The influence of wrist posture on the time and frequency EMG signal measures of forearm muscles

Expressivity attributed to music affects the smoothness of bowing movements in violinists

Playing music is a complex task that relies on the combination of musicians' technical and expressive skills. While the literature has investigated the effects of musical expressivity on the listeners, the way how technical difficulty and emotional expressivity affect musicians during playing has surprisingly received no attention. In an attempt to fill this gap in the literature, we collected behavioral and physiological data from twelve violinists playing 29 pieces that included both technical exercises and excerpts from classical repertoire for violin. After playing each stimulus, participants rated it for emotional expressivity and technical difficulty. During the entire session, cardiac parameters and electrodermal activity were collected, together with the kinematic parameters of the bowing gesture. A set of Linear Mixed-Effect (LME) models suggested that emotional expressivity attributed to music affected the fluidity of bowing (i.e., smoothness), with the excerpts rated as more expressive being performed in a less smooth way. In contrast, LME models revealed no effects of expressivity and technical difficulty on any of the physiological parameters of violinists. Our results offer novel insights into the psychophysiological dynamics that link motor parameters with musical expressivity. These findings could influence educational practices in music and deepen our understanding of aesthetic emotions.

How does the consecutive use of intraoral scanners affect musculoskeletal health? A preliminary clinical study

BACKGROUND

Minimizing muscle strain and reducing the risk of musculoskeletal disorders associated with intraoral scanner (IOS) usage require ergonomic awareness, device selection, and workplace adjustments in dental practice. This preliminary clinical study aimed to simulate intraoral scanning tasks using wired and wireless IOSs and assess muscle activation and fatigue for both types.

MATERIALS AND METHODS

Fourteen participants performed intraoral scanning tasks using wired and wireless IOSs (i700; MEDIT), with weights of 280 g and 328 g, respectively. The same computer system and software conditions were maintained for both groups (N = 14 per IOS group). Electrodes were placed on arm, neck, and shoulder muscles, and maximal voluntary contraction (MVC) was measured. Surface electromyography (EMG) was performed during the simulation, and EMG values were normalized using MVC. The root mean square EMG (%MVC) and muscle fatigue (%) values were calculated. Statistical comparisons were performed using the Mann-Whitney U and Friedman tests, with the Bonferroni adjustment for multiple comparisons (α = 0.05).

RESULTS

Arm (flexor digitorum superficialis) and neck muscles (left sternocleidomastoid and left splenius capitis) showed significantly higher EMG values with wireless IOS (P < 0.05). The neck (left sternocleidomastoid and right levator scapulae) and shoulder muscles (right trapezius descendens) demonstrated significantly higher muscle fatigue with wireless IOS (P < 0.05).

CONCLUSIONS

The consecutive use of heavier wireless IOS may increase the risk of muscle activation and fatigue in certain muscles, which may have clinical implications for dentists in terms of ergonomics and musculoskeletal health.

Strain-invariant stretchable radio-frequency electronics

Wireless modules that provide telecommunications and power-harvesting capabilities enabled by radio-frequency (RF) electronics are vital components of skin-interfaced stretchable electronics1-7. However, recent studies on stretchable RF components have demonstrated that substantial changes in electrical properties, such as a shift in the antenna resonance frequency, occur even under relatively low elastic strains8-15. Such changes lead directly to greatly reduced wireless signal strength or power-transfer efficiency in stretchable systems, particularly in physically dynamic environments such as the surface of the skin. Here we present strain-invariant stretchable RF electronics capable of completely maintaining the original RF properties under various elastic strains using a 'dielectro-elastic' material as the substrate. Dielectro-elastic materials have physically tunable dielectric properties that effectively avert frequency shifts arising in interfacing RF electronics. Compared with conventional stretchable substrate materials, our material has superior electrical, mechanical and thermal properties that are suitable for high-performance stretchable RF electronics. In this paper, we describe the materials, fabrication and design strategies that serve as the foundation for enabling the strain-invariant behaviour of key RF components based on experimental and computational studies. Finally, we present a set of skin-interfaced wireless healthcare monitors based on strain-invariant stretchable RF electronics with a wireless operational distance of up to 30 m under strain.

A randomized controlled trial on the effectiveness of mirror therapy in improving strength, range of movement and muscle activity, in people with carpal tunnel syndrome

BACKGROUND

There is little information on the potential effects of mirror therapy (MT) on motor recovery in individuals with Carpal Tunnel Syndrome (CTS).

PURPOSE

To compare the effectiveness of a MT protocol versus a therapeutic exercise (TE) protocol, in improving strength, range of motion (ROM), muscle activity, pain, and functionality in patients with CTS.

STUDY DESIGN

Randomized clinical trial.

METHODS

Thirty-nine participants with unilateral CTS were divided into two groups: (i) MT group (n = 20) that followed an exercise protocol applied to the unaffected hand reflected in a mirror, and (ii) TE group (n = 19) that followed the same exercise protocol using the unaffected hand but without a mirror. Strength, wrist ROM, muscle activity, pain and functionality, were assessed at baseline (T0), after treatment (T1) and one month after treatment (T2).

RESULTS

At T1, the MT group showed significantly higher wrist flexion-extension ROM compared to TE (p = 0.04, d = 0.8), maintained at T2 (p = 0.02, d = 0.8). No significant changes were observed in ulnar-radius deviation, pronosupination, or fatigue following either MT or TE (p > 0.05). MT exhibited enhanced handgrip strength at T1 (p = 0.001, d = 0.7), as well as an increase in the extensor carpi radialis (ECR) and flexor carpi radialis (FCR) maximum muscle activity (p = 0.04, d = 1.0; p = 0.03, d = 0.4). At T1, both groups decreased pain (p = 0.002, d = 1.1; p = 0.02, d = 0.7), and improved functionality (p < 0.001, d = 0.8; p = 0.01, d = 0.5) (MT and TE respectively).

DISCUSSION

MT led to enhancements in wrist flexion-extension movement, handgrip strength and functionality unlike TE. MT notably increased muscle activity, particularly in the ECR and FCR muscles.

CONCLUSIONS

MT is a favorable strategy to improve wrist flexion-extension ROM, handgrip strength, ECR and FCR muscle activity, and functionality in people with unilateral CTS.

How Does the Use of an Intraoral Scanner Affect Muscle Fatigue? A Preliminary In Vivo Study

The purpose of this study was to evaluate muscle activation and fatigue in the operator during tooth preparation and intraoral scanning by simulating these tasks in two types of dental unit chair systems (UCS). Six participants were recruited, and the above tasks were simulated. Electrodes were placed on the skin over five types of muscles (arm, neck, and shoulder muscles), and the maximal voluntary contraction (MVC) was measured. Electromyography (EMG) was assessed during the simulation, and EMG values were normalized using MVC. The root mean square (RMS) EMG (%MVC) and muscle fatigue (%) were calculated. Owing to a lack of normal distribution of the data, Mann−Whitney U test and Kruskal−Wallis H test were performed for statistical comparison, and Bonferroni adjustment was performed for multiple comparisons (α = 0.05). There was no significant difference in RMS EMG between the two types of dental UCS (intraoral scanning, p = 0.237; tooth preparation, p = 0.543). Moreover, the RMS EMG and muscle fatigue were not significantly different between the two tasks (p > 0.05). There was significant muscle fatigue after the intraoral scanner use was simulated thrice (p < 0.001). It is necessary to refrain from performing continuous intraoral scanning and tooth preparation and to take appropriate rest to reduce the incidence of musculoskeletal disorders in dentists in clinical settings.

A Co-driven Functional Electrical Stimulation Control Strategy by Dynamic Surface Electromyography and Joint Angle

Functional electrical stimulation (FES) is widely used in neurorehabilitation to improve patients’ motion ability. It has been verified to promote neural remodeling and relearning, during which FES has to produce an accurate movement to obtain a good efficacy. Therefore, many studies have focused on the relationship between FES parameters and the generated movements. However, most of the relationships have been established in static contractions, which leads to an unsatisfactory result when applied to dynamic conditions. Therefore, this study proposed a FES control strategy based on the surface electromyography (sEMG) and kinematic information during dynamic contractions. The pulse width (PW) of FES was determined by a direct transfer function (DTF) with sEMG features and joint angles as the input. The DTF was established by combing the polynomial transfer functions of sEMG and joint torque and the polynomial transfer functions of joint torque and FES. Moreover, the PW of two FES channels was set based on the muscle synergy ratio obtained through sEMG. A total of six healthy right-handed subjects were recruited in this experiment to verify the validity of the strategy. The PW of FES applied to the left arm was evaluated based on the sEMG of the right extensor carpi radialis (ECR) and the right wrist angle. The coefficient of determination (R²) and the normalized root mean square error (NRMSE) of FES-included and voluntary wrist angles and torques were used to verify the performance of the strategy. The result showed that this study achieved a high accuracy (R² = 0.965 and NRMSE = 0.047) of joint angle and a good accuracy (R² = 0.701 and NRMSE = 0.241) of joint torque reproduction during dynamic movements. Moreover, the DTF in real-time FES system also had a nice performance of joint angle fitting (R² = 0.940 and NRMSE = 0.071) and joint torque fitting (R² = 0.607 and NRMSE = 0.303). It is concluded that the proposed strategy is able to generate proper FES parameters based on sEMG and kinematic information for dynamic movement reproduction and can be used in a real-time FES system combined with bilateral movements for better rehabilitation.

Mechanically and electrically durable, stretchable electronic textiles for robust wearable electronics

A monolithic integration of high-performance soft electronic modules into various fabric materials has enabled a paradigm shift in wearable textile electronics. However, the current textile electronics have struggled against fatigue under repetitive deformation due to the absence of materials and structural design strategies for imparting electrical and mechanical robustness to individual fibers. Here, we report a mechanically and electrically durable, stretchable electronic textile (MED-ET) enabled by a precisely controlled diffusion of tough self-healing stretchable inks into fibers and an adoption of the kirigami-inspired design. Remarkably, the conductive percolative pathways in the fabric of MED-ET even under a harshly deformed environment were stably maintained due to an electrical recovery phenomenon which originates from the spontaneous rearrangement of Ag flakes in the self-healing polymer matrix. Specifically, such a unique property enabled damage-resistant performance when repetitive deformation and scratch were applied. In addition, the kirigami-inspired design was capable of efficiently dissipating the accumulated stress in the conductive fabric during stretching, thereby providing high stretchability (a tensile strain of 300%) without any mechanical fracture or electrical malfunction. Finally, we successfully demonstrate various electronic textile applications such as stretchable micro-light-emitting diodes (Micro-LED), electromyogram (EMG) monitoring and all-fabric thermoelectric devices (F-TEG).

Stretchable MED-ET was fabricated by a soaking process of self-healing stretchable Ag ink. Conductive pathways in MED-ET under a damaged environment were stably maintained due to an electrical recovery phenomenon which enables a robust device system.

Influence of virtual keyboard design and usage posture on typing performance and muscle activity during tablet interaction

This study aimed to determine the effects of virtual keyboard designs and postures on task performance and muscle activity during tablet use. Eighteen healthy adults were randomly assigned to one of three postures (DESK, LAP, BED) to complete six sessions of 60-minute typing on a tablet with three virtual keyboards (STD, WIDE, SPLIT) twice in an experimental laboratory. Keystroke dynamics and muscle activity of the forearm and neck-shoulder regions were measured by electromyography. The split virtual keyboard was found to be associated with faster typing speed (SPLIT vs STD, p = .015; SPLIT vs WIDE, p < .001) and decreased muscle activity of extensor digitorum communis (SPLIT vs STD, p = .021). Lap posture was associated with faster typing speed (p = .018) and higher forearm muscle activity (p < .05). Typing performance decreased (p < .001) with elevated neck extensor muscle activity (p = .042) when the task duration prolonged. The split virtual keyboard showed potential to improve tablet ergonomics under various postures. Practitioner Summary: Tablets have become widely used for a variety of tasks and have gradually expanded into the realm of mobile productivity and education. Adequate designs of virtual keyboards for tablets show the potential for increased task performance and decreased muscle activity pertinent to typing activity and posture constraints imposed by non-traditional work positions. Abbreviations: WPM: words per minute; IKI: inter-key press interval; EMG: electromyography; EDC: extensor digitorum communis; FDS: flexor digitorum superficialis; CES: cervical erector spinae; UT: upper trapezius; EA: electrical activity; MVC: maximum voluntary contraction; APDF: amplitude probability distribution function.

The effect of wrist posture on extrinsic finger muscle activity during single joint movements

Wrist posture impacts the muscle lengths and moment arms of the extrinsic finger muscles that cross the wrist. As a result, the electromyographic (EMG) activity associated with digit movement at different wrist postures must also change. We sought to quantify the posture-dependence of extrinsic finger muscle activity using bipolar fine-wire electrodes inserted into the extrinsic finger muscles of able-bodied subjects during unrestricted wrist and finger movements across the entire range of motion. EMG activity of all the recorded finger muscles were significantly different (p < 0.05, ANOVA) when performing the same digit movement in five different wrist postures. Depending on the wrist posture, EMG activity changed by up to 70% in individual finger muscles for the same movement, with the highest levels of activity observed in finger extensors when the wrist was extended. Similarly, finger flexors were most active when the wrist was flexed. For the finger flexors, EMG variations with wrist posture were most prominent for index finger muscles, while the EMG activity of all finger extensor muscles were modulated in a similar way across all digits. In addition to comprehensively quantifying the effect of wrist posture on extrinsic finger EMG activity in able-bodied subjects, these results may contribute to designing control algorithms for myoelectric prosthetic hands in the future.

Using infrared imaging for assessment of muscular activity in the forearm of surgeons in the performance of laparoscopic tasks

Surgeons working in laparoscopic surgery are subjected to hard working conditions because of the poor ergonomic characteristics of the workplace. The improvement in the working conditions requires the use of reliable techniques for the assessment of muscular activity. In this article infrared imaging is used and compared with electromyography for the evaluation of muscle activity in the performance of laparoscopic surgical tasks. Electromyography has been widely used for the evaluation of the electrical activity produced by the muscles in the performance of surgery. On the contrary, infrared imaging is an innovative technique that has not been sufficiently explored. An experimental evaluation was carried out using a thermography camera and recording the infrared images from volunteers in different tests. Pearson's correlation was obtained between the electromyography and thermographic measurements in two stages: Endurance Stage (best value: ρ = 0.8401 with p < 0.01) and Surgical Task (best value: ρ = 0.8309 with p < 0.01). The article demonstrates that infrared imaging is a valuable technique for the evaluation of muscle activity in laparoscopic surgery, and it can be compared with electromyography. The main advantages of infrared imaging are that it allows remote measurement and provides activity information in the whole area of interest. However, drawbacks such as delayed response of the infrared imaging due to thermal conductivity of the skin should be considered. Electromyography only provides information in the location of the electrodes, but it is a real-time response. For these reasons, the techniques complement each other.

An Ultrastretchable and Self-Healable Nanocomposite Conductor Enabled by Autonomously Percolative Electrical Pathways

Both self-healable conductors and stretchable conductors have been previously reported. However, it is still difficult to simultaneously achieve high stretchability, high conductivity, and self-healability. Here, we observed an intriguing phenomenon, termed "electrical self-boosting", which enables reconstructing of electrically percolative pathways in an ultrastretchable and self-healable nanocomposite conductor (over 1700% strain). The autonomously reconstructed percolative pathways were directly verified by using microcomputed tomography and in situ scanning electron microscopy. The encapsulated nanocomposite conductor shows exceptional conductivity (average value: 2578 S cm^-1; highest value: 3086 S cm^-1) at 3500% tensile strain by virtue of efficient strain energy dissipation of the self-healing polymer and self-alignment and rearrangement of silver flakes surrounded by spontaneously formed silver nanoparticles and their self-assembly in the strained self-healing polymer matrix. In addition, the conductor maintains high conductivity and stretchability even after recovered from a complete cut. Besides, a design of double-layered conductor enabled by the self-bonding assembly allowed a conducting interface to be located on the neutral mechanical plane, showing extremely durable operations in a cyclic stretching test. Finally, we successfully demonstrated that electromyogram signals can be monitored by our self-healable interconnects. Such information was transmitted to a prosthetic robot to control various hand motions for robust interactive human-robot interfaces.

The effect of two types of maximal voluntary contraction and two electrode positions in field recordings of forearm extensor muscle activity during hotel room cleaning

Purpose. This study aimed to investigate the effects of using hand grip or resisted wrist extension as the reference contraction, and two electrode positions, on field recordings of forearm extensor muscle activity. Materials and methods. Right forearm extensor muscle activity was recorded using two electrode pairs (over the most prominent part (position 2) and proximal to that (position 1)) during one working day in 13 female hotel housekeepers. Each subject performed the two maximal voluntary contractions (MVCs), and the electrical activity obtained during these (maximal voluntary electrical activity (MVE)) was used for normalization. Each set of recordings was analysed twice, once using hand grip as the MVC and once using resisted wrist extension. Results. Resisted wrist extension showed a higher group mean MVE than hand grip. Position 2 had higher correlation between MVE and force during the MVCs. The workload during cleaning was lower when using resisted wrist extension as reference than when using hand grip (24%MVE vs 46%MVE; p = 0.002 at position 2) for the 90th percentile. The workload (99th percentile) was overestimated in two subjects when using hand grip as reference. Conclusions. Problems associated with poorly activated forearm extensors can be overcome by using resisted wrist extension as reference.

Comparing two methods to record maximal voluntary contractions and different electrode positions in recordings of forearm extensor muscle activity: Refining risk assessments for work-related wrist disorders

BACKGROUND:

Wrist disorders are common in force demanding industrial repetitive work. Visual assessment of force demands have a low reliability, instead surface electromyography (EMG) may be used as part of a risk assessment for work-related wrist disorders. For normalization of EMG recordings, a power grip (hand grip) is often used as maximal voluntary contraction (MVC) of the forearm extensor muscles. However, the test-retest reproducibility is poor and EMG amplitudes exceeding 100% have occasionally been recorded during work. An alternative MVC is resisted wrist extension, which may be more reliable.

OBJECTIVE:

To compare hand grip and resisted wrist extension MVCs, in terms of amplitude and reproducibility, and to examine the effect of electrode positioning.

METHODS:

Twelve subjects participated. EMG from right forearm extensors, from four electrode pairs, was recorded during MVCs, on three separate occasions.

RESULTS:

The group mean EMG amplitudes for resisted wrist extension were 1.2–1.7 times greater than those for hand grip. Resisted wrist extension showed better reproducibility than hand grip.

CONCLUSIONS:

The results indicate that the use of resisted wrist extension is a more accurate measurement of maximal effort of wrist extensor contractions than using hand grip and should increase the precision in EMG recordings from forearm extensor muscles, which in turn will increase the quality of risk assessments that are based on these.

Evaluation of pliers' grip spans in the maximum gripping task and sub-maximum cutting task

A total of 25 males participated to investigate the effects of the grip spans of pliers on the total grip force, individual finger forces and muscle activities in the maximum gripping task and wire-cutting tasks. In the maximum gripping task, results showed that the 50-mm grip span had significantly higher total grip strength than the other grip spans. In the cutting task, the 50-mm grip span also showed significantly higher grip strength than the 65-mm and 80-mm grip spans, whereas the muscle activities showed a higher value at 80-mm grip span. The ratios of cutting force to maximum grip strength were also investigated. Ratios of 30.3%, 31.3% and 41.3% were obtained by grip spans of 50-mm, 65-mm, and 80-mm, respectively. Thus, the 50-mm grip span for pliers might be recommended to provide maximum exertion in gripping tasks, as well as lower maximum-cutting force ratios in the cutting tasks.

The Potential Risk Factors Relevant to Lateral Epicondylitis by Wrist Coupling Posture

The use of awkward wrist postures and unskilled techniques might induce lateral epicondylitis. This study thus investigated the effects of wrist deviation combined with extension and movement velocity on the dynamic performances of the wrist muscles during the coupling posture via a custom-made bi-planar isokinetic dynamometer. Thirty subjects were recruited to perform the isokinetic testing. We measured the muscle strengths and activities for the wrist extensors and flexors during concentric and eccentric contractions at three movement velocities, 30°s^-1, 90°s^-1, and 180°s^-1, combined with three wrist postures, neutral position (NP), radial deviation (RD), and ulnar deviation (UD). The root mean square (RMS) of the electromyographic signal in the extensor digitorum communis (EDC), normalized peak torque of extensors, and ratio of normalized peak torque between wrist extensors and flexors, were all greater in the NP than RD and UD in both contractions. The ratio of RMS between EDC and flexor digitorum superficialis (FDS) had a significantly greater value in RD than UD during the concentric contraction. The EDC showed significantly higher activity at the fast velocity in both contractions. Nevertheless, a significantly higher RMS of the electromyographic signal between EDC and FDS and the ratio of strength between wrist extensors and flexors were found at slow velocity in both contractions. The wrist deviation combined with extension and movement velocity of the wrist joint should thus be considered as influential factors which might alter the dynamic performances, and may result in further injury of the elbow joint.

Investigation of the EMG-time relationship of the biceps Brachii muscle during contractions

[Purpose] This study investigated the changes in the slope of EMG-time curves (relationship) at the maximal and different levels of dynamic (eccentric and concentric) and static (isometric) contractions. [Subjects and Methods] The subject was a 17 year-old male adolescent. The surface EMG signal of the dominant arm’s biceps brachii (BB) was recorded through electrodes placed on the muscle belly. [Results] The results obtained during the contractions show that the regression slope was very close to 1.00 during concentric contraction, whereas those of eccentric and isometric contractions were lower. Significant differences were found for the EMG amplitude and time lags among the contractions. [Conclusion] The results show that the EMG signal of the BB varies among the three modes of contraction and the relationship of the EMG amplitude with a time lag gives the best fit during concentric contraction.