Non-fatigue Conditions Research Articles

Generation of synthetic surface electromyography signals under fatigue conditions for varying force inputs using feedback control algorithm.

Surface electromyography is a non-invasive technique used for recording the electrical activity of neuromuscular systems. These signals are random, complex and multi-component. There are several techniques to extract information about the force exerted by muscles during any activity. This work attempts to generate surface electromyography signals for various magnitudes of force under isometric non-fatigue and fatigue conditions using a feedback model. The model is based on existing current distribution, volume conductor relations, the feedback control algorithm for rate coding and generation of firing pattern. The result shows that synthetic surface electromyography signals are highly complex in both non-fatigue and fatigue conditions. Furthermore, surface electromyography signals have higher amplitude and lower frequency under fatigue condition. This model can be used to study the influence of various signal parameters under fatigue and non-fatigue conditions.

Analyzing Origin of Multifractality of Surface Electromyography Signals in Dynamic Contractions

The aim of this study is to analyze the origin of multifractality of surface electromyography (sEMG) signals during dynamic contraction in nonfatigue and fatigue conditions. sEMG signals are recorded from triceps brachii muscles of 22 healthy subjects. The signals are divided into six equal segments on time scale for normalization. The first and sixth segments are considered as the nonfatigue and fatigue conditions, respectively. The source of multifractality can be due to correlation and probability distribution. The original sEMG series are transformed into shuffled and surrogate series. These three series namely, original, shuffled, and surrogate series in the nonfatigue and fatigue conditions are subjected to multifractal detrended fluctuation analysis (MFDFA) and features are extracted. The results indicate that sEMG signals exhibit multifractal behavior. Further investigation revealed that origin of multifractality is primarily due to correlation. The origin of multifractality due to correlation is quantified as 80% in nonfatigue and 86% in fatigue conditions. This method of multifractal analysis may be useful for analyzing the progressive changes in muscle contraction in varied neuromuscular studies.

Analysis of biceps brachii sEMG signal using Multiscale Fuzzy Approximate Entropy.

In this work, an attempt has been made to differentiate sEMG signals under muscle fatigue and non-fatigue conditions using multiscale features. Signals are recorded from biceps brachii muscle of 50 normal adults during repetitive dynamic contractions. After preprocessing, the signal is divided into six segments, out of which first and last segments are considered for this analysis. Fuzzy Approximate Entropy (fApEn) is computed for each subject in the time scales ranging from 1 to 10. Features such as median, low scale median and high scale median are extracted from Multiscale Fuzzy Approximate Entropy (MSfApEn) and used for further analysis. The results show an increase in amplitude of the sEMG signals under fatigue condition. The MSfApEn values are higher in the case of nonfatigue indicating more complexity. The features extracted for the series are effective in differentiating the two conditions. The statistical t test performed indicated high statistical significance (p-value <;<;0.001) It appears that this method of analysis can be used for clinical evaluation of muscles.

Multiscale feature based analysis of surface EMG signals under fatigue and non-fatigue conditions.

In this work, an attempt has been made to differentiate sEMG signals under muscle fatigue and non-fatigue conditions using multiscale features. Signals are recorded from biceps brachii muscle of 50 normal adults during repetitive dynamic contractions. After prescribed preprocessing, each signal is divided into six segments out of which first and last segments are considered in this analysis. Multiscale RMS (MSRMS) and Multiscale Permutation Entropy (MSPE) are computed for each subject in the time scales ranging from 1 to 50. The median values of the MSRMS and MSPE are calculated for further analysis. The results show an increase in amplitude for sEMG signals under fatigue condition. MSRMS values are found to be significantly higher in fatigue. An approximately constant difference in MSRMS value between fatigue and non-fatigue condition is observed over the entire time scale with a negative slope. Further, the median of MSRMS values for each subject is able to distinguish fatigue and non-fatigue conditions. Similar analysis on MSPE showed significant difference between fatigue and non-fatigue cases and lower values of MSPE is observed in fatigue. It is also observed that the median value of MSRMS and MSPE are able to distinguish these conditions. t-test for MSRMS, MSPE and their median value show high statistical significance. It appears that this method of analysis can be used for clinical evaluation of muscles.

Extraction and analysis of multiple time window features associated with muscle fatigue conditions using sEMG signals

In this work, an attempt has been made to differentiate surface electromyography (sEMG) signals under muscle fatigue and non-fatigue conditions with multiple time window (MTW) features. sEMG signals are recorded from biceps brachii muscles of 50 volunteers. Eleven MTW features are extracted from the acquired signals using four window functions, namely rectangular windows, Hamming windows, trapezoidal windows, and Slepian windows. Prominent features are selected using genetic algorithm and information gain based ranking. Four different classification algorithms, namely naïve Bayes, support vector machines, k-nearest neighbour, and linear discriminant analysis, are used for the study. Classifier performances with the MTW features are compared with the currently used time- and frequency-domain features. The results show a reduction in mean and median frequencies of the signals under fatigue. Mean and variance of the features differ by an order of magnitude between the two cases considered. The number of features is reduced by 45% with the genetic algorithm and 36% with information gain based ranking. The k-nearest neighbour algorithm is found to be the most accurate in classifying the features, with a maximum accuracy of 93% with the features selected using information gain ranking.

Non-linear dynamics of lower leg muscle surface electromyogram during repeated plantar flexion

This study investigated non-linear behaviour of gastrocnemius medialis (calf muscle) surface electromyogram (EMG) collected during repeated plantar flexion in both fatigue and non-fatigue conditions. Data were collected in the beginning and immediately after the participant reported fatigue. The study used the phase space reconstruction method to estimate the largest Lyapunov exponents and Kaplan–Yorke dimension of EMG signals. Positive Lyapunov exponent and fractional Kaplan–Yorke dimension values confirmed the presence of chaotic behaviour in the EMG readings. A paired sample t-test showed that the mean largest Lyapunov exponent following fatigue onset was significantly higher than before fatigue (p < 0.05) for right, left and combined right and left gastrocnemius muscles. A logistic regression model revealed the largest Lyapunov exponent as a significant predictor of fatigue onset with a high odds ratio. However, these measures were not found to be good predictors of postural stability as measured by the centre of pressure data.

The effect of plantar flexor muscle fatigue on postural control

Objective Previous studies have demonstrated that ankle muscle fatigue alters postural sway. Our aim was to better understand postural control mechanisms during upright stance following plantar flexor fatigue. Method Ten healthy young volunteers, 25.7 ± 2.2 years old, were recruited. Foot center-of-pressure (CoP) displacement data were collected during narrow base upright stance and eyes closed (i.e. blindfolded) conditions. Subjects were instructed to stand upright and as still as possible on a force platform under five test conditions: (1) non-fatigue standing on firm surface; (2) non-fatigue standing on foam; (3) ankle plantar flexor fatigue, standing on firm surface; (4) ankle plantar flexor fatigue, standing on foam; and (5) upper limb fatigue, standing on firm surface. An average of the ten 30-s trials in each of five test conditions was calculated to assess the mean differences between the trials. Traditional measures of postural stability and stabilogram-diffusion analysis (SDA) parameters were analyzed. Results Traditional center of pressure parameters were affected by plantar flexor fatigue, especially in the AP direction. For the SDA parameters, plantar flexor fatigue caused significantly higher short-term diffusion coefficients, and critical displacement in both mediolateral (ML) and anteroposterior (AP) directions. Long-term postural sway was different only in the AP direction. Conclusions Localized plantar flexor fatigue caused impairment to postural control mainly in the Sagittal plane. The findings indicate that postural corrections, on average, occurred at a higher threshold of sway during plantar flexor fatigue compared to non-fatigue conditions.

Effects of Fatigue Due to Contraction of Evertor Muscles on the Ankle Joint Position Sense in Male Soccer Players

Background The high incidence of ankle sprains that occur later in matches suggests that fatigue may contribute to altered neuromuscular control of the ankle. Moreover, deficits in ankle joint position sense (JPS) were seen in patients with a history of recurrent ankle sprains. It has been hypothesized that ankle sprains may be related to altered ankle JPS as a consequence of fatigue. Purpose To evaluate if fatiguing contractions of evertor muscles alter the ankle JPS. Study Design Controlled laboratory study. Methods Thirty-six soccer players (age, 24.7 ± 1.3 years; height, 183.7 ± 8.2 cm; weight, 78.9 ± 7.9 kg) were recruited. Subjects were asked to recognize 2 positions (15° of inversion and maximal active inversion minus 5°) for 2 conditions: normal and fatigue. Muscular fatigue was induced in evertor muscles of the dominant leg by using isometric contractions. The average of the absolute and variable errors of 3 trials were recorded for both fatigue and nonfatigue conditions. A matched control group of 36 soccer players (age, 23.9 ± 0.9 years; height, 181.2 ± 6.9 cm; weight, 77.8 ± 6.5 kg) was asked to recognize the same positions, before a soccer match and after 45 minutes of playing, and their same scores were recorded. Finally, results of the 2 groups were compared. Results There was significant decrease in subjects’ ability to recognize passive and active repositioning of their ankle after a fatigue protocol (P < .001). Passive and active JPS were reduced after playing (P < .001). There was no significant difference between 2 groups in the results of JPS before and after the intervention (P > .1). Conclusion The acuity of the ankle JPS is reduced subsequent to a fatigue protocol and after a soccer match. Clinical Relevance Evaluation of athletes’ ankle JPS before returning to physical activity may prevent further injuries.

Multi-objective optimisation method for posture prediction and analysis with consideration of fatigue effect and its application case

Automation techniques have been widely used in the manufacturing industry, but there are still many manual handling operations required in assembly and maintenance work. Inappropriate posture and physical fatigue might result in musculoskeletal disorders (MSDs) in such physical jobs. In ergonomics and occupational biomechanics, virtual human modelling techniques have been employed to optimize manual operations in the design stage so as to avoid or decrease risk of MSD. In these methods, physical fatigue is only considered to minimize muscle or joint stress, while the effect of fatigue along time on posture is not often considered, although worker’s motion strategies and postures under physical fatigue are different from those under non-fatigue conditions. In this paper, based on related literatures and multiple-objective optimisation method (MOO), a new posture prediction and analysis method is proposed for predicting the optimal posture under non-fatigue and fatigue conditions and evaluating the physical fatigue in manual material handling operation. The posture prediction and analysis problem is mathematically described, and a special application case is demonstrated for analyzing a drilling assembly operation in European Aeronautic Defence and Space Company (EADS).

Shifting of activation center in the brain during muscle fatigue: An explanation of minimal central fatigue?

Accumulating evidence suggests that the overall level of cortical activation controlling a voluntary motor task that leads to significant muscle fatigue does not decrease as much as the activation level of the motoneuron pool projecting to the muscle. One possible explanation for this “muscle fatigue>cortical fatigue” phenomenon is that the brain is an organ with built-in redundancies: it has multiple motor centers and parallel pathways, and the center of activation may shift from one location to another when neurons in the previous location become fatigued. This hypothesis was tested by estimating the changes of source locations of high-density (64 channels) scalp electroencephalographic (EEG) signals collected during both fatigue and non-fatigue motor tasks. A current dipole model was used to estimate the EEG sources. The fatigue motor task induced significant muscle fatigue, and the non-fatigue task did not. The EEG signal source that indicated the center of brain activation showed substantial location shifts during the fatigue motor task. The shifts could not be explained by variations of source locations caused by error estimated from the non-fatigue task EEG and simulated data. Compared to the non-fatigue condition, the weighted-center of the source locations for all the participants shifted toward the right hemisphere (ipsilateral to the muscle activation), anterior, and inferior cortical regions under the fatigue condition. Fatigue did not alter dipole (source-signal) strength or the overall level of brain activation. The brain may avoid fatigue by shifting neuron populations that participate in a fatiguing motor task.

Do Ankle Foot Orthoses Modify Postural Control during Bipedal Quiet Standing Following a Localized Fatigue of the Ankle Muscles?

The purpose of the present experiment was to investigate the effects of wearing ankle foot orthoses (AFO) on postural control during bipedal quiet standing following a localized fatigue of the ankle muscles. To this aim, eight young healthy subjects were asked to stand upright as immobile as possible with and without AFO in two conditions of non-fatigue and fatigue of the ankle muscles. The center of foot pressure displacements (CoP) were recorded using a force platform. Larger CoP displacements in the fatigue than non-fatigue condition were observed without AFO along both the medio-lateral and antero-posterior axes. Interestingly, with AFO, these destabilizing effects were not observed along the medio-lateral axis. Altogether, the present findings suggested that the AFO allowed the subjects to limit the postural perturbation induced by a localized fatigue of the ankle muscles during bipedal quiet standing.

Patellar Taping Does Not Affect the Onset of Activities of Vastus Medialis Obliquus and Vastus Lateralis Before and After Muscle Fatigue

This study examined the immediate effect of patellar taping with a standard force on the onset of vastus medialis obliquus and vastus lateralis activities before and after muscle fatigue in able-bodied subjects. This study tested 29 mature able-bodied subjects. The surface electromyographic onset time of their vastus medialis obliquus and vastus lateralis was measured after a posteroanterior perturbation at the knee in a single-legged standing position. The measurements were taken under three conditions in random order of true patellar taping, sham patellar taping, and no patellar taping. Afterward, subjects performed a knee-extension exercise until their quadriceps fatigued, and the above tests were repeated to test the effect of fatigue on the outcome. There was no statistically significant difference with patellar taping on the electromyographic onset time of the vastus medialis obliquus and vastus lateralis compared with the placebo-taping and no-taping conditions (P = 0.455). There was no statistically significant difference in onset of vastus medialis obliquus and vastus lateralis muscles before and after muscle fatigue (P = 0.304). The present study suggests that patellar taping does not enhance the temporal activation of vastus medialis obliquus in both fatigue and nonfatigue conditions on able-bodied subjects.

Effects of Lower Extremity Fatigue on Indices of Balance

Context:Use of selective joints in fatiguing protocols might not represent athletic activity and limits generalizability.Objective:To quantify changes in balance indices after a generalized fatiguing activity.Design:Repeated measures.Setting:Clinical laboratory.Participants:16 men (24 ± 3 y) with no orthopedic problems.Intervention:Balance was assessed using the KAT-2000 system before (PRE) and immediately (IMMED) and 10 min (10MIN) after serial Wingate tests and at similar time points under nonfatigue conditions.Main Outcome Measures:Balance index (BI), fore:back ratio, and right:left ratio.Results:MANOVA revealed a significant Condition × Time effect (P = .023). ANOVA revealed that only BI was significant for the condition, time, and Condition × Time effects (P = .020, .007, and .003, respectively). BI increased PRE to IMMED, decreased IMMED to 10MIN, and was different from the nonfatigue condition only for IMMED (P = .002, &lt; .001, and &lt; .001, respectively).Conclusions:Fatigue adversely affects BI; recovery might occur within 10 min.

Changes in lifting dynamics after localized arm fatigue

The purposes of this study were (1) to compare the lifting strategies during arm fatigue and non-fatigue conditions and (2) to evaluate the effects of localized arm fatigue on L5/S1 compressive forces during lifting. The hypothesis was that isometrically induced arm fatigue can alter the lifting strategy selection resulting in an increase in the initial acceleration and leading to an increase in lower back stress. Biomechanical analyses of lifting were done before and after the performance of holding activity to induce arm muscle fatigue. Differences in the lifting strategies used including the accelerated effect, pre-lifting technique, and stiffening of the arms were monitored to determine their influence on L5/S1 compressive forces under various load and range conditions. The results show that lifting strategy changed significantly after arm fatigue, especially when the load was less than 20 kg. These changes included the use of increasingly stooped and accelerated techniques adopted at the beginning of the lift and stiffening of the arms at the end of the lift. Arm fatigue resulted in increased compressive forces at the L5/S1 disc due to the use of accelerated techniques and the inherent disadvantage of these techniques in the pre-lifting posture. In this study, lifting strategies changed as a function of arm fatigue, resulting in increased lower back loading. These findings suggest that whole-body lifting should be avoided after localized arm fatigue in order to decrease the risk of injury to the lower back. Relevance to industry Some industrial activities rely on the lifting of objects after arm holding or carrying tasks. Such tasks may lead to localized arm fatigue and become a dominant factor in workers choice of a lifting strategy. This study investigated the strategies adopted in response to changes in arm fatigue and their effects on the L5/S1 compressive forces during lifting. The results may have implications for lifting job design and provide useful information for further study in the prevention of low-back injuries.

Reduced servo-control of fatigued human finger extensor and flexor muscles.

1. In healthy human subjects holding the index finger semi-extended at the metacarpophalangeal joint against a moderate load, electromyographic (EMG) activity was recorded from the finger extensor and flexor muscles during different stages of muscle fatigue. The aim was to study the effect of muscle fatigue on the level of background EMG activity and on the reflex responses to torque pulses causing sudden extensor unloadings. Paired comparisons were made between the averaged EMG and finger deflection responses under two conditions: (1) at a stage of fatigue (following a sustained co-contraction) when great effort was required to maintain the finger position, and (2) under non-fatigue conditions while the subject tried to produce similar background EMG levels to those in the corresponding fatigue trials. 2. Both the unloading reflex in the extensor and the concurrent stretch reflex in the flexor were significantly less pronounced and had a longer latency in the fatigue trials. Consequently, the finger deflections had a larger amplitude and were arrested later in the fatigue trials. 3. It is concluded that--with avoidance of 'automatic gain compensation', i.e. reflex modifications attributable to differences in background EMG levels--the servo-like action of the unloading and stretch reflexes is reduced in fatigued finger extensor and flexor muscles.

Fatigue in Learning and Performance of a Gross Tracking Task

A total of 75 10-sec. trials on a novel gross two-handed tracking task were given to 58 Ss over 2 days. Following the first 3 trials under control non-fatigue conditions, the experimental group performed a 4-min. initial exercise bout and further 1-min. bouts that were interpolated between 1-min. periods of continuous practice on the learning task. The control group followed the same procedures except that a vowel-cancelling task was substituted for the exercise task. The view that moderately heavy levels of physical fatigue cause little or no impairment in the learning and performance of motor skills which depend highly upon exteroceptive information was supported by the results.