.034, ES=1.02). There were no further significant changes between groups for other outcome measures. Similar trends for an earlier TTP were observed for the posterior segment of GMed following the targeted intervention (P = 0.095, ES=0.87). The earlier TTP in the posterior segments of both GMin and GMed post-intervention resembled patterns observed in a healthy young population. SignificanceA targeted gluteal intervention can positively impact activity in posterior GMin during gait in people with hip OA when compared to a sham intervention.

Muscle Activity in Primary Shoulder Movers is Associated with Increases in Translational Glenohumeral Stiffness

<h3>Research Objectives</h3> Rotator cuff muscles are commonly regarded as the main stabilizers of the glenohumeral joint, but recent modeling work from our group suggests that muscles which primarily move the shoulder also contribute substantially to glenohumeral stiffness. The objective of this study was to evaluate this possibility in experiments designed to assess the relationship between muscle activity in the primary shoulder movers and glenohumeral stiffness. <h3>Design</h3> Cross-sectional study. <h3>Setting</h3> Biomechanics research laboratory. <h3>Participants</h3> 15 healthy adults (8F/7M, 26±4 years) with no shoulder pain or injury. <h3>Interventions</h3> N/A. <h3>Main Outcome Measures</h3> We measured translational glenohumeral stiffness (resistance to humeral head translation to quantify glenohumeral stability) using a linear motor that applied 15 mm stochastic anterior-posterior perturbations to the proximal humerus. Measurements were made as participants generated submaximal isometric torques. We used system identification to estimate stiffness from the applied forces and measured displacements. Active stiffness was defined as the increase in glenohumeral stiffness during torque generation compared to during no torque generation. Electromyography measurements (EMGs) were recorded from 3 rotator cuff muscles (intramuscular electrodes: supraspinatus, infraspinatus, subscapularis) and 6 primary shoulder movers (surface electrodes: anterior/middle/posterior deltoid, pectoralis major, latissimus dorsi, teres major). We used linear mixed effects models to characterize the relationship between EMGs and active stiffness. <h3>Results</h3> EMGs in rotator cuff muscles and primary shoulder movers were positively correlated with active stiffness. EMGs recorded from only the primary shoulder movers better predicted stiffness during active contractions than EMGs recorded from only the rotator cuff muscles (R2=0.80 vs. R2=0.56; P< 0.001). Including EMGs recorded from all muscles improved the fit compared to the model with only primary shoulder movers (R2=0.84 vs. R2=0.80; P< 0.001), but this difference was small. <h3>Conclusions</h3> Our results provide additional evidence that the primary shoulder movers contribute to glenohumeral stability. The stabilizing potential of these muscles should be considered when designing and implementing rehabilitation protocols used to treat individuals with reduced glenohumeral stability, such as following shoulder dislocations. <h3>Author(s) Disclosures</h3> Funded by the NIH (F31AR074288, T32GM008152, UL1TR001422), the American Society of Biomechanics, and Northwestern University.

Blind identification of the spinal cord output in humans with high-density electrode arrays implanted in muscles.

Invasive electromyography opened a new window to explore motoneuron behavior in vivo. However, the technique is limited by the small fraction of active motoneurons that can be concurrently detected, precluding a population analysis in natural tasks. Here, we developed a high-density intramuscular electrode for in vivo human recordings along with a fully automatic methodology that could detect the discharges of action potentials of up to 67 concurrently active motoneurons with 99% accuracy. These data revealed that motoneurons of the same pool receive common synaptic input at frequencies up to 75 Hz and that late-recruited motoneurons inhibit the discharges of those recruited earlier. These results constitute an important step in the population coding analysis of the human motor system in vivo.

Use of regenerative peripheral nerve interfaces and intramuscular electrodes to improve prosthetic grasp selection: a case study

Objective. Advanced myoelectric hands enable users to select from multiple functional grasps. Current methods for controlling these hands are unintuitive and require frequent recalibration. This case study assessed the performance of tasks involving grasp selection, object interaction, and dynamic postural changes using intramuscular electrodes with regenerative peripheral nerve interfaces (RPNIs) and residual muscles. Approach. One female with unilateral transradial amputation participated in a series of experiments to compare the performance of grasp selection controllers with RPNIs and intramuscular control signals with controllers using surface electrodes. These experiments included a virtual grasp-matching task with and without a concurrent cognitive task and physical tasks with a prosthesis including standardized functional assessments and a functional assessment where the individual made a cup of coffee (‘Coffee Task’) that required grasp transitions. Main results. In the virtual environment, the participant was able to select between four functional grasps with higher accuracy using the RPNI controller (92.5%) compared to surface controllers (81.9%). With the concurrent cognitive task, performance of the virtual task was more consistent with RPNI controllers (reduced accuracy by 1.1%) compared to with surface controllers (4.8%). When RPNI signals were excluded from the controller with intramuscular electromyography (i.e. residual muscles only), grasp selection accuracy decreased by up to 24%. The participant completed the Coffee Task with 11.7% longer completion time with the surface controller than with the RPNI controller. She also completed the Coffee Task with 11 fewer transition errors out of a maximum of 25 total errors when using the RPNI controller compared to surface controller. Significance. The use of RPNI signals in concert with residual muscles and intramuscular electrodes can improve grasp selection accuracy in both virtual and physical environments. This approach yielded consistent performance without recalibration needs while reducing cognitive load associated with pattern recognition for myoelectric control (clinical trial registration number NCT03260400).

Transcranial magnetic stimulation set-up for small animals

Transcranial magnetic stimulation (TMS) is widely applied on humans for research and clinical purposes. TMS studies on small animals, e.g., rodents, can provide valuable knowledge of the underlying neurophysiological mechanisms. Administering TMS on small animals is, however, prone to technical difficulties, mainly due to their small head size. In this study, we aimed to develop an energy-efficient coil and a compatible experimental set-up for administering TMS on rodents. We applied a convex optimization process to develop a minimum-energy coil for TMS on rats. As the coil windings of the optimized coil extend to a wide region, we designed and manufactured a holder on which the rat lies upside down, with its head supported by the coil. We used the set-up to record TMS-electromyography, with electromyography recorded from limb muscles with intramuscular electrodes. The upside-down placement of the rat allowed the operator to easily navigate the TMS without the coil blocking their field of view. With this paradigm, we obtained consistent motor evoked potentials from all tested animals.