Forearm Muscle Activity Research Articles

Exploring forearm muscle coordination and training applications of various grip positions during maximal isometric finger dead-hangs in rock climbers.

Maximal isometric finger dead-hangs are used in rock climbing to strengthen finger flexors. Although various grip positions are often used when performing finger dead-hangs, little is known regarding how these grip positions can affect forearm muscle activity. Understanding how forearm muscles are recruited during dead-hangs could help foreseeing the potential for training of different grip positions. The aim of the present study was to explore the training applications of the various grip positions by comparing the activity of forearm muscles during maximal dead-hangs in rock climbers. Twenty-five climbers performed maximal dead-hangs in three climbing-specific grip positions: CRIMP, SLOPE, and SLOPER. We recorded the maximal loads used and the sEMG of the flexor digitorum profundus (FDP), the flexor digitorum superficialis (FDS), the flexor carpi radialis (FCR), and the extensor digitorum communis (EDC). Individual and global (sum of all muscles) root mean square (RMS) and neuromuscular efficiency (NME) values were computed. Repeated measures analysis were performed to assess grip differences (p<0.05). SLOPER showed the largest maximal load values among the three grip positions (p<0.001, d≥2.772). Greater global (p≤0.044, d≥0.268), FDS (p≤0.005, d≥0.277), and FCR (p<0.001, d≥1.049) activity was observed for the SLOPER compared to CRIMP and SLOPE, while EDC (p≤0.005, d≥0.505) showed lower activity in the SLOPER compared to the other two grip positions. SLOPER presented the highest global (p<0.001, d≥0.629), FDP (p<0.001, d ≥ 0.777), FDS (only CRIMP vs SLOPER: p < 0.001, d = 0.140), and EDC NME (p < 0.001, d ≥ 1.194). The CRIMP showed greater FDS activity (p = 0.001, d = 0.386) and lower NME (p = 0.003, d = 0.125) compared to SLOPE. These results revealed that, under maximum intensity conditions, SLOPER could stimulate the FDS and FCR better than the other grip positions at the expense of using greater loads. Similarly, maximum CRIMP dead-hang could better stimulate the FDS than the SLOPE, even when using similar loads.

Comparison of Grip Strength, Forearm Muscle Activity, and Shock Transmission between the Forehand Stroke Technique of Experienced and Recreational Tennis Players Using a Novel Wearable Device.

Upper limb tennis injuries are primarily chronic, resulting from repetitive overuse. We developed a wearable device which simultaneously measures risk factors (grip strength, forearm muscle activity, and vibrational data) associated with elbow tendinopathy development resulting from tennis players' technique. We tested the device on experienced (n = 18) and recreational (n = 22) tennis players hitting forehand cross-court at both flat and topspin spin levels under realistic playing conditions. Using statistical parametric mapping analysis, our results showed that all players showed a similar level of grip strength at impact, regardless of spin level, and the grip strength at impact did not influence the percentage of impact shock transfer to the wrist and elbow. Experienced players hitting with topspin exhibited the highest ball spin rotation, low-to-high swing path brushing action, and shock transfer to the wrist and elbow compared to the results obtained while hitting the ball flat, or when compared to the results obtained from recreational players. Recreational players exhibited significantly higher extensor activity during most of the follow through phase compared to the experienced players for both spin levels, potentially putting them at greater risk for developing lateral elbow tendinopathy. We successfully demonstrated that wearable technologies can be used to measure risk factors associated with elbow injury development in tennis players under realistic playing conditions.

Stability of the distal radioulnar joint with and without activation of forearm muscles.

The purpose of this study was to quantify the effect of the flexor carpi ulnaris and the extensor carpi ulnaris muscles on distal radioulnar joint stability. The anteroposterior ulnar head translation in relation to the radius was measured sonographically when the forearm was in a neutral resting position and when the hand was actively pressed on to a surface, with and without intentional flexor carpi ulnaris and extensor carpi ulnaris activation, while also being monitored by an electromyogram. Data on 40 healthy participants indicated a mean anteroposterior translation in the distal radioulnar joint of 4.1 mm (SD 1.08) without and 1.2 mm (SD 0.54) with muscle activation. Our results indicate that intentional ulnar forearm muscle activation results in 70% less anteroposterior ulnar head translation and greater distal radioulnar joint stability. Therefore, the flexor carpi ulnaris and extensor carpi ulnaris muscles serve as dynamic stabilizers of the distal radioulnar joint. This finding may be clinically significant since ulnar forearm muscles strengthening may increase distal radioulnar joint stability.

Surface electromyographic characteristics of forearm muscles after ulnar and radius fracture inchildren.

To evaluate the characteristics of forearm muscle activity in children with ulnar and radius fractures during different follow-up periods by surface electromyography. A retrospective analysis was performed on 20 children with ulnar and radius fractures treated with an elastic intramedullary nail from October 2020 to December 2021. All children were treated with transcubital casts after surgery. At 2 months and before taking out the elastic intramedullary nail, surface electromyographic signals were collected on the flexor/extension of the wrist and the maximum arbitrary isometric contraction of the grip strength in the forearm flexor and extensor muscles of the forearm. The root-mean-square values and integrated EMG values of the superficial flexor and extensor digitalis of the healthy side and the affected side were collected at the last follow-up and 2 months after surgery, and the co-systolic ratio was calculated. The root-mean-square values and co-systolic ratio were compared and analyzed, and the Mayo wrist function score was evaluated. The mean follow-up time was (8.4 ± 2.85) months. Mayo scores were (87.42 ± 13.01) and (97.69 ± 4.50) points at the last follow-up and two months after surgery, respectively (p < 0.05). In the test of grip strength, 2 months after surgery, the grip strength of the affected side was lower than that of the healthy side (p < 0.05), and the maximum and mean values of the superficial flexor of the affected side were lower than those of the healthy side (p < 0.05). At the last follow-up, there was no difference in the grip strength between the affected side and the healthy side (p > 0.05), and no difference in the maximum RMS, mean RMS and cooperative contraction ratio of the superficial flexor and digital extensor muscles between the affected side and the healthy side (p > 0.05). Satisfactory results can be obtained after elastic intramedullary napping in children with ulnar and radius fractures. However, 2 months after surgery, the grip strength of the affected side is small, and the electrical activity of the forearm muscle is low during flexion and extension activities of the wrist joint, which has not returned to normal, suggesting that children orthopaedic clinicians should remind children to conduct timely and effective rehabilitation training after the removal of the cast.

Understanding the biomechanics of the forearm during the dart thrower's motion.

This study investigated the contribution of different forearm muscles, namely the flexor carpi ulnaris, extensor carpi radialis longus and brevis, extensor carpi ulnaris and flexor carpi radialis, during the dart thrower's motion. Thirteen healthy participants were recruited. The forearm muscle activation patterns during the dart thrower's motion were measured using surface electromyography. The average root mean square for the extensor carpi ulnaris was found to be the highest during the dart thrower's motion. Muscle activations during the dart thrower's motion were heterogeneous among the participants. The results suggest the rehabilitation protocol for patients with wrist injuries should be reconsidered.

Toward Early and Objective Hand Osteoarthritis Detection by Using EMG during Grasps.

The early and objective detection of hand pathologies is a field that still requires more research. One of the main signs of hand osteoarthritis (HOA) is joint degeneration, which causes loss of strength, among other symptoms. HOA is usually diagnosed with imaging and radiography, but the disease is in an advanced stage when HOA is observable by these methods. Some authors suggest that muscle tissue changes seem to occur before joint degeneration. We propose recording muscular activity to look for indicators of these changes that might help in early diagnosis. Muscular activity is often measured using electromyography (EMG), which consists of recording electrical muscle activity. The aim of this study is to study whether different EMG characteristics (zero crossing, wavelength, mean absolute value, muscle activity) via collection of forearm and hand EMG signals are feasible alternatives to the existing methods of detecting HOA patients' hand function. We used surface EMG to measure the electrical activity of the dominant hand's forearm muscles with 22 healthy subjects and 20 HOA patients performing maximum force during six representative grasp types (the most commonly used in ADLs). The EMG characteristics were used to identify discriminant functions to detect HOA. The results show that forearm muscles are significantly affected by HOA in EMG terms, with very high success rates (between 93.3% and 100%) in the discriminant analyses, which suggest that EMG can be used as a preliminary step towards confirmation with current HOA diagnostic techniques. Digit flexors during cylindrical grasp, thumb muscles during oblique palmar grasp, and wrist extensors and radial deviators during the intermediate power-precision grasp are good candidates to help detect HOA.

Muscle Activity Characteristics of the Pronator Teres during Throwing in Baseball Pitchers: A Pilot Study.

The pronator teres muscle is a major dynamic stabilizer of elbow valgus stress during throwing. This study aims to investigate pronator teres muscle activation during breaking ball pitching in baseball pitchers. Twelve male college baseball players with more than eight years of baseball experience were included in this study. A wireless surface electromyography (EMG) system was used to measure the activation of the forearm muscles and record EMG data during fastball and curveball pitching. Peak pronator teres muscle activation during curveball pitching was greater than that during fastball pitching (p = 0.03). There was no difference in the muscle activation of the other forearm muscles (p > 0.05). These results indicate that increased muscle activity in the pronator teres may contribute to stiffness and induce pronator teres syndrome or medial elbow injuries related to the overuse of the pronator teres, especially during curveball pitching. Controlling curveball throws contributes to player coaching and conditioning for the prevention of elbow joint disorders and pronator teres syndrome.

Time-Based and Path-Based Analysis of Upper-Limb Movements during Activities of Daily Living.

Patients after stroke need to re-learn functional movements required for independent living throughout the rehabilitation process. In the study, we used a wearable sensory system for monitoring the movement of the upper limbs while performing activities of daily living. We implemented time-based and path-based segmentation of movement trajectories and muscle activity to quantify the activities of the unaffected and the affected upper limbs. While time-based segmentation splits the trajectory in quants of equal duration, path-based segmentation isolates completed movements. We analyzed the hand movement path and forearm muscle activity and introduced a bimanual movement parameter, which enables differentiation between unimanual and bimanual activities. The approach was validated in a study that included a healthy subject and seven patients after stroke with different levels of disabilities. Path-based segmentation provides a more detailed and comprehensive evaluation of upper limb activities, while time-based segmentation is more suitable for real-time assessment and providing feedback to patients. Bimanual movement parameter effectively differentiates between different levels of upper limb involvement and is a clear indicator of the activity of the affected limb relative to the unaffected limb.

Forearm Muscle Activity During the Handgrip Test in Breast Cancer Survivors: A Cross-Sectional Study

Introduction/BackgroundBreast cancer survivors (BCS) frequently show upper limb dysfunctions. The forearm muscle activity measured by surface electromyography (sEMG) in this population has not been studied. This study aimed to describe forearm muscle activity in BCS, as well as to assess its possible relationship with other variables related to upper limb functionality and cancer-related fatigue (CRF). Materials and MethodsA cross-sectional study was carried out including 102 BCS as volunteers at a secondary care in Malaga, Spain. BCS were included if they were aged between 32 and 70 years old, without evidence of cancer recurrence at the time of recruitment. The forearm muscle activity (microvolts, µV) was assessed by sEMG during the handgrip test. The handgrip strength was assessed by dynamometry (kg), the upper limb functionality (%) was measured by the upper limb functional index (ULFI) questionnaire and the CRF was also assessed by revised Piper Fatigue Scale (0-10 points). ResultsBCS reported reduced forearm muscle activity (287.88 µV) and reduced handgrip strength (21.31 Kg), a good upper limb functionality (68.85%), and a moderate cancer-related fatigue (4.74). Forearm muscle activity showed a poor significant correlation (r = –0.223, P = .038) with the CRF. Handgrip strength showed a poor correlation with the upper limb functionality (r = 0.387, P < .001) and age (r=-0.200, P = .047). ConclusionBCS showed a reduced forearm muscle activity. BCS also presented a poor correlation between forearm muscle activity and handgrip strength. Both outcomes tended to lower values with higher levels of CRF, while preserving a good upper limb functionality.

Challenges in evaluating forearm muscle activity based on the compound muscle action potential of the flexors of the whole forearm

ObjectiveMuscle strength, which correlates with the compound muscle action potential (CMAP), can also be estimated by measuring the CMAP. Therefore, we evaluated the CMAP of the flexor muscles of the whole forearm to identify their muscle strength. MethodsFourteen healthy volunteers were enrolled. The elbow was determined to be the stimulation point, and the recording site for the flexor muscles of the whole forearm was set at approximately 8 cm distal to the elbow. We prospectively evaluated the baseline-to-peak amplitude of the CMAP of the whole forearm flexor muscles (WFFM), including that obtained from the median nerve stimulation (WFFMm), ulnar nerve stimulation (WFFMu), and their sum (WFFMsum). Additionally, we analyzed the relationships between WFFMm and WFFMu amplitudes with other quantitative parameters, including grip strength and routine CMAP amplitudes. ResultsThe CMAP’s test–retest analysis revealed high reliability. Grip power was significantly correlated with WFFMm and WFFMsum and mildly correlated with WFFMu. Tip-pinch strength with WFFMm and flexor pollicis longus (FPL) measurements correlated significantly. Lateral-pinch strength was significantly correlated with the first dorsal interosseous muscle (FDI) measurements but not with WFFM. The abductor digiti minimi (ADM) and abductor pollicis brevis (APB) were not correlated with grip power or pinch strength. ConclusionsBy electrophysiology examination, this study demonstrated that WFFMm is involved in grip power and other pinch strengths. This method may serve as a novel tool for measurement of distal muscle strengths. SignificanceThis is the first study to attempt to evaluate the muscle strength of forearm flexor muscles by measuring the CMAP.

Measurement of Forearm Muscle Activity and Elbow Angle of the Elderly in Using Different Types of Cane Handles through Electromyography (EMG) and Kinovea Software

Elderly individuals often experience physical limitations, leading to a decline in their walking ability and an increased risk of falling. Falls among the elderly are a critical issue that can be minimized by using walking aids such as a Cane. However, the use of a cane poses other risks, such as injuries like carpal tunnel syndrome (CTS), caused by repetitive hand movements and changes in hand angles. The objective of this research is to select the appropriate cane handle to minimize the strain on the wrist by analyzing forearm muscle signals measured using EMG (Electromyography) combined with angle measurements using Kinovea software. The study involved 8 elderly subjects who regularly used a cane during walking gait tests. The distribution of the load during walking with the cane was assessed. The results, in the form of EMG data, were segmented based on time and angles, allowing the extraction of features using the root mean square (RMS) method. The next step involved conducting a three-way ANOVA statistical test for experimental design and identifying interactions between each factor. The findings revealed that the cane handle with a fritz-type grip, positioned posteriorly, and used during the initial phase of walking had the lowest values, measuring 50.373 μV for the fritz cane, 52.03 μV for the posterior position, and 56.74 μV for the initial angle. This indicates that a cane with a fritz handle distributes the load on the forearm towards the wrist more minimally, reducing the risk of CTS.

Automated and Continuous Fatigue Monitoring in Construction Workers Using Forearm EMG and IMU Wearable Sensors and Recurrent Neural Network.

About 40% of the US construction workforce experiences high-level fatigue, which leads to poor judgment, increased risk of injuries, a decrease in productivity, and a lower quality of work. Therefore, it is essential to monitor fatigue to reduce its adverse effects and prevent long-term health problems. However, since fatigue demonstrates itself in several complex processes, there is no single standard measurement method for fatigue detection. This study aims to develop a system for continuous workers' fatigue monitoring by predicting the aerobic fatigue threshold (AFT) using forearm muscle activity and motion data. The proposed system consists of five modules: Data acquisition, activity recognition, oxygen uptake prediction, maximum aerobic capacity (MAC) estimation, and continuous AFT monitoring. The proposed system was evaluated on the participants performing fourteen scaffold-building activities. The results show that the AFT features have achieved a higher accuracy of 92.31% in assessing the workers' fatigue level compared to heart rate (51.28%) and percentage heart rate reserve (50.43%) features. Moreover, the overall performance of the proposed system on unseen data using average two-min AFT features was 76.74%. The study validates the feasibility of using forearm muscle activity and motion data to workers' fatigue levels continuously.

Effects of multidirectional elastic tape on forearm muscle activity and wrist extension during submaximal gripping in individuals with lateral elbow tendinopathy: A randomised crossover trial

BackgroundLateral elbow tendinopathy is associated with changes to forearm muscle activity and wrist posture during gripping. Multidirectional elastic tape is thought to exert a deloading effect on underlying musculotendinous structures, which could potentially alter muscle activity or wrist posture. MethodsThis single-blinded randomised crossover trial compared the immediate effects of tensioned multidirectional elastic tape, untensioned control tape, and no tape, in individuals with lateral elbow tendinopathy. Muscle activity of extensor carpi radialis longus and brevis, extensor carpi ulnaris, and extensor digitorum and wrist extension angle were recorded during a submaximal gripping task. Muscle activity was normalised to the maximum amplitude recorded during maximal grip. Change scores were calculated (post-condition minus baseline). Repeated-measure analyses of variance were used to examine between-condition differences. Findings27 participants (16 males, mean age (SD): 48.6 (11.9) years) underwent all conditions. Extensor digitorum muscle activity was reduced during the multidirectional elastic tape, compared to control tape and no tape (MD −5.6% [95%CI: −9.9 to −1.3], MD −5.8% [95%CI: −10.2 to −1.4], respectively). Extensor carpi ulnaris muscle activity was reduced during the multidirectional elastic tape, compared to the control tape (mean difference [MD] −3.2% [95%CI: −5.3 to −1.1]), but increased during the control tape, compared to the no tape (MD 2.9% [95%CI: 0.8 to 5.0]). No differences were observed in extensor carpi radialis brevis or longus muscle activity, or extension wrist angle between conditions. InterpretationA decreased in extensor carpi ulnaris and extensor digitorum muscle activity during multidirectional elastic tape may be evidence of a deloading effect during submaximal gripping.

Ergonomic design and evaluation of gemstone polishing workstation

Objectives. Gemstone polishers suffer from musculoskeletal problems due to constrained working postures, substantially influenced by the poor design of conventional gemstone polishing workstations. The present study investigated the effects of three workstation adjustment parameters (illumination at workstation, polishing height, tool post position) on postural angle, muscle activity and perceived postural discomfort in order to develop recommendations for new gemstone polishing workstations. Methods. Twelve professional gemstone polishers performed the polishing task on a prototype test-rig in 27 different test conditions. Taguchi’s L27 orthogonal array was employed to estimate the optimum setting for gemstone polishing workstation design. Results. Study variables had a significant influence on postural angles. Polishing height substantially influenced muscle activity and perceived discomfort in the shoulder and lower back region. Tool post position was found to be the determinant factor for forearm muscle activity and perceived discomfort in the wrist/forearm region. Based on the findings, illumination of 1500 lux, polishing at 15 cm above the elbow height and a 20° tool position was recommended. Conclusions. Our findings present an alternative approach to using Taguchi’s design of experiment for workstation improvement, which has received very little attention in ergonomics studies. A confirmation test was conducted to validate the study recommendations.

Force At A Set Voluntary Forearm Muscle Activation Conforms To Muscle Oxygenation At High Intensities

In electrically stimulated muscle, the oxygen conforming response of skeletal muscle is characterized by a down regulation of muscle force for a given electromyography (EMG) when oxygen delivery is reduced, which is rapidly (within 60-sec) reversed when oxygen delivery is restored. Whether this oxygen conforming response exists in voluntary human exercise is unknown. PURPOSE: To test the hypotheses that oxygen conforming 1) occurs during voluntary handgrip exercise 2) is exercise intensity dependent 3) is independent of sex. METHODS: In 6-men and 6-women, handgrip force, forearm EMG, oxyhemoglobin (O2Hb, %) and mean blood velocity (MBV, cm/s) were measured while participants completed 15-min of rhythmic handgrip exercise targeting a forearm EMG equal to that required to achieve 50, 75 and 90% of critical power handgrip force output. At minute 7, 4-min of brachial artery compression was either completed to reduce MBV by ~50% (experimental, EX) or compression was completed next to the brachial artery to simulate compression without affecting MBV (sham, SH). Exercise continued for 4-min after ending compression. RESULTS:Compression: At 4-min, forearm MBV was reduced in all intensities (50%, EX: 11.62 ± 1.44, SH: 24.57 ± 3.07; 75%, EX: 13.64 ± 1.65, SH: 34.35 ± 4.82; 90%, EX:16.71 ± 2.18, SH: 38.63 ± 3.58, all P < 0.05), O2Hb was reduced in 50% (EX: 62.68 ± 5.10, SH: 70.97 ± 4.63, P < 0.05) and 90% (EX: 49.53 ± 3.98, SH: 70.80 ± 2.93, P < 0.05) intensities but not the 75% intensity (EX: 54.95 ± 4.79, SH: 64.37 ± 3.59, P = 0.08). The amount of force produced per EMG (Force/EMG) was reduced in the 75% (EX: 0.90 ± 0.03, SH: 1.01 ± 0.02, P < 0.05) and 90% (EX: 0.86 ± 0.27, SH: 1.01 ± 0.02, P < 0.05) intensities but not the 50% (EX: 0.97 ± 0.03, SH: 1.00 ± 0.02, P > 0.05) intensity. End compression: Forearm MBV and O2Hb was restored within 30-sec for all intensities (90%, EX: 55.98 ± 11.15; SH: 70.72 ± 9.93, P = 0.1289) and force/EMG was restored within 60-sec for 90% (EX: 0.98 ± 0.02; SH: 1.02 ± 0.02, P = 0.279) and 75% (EX: 0.98 ± 0.02; SH: 0.98 ± 0.02, P = 0.929). No sex differences were observed. CONCLUSION: 1) The rapid restoration of force/EMG (within 60-sec) upon restoration of O2Hb is consistent with the existence of an oxygen conforming response in voluntary human exercise that 2) exists only at higher intensities (75% and 90%). 3) This response is independent of sex.

Muscle contraction force conforms to muscle oxygenation during constant-activation voluntary forearm exercise.

What is the central question of this study? In electrically stimulated skeletal muscle, force production is downregulated when oxygen delivery is compromised and rapidly restored upon oxygen delivery restoration. Whether 'oxygen conforming' of force production occurs during voluntary muscle activation in humans and whether it is exercise intensity dependent remains unknown. What is the main finding and its importance? Here, we show in humans that force at a given voluntary muscle activation does conform to a decrease in oxygen delivery and recovers rapidly and completely with restoration of oxygen delivery. This oxygen-conforming response of contraction force appears to happen only at higher intensities. In electrically stimulated skeletal muscle, force production is downregulated when oxygen delivery is compromised and rapidly restored upon restoration of oxygen delivery in the absence of cellular disturbance. Whether this 'oxygen-conforming' response of force occurs and is exercise intensity dependent during stable voluntary muscle activation in humans is unknown. In 12 participants (six female), handgrip force, forearm muscle activation (EMG), muscle oxygenation and forearm blood flow (FBF) were measured during rhythmic handgrip exercise at forearm EMG achieving 50, 75 or 90% critical impulse (CI). Four minutes of brachial artery compression to reduce FBF by ∼60% (Hypoperfusion) or sham compression (adjacent to artery; Control) was performed during exercise. Sham compression had no effect. Hypoperfusion rapidly reduced muscle oxygenation at all exercise intensities, resulting in contraction force per muscle activation (force/EMG) progressively declining over 4min by ∼16% at both 75 and 90% CI. No force/EMG decline occurred at 50% CI. Rapid restoration of muscle oxygenation after compression was closely followed by force/EMG such that it was not different from Control within 30s for 90% CI and after 90s for 75% CI. Our findings reveal that an oxygen-conforming response does occur in voluntary exercising muscle in humans. Within the exercise modality and magnitude of fluctuation of oxygenation in this study, the oxygen-conforming response appears to be exercise intensity dependent. Mechanisms responsible for this oxygen-conforming response have implications for exercise tolerance and warrant investigation.

Effects of an active hand exoskeleton on forearm muscle activity in industrial assembly grips.

The Bioservo Ironhand® is a commercially available active hand exoskeleton for reducing grip-induced stress. The study aimed at quantifying the effect of the Ironhand® exoskeleton on the myoelectric muscle activity of forearm flexor and extensor muscles in three relevant assembly grip tasks: 2-Finger-grip (2Finger), 5-Finger-grip (5Finger) and Full grip (FullGrip). Twenty-two subjects were tested in three different exoskeleton conditions for each grip task (overall 3×3×10 = 90 repetitions in randomized order): Exoskeleton off (Off), Exoskeleton on, "locking tendency" 0% (On_LT0), and Exoskeleton on, "locking tendency" 85% (On_LT85). Muscle activity was measured at 25% of the participant's maximum grip force using two EMG sensors at the M. flexor digitorum superficialis (M.FDS) and one at the M. extensor digitorum (M.ED). The effect of the Ironhand® exoskeleton varied depending on the grip task and the participant's sex. A statistically significant reduction in muscle activity of the M.FDS was found only for male subjects in the FullGrip condition. No reduction of muscular activity in the M.FDS was found for the other grip tasks (2Finger, 5Finger). For the females in the 2Finger condition, mean muscle activity of M.FDS even increased significantly in On_LT0 compared to Off. Besides differences between grip tasks and sex, the current study revealed substantial individual differences. In addition to testing for statistical significance, a detailed exploratory analysis of exoskeleton effects at subject level should be performed to evaluate these from a safety and regulatory perspective.

The effects of isometric hand grip force on wrist kinematics and forearm muscle activity during radial and ulnar wrist joint perturbations.

The purpose of this work was to investigate forearm muscle activity and wrist angular displacement during radial and ulnar wrist perturbations across various isometric hand grip demands. Surface electromyography (EMG) was recorded from eight muscles of the upper extremity. A robotic device delivered perturbations to the hand in the radial and ulnar directions across four pre-perturbation grip magnitudes. Angular displacement and time to peak displacement following perturbations were evaluated. Muscle activity was evaluated pre- and post-perturbation. Results showed an inverse relationship between grip force and angular displacement (p ≤ 0.001). Time to peak displacement decreased as grip force increased (p ≤ 0.001). There was an increase in muscle activity with higher grip forces across all muscles both pre-and post-perturbation (p ≤ 0.001) and a greater average muscle activity in ulnar as compared to radial deviation (p = 0.02). This work contributes to the wrist joint stiffness literature by relating wrist angular displacement to grip demands during novel radial/ulnar perturbations and provides insight into neuromuscular control strategies.

Estimating muscle activation from EMG using deep learning-based dynamical systems models

Objective. To study the neural control of movement, it is often necessary to estimate how muscles are activated across a variety of behavioral conditions. One approach is to try extracting the underlying neural command signal to muscles by applying latent variable modeling methods to electromyographic (EMG) recordings. However, estimating the latent command signal that underlies muscle activation is challenging due to its complex relation with recorded EMG signals. Common approaches estimate each muscle’s activation independently or require manual tuning of model hyperparameters to preserve behaviorally-relevant features. Approach. Here, we adapted AutoLFADS, a large-scale, unsupervised deep learning approach originally designed to de-noise cortical spiking data, to estimate muscle activation from multi-muscle EMG signals. AutoLFADS uses recurrent neural networks to model the spatial and temporal regularities that underlie multi-muscle activation. Main results. We first tested AutoLFADS on muscle activity from the rat hindlimb during locomotion and found that it dynamically adjusts its frequency response characteristics across different phases of behavior. The model produced single-trial estimates of muscle activation that improved prediction of joint kinematics as compared to low-pass or Bayesian filtering. We also applied AutoLFADS to monkey forearm muscle activity recorded during an isometric wrist force task. AutoLFADS uncovered previously uncharacterized high-frequency oscillations in the EMG that enhanced the correlation with measured force. The AutoLFADS-inferred estimates of muscle activation were also more closely correlated with simultaneously-recorded motor cortical activity than were other tested approaches. Significance. This method leverages dynamical systems modeling and artificial neural networks to provide estimates of muscle activation for multiple muscles. Ultimately, the approach can be used for further studies of multi-muscle coordination and its control by upstream brain areas, and for improving brain-machine interfaces that rely on myoelectric control signals.

An electromyographic assessment pilot study on the reliability of the forearm muscles during multi-planar maximum voluntary contraction grip and wrist articulation in young males.

Electromyographic systems are widely used in scientific and clinical practice. The reproducibility and reliability of these measures are crucial when conducting scientific research and collecting experimental data. To test the reliability of surface electromyography signals from both the Flexor Digitorum Superficialis (FDS) and Extensor Carpi Radialis Brevis (ECRB) muscles of both the left and right arms during an individual, static multi-planar maximum voluntary contraction handgrip task using the Myon 320 system (Myon AG, Switzerland). Eight right-handed male participants performed two maximal handgrip tests in five separate wrist positions using both hands. Muscle activity was recorded from both forearms. Reliability was measured using the Standard Error of Measurement (SEM), Coefficient of Variation (CV) and Intra-class correlation coefficients. Wrist joint position correlations within and between the FDS and ECRB muscle activities were also analysed. Absolute reliability was shown across all positions for both hands with CV and SEM recorded at below 10%. The output measures indicate that the Myon 320 system (Myon AG, Switzerland) produces good to fair reliability when assessing forearm muscle activity. Correlations in the left FDS muscles were negative. Correlations between the left ECRB and left FDS muscles were variable but positive between the right ECRB and right FDS muscles. The data sets retrieved from all participants were reliably evaluated. Wrist position correlations within and between the FDS and ECRB muscles may have been influenced by hand dominance. The findings demonstrate that the methods and systems outlined in this study can be used reliably in future research.