Mean Power Frequency Research Articles

Electromyographic and mechanomyographic responses of the biceps brachii during concentric and eccentric muscle actions to failure at high and low relative loads.

This study examined neuromuscular responses of the biceps brachii (BB) for concentric and eccentric muscle actions during bilateral, dynamic constant external resistance (DCER), reciprocal forearm flexions and extensions to failure at high (80% 1 repetition maximum [1RM]) and low (30% 1RM) relative loads. Nine women completed 1RM testing and repetitions to failure (RTF) at 30 and 80% 1RM. Electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) signals were measured from the BB. Analyses included repeated measures ANOVAs (p < 0.05) and post-hoc pairwise comparisons with Bonferroni corrected alpha of p < 0.008 and p < 0.01 for between and within factor pairwise comparisons, respectively. EMG AMP and MPF were significantly greater for concentric than eccentric muscle actions, regardless of load or time. However, time course of change analysis revealed parallel increases in EMG AMP for concentric and eccentric muscle actions during the RTF trials at 30% 1RM, but no change at 80% 1RM. There were significant increases in MMG AMP during concentric muscle actions, but decreases or no change during eccentric muscle actions. EMG and MMG MPF decreased over time, regardless of muscle action type and loading condition. The greater EMG AMP and MPF values during concentric compared to eccentric muscle actions may reflect the difference in the efficiency characteristic of these muscle actions. The neuromuscular responses suggested that fatigue may be mediated by recruitment of additional motor units with lower firing rates during concentric muscle actions, and changes in motor unit synchronization during eccentric muscle actions.

Limited Effects of Age on the Use of the Ankle and Counter-Rotation Mechanism in the Sagittal Plane

During standing the center of mass (CoM) can be controlled relative to the base of support by applying ankle moments to shift the center of pressure (CoP mechanism). An additional mechanism is the counter-rotation mechanism, i.e., changing the angular momentum of segments around the CoM to change the direction of the ground reaction force. In this study, we assessed anteroposterior balance performance and the related use of these postural control mechanisms in children, younger and older adults. Sixteen children (6-9y), 17 younger adults (18-24y) and eight older adults (65-80y) performed bipedal upright standing trials of 16 seconds on a rigid surface and on three balance boards that could freely move in the sagittal plane, varying in height (15-19 cm). Full body kinematics were measured. Performance related outcome measures, i.e., the number of trials with balance loss and the Root Mean Square of the time series of the CoM acceleration (due to the CoP and counter-rotation mechanism) and the contributions of the CoP and counter-rotation mechanism to the CoM acceleration (in %) were calculated. Furthermore, selected kinematic measures, i.e., the orientation of the board and head and the Mean Power Frequency of board orientation and of CoM acceleration were calculated. Compared to younger adults, children and older adults showed a poorer balance performance. Across age groups and conditions, the contribution of the CoP mechanism to the total CoM acceleration was dominant, i.e., 95%-108%. The contribution of the counter-rotation mechanism was limited, i.e., 19%-31% (with totals higher than 100% indicating opposite effects of both mechanisms), since the counter-rotation mechanism would conflict with stabilizing the head in space. Furthermore, children did use the counter-rotation mechanism relatively more to accelerate the CoM compared to younger adults as they are possibly still learning to limit the contribution of the counter-rotation mechanism.

Effects of load matched isokinetic versus isotonic blood flow restricted exercise on neuromuscular and muscle function

ABSTRACT The purpose of this investigation was to examine neuromuscular function, muscle fatigue, rating of perceived exertion (RPE), and muscle swelling between isokinetic and isotonic leg extensions with blood flow restriction (BFR). Fourteen (21 ± 2years; 160cm ± 3.8; 61kg ± 9.1) trained women performed 75 (1 × 30,3 × 15) submaximal (30% of maximal strength), unilateral, isokinetic and isotonic leg extensions with BFR (60% of total arterial occlusion pressure). Before and after exercise, subjects performed maximal voluntary isometric contractions (MVIC) and muscle thickness (MT) was assessed with ultrasound. RPE was recorded across all sets and surface electromyography (EMG) was assessed during the MVIC muscle actions. Separate repeated measures ANOVAs were used to examine MVIC, MT, RPE and neuromuscular function. There were greater reductions in MVIC torque and EMG mean power frequency following isotonic (46.2 ± 17.1%; 16.4 ± 7.9%) than isokinetic (17.9 ± 10.9%;6.5 ± 6.3%). RPE was also higher during isotonic (7.5 ± 2.2), than isokinetic (5.7 ± 1.9). There were no differences in EMG amplitude or MT increases (20 ± 2.1%) between conditions. Isotonic BFR elicited greater fatigue-induced decreases in muscular strength and greater RPE than isokinetic BFR, but similar MT and muscle excitation responses for both conditions. Therefore, both isokinetic and isotonic may induce similar acute physiological responses, but isotonic BFR was associated with greater muscle fatigue and perceived effort. Highlights Exercise modality affects the fatigue and perceptual responses when applying blood flow restriction. Despite greater utility, isotonic blood flow restriction was associated greater fatigue and perceived effort. Isotonic and isokinetic blood flow restriction elicited comparable neural changes.

Visual feedback-dependent modulation of arousal, postural control, and muscle stretch reflexes assessed in real and virtual environments.

The mechanisms regulating neuromuscular control of standing balance can be influenced by visual sensory feedback and arousal. Virtual reality (VR) is a cutting-edge tool for probing the neural control of balance and its dependence on visual feedback, but whether VR induces neuromodulation akin to that seen in real environments (eyes open vs. closed or ground level vs. height platform) remains unclear. Here we monitored 20 healthy young adults (mean age 23.3 ± 3.2 years; 10 females) during four conditions of quiet standing. Two real world conditions (eyes open and eyes closed; REO and REC) preceded two eyes-open virtual 'low' (ground level; VRL) and 'high' (14 m height platform; VRH) conditions. We measured arousal via electrodermal activity and psychosocial questionnaires rating perceived fear and anxiety. We recorded surface electromyography over the right soleus, medial gastrocnemius, and tibialis anterior, and performed force plate posturography. As a proxy for modulations in neural control, we assessed lower limb reflexive muscle responses evoked by tendon vibration and electrical stimulation. Physiological and perceptual indicators of fear and anxiety increased in the VRH condition. Background soleus muscle activation was not different across conditions; however, significant increases in muscle activity were observed for medial gastrocnemius and tibialis anterior in VRH relative to REO. The mean power frequency of postural sway also increased in the VRH condition relative to REO. Finally, with a fixed stimulus level across conditions, mechanically evoked reflexes remained constant, while H-reflex amplitudes decreased in strength within virtual reality. Notably, H-reflexes were lower in the VRL condition than REO, suggesting that these ostensibly similar visual environments produce different states of reflexive balance control. In summary, we provide novel evidence that VR can be used to modulate upright postural control, but caution that standing balance in analogous real and virtual environments may involve different neural control states.

Linear spectrum and non-linear complexity features of lumbar muscle surface electromyography between people with and without non-specific chronic low back pain during Biering-Sorensen test.

This study aimed to investigate the electromyographic parameters of lumbar muscles during the Biering-Sorensen test (BST) in people with and without non-specific chronic low back pain (NCLBP). Thirteen healthy controls and thirteen NCLBP patients participated in the current study, where they performed the 90s-BST, while the surface electromyography (sEMG) was recorded from the erector spinae (ES) at L1 and L3 level and lumbar multifidus (LM) at L5 level, bilaterally. Spectral and nonlinear analyses were applied by calculating mean power frequency (MPF), fractal dimension (FD) and the percentage of determinism (%DET) in the 10-second non-overlapping time-windows and EMG-EMG coherence during the first half and second half of the BST. Also, the slopes of the linear fitting curves of MPF, FD and %DET were calculated. NCLBP group had significantly lower rates of changes in MPF, FD and %DET compared to asymptomatic controls in the ES(L3) and LM. Coherence in left-right LM and in the right ES-LM increased significantly in the gamma band in the Control group with no increase in the NCLBP group. Our findings indicated that compared to people with NCLBP, the sEMG signals of lumbar muscles of people without NCLBP were more regular and less complex during the 90s-BST.

Propeller control for takeoff of a heavily loaded coaxial compound helicopter

AbstractAlthough a coaxial compound helicopter can takeoff without propeller in the normal condition, the distance should be as short as possible for obstacle avoidance when the vehicle operates in a confined area with heavy loads. Therefore, a suitable propeller control is required to improve the takeoff performance while the total power consumption is no more than the available power. The path is predicted by applying trajectory optimisation. Several varying takeoff parameters, including attitude, liftoff speed and obstacle height, are considered for optimum global performance. Three path indicators are proposed. Apart from typical distance and pilot workload, path sensitivity is quantified based on deviation from takeoff parameter variation. Results indicated that low propeller thrust at hover and moderate allocation on the propeller through flight is recommended. The aircraft achieves significantly improved takeoff performance compared to flight with pure rotors while maintaining the maximum takeoff weight. The distance is shortened by 12.6%, and the longitudinal pilot workload is alleviated by 9.8% and 7.3% from mean and maximum power frequency aspects. Besides, the path is less sensitive to takeoff parameter variations, such as speed, altitude and height.

Neuromuscular fatigue in autoimmune myasthenia gravis: A cross-sectional study

ObjectivesTo investigate the presence of increased neuromuscular fatigue (NMF) in individuals with myasthenia gravis (IwMG), compared to healthy controls. A secondary aim was to assess associations between NMF, strength and perceived health-related quality of life (HRQoL) and symptom severity in IwMG. MethodsIn this cross-sectional study, we assessed NMF using classical myoelectrical indicators (root mean square: RMS, mean power frequency: MPF) obtained from surface electromyography (sEMG) during a sustained submaximal isometric contraction of the right Biceps Brachii and the right Vastus Lateralis and by evaluating the post-effort decline in peak torque following a fatiguing task consisting of a 40-second sustained isometric contraction. Relationships with MG-specific clinical scores (Myasthenia Muscle Score for symptom severity, MGQOL-15-F for HRQoL) were investigated. ResultsForty-one females with MG were compared to 18 control females of similar age. IwMG demonstrated reduced strength in both muscle groups, compared to control subjects. In both populations and both limbs, NMF was demonstrated by an increase in RMS and a decrease in MPF. However, IwMG did not demonstrate greater NMF based on these myoelectrical indicators nor based on post-effort peak torque decline. DiscussionDespite a decrease in baseline strength, IwMG did not display greater NMF in this specific experimental paradigm. This cohort consisted of individuals with mild-to-moderately severe MG which was well-controlled and stable. Further studies are warranted to identify simple and reliable methods to measure NMF in MG and to understand the relationship between NMF and perceived fatigue in activities of daily living for IwMG.

A New Approach to Quantifying Muscular Fatigue Using Wearable EMG Sensors during Surgery: An Ergonomic Case Study.

(1) Background: Surgeons are exposed to musculoskeletal loads that are comparable to those of industrial workers. These stresses are harmful for the joints and muscles and can lead to musculoskeletal disorders (MSD) and working incapacity for surgeons. In this paper, we propose a novel ergonomic and visualization approach to assess muscular fatigue during surgical procedures. (2) Methods: The activity of eight muscles from the shoulder girdle and the cervical/lumbar spines were evaluated using position and electromyographic wearable sensors while a surgeon performed an arthroscopic rotator-cuff surgery on a patient. The time and frequency-domain variables of the root-mean-square amplitude and mean power frequency, respectively, were calculated from an electromyographic signal. (3) Results: The entire surgical procedure lasted 73 min and was divided into 10 sub-phases associated with specific level of muscular activity and fatigue. Most of the muscles showed activity above 60%, while the middle trapezius muscles were almost constantly activated (>20%) throughout the surgical procedure. (4) Conclusion: Wearable sensors can be used during surgical procedure to assess fatigue. Periods of low-to-high activity and fatigue can be evaluated and visualized during surgery. Micro-breaks throughout surgical procedures are suggested to avoid fatigue and to prevent the risk of developing MSD.

Effect of laser acupuncture combined with electrical stimulation on recovery from exercise fatigue in mice

In sports events, the rapid recovery after high-intensity training or sport competition performance is very important for athletes’ performance and health. The aim of this study is to evaluate the effect of laser acupuncture and electrical stimulation on the recovery from exercise fatigue, using mice with swimming fatigue as experimental model and the electromyography (EMG) and the Raman spectroscopy of blood as evaluation indicators. Root mean square (RMS) and mean power frequency (MPF) of EMG were analyzed after laser acupuncture and electrical stimulation. The amplitude frequency combined analysis (JASA) showed that the proportion of muscles in the fatigue recovery area of the control group, the laser acupuncture group, the multi-channel laser acupuncture group and the laser combined with electrical stimulation group were 34.78%, 39.13%, 39.13% and 43.48%, respectively. Raman spectroscopy of the mice blood during fatigue recovery showed there is a significant difference between the multi-channel laser acupuncture group and the laser combined with electric stimulation group compared with the recovery period and fatigue period ([Formula: see text]) at the peak of 997[Formula: see text]cm[Formula: see text] and the laser combined electrical stimulation group had a statistical difference in the recovery period compared with the fatigue period ([Formula: see text]) at the peak of 1561[Formula: see text]cm[Formula: see text]. The results showed that laser acupuncture combined with electrical stimulation was beneficial to fatigue recovery in mice, and had the potential value in sports fatigue recovery.

Development of Consumer-Friendly Surface Electromyography System for Muscle Fatigue Detection

In this study, a low-cost, wireless, and smartphone-controlled surface electromyography (EMG) system was designed and developed for consumers, and the recorded EMG signals were evaluated against a reference laboratory EMG system during fatiguing contraction. Using commercially available inexpensive components, the components of the EMG signal-acquisition circuit were optimized, and a microcontroller was combined with a Bluetooth module. The EMG signals were then converted from analog to digital signals and transmitted to a smartphone via Bluetooth serial communication. EMG signals from the biceps brachii of six healthy subjects were recorded separately using two EMG systems during sustained submaximal isometric contraction until the endurance limit was reached. The root mean square (RMS) and mean power frequency (MPF) of the EMG signals were calculated. The results indicated that both the EMG systems exhibited a characteristic progressive increase in EMGRMS and decrease in EMGMPF during sustained isometric contraction. The relative agreement between the two EMG systems, assessed by intraclass correlation coefficient (ICC), was excellent for EMGRMS (ICC 0.933, P < 0.001) and moderate for EMGMPF (ICC 0.662, P =0.049). The cost of the sensor components in the hardware was ¥ 8,486 per unit. The proposed consumer-friendly EMG system, which is inexpensive and highly versatile in terms of wireless and smartphone accessibility, can detect the phenomenon associated with increased amplitude and low-frequency components during muscle fatigue contraction with a magnitude similar to that of the commercially available laboratory EMG systems.

Neuromuscular and mean force changes during a fatiguing bout of exercise with and without blood flow restriction

Surface electromyography (EMG) and mean force can be used to identify motor unit excitation and fatigue. Low-load resistance training with blood flow restriction (LL+BFR) may result in earlier fatigue and maximal muscle fibre recruitment compared to low-load resistance training (LL). The purpose of this investigation was to examine EMG and force responses during LL versus LL+BFR. Thirteen males (mean ± standard deviation = 24±4 years) completed a bout (1×30) of leg extension muscle actions at 30% of their 1 repetition maximum LL and LL+BFR while force, EMG amplitude, and EMG mean power frequency (EMG MPF) were recorded. EMG amplitude increased (74.2%) and EMG MPF decreased (22.6%) similarly during both conditions. There was no significant difference in mean force during the first 3 repetitions between LL+BFR (477.3±132.3 N) and LL (524.3±235.1 N) conditions, but mean force was lower during the last 3 repetitions for LL+BFR (459.7±179.3 N) compared to LL (605.4±276.4 N). The results of the present study indicated that a fatiguing bout of leg extension muscle actions performed LL and LL+BFR elicited similar neuromuscular responses. There was a significant difference in mean force during the last 3 repetitions (LL&gt;LL+BFR) that may have been due to differences in the time spent near peak force.

Neuromuscular characteristics of agonists and antagonists during maximal eccentric knee flexion in soccer players with a history of hamstring muscle injuries.

Muscle strain injuries (MSIs) in the hamstrings are among the most prevalent injuries in elite soccer. We aimed to examine the relation between biomechanical maladaptation in eccentric strength and neuromuscular factors separated by their time and frequency domains. 20 elite soccer players with a previous history of unilateral MSI in the M. biceps femoris (BF) long head and 20 without MSI participated. Knee flexion torques, rate of torque development (RTD) and electromyographic signals (EMG) of the BF, the M. semitendinosus (SMT) and knee extensors were obtained during unilateral maximal eccentric knee flexions performed at slow (30°/s) and fast (120°/s) angular speeds. Root mean squares and mean power frequency (MF) was calculated. In the group with a history of MSI, reduced maximal eccentric flexion torque (slow eccentrics -8±11, p<0.05; fast eccentrics -18±13 N*m, p<0.05) and RTD (-33±28 N*m/s, p<0.05; -95±47 N*m/s, p<0.05) concomitantly occurred with diminished agonistic myoelectrical activities (-4±5% of MVC, p<0.05; -10±7% of MVC, p<0.05) and MFs (-24±13 Hz, p<0.05; -24±18 Hz, p<0.05) in the BF. Simultaneously, antagonistic myoelectric activity was elevated (+4±3% of MVC, p<0.05; +3±3% of MVC, p<0.05) in MSI affected legs as compared to unaffected legs for both eccentric contractions. Deficits in myoelectrical activity (r2 = 0.715, p<0.05; r2 = 0.601, p<0.05) and MF (r2 = 0.484, p<0.05; r2 = 0.622, p<0.05) correlated with deficits in maximal torque in the affected leg in the MSI group. Analysis of SMT demonstrated no significant differences. Positive relationships between neuromuscular deficits and the reduced eccentric strength profile underpin neuronal inhibition after MSI. This persistent involvement of dysfunctional synergist and antagonist neural hamstring function in strength weakness is of clinical relevance in sports medicine for prevention and rehabilitation.

Load-Specific Performance Fatigability, Coactivation, and Neuromuscular Responses to Fatiguing Forearm Flexion Muscle Actions in Women.

Benitez, B, Dinyer-McNeeley, TK, McCallum, L, Kwak, M, Succi, PJ, and Bergstrom, HC. Load-specific performance fatigability, coactivation, and neuromuscular responses to fatiguing forearm flexion muscle actions in women. J Strength Cond Res 37(4): 769-779, 2023-This study examined the effects of fatiguing, bilateral, dynamic constant external resistance (DCER) forearm flexion on performance fatigability, coactivation, and neuromuscular responses of the biceps brachii (BB) and triceps brachii (TB) at high (80% 1 repetition maximum [1RM]) and low (30% 1RM) relative loads in women. Ten women completed 1RM testing and repetitions to failure (RTF) at 30 and 80% 1RM. Maximal voluntary isometric force was measured before and after RTF. Electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) signals were measured from the BB and TB. Performance fatigability was greater (p < 0.05) after RTF at 30% (%∆ = 41.56 ± 18.61%) than 80% (%∆ = 19.65 ± 8.47%) 1RM. There was an increase in the coactivation ratio (less coactivation) between the initial and final repetitions at 30%, which may reflect greater increases in agonist muscle excitation (EMG AMP) relative to the antagonist for RTF at 30% than 80% 1RM. The initial repetitions EMG AMP was greater for 80% than 30% 1RM, but there was no difference between loads for the final repetitions. For both loads, there were increases in EMG MPF and MMG AMP and decreases in MMG MPF that may suggest fatigue-dependent recruitment of higher-threshold motor units. Thus, RTF at 30 and 80% 1RM during DCER forearm flexion may not necessitate additional muscle excitation to the antagonist muscle despite greater fatigability after RTF at 30% 1RM. These specific acute performance and neuromuscular responses may provide insight into the unique mechanism underlying adaptations to training performed at varying relative loads.

Coactivation does not contribute to fatigue-induced decreases in torque during reciprocal, isokinetic muscle actions

BACKGROUND: Studies of coactivation have typically utilized single movement isometric or isokinetic fatiguing muscle actions. OBJECTIVE: The purpose of the current study was to examine coactivation of the biceps brachii (BB) and triceps brachii (TB) in response to a maximal, reciprocal, isokinetic fatiguing task of the forearm flexors and extensors at slow (60∘/s) and moderate (180∘/s) isokinetic velocities in men. METHODS: Ten men (mean ± SD: age = 21.6 ± 1.3 years) completed 50 consecutive, maximal, reciprocal, isokinetic muscle actions of the right forearm flexors and extensors at 60 and 180∘/s. The amplitude (AMP) and mean power frequency (MPF) contents of the electromyographic (EMG) and mechanomyographic (MMG) signals from the BB and TB were recorded simultaneously throughout the fatiguing task. Repeated measures ANOVAs with Tukey post hocs were used to determine mean differences for the torque and neuromuscular parameters across repetitions. RESULTS: The torque analyses indicated greater fatigability at 180∘/s, compared to 60∘/s (p= 0.02). There were no significant changes in EMG AMP for either muscle during flexion or extension at 60∘/s (p&gt; 0.05). At 180∘/s, there were significant increases in agonist EMG AMP (p= 0.01 to 0.004), however, no changes in antagonist EMG AMP (p&gt; 0.05). For EMG MPF, there were significant decreases during flexion and extension (p&lt; 0.001 to p= 0.02) at both velocities, collapsed across muscle. There were no significant (p&gt; 0.05) changes across repetition for MMG AMP or MPF. CONCLUSIONS: This study indicated velocity-specific responses to fatigue, with a greater magnitude of fatigability at 180∘/s. Furthermore, despite increases in EMG AMP of the agonist muscles at 180∘/s only, it was not sufficient to alter the ratio of coactivation, likely due to common neural drive between muscles. Thus, the decreases in torque in the present study were not attributable to increases in coactivation.

Muscle fatigue response of rotator cuff muscles in different postures

IntroductionMuscle fatigue is a leading cause of rotator cuff (RC) pathologies. Scapular orientation affected by changes in the thoracic spine account for differences in body postures leading to altered RC muscle activation. This posture-related alteration in RC muscle activation and its fatigue response needs to be analyzed.Materials and methodsThis study included 50 healthy shoulders with no coexisting spine pathologies. Raw data were recorded using electromyography sensors for RC muscles during two isometric maneuvers of abduction and external rotation, performed at 30% maximum voluntary contraction at 30°, 45°, and 90° arm elevation in sitting and standing. The raw data were analyzed in DataLITE® software, and the mean power frequency (MPF) was extracted to analyze the fatigue response of RC muscles. The Wilcoxon signed-rank test and Kruskal–Wallis test with Bonferroni corrections analyzed fatigue differences between postures and various activities. P < 0.05 was considered significant for the results.ResultsSupraspinatus muscle demonstrated significant fatigue at 90° of arm elevation in standing as compared to sitting (MPF −5.40: −5.41; P = 0.03) posture. Between the three elevation angles, all the RC muscles showed increased fatigue at 90° (MPF range −5.22 to −6.64). When compared between abduction and external rotation, only infraspinatus showed fatigue in external rotation (MPF range −5.42 to −6.08). Among all the three RC muscles, infraspinatus showed the maximum fatigue of MPF −6.64 when compared to supraspinatus −5.22 and teres minor −5.36.ConclusionThe findings indicate that alterations in the body postures and different elevation angles affect the RC muscles’ fatigue response.

Sex-specific myoelectric manifestations of localized fatigue during a multi-joint repetitive task

We have previously demonstrated that fatigue at different locations impacts joint angles, angular variability, and coordination variability differently. However, the neuromuscular control aspects underlying these kinematic changes have never been demonstrated. Seventeen young adults (8 males) were recruited. Electromyographic electrodes were placed on: upper trapezius, pectoralis major, anterior and middle deltoid, biceps and triceps brachii, and left and right erector spinae. Subjects performed the repetitive pointing task (RPT) at 1 Hz for 30 s before and after localized fatigue tasks, which consisted of one shoulder, one elbow and one lower back isometric fatiguing protocols until exhaustion in randomized order. Electromyographic amplitude (RMS), variability (SD) and mean power frequency (MnPF) were calculated for each of the pre-fatigue and post-fatigue RPT trials. There were sex × fatigue location interaction effects on upper trapezius RMS (p = 0.038) with males’ values increasing the most after shoulder fatigue. Females’ triceps brachii RMS was greater compared to males after shoulder, elbow, and trunk fatigue (p = 0.003, p = 0.001 and p = 0.007 respectively). There were sex × fatigue location effects on left erector spinae MnPF (p = 0.011) with males and females’ values decreasing the most after trunk fatigue, but more so in males. Results demonstrate that males and females compensate differently during a repetitive pointing task when their elbows, shoulders and trunks are locally fatigued, which could have implications on sex-specific workplace injury risks. See Table 1 for acronyms.

Resting-state Brain Network Analysis And Prediction: An Eeg Study On Exercise-induced Muscle Fatigue

PURPOSE: Exercise-induced muscle fatigue is a complex physiological phenomenon involving the central and peripheral nervous systems, and the tolerance of fatigue has a large variability among subjects. The present study has been designed to find an effective way for predicting muscle fatigue and probing the neural mechanism of fatigue by a resting-state EEG network. METHODS: In this study, thirteen elite athletes (female) were enrolled to take part in an elbow flexion and extension task. Five-minute before- and after-fatigue-exercise resting-state EEG and fatiguing task electromyography (EMG) data were recorded. Based on the graph theory, we constructed the resting-state EEG network, and compared the network differences before- and after-task. To further validate, the correlation between the before-fatigue resting-state EEG network properties and the EMG-related fatigue indexes Mean power frequency(MPF) during exercise was profiled. Finally, a prediction model based on the before-fatigue resting-state EEG network property, including Clustering coefficient (CC), local efficiency (Le), global efficiency (Ge), and characteristic path length (CPL), was established to predict the EMG related fatigue indexes after fatigue. RESULTS: Firstly, the results of this study demonstrated a significant relationship between the resting-state brain network and muscle fatigue during exercise(P < 0.05). Secondly, we also validate that a significant relationship between resting-state brain network properties and MPF (P < 0.05). Finally, the study proved that the before-fatigue resting-state EEG network single property could predict the fatigue tolerance for individual subject accurately (CC: r = 0.651, P < 0.05; CPL: r = 0.592, P < 0.05; Ge: r = 0.603, P < 0.05; Le: r = 0.654, P < 0.05). CONCLUSION: In all, the resting-state brain network may provide indicators for the monitoring and prediction of muscle fatigue in athletes, in the meantime, provide biological markers for recognition and regulation of muscle fatigue based on BCI.

Coactivation During Fatiguing, Maximal, Reciprocal, Isokinetic Forearm Flexion And Extension Muscle Actions Using Mechanomyography

Purpose: Mechanomyography (MMG) has rarely been used to examine coactivation responses during fatiguing tasks. Under some conditions, MMG amplitude (AMP) provides insights into motor unit (MU) recruitment, while MMG mean power frequency (MPF) provides a qualitative description of the global firing rate of the unfused activated motor units. Thus, the purpose of the present study was to use MMG to examine coactivation of the agonist and antagonist muscles during fatiguing reciprocal forearm extension (EXT) and flexion (FLEX) muscle actions. Methods: Ten men (mean ± SD: age = 21.6 ± 1.3 yrs; body mass = 80.9 ± 6.5 kg; height = 179.1 ± 5.9 cm) completed 50 consecutive, maximal, reciprocal, isokinetic forearm EXT and FLEX muscle actions at 60 and 180°·s-1. The AMP and MPF contents of the MMG signals from the biceps (BB) and triceps (TB) were recorded simultaneously throughout the fatiguing task. The MMG and torque values were averaged across 5 consecutive repetitions and normalized to the value from repetition five. A 2 (Speed: 60 and 180°·s-1) x 2 (Muscle: TB and BB) x 2 (Movement: EXT and FLEX) x 10 (Repetitions: 5 - 50) RMANOVA was used to determine mean differences for AMP and MPF. A 2 (Speed) x 2 (Movement) x 10 (Repetitions) RMANOVA was used to determine mean differences for torque. Results: The statistical analyses indicated that for EXT, MMG AMP was greater at 180°·s-1 than 60°·s-1 (p = 0.04) for both the TB and BB. For FLEX, MMG AMP for the TB was greater at 180°·s-1 than 60°·s-1 (p < 0.01), however, there was no significant difference between speeds for the BB. For MMG MPF during EXT, the TB was significantly greater than the BB (p < 0.01). For FLEX, there was no significant difference between muscles. There were significant (p < 0.05) reductions in torque throughout the fatiguing task for both EXT and FLEX. Conclusion: The results indicated that during forearm EXT and FLEX, the faster velocity muscle actions exhibited greater lateral oscillations than the slower velocities, likely due to differences in the contributions of fast and slow fibers to torque production. In addition, the TB exhibited a greater global MU firing rate, as suggested by the MMG MPF responses, than the BB during forearm EXT. Thus, the fatigued-induced decrease in torque was not attributable to changes in coactivation.

Intelligent Scanning Detection System of Muscle Exercise Fatigue Based on Surface Electromyography.

In order to use the surface EMG signal to automatically detect the muscle fatigue state, a research method of the muscle exercise fatigue intelligent scanning detection system based on surface EMG was proposed, and the sEMG signal features of 10 subjects before and after fatigue were extracted. A time-varying parameter autoregressive model is established. By introducing the Legendre basis function, the parameter identification of the linear nonstationary process is transformed into the parameter identification of the linear time-invariant system. Combined with the correlation index, the optimal Legendre base function dimension of the time-varying system parameter estimation can be obtained, then the best model fitting effect can be obtained, and the time-invariant parameters are solved by the least square method. Using the rate of change of the first time-varying parameter (ARC1) of the autoregressive model before and after fatigue as an index to detect muscle fatigue sensitivity, a two-tailed t test was used to compare the mean power frequency (MPF) and the median frequency (MF) with the rate of change. The results showed that the change rates of ARC1, MPF, and MF before and after fatigue were34.33% ± 2.5%, 68% + 2.03%, and 22.80% + 2.19%, which were 41% and 25%, respectively. The rate of change of ACR1 was significantly higher than that of MPF and MF (P < 0.05). When detecting muscle fatigue by sEMG signal, it has the advantages of short time and high sensitivity. It can be used for online real-time analysis of muscle fatigue, providing a potential analysis tool for limb muscle strain, rehabilitation, and ergonomics assessment.

Feature layer fusion of linear features and empirical mode decomposition of human EMG signal

To explore the influence of the fusion of different features on recognition, this paper took the electromyogram (EMG) signals of rectus femoris under different motions (walk, step, ramp, squat, and sitting) as signals, linear features (time-domain features (variance (VAR) and root mean square (RMS)), frequency-domain features (mean frequency (MF) and mean power frequency (MPF)), and nonlinear features (EMD) of the signals were extracted. Two feature fusion algorithms, the series splicing method and complex vector method, were designed, which were verified by a double hidden layer error back propagation (BP) neural network. Results show that with the increase of the types and complexity of feature fusions, the recognition rate of the EMG signal to actions is gradually improved. When the EMG signal is used in the series splicing method, the recognition rate of time-domain ​+ ​frequency-domain ​+ ​empirical mode decomposition (TD ​+ ​FD ​+ ​EMD) splicing is the highest, and the average recognition rate is 92.32%. And this value is raised to 96.1% by using the complex vector method, and the variance of the BP system is also reduced.