Electromyographic models to assess muscle fatigue

The deflection of fatigued neck

The human neck is a unique mechanical structure, highly flexible but fatigue prone. The rising prevalence of neck pain and chronic injuries has been attributed to increasing exposure to fatigue loading in activities such as prolonged sedentary work and overuse of electronic devices. However, a causal relationship between fatigue and musculoskeletal mechanical changes remains elusive. This work aimed to establish this relationship through a unique experiment design, inspired by a cantilever beam mechanical model of the neck, and an orchestrated deployment of advanced motion-force measurement technologies including dynamic stereo-radiographic imaging. As a group of 24 subjects performed sustained-till-exhaustion neck exertions in varied positions-neutral, extended, and flexed, their cervical spine musculoskeletal responses were measured. Data verified the occurrence of fatigue and revealed fatigue-induced neck deflection which increased cervical lordosis or kyphosis by 4-5° to 11°, depending on the neck position. This finding and its interpretations render a renewed understanding of muscle fatigue from a more unified motor control perspective as well as profound implications on neck pain and injury prevention.

Music and Caffeine Intake Effects on Gait, and Its Relationship with Psychological Parameters, in Middle-Aged Women

Purpose

This study aimed to explore the combined effects of caffeine intake and listening to music on walking parameters, and its relationship with psychological variables (fatigue and exercise enjoyment) in middle-aged women.

Patients and Methods

Sixteen healthy middle-aged women, aged between 50 and 60 years old, participated in this study. Their walking parameters (distance, number of steps, steps number/minute, cadence and walking speed) were assessed using the 6-minute walking test (6MWT) in four task conditions: in no-music/no-caffeine, no-music/with caffeine, with music/no-caffeine, and with music/with caffeine conditions. Besides, exercise enjoyment and fatigue were evaluated using the Physical Activity Enjoyment Scale (PACES-8) and rating of perceived exertion (RPE) questionnaires, respectively.

Results

As a result, we found that 100 mg of caffeine intake significantly (p < 0.05) improved walking parameters such as distance, cadence and number of steps during both simple (p < 0.05) and dual-task, while listening to preferred music, where optimal results were found (p < 0.01) with a large effect size (η2p >0.14). Listening to music was sufficient to significantly improve the distance (p < 0.001), cadence (p < 0.001), and walking speed (p < 0.05) values. Besides, both caffeine intake and/or listening to music significantly (p < 0.05 with large effect size (η2p >0.14)) decreased the feeling of fatigue and increased exercise enjoyment while walking in healthy middle-aged women.

Conclusion

In conclusion, caffeine intake seems to positively influence gait capacities, and its combined effects with listening to music, mainly preferred ones, would boost these beneficial effects in middle-aged women.

Time Course of Neuromuscular Fatigue During Different Resistance Exercise Loadings in Power Athletes, Strength Athletes, and Nonathletes

ABSTRACT

Kotikangas, J, Walker, S, Peltonen, H, and Häkkinen, K. Time course of neuromuscular fatigue during different resistance exercise loadings in power athletes, strength athletes, and nonathletes. J Strength Cond Res 38(7): 1231-1242, 2024-Training background may affect the progression of fatigue and neuromuscular strategies to compensate for fatigue during resistance exercises. Thus, our aim was to examine how training background affects the time course of neuromuscular fatigue in response to different resistance exercises. Power athletes (PA, n = 8), strength athletes (SA, n = 8), and nonathletes (NA, n = 7) performed hypertrophic loading (HL, 5 × 10 × 10RM), maximal strength loadings (MSL, 7 × 3 × 3RM) and power loadings (PL, 7 × 6 × 50% of 1 repetition maximum) in back squat. Average power (AP), average velocity (VEL), surface electromyography (sEMG) amplitude (sEMGRMS), and sEMG mean power frequency (sEMGMPF) were measured within all loading sets. During PL, greater decreases in AP occurred from the beginning of SET1 to SET7 and in VEL to both SET4 and SET7 in NA compared with SA (p < 0.01, g > 1.84). During HL, there were various significant group × repetition interactions in AP within and between sets (p < 0.05, ηp2 > 0.307), but post hoc tests did not indicate significant differences between the groups (p > 0.05, g = 0.01-0.93). During MSL and HL, significant within-set and between-set decreases occurred in AP (p < 0.001, ηp2 > 0.701) and VEL (p < 0.001, ηp2 > 0.748) concurrently with increases in sEMGRMS (p < 0.01, ηp2 > 0.323) and decreases in sEMGMPF (p < 0.01, ηp2 > 0.242) in all groups. In conclusion, SA showed fatigue resistance by maintaining higher AP and VEL throughout PL. During HL, PA tended to have the greatest initial fatigue response in AP, but between-group comparisons were nonsignificant despite large effect sizes (g > 0.8). The differences in the progression of neuromuscular fatigue may be related to differing neural activation strategies between the groups, but further research confirmation is required.

The impact of positive-pressure breathing apparatus on muscle fatigue of volunteer firefighter

Muscle fatigue is one of the leading causes that contributes tremendously to injuries among volunteer firefighters in the workplace. The purpose of this study was to investigate the impact of positive-pressure breathing apparatus on muscle fatigue in the shoulder, back, and legs of volunteer firefighters. A total of 60 volunteer firefighters were recruited to perform a running task on a motorized treadmill in a controlled laboratory environment. Surface electromyography and rating of perceived exertion scores were collected from all participants every 60 seconds during the running task. Results show that the median frequency values for all measured muscle groups were significantly lower, and the rating of perceived exertion score was significantly higher after running with the positive-pressure breathing apparatus. Meanwhile, there were no significant differences in the median frequency values for the upper trapezius, erector spinae, and biceps femoris between the initial and final periods of running task without load. However, the median frequency values with load for gastrocnemius, rectus femoris, and tibialis anterior exhibited a greater downward trend compared to those without load. Additionally, using a breathing apparatus can cause asymmetric muscle fatigue in bilateral upper trapezius, erector spinae, gastrocnemius, and tibialis anterior muscles. The decreased performance due to muscle fatigue increases the risk of accidents, thereby posing a threat to the safety of volunteer firefighters. This study offers valuable insights into the effects of positive-pressure breathing apparatus on muscle fatigue among volunteer firefighters. These results may serve as a reference for developing improved fatigue management strategies and optimizing the design features of breathing apparatus.

Neuromechanical Differences between Pronated and Supinated Forearm Positions during Upper-Body Wingate Tests

Arm-cycling is a versatile exercise modality with applications in both athletic enhancement and rehabilitation, yet the influence of forearm orientation remains understudied. Thus, this study aimed to investigate the impact of forearm position on upper-body arm-cycling Wingate tests. Fourteen adult males (27.3 ± 5.8 years) underwent bilateral assessments of handgrip strength in standing and seated positions, followed by pronated and supinated forward arm-cycling Wingate tests. Electromyography (EMG) was recorded from five upper-extremity muscles, including anterior deltoid, triceps brachii lateral head, biceps brachii, latissimus dorsi, and brachioradialis. Simultaneously, bilateral normal and propulsion forces were measured at the pedal-crank interface. Rate of perceived exertion (RPE), power output, and fatigue index were recorded post-test. The results showed that a pronated forearm position provided significantly (p < 0.05) higher normal and propulsion forces and triceps brachii muscle activation patterns during arm-cycling. No significant difference in RPE was observed between forearm positions (p = 0.17). A positive correlation was found between seated handgrip strength and peak power output during the Wingate test while pronated (dominant: p = 0.01, r = 0.55; non-dominant: p = 0.03, r = 0.49) and supinated (dominant: p = 0.03, r = 0.51; don-dominant: p = 0.04, r = 0.47). Fatigue changed the force and EMG profile during the Wingate test. In conclusion, this study enhances our understanding of forearm position's impact on upper-body Wingate tests. These findings have implications for optimizing training and performance strategies in individuals using arm-cycling for athletic enhancement and rehabilitation.

Research application of session-RPE in monitoring the training load of elite endurance athletes

Purpose

TRIMP and sRPE are both representative indicators of training load(TL), and the correlation between two has been widely demonstrated across various sports. The aim of this study was to investigate the reliability of sRPE-TRIMP correlation across different intensities/duration of training in cross-country skiing, and whether sRPE can serve as an validity supplement to TRIMP data in cases of lost heart rate data.

Method

10 athletes were used as the experimental objects. The intensity, duration and RPE of 273 different types of training sessions were collected, and statistical methods were used for data analysis.

Results

1. There was a significant correlation between sRPE and TRIMP (r = 0.68, p < 0.05), but the correlation differs among the LIT, MIT and HIT groups (r = 0.70, 0.46, r = 0.31, p < 0.05) 2. sRPE-TRIMP correlation among three different time duration in the LIT group (0-60 min, 60-120 min and 120-180 min), are all highly significant (r = 0.70, 0.67, 0.69, p < 0.05) and the LRsRPE-TRIMP of 3 duration have no significant differences (chow test, p > 0.05). 3. The difference in actual training duration between samples was the main reason for the difference in the application effect of sRPE, because the actual training duration ratio of LIT was 89.7 ± 16.4%; MIT, 98.5 ± 6.2%; and HIT, 94.4 ± 13.5%.

Conclusion

1. The linear relationship between sRPE and TRIMP (LRsRPE-TRIMP) is more significant in LIT compared to that in MIT and HIT. 2. Variations in the duration of LIT sessions do not affect the consistency of the relationship between sRPE and TRIMP. 3. Discrepancies between actual and planned training durations directly impact the significance of the LRsRPE-TRIMP.

Review and comparison of linear algorithms to quantify muscle fatigue based on sEMG signals

Surface electromyography techniques are widely used in field of motion analysis and ergonomics combining precise muscular activation assessment with low-invasiveness and wearability. The aim of this investigation is to identify the myoelectrical manifestations of fatigue and to compare the effectiveness of sEMG-based quantitative indices for fatigue assessment. The investigated indexes are the ARV and RMS signal amplitudes, the mean frequency, the median frequency, the Dimitrov index, the instantaneous mean frequency and Wavelet distribution-based WIRE51 index. Two different protocols were developed, and the activity of the lateral deltoid and middle trapezius muscles was recorded. The WIRE51 index is found to have the highest sensitivity in the detection of the difference between the repetitions of each exercise for both protocols. Due to the lack of a unified standard for the performance comparison of fatigue indices, a correlation analysis was carried out between the result provided by the indices and the subjective fatigue perception employing the RPE scale.

Analysis of pelvic floor muscle electromyography parameters in women with or without sexual dysfunction

Background To investigate the differences in pelvic floor muscle (PFM) electromyography (EMG) parameters between women with or without sexual dysfunction (FSD) and their correlations. Methods Women who voluntarily participated in a questionnaire-based survey on sexual function and underwent PFM EMG in Weifang People's Hospital during the period from March 2021 to December 2021 were retrospectively enrolled. The female sexual (dys)function was measured using the Female Sexual Function Index. Glazer PFM EMG was performed using a Melander instrument (MLD A2 Deluxe). The differences in PFM EMG parameters between women with or without FSD were compared, and the relationships between PFM EMG parameters and FSD were analysed using multiple linear regression models. Results A total of 305 women were enrolled, with 163 in the FSD group and 142 in the non-FSD group. Comparisons of PFM EMG parameters between these two groups revealed that the FSD group had significantly higher peak EMG amplitude during the phasic (flick) contractions and shorter recovery latency during the tonic contractions than the non-FSD group (both P P Conclusions The results of the pelvic floor EMG in this study suggest that the pelvic floor muscles of women with FSD may be more susceptible to fatigue, and may have poorer coordination of their pelvic floor muscles.

An assessment of co-contraction in reinnervated muscle

Aim: To investigate co-contraction in reinnervated elbow flexor muscles following a nerve transfer. Materials & methods: 12 brachial plexus injury patients who received a nerve transfer to reanimate elbow flexion were included in this study. Surface electromyography (EMG) recordings were used to quantify co-contraction during sustained and repeated isometric contractions of reinnervated and contralateral uninjured elbow flexor muscles. Reuslts: For the first time, this study reveals reinnervated muscles demonstrated a trend toward higher co-contraction ratios when compared with uninjured muscle and this is correlated with an earlier onset of muscle fatigability. Conclusion: Measurements of co-contraction should be considered within muscular function assessments to help drive improvements in motor recovery therapies.

Facial electromyography during exercise using soft electrode array: A feasibility study

The use of wearable sensors for real-time monitoring of exercise-related measures has been extensively studied in recent years (e.g., performance enhancement, optimizing athlete's training, and preventing injuries). Surface electromyography (sEMG), which measures muscle activity, is a widely researched technology in exercise monitoring. However, due to their cumbersome nature, traditional sEMG electrodes are limited. In particular, facial EMG (fEMG) studies in physical training have been limited, with some scarce evidence suggesting that fEMG may be used to monitor exercise-related measurements. Altogether, sEMG recordings from facial muscles in the context of exercise have been examined relatively inadequately. In this feasibility study, we assessed the ability of a new wearable sEMG technology to measure facial muscle activity during exercise. Six young, healthy, and recreationally active participants (5 females), performed an incremental cycling exercise test until exhaustion, while facial sEMG and vastus lateralis (VL) EMG were measured. Facial sEMG signals from both natural expressions and voluntary smiles were successfully recorded. Stable recordings and high-resolution facial muscle activity mapping were achieved during different exercise intensities until exhaustion. Strong correlations were found between VL and multiple facial muscles' activity during voluntary smiles during exercise, with statistically significant coefficients ranging from 0.80 to 0.95 (p<0.05). This study demonstrates the feasibility of monitoring facial muscle activity during exercise, with potential implications for sports medicine and exercise physiology, particularly in monitoring exercise intensity and fatigue.

Myoelectric, Myo-Oxygenation, and Myotonometry Changes during Robot-Assisted Bilateral Arm Exercises with Varying Resistances

Robot-assisted bilateral arm training has demonstrated its effectiveness in improving motor function in individuals post-stroke, showing significant enhancements with increased repetitions. However, prolonged training sessions may lead to both mental and muscle fatigue. We conducted two types of robot-assisted bimanual wrist exercises on 16 healthy adults, separated by one week: long-duration, low-resistance workouts and short-duration, high-resistance exercises. Various measures, including surface electromyograms, near-infrared spectroscopy, heart rate, and the Borg Rating of Perceived Exertion scale, were employed to assess fatigue levels and the impacts of exercise intensity. High-resistance exercise resulted in a more pronounced decline in electromyogram median frequency and recruited a greater amount of hemoglobin, indicating increased muscle fatigue and a higher metabolic demand to cope with the intensified workload. Additionally, high-resistance exercise led to increased sympathetic activation and a greater sense of exertion. Conversely, engaging in low-resistance exercises proved beneficial for reducing post-exercise muscle stiffness and enhancing muscle elasticity. Choosing a low-resistance setting for robot-assisted wrist movements offers advantages by alleviating mental and physiological loads. The reduced training intensity can be further optimized by enabling extended exercise periods while maintaining an approximate dosage compared to high-resistance exercises.

Stretchable, Flexible, Breathable, Self-Adhesive Epidermal Hand sEMG Sensor System

Hand function rehabilitation training typically requires monitoring the activation status of muscles directly related to hand function. However, due to factors such as the small surface area for hand-back electrode placement and significant skin deformation, the continuous real-time monitoring of high-quality surface electromyographic (sEMG) signals on the hand-back skin still poses significant challenges. We report a stretchable, flexible, breathable, and self-adhesive epidermal sEMG sensor system. The optimized serpentine structure exhibits a sufficient stretchability and filling ratio, enabling the high-quality monitoring of signals. The carving design minimizes the distribution of connecting wires, providing more space for electrode reservation. The low-cost fabrication design, combined with the cauterization design, facilitates large-scale production. Integrated with customized wireless data acquisition hardware, it demonstrates the real-time multi-channel sEMG monitoring capability for muscle activation during hand function rehabilitation actions. The sensor provides a new tool for monitoring hand function rehabilitation treatments, assessing rehabilitation outcomes, and researching areas such as prosthetic control.

Effects of caffeine supplementation on anaerobic power and muscle activity in youth athletes

This study aimed to investigate the effects of caffeine ingestion on anaerobic performance and muscle activity in young athletes. In this randomized, double-blind, and placebo-controlled study, ten highly trained male post-puberal futsal players aged 15.9 ± 1.2 years conducted two laboratory sessions. Athletes performed the Wingate test 60 min after ingestion of caffeine (CAF, 6 mg/kg body mass) or placebo (PL, dextrose) (blinded administration). Peak power, mean power, and the fatigue index were assessed. During the performance of the Wingate test, electromyographic (EMG) data were recorded from selected lower limbs muscles to determine the root mean square (RMS), mean power frequency (MPF), and median power frequency (MDPF) as frequency domain parameters and wavelet (WT) as time-frequency domain parameters. Caffeine ingestion increased peak (0.80 ± 0.29 W/Kg; p = 0.01; d = 0.42) and mean power (0.39 ± 0.02 W/Kg; p = 0.01; d = 0.26) but did not significantly affect the fatigue index (52.51 ± 9.48%, PL: 49.27 ± 10.39%; p = 0.34). EMG data showed that the MPF and MDPF parameters decreased and the WT increased, but caffeine did not have a significant effect on these changes (p > 0.05). Moreover, caffeine ingestion did not significantly affect RMS changes in the selected muscles (p > 0.05). Here we showed that acute caffeine ingestion improved anaerobic performance without affecting EMG parameters in young male futsal athletes.

Impact of Starting Knee Flexion Angle on Muscle Activity and Performance during Plyometrics without Jumping

Most of the existing research has focused on jump plyometrics, where landing reaction forces must be dissipated among lower limb articulations. In contrast, the investigation of resisted plyometrics without jumping, devoid of such landing forces, remains relatively limited. This study aimed to (i) investigate the impact of resisted plyometrics without jumping at two knee flexion angles (60 and 90 degrees) on vastus muscle activity relative to limb dominance and (ii) assess strength, power, and work during the concentric-eccentric phases of these exercises. Thirty-one healthy participants underwent quantification of lower limb muscle amplitude, strength, power, and work during resisted plyometrics without jumping from both 60° and 90° knee flexion positions. After anthropometric evaluations, participants used a dynamometer with a load equal to 80% of body weight while wireless surface electromyography electrodes recorded data. Statistical analyses utilized paired t-tests or nonparametric equivalents and set significance at p ≤ 0.05. Results showed significantly higher muscle activity in the vastus medialis (VM) (dominant: 47.4%, p = 0.0008, rs = 0.90; nondominant: 54.8%, p = 0.047, rs = 0.88) and vastus lateralis (VL) (dominant: 46.9%, p = 0.0004, rs = 0.86; nondominant: 48.1%, p = 0.021, rs = 0.67) muscles when exercises started at 90° knee flexion, regardless of limb dominance. Substantial intermuscle differences occurred at both 60° (50.4%, p = 0.003, rs = 0.56) and 90° (54.8%, p = 0.005, rs = 0.62) knee flexion, favoring VM in the nondominant leg. Concentric and eccentric strength, power, and work metrics significantly increased when initiating exercises from a 90° position. In conclusion, commencing resisted plyometrics without jumping at a 90° knee flexion position increases VM and VL muscle activity, regardless of limb dominance. Furthermore, it enhances strength, power, and work, emphasizing the importance of knee flexion position customization for optimizing muscle engagement and functional performance.

Wrist Extensor Muscle Fatigue During a Dual Task With Two Muscular and Cognitive Load Levels in Younger and Older Adults

OBJECTIVE

To examine the effect of concurrent physical and cognitive demands as well as age on indicators of muscle fatigue at the wrist.

BACKGROUND

There are few studies examining risk indicators for musculoskeletal disorders associated with work-related physical and cognitive demands that often occur simultaneously in the workplace.

METHODS

Twenty-four gender-balanced older and 24 gender-balanced younger (mean age 60 and 23 years) participants performed four 30 min dual tasks. Tasks differed by the muscular load level during force tracking: 5% and 10% of maximum voluntary contraction force (MVC) and concurrent cognitive demands on the working memory: easy and difficult. Muscle fatigue was assessed by MVC decline and changes in surface electromyography (increased root mean square: RMS, decreased median frequency: MF) at the extensor digitorum (ED) and extensor carpi ulnaris (EU).

RESULTS

A decline in MVC was found in all participants when tracking was performed at 10% MVC (mean ± SD: 137.9 ± 49.2 - 123.0 ± 45.3 N). Irrespective of age, muscular, or cognitive load, RMS increased (ED 12.3 ± 6.5 - 14.1 ± 7.0% MVE, EU 15.4 ± 7.6 - 16.9 ± 8.6% MVE) and MF decreased (ED 85.4 ± 13.6 - 83.2 ± 12.8 Hz, EU 107.2 ± 17.1 - 104.3 ± 16.7 Hz) in both muscles. However, changes in MF of EU tended to be more pronounced in the older group at higher cognitive and lower muscular load, without reaching statistical significance.

CONCLUSION

Maximum voluntary contraction indicated no interaction between muscle fatigue, cognitive load, or age. However, the tendencies toward altered muscle activity due to an increase in cognitive load and older age suggest muscular adaptations while maintaining tracking performance during the onset of fatigue signs in the sEMG signal.

APPLICATION

If the tendencies in muscle activity are confirmed by further studies, ergonomic assessments in industrial workplaces should consider cognitive load and age when describing the risk of musculoskeletal disorders.

Data-Driven Approach for Upper Limb Fatigue Estimation Based on Wearable Sensors

Muscle fatigue is defined as a reduced ability to maintain maximal strength during voluntary contraction. It is associated with musculoskeletal disorders that affect workers performing repetitive activities, affecting their performance and well-being. Although electromyography remains the gold standard for measuring muscle fatigue, its limitations in long-term work motivate the use of wearable devices. This article proposes a computational model for estimating muscle fatigue using wearable and non-invasive devices, such as Optical Fiber Sensors (OFSs) and Inertial Measurement Units (IMUs) along the subjective Borg scale. Electromyography (EMG) sensors are used to observe their importance in estimating muscle fatigue and comparing performance in different sensor combinations. This study involves 30 subjects performing a repetitive lifting activity with their dominant arm until reaching muscle fatigue. Muscle activity, elbow angles, and angular and linear velocities, among others, are measured to extract multiple features. Different machine learning algorithms obtain a model that estimates three fatigue states (low, moderate and high). Results showed that between the machine learning classifiers, the LightGBM presented an accuracy of 96.2% in the classification task using all of the sensors with 33 features and 95.4% using only OFS and IMU sensors with 13 features. This demonstrates that elbow angles, wrist velocities, acceleration variations, and compensatory neck movements are essential for estimating muscle fatigue. In conclusion, the resulting model can be used to estimate fatigue during heavy lifting in work environments, having the potential to monitor and prevent muscle fatigue during long working shifts.

Changes in Neck and Shoulder Muscles Fatigue Threshold When Using a Passive Head/Neck Supporting Exoskeleton During Repetitive Overhead Tasks

OBJECTIVE

This study aimed to investigate the effects of a head/neck supporting exoskeleton (HNSE) on the electromyographic fatigue threshold (EMGFT) of the neck and shoulder muscles during a simulated overhead work task.

BACKGROUND

Overhead work is a well-known risk factor for neck and shoulder musculoskeletal disorders due to the excessive strain imposed on the muscles and joints in these regions.

METHOD

Fourteen healthy males performed a repetitive overhead nut fastening/unfastening task to exhaustion while wearing and not wearing the HNSE at two neck extension angles (40% and 80% of neck maximum range of motion). Electromyographic signals were continuously recorded from the right and left sternocleidomastoid (SCMR, SCML), splenius capitis (SCR, SCL), upper trapezius (UTR, UTL), and anterior deltoid (ADR, ADL) muscles. The normalized electromyographic amplitude (nEMG) data was time normalized, and a bisegmental linear regression was applied to determine the muscle fatigue break point.

RESULTS

The results showed a significant increase in fatigue threshold time in the SCMR (p < .001), SCML (p = .002), and UTR (p = .037) muscles when the HNSE was used. However, the EMGFT times for the right and left deltoid and left trapezius muscles showed a nonsignificant reduction due to the head/neck support exoskeleton use. In addition, the neck extension angle did not reveal a significant effect on muscles' EMGFT time.

CONCLUSION

Overall, the findings confirmed a significant delay in fatigue onset in sternocleidomastoid muscles, as measured by the electromyographic fatigue threshold. This finding suggests that the HNSE can be an effective ergonomic intervention for reducing the risk of musculoskeletal disorders in overhead workers. However, further studies are needed to investigate the effect of the HNSE at other neck extension angles and more realistic tasks to ensure the generalizability of our results.

APPLICATION

The present findings emphasize the application of the fatigue onset time to evaluate the effectiveness of ergonomic interventions, including exoskeletons, which can subsequently be utilized to alleviate postural demands and reduce the risk of musculoskeletal disorders.

Analysis of Kinematic and Muscular Fatigue in Long-Distance Swimmers

Muscle fatigue is a complex phenomenon that is influenced by the type of activity performed and often manifests as a decline in motor performance (mechanical failure). The purpose of our study was to investigate the compensatory strategies used to mitigate mechanical failure. A cohort of 21 swimmers underwent a front-crawl swimming task, which required the consistent maintenance of a constant speed for the maximum duration. The evaluation included three phases: non-fatigue, pre-mechanical failure, and mechanical failure. We quantified key kinematic metrics, including velocity, distance travelled, stroke frequency, stroke length, and stroke index. In addition, electromyographic (EMG) metrics, including the Root-Mean-Square amplitude and Mean Frequency of the EMG power spectrum, were obtained for 12 muscles to examine the electrical manifestations of muscle fatigue. Between the first and second phases, the athletes covered a distance of 919.38 ± 147.29 m at an average speed of 1.57 ± 0.08 m/s with an average muscle fatigue level of 12%. Almost all evaluated muscles showed a significant increase (p < 0.001) in their EMG activity, except for the latissimus dorsi, which showed a 17% reduction (ES 0.906, p < 0.001) during the push phase of the stroke cycle. Kinematic parameters showed a 6% decrease in stroke length (ES 0.948, p < 0.001), which was counteracted by a 7% increase in stroke frequency (ES -0.931, p < 0.001). Notably, the stroke index also decreased by 6% (ES 0.965, p < 0.001). In the third phase, characterised by the loss of the ability to maintain the predetermined rhythm, both EMG and kinematic parameters showed reductions compared to the previous two phases. Swimmers employed common compensatory strategies for coping with fatigue; however, the ability to maintain a predetermined motor output proved to be limited at certain levels of fatigue and loss of swimming efficiency (Protocol ID: NCT06069440).

Vibration comfort assessment of tractor drivers based on sEMG and vibration signals

In order to comprehensively evaluate the driver's vibration comfort under different vibration conditions, eighteen subjects were required to drive a tractor at different speeds on field and asphalt roads respectively in the real vehicle experiment. The sEMG signals and vibration acceleration signals of the subjects were recorded. And the time-frequency domain analysis of sEMG signals and acceleration signals were used to determine the relationship among the characteristic indexes, tractor speed and road surfaces. The relevance analysis showed that there was a significant correlation between the integral electromyography (iEMG) and median frequency (MF) of the middle scalene muscle, erector spinae muscle and gastrocnemius muscle, the RMS of weighted acceleration (aw) of the neck, waist and legs, and the subjective comfort feelings. It was proven that the tractor speed had a significant impact on human body vibration based on the ANOVA result (p < 0.05). With the increase of running speed, the time domain indexes of sEMG signals including iEMG, RMS and the vibration acceleration signals of the testing body parts increased significantly, while the amplitudes of frequency domain indexes decreased. Therefore, a quantitative regression evaluation model for the comfort of the neck, waist and legs integrating the sEMG and vibration signals was established, and its relative errors were 5.05, 4.38 and 6.12% respectively. This proposed assessment model can combine characteristics of the partial and overall vibration response of human body effectively, predict the tractor driver's vibration comfort accurately, provide a theoretical basis for the evaluation of tractor cab vibration comfort.

Enhanced low-threshold motor unit capacity during endurance tasks in patients with spinal muscular atrophy using pyridostigmine

OBJECTIVE

To investigate the electrophysiological basis of pyridostigmine enhancement of endurance performance documented earlier in patients with spinal muscular atrophy (SMA).

METHODS

We recorded surface electromyography (sEMG) in four upper extremity muscles of 31 patients with SMA types 2 and 3 performing endurance shuttle tests (EST) and maximal voluntary contraction (MVC) measurements during a randomized, double blind, cross-over, phase II trial. Linear mixed effect models (LMM) were used to assess the effect of pyridostigmine on (i) time courses of median frequencies and of root mean square (RMS) amplitudes of sEMG signals and (ii) maximal RMS amplitudes during MVC measurements. These sEMG changes over time indicate levels of peripheral muscle fatigue and recruitment of new motor units, respectively.

RESULTS

In comparison to a placebo, patients with SMA using pyridostigmine had fourfold smaller decreases in frequency and twofold smaller increases in amplitudes of sEMG signals in some muscles, recorded during ESTs (p < 0.05). We found no effect of pyridostigmine on MVC RMS amplitudes.

CONCLUSIONS

sEMG parameters indicate enhanced low-threshold (LT) motor unit (MU) function in upper-extremity muscles of patients with SMA treated with pyridostigmine. This may underlie their improved endurance.

SIGNIFICANCE

Our results suggest that enhancing LT MU function may constitute a therapeutic strategy to reduce fatigability in patients with SMA.

Challenges of neural interfaces for stroke motor rehabilitation

More than 85% of stroke survivors suffer from different degrees of disability for the rest of their lives. They will require support that can vary from occasional to full time assistance. These conditions are also associated to an enormous economic impact for their families and health care systems. Current rehabilitation treatments have limited efficacy and their long-term effect is controversial. Here we review different challenges related to the design and development of neural interfaces for rehabilitative purposes. We analyze current bibliographic evidence of the effect of neuro-feedback in functional motor rehabilitation of stroke patients. We highlight the potential of these systems to reconnect brain and muscles. We also describe all aspects that should be taken into account to restore motor control. Our aim with this work is to help researchers designing interfaces that demonstrate and validate neuromodulation strategies to enforce a contingent and functional neural linkage between the central and the peripheral nervous system. We thus give clues to design systems that can improve or/and re-activate neuroplastic mechanisms and open a new recovery window for stroke patients.

sEMG-based prediction of human forearm movements utilizing a biomechanical model based on individual anatomical/ physiological measures and a reduced set of optimization parameters

For assistive devices such as active orthoses, exoskeletons or other close-to-body robotic-systems, the immediate prediction of biological limb movements based on biosignals in the respective control system can be used to enable intuitive operation also by untrained users e.g. in healthcare, rehabilitation or industrial scenarios. Surface electromyography (sEMG) signals from the muscles that drive the limbs can be measured before the actual movement occurs and, hence, can be used as source for predicting limb movements. The aim of this work was to create a model that can be adapted to a new user or movement scenario with little measurement and computing effort. Therefore, a biomechanical model is presented that predicts limb movements of the human forearm based on easy to measure sEMG signals of the main muscles involved in forearm actuation (lateral and long head of triceps and short and long head of biceps). The model has 42 internal parameters of which 37 were attributed to 8 individually measured physiological measures (location of acromion at the shoulder, medial/lateral epicondyles as well as olecranon at the elbow, and styloid processes of radius/ulna at the wrist; maximum muscle forces of biceps and triceps). The remaining 5 parameters are adapted to specific movement conditions in an optimization process. The model was tested in an experimental study with 31 subjects in which the prediction quality of the model was assessed. The quality of the movement prediction was evaluated by using the normalized mean absolute error (nMAE) for two arm postures (lower, upper), two load conditions (2 kg, 4 kg) and two movement velocities (slow, fast). For the resulting 8 experimental combinations the nMAE varied between nMAE = 0.16 and nMAE = 0.21 (lower numbers better). An additional quality score (QS) was introduced that allows direct comparison between different movements. This score ranged from QS = 0.25 to QS = 0.40 (higher numbers better) for the experimental combinations. The above formulated aim was achieved with good prediction quality by using only 8 individual measurements (easy to collect body dimensions) and the subsequent optimization of only 5 parameters. At the same time, just easily accessible sEMG measurement locations are used to enable simple integration, e.g. in exoskeletons. This biomechanical model does not compete with models that measure all sEMG signals of the muscle heads involved in order to achieve the highest possible prediction quality.

A new force profile signal for a convex solution of muscle force estimation from electromyographic signals. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2023;2023:1-4. [PMID: 38082591 DOI: 10.1109/embc40787.2023.10340594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

High-Density Surface Electromyography (HD-sEMG) is a non-invasive technique for measuring the electrical activity of a muscle with multiple, closely spaced electrodes. Estimation of muscle force is one of the applications of HD-sEMG. Usually, validating different EMG-Force models entails simple movements limited to laboratory settings. The validity of these models in more ecological conditions, requesting force production over a wide frequency band, remains unknown. In this study, we, therefore, compare the results of force prediction using four different types of input force profiles that can be representative of daily life activities, and we investigate whether the crest factor of these different input signals affects force prediction. For predicting the force from sEMG signals, we used our real-time and convex methods. HD-sEMG signals were recorded with 144 channels from the biceps brachii, brachioradialis, and triceps (long, lateral, and medial head) muscles of 24 healthy subjects during random signal, random phase, Schroeder phase, and minimum crest factor (crestmin) signal. The correlation and coefficient of determination (R2) between measured and predicted forces were calculated for the different force feedback profiles. The crestmin signal showed significantly better results based on statistical tests (P-value < 0.05), with correlation and R2 equal to 0.92±0.03 and 0.86±0.05, respectively. The results demonstrate that the crest factor of input signals is a crucial parameter that can impact the performance of EMG-Force models and must be considered during training.Clinical Relevance- This study demonstrates that lower crest factor multisine force profiles result in improved fitness for force prediction and can be used as an alternative to random signals.

Analysis of the Hanging Actions and Operating Heights of Storage Furniture Suitable for the Elderly

The current functional scale design of storage furniture which the elderly use does not meet their needs, and unsuitable storage furniture may bring many physiological and psychological problems to their daily lives. The purpose of this study is to start with the hanging operation, to study the factors influencing the hanging operation heights of elderly people undergoing self-care in a standing posture and to determine the research methods to be used to study the appropriate hanging operation height of the elderly so as to provide data and theoretical support for the functional design scale of storage furniture suitable for the elderly. This study quantifies the situations of elderly people's hanging operation through an sEMG test performed on 18 elderly people at different hanging heights combined with a subjective evaluation before and after the operation and a curve fitting between the integrated sEMG indexes and the test heights. The test results show that the height of the elderly subjects had a significant effect on the hanging operation, and the main power muscles of the suspension operation were the anterior deltoid, upper trapezius and brachioradialis. Elderly people in different height groups had their own performance of the most comfortable hanging operation ranges. The suitable range for the hanging operation was 1536-1728 mm for seniors aged 60 or above whose heights were within the range of 1500-1799 mm, which could obtain a better action view and ensure the comfort of the operation. External hanging products, such as wardrobe hangers and hanging hooks, could also be determined according to this result.

Effects of Muscle Fatigue and Recovery on the Neuromuscular Network after an Intermittent Handgrip Fatigue Task: Spectral Analysis of Electroencephalography and Electromyography Signals

Mechanisms underlying exercise-induced muscle fatigue and recovery are dependent on peripheral changes at the muscle level and improper control of motoneurons by the central nervous system. In this study, we analyzed the effects of muscle fatigue and recovery on the neuromuscular network through the spectral analysis of electroencephalography (EEG) and electromyography (EMG) signals. A total of 20 healthy right-handed volunteers performed an intermittent handgrip fatigue task. In the prefatigue, postfatigue, and postrecovery states, the participants contracted a handgrip dynamometer with sustained 30% maximal voluntary contractions (MVCs); EEG and EMG data were recorded. A considerable decrease was noted in EMG median frequency in the postfatigue state compared with the findings in other states. Furthermore, the EEG power spectral density of the right primary cortex exhibited a prominent increase in the gamma band. Muscle fatigue led to increases in the beta and gamma bands of contralateral and ipsilateral corticomuscular coherence, respectively. Moreover, a decrease was noted in corticocortical coherence between the bilateral primary motor cortices after muscle fatigue. EMG median frequency may serve as an indicator of muscle fatigue and recovery. Coherence analysis revealed that fatigue reduced the functional synchronization among bilateral motor areas but increased that between the cortex and muscle.

A New Approach to Noninvasive-Prolonged Fatigue Identification Based on Surface EMG Time-Frequency and Wavelet Features

In sports, fatigue management is vital as adequate rest builds strength and enhances performance, whereas inadequate rest exposes the body to prolonged fatigue (PF) or also known as overtraining. This paper presents PF identification and classification based on surface electromyography (EMG) signals. An experiment was performed on twenty participants to investigate the behaviour of surface EMG during the inception of PF. PF symptoms were induced in accord with a five-day Bruce Protocol treadmill test on four lower extremity muscles: the biceps femoris (BF), rectus femoris (RF), vastus medialis (VM), and vastus lateralis (VL). The results demonstrate that the experiment successfully induces soreness, unexplained lethargy, and performance decrement and also indicate that the progression of PF can be observed based on changes in frequency features (ΔF _med and ΔF _mean) and time features (ΔRMS and ΔMAV) of surface EMG. This study also demonstrates the ability of wavelet index features in PF identification. Using a naïve Bayes (NB) classifier exhibits the highest accuracy based on time and frequency features with 98% in distinguishing PF on RF, 94% on BF, 9% on VL, and 97% on VM. Thus, this study has positively indicated that surface EMG can be used in identifying the inception of PF. The implication of the findings is significant in sports to prevent a greater risk of PF.

SELENON-Related Myopathy Across the Life Span, a Cross-Sectional Study for Preparing Trial Readiness

BACKGROUND

SELENON(SEPN1)-related myopathy (SELENON-RM) is a rare congenital neuromuscular disease characterized by proximal and axial muscle weakness, spinal rigidity, scoliosis and respiratory impairment. No curative treatment options exist, but promising preclinical studies are ongoing. Currently, natural history data are lacking, while selection of appropriate clinical and functional outcome measures is needed to reach trial readiness.

OBJECTIVE

We aim to identify all Dutch and Dutch-speaking Belgian SELENON-RM patients, deep clinical phenotyping, trial readiness and optimization of clinical care.

METHODS

This cross-sectional, single-center, observational study comprised neurological examination, functional measurements including Motor Function Measurement 20/32 (MFM-20/32) and accelerometry, questionnaires, muscle ultrasound, respiratory function tests, electro- and echocardiography, and dual-energy X-ray absorptiometry.

RESULTS

Eleven patients with genetically confirmed SELENON-RM were included (20±13 (3-42) years, 73% male). Axial and proximal muscle weakness were most pronounced. The mean MFM-20/32 score was 71.2±15.1%, with domain 1 (standing and transfers) being most severely affected. Accelerometry showed a strong correlation with MFM-20/32. Questionnaires revealed impaired quality of life, pain and problematic fatigue. Muscle ultrasound showed symmetrically increased echogenicity in all muscles. Respiratory function, and particularly diaphragm function, was impaired in all patients, irrespective of the age. Cardiac assessment showed normal left ventricular systolic function in all patients but abnormal left ventricular global longitudinal strain in 43% of patients and QRS fragmentation in 80%. Further, 80% of patients showed decreased bone mineral density on dual-energy X-ray absorptiometry scan and 55% of patients retrospectively experienced fragility long bone fractures.

CONCLUSIONS

We recommend cardiorespiratory follow-up as a part of routine clinical care in all patients. Furthermore, we advise vitamin D supplementation and optimization of calcium intake to improve bone quality. We recommend management interventions to reduce pain and fatigue. For future clinical trials, we propose MFM-20/32, accelerometry and muscle ultrasound to capture disease severity and possibly disease progression.

Are proximal and distal neuromuscular parameters able to predict hip and knee frontal plane kinematics during single-leg landing?

OBJECTIVE

To determine if proximal and distal neuromuscular parameters (EMG amplitude and median frequency - MDF) can predict frontal plane kinematics during single-leg landing.

STUDY DESIGN

Cross sectional study.

SETTING

Laboratory.

PARTICIPANTS

Fifteen participants (7 female) performed six single-leg landings with measures of frontal plane kinematics and EMG obtained 230 ms after first foot contact, totalizing 90 landings.

MAIN OUTCOME MEASURES

(i) 2D hip adduction [hip ADD] and knee frontal plane projection angle [knee FPPA]; (ii) EMG amplitude and MDF of gluteus medius [GMed], tensor fascia latae [TFL], peroneus longus [PL] and tibialis anterior [TA].

RESULTS

We observed that MDF of TA was a significant predictor of hip ADD (p = 0.037; β = -0.049 Hz; R²c = 0.30). Also, MDF of PL was significant predictor of knee FPPA (p = 0.043; β = 0.042 Hz; R²c = 0.37). Hip muscles and EMG amplitude parameters were not considered predictors of frontal plane kinematics.

CONCLUSION

The firing frequency of ankle muscles predicted the variance of hip and knee frontal plane kinematics during single-leg landing.

The use of non-linear tools to analyze the variability of force production as an index of fatigue: A systematic review

Background: Fatigue is a process that results in a decreased ability to produce force, and which could eventually affect performance and increase the risk of injury. Force variability analysis has been proposed to describe the level of fatigue with the purpose of detecting the development of fatigue. Variability is credited to play a functional and adaptive role through which the components of a system self-organize to solve a motor problem. Non-linear tools have been applied to analyze the variability of physiological signals, revealing that the structure of motor fluctuations provides relevant information about the functional role of variability. It has been suggested that the presence of lower complexity in the variability structure could reveal a less functional and adaptative state (e.g., ageing or illness). In the last years, an increased number of studies have applied these techniques to force variability analysis in relation to fatigue. Objective: To provide an overview of the current knowledge on the use of non-linear tools on force variability as a fatigue index. Methods: Following PRISMA guidelines, a systematic search of SPORTDiscus, Scopus, Web of Science and PubMed was carried out. Studies included were: a) original studies that analyzed the effect of fatigue on humans during an action focused on force production; b) published studies with their title and abstract in English; c) studies that applied non-linear tools on a signal directly related to force production. Results: Twenty-five studies were included in this review. The relationship between fatigue and the complexity of force variability, the type of action and relative intensity, the nature of the signal and the non-linear tools used, and the methods of data acquisition and processing were identified. Conclusion: The articles reviewed suggest that fatigue leads to a decrease in complexity mostly in isometric contractions, but this is not as clear in dynamic contractions. This fatigue-induced loss of complexity seems to be a result of changes in the nervous system at the central level, albeit triggered by peripheral mechanisms. It should be noted that non-linear tools are affected by the relative intensity of contraction, non-stationarity, and the acquisition and treatment of the signal.

Lower limb muscle fatigue after uphill walking in children with unilateral spastic cerebral palsy

Fatigue during walking is a common complaint in cerebral palsy (CP). The primary purpose of this study is to investigate muscle fatigue from surface electromyography (sEMG) measurements after a treadmill-based fatigue protocol with increasing incline and speed in children with CP with drop foot. The secondary purpose is to investigate whether changes in sagittal kinematics of hip, knee and ankle occur after fatigue. Eighteen subjects with unilateral spastic CP performed the protocol while wearing their ankle-foot orthosis and scored their fatigue on the OMNI scale of perceived exertion. The median frequency (MF) and root mean square (RMS) were used as sEMG measures for fatigue and linear mixed effects model were applied. The MF was significantly decreased in fatigued condition, especially in the affected leg and in the tibialis anterior and peroneus longus muscle. The RMS did not change significantly in fatigued condition, while the OMNI fatigue score indicated patients felt really fatigued. No changes in sagittal kinematics of hip, knee and ankle were found using statistical non-parametric mapping. In conclusion, the current fatigue protocol seems promising in inducing fatigue in a population with CP with drop foot and it could be used to expand knowledge on muscle fatigue during walking in CP.

Post-viral fatigue in COVID-19: A review of symptom assessment methods, mental, cognitive, and physical impairment

Coronavirus 2 is responsible for Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2), and the main sequela is persistent fatigue. Post-viral fatigue is common and affects patients with mild, asymptomatic coronavirus disease-2019 (COVID-19). However, the exact mechanisms involved in developing post-COVID-19 fatigue remain unclear. Furthermore, physical and cognitive impairments in these individuals have been widely described. Therefore, this review aims to summarize and propose tools from a multifaceted perspective to assess COVID-19 infection. Herein, we point out the instruments that can be used to assess fatigue in long-term COVID-19: fatigue in a subjective manner or fatigability in an objective manner. For physical and mental fatigue, structured questionnaires were used to assess perceived symptoms, and physical and cognitive performance assessment tests were used to measure fatigability using reduced performance.

Effect of Mental Task on Sex Differences in Muscle Fatigability: A Review

Previous research demonstrated that there are observable sex differences in developing muscle fatigue when mental task during fatiguing activity is present; however, there is no available review on this matter. Therefore, this review aimed to summarize the findings of previous studies investigating the effect of mental task on muscle fatigue in men and women. To conduct the review, we utilized searches using the electronic databases Web of Science, PubMed, Scopus, and EBSCO Cinahl Ultimate. The studies included had no limited publication date and examined the effects of mental task on muscle fatigue in a healthy adult population of any age. The evaluation was performed using the following criteria: time to failure, or subjective scale in various modifications (visual analog scale-VAS, rate of perceived effort-RPE, rate of perceived fatigue-RPF, rate of perceived discomfort-RPD). A total of seven studies met the set criteria, which were subsequently analyzed. Heavy mental task (more demanding math tasks) can reduce the time to failure for both men and women, with the reduction being more pronounced for women than for men. For light mental task (simple math tasks), no reduction in time to failure was observed to a great extent. The mental task in any of the included studies did not affect the subjective perception of fatigue, effort, discomfort, or pain. Although the studies investigating the effect of mental task on sex differences in muscle fatigability are limited, based on our findings we can assume that in jobs requiring heavier mental task, women may be more prone to the faster development of muscle fatigue; thus, employers might consider paying attention to the possibility of adequate rest.

Are the antagonist muscle fatigued during a prolonged isometric fatiguing elbow flexion at very low forces for young adults?

The aim of this study was to examine whether antagonist muscles may be fatigued during a prolonged isometric fatiguing elbow flexion at very low forces. Twelve healthy male subjects sustained an isometric elbow flexion at 10% maximal voluntary contraction torque until exhaustion while multichannel electromyographic signals were collected from the biceps brachii (BB) and triceps brachii (TB). Muscle fiber conduction velocity (CV) and fractal dimension (FD) of both muscles were calculated to reflect peripheral and central fatigue. CV and FD of TB as well as FD of BB decreased progressively during the sustained fatiguing contraction, while the CV of BB declined at the beginning of the contraction and then increased progressively until the end of the contraction. The result may indicate that during the sustained low-force isometric fatiguing contraction, antagonist muscle may be peripherally fatigued, and changes in coactivation activities were modulated not only by central neuronal mechanisms of common drive but also by peripheral metabolic factors.

The hamstrings are more impacted than the quadriceps after severe ankle sprain

Ankle sprains (AS) are common in the military population, with a prevalence 5 to 8 times higher than that for civilians. The aim of this study was to evaluate in patients with severe AS the impact of disuse on thigh muscle induced by unloading and immobilization due to care. This study focused on muscle trophicity and dynamometric strength. In this observational prospective study, assessments were repeated at 3 visits: close to injury, 15 and 30 days following the sprain. The injured limb was compared to the contralateral limb. A dynamometer assessment was used to monitor changes in strength and fatigue of the thigh muscles of both limbs. Isometric and isokinetic concentric evaluation of peak torque (PTiso and PTdyn), total work (Wt), and peak torque time integral (IPT) of thigh muscles. Full follow-up was obtained in 30 subjects. The injured limbs showed significant deficits in the mean (SD). The quadriceps PTiso and IPT deficits were -12.6% ± 1.9% (P < .0001) and -13.27% ± 1.8% (P < .0001), respectively. The quadriceps PTdyn showed a significant deficit since V2 (-12.2.5% ± 2.0). The quadriceps Wt presented a significant deficit of -4.2% ± 2.4 (P < .0007) at 1 month. The hamstring PTdyn deficit presented a mean loss of -16.5% ± 2.4% (P < .0001). The hamstring Wt deficit was -13.7% ± 2.3% (P < .001). The analysis of variance showed that the grade of the sprain had a significant effect on the quadriceps PTq deficit (P < .016) but not the type of discharge. Our study showed that disuse leads to a significant deficit in the strength of knee muscles within 1 month. It is noteworthy that the hamstrings are more affected than the quadriceps. The rehabilitation protocol to prevent the risk of iterative ankle injuries and secondary knee injuries should incorporate early training of both quadriceps and hamstrings.

Effect of fatigue on kinematics, kinetics and muscle activities of lower limbs during gait

Muscle fatigue, as a serious social problem, affects the performance of daily living activities, especially for workers. Decrease of movement control ability caused by muscle fatigue is one of the risk and intrinsic factors for occupational accidents, such as slips, trips, falls, etc. In order to reduce the accident rate and optimize the existing prevention measures, it is necessary to investigate the effect of fatigue on kinematics, kinetics, and muscle activities of human body. In this paper, 26 healthy participants were recruited. The kinematics and kinetics analysis of lower limb joints, and surface electromyograms (sEMG) time-domain and frequency-domain analysis of lower limb periarticular muscles were utilized to investigate the effects of muscle fatigue. The results showed that the fatigue reduced the range-of-motion (RoM) of the lower limb joints. Smaller plantarflexion, knee flexion and hip flexion angles, and greater dorsiflexion angles were observed after fatigue. For the joint moment, the fatigue did not alter the joint moments except for the smaller knee flexion moment. For the joint power, the fatigue decreased the generation power of ankle, knee and hip joint and the absorption power of ankle and knee joints, whereas increased the absorption power of hip joint. Besides, the fatigue increased the normalized integrated sEMG (iEMG) and root-mean-square (RMS) of sEMG, and shifted the median frequency (MF) and mean power frequency (MPF) of sEMG toward lower frequencies. The results from the present study concluded that the muscle fatigue changed the kinematics, kinetics and muscle activities of lower limbs during gait, and then could increase the risk rate of occupational accidents.

Effect of social media overload on college students’ academic performance under the COVID-19 quarantine

Features and relevant services of online social media have been attracting users during the COVID-19 pandemic. Previous studies have shown that college students tend to use social media more frequently than other groups. However, in being affected by social media overload, the social media use behaviors of many college students have been out of their control in terms of their capabilities or cognition. Based on the stressor–strain–outcome (SSO) model and the theory of compensatory internet use (TCIU), we developed a research model to study the causes of social media overload and its impact on college students’ academic performance during the COVID-19 pandemic. A total of 441 valid responses from college students through questionnaires in China are collected via purposive sampling and used in the data analysis. This study conducts PLS-SEM to analyze collected data, finding that boredom proneness is associated with overload (stress), which has a bearing on social media overload (strain) and the reduction in final performance (outcome). Through illustrating the psychological and behavioral conditions that hinder the academic performance of students, this study provides deeper insights into students’ uncontrollable use of social media. Moreover, with respect to the identified antecedents, this study aims to find solutions to mitigate the impact of social media overload resulting from boredom proneness on the academic performance of college students.

A Simulation Study to Assess the Factors of Influence on Mean and Median Frequency of sEMG Signals during Muscle Fatigue

Mean and Median frequency are typically used for detecting and monitoring muscle fatigue. These parameters are extracted from power spectral density whose estimate can be obtained by several techniques, each one characterized by advantages and disadvantages. Previous works studied how the implementation settings can influence the performance of these techniques; nevertheless, the estimation results have never been fully evaluated when the power density spectrum is in a low-frequency zone, as happens to the surface electromyography (sEMG) spectrum during muscle fatigue. The latter is therefore the objective of this study that has compared the Welch and the autoregressive parametric approaches on synthetic sEMG signals simulating severe muscle fatigue. Moreover, the sensitivity of both the approaches to the observation duration and to the level of noise has been analyzed. Results showed that the mean frequency greatly depends on the noise level, and that for Signal to Noise Ratio (SNR) less than 10dB the errors make the estimate unacceptable. On the other hand, the error in calculating the median frequency is always in the range 2-10 Hz, so this parameter should be preferred in the tracking of muscle fatigue. Results show that the autoregressive model always outperforms the Welch technique, and that the 3rd order continuously produced accurate and precise estimates; consequently, the latter should be used when analyzing severe fatiguing contraction.

A Systematic Review on Evaluation Strategies for Field Assessment of Upper-Body Industrial Exoskeletons: Current Practices and Future Trends

With rising manual work demands, physical assistance at the workplace is crucial, wherein the use of industrial exoskeletons (i-EXOs) could be advantageous. However, outcomes of numerous laboratory studies may not be directly translated to field environments. To explore this discrepancy, we conducted a systematic review including 31 studies to identify and compare the approaches, techniques, and outcomes within field assessments of shoulder and back support i-EXOs. Findings revealed that the subjective approaches [i.e., discomfort (23), usability (22), acceptance/perspectives (21), risk of injury (8), posture (3), perceived workload (2)] were reported more common (27) compared to objective (15) approaches [muscular demand (14), kinematics (8), metabolic costs (5)]. High variability was also observed in the experimental methodologies, including control over activity, task physics/duration, sample size, and reported metrics/measures. In the current study, the detailed approaches, their subject-related factors, and observed trends have been discussed. In sum, a new guideline, including tools/technologies has been proposed that could be utilized for field evaluation of i-EXOs. Lastly, we discussed some of the common technical challenges experimenters face in evaluating i-EXOs in field environments. Efforts presented in this study seek to improve the generalizability in testing and implementing i-EXOs.

Changes in Muscle Activation During and After a Shoulder-Fatiguing Task: A Comparison of Elite Female Swimmers and Water Polo Players

This study compared female athletes with different aquatic sports expertise in their neuromuscular activation before, during, and after a shoulder internal rotation fatigue protocol. Eleven water polo players, 12 swimmers, and 14 controls completed concentric maximal voluntary external and internal shoulder rotations before and after a fatigue protocol consisting of concentric internal rotations at 50% of maximal voluntary contraction for at least 3 min or until reporting a rating of perceived effort RPE of 8/10 or higher. Muscle activation was measured for the maximal voluntary contractions, as well as for the first (T1), middle (T2), and third (T3) minute of the fatigue protocol using surface electromyography (EMG) on pectoralis major, anterior and posterior deltoid, upper and middle trapezius, and latissimus dorsi. Intramuscular EMG was used for supraspinatus, infraspinatus, and subscapularis. Pre-fatigue internal rotation torque was significantly correlated with shorter task duration (r = −0.39, p = 0.02), with water polo players producing significantly greater torque than controls but having significantly lower endurance. Swimmers demonstrated decreased latissimus dorsi activation at T3 compared to T2 (p = 0.020, g = 0.44) and T1 (p = 0.029, g = 0.74), differing from water polo players and controls who exhibited increased agonist activation and decreased activation of stabilizers. Comparing the pre-fatigue to the post-fatigue maximal shoulder rotations, water polo players had decreased activation in subscapularis (p = 0.018, g = 0.67); all groups had decreased activation in latissimus dorsi (p < 0.001), though swimmers demonstrated a large effect (g = 0.97); and controls had decreased activation in supraspinatus (p = 0.005, g = 0.71). Together, these results suggest that sports expertise may be associated with different muscle activation both while and after fatigue is induced. Further research should continue to explore sports-specific patterns of muscle recruitment and fatigue adaptations, as well as if certain strategies are adaptive or maladaptive. This may have important consequences for injury prevention among athletes who perform repetitive overhead movements in their sports and who are susceptible to overuse injuries.

Muscle Co-Contraction Detection in the Time-Frequency Domain

Background: Muscle co-contraction plays a significant role in motion control. Available detection methods typically only provide information in the time domain. The current investigation proposed a novel approach for muscle co-contraction detection in the time–frequency domain, based on continuous wavelet transform (CWT). Methods: In the current study, the CWT-based cross-energy localization of two surface electromyographic (sEMG) signals in the time–frequency domain, i.e., the CWT coscalogram, was adopted for the first time to characterize muscular co-contraction activity. A CWT-based denoising procedure was applied for removing noise from the sEMG signals. Algorithm performances were checked on synthetic and real sEMG signals, stratified for signal-to-noise ratio (SNR), and then validated against an approach based on the acknowledged double-threshold statistical algorithm (DT). Results: The CWT approach provided an accurate prediction of co-contraction timing in simulated and real datasets, minimally affected by SNR variability. The novel contribution consisted of providing the frequency values of each muscle co-contraction detected in the time domain, allowing us to reveal a wide variability in the frequency content between subjects and within stride. Conclusions: The CWT approach represents a relevant improvement over state-of-the-art approaches that provide only a numerical co-contraction index or, at best, dynamic information in the time domain. The robustness of the methodology and the physiological reliability of the experimental results support the suitability of this approach for clinical applications.

Assessment of a Passive Lumbar Exoskeleton in Material Manual Handling Tasks under Laboratory Conditions

Manual material handling tasks in industry cause work-related musculoskeletal disorders. Exoskeletons are being introduced to reduce the risk of musculoskeletal injuries. This study investigated the effect of using a passive lumbar exoskeleton in terms of moderate ergonomic risk. Eight participants were monitored by electromyogram (EMG) and motion capture (MoCap) while performing tasks with and without the lumbar exoskeleton. The results showed a significant reduction in the root mean square (VRMS) for all muscles tracked: erector spinae (8%), semitendinosus (14%), gluteus (5%), and quadriceps (10.2%). The classic fatigue parameters showed a significant reduction in the case of the semitendinosus: 1.7% zero-crossing rate, 0.9% mean frequency, and 1.12% median frequency. In addition, the logarithm of the normalized Dimitrov’s index showed reductions of 11.5, 8, and 14% in erector spinae, semitendinosus, and gluteus, respectively. The calculation of range of motion in the relevant joints demonstrated significant differences, but in almost all cases, the differences were smaller than 10%. The findings of the study indicate that the passive exoskeleton reduces muscle activity and introduces some changes of strategies for motion. Thus, EMG and MoCap appear to be appropriate measurements for designing an exoskeleton assessment procedure.

Direct Effect of Local Cryotherapy on Muscle Stimulation, Pain and Strength in Male Office Workers with Lateral Epicondylitis, Non-Randomized Clinical Trial Study

Background: Local cryotherapy (LC) is one of the physiotherapeutic methods used in the conservative treatment of lateral epicondylitis (LE). The aim of the study was to verify the direct effect of a single LC procedure on the clinical symptoms of lateral epicondylitis enthesopathy (pain, pain free grip, PFG) and its effect on the bioelectrical properties of the wrist extensor muscles at rest, on maximal contraction and isometric contraction during fatigue. Methods: The study group was 28 men (35.4 ± 6.13 years) with confirmed unilateral epicondylitis. The performed procedures included the assessment of pain (visual analogue scale, VAS), PFG and ARMS (root-mean-square amplitude) and mean frequencies (MNF) of the sEMG signal before (T0) and after (T1) LC on the side with enthesopathy (ECRE) and without enthesopathy (ECRN/E). Results: There was an increase in the ARMS values of the signals recorded during rest and MVC from the ECR muscles both with and without enthesopathy (p = 0.0001, p = 0.006), an increased PFG after LC only on the side with LE (p < 0.0001) and decreased pain (p < 0.0001). During isometric fatigue contraction, a higher ARMS on both the ECRE side (p < 0.0001) and the ECRN/E side (p < 0.0001) was observed after LC treatment, and a lower MNF was observed on both the ECRN/E side (p < 0.0001) and the ECRE side (p < 0.0001) after LC. Conclusions: LC reduces the pain and increases PFG and muscle excitation expressed by ARMS and seems to delay muscle fatigue.

Muscle Fatigue and Swimming Efficiency in Behind and Lateral Drafting

Drafting in swimming is a tactic in which an athlete (drafter) swims in the wave of another athlete (leader). Our aim was to compare the effects of this tactic on the drafter, as far as muscle fatigue, muscle activity, and swimming efficiency are concerned. Fifteen drafters performed three 200 m front crawl trials at a controlled submaximal pace in three configurations: Behind Drafting (BD), Lateral Drafting (LD), and Free Swimming (FS). Muscle fatigue, muscle activity, and swimming efficiency were obtained by surface electromyography (EMG) and video analysis from flexor carpi radialis, triceps brachii, latissimus dorsi, and rectus femoris muscles. The outcome measures were: time slope of Mean Frequency (MNF), for muscle fatigue; time slope of Root Mean Square (RMS), for muscle activity; and Stroke Index (SI) for swimming efficiency. Negative variations of MNF were 5.1 ± 1.7%, 6.6 ± 4.1%, and 11.1 ± 2.7% in BD, LD, and FS, respectively. Statistical significance was found for all cases except for the rectus femoris. Positive variations of RMS were 3.4 ± 1.2%, 4.7 ± 2.7%, and 7.8 ± 4.6% in BD, LD, and FS, respectively. Statistical significance was found only for the slopes of latissimus dorsi in FS and LD. The largest mean in SI was measured in the BD (2.01 m²/s), while the smallest was measured in the FS (1.86 m²/s). BD was found to be the best swimming configuration, in terms of lower muscle fatigue and higher swimming efficiency. Also, LD resulted to be advantageous with respect to FS.

Validity of using perceived exertion to assess muscle fatigue during resistance exercises

BACKGROUND

The rating of perceived exertion (RPE) is correlated with physiological variables. The purpose of this study was to assess the validity of using the Borg CR-10 scale and velocity to predict muscle fatigue assessed by surface electromyography during single joint resistance exercises.

METHODS

Fifteen healthy males underwent different fatigue levels of unilateral elbow flexion (EF) and knee extension (KE), consisting of low, medium, and high volumes at 65% of their one-repetition maximum. The RPEs, spectral fatigue index (SFI), and mean velocity of the experimental exercises were assessed throughout the trials.

RESULTS

Significant differences in overall RPE (p < 0.001) and average SFI (p < 0.001) were observed between the conditions in both exercises. Significant changes in RPE and SFI (p < 0.001) were observed throughout the EF, whereas a SFI increase (p < 0.001) was only observed at the end point of KE. Multiple regression analyses revealed two significant models (p < 0.001) for the prediction of muscle fatigue during EF (R² = 0.552) and KE (R² = 0.377).

CONCLUSIONS

Muscle fatigue resulted in similar increases in perceptual responses, demonstrating that RPE is useful for assessing fatigue when resistance exercise is performed. However, velocity changes may not reflect muscle fatigue correctly when exercise is no longer performed in an explosive manner. We recommend combining RPE responses with velocity changes to comprehensively assess muscle fatigue during clinical and sports situations.

A Study on the Relationship between RPE and sEMG in Dynamic Contraction Based on the GPR Method

The rating of perceived exertion (RPE) and surface electromyography (sEMG) describe exercise intensity subjectively and objectively, while there has been a lack of research on the relationship between them during dynamic contractions to predict exercise intensity, comprehensively. The purpose of this study was to establish a model of the relationship between sEMG and RPE during dynamic exercises. Therefore, 20 healthy male subjects were organized to perform an incremental load test on a cycle ergometer, and the subjects’ RPEs (Borg Scale 6–20) were collected every minute. Additionally, the sEMGs of the subjects’ eight lower limb muscles were collected. The sEMG features based on time domain, frequency domain and time–frequency domain methods were extracted, and the relationship model was established using Gaussian process regression (GPR). The results show that the sEMG and RPE of the selected lower limb muscles are significantly correlated (p < 0.05) but that they have different monotonic correlation degrees. The model that was established with all three domain features displayed optimal performance and when the RPE was 13, the prediction error was the smallest. The study is significant for lower limb muscle training strategy and quantification of training intensity from both subjective and objective aspects, and lays a foundation for sEMG further applications in rehabilitation medicine and sports training.

Towards functional robotic training: motor learning of dynamic tasks is enhanced by haptic rendering but hampered by arm weight support

Background

Current robot-aided training allows for high-intensity training but might hamper the transfer of learned skills to real daily tasks. Many of these tasks, e.g., carrying a cup of coffee, require manipulating objects with complex dynamics. Thus, the absence of somatosensory information regarding the interaction with virtual objects during robot-aided training might be limiting the potential benefits of robotic training on motor (re)learning. We hypothesize that providing somatosensory information through the haptic rendering of virtual environments might enhance motor learning and skill transfer. Furthermore, the inclusion of haptic rendering might increase the task realism, enhancing participants’ agency and motivation. Providing arm weight support during training might also enhance learning by limiting participants’ fatigue.

Methods

We conducted a study with 40 healthy participants to evaluate how haptic rendering and arm weight support affect motor learning and skill transfer of a dynamic task. The task consisted of inverting a virtual pendulum whose dynamics were haptically rendered on an exoskeleton robot designed for upper limb neurorehabilitation. Participants trained with or without haptic rendering and with or without weight support. Participants’ task performance, movement strategy, effort, motivation, and agency were evaluated during baseline, short- and long-term retention. We also evaluated if the skills acquired during training transferred to a similar task with a shorter pendulum.

Results

We found that haptic rendering significantly increases participants’ movement variability during training and the ability to synchronize their movements with the pendulum, which is correlated with better performance. Weight support also enhances participants’ movement variability during training and reduces participants’ physical effort. Importantly, we found that training with haptic rendering enhances motor learning and skill transfer, while training with weight support hampers learning compared to training without weight support. We did not observe any significant differences between training modalities regarding agency and motivation during training and retention tests.

Conclusion

Haptic rendering is a promising tool to boost robot-aided motor learning and skill transfer to tasks with similar dynamics. However, further work is needed to find how to simultaneously provide robotic assistance and haptic rendering without hampering motor learning, especially in brain-injured patients.

Trial registrationhttps://clinicaltrials.gov/show/NCT04759976

Supplementary Information

The online version contains supplementary material available at 10.1186/s12984-022-00993-w.

The Association between Symmetrical or Asymmetrical High-Arched Feet and Muscle Fatigue in Young Women

The foot arches are responsible for proper foot loading, optimal force distribution, and transmission throughout the soft tissues. Since the foot arch is an elastic structure, able to adapt to forces transmitted by the foot, it was reported that low arch is related to excessive foot pronation, while high arched foot is more rigid and inflexible. Therefore, it is also probable, that foot arch alterations may change the force transmission via myofascial chains. The objective of this study was to evaluate the effect of symmetrical and asymmetrical excessive feet arching on muscle fatigue in the distal body parts such as the lower limbs, trunk, and head. Seventy-seven women (25.15 ± 5.97 years old, 62 ± 10 kg, 167 ± 4 cm) were assigned to three groups according to the foot arch index (Group 1—both feet with normal arch, Group 2—one foot with normal arch and the other high-arched, Group 3—both feet with high-arch). The bioelectrical activity of the right and left hamstrings muscles, erector spine, masseter, and temporalis muscle was recorded by sEMG during the isometric contraction lasting for 60 s. The stable intensity of the muscle isometric contraction was kept for all the time during the measurement. Mean frequency difference (%), slope (Hz), and intercept (Hz) values were calculated for muscle fatigue evaluation. No differences were observed in fatigue variables for all evaluated muscles between the right and left side in women with symmetrical foot arches, but in the group with asymmetric foot arches, the higher muscle fatigue on the normal-arched side compared to the high-arched side was noted. Significantly greater values of the semitendinosus—semimembranosus muscle frequency difference was observed on the normal-arched side compared to the high-arched side (p = 0.04; ES = 0.52; −29.5 ± 9.1% vs. −24.9 ± 8.4%). In the group with asymmetric foot arches, a significantly higher value of lumbar erector spinae muscle frequency slope (p = 0.01; ES = 1.32; −0.20 ± 0.04 Hz vs. −0.14 ± 0.05 Hz) and frequency difference (p = 0.04; ES = 0.92; −7.8 ± 3.1% vs. −4.8 ± 3.4%) were observed on the high-arched foot side compared to the side with normal foot arching. The thoracic erector spine muscle frequency slope was significantly larger in women with asymmetrical arches than in those with both feet high-arched (right side: p = 0.01; ES = 1.25; −0.20 ± 0.08 Hz vs. −0.10 ± 0.08 Hz); (left side: p = 0.005; ES = 1,17; −0.19 ± 0.04 Hz vs. −0.13 ± 0.06 Hz) and compared to those with normal feet arches (right side: p = 0.02; ES = 0.58; −0.20 ± 0.08 Hz vs. −0.15 ± 0.09 Hz); (left side: p = 0.005; ES = 0.87; −0.19 ± 0.04 Hz vs. −0.14 ± 0.07 Hz). In the group with asymmetric foot arches, the frequency difference was significantly higher compared to those with both feet high-arched (right side: p = 0.01; ES = 0.87; −15.4 ± 6.8% vs. 10.4 ± 4.3%); (left side: p = 0.01; ES = 0.96; 16.1 ± 6.5% vs. 11.1 ± 3.4%). In the group with asymmetric foot arches, a significantly higher value of the masseter muscle frequency difference was observed on the high-arched side compared to the normal-arched side (p = 0.01; ES = 0.95; 6.91 ± 4.1% vs. 3.62 ± 2.8%). A little increase in the longitudinal arch of the foot, even though such is often not considered as pathological, may cause visible changes in muscle function, demonstrated as elevated signs of muscles fatigue. This study suggests that the consequences of foot high-arching may be present in distal body parts. Any alterations of the foot arch should be considered as a potential foot defect, and due to preventing muscle overloading, some corrective exercises or/and corrective insoles for shoes should be used. It can potentially reduce both foot overload and distant structures overload, which may diminish musculoskeletal system pain and dysfunctions.

Chronic asthenia in patients who have undergone endocrine neck surgery

INTRODUCTION

The impact of chronic asthenia after thyroidectomy has been evaluated in two previous studies comparing total thyroidectomy and hemithyroidectomy. We compared its impact on patients undergoing thyroidectomy, parathyroidectomy for primary hyperparathyroidism, and cholecystectomy.

METHODS

Patients recruited for surgery (233 consecutive total thyroidectomies for non-toxic multinodular goiter, Group I, 43 consecutive parathyroidectomies for primary hyperparathyroidism, group II and a sample of 43 laparoscopic cholecystectomies, group III) were compared at three times: pre-operative, 6 months after surgery, 1 year after surgery. A brief fatigue inventory (BFI) was administered to assess asthenia. We excluded intermediate or high-risk thyroid carcinomas, Grave's disease, obese patients, secondary and tertiary hyperparathyroidism, vitamin D deficiency, and acute cholecystitis. In the postoperative period, patients who had undergone complications of each surgical procedure were also excluded. Demographics, smoking, alcohol abuse, chronic diseases (renal, cardiac, pulmonary, hepatic, and diabetes mellitus), anxiety and depression were noted.

RESULTS

In Group I the significant increase of asthenia during the three periods of detection (p < 0.001) was confirmed. Renal failure further increased the risk of asthenia. In Group II, asthenia after 6 months and 1 year after surgery decreased significantly (p < 0.001). In Group III, the variations in BFI during the three periods were not significant.

CONCLUSIONS

Asthenia is a frequent sequela of total thyroidectomy, also in comparison with other types of surgery. Patients undergoing thyroidectomy must be informed of the possible implications of surgery, which should be calibrated on the strict application of guidelines.

Retentive capacity of power output and linear versus non-linear mapping of power loss in the isotonic muscular endurance test

The limit of dynamic endurance during repetitive contractions has been referred to as the point of muscle fatigue, which can be measured by mechanical and electrophysiological parameters combined with subjective estimates of load tolerance for revealing the human real-world capacity required to work continuously. In this study, an isotonic muscular endurance (IME) testing protocol under a psychophysiological fatigue criterion was developed for measuring the retentive capacity of the power output of lower limb muscles. Additionally, to guide the development of electrophysiological evaluation methods, linear and non-linear techniques for creating surface electromyography (sEMG) models were compared in terms of their ability to estimate muscle fatigue. Forty healthy college-aged males performed three trials of an isometric peak torque test and one trial of an IME test for the plantar flexors and knee and hip extensors. Meanwhile, sEMG activity was recorded from the medial gastrocnemius, lateral gastrocnemius, vastus medialis, rectus femoris, vastus lateralis, gluteus maximus, and biceps femoris of the right leg muscles. Linear techniques (amplitude-based parameters, spectral parameters, and instantaneous frequency parameters) and non-linear techniques (a multi-layer perception neural network) were used to predict the time-dependent power output during dynamic contractions. Two mechanical manifestations of muscle fatigue were observed in the IME tests, including power output reduction between the beginning and end of the test and time-dependent progressive power loss. Compared with linear mapping (linear regression) alone or a combination of sEMG variables, non-linear mapping of power loss during dynamic contractions showed significantly higher signal-to-noise ratios and correlation coefficients between the actual and estimated power output. Muscular endurance required in real-world activities can be measured by considering the amount of work produced or the activity duration via the recommended IME testing protocol under a psychophysiological termination criterion. Non-linear mapping techniques provide more powerful mapping of power loss compared with linear mapping in the IME testing protocol.