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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A number of studies have been published that have used variables of the electromyogram (EMG) power spectrum during dynamic exercise. Despite these studies there is a shortage of studies of the validity of surface EMG registrations during repetitive dynamic contractions with respect to fatigue. The aim of this study was to investigate if the surface EMG variables mean frequency (MNF [Hz]) and the signal amplitude (RMS [microV]) are valid indicators of muscular fatigue (defined as "any exercise-induced reduction in the capacity to generate force or power output") during maximum repeated isokinetic knee extensions (i.e. criterion validity using peak torque). Twenty-one healthy volunteers performed 100 isokinetic knee extensions at 90 degrees s(-1). EMG signals were recorded from the vastus lateralis, the rectus femoris and the vastus medialis of the right thigh by surface electrodes. MNF and RMS of the EMG together with peak torque (PT [Nm]) were determined for each contraction. MNF showed consequently higher correlation coefficients with PT than RMS did. Positive correlations generally existed between MNF and PT. The majority of the subjects had positive correlations between RMS and PT (i.e. decreases both in PT and in RMS). In conclusion, at the individual level MNF generally - in contrast to RMS - showed good criterion validity with respect to biomechanical fatigue during dynamic maximum contractions.
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PMID:Criterion validation of surface EMG variables as fatigue indicators using peak torque: a study of repetitive maximum isokinetic knee extensions. 1096 95

This cross-sectional study aimed at investigating the influence of occupational exposure to static and highly repetitive work involving the neck and shoulder muscles, myalgia of and tender point in the trapezius muscle on biomechanical output, and electromyogram (EMG) variables (mean frequency MNF, signal amplitude and ability to relax) during maximal forward flexions of the shoulder muscles. Groups of 25 cleaners suffering from chronic myalgia of the trapezius muscle, 25 cleaners free from myalgia of the trapezius muscle and 21 teachers performed 150 forward flexions using an isokinetic dynamometer. Perception of fatigue was reported and surface EMG was recorded from four muscles during the endurance test. The cleaners were stronger than the teachers. Myalgia was associated with lower levels of endurance and a high degree of perceived fatigue. The ability to relax the trapezius muscle decreased with age and was even lower in cleaners with and without myalgia. Higher MNF of the deltoid muscle but not of the trapezius muscle was found in the group suffering from myalgia compared to the groups free from myalgia. This cross-sectional study indicated that myalgia of the trapezius muscle did not influence the strength but did influence the endurance of the forward flexor muscles of cleaners. The observed decrease in the ability to relax the trapezius muscle in cleaners compared to healthy teachers might be indicative of a future insufficiency in the muscle. Prospective studies are needed to define the significance of the results presented here.
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PMID:Mechanical performance and electromyography during repeated maximal isokinetic shoulder forward flexions in female cleaners with and without myalgia of the trapezius muscle and in healthy controls. 1113 62

Two physiological factors are assumed in this paper to mainly determine the myoelectric manifestations of fatigue: (1) the decrease of the conduction velocity (CV) of motor unit action potentials (MUAP) (peripheral fatigue), and (2) the increase of MU synchronization by the central nervous system (central fatigue). To describe separately the peripheral and central components of the myoelectric manifestations of fatigue, we investigated the following indexes: (1) mean spectral frequency - MNF, (2) median spectral frequency - MDF, (3) root mean square - RMS, (4) average rectified value - ARV, (5) estimation of muscle fiber conduction velocity - ECV, (6) percentage of determinism - %DET, (7) spectral indexes defined as the ratio between signal spectral moments - FI(k), (8) MNF estimated by autoregressive analysis - MNF(AR), (9) MNF estimated by Choi-Williams time-frequency representation - MNF(CWD), (10) MNF estimated by continuous wavelet transform - MNF(CWT), (11) signal entropy - S, (12) fractal dimension - FD. The indexes were tested with a set of synthetic EMG signals, with different CV distribution and level of MU synchronization. The indexes were calculated on epochs of 0.5s. It was observed that ECV is uncorrelated with the level of simulated synchronization (promising index of peripheral fatigue). On the other hand FD was the index least affected by CV changes and most related to the level of synchronism (promising index of central fatigue). A representative application to some experimental signals from vastus lateralis muscle during an isometric endurance test supported the results of the simulations. The vector (ECV, FD) is suggested to provide selective indications of peripheral and central fatigue. The description of EMG fatigue by a bi-dimensional vector opens new perspectives in the assessment of muscle properties, with potential application in both clinical and sport sciences.
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PMID:A bi-dimensional index for the selective assessment of myoelectric manifestations of peripheral and central muscle fatigue. 1882 75

The study of fatigue is an important tool for diagnostics of disease, sports, ergonomics and robotics areas. This work deals with the analysis of sEMG most important fatigue muscle indicators with use of signal processing in isometric and isotonic tasks with the propose of standardizing fatigue protocol to select the data acquisition and processing with diagnostic proposes. As a result, the slope of the RMS, ARV and MNF indicators were successful to describe the fatigue behavior expected. Whereas that, MDF and AIF indicators failed in the description of fatigue. Similarly, the use of a constant load for sEMG data acquisition was the best strategy in both tasks.
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PMID:Comparative muscle study fatigue with sEMG signals during the isotonic and isometric tasks for diagnostics purposes. 2225 90

To evaluate the time course of EMG frequency changes during a three-minute maximal effort cycling test (3MT) session and to examine which parameter between mean (MNF) and median (MDF) frequency is more suitable for evaluation of changes in neuromuscular function throughout a 3MT. Eighteen recreationally-active men volunteered to participate in this study. Maximum voluntary contraction (MVC) was measured using a dynamometer to determine maximal EMG frequency of the vastus lateralis (VL) of the kicking leg during isometric knee extension. A maximal oxygen consumption test (VO2peak) on a cycle ergometer was performed to establish the appropriate load profile for the 3MT which was completed after a period of at least 48 hours. MNF, MDF and power output (PO) values were measured at 10-second epochs throughout the duration of the 3MT. Repeated measures analysis of variance was used to compare the changes in EMG frequency, relative to maximal values from the MVC, and change in PO during the testing procedure. MNF, Root Mean Square (RMS), and PO significantly decreased during the 3MT, while MDF did not change significantly. Statistically, EMG frequency and PO decreased at first and remained constant in response to the 3MT, which may be reflective of differing patterns of muscle fiber type fatigue throughout the testing session. Due to decreased variability, changes in neuromuscular function during this protocol may be better evaluated using MNF than MDF. Key pointsEMG frequency decreased initially and remained constant in response to all-out cycling test.The change in EMG frequency and power output were similar during all-out cycling test.MNF may be better than MDF for neuromuscular function evaluation during all-out cycling test due to decreased variability.
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PMID:Evaluation of Electromyographic Frequency Domain Changes during a Three-Minute Maximal Effort Cycling Test. 2598 96

The increased popularization of cycling has brought an increase in cycling-related injuries, which has been suggested to be associated with muscle fatigue. However, it still remains unclear on the utility of different EMG indices in muscle fatigue evaluation induced by cycling exercise. In this study, ten cyclist volunteers performed a 30-second all-out cycling exercise after a warm-up period. Surface electromyography (sEMG) from vastus lateralis muscle (VL) and power output and cadence were recorded and EMG RMS, MF and MPF based on Fourier Transform, MDF and MNF based on wavelet packet transformation, and C(n) based on Lempel-Ziv complexity algorithm were calculated. Utility of the indices was compared based on the grey rational grade of sEMG indices and power output and cadence. The results suggested that MNF derived from wavelet packet transformation was significantly higher than other EMG indices, indicating the potential application for fatigue evaluation induced by all-out cycling exercise.
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PMID:A Comparative Study of EMG Indices in Muscle Fatigue Evaluation Based on Grey Relational Analysis during All-Out Cycling Exercise. 2985 May 88