sEMG Feature Analysis on Forearm Muscle Fatigue During Isometric Contractions

In order to detect and assess the muscle fatigue state with the surface electromyography(sEMG) characteristic parameters,this paper carried out a series of isometric contraction experiments to induce the fatigue on the forearm muscles from four subjects,and recorded the sEMG signals of the flexor carpi ulnaris.sEMG's median frequency(MDF) and mean frequency(MF) were extracted by short term Fourier transform(STFT),and the root mean square(RMS) of wavelet coefficients in the frequency band of 5—45 Hz was obtained by continuous wavelet transform(CWT).The results demonstrate that both MDF and MF show downward trends within 1 min; however,RMS shows an upward trend within the same time.The three parameters are closely correlated with absolute values of mean correlation coefficients greater than 0.8.It is suggested that the three parameters above can be used as reliable indicators to evaluate the level of muscle fatigue during isometric contractions.

Multifractal analysis of surface EMG signals for assessing muscle fatigue during static contractions

This study is aimed at assessing muscle fatigue during a static contraction using multifractal analysis and found that the surface electromyographic （SEMG） signals characterized multiffactality during a static contraction. By applying the method of direct determination ofthef（a） singularity spectrum, the area of the multifractal spectrum of the SEMG signals was computed. The results showed that the spectrum area significantly increased during muscle fatigue. Therefore the area could be used as an assessor of muscle fatigue. Compared with the median frequency （MDF）--the most popular indicator of muscle fatigue, the spectrum area presented here showed higher sensitivity during a static contraction. So the singularity spectrum area is considered to be a more effective indicator than the MDF for estimating muscle fatigue.

Exercise-induced muscle fatigue in the unaffected knee joint and its influence on postural control and lower limb kinematics in stroke patients

This study aimed to investigate the effects of exercise-induced muscle fatigue in the unaffected knee joint on postural control and kinematic changes in stroke patients. Forty participants（20 stroke patients, 20 age-matched healthy participants） were recruited. To induce fatigue, maximum voluntary isometric contractions were performed in the unaffected knee joint in a Leg Extension Rehab exercise machine using the pneumatic resistance. We measured static and dynamic balance and lower-limb kinematics during gait. Changes in postural control parameters anteroposterior sway speed and total center of pressure distance differed significantly between the stroke and control groups. In addition, changes in gait kinematic parameters knee and ankle angles of initial contact differed significantly between stroke（paretic and non-paretic） and control groups. Muscle fatigue in the unaffected knee and ankle impaired postural control and debilitates kinematic movement of ipsilateral and contralateral lower limbs, and may place the fatigued stroke patients at greater risk for falls.

Muscle fatigue in women with primary biliary cirrhosis:Spectral analysis of surface electromyography

AIM： To evaluate the myoelectric manifestations of peripheral fatigability in patients with primary biliary cirrhosis in comparison to healthy subjects. METHODS： Sixteen women with primary biliary cirrhosis without comorbidity and 13 healthy women matched for age and body mass index （BMI） completed the selfreported questionnaire fatigue impact scale. All subjects underwent surface electromyography assessment of peripheral fatigability. Anterior tibial muscle isometric voluntary contraction was executed for 20 s at 80% of maximal voluntary isometric contraction. During the exercise electromyographic signal series were recorded and root mean square （expression of central drive） as well as mean and median of electromyographic signal frequency spectrum （estimates of muscle fatigability） were com- puted. Each subject executed the trial two times. EMG parameters were normalized, then linear regression was applied and slopes were calculated. RESULTS： Seven patients were fatigued （median fatigue impact scale score： 38, range： 26-66） and 9 were not fatigued （median fatigue impact scale score： 7, range： 0-17）. The maximal voluntary isometric contraction was similar in patients （82, 54-115 N） and controls （87, 74-101 N）, and in patients with high （81, 54-115 N） and low fatigue impact scale scores （86, 65-106 N）. Root mean square as well as mean and median of frequency spectrum slopes were compared with the Mann-Whitney U test, and no significant difference was found between fatigued and non-fatigued patients and controls. CONCLUSION： No instrumental evidence of peripheral fatigability can be found in women with primary biliary cirrhosis but no comorbidity, suggesting that fatigue in such patients may be of central origin.

Real-time surface electromyography in Parkinson's disease patients during exercise-induced muscle fatigue

To explore the mechanisms underlying exercise-induced local muscle fatigue in patients with idiopathic Parkinson＇s disease （PD）,we used surface electromyography to record myoelectric signals from the tibialis anterior muscle during isometric contraction-induced fatigue until exhaustion.The results revealed no significant differences between patients with idiopathic PD and healthy controls in maximum voluntary contraction of the tibialis anterior muscle.The basic characteristics of surface electromyography were also similar between the two groups.The duration of isometric contraction at 50% maximum voluntary contraction was shortened in PD patients.In addition,PD patients exhibited a stronger increase in mean square amplitude,but a weaker decrease in median frequency and mean power frequency compared with healthy controls during isometric contraction.The skeletal muscles of PD patients revealed specificity of surface electromyography findings,indicating increased fatigability compared with healthy controls.

Real Time Monitoring of Muscle Fatigue with IoT and Wearable Devices

Wearable monitoring devices are in demand in recent times for monitoring daily activities including exercise.Moreover,it is widely utilizing for preventing injuries of athletes during a practice session and in few cases,it leads to muscle fatigue.At present,emerging technology like the internet of things(IoT)and sensors is empowering to monitor and visualize the physical data from any remote location through internet connectivity.In this study,an IoT-enabled wearable device is proposing for monitoring and identifying the muscle fatigue condition using a surface electromyogram(sEMG)sensor.Normally,the EMG signal is utilized to display muscle activity.Arduino controller,Wi-Fi module,and EMG sensor are utilized in developing the wearable device.The Time-frequency domain spectrum technique is employed for classifying the threemuscle fatigue conditions including meanRMS,mean frequency,etc.A real-time experiment is realized on six different individuals with developed wearable devices and the average RMS value assists to determine the average threshold of recorded data.The threshold level is analyzed by calculating the mean RMS value and concluded three fatigue conditions as>2V:Extensive);1–2V:Moderate,and<1V:relaxed.The warning alarm system was designed in LabVIEW with three color LEDs to indicate the different states of muscle fatigue.Moreover,the device is interfaced with the cloud through the internet provided with a Wi-Fi module embedded in wearable devices.The data available in the cloud server can be utilized for forecasting the frequency of an individual to muscle fatigue.

Electromyographical Study on Muscle Fatigue in Repetitive Forearm Tasks

The purpose of this study was to examine whether repetitive muscle tasks in low weight load might influence the fatigue of forearm muscles, and to identify ergonomic risk factors of forearm muscle fatigue in these tasks. Sixteen healthy male volunteers performed eight wrist extensions in different frequency, weight and angle loads while being instructed to keep a dominant upper limb posture as constant as possible. Surface electromyograph （sEMG） was recorded from right extensors digitorium （ED）, flexor carpi radialis （FCR）, flexor carpi ulnaris （FCU） and extensor carpi ulnaris （ECU） during the task performance. Our results showed that mean power frequency （MPF） and median frequency （MF） values of ED, FCR and FCU were significantly lower （P〈0.05） at high frequency load level than at low load level. However, MPF and MF values of ED were significantly lower （P〈0.01） in higher load groups of frequency, angle and weight than in lower load groups. These results indicated that the fatigue of muscles varied in the same task, and the number-one risk factor of ECU, ED and FCR was angle load.

New trends in treatment of muscle fatigue throughout rehabilitation of elderlies with motor neuron diseases

Muscle fatigue is a problem in rehabilitation,particularly in elderlies and patients with motor neuron diseases.There are high contradictions in the effectiveness of the used methods to decrease muscle fatigue during rehabilitation.They mainly concentrate on increasing rest periods,decreasing training load,or using an ascending intensity of manner of exercise.The training should focus on the newly discovered sensory system of muscle fatigue because of the important role of the sensory system in driving the motor system.Thus,this editorial provides insight on using proprioceptive training to enhance the sensory system of muscle fatigue.

Evaluation of upper limb muscle fatigue based on surface electromyography

Fatigue is believed to be a major contributory factor to occupational injuries in machine operators.The development of accurate and usable techniques to measure operator fatigue is therefore important.In this study,we used a novel method based on surface electromyography (sEMG) of the biceps brachii and the Borg scale to evaluate local muscle fatigue in the upper limb after isometric muscle action.Thirteen young males performed isometric actions with the upper limb at different force levels.sEMG activities of the biceps brachii were recorded during the actions.Borg scales were used to evaluate the subjective sensation of local fatigue of the biceps brachii after the actions.sEMG activities were analyzed using the one-third band octave method,and an equation to determine the degree of fatigue was derived based on the relationship between the variable and the Borg scale.The results showed that the relationship could be expressed by a conic curve,and could be used to evaluate muscle fatigue during machine operation.

Evaluation of Muscle Fatigue Based on Surface Electromyography and Subjective Assessment

To investigate the relationship between surface electromyography and subjective assessment of muscle fatigue, 20 young male volunteers participated in the experiment of pistol holding and aiming. sE MG of the anterior deltoid was recorded during the entire process, while fatigue assessments(Borg scale) were collected every 30 s. We divided the signal into several parts and then octave band method was used to calculate mean energy of each part, an equation was derived based on the relationship between the mean energy of sE MG and Borg scale. The results showed that the degree of local muscle fatigue could be described by a cubic curve, and could be used to evaluate and monitor muscle fatigue.

Corticospinal excitability during motor imagery is diminished by continuous repetition-induced fatigue

Application of continuous repetition of motor imagery can improve the performance of exercise tasks.However,there is a lack of more detailed neurophysiological evidence to support the formulation of clear standards for interventions using motor imagery.Moreover,identification of motor imagery intervention time is necessary because it exhibits possible central fatigue.Therefore,the purpose of this study was to elucidate the development of fatigue during continuous repetition of motor imagery through objective and subjective evaluation.The study involved two experiments.In experiment 1,14 healthy young volunteers were required to imagine grasping and lifting a 1.5-L plastic bottle using the whole hand.Each participant performed the motor imagery task 100 times under each condition with 48 hours interval between two conditions:500 mL or 1500 mL of water in the bottle during the demonstration phase.Mental fatigue and a decrease in pinch power appeared under the 1500-mL condition.There were changes in concentration ability or corticospinal excitability,as assessed by motor evoked potentials,between each set with continuous repetition of motor imagery also under the 1500-mL condition.Therefore,in experiment 2,12 healthy volunteers were required to perform the motor imagery task 200 times under the 1500-mL condition.Both concentration ability and corticospinal excitability decreased.This is the first study to show that continuous repetition of motor imagery can decrease corticospinal excitability in addition to producing mental fatigue.This study was approved by the Institutional Ethics Committee at the Nagasaki University Graduate School of Biomedical and Health Sciences(approval No.18121302)on January 30,2019.

Effects of progressive muscle relaxation therapy on Maintenance hemodialysis patients:a systematic review and meta-analysis

Objective:This study aimed to evaluate the effects of progressive relaxation therapy on patients with maintenance hemodialysis.Methods:A literature search was performed using PubMed,Embase,Cochrane Library,China National Knowledge Infrastructure,and Wanfang Data from inception to July 2020.Randomized controlled trials on the use of progressive muscle relaxation therapy in maintenance hemodialysis patients were selected.The primary outcomes were the depression and anxiety.Secondary outcomes included fatigue and sleep.Two reviewers proceeded study selection and quality assessment of included trials and performed heterogeneity of included studies before meta-analysis.Results:A total of 8 studies,which comprised a total of 668 participants were included in the final meta-analysis.The results showed that progressive muscle relaxation therapy could reduce the depression of patients(MD=-5.11,95%CI:-6.74 to-3.48,P<0.001),reduce the anxiety(SMD=-1.27,95%CI:-1.73 to-0.82,P<0.001),relieve fatigue symptoms(MD=-0.87,95%CI:-1.20 to-0.53,P<0.001),improve the sleep quality(MD=-1.69,95%CI:-1.95 to-1.42,P<0.001).Conclusion:Progressive muscle relaxation therapy has positive effects on depression,anxiety,fatigue and sleep quality in patients with maintenance hemodialysis.While concurrent evidence is insufficient,and further studies of high quality are needed to strengthen the conclusion.

Detection of an increase in EMG regularity during fatiguing contractions

The changes in the evolvement patterns of surface electromyography（EMG）signals during both static and dynamic fatiguing contractions are studied.The main finding is that the EMG signal tends to be more and more regular as muscle fatigues.An increase in the summation of all the regular evolvement patterns denoted by Dreg reflects such a tendency.Compared with traditional measurements,Dreg shows less variability among subjects when characterizing a fatigue process.In addition,the calculation of Dreg in the time domain is free from the restrictions disturbing those of spectral parameters.The detection of an increase in the EMG regularity not only proposes a new and easy way to inspect changes in EMG during the fatigue process,but also provides strong supports to estimate muscle fatigue by means of nonlinear analysis methods such as entropy and complexity measures.The detection method of signal regularity can also be applied to other physiological signals.

Surface EMG Observation and Isokinetic Test on Pressing-kneading Manipulations for Exercise Fatigue of Anterior Tibial Muscle

Objective： To observe the therapeutic effect of An-pressing and Rou-kneading manipulations for exercise fatigue of the anterior tibial muscle. Methods： Sixty healthy subjects were randomly divided into two groups, 30 in each group. Isokinetic test training was employed to induce left anterior tibial muscle fatigue. After this, subjects in the observation group received 5 min of tuina treatment, while subjects in the control group just lay down for 5 min. Then the integral myoelectricity, maximum amplitude, mean frequency and slope of the anterior tibial muscle and gastrocnemius muscle were measured using a surface electromyography （EMG） during the passive movements of the ankle joints in two groups. Results： Before treatment, the integral myoelectricity, maximum amplitude, mean frequency and slope of the anterior tibial muscle during exercise in two groups were consistent under isokinetic mode （P〉0.05）. After 5 min of tuina or rest, the myoelectric signals during exercise in two groups were both decreased. However, subjects in the observation group obtained a remarkably increased gain and gain rates of myoelectric signal than the control group （P〈0.05）. This indicates that the myoelectric signals were not fully recovered, but tuina has a better effect than rest on improving the myoelectric signal of the anterior tibia. Conclusion： Rest and tuina can both improve muscle fatigue. Tuina can obtain a better effect within the same time frame.

Optimal Design of Bicycle Frame Parameters Considering Biomechanics

With the development of technology and the change of market demands,the trend in middle and high grade bicycle manufacturing is developed toward small-volume,multi-species,and customer-oriented production.Therefore,human element should be fully considered in design so that the bicycle has the best cycling performance for the specific rider.Currently,customized design is difficult to achieve since feature parameters of the rider are not included in the design.The design of bicycle frame is the most important in bicycle design.The relative positions among the saddle,handlebar and central axis are defined as the bicycle three-pivot,they are the main parameters in bicycle frame design.In conventional bicycle design,frame parameters are merely relevant to bicycle types.On the basis of the principles of biomechanics and ergonomics knowledge,this paper presents a design method for bicycle three-pivot considering feature parameters of the rider by dynamic simulation.Firstly,a dynamic model of rider-bicycle system is built for a special rider,and a serial of simulation experiments is designed by uniform test method.Then,a mathematical model is built between the three-pivot position and the square of lower limb muscle stress by using simulation and regression analysis of the rider-bicycle system.The optimal three-pivot position parameters are obtained by setting the minimal of the square of the lower limb muscle stress as the objective.Therefore,the optimal parameters are gained for the specific rider.Finally,various results are gained for different riders based on the same design process.The function between feature parameters of the rider and the optimum three-pivot position parameters is built by regression.Bicycle design considering biomechanics can be divided into three main steps：calculating the three-pivot position,designing the geometrical structure of the bicycle frame and analyzing frame strength,and selecting appropriate parts and assembling the bicycle.Bicycle design considering biomechanics changes the conventional bicycle design and realizes customized design by considering human element in the design process.

Fatigability during volitional walking in incomplete spinal cord injury: cardiorespiratory and motor performance considerations

Fatigability describes the decline in force production（i.e., performance fatigability） and/or changes in sensations regulating performance（i.e., perceived fatigability） during whole-body activity and poses a major challenge to those living with spinal cord injuries（SCI）. After SCI, the inability to overcome disruptions to metabolic homeostasis due to cardiorespiratory limitations and physical deconditioning may contribute to increased fatigability severity. The increased susceptibility to fatigability may have implications for motor control strategies and motor learning. Locomotor training approaches designed to reduce fatigability and enhance aerobic capacity in combination with motor learning may be advantageous for promoting functional recovery after SCI. Future research is required to advance the understanding of the relationship between fatigability, cardiorespiratory function and motor performance following SCI.

Optimal Design of Mountain Bicycle Based on Biomechanics

To achieve better cycling performance and vibration comfort of mountain bicycle, the optimization of frame structural parameters and rear suspension scale parameters is investigated based on biomechanics.Firstly, the quadratic sum of rider lower limb muscles stresses is presented as the evaluation criterion of muscle fatigue.By taking the criterion as the objective function, the relative positions of three pivot points of frame are optimized to ensure that the frame structural parameters match the stature o...

Squat,Stoop,or Semi-squat:A Comparative Experiment on Lifting Technique

There are actually no sufficient data for lifting technique assessment.A laboratory study was undertaken to determine the effect of 3 regular lifting techniques on erector muscle activation,cardiovascular strain and subjective response.Thirty student volunteers participated in the study,and were required to lift a weight with different techniques.Stoop-,squat-,semi-squat-lifting resulted in 3,2 and 1 time of the highest percentage of the maximum voluntary electrical activation(MVE%) respectively.In the same order,the lowest median frequency(MF) existed 1,1 and 2 times.Muscle fatigue was 4 times in squat,36 in semi-squat and 43 in stoop lifting.Heart rate was the highest in squat and lowest in stoop respectively,with a middle level in semi-squat lifting.It may be recommended to adopt mainly the semi-squat technique for daily lifting works.For heavy lifting,it should use the squat technique.Stoop lifting may also be used alternatively but for light things.

The Influence of Window Length Analysis on the Time and Frequency Domain of Mechanomyographic and Electromyographic Signals of Submaximal Fatiguing Contractions

Mechanomyography (MMG) acquires the oscillatory waves of contracting muscles. Electromyography (EMG) is a tool for monitoring muscle overall electrical activity. During muscle contractions, both techniques can investigate the changes that occur in the muscle properties. EMG and MMG parameters have been used for detecting muscle fatigue with diverse test protocols, sensors and filtering. Depending on the analysis window length (WLA), monitoring physiological events could be compromised due to imprecision in the determination of parameters. Therefore, this study investigated the influence of WLA variation on different MMG and EMG parameters during submaximal isometric contractions monitoring MMG and EMG parameters. Ten male volunteers performed isometric contractions of elbow joint. Triaxial accelerometer-based MMG sensor and EMG electrodes were positioned on the biceps brachii muscle belly. Torque was monitored with a load cell. Volunteers remained seated with hip and elbow joint at angles of 110° and 90°, respectively. The protocol consisted in maintaining torque at 70% of maximum voluntary contraction as long as they could. Parameter data of EMG and the modulus of MMG were determined for four segments of the signal. Statistical analysis consisted of analyses of variance and Fisher’s least square differences post-hoc test. Also, Pearson’s correlation was calculated to determine whether parameters that monitor similar physiological events would have strong correlation. The modulus of MMG mean power frequency (MPF) and the number of crossings in the baseline could detect changes between fresh and fatigued muscle with 1.0 s WLA. MPF and the skewness of the spectrum (μ3), parameters related to the compression of the spectrum, behaved differently when monitored with a triaxial MMG sensor. The EMG results show that for the 1.0 s and 2.0 s WLAs have normalized RMS difference with fatigued muscle and that there was strong correlation between parameters of different domains.

An Interfacial Gel Electrode Patch with Tunable Hydrogen Bond Network for Electromyographic Sensing and Discrimination

The sensitivity and fidelity of surface electromyography(sEMG)signal monitoring is critical for muscle status and fatigue assessment,prosthetic control,and gesture recognition.However,the incompatible skin-electrode interface and complex electrophysiological environment restrict the sensitive acquisition and accurate analysis of sEMG signals.Focused on the impedance of the skin-electrode interface issue,we developed an interfacial gel electrode patch with a tunable hydrogen bond network to simultaneously achieve a conformal interface,suitable adhesion,and high conductivity for sEMG signal monitoring.By exploiting hydroxyethylidene diphosphonic acid(HEDP)and 2-hydroxyphosphono-acetic acid(HPAA)as hydrogen bonding regulators were introduced into the polyvinyl alcohol(PVA)-based hydrogel network to regulate the hydrogen bond cross-linking network.As a result,the balance of elastic modulus,adhesion,and electrical conductivity of PVA-HEDP-HPAA(PHH)hydrogel are achieved.The reliable electrodeskin interface is manipulated to achieve conformal contact by matching the elastic modulus,reducing the gap of electrode-skin interface by adhesion,and promoting ion and electron conduction by electrical conductivity.The PHH electrode patches exhibit a lower interfacial impedance(12.56 kΩ)and a signal-to-noise ratio of 38.09±1.28 dB for accurate analysis of muscle strength and evaluation of the fatigue state.With the assistance of the artificial neural network algorithm,seven gestures can be recognized with 100%prediction accuracy.The interfacial gel electrode patch contributes a bio-matching electrophysiological platform for prosthetic control,human–machine interaction,and clinical or athletic auxiliary monitoring.